Huron Coast from Fort Gratiot to Michilimackinac.—About two hundred and thirty miles lie stretched out between these two points. Lake Huron charms the eye, with the view of its freshness and oceanic expanse. But the entrance is without rock scenery, and the student of its geology must be a patient gleaner along its shores. Long coasts of sand and gravel extend before the eye, and they are surmounted, at a moderate elevation, with a dense foliage, which limits the view of its structure to a narrow line. Portions of this coast are heavily loaded with the primitive debris[212]from the North. These are found, in some places, in heavy masses, but all are more or less abraded, showing that they have been transported from their original beds. In one of these, I observed crystals of staurotide.The first section of this coast reaches from Fort Gratiot to Point aux Barques, a distance of about seventy-five miles. Nearly midway lies the White Rock, a very large boulder of whitish-gray semi-crystalline limestone, lying off the shore about half a mile, in water of about one and a half fathom's depth. It is the effect of gulls lighting upon this rock, and not the intensity of the color of the stone, that has originated the name—which is a translation of theRoche Blancheof the oldervoyageurs. The Detroit clay-formation still characterizes the coast.First Emergence of Rock, in place, above the Surface.—We are passing, in this section, along and near to the outcrop of the secondary strata of the peninsula, but these strata are covered with a heavy deposit of diluvial clays, sands, and pebble drift. The first emergence of fixed rocks, above the line of the drift, occurs after passing Elm Creek in the advance to Ship Point (Pointe aux Barques). It is a species of coarse gray, loosely compacted sandstone, in horizontal layers. This rock continues to characterize the coast to and around the Ship Point promontory into Saganaw Bay. It possesses a few fossil remains of corallines; but the rock is not of sufficient compactness and durability for architectural purposes. It is conjectured to be one of the outlying series of the coal measures, of which this coast exhibits, further on, other evidences.Saganaw Bay.—The phenomena of this large body of water, which is some sixty miles long, appear to indicate an original rent in the stratification, having its centre of action very deep. If the peninsula of Michigan be likened to a huge fish's head, this bay may be considered as its open mouth. We crossed the inner bay from Point aux Chenes, where it is estimated to be twenty miles across.[213]The traverse is broken by an island, to which the Indians, with us, applied the name of Sha-wan-gunk.[214]It is composed of a dark-colored limestone, of dull and earthy fracture and compact structure. It presents broken and denuded edges at the water level. I observed in it nodular masses of chalcedony and calc. spar. The margin of the island bears fragments of the boulder stratum.Highlands of Sauble.—On crossing the bay, these highlands present themselves to view in the distance. They are the north-eastern verge of the most elevated central strata of the peninsula. Their structure can only be inferred from the formations alongthe margin of the lake, extending by Thunder Bay and Presque Isle, and the Isles of Bois Blanc and Round Island to Michilimackinac. At Thunder Bay, the compact limestone of the Saganaw Islands reappears, and is constantly in sight from this point to Presque Isle. It exists in connection with bituminous shale, at an island in Thunder Bay. It is of a dark carbonaceous character on the main opposite Middle Island, at a point which is called by the IndiansSho-sho-ná-bi-kó-king, or Place of the Smooth Rock. I noticed at this point the cyathophyllum helianthoides in abundance, and easily detached them from the rock. The more compact portions of this formation in the approach to Presque Isle, disclosed the ammonite, two species of the gorgonia, and the fragment of a species of chambered shell, whose character is indeterminate.Much of the coast was footed, as the winds were adverse, and its debris thus subjected to a careful scrutiny. Wherever the limestone was broken up or receded from the water, long lines of yellow beach-sand and lake-gravel, including members of the erratic block stratum, intervened. In some localities, local beds of iron sand occur.Michilimackinac.[215]—The approach to this island was screened from our view by the woody shores and forests of Bois Blanc, an island of some twelve miles in length lying off the main land; and the view of it first burst upon us in the narrow channel between it and Round Island. It is a striking geological monument of mutations. Here the calcareous rock, which had before exhibited itself in low ledges along the shore is piled up in masses, which reach an extreme altitude of three hundred and twelve feet. About two hundred feet of this elevation is precipitous on its south, east, and west edge. A hundred feet or more is piled up on its centre, part rock and part soil, in a crowning shape. The highest part of this apex, which is surmounted by the ruins of Fort Holmes, consists of the drift stratum, among which are boulders of sienite, and other foreign rocks. A locality of these abraded boulder-rocks, near the Dousman farm, is worthy of a visit from all who take an interest in the phenomena of boulders dispersedover the continent. The fishermen represent the water around this island to be eighty fathoms in depth. Yet, across these waters, to the utmost altitude of the island, these blocks of foreign rock have been transported. No force capable of effecting this is now known. And the argument of their having been transported on cakes of ice, in the nascent periods of the globe, is rendered stronger by these appearances than any geological proofs which I have yet seen.Distinctive Character of the Mackinac Limestone.—Nothing appears so completely to puzzle the observer as the first glance at this rock. It is different in appearance from the calcareous rocks, to which my attention has heretofore been called in Western New York, and in Missouri and Illinois. The difficulty is to find a point of comparison. I walked entirely around the island, partly in water, the northern shores being comparatively low. There appeared to be three layers. The first, which rises up from the depths of the lake, scarcely, if at all, reaches the water level. Upon this is superimposed a vesicular rock, of which the vesicles are filled with carbonate of lime in the state of agaric mineral. By exposure to the air, this substance readily decomposes, and assumes an almost limey whiteness, and sometimes a complete pulverulent state. The reticular, or vesicular lines, by which the mass is held together, are thus weakened, and large masses of the craggy parts fall, and assume the condition of debris at the water's edge. Some conditions of the reticulated filaments are covered with minute crystals of cal. spar; others of minutely crystallized quartz. There appear, at other localities, in low positions, layers of quartz in the condition of a coarse bluish, flinty, striped agate. The entire stratum appears to be a reproduced mass, which is plainly denoted, if I mistake not, by some imbedded masses of an elder lime-rock. The whole stratum is too shelly and fissured to be of value for economical purposes. It yields neither quicklime nor building stone.Fort Mackinac is erected on the summit of this stratum. The two objects of curiosity, called the Arched Rock, and the point called Robinson's Folly, are evidences of this tendency of the cliffs to disintegration. The superior stratum which constitutes the nucleus of the Fort Holmes' summit, contains more silex, diffused throughout its structure. It is, however, of a loose, thoughhard and shelly character; and has, in the geological mutations of the island been chiefly demolished and washed away. The monumental mass of this period of demolition, called the Sugar Loaf, is a proof that it contained, either by its shape, or otherwise, a superior power of resisting these means of ancient prostration. Striking as it now appears, this is the simple story which it tells. Its apex is probably level, or nearly so, with the Fort Holmes's summit. Over the whole island, after these demolitions, the drift stratum was deposited.The German geognosts apply the termmushelkalk, to this species of calcareous rock. It is, apparently, the magnesian limestone of English writers.Ancient Water Lines.—Such marks appear on the most compact parts of the cliffs, denoting the water to have stood, during the ancient boundaries of the lake, at higher levels.Lake Action.—It is known that strong currents set into the Straits of Michilimackinac, and out of it, from Lake Michigan, at this point. The fishermen, who set their nets at four hundred feet in the waters, often bring up, entangled in their nets, large compact masses of limestone, which have been fretted into a kind of lacework, by the rotatory motion of little pebbles and grains of sand, kept in perpetual motion by the water at the bottom of the lake.Organic Impressions.—There are cast up among the lake debris of this island, casts of some species of orthocaratites, ammonites, and madrepores, which appear to be derived from the calcareous rocks in place in the basin of Lake Huron. But the rock strata of the island itself appear to be singularly destitute of these remains. The only species which I have noticed, is one that was thrown up from a well attempted to be dug, on the apex of Fort Holmes, by the British troops, while they held possession of the island in 1813, 1814, and 1815. But this is uniformly fragmentary. It has the precise appearance of the head of a trilobite, but never reveals the whole of the lateral lobes, nor any of the essential connecting parts. It is silicious.Gyseus Formation.—Evidences of the extension of this formation to this vicinity were brought to my notice; in consequence of which I visited the St. Martin's Islands, which belong to the Mackinac group. Masses of gypsum were found imbedded in thesoil, both of the fibrous and compact variety. These islands are low diluvial formations. Similar masses are found on Goose Island; and the mineral has been found at Point St. Ignace on the main land.Taken in connection with the discovery of this mineral, at a subsequent part of the journey on Grand River, the indications of the series of the saline group of rocks, so prevalent in the Mississippi Valley, are quite clear up to this extreme point, which is, however, very near the northern verge of this group.Honeycombed Rocks.—As evidences of existing lake action, it has already been mentioned that the fishermen bring up, from great depths in the straits, pieces of compact limestone, completely fretted and excavated by small pebbles, which are kept in motion by the strong currents which prevail at profound depths. The process of their formation by these currents is such, as in some instances to give the appearance of cellepores, and analogous forms of organic life. I have seen nothing in these carious forms which does not reveal the mechanical action of these waters.Pseudomorphic Forms.—Amongst the limestone debris, of recent date, found on these shores, are pieces of rock which have an appearance as if they had been punctured with a lancet, or blade of a penknife. These incisions are numerous, and from their regularity, appear to have been moulded on some crystals which have subsequently decayed. Yet, there are difficulties in supposing such to have been the origin of these small angular orifices.Whenever these masses are examined by obtaining a fresh fracture, they are found to consist of the compact gray and semi-granular rock of the inferior Mackinac group, but in no instance of the vesicular or silicious varieties. These blocks appear to be identical in character with the White Rock, before noticed.North Shore of Lake Huron.—The next portion of the country examined was that of the north shores of the lake, extending from Michilimackinac to Point Detour, the west Cape of the Straits of St. Mary's, a distance computed to be forty miles. The calcareous rock, such as it appears in the inferior stratum of Mackinac, extends along this coast. The first three leagues of it, consist of an open traverse across an arm of the lake. GooseIsland offers a shelter to the voyager, which is generally embraced. It consists of an accumulation of pebbles and boulders on a reef, with a light soil, resting on the lower limestone. It does not, perhaps, at any point, rise to an elevation of more than eight or ten feet above the water. Outard Point, a short league, or rather three miles further, exhibits the same underlying formation of rock, which is found wherever solid points put out into the lake, during the entire distance. The chain of islands called Chenos, extends about twenty miles, and affords shelter during storms to boatmen and canoemen, who are compelled to pass this coast. Large masses of the rock, with its angles quite entire, lie along parts of the shore, and appear to have been but recently detached. The intervals between these blocks and points of coast, are formed of the loose sand and pebbles of the lake, which are more or less affected by every tempest. The only organic remains and impressions are drift-specimens, which have been driven about by the waves, and are abraded. Broken valves of the anadonta, occasionally found in similar positions, denote that this species exists in the region, but that the outer localities of the coast are entirely unfavorable to their growth.Drummond Island.—This island, now in the possession of British troops, who removed from Michilimackinac in 1816, is the western terminus of the Manatouline chain. We did not visit it, but learn from authentic sources, that it is a continuation of the nether Mackinac limestone—and that the locality abounds in loose petrifactions, which appear to have belonged to an upper stratum of the rock, now disrupted.[216]Straits of St. Mary's.—These straits, and the river which falls into their head, connect Lakes Huron and Superior. They appear to occupy the ancient line of junction between the great calcareous and granitic series of rocks on the continent. The limestone, which has been noticed along the north shore of theHuron from Michilimackinac, and which continues, with interruptions of water only, from Detour to Drummond Island, and the Manatoulines, is to be noticed up the straits as high as Isle a la Crosse, where the last locality of a pure carbonate of lime appears to occur. The island of St. Joseph is chiefly primitive rock, and its south end is heavily loaded with granitic, porphyritic, and quartz boulders. The north shores of the river, opposite and above this island, are entirely of the granitic series, which continues to Gros Cape of Lake Superior. On reaching theNebeesh,[217]or Sailor's Encampment Island, sandstone rocks of a red color present themselves, and are found also on the American side of the river, and continue to characterize it to the Falls, or Sault de Ste. Marie,[218]and to Point Iroquois and Isle Parisien in Lake Superior.The Sault of St. Mary's isuponandoverthis red sandstone. The river makes several successive leaps, of a few feet at a time, in its central channel, falling, altogether, about twenty-two feet in half a mile. This gives it a foaming appearance, and the volume pours a heavy murmur on the ear.[219]It is, of course, a complete interruption to the navigation of vessels, which can, however, come to anchor near its foot, while barges may be pushed up, empty, on the American shore. The water-power created by such a change of level, is such as must commend the spot, at a future period, to manufacturers, lumbermen, and miners. The foot of these falls is heavily incumbered, both with masses of the disrupted sand-rock[220]and granitic and conglomerate boulders.Red Sandstone of Lake Superior.—That this is the old red sandstone, may be inferred simply from the fact that, althoughdeposited originally in horizontal beds, its position has been disturbed in many localities.Plastic Clay Stratum of the Lakes.—The northern extremity of Muddy Lake—a sheet of water some twenty miles in length—is the head of the straits, and the beginning of the River St. Mary's. This sheet of water has the property of being rendered slightly whitish, or turbid, by continuous winds. Its bottom appears to be formed of the same plastic blue clay which obstructs the passage of vessels of large draft on the St. Clair flats, and forms an impediment of a similar kind in this river in Lake George. This stratum seems to be the result of causes not now in operation. If dredged through, or excavated, there is no reason to suppose it would again accumulate; for the waters of the lake are clear and pure, and carry down no deposit of the kind. These clay deposits remain to attest physical changes which are past. They denote the demolition of formations of slate in the upper regions, which have been broken down and washed away when the dominion of the waters was far more potential than they now are.This formation is favorable to the growth of some species of fresh-water shells. I observed several species of the anadonta and the plenorbis, and think, from the broken valves, that research would develop others.Porphyry and Conglomerate Boulders.—A formation of red jasper, in common white quartz, exists, in the bed of intersection, on the southeastern foot of Sugar Island. The fragments of jasper are of a bright vermil red, quite opaque, and have preserved their angles. I had observed fragments of the formation along the shores of the lower part of the straits, and even picked up some specimens, entirely abraded, however, on the south shores of the Huron, between the White Rock and Michilimackinac—a proof of the course of the drift.The granitic conglomerates appear quite conclusive, one would think, of the results of fusion. The attraction of aggregation would seem inadequate to hold together such diverse masses. In these curious and striking masses we see the red feldspathic granite, black and shining hornblende rock, white fatty quartz, and striped jasper, held together as firmly, and polished by attrition as completely, as if they were—what they are not—the results of crystallization in this aggregate form.Erratic Block Group.—Wherever, in fact, the geologist sets his foot, on the shores of the upper lakes, he finds himself on the great drift stratum, and cannot but revert to that era when waters, on a grander scale, swept over these plains, and the lakes played rampantly over wider areas.[221]Basin of Lake Superior.—We entered this island sea as if by a kind of geological gate, in which the sandstone cliffs of Point Iroquois, on the one hand, stand opposite to the granitical hills of Gross Cape on the other.In order to conceive of its geology, it may subserve the purposes of description to compare it to a vast basonic crater. The rim of this crater has been estimated, by Sir Alexander Mackenzie, at fifteen hundred miles. The primitive formations of Labrador and Hudson's Bay coasts come up, so as to form the eastern and northern sides of the rim, around which they stand in cliffs of sienitic greenstone and hornblendic rocks, in some places a thousand feet high. On its south and southwest shores, this formation of the elder class of rocks forms also a considerable portion of the coast; as in the rough tract of Granite Point, the Porcupine and Iron River Mountains, and the primitive tract west of Chegoimegon, or Lapointe. It will serve to denote the broken character of this rim, if we state that the entire plain of the lake, running against and fitting to this rim, was originally filled up with the red, gray, and mottled sandstone, which gave way and fell in at localities west of the great Keweena Peninsula, converting its bottom into an anteclinal axis.Volcanic action, to which this disturbance in its westerlybearings may be attributed, appears to have thrown up the trap-rocks of the Pic, of the Porcupine chain, of the Isle Royal group, and other trap islands, and the long peninsula of Keweena. This system of forces appears to have spent itself from the northeast to the southwest. The shocks brought with them the elements of the copper and other metallic bodies which characterize the trap-rock. They exhausted their power, on the American side, west of the granitic tract of Chocolate and Dead Rivers, and the Totosh and Cradle-Top Mountains. The most violent disturbance took place at the west of the Keweena Peninsula, and thence it was propagated in the direction of the higher Ontonagon, the Iron, and the Montreal rivers.This disturbance of the level of the sandstone produced undulations, which are observable on the St. Mary's, where the variation from a level is not more than eight or ten degrees. They left portions of it—as between Isle au Train and the Firesteel River—undisturbed; and they threw other portions of it—as between Iron and Montreal rivers—almost completely on their edges.The entire north shore from Gargontwa to the old Grand Portage, inclusive of the Michepicotin and Pic regions, cannot be particularly alluded to, as that part of the coast was not visited; but the accounts of observers represent it as consisting of trap-rocks. Without the application of such forces, it appears impossible to understand the geology of this lake, or to account for the sectional and disturbed formations.The lake itself, whose depth is great, and which has an extreme length of about 500 miles, by an extreme width of some 180, is endowed with powerful means of existing elemental action. This consists almost entirely of the force of its winds and long, sweeping waves. Its bottom may, in this light, be looked upon as an immense mortar or triturating apparatus, in which its sandstones, trap-boulders, and pebbles are driven about and comminuted. This power has greatly changed its configuration, and the process of these mutations is daily going on.It is only by such a power of geological action that we can account for the powerful demolitions and inroads which it has made upon some parts of its southern borders. The coasts of the Pictured Rocks, which have a prominent development of about12 to 15 miles, consist in horizontal strata of coarse gray sandstone, of little cohering power. The effect of waves beating upon rocks is to communicate a curved line. This has operated to excavate numerous and extensive caves into the coast. These, after reaching hundreds of feet, have in some cases united. The effect is to isolate portions of the coast, and to leave it in fearful pinnacles, having many of the architectural characters of Gothic or Doric ruins.The portion of coast immediately west of Grand Marrais is scarcely less unique. It denotes the effect of the prostrating power of the lake in another way. The sandstone of parts of the coast, ground down into yellow sand by this vast machinery, is lifted up by the winds as soon as it reaches the point of dryness, and heaped up into vast dunes. Standing trees are buried in these tempests of sand, and its effect is, for about nine miles along the coast, to present, at an elevation of several hundred feet, a scene of arid desolation, which can only be equalled by the Arabic deserts.A dyke of trap seems once to have extended from the north shore to Point Keweena; but, if so, it has been prostrated, and its contents—veins and deposits, silicious and metallic—scattered profusely around the shores of the lakes. A cause less general is hardly sufficient to account for the wide distribution of fragments of the copper veins and vein-stones which have so long been noticed as characters of this lake. The basal remains of this antique dyke form the peninsula of Keweena. The tempests beating against this barrier from the northwest, have ripped up terrific areas from the solid rock, and left its covering, amygdaloid and rubblestones, in fantastic patches upon the more solid parts, or constituting islands in front of them.Structure of its Southern Coast.—The estimated distance from Sault Ste. Marie to Fond du Lac is a fraction over 500 miles. The sandstone, as it appears in the Falls of the St. Mary's, does not appear to be entirely level. It exhibits an undulation of about 8° or 10°, dipping to west-northwest. Two instances of this waved stratification of the Lake Superior sandstone deserve notice. The first terminates at the intersection of red sand rock at la Point des Grande Sables with the beginning of the horizontal strata of the Pictured Rocks. We again observe an inclination of the strata of a few degrees at Grand Island, which is moreingfish River, and appears to dip at Isle aux Trains, about twenty miles northeast. The scenery is peculiarly soft and pleasing in passing the Huron Islands, a granitic group, and directing the view, as in the sketch, to the coast and the rough granitical hills rising behind Huron Bay. The strata are level, as shown above, around the Bay of Presque Isle and Granite Point, and continue so, resting on the roots of the granitical tract of theTötosh, or Schoolcraft, and Cradletop Mountains, and at Point aux Beignes, and Keweena Bay. This level position of the rock is preserved to the south cape of the shallow bay of the Bete Gre, on the north, at which the trap-dykes of the peninsula first begin; and so continues after passing that rugged coast of the vitreous series of that remarkable point, to and beyond Eagle River and Sandy Bay, in the approach to the portage of the Keweena.The same horizontality is observed on the headland west of it, and upon all the points and headlands to Misery and Firesteel Rivers and the mouth of the Ontonagon. The trap-dyke of Keweena crosses this river about ten miles, in a direct line, inland.At Iron River, we observe a stratum of compact gray grauwacke, over the hackly bed of which that river forces its way during the spring months, and stands in tanks and pools during the summer. On reaching the foot of the Porcupine Mountains, the sandstone, which is here of a dark chocolate color, with quartz pebbles of the bigness of a pigeon's egg, and organic remains of paleozoic type, is found to be tilted up into nearly a vertical position, as shown in the sketch. The grauwacke reappears, in a most striking manner, at the Falls of Presque Isle River, where the whole mass of water precipitated from the highlands drops into a vast pot-hole, a hundred feet wide and perhaps twice that depth. The whole upper series of rocks, from the Porcupine Cliffs west to the Montreal River, is a conglomerate. At the Falls of the Montreal, the river drops over the vertical edges of the red sandstone. Beyond the Bay of St. Chares, at Lapointe Chegoimigon, masses of sienitic mountains arise, which have their apex near La Riviere de Fromboise.The Islands of the Twelve Apostles, or Federation Group, appear to be all based on the sienitic or trap, with overlying red sandstone; which latter again reappears on the point of the entrance into Fond du Lac Bay, and marks its southern coast, tillnear the entrance of the Brulé, or Misakoda River, as seen in the illustration beneath. Shores of sand then intercept its view to the entrance of the River St. Louis, and up its channel to its first rapids, about eighteen miles, where the red sandstone again appears, as the first series of the Cabotian Mountains.Serpentine Rock.—At the nearest point north of Rivier du Mort is a headland of this rock, jutting out from the granitical formation. Lapping against it, at the mouth of the river, is a curious formation of magnesian breccia. The serpentine rock appears, in nearly every locality examined, to be highly charged with particles of chromate of iron. It may be expected to yield the usual magnesian minerals.[222]Its position is between the Carp River and Granite Point, in the Bay of Presque Isle, or rather Chocolate River, for that river pours into this bay by far the largest quantity of water.[223]Ancient Drift-Stratum.—In the intervals between the points and headlands, where the rock formation is exposed by streams or gorges, the drift, or erratic boulder stratum, is found. Such is its position beneath the sand-dunes of the Grandes Sables, and in the elder plains and uplands, stretching with interruptions on the coast from the head of the Mary's valley to that of the St. Louis. The edge of this formation is composed of the sand and loose pebbles and boulders of the lake. Mighty as are the existing causes of action of the lake in beating down and disrupting strata of every kind, and in reproducing alluvial lands and dunes, they are weak and local when compared to the causes which have spread these ponderous boulders, and drift masses over latitudes and longitudes which appear to be limited only by the leading elevations of the continent. That oceanic torrents of water, suddenly heaped on the land, and wedged into compactness and power now unknown to it, is after all, the most plausible theory of the dispersion of this formation, and this theory avoids the necessary local one of the glacial dispersion which presupposes a very low temperature over the whole surface of the globe.Kaugwudju.[224]—This imposing mass of the trap-rocks is the highest on the southern shores of Lake Superior. The following outlines of it are taken from a point on the approach to the Ontonagon River, about forty miles distant.They rise to their apex about thirty miles west of that stream, in north lat. 46° 52´ 2´´, as observed by Captain Douglass. They are distant three hundred and fifty miles from St. Mary's. In a serene day they present a lofty outline, and were seen by us from the east, at the distance of about eighty miles. The Indians represent them to have a deep tarn, with very imposing perpendicular walls, at one of the highest points. If Lake Superior be estimated at six hundred and forty feet above the Atlantic, as my notes indicate, its peaks are higher than any estimates we have of the source of the Mississippi, and are, at least, the highest elevations on this part of the continent. The granitical tract of the St. Francis, Missouri,[225]and of the quartz high lands of Wachita, Arkansas, the only two known primitive elevations between the Rocky and Alleghany chains, are far less elevated.I have now taken a rapid glance at the formations along the southern shore of the lake between St. Mary's and Fond du Lac; but have passed by some features which may be thought to merit attention.Existing Lake Drift.—The gleaner among the rock debris of this lake has a field of labor which is not dissimilar to that of the fossilist. If he has not, so to say, to put joint to joint, to establish his conclusions, he has a mineralogical adjustment to make every way as obscure. A boulder of sienite, or a mass of sandstone, or grauwacke, may be easily referred to a contiguous rock. But when the observer meets with species which are apparently foreign to the region, he is placed in a dilemma between the toil of an impossible scrutiny and the danger of an unlicensed conjecture.Among the more common masses which may be assigned a locality within the compass of the lake, are granites, sienites, hornblendes, greenstones, schists, traps, grauwackes, sandstones, porphyries, quartz rocks, serpentines, breccias, amygdaloids, amphiboles,and a variety of masses in which epidote and hornblende are essential constituents. With these, the coast mineralogist must associate, in place or out of place, agates, chalcedonies, carnelians, zeolite, prehnite, calcareous spar, crystalline quartz, amethystine quartz, coarse jaspers, noble serpentine, iron-sand, iron-glance, sulphate of lead, chromate of iron, native copper, carbonate of copper, and various species of pyrites. These were, at least, my principal rewards for about eighteen days' labor, in scrutinizing, at every possible point, its lengthened and varied coasts.Cupreous Formation.—The whole region, above Grand Island at least, appears to have been the theatre of trap-dykes, and an extensive action from beneath, which brought to the surface the elements of the formation of copper veins. These have not been much explored; but, so far as observation goes, there are evidences which cannot be resisted, that the region contains this metal in various shapes and great abundance. I refer to my report of the 6th of November, 1820, for evidences of a valuable deposit of this metal in the valley of the Ontonagon River, and at other points. I found the metal in its native state at various other localities, and always under physical evidences which denoted its existence, in the geological column of the lake, in quantity. These indications were confined almost exclusively to the area intervening between the peninsula of Keweena, and La Pointe Chegoimegon, a distance of about one hundred and fifty miles. Of this district, the two extremities would make the Ontonagon Valley about the centre.[226]A profile of one of the detached pieces, found in the Ontonagon Valley, and forwarded to you by Mr. Van Rensselaer, is herewith given.Vitric Boulders.—Among the debris of Lake Superior are masses of trachyte, and also small pieces of the sienitic series, in which the red feldspar has a calcined appearance, the quartz being, at the same time, converted into a perfectly vitreous texture. Similar productions, but not of the same exact character, exist on the sandy summits of the Grande Sable. Theseexhibit an exterior of glistening cells or orifices: it may be possible that they have been produced by fusion; but I think not. The smooth cells appear like grains of sand hurled by the winds over these bleak dunes. I have brought from that locality a single specimen of pitchstone, perfectly resinous, bleak and shining.La Pointe Chegoimegon.—A sketch of these islands, as given in the Narrative, denotes that their number is greatly underrated, and will serve to show the configuration of a very marked part of the Superior coast. It must, hereafter, become one of the principal harbors and anchoring-ground for vessels of the lake.Valley of the St. Louis River.—The St. Louis River takes its rise on the southern side of the Hauteur des Terres, being the same formation of the drift and erratic block stratum which gives origin, at a more westerly point, to the Mississippi. Its tributaries lie northwest of the Rainy Lakes. Vermilion Lake, a well-known point of Indian trade, is a tributary to its volume, which is large, and its outlet rushes with a great impetus to the lake. At what height its sources lie above Lake Superior, we can only conjecture. It was estimated to have a fall of two hundred and nine feet to the head of the Portage aux Coteaux, and may have a similar rise above.By far its most distinguishing feature is its passage at the Grand Portage through the Cabotian Mountains. We entered it at Fond du Lac and pursued up its channel through alluvial grounds, in which it winds with a deep channel about nineteen or twenty miles to the foot of its first rapids. This point was found one mile above the station of the American Fur Company's trading-house. Here we encountered the first rock stratum, in the shape of our old geological acquaintance, the old red sandstone of Lake Superior. It was succeeded in the first sixteen miles, in the course of which the river is estimated to fall two hundred feet—most of it in the first twenty-nine miles—by trap, argillite, and grauwacke. Through these barriers the water forces its way, producing a series of rapids and falls which the observer often beholds with amazement. The river is continually in a foam for nine miles, and the wonder is that such a furious and heavy volume of water should not have prostrated everything before it. The sandstone, grauwacke, and the argillite, the latterof which stands on its edges, have opposed but a feeble barrier; but the trap species, resisting with the firmness, as it has the color of cast-iron, stand in masses which threaten the life and safety of everything which may be hurled against them. I found a loose specimen of sulphuret of lead and some common quartz in place in the slate rock, a vein of clorite slate, and a locality of coarse graphite, to reward my search.The Portage aux Coteaux, which is over the basetting edges of the argillite, will give a lively idea of the effects of this rock upon the feet of the loaded voyageurs.The sandstone is last seen near the Galley on the Nine Mile Portage. Above the Knife Portage, some eight miles higher, vast black boulders of hornblendic and basaltic blocks, are more frequent; and these masses are observed to be more angular in their shapes than the boulders and blocks of kindred character encountered on the shores of Lakes Superior and Huron. There is a vast sphagnous formation, which spreads westwardly from the head of the Coteau Portage, and gives rise to the remote tributaries of Milles lac and Rum River. Much of this consists of what the Indians termmuskeeg, or elastic bog. Hurricanes and tempests have made fearful inroads upon areas of its timber, and it is seldom crossed, even by the Indians. This tract lies east of the summit of sand-hills and drift, which environ Sandy Lake, theKomtagumaof the Chippewas. The portage of the Savanna River, a tributary of the St. Louis, is the route pursued by persons with canoes; there is no other species of water craft adapted to this navigation. But wherever crossed, this swamp-land tract imposes labor and toil which are of no ordinary cast. It is the equivalent of the argillite which has been broken down and disintegrated, forming beds of clay soil which are impervious to the water, and we way regard this ancient slate formation of the true source of the St. Lawrence tributaries, as the remote origin of those extensive beds of an argillaceous kind, which exist at many places in the lower lakes and plains.Immediately west of the Savanna Portage, the Komtaguma summit is reached. This summit consists wholly of arid pebble and boulder drift of the elder period. It exhibits evidences of broken-down amygdaloids, which not only furnish a part of its pebbles, but also of the contents of this stratum, in numerousagates and other subspecies of the quartz family which are found scattered over the surface. This is, in fact, the origin of that extensive diffusion of these species, which is found in the valley of the Upper Mississippi, as at Lake Pepin, &c., and which has even been traced, in small pieces, as low as St. Louis and Herculaneum in Missouri.[227]We may conclude that the ancient sandstones, slates, and rubblestone, and amygdaloids, of which traces still remain, were swept from the summit of the Mississippi by those ancient floods which appear to have diffused the boulder drift from the North.Sandy Lake.—The first view of this body of water was obtained from one of those eminences situated at the influx of the west Savanna River.This lake is bounded, on its western borders, by the delta of the Mississippi; its outlet is about two miles in length. We here first beheld the object of our search. The soil on its banks is of the richest alluvial character. From this point, dense forests and a moderately elevated soil, varying from three or four to fifteen feet, confined the view, on either side, during more than two days' march. On the third day after leaving Sandy Lake, at an early hour, we reached the Falls of Pakágama. Here the rock strata show themselves for the first time on the Mississippi, in a prominent ledge of quartz rock of a gray color. Through this formation the Mississippi, here narrowed to less than half its width, forces a passage. The fall of its level in about fifty rods may be sixteen or eighteen feet. There is no cascade or leap, properly so called, but a foaming channel of extraordinary velocity, which it is alike impossible to ascend or descend with any species of water craft. It lies in the shape of an elbow. We made the portage on the north side.Pakágama Summit.—The observer, when he has surmounted the summit, immediately enters on a theatre of savannas, level to the eye, and elevated but little above the water. Vistas of grass, reeds, and aquatic plants spread in every direction. On these grassy plains the river winds about, doubling and redoubling on itself, and increasing its cord of distance in a ratio which, by the most moderate computation, would seem extravagant. On thoseplateaux, and the small rivers and lakes connected with them, the wild rice reaches the highest state of perfection.Our men toiled with their paddles till the third day, through this unparalleled maze of water and plants, when we reached the summit of the Upper Red Cedar or Cass Lake, where we encamped. In this distance no rock strata appeared, nor any formation other than a jutting ridge of sand, or an alluvial plain. Plateau on plateau had, indeed, carried us from one level or basin to another, like a pair of steps, till we had reached our extreme height.Cass Lake Basin.—From estimates made, this lake is shown to lie at thirteen hundred and thirty feet above the Atlantic.[228]This is a small elevation, when we consider it as lying on the southern flank of the transverse formation which forms the connecting link with the Rocky Mountains. A rise or a subsidence of this part of the continent to this amount, would throw the Hudson's Bay and Arctic waters down the Mississippi valley. The scenery of its coasts is in part arenaceous plains, and in part arable land, yielding corn to the Indians.Sources of the Mississippi.—In order to understand the geology of this region, it is necessary to premise, that the St. Lawrence, the Hudson's Bay, and the Mexican Gulf waters are separated by a ridge or watershed of diluvial hills, called the Hauteur des Terres, which begins immediately west of the basin of the Rainy Lakes and Rainy Lake River. This high ground subtends the utmost sources of the Mississippi, and reaches to the summit of Ottertail Lake, where it divides the tributaries of the Red River of Lake Winnepec from those of the Des Corbeau, or Great Crow-Wing River.Within this basin, which circumscribes a sweep of several hundred miles, there appears to have been deposited, upon the trap and primary rocks which form its nucleus, a sedimentary argillaceous deposit, capable of containing water. Upon this, the sand and pebble drift reposes in strata of unequal thickness, and the sand is often developed in ridges and plains, bearing species of the pine. The effect has been, that the immense amount ofvapor condensed upon these summits, and falling in dews, rains, and snows, being arrested by the impervious subsoil of clay, has concentrated itself in innumerable lakes, of all imaginable forms, from half a mile to thirty miles long. These are connected by a network of rivers, which pour their redundancy into the Mississippi, and keep up a circulation over the whole vast area. The sand plains often resting around the shores of these lakes create the impression of bodies of water resting on sand, which is a fallacy. Some of these bodies of water are choked up, or not well drained, and overflow their borders, forming sphagnous tracts. Hence the frequent succession of arid sand plains, impassable muskeegs, and arable areas on the same plateaux. Every system of the latter, of the same altitude, constitutes a plateau. The highest of these is the absolute source of the Mississippi waters. The next descending series forms another plateau, and so on, till the river finally plunges over St. Anthony's Falls.In this descending series of plateaux, the Cass, Leech Lake, and Little Lake Winnipec form the third and fourth levels.In descending the Mississippi below the Pakágama, the first stratum of rock, which rises through the delta of the river, occurs between the mouth of the Nokasippi and Elm Rivers, below the influx of the Great De Corbeau. This rock, which is greenstone trap, rises conspicuously in the bed of the stream, in a rocky isle seated in the rapid called—I know not with what propriety—theBig Falls, orGrande Chute. The precipitous and angular falls of this striking object decide that the bed of the stream is at this point on the igneous granitical and greenstone series. This formation is seen at a few points above the water, until we pass some bold and striking eminences of shining and highly crystalline hornblendic sienite, which rises in the elevation called by us Peace Rock, on the left bank, near the Osaukis Rapids. This rock lies directly opposite to the principal encampment on the 27th of July, which was on an elevated prairie on the west bank. To this point a delegation of Sioux had ascended on an embassy of peace from Fort Snelling to the Chippewas, having affixed on a pole what the exploring party called a bark letter, the ideas being represented symbolically by a species of picture writing, or hieroglyphics. In allusion to this embassy, this locality was called thePeace Rock. This rock is sienite. It is highly crystalline, and extends several miles. Its position must be, from the best accounts, in north latitude about 44° 30´. From this point to Rum River, a distance of seventy miles, no other point of the intrusion of this formation above the prairie soil was observed.Introduction of the Palæontological Rocks.—After passing some fifty miles below this locality there are evidences that the river, in its progress south, has now reached the vicinity of the great carboniferous and metalliferous formations, which, for so great a length, and in so striking a manner, characterize both banks of the Mississippi below St. Anthony's Falls. About nine or ten miles before reaching these Falls, this change of geological character is developed; and on reaching the Falls the river is found to be precipitated, at one leap, over strata of white sandstone, overlaid by the metalliferous limestone. The channel is divided by an island, and drops in single sheets, about sixteen to eighteen feet, exclusive of the swift water above the brink, or of the rapids for several hundred yards below. This sandstone is composed of grains of pure and nearly limpid quartz, held together by the cohesion of aggregation. If my observations were well taken it embraces, sparingly, orbicular masses of hornblende. It is horizontal, and constitutes, in some places, walls of stratification, which are remarkable for their whiteness and purity. This sandstone is overlaid by the cliff limestone, the same in character, which assumes at some points a silicious, and at others, a magnesian character. It is manifestly the same great metalliferous rock which accompanies the lead ore of Missouri and mines of Peosta or Dubuque. There rests upon it the elder drift stratum of boulders, pebble, and loam, which marks the entire valley. This latter embraces boulders of quartz and hornblende rock, along with limestones and sandstones. It is overlaid by about eighteen inches of black alluvial carbonaceous mould.From St. Anthony's Falls the river is perpetually walled on either side with those high and picturesque cliffs which give it so imposing and varied an appearance, and its current flows on with a majesty which seems to the imagination to make it rejoice in its might, confident of a power which will enable it to reach and carry its name to the ocean in its unchanged integrity.St. Peter's River and Valley.—The importance, fertility,and value of this tributary have particularly impressed every member of the party. Its position as the central point of the Sioux power, and its border position to the Chippewas, the representative tribe of the great Algonquin family, render it now a place of note, which fully justifies the policy of the department in establishing a military post at the confluence of the river; and the importance cannot soon pass away, in the progress of the settlement of the Mississippi Valley.[229]It is the great route of communication with the valley of the Red River of the North, and the agricultural and trading settlements of Lord Selkirk in that fertile valley, and its complete exploration by a public officer is desirable, if not demanded.[230]Of its geological character but little is known, and that connects it with both the great formations which have been noticed as succeeding each other at the great Peace Rock. That the granitical formation reaches it at a high point is probable, from the large reported boulders. The Indians bring from the blue earth fork of it, one of their most esteemed green and blue argillaceous pigments, of which the coloring matter appears to be carbonate of copper. They also bring from the Coteau des Prairie, probably Carver's "shining mountains," specimens of that fine and beautiful red pipe stone, which has so long been known to be used by them for that purpose. This mineral is fissile, and moderately hard, which renders it fit for their peculiar ripe sculptures. I found small masses of native copper in the drift stratum at the mouth of this stream, on the top of the cliffs on the Mississippi, opposite the mouth of the St. Peter's.Crystalline Sand Rock.—This stratum reveals the same crystalline structure which is so remarkable in the sandstone caves, near the Potosi road, in the county of St. Genevieve, Missouri; and the sand obtained from it, like that mineral, would probably fuse, with alkali, in a moderate heat, and constitute an excellent material for the manufacture of glass. It is also, like the Missouri sandstone, cavernous. In both situations, these caves appear to be due to water escaping through fissures of the rock, where its cohesion is feeble, carrying it away grain by grain.In stopping at one of these caves, about twelve miles below St. Peter's, we found this cause of structure verified by a lively spring and pond of limpid water flowing out of it.Valley of the St. Croix.—This river originates in an elevated range of the elder sand and pebble drift, which lies on the summit between the Mississippi system of formations, and the Lake Superior basin. It communicates with the Brulé, which is "Goddard's River" of Carver, and with the Mauvaise or Bad River of that basin. Specimens of native copper have been found on Snake River, one of its tributaries.[231]Geological Monuments.—In descending the river for the distance of about one hundred miles below St. Anthony's Falls, my attention was arrested, on visiting the high grounds, by a species of natural monuments, which appear as if made by human hands seen at a distance, but appear to be the results of the degradation and wasting away, on the Huttonian theory, of all but these, probably harder, portions of the strata.Lake Pepin.—This sheet commends itself to notice by its extent and picturesque features. It is an expansion of the river, about twenty-four miles long, and two or three wide. Both its borders and bed reveal the drift stratum, and the observer recognizes here, boulders of the peculiar stratification which has, in ancient periods, characterized the high plateaux about the sources of the river. Such are its hornblendic, sienite, quartz, trap, and amygdaloid pebbles, and that variety of the quartz family which assumes the form of the agate and other kindred species. Moved as these materials are annually, lower and lower, by the impetus of the stream, other supplies, it may be inferred, are still furnished by the shifting sand and gravel bars from above. The mass must submit to considerable abrasion by this change, and the diminished size of the drifted masses become a sort of measure of the distance at which they are found from their parent beds.Chippewa River.—This stream is the first to bring in a vast mass of moving sand. Its volume of water is large, which it gathers from the high diluvial plains that spread southwest of the Porcupine Mountains, and about the sources of the Wisconsin,the Montreal, and the St. Croix Rivers, with which it originates.Trompeldo(Le Montaine des Tromps d'Eaux).—This island mountain stands as if to dispute the passage of the Mississippi, whose channel it divides into two portions. Distinct from its height, which appears to correspond with the contiguous cliffs, and in the large amount of fresh debris at its base, it presents nothing peculiar in its geology.Painted Rock.—This vicinity is chiefly noted for its large and fine specimens of fresh-water shells.Wisconsin.—Like the Chippewa, this stream brings down in its floods, vast quantities of loose sand, which tend to the formation of bars and temporary islands. It originates in the same elevated plains, and bespeaks a considerable area at its sources, which must be arid. It is a region, however, in which lakes and rice lands abound, and it may, in this respect, be geologically of the same formation as the higher plateaux of the Mississippi, above the Sandy Lake summit. Its sides produce many species to enrich our fresh-water Conchology.Lead Mines of Peosta and Dubuque.—In my researches into the mineral geography of Missouri, in 1818 and 1819, I had explored a district of country between the rivers Merrimak and St. Francis, and on the Ozarks, which revealed many traits which it has in common with the Upper Mississippi. There, as here, the mineral deposits appear to be, in many cases, in a red marly clay, whether the clay is overlaid by the calcareous rock or not. There, as here, also, the limestone and sandstone strata are perfectly horizontal. The leads of ore appear, in this section, to be followed with more certainty, agreeable to the points of the compass; but this may happen, to some extent, because the practice of mining on individual account, with windlass and buckets, in the Missouri district, has led common observers to be more indifferent to exact scientific methods. To say that the digging, at these mines, is equally, or more productive, is perhaps just. Capital and labor have been rewarded in both sections of the country, in proportion as they have been perseveringly and judiciously expended.I found much of the ore, which is a sulphuret, at Dubuque's Mines, lying in east and west leads. These leads were generallypursued in caves, or, more properly, fissures in the rock. In one of the excavations which I visited, the digging was continued horizontally under the first stratum of rock, after an excavation had been made perpendicularly, through the top soil and calcareous rock, perhaps thirty feet. The ore is a broad-grained cubical galena, easily reduced, and bids fair very greatly to enhance the value and resources of this section of the West.Similar mines exist at Mississinawa, and the River Au Fevé,[232]both on the eastern or left bank of the Mississippi. And a system of leasing or management, such as I have suggested for the Missouri mines, appears equally desirable.Quartz Geodes.—The amount of silex in the cliff limestone is such, in some conditions of it, as to justify the term silico-calcareous. This condition of the rock at the passage of the Mississippi through the Rock River and Des Moines Rapids, is such as to produce a very striking locality of highly crystalline quartz geodes, which accumulates in the bed of the stream. Many of these geodes are from a foot to twenty-two inches in diameter, and on breaking them they exhibit resplendent crystals of limpid quartz. Sometimes these are amethystine; in other cases they present surfaces of chalcedony or cacholong. The latter minerals, if obtained from the rock, and before unduly hardening by exposure, would probably furnish a suitable basis for lapidaries.Intermediate Country in the Direction to Green Bay.—There is a line which separates, on the north, the granitical and trap region from the metal-bearing limestone, and its supporting sandstone. This formation of the elder series of rocks, having been traced to the south shore of Lake Superior, and having been seen to constitute the supporting bed of the alluviums and diluviums of the Upper Mississippi, above the Peace Rock, it may subserve the purpose of inquiry to trace this line of junction by its probable and observed boundaries.The line may be commenced where it crosses the Mississippi, at the Peace Rock, and extended to the St. Croix, the falls of which are on the trap-rock, to the sources of the Chippewa at Lac du Flambeau, and the Wisconsin near Plover Portage. The source of Fox River runs amid uprising masses of sienite, and this formation appears to pass thence northeasterly, across theUpper Menominee, to the district of the Totosh and Cradle-Top Mountains, west of Chocolate River, on the shores of Lake Superior.I observed the crystalline sandstone and its overlying cliff limestone, along the valley of the Wisconsin, where ancient excavations for lead ore have been made. There is an entire preservation of its characters, and no reason occurs why its mineralogical contents should not prove, in some positions, as valuable as they have been found in Missouri, or in the Dubuque district west of the Mississippi.On reaching the Wisconsin Portage, the limestone is found to have been swept by diluvial action, from its supporting sand rock. Such is its position not far north of the highest of the four lakes, and again at Lake Puckway, in descending the Fox River; consequently, there are no lead discoveries in this region. On coming to the calcareous rock, which is developed along the channel of the river, below Winnebago Lake, it appears rather to belong to the lake system of deposits. Its superior stratum lies in patches, or limited districts, which appear to have been left by drift action. Petrefactions are found in these districts, and the character of the rock is dark, compact, or shelly. The lower series of deposits, such as they appear at the Kakala Rapids, at Washington Harbor, in the entrance to Green Bay, and in the cliffs north of Sturgeon Bay and Portage, are manifestly of the same age and general character as the inferior stratum of Michilimackinac and the Manatouline chain.Basin of Lake Michigan.—This basin, stretching from the north to the south nearly four hundred miles, lies deeply in the series of formation of limestones, sandstone, and schists, to which we apply the term of the Michilimackinac system. Its north and west shores are skirted from Green Bay to a point north of the Sheboygan, with the calcareous stratum. At this point, the ancient drift, the lacustrine clay of Milwaukie and the prairie diluvium of Chicago, constitute a succession, of which the surface is a slightly waving line of the most fertile soils.Among the pebbles cast ashore at the southern head of this lake I observed slaty coal. It seems, indeed, the only one of the lakes which reaches south into the coal basin of Illinois. If the level at which coal is found on the Illinois were followed through, itwould issue in the basin of the lake below low-water mark. Digging for this mineral on the Chicago summit, promises indeed not to be unsupported by sound hypothesis.After passing Chicago, of which a sketch is added, the sands which begin to accumulate at the Konamik, the River du Chemin, and the St. Joseph's River,[233]appear in still more prominent ridges, skirting the eastern coasts to and beyond Grand River. These sands, which are the accumulations of winds, are cast on the arable land, much in the manner that has been noticed at the Grand Sable on Lake Superior, and reach the character of striking dunes at the coast denominated the Sleeping Bear. The winds which periodically set from the western shore, produce continual abrasions of its softer materials, and are the sole cause of these intrusive sand-hills. Pent up behind them, the water is a cause of malaria to local districts of country, and many of the small rivers upon this side are periodically choked with sand. The sketch transmitted of this bleak dune-coast (omitted here), as it is seen at the mouth of Maskigon Lake, will convey a false idea of the value of this coast, even half a mile from the spot where the surf beats. It is designed to show the air of aridity which the mere coast line presents. The stratification regains its ordinary level and appearance before reaching the Plate or Omicomico River, and the peninsula of the Grand Traverse Bay, and the settlements of the Ottawa Indians on Little Traverse Bay, afford tracts of fertile lands. Point Wagonshonce consists of a stratum of limestone of little elevation, which constitutes the southeast cape of the strait. Here a lighthouse is needed to direct the mariner.Lake Huron.—Notices of this sheet of water have been given in our outward voyage. It appears rather as the junction of separate lakes which have had their basins fretted into one another, than as one original lake. Michigan is connected with it through the Straits of Michilimackinac. The Georgian Bay, north of the Manatouline chain, seems quite distinct. The Saganaw Bay is an element of another kind. The Manitouline chain separates the calcareous and granitic region, and its numerous trap and basaltic islands towards the north shore, of which there are many thousands,denote that it has been the scene of geological disturbance of an extraordinary kind.Ulterior Conclusions.—In taking these several views of the geological structure of the Northwest—of the Lake Superior basin, and of the valleys of the St. Louis River—the region about the Upper Mississippi, its striking change at the Falls of St. Anthony—and the valleys of the Wisconsin and Fox Rivers, and the basins of Lakes Michigan and Huron, I am aware of the temerity of my task. Allowance must, however, be made for the rapidity of my transit over regions where the question was often the safety and personal subsistence of the party. A very large and diversified area was passed over in a short time. At no place was it possible to make elaborate observations. A thousand inconveniences were felt, but they were felt as the pressure of so many small causes impeding the execution of a great enterprise. A sketch has been made, which, it is hoped, will reveal something of the physical history and lineaments of the country. These glimpses at wild scenes, heretofore hid from the curious eye of man, have been made, at all points, with the utmost avidity. I have courted every opportunity to accumulate facts, and I owe much to the distinguished civilian who has led the party so successfully through scenes of toil and danger, not always unexpected, but always met in a calm, bold, and proper spirit, which has served to inspire confidence in all; to him, and to each one of my associates, I owe much on the score of comity and personal amenity and forbearance; and I have been made to feel, in the remotest solitudes, how easy it is to execute a duty when all conspire to facilitate it.The views herein expressed are generalized in two geological maps (hereto prefixed), which, it is believed, will help to fix the facts in the mind. They exhibit the facts noticed, in connection with the theory established by them, and by all my observations, of the construction of this part of the continent.The mineralogy of the regions visited is condensed in the following summary, drawn from my notes, which, it is believed, constitutes an appropriate conclusion to this report.With the exception of one species, namely, the ores of copper, the region has not proved as attractive in this department as Ifound the metalliferous surface of Missouri. There are but few traces of mining, and those of an exceedingly ancient character, in the copper region of Lake Superior. The excavations in search of lead ore on the Upper Mississippi do not date back many years, but the indications are such as to show that few countries, even Missouri, exceed them in promises of mineral wealth.I have employed the lapse of time between the termination of the exploration and the present moment, to extend my mineralogical observations to some parts of the Mississippi Valley which were not included in the line of the expedition, but which were visited in the following year, in the service of the Government, namely, the Miami of the Lakes, and Wabash Valleys, the Cave in Rock Region in Lower Illinois, and the Valley of the River Illinois. The whole is concentrated in the following notices:—Tabular View of Minerals observed in the Northwest.I. ORES.Genera.Species.Subspecies.Varieties.MetallicmineralsCopperNative copper.Green carbonate of copperFibrous.Compact.LeadSulphuret of leadCommon.ZincSulphuret of zincBlende.IronSulphuret of ironCommon.Radiated.Spheroidal.Cellular.Hepatie.Magnetic oxide of ironIron sand.Specular oxide of iron.Micaceous.Red oxide of ironOchrey.Scaly.Compact.Brown oxide of ironOchrey.Silver.II. EARTHS AND STONES.Genus.Species.Varieties.Silicious mineralsQuartzCommon quartzMilky.Radiated.Tabular.Greasy.Granular.Arenaceous.Pseudomorphous.Amethystine.Amethyst.Ferruginous quartzYellow.Red.Prase.ChalcedonyCommon.Cacholong.Carnelian.Sardonyx.Agate.Hornstone.JasperCommon.Striped.Red.Heliotrope.OpalCommon.Silicious slateCommon.Basanite.PetrosilexMicaCommon.Gold yellow.SchorlCommon.Indicolite.FeldsparCommon.PrehniteRadiated.HornblendeCommon.Actynolite.WoodstoneMineralized wood.Agatized wood.CalcareousMineralsCarbonate of limeCalcareous sparCrystalized.Lamellar.Granular limestoneCompact limestoneCommon.Earthy.Agaric mineralCommon.Fossil farina.Concreted carbonate of limeOolite.Calcareous sinterStalactite.Stalagmite.Calcareous tufa.Pseudomorphous carbonate of lime.MarlLudus helmontii.Sulphate of limeGypsumFibrous.Granular.Granularly foliated.Earthy.Fluate of limeFluorspar.Genus.Varieties.Aluminous mineralsArgillaceous slateArgillite.Bituminous shale.ChloriteChlorite slate.Staurotide.ClayPotters' clay.Pipe clay.Variegated clay.Blue sulphated clay.Green sulphated clay.Opwagunite.Magnesian mineralsSerpentineCommon serpentine.SteatiteSteatite.AsbestusCom. asbestus.Barytic mineralsSulphate of barytesLamellar.StrontianSulphate of strontianFoliated.III.COMBUSTIBLES.Bituminous mineralsBitumenPetroleum.Maltha.Asphaltum.GraphiteGranular graphite.CoalSlate coal.IV. SALTS.SodaMuriate of sodaNative salt.Salt springs.Alkaline sulphate of aluminaAlum.
Huron Coast from Fort Gratiot to Michilimackinac.—About two hundred and thirty miles lie stretched out between these two points. Lake Huron charms the eye, with the view of its freshness and oceanic expanse. But the entrance is without rock scenery, and the student of its geology must be a patient gleaner along its shores. Long coasts of sand and gravel extend before the eye, and they are surmounted, at a moderate elevation, with a dense foliage, which limits the view of its structure to a narrow line. Portions of this coast are heavily loaded with the primitive debris[212]from the North. These are found, in some places, in heavy masses, but all are more or less abraded, showing that they have been transported from their original beds. In one of these, I observed crystals of staurotide.
The first section of this coast reaches from Fort Gratiot to Point aux Barques, a distance of about seventy-five miles. Nearly midway lies the White Rock, a very large boulder of whitish-gray semi-crystalline limestone, lying off the shore about half a mile, in water of about one and a half fathom's depth. It is the effect of gulls lighting upon this rock, and not the intensity of the color of the stone, that has originated the name—which is a translation of theRoche Blancheof the oldervoyageurs. The Detroit clay-formation still characterizes the coast.
First Emergence of Rock, in place, above the Surface.—We are passing, in this section, along and near to the outcrop of the secondary strata of the peninsula, but these strata are covered with a heavy deposit of diluvial clays, sands, and pebble drift. The first emergence of fixed rocks, above the line of the drift, occurs after passing Elm Creek in the advance to Ship Point (Pointe aux Barques). It is a species of coarse gray, loosely compacted sandstone, in horizontal layers. This rock continues to characterize the coast to and around the Ship Point promontory into Saganaw Bay. It possesses a few fossil remains of corallines; but the rock is not of sufficient compactness and durability for architectural purposes. It is conjectured to be one of the outlying series of the coal measures, of which this coast exhibits, further on, other evidences.
Saganaw Bay.—The phenomena of this large body of water, which is some sixty miles long, appear to indicate an original rent in the stratification, having its centre of action very deep. If the peninsula of Michigan be likened to a huge fish's head, this bay may be considered as its open mouth. We crossed the inner bay from Point aux Chenes, where it is estimated to be twenty miles across.[213]The traverse is broken by an island, to which the Indians, with us, applied the name of Sha-wan-gunk.[214]It is composed of a dark-colored limestone, of dull and earthy fracture and compact structure. It presents broken and denuded edges at the water level. I observed in it nodular masses of chalcedony and calc. spar. The margin of the island bears fragments of the boulder stratum.
Highlands of Sauble.—On crossing the bay, these highlands present themselves to view in the distance. They are the north-eastern verge of the most elevated central strata of the peninsula. Their structure can only be inferred from the formations alongthe margin of the lake, extending by Thunder Bay and Presque Isle, and the Isles of Bois Blanc and Round Island to Michilimackinac. At Thunder Bay, the compact limestone of the Saganaw Islands reappears, and is constantly in sight from this point to Presque Isle. It exists in connection with bituminous shale, at an island in Thunder Bay. It is of a dark carbonaceous character on the main opposite Middle Island, at a point which is called by the IndiansSho-sho-ná-bi-kó-king, or Place of the Smooth Rock. I noticed at this point the cyathophyllum helianthoides in abundance, and easily detached them from the rock. The more compact portions of this formation in the approach to Presque Isle, disclosed the ammonite, two species of the gorgonia, and the fragment of a species of chambered shell, whose character is indeterminate.
Much of the coast was footed, as the winds were adverse, and its debris thus subjected to a careful scrutiny. Wherever the limestone was broken up or receded from the water, long lines of yellow beach-sand and lake-gravel, including members of the erratic block stratum, intervened. In some localities, local beds of iron sand occur.
Michilimackinac.[215]—The approach to this island was screened from our view by the woody shores and forests of Bois Blanc, an island of some twelve miles in length lying off the main land; and the view of it first burst upon us in the narrow channel between it and Round Island. It is a striking geological monument of mutations. Here the calcareous rock, which had before exhibited itself in low ledges along the shore is piled up in masses, which reach an extreme altitude of three hundred and twelve feet. About two hundred feet of this elevation is precipitous on its south, east, and west edge. A hundred feet or more is piled up on its centre, part rock and part soil, in a crowning shape. The highest part of this apex, which is surmounted by the ruins of Fort Holmes, consists of the drift stratum, among which are boulders of sienite, and other foreign rocks. A locality of these abraded boulder-rocks, near the Dousman farm, is worthy of a visit from all who take an interest in the phenomena of boulders dispersedover the continent. The fishermen represent the water around this island to be eighty fathoms in depth. Yet, across these waters, to the utmost altitude of the island, these blocks of foreign rock have been transported. No force capable of effecting this is now known. And the argument of their having been transported on cakes of ice, in the nascent periods of the globe, is rendered stronger by these appearances than any geological proofs which I have yet seen.
Distinctive Character of the Mackinac Limestone.—Nothing appears so completely to puzzle the observer as the first glance at this rock. It is different in appearance from the calcareous rocks, to which my attention has heretofore been called in Western New York, and in Missouri and Illinois. The difficulty is to find a point of comparison. I walked entirely around the island, partly in water, the northern shores being comparatively low. There appeared to be three layers. The first, which rises up from the depths of the lake, scarcely, if at all, reaches the water level. Upon this is superimposed a vesicular rock, of which the vesicles are filled with carbonate of lime in the state of agaric mineral. By exposure to the air, this substance readily decomposes, and assumes an almost limey whiteness, and sometimes a complete pulverulent state. The reticular, or vesicular lines, by which the mass is held together, are thus weakened, and large masses of the craggy parts fall, and assume the condition of debris at the water's edge. Some conditions of the reticulated filaments are covered with minute crystals of cal. spar; others of minutely crystallized quartz. There appear, at other localities, in low positions, layers of quartz in the condition of a coarse bluish, flinty, striped agate. The entire stratum appears to be a reproduced mass, which is plainly denoted, if I mistake not, by some imbedded masses of an elder lime-rock. The whole stratum is too shelly and fissured to be of value for economical purposes. It yields neither quicklime nor building stone.
Fort Mackinac is erected on the summit of this stratum. The two objects of curiosity, called the Arched Rock, and the point called Robinson's Folly, are evidences of this tendency of the cliffs to disintegration. The superior stratum which constitutes the nucleus of the Fort Holmes' summit, contains more silex, diffused throughout its structure. It is, however, of a loose, thoughhard and shelly character; and has, in the geological mutations of the island been chiefly demolished and washed away. The monumental mass of this period of demolition, called the Sugar Loaf, is a proof that it contained, either by its shape, or otherwise, a superior power of resisting these means of ancient prostration. Striking as it now appears, this is the simple story which it tells. Its apex is probably level, or nearly so, with the Fort Holmes's summit. Over the whole island, after these demolitions, the drift stratum was deposited.
The German geognosts apply the termmushelkalk, to this species of calcareous rock. It is, apparently, the magnesian limestone of English writers.
Ancient Water Lines.—Such marks appear on the most compact parts of the cliffs, denoting the water to have stood, during the ancient boundaries of the lake, at higher levels.
Lake Action.—It is known that strong currents set into the Straits of Michilimackinac, and out of it, from Lake Michigan, at this point. The fishermen, who set their nets at four hundred feet in the waters, often bring up, entangled in their nets, large compact masses of limestone, which have been fretted into a kind of lacework, by the rotatory motion of little pebbles and grains of sand, kept in perpetual motion by the water at the bottom of the lake.
Organic Impressions.—There are cast up among the lake debris of this island, casts of some species of orthocaratites, ammonites, and madrepores, which appear to be derived from the calcareous rocks in place in the basin of Lake Huron. But the rock strata of the island itself appear to be singularly destitute of these remains. The only species which I have noticed, is one that was thrown up from a well attempted to be dug, on the apex of Fort Holmes, by the British troops, while they held possession of the island in 1813, 1814, and 1815. But this is uniformly fragmentary. It has the precise appearance of the head of a trilobite, but never reveals the whole of the lateral lobes, nor any of the essential connecting parts. It is silicious.
Gyseus Formation.—Evidences of the extension of this formation to this vicinity were brought to my notice; in consequence of which I visited the St. Martin's Islands, which belong to the Mackinac group. Masses of gypsum were found imbedded in thesoil, both of the fibrous and compact variety. These islands are low diluvial formations. Similar masses are found on Goose Island; and the mineral has been found at Point St. Ignace on the main land.
Taken in connection with the discovery of this mineral, at a subsequent part of the journey on Grand River, the indications of the series of the saline group of rocks, so prevalent in the Mississippi Valley, are quite clear up to this extreme point, which is, however, very near the northern verge of this group.
Honeycombed Rocks.—As evidences of existing lake action, it has already been mentioned that the fishermen bring up, from great depths in the straits, pieces of compact limestone, completely fretted and excavated by small pebbles, which are kept in motion by the strong currents which prevail at profound depths. The process of their formation by these currents is such, as in some instances to give the appearance of cellepores, and analogous forms of organic life. I have seen nothing in these carious forms which does not reveal the mechanical action of these waters.
Pseudomorphic Forms.—Amongst the limestone debris, of recent date, found on these shores, are pieces of rock which have an appearance as if they had been punctured with a lancet, or blade of a penknife. These incisions are numerous, and from their regularity, appear to have been moulded on some crystals which have subsequently decayed. Yet, there are difficulties in supposing such to have been the origin of these small angular orifices.
Whenever these masses are examined by obtaining a fresh fracture, they are found to consist of the compact gray and semi-granular rock of the inferior Mackinac group, but in no instance of the vesicular or silicious varieties. These blocks appear to be identical in character with the White Rock, before noticed.
North Shore of Lake Huron.—The next portion of the country examined was that of the north shores of the lake, extending from Michilimackinac to Point Detour, the west Cape of the Straits of St. Mary's, a distance computed to be forty miles. The calcareous rock, such as it appears in the inferior stratum of Mackinac, extends along this coast. The first three leagues of it, consist of an open traverse across an arm of the lake. GooseIsland offers a shelter to the voyager, which is generally embraced. It consists of an accumulation of pebbles and boulders on a reef, with a light soil, resting on the lower limestone. It does not, perhaps, at any point, rise to an elevation of more than eight or ten feet above the water. Outard Point, a short league, or rather three miles further, exhibits the same underlying formation of rock, which is found wherever solid points put out into the lake, during the entire distance. The chain of islands called Chenos, extends about twenty miles, and affords shelter during storms to boatmen and canoemen, who are compelled to pass this coast. Large masses of the rock, with its angles quite entire, lie along parts of the shore, and appear to have been but recently detached. The intervals between these blocks and points of coast, are formed of the loose sand and pebbles of the lake, which are more or less affected by every tempest. The only organic remains and impressions are drift-specimens, which have been driven about by the waves, and are abraded. Broken valves of the anadonta, occasionally found in similar positions, denote that this species exists in the region, but that the outer localities of the coast are entirely unfavorable to their growth.
Drummond Island.—This island, now in the possession of British troops, who removed from Michilimackinac in 1816, is the western terminus of the Manatouline chain. We did not visit it, but learn from authentic sources, that it is a continuation of the nether Mackinac limestone—and that the locality abounds in loose petrifactions, which appear to have belonged to an upper stratum of the rock, now disrupted.[216]
Straits of St. Mary's.—These straits, and the river which falls into their head, connect Lakes Huron and Superior. They appear to occupy the ancient line of junction between the great calcareous and granitic series of rocks on the continent. The limestone, which has been noticed along the north shore of theHuron from Michilimackinac, and which continues, with interruptions of water only, from Detour to Drummond Island, and the Manatoulines, is to be noticed up the straits as high as Isle a la Crosse, where the last locality of a pure carbonate of lime appears to occur. The island of St. Joseph is chiefly primitive rock, and its south end is heavily loaded with granitic, porphyritic, and quartz boulders. The north shores of the river, opposite and above this island, are entirely of the granitic series, which continues to Gros Cape of Lake Superior. On reaching theNebeesh,[217]or Sailor's Encampment Island, sandstone rocks of a red color present themselves, and are found also on the American side of the river, and continue to characterize it to the Falls, or Sault de Ste. Marie,[218]and to Point Iroquois and Isle Parisien in Lake Superior.
The Sault of St. Mary's isuponandoverthis red sandstone. The river makes several successive leaps, of a few feet at a time, in its central channel, falling, altogether, about twenty-two feet in half a mile. This gives it a foaming appearance, and the volume pours a heavy murmur on the ear.[219]It is, of course, a complete interruption to the navigation of vessels, which can, however, come to anchor near its foot, while barges may be pushed up, empty, on the American shore. The water-power created by such a change of level, is such as must commend the spot, at a future period, to manufacturers, lumbermen, and miners. The foot of these falls is heavily incumbered, both with masses of the disrupted sand-rock[220]and granitic and conglomerate boulders.
Red Sandstone of Lake Superior.—That this is the old red sandstone, may be inferred simply from the fact that, althoughdeposited originally in horizontal beds, its position has been disturbed in many localities.
Plastic Clay Stratum of the Lakes.—The northern extremity of Muddy Lake—a sheet of water some twenty miles in length—is the head of the straits, and the beginning of the River St. Mary's. This sheet of water has the property of being rendered slightly whitish, or turbid, by continuous winds. Its bottom appears to be formed of the same plastic blue clay which obstructs the passage of vessels of large draft on the St. Clair flats, and forms an impediment of a similar kind in this river in Lake George. This stratum seems to be the result of causes not now in operation. If dredged through, or excavated, there is no reason to suppose it would again accumulate; for the waters of the lake are clear and pure, and carry down no deposit of the kind. These clay deposits remain to attest physical changes which are past. They denote the demolition of formations of slate in the upper regions, which have been broken down and washed away when the dominion of the waters was far more potential than they now are.
This formation is favorable to the growth of some species of fresh-water shells. I observed several species of the anadonta and the plenorbis, and think, from the broken valves, that research would develop others.
Porphyry and Conglomerate Boulders.—A formation of red jasper, in common white quartz, exists, in the bed of intersection, on the southeastern foot of Sugar Island. The fragments of jasper are of a bright vermil red, quite opaque, and have preserved their angles. I had observed fragments of the formation along the shores of the lower part of the straits, and even picked up some specimens, entirely abraded, however, on the south shores of the Huron, between the White Rock and Michilimackinac—a proof of the course of the drift.
The granitic conglomerates appear quite conclusive, one would think, of the results of fusion. The attraction of aggregation would seem inadequate to hold together such diverse masses. In these curious and striking masses we see the red feldspathic granite, black and shining hornblende rock, white fatty quartz, and striped jasper, held together as firmly, and polished by attrition as completely, as if they were—what they are not—the results of crystallization in this aggregate form.
Erratic Block Group.—Wherever, in fact, the geologist sets his foot, on the shores of the upper lakes, he finds himself on the great drift stratum, and cannot but revert to that era when waters, on a grander scale, swept over these plains, and the lakes played rampantly over wider areas.[221]
Basin of Lake Superior.—We entered this island sea as if by a kind of geological gate, in which the sandstone cliffs of Point Iroquois, on the one hand, stand opposite to the granitical hills of Gross Cape on the other.
In order to conceive of its geology, it may subserve the purposes of description to compare it to a vast basonic crater. The rim of this crater has been estimated, by Sir Alexander Mackenzie, at fifteen hundred miles. The primitive formations of Labrador and Hudson's Bay coasts come up, so as to form the eastern and northern sides of the rim, around which they stand in cliffs of sienitic greenstone and hornblendic rocks, in some places a thousand feet high. On its south and southwest shores, this formation of the elder class of rocks forms also a considerable portion of the coast; as in the rough tract of Granite Point, the Porcupine and Iron River Mountains, and the primitive tract west of Chegoimegon, or Lapointe. It will serve to denote the broken character of this rim, if we state that the entire plain of the lake, running against and fitting to this rim, was originally filled up with the red, gray, and mottled sandstone, which gave way and fell in at localities west of the great Keweena Peninsula, converting its bottom into an anteclinal axis.
Volcanic action, to which this disturbance in its westerlybearings may be attributed, appears to have thrown up the trap-rocks of the Pic, of the Porcupine chain, of the Isle Royal group, and other trap islands, and the long peninsula of Keweena. This system of forces appears to have spent itself from the northeast to the southwest. The shocks brought with them the elements of the copper and other metallic bodies which characterize the trap-rock. They exhausted their power, on the American side, west of the granitic tract of Chocolate and Dead Rivers, and the Totosh and Cradle-Top Mountains. The most violent disturbance took place at the west of the Keweena Peninsula, and thence it was propagated in the direction of the higher Ontonagon, the Iron, and the Montreal rivers.
This disturbance of the level of the sandstone produced undulations, which are observable on the St. Mary's, where the variation from a level is not more than eight or ten degrees. They left portions of it—as between Isle au Train and the Firesteel River—undisturbed; and they threw other portions of it—as between Iron and Montreal rivers—almost completely on their edges.
The entire north shore from Gargontwa to the old Grand Portage, inclusive of the Michepicotin and Pic regions, cannot be particularly alluded to, as that part of the coast was not visited; but the accounts of observers represent it as consisting of trap-rocks. Without the application of such forces, it appears impossible to understand the geology of this lake, or to account for the sectional and disturbed formations.
The lake itself, whose depth is great, and which has an extreme length of about 500 miles, by an extreme width of some 180, is endowed with powerful means of existing elemental action. This consists almost entirely of the force of its winds and long, sweeping waves. Its bottom may, in this light, be looked upon as an immense mortar or triturating apparatus, in which its sandstones, trap-boulders, and pebbles are driven about and comminuted. This power has greatly changed its configuration, and the process of these mutations is daily going on.
It is only by such a power of geological action that we can account for the powerful demolitions and inroads which it has made upon some parts of its southern borders. The coasts of the Pictured Rocks, which have a prominent development of about12 to 15 miles, consist in horizontal strata of coarse gray sandstone, of little cohering power. The effect of waves beating upon rocks is to communicate a curved line. This has operated to excavate numerous and extensive caves into the coast. These, after reaching hundreds of feet, have in some cases united. The effect is to isolate portions of the coast, and to leave it in fearful pinnacles, having many of the architectural characters of Gothic or Doric ruins.
The portion of coast immediately west of Grand Marrais is scarcely less unique. It denotes the effect of the prostrating power of the lake in another way. The sandstone of parts of the coast, ground down into yellow sand by this vast machinery, is lifted up by the winds as soon as it reaches the point of dryness, and heaped up into vast dunes. Standing trees are buried in these tempests of sand, and its effect is, for about nine miles along the coast, to present, at an elevation of several hundred feet, a scene of arid desolation, which can only be equalled by the Arabic deserts.
A dyke of trap seems once to have extended from the north shore to Point Keweena; but, if so, it has been prostrated, and its contents—veins and deposits, silicious and metallic—scattered profusely around the shores of the lakes. A cause less general is hardly sufficient to account for the wide distribution of fragments of the copper veins and vein-stones which have so long been noticed as characters of this lake. The basal remains of this antique dyke form the peninsula of Keweena. The tempests beating against this barrier from the northwest, have ripped up terrific areas from the solid rock, and left its covering, amygdaloid and rubblestones, in fantastic patches upon the more solid parts, or constituting islands in front of them.
Structure of its Southern Coast.—The estimated distance from Sault Ste. Marie to Fond du Lac is a fraction over 500 miles. The sandstone, as it appears in the Falls of the St. Mary's, does not appear to be entirely level. It exhibits an undulation of about 8° or 10°, dipping to west-northwest. Two instances of this waved stratification of the Lake Superior sandstone deserve notice. The first terminates at the intersection of red sand rock at la Point des Grande Sables with the beginning of the horizontal strata of the Pictured Rocks. We again observe an inclination of the strata of a few degrees at Grand Island, which is moreingfish River, and appears to dip at Isle aux Trains, about twenty miles northeast. The scenery is peculiarly soft and pleasing in passing the Huron Islands, a granitic group, and directing the view, as in the sketch, to the coast and the rough granitical hills rising behind Huron Bay. The strata are level, as shown above, around the Bay of Presque Isle and Granite Point, and continue so, resting on the roots of the granitical tract of theTötosh, or Schoolcraft, and Cradletop Mountains, and at Point aux Beignes, and Keweena Bay. This level position of the rock is preserved to the south cape of the shallow bay of the Bete Gre, on the north, at which the trap-dykes of the peninsula first begin; and so continues after passing that rugged coast of the vitreous series of that remarkable point, to and beyond Eagle River and Sandy Bay, in the approach to the portage of the Keweena.
The same horizontality is observed on the headland west of it, and upon all the points and headlands to Misery and Firesteel Rivers and the mouth of the Ontonagon. The trap-dyke of Keweena crosses this river about ten miles, in a direct line, inland.
At Iron River, we observe a stratum of compact gray grauwacke, over the hackly bed of which that river forces its way during the spring months, and stands in tanks and pools during the summer. On reaching the foot of the Porcupine Mountains, the sandstone, which is here of a dark chocolate color, with quartz pebbles of the bigness of a pigeon's egg, and organic remains of paleozoic type, is found to be tilted up into nearly a vertical position, as shown in the sketch. The grauwacke reappears, in a most striking manner, at the Falls of Presque Isle River, where the whole mass of water precipitated from the highlands drops into a vast pot-hole, a hundred feet wide and perhaps twice that depth. The whole upper series of rocks, from the Porcupine Cliffs west to the Montreal River, is a conglomerate. At the Falls of the Montreal, the river drops over the vertical edges of the red sandstone. Beyond the Bay of St. Chares, at Lapointe Chegoimigon, masses of sienitic mountains arise, which have their apex near La Riviere de Fromboise.
The Islands of the Twelve Apostles, or Federation Group, appear to be all based on the sienitic or trap, with overlying red sandstone; which latter again reappears on the point of the entrance into Fond du Lac Bay, and marks its southern coast, tillnear the entrance of the Brulé, or Misakoda River, as seen in the illustration beneath. Shores of sand then intercept its view to the entrance of the River St. Louis, and up its channel to its first rapids, about eighteen miles, where the red sandstone again appears, as the first series of the Cabotian Mountains.
Serpentine Rock.—At the nearest point north of Rivier du Mort is a headland of this rock, jutting out from the granitical formation. Lapping against it, at the mouth of the river, is a curious formation of magnesian breccia. The serpentine rock appears, in nearly every locality examined, to be highly charged with particles of chromate of iron. It may be expected to yield the usual magnesian minerals.[222]Its position is between the Carp River and Granite Point, in the Bay of Presque Isle, or rather Chocolate River, for that river pours into this bay by far the largest quantity of water.[223]
Ancient Drift-Stratum.—In the intervals between the points and headlands, where the rock formation is exposed by streams or gorges, the drift, or erratic boulder stratum, is found. Such is its position beneath the sand-dunes of the Grandes Sables, and in the elder plains and uplands, stretching with interruptions on the coast from the head of the Mary's valley to that of the St. Louis. The edge of this formation is composed of the sand and loose pebbles and boulders of the lake. Mighty as are the existing causes of action of the lake in beating down and disrupting strata of every kind, and in reproducing alluvial lands and dunes, they are weak and local when compared to the causes which have spread these ponderous boulders, and drift masses over latitudes and longitudes which appear to be limited only by the leading elevations of the continent. That oceanic torrents of water, suddenly heaped on the land, and wedged into compactness and power now unknown to it, is after all, the most plausible theory of the dispersion of this formation, and this theory avoids the necessary local one of the glacial dispersion which presupposes a very low temperature over the whole surface of the globe.
Kaugwudju.[224]—This imposing mass of the trap-rocks is the highest on the southern shores of Lake Superior. The following outlines of it are taken from a point on the approach to the Ontonagon River, about forty miles distant.
They rise to their apex about thirty miles west of that stream, in north lat. 46° 52´ 2´´, as observed by Captain Douglass. They are distant three hundred and fifty miles from St. Mary's. In a serene day they present a lofty outline, and were seen by us from the east, at the distance of about eighty miles. The Indians represent them to have a deep tarn, with very imposing perpendicular walls, at one of the highest points. If Lake Superior be estimated at six hundred and forty feet above the Atlantic, as my notes indicate, its peaks are higher than any estimates we have of the source of the Mississippi, and are, at least, the highest elevations on this part of the continent. The granitical tract of the St. Francis, Missouri,[225]and of the quartz high lands of Wachita, Arkansas, the only two known primitive elevations between the Rocky and Alleghany chains, are far less elevated.
I have now taken a rapid glance at the formations along the southern shore of the lake between St. Mary's and Fond du Lac; but have passed by some features which may be thought to merit attention.
Existing Lake Drift.—The gleaner among the rock debris of this lake has a field of labor which is not dissimilar to that of the fossilist. If he has not, so to say, to put joint to joint, to establish his conclusions, he has a mineralogical adjustment to make every way as obscure. A boulder of sienite, or a mass of sandstone, or grauwacke, may be easily referred to a contiguous rock. But when the observer meets with species which are apparently foreign to the region, he is placed in a dilemma between the toil of an impossible scrutiny and the danger of an unlicensed conjecture.
Among the more common masses which may be assigned a locality within the compass of the lake, are granites, sienites, hornblendes, greenstones, schists, traps, grauwackes, sandstones, porphyries, quartz rocks, serpentines, breccias, amygdaloids, amphiboles,and a variety of masses in which epidote and hornblende are essential constituents. With these, the coast mineralogist must associate, in place or out of place, agates, chalcedonies, carnelians, zeolite, prehnite, calcareous spar, crystalline quartz, amethystine quartz, coarse jaspers, noble serpentine, iron-sand, iron-glance, sulphate of lead, chromate of iron, native copper, carbonate of copper, and various species of pyrites. These were, at least, my principal rewards for about eighteen days' labor, in scrutinizing, at every possible point, its lengthened and varied coasts.
Cupreous Formation.—The whole region, above Grand Island at least, appears to have been the theatre of trap-dykes, and an extensive action from beneath, which brought to the surface the elements of the formation of copper veins. These have not been much explored; but, so far as observation goes, there are evidences which cannot be resisted, that the region contains this metal in various shapes and great abundance. I refer to my report of the 6th of November, 1820, for evidences of a valuable deposit of this metal in the valley of the Ontonagon River, and at other points. I found the metal in its native state at various other localities, and always under physical evidences which denoted its existence, in the geological column of the lake, in quantity. These indications were confined almost exclusively to the area intervening between the peninsula of Keweena, and La Pointe Chegoimegon, a distance of about one hundred and fifty miles. Of this district, the two extremities would make the Ontonagon Valley about the centre.[226]A profile of one of the detached pieces, found in the Ontonagon Valley, and forwarded to you by Mr. Van Rensselaer, is herewith given.
Vitric Boulders.—Among the debris of Lake Superior are masses of trachyte, and also small pieces of the sienitic series, in which the red feldspar has a calcined appearance, the quartz being, at the same time, converted into a perfectly vitreous texture. Similar productions, but not of the same exact character, exist on the sandy summits of the Grande Sable. Theseexhibit an exterior of glistening cells or orifices: it may be possible that they have been produced by fusion; but I think not. The smooth cells appear like grains of sand hurled by the winds over these bleak dunes. I have brought from that locality a single specimen of pitchstone, perfectly resinous, bleak and shining.
La Pointe Chegoimegon.—A sketch of these islands, as given in the Narrative, denotes that their number is greatly underrated, and will serve to show the configuration of a very marked part of the Superior coast. It must, hereafter, become one of the principal harbors and anchoring-ground for vessels of the lake.
Valley of the St. Louis River.—The St. Louis River takes its rise on the southern side of the Hauteur des Terres, being the same formation of the drift and erratic block stratum which gives origin, at a more westerly point, to the Mississippi. Its tributaries lie northwest of the Rainy Lakes. Vermilion Lake, a well-known point of Indian trade, is a tributary to its volume, which is large, and its outlet rushes with a great impetus to the lake. At what height its sources lie above Lake Superior, we can only conjecture. It was estimated to have a fall of two hundred and nine feet to the head of the Portage aux Coteaux, and may have a similar rise above.
By far its most distinguishing feature is its passage at the Grand Portage through the Cabotian Mountains. We entered it at Fond du Lac and pursued up its channel through alluvial grounds, in which it winds with a deep channel about nineteen or twenty miles to the foot of its first rapids. This point was found one mile above the station of the American Fur Company's trading-house. Here we encountered the first rock stratum, in the shape of our old geological acquaintance, the old red sandstone of Lake Superior. It was succeeded in the first sixteen miles, in the course of which the river is estimated to fall two hundred feet—most of it in the first twenty-nine miles—by trap, argillite, and grauwacke. Through these barriers the water forces its way, producing a series of rapids and falls which the observer often beholds with amazement. The river is continually in a foam for nine miles, and the wonder is that such a furious and heavy volume of water should not have prostrated everything before it. The sandstone, grauwacke, and the argillite, the latterof which stands on its edges, have opposed but a feeble barrier; but the trap species, resisting with the firmness, as it has the color of cast-iron, stand in masses which threaten the life and safety of everything which may be hurled against them. I found a loose specimen of sulphuret of lead and some common quartz in place in the slate rock, a vein of clorite slate, and a locality of coarse graphite, to reward my search.
The Portage aux Coteaux, which is over the basetting edges of the argillite, will give a lively idea of the effects of this rock upon the feet of the loaded voyageurs.
The sandstone is last seen near the Galley on the Nine Mile Portage. Above the Knife Portage, some eight miles higher, vast black boulders of hornblendic and basaltic blocks, are more frequent; and these masses are observed to be more angular in their shapes than the boulders and blocks of kindred character encountered on the shores of Lakes Superior and Huron. There is a vast sphagnous formation, which spreads westwardly from the head of the Coteau Portage, and gives rise to the remote tributaries of Milles lac and Rum River. Much of this consists of what the Indians termmuskeeg, or elastic bog. Hurricanes and tempests have made fearful inroads upon areas of its timber, and it is seldom crossed, even by the Indians. This tract lies east of the summit of sand-hills and drift, which environ Sandy Lake, theKomtagumaof the Chippewas. The portage of the Savanna River, a tributary of the St. Louis, is the route pursued by persons with canoes; there is no other species of water craft adapted to this navigation. But wherever crossed, this swamp-land tract imposes labor and toil which are of no ordinary cast. It is the equivalent of the argillite which has been broken down and disintegrated, forming beds of clay soil which are impervious to the water, and we way regard this ancient slate formation of the true source of the St. Lawrence tributaries, as the remote origin of those extensive beds of an argillaceous kind, which exist at many places in the lower lakes and plains.
Immediately west of the Savanna Portage, the Komtaguma summit is reached. This summit consists wholly of arid pebble and boulder drift of the elder period. It exhibits evidences of broken-down amygdaloids, which not only furnish a part of its pebbles, but also of the contents of this stratum, in numerousagates and other subspecies of the quartz family which are found scattered over the surface. This is, in fact, the origin of that extensive diffusion of these species, which is found in the valley of the Upper Mississippi, as at Lake Pepin, &c., and which has even been traced, in small pieces, as low as St. Louis and Herculaneum in Missouri.[227]We may conclude that the ancient sandstones, slates, and rubblestone, and amygdaloids, of which traces still remain, were swept from the summit of the Mississippi by those ancient floods which appear to have diffused the boulder drift from the North.
Sandy Lake.—The first view of this body of water was obtained from one of those eminences situated at the influx of the west Savanna River.
This lake is bounded, on its western borders, by the delta of the Mississippi; its outlet is about two miles in length. We here first beheld the object of our search. The soil on its banks is of the richest alluvial character. From this point, dense forests and a moderately elevated soil, varying from three or four to fifteen feet, confined the view, on either side, during more than two days' march. On the third day after leaving Sandy Lake, at an early hour, we reached the Falls of Pakágama. Here the rock strata show themselves for the first time on the Mississippi, in a prominent ledge of quartz rock of a gray color. Through this formation the Mississippi, here narrowed to less than half its width, forces a passage. The fall of its level in about fifty rods may be sixteen or eighteen feet. There is no cascade or leap, properly so called, but a foaming channel of extraordinary velocity, which it is alike impossible to ascend or descend with any species of water craft. It lies in the shape of an elbow. We made the portage on the north side.
Pakágama Summit.—The observer, when he has surmounted the summit, immediately enters on a theatre of savannas, level to the eye, and elevated but little above the water. Vistas of grass, reeds, and aquatic plants spread in every direction. On these grassy plains the river winds about, doubling and redoubling on itself, and increasing its cord of distance in a ratio which, by the most moderate computation, would seem extravagant. On thoseplateaux, and the small rivers and lakes connected with them, the wild rice reaches the highest state of perfection.
Our men toiled with their paddles till the third day, through this unparalleled maze of water and plants, when we reached the summit of the Upper Red Cedar or Cass Lake, where we encamped. In this distance no rock strata appeared, nor any formation other than a jutting ridge of sand, or an alluvial plain. Plateau on plateau had, indeed, carried us from one level or basin to another, like a pair of steps, till we had reached our extreme height.
Cass Lake Basin.—From estimates made, this lake is shown to lie at thirteen hundred and thirty feet above the Atlantic.[228]This is a small elevation, when we consider it as lying on the southern flank of the transverse formation which forms the connecting link with the Rocky Mountains. A rise or a subsidence of this part of the continent to this amount, would throw the Hudson's Bay and Arctic waters down the Mississippi valley. The scenery of its coasts is in part arenaceous plains, and in part arable land, yielding corn to the Indians.
Sources of the Mississippi.—In order to understand the geology of this region, it is necessary to premise, that the St. Lawrence, the Hudson's Bay, and the Mexican Gulf waters are separated by a ridge or watershed of diluvial hills, called the Hauteur des Terres, which begins immediately west of the basin of the Rainy Lakes and Rainy Lake River. This high ground subtends the utmost sources of the Mississippi, and reaches to the summit of Ottertail Lake, where it divides the tributaries of the Red River of Lake Winnepec from those of the Des Corbeau, or Great Crow-Wing River.
Within this basin, which circumscribes a sweep of several hundred miles, there appears to have been deposited, upon the trap and primary rocks which form its nucleus, a sedimentary argillaceous deposit, capable of containing water. Upon this, the sand and pebble drift reposes in strata of unequal thickness, and the sand is often developed in ridges and plains, bearing species of the pine. The effect has been, that the immense amount ofvapor condensed upon these summits, and falling in dews, rains, and snows, being arrested by the impervious subsoil of clay, has concentrated itself in innumerable lakes, of all imaginable forms, from half a mile to thirty miles long. These are connected by a network of rivers, which pour their redundancy into the Mississippi, and keep up a circulation over the whole vast area. The sand plains often resting around the shores of these lakes create the impression of bodies of water resting on sand, which is a fallacy. Some of these bodies of water are choked up, or not well drained, and overflow their borders, forming sphagnous tracts. Hence the frequent succession of arid sand plains, impassable muskeegs, and arable areas on the same plateaux. Every system of the latter, of the same altitude, constitutes a plateau. The highest of these is the absolute source of the Mississippi waters. The next descending series forms another plateau, and so on, till the river finally plunges over St. Anthony's Falls.
In this descending series of plateaux, the Cass, Leech Lake, and Little Lake Winnipec form the third and fourth levels.
In descending the Mississippi below the Pakágama, the first stratum of rock, which rises through the delta of the river, occurs between the mouth of the Nokasippi and Elm Rivers, below the influx of the Great De Corbeau. This rock, which is greenstone trap, rises conspicuously in the bed of the stream, in a rocky isle seated in the rapid called—I know not with what propriety—theBig Falls, orGrande Chute. The precipitous and angular falls of this striking object decide that the bed of the stream is at this point on the igneous granitical and greenstone series. This formation is seen at a few points above the water, until we pass some bold and striking eminences of shining and highly crystalline hornblendic sienite, which rises in the elevation called by us Peace Rock, on the left bank, near the Osaukis Rapids. This rock lies directly opposite to the principal encampment on the 27th of July, which was on an elevated prairie on the west bank. To this point a delegation of Sioux had ascended on an embassy of peace from Fort Snelling to the Chippewas, having affixed on a pole what the exploring party called a bark letter, the ideas being represented symbolically by a species of picture writing, or hieroglyphics. In allusion to this embassy, this locality was called thePeace Rock. This rock is sienite. It is highly crystalline, and extends several miles. Its position must be, from the best accounts, in north latitude about 44° 30´. From this point to Rum River, a distance of seventy miles, no other point of the intrusion of this formation above the prairie soil was observed.
Introduction of the Palæontological Rocks.—After passing some fifty miles below this locality there are evidences that the river, in its progress south, has now reached the vicinity of the great carboniferous and metalliferous formations, which, for so great a length, and in so striking a manner, characterize both banks of the Mississippi below St. Anthony's Falls. About nine or ten miles before reaching these Falls, this change of geological character is developed; and on reaching the Falls the river is found to be precipitated, at one leap, over strata of white sandstone, overlaid by the metalliferous limestone. The channel is divided by an island, and drops in single sheets, about sixteen to eighteen feet, exclusive of the swift water above the brink, or of the rapids for several hundred yards below. This sandstone is composed of grains of pure and nearly limpid quartz, held together by the cohesion of aggregation. If my observations were well taken it embraces, sparingly, orbicular masses of hornblende. It is horizontal, and constitutes, in some places, walls of stratification, which are remarkable for their whiteness and purity. This sandstone is overlaid by the cliff limestone, the same in character, which assumes at some points a silicious, and at others, a magnesian character. It is manifestly the same great metalliferous rock which accompanies the lead ore of Missouri and mines of Peosta or Dubuque. There rests upon it the elder drift stratum of boulders, pebble, and loam, which marks the entire valley. This latter embraces boulders of quartz and hornblende rock, along with limestones and sandstones. It is overlaid by about eighteen inches of black alluvial carbonaceous mould.
From St. Anthony's Falls the river is perpetually walled on either side with those high and picturesque cliffs which give it so imposing and varied an appearance, and its current flows on with a majesty which seems to the imagination to make it rejoice in its might, confident of a power which will enable it to reach and carry its name to the ocean in its unchanged integrity.
St. Peter's River and Valley.—The importance, fertility,and value of this tributary have particularly impressed every member of the party. Its position as the central point of the Sioux power, and its border position to the Chippewas, the representative tribe of the great Algonquin family, render it now a place of note, which fully justifies the policy of the department in establishing a military post at the confluence of the river; and the importance cannot soon pass away, in the progress of the settlement of the Mississippi Valley.[229]It is the great route of communication with the valley of the Red River of the North, and the agricultural and trading settlements of Lord Selkirk in that fertile valley, and its complete exploration by a public officer is desirable, if not demanded.[230]
Of its geological character but little is known, and that connects it with both the great formations which have been noticed as succeeding each other at the great Peace Rock. That the granitical formation reaches it at a high point is probable, from the large reported boulders. The Indians bring from the blue earth fork of it, one of their most esteemed green and blue argillaceous pigments, of which the coloring matter appears to be carbonate of copper. They also bring from the Coteau des Prairie, probably Carver's "shining mountains," specimens of that fine and beautiful red pipe stone, which has so long been known to be used by them for that purpose. This mineral is fissile, and moderately hard, which renders it fit for their peculiar ripe sculptures. I found small masses of native copper in the drift stratum at the mouth of this stream, on the top of the cliffs on the Mississippi, opposite the mouth of the St. Peter's.
Crystalline Sand Rock.—This stratum reveals the same crystalline structure which is so remarkable in the sandstone caves, near the Potosi road, in the county of St. Genevieve, Missouri; and the sand obtained from it, like that mineral, would probably fuse, with alkali, in a moderate heat, and constitute an excellent material for the manufacture of glass. It is also, like the Missouri sandstone, cavernous. In both situations, these caves appear to be due to water escaping through fissures of the rock, where its cohesion is feeble, carrying it away grain by grain.In stopping at one of these caves, about twelve miles below St. Peter's, we found this cause of structure verified by a lively spring and pond of limpid water flowing out of it.
Valley of the St. Croix.—This river originates in an elevated range of the elder sand and pebble drift, which lies on the summit between the Mississippi system of formations, and the Lake Superior basin. It communicates with the Brulé, which is "Goddard's River" of Carver, and with the Mauvaise or Bad River of that basin. Specimens of native copper have been found on Snake River, one of its tributaries.[231]
Geological Monuments.—In descending the river for the distance of about one hundred miles below St. Anthony's Falls, my attention was arrested, on visiting the high grounds, by a species of natural monuments, which appear as if made by human hands seen at a distance, but appear to be the results of the degradation and wasting away, on the Huttonian theory, of all but these, probably harder, portions of the strata.
Lake Pepin.—This sheet commends itself to notice by its extent and picturesque features. It is an expansion of the river, about twenty-four miles long, and two or three wide. Both its borders and bed reveal the drift stratum, and the observer recognizes here, boulders of the peculiar stratification which has, in ancient periods, characterized the high plateaux about the sources of the river. Such are its hornblendic, sienite, quartz, trap, and amygdaloid pebbles, and that variety of the quartz family which assumes the form of the agate and other kindred species. Moved as these materials are annually, lower and lower, by the impetus of the stream, other supplies, it may be inferred, are still furnished by the shifting sand and gravel bars from above. The mass must submit to considerable abrasion by this change, and the diminished size of the drifted masses become a sort of measure of the distance at which they are found from their parent beds.
Chippewa River.—This stream is the first to bring in a vast mass of moving sand. Its volume of water is large, which it gathers from the high diluvial plains that spread southwest of the Porcupine Mountains, and about the sources of the Wisconsin,the Montreal, and the St. Croix Rivers, with which it originates.
Trompeldo(Le Montaine des Tromps d'Eaux).—This island mountain stands as if to dispute the passage of the Mississippi, whose channel it divides into two portions. Distinct from its height, which appears to correspond with the contiguous cliffs, and in the large amount of fresh debris at its base, it presents nothing peculiar in its geology.
Painted Rock.—This vicinity is chiefly noted for its large and fine specimens of fresh-water shells.
Wisconsin.—Like the Chippewa, this stream brings down in its floods, vast quantities of loose sand, which tend to the formation of bars and temporary islands. It originates in the same elevated plains, and bespeaks a considerable area at its sources, which must be arid. It is a region, however, in which lakes and rice lands abound, and it may, in this respect, be geologically of the same formation as the higher plateaux of the Mississippi, above the Sandy Lake summit. Its sides produce many species to enrich our fresh-water Conchology.
Lead Mines of Peosta and Dubuque.—In my researches into the mineral geography of Missouri, in 1818 and 1819, I had explored a district of country between the rivers Merrimak and St. Francis, and on the Ozarks, which revealed many traits which it has in common with the Upper Mississippi. There, as here, the mineral deposits appear to be, in many cases, in a red marly clay, whether the clay is overlaid by the calcareous rock or not. There, as here, also, the limestone and sandstone strata are perfectly horizontal. The leads of ore appear, in this section, to be followed with more certainty, agreeable to the points of the compass; but this may happen, to some extent, because the practice of mining on individual account, with windlass and buckets, in the Missouri district, has led common observers to be more indifferent to exact scientific methods. To say that the digging, at these mines, is equally, or more productive, is perhaps just. Capital and labor have been rewarded in both sections of the country, in proportion as they have been perseveringly and judiciously expended.
I found much of the ore, which is a sulphuret, at Dubuque's Mines, lying in east and west leads. These leads were generallypursued in caves, or, more properly, fissures in the rock. In one of the excavations which I visited, the digging was continued horizontally under the first stratum of rock, after an excavation had been made perpendicularly, through the top soil and calcareous rock, perhaps thirty feet. The ore is a broad-grained cubical galena, easily reduced, and bids fair very greatly to enhance the value and resources of this section of the West.
Similar mines exist at Mississinawa, and the River Au Fevé,[232]both on the eastern or left bank of the Mississippi. And a system of leasing or management, such as I have suggested for the Missouri mines, appears equally desirable.
Quartz Geodes.—The amount of silex in the cliff limestone is such, in some conditions of it, as to justify the term silico-calcareous. This condition of the rock at the passage of the Mississippi through the Rock River and Des Moines Rapids, is such as to produce a very striking locality of highly crystalline quartz geodes, which accumulates in the bed of the stream. Many of these geodes are from a foot to twenty-two inches in diameter, and on breaking them they exhibit resplendent crystals of limpid quartz. Sometimes these are amethystine; in other cases they present surfaces of chalcedony or cacholong. The latter minerals, if obtained from the rock, and before unduly hardening by exposure, would probably furnish a suitable basis for lapidaries.
Intermediate Country in the Direction to Green Bay.—There is a line which separates, on the north, the granitical and trap region from the metal-bearing limestone, and its supporting sandstone. This formation of the elder series of rocks, having been traced to the south shore of Lake Superior, and having been seen to constitute the supporting bed of the alluviums and diluviums of the Upper Mississippi, above the Peace Rock, it may subserve the purpose of inquiry to trace this line of junction by its probable and observed boundaries.
The line may be commenced where it crosses the Mississippi, at the Peace Rock, and extended to the St. Croix, the falls of which are on the trap-rock, to the sources of the Chippewa at Lac du Flambeau, and the Wisconsin near Plover Portage. The source of Fox River runs amid uprising masses of sienite, and this formation appears to pass thence northeasterly, across theUpper Menominee, to the district of the Totosh and Cradle-Top Mountains, west of Chocolate River, on the shores of Lake Superior.
I observed the crystalline sandstone and its overlying cliff limestone, along the valley of the Wisconsin, where ancient excavations for lead ore have been made. There is an entire preservation of its characters, and no reason occurs why its mineralogical contents should not prove, in some positions, as valuable as they have been found in Missouri, or in the Dubuque district west of the Mississippi.
On reaching the Wisconsin Portage, the limestone is found to have been swept by diluvial action, from its supporting sand rock. Such is its position not far north of the highest of the four lakes, and again at Lake Puckway, in descending the Fox River; consequently, there are no lead discoveries in this region. On coming to the calcareous rock, which is developed along the channel of the river, below Winnebago Lake, it appears rather to belong to the lake system of deposits. Its superior stratum lies in patches, or limited districts, which appear to have been left by drift action. Petrefactions are found in these districts, and the character of the rock is dark, compact, or shelly. The lower series of deposits, such as they appear at the Kakala Rapids, at Washington Harbor, in the entrance to Green Bay, and in the cliffs north of Sturgeon Bay and Portage, are manifestly of the same age and general character as the inferior stratum of Michilimackinac and the Manatouline chain.
Basin of Lake Michigan.—This basin, stretching from the north to the south nearly four hundred miles, lies deeply in the series of formation of limestones, sandstone, and schists, to which we apply the term of the Michilimackinac system. Its north and west shores are skirted from Green Bay to a point north of the Sheboygan, with the calcareous stratum. At this point, the ancient drift, the lacustrine clay of Milwaukie and the prairie diluvium of Chicago, constitute a succession, of which the surface is a slightly waving line of the most fertile soils.
Among the pebbles cast ashore at the southern head of this lake I observed slaty coal. It seems, indeed, the only one of the lakes which reaches south into the coal basin of Illinois. If the level at which coal is found on the Illinois were followed through, itwould issue in the basin of the lake below low-water mark. Digging for this mineral on the Chicago summit, promises indeed not to be unsupported by sound hypothesis.
After passing Chicago, of which a sketch is added, the sands which begin to accumulate at the Konamik, the River du Chemin, and the St. Joseph's River,[233]appear in still more prominent ridges, skirting the eastern coasts to and beyond Grand River. These sands, which are the accumulations of winds, are cast on the arable land, much in the manner that has been noticed at the Grand Sable on Lake Superior, and reach the character of striking dunes at the coast denominated the Sleeping Bear. The winds which periodically set from the western shore, produce continual abrasions of its softer materials, and are the sole cause of these intrusive sand-hills. Pent up behind them, the water is a cause of malaria to local districts of country, and many of the small rivers upon this side are periodically choked with sand. The sketch transmitted of this bleak dune-coast (omitted here), as it is seen at the mouth of Maskigon Lake, will convey a false idea of the value of this coast, even half a mile from the spot where the surf beats. It is designed to show the air of aridity which the mere coast line presents. The stratification regains its ordinary level and appearance before reaching the Plate or Omicomico River, and the peninsula of the Grand Traverse Bay, and the settlements of the Ottawa Indians on Little Traverse Bay, afford tracts of fertile lands. Point Wagonshonce consists of a stratum of limestone of little elevation, which constitutes the southeast cape of the strait. Here a lighthouse is needed to direct the mariner.
Lake Huron.—Notices of this sheet of water have been given in our outward voyage. It appears rather as the junction of separate lakes which have had their basins fretted into one another, than as one original lake. Michigan is connected with it through the Straits of Michilimackinac. The Georgian Bay, north of the Manatouline chain, seems quite distinct. The Saganaw Bay is an element of another kind. The Manitouline chain separates the calcareous and granitic region, and its numerous trap and basaltic islands towards the north shore, of which there are many thousands,denote that it has been the scene of geological disturbance of an extraordinary kind.
Ulterior Conclusions.—In taking these several views of the geological structure of the Northwest—of the Lake Superior basin, and of the valleys of the St. Louis River—the region about the Upper Mississippi, its striking change at the Falls of St. Anthony—and the valleys of the Wisconsin and Fox Rivers, and the basins of Lakes Michigan and Huron, I am aware of the temerity of my task. Allowance must, however, be made for the rapidity of my transit over regions where the question was often the safety and personal subsistence of the party. A very large and diversified area was passed over in a short time. At no place was it possible to make elaborate observations. A thousand inconveniences were felt, but they were felt as the pressure of so many small causes impeding the execution of a great enterprise. A sketch has been made, which, it is hoped, will reveal something of the physical history and lineaments of the country. These glimpses at wild scenes, heretofore hid from the curious eye of man, have been made, at all points, with the utmost avidity. I have courted every opportunity to accumulate facts, and I owe much to the distinguished civilian who has led the party so successfully through scenes of toil and danger, not always unexpected, but always met in a calm, bold, and proper spirit, which has served to inspire confidence in all; to him, and to each one of my associates, I owe much on the score of comity and personal amenity and forbearance; and I have been made to feel, in the remotest solitudes, how easy it is to execute a duty when all conspire to facilitate it.
The views herein expressed are generalized in two geological maps (hereto prefixed), which, it is believed, will help to fix the facts in the mind. They exhibit the facts noticed, in connection with the theory established by them, and by all my observations, of the construction of this part of the continent.
The mineralogy of the regions visited is condensed in the following summary, drawn from my notes, which, it is believed, constitutes an appropriate conclusion to this report.
With the exception of one species, namely, the ores of copper, the region has not proved as attractive in this department as Ifound the metalliferous surface of Missouri. There are but few traces of mining, and those of an exceedingly ancient character, in the copper region of Lake Superior. The excavations in search of lead ore on the Upper Mississippi do not date back many years, but the indications are such as to show that few countries, even Missouri, exceed them in promises of mineral wealth.
I have employed the lapse of time between the termination of the exploration and the present moment, to extend my mineralogical observations to some parts of the Mississippi Valley which were not included in the line of the expedition, but which were visited in the following year, in the service of the Government, namely, the Miami of the Lakes, and Wabash Valleys, the Cave in Rock Region in Lower Illinois, and the Valley of the River Illinois. The whole is concentrated in the following notices:—
Tabular View of Minerals observed in the Northwest.