Chapter 10

[CB]See Lindenkohl in American Journal of Science, for June, 1891.

Fig. 51.—New York harbor in preglacial times looking south, from south end of New York Island (Newberry).

To this period must probably be referred also the formation of the gorge, or more properly fiord, of the Saguenay, which joins the St. Lawrence below Quebec. The great depth of this fiord is certainly surprising, since, according to Sir William Dawson, its bottom, for fifty miles above the St. Lawrence, is 840 feet below the sea-level, while the bordering cliffs are in some places 1,500 feet above the water. The average width is something over a mile.

It seems impossible to account for such a deep gorge extending so far below the sea-level, except upon the supposition of a long-continued continental elevation, which should allow the stream to form a cañon to an extent somewhat comparable with that of the cañons of the Colorado and other rivers in the far West. Then, upon the subsidence of the continent to the present level, it would remain partially or wholly submerged, as we find it at the present time. During the Glacial period it was so filled with ice as to prevent silting up. The rivers entering the Pacific Ocean, both in the United States and in British Columbia, are also lost in submerged channels extending out to the deeper waters of the Pacific basin in a manner closely similar to the Atlantic streams which have been mentioned.

During this continental elevation which preceded, accompanied, and perhaps brought on the Glacial period, erosion must have proceeded with great intensity along all the lines of drainage, and throughout the whole region which is now covered, and to a considerable extent smoothed over, by glacial deposits, and the whole country must have presented a very different appearance from what it does now.

A pretty definite idea of its preglacial condition can probably be formed by studying the appearance of the regions outside of and adjoining that which was covered by the continental glacier. The contrast between the glaciated and the unglaciated region is striking in several respects aside from the presence and absence of transported rocks and otherdébris, but in nothing is it greater than in the extent of river erosion which is apparent upon the surface. For example, upon the western flanks of the Alleghanies the regions south of the glacial limit is everywhere deeply channeled by streams. Indeed, so long have they evidently been permitted to work in their present channels that, wherever there have been waterfalls, theyhave receded to the very head-waters, and no cataracts exist in them at the present time. Nor are there in the unglaciated region any lakes of importance, such as characterize the glaciated region. If there have been lakes, the lapse of time has been sufficient for their outlets to lower their beds sufficiently to drain the basins dry.

On entering the glaciated area all this is changed. The ice-movement has everywhere done much to wear down the hills and fill the valleys, and, where there wasdébrisenough at command, it has obliterated the narrow gorges originally occupied by the preglacial streams. Thus it has completely changed the minor lines of superficial drainage, and in many instances has produced most extensive and radical changes in the whole drainage system of the region. In the glaciated area, channels buried beneath glaciateddébrisare of frequent occurrence, while many of the streams which occupy their preglacial channels are flowing at a very much higher level than formerly, the lower part of the channel having been silted up by the superabundantdébrisaccessible since the glacial movement began.

Buried Outlets and Channels.

It is easy to see how the great number of shallow lakes which frequent the glaciated region were formed by the irregular deposition of glacialdébris, but it is somewhat more difficult to trace out the connection between the Glacial period and the Great Lakes of North America, several of which are of such depth that their bottoms are some hundreds of feet below the sea-level, Lake Erie furnishing the only exception. This lake is so shallow that it is easy to see how its basin may have been principally formed by river erosion, while it is evident that such must have been the mode of its formation, since it is surrounded by sedimentary strata lying nearly in a horizontal position.

Fig. 52.—Section across the valley of the Cuyahoga River, twenty miles above its mouth (Claypole).

That Lake Erie is really nothing but a “glacial mill-pond” is proved also by much direct evidence, especially that derived from the depth of the buried channels of the streams flowing into it from the south. Of these, the Cuyahoga River, which enters the lake at Cleveland, has been most fully investigated. In searching for oil, some years ago, borings were made at many places for twenty-five miles above the mouth of the river. As a result, it appeared that for the whole distance the rocky bottom of the gorge was about two hundred feet below the present bottom of the river, while the river itself is two or three hundred feet below the general level of the country, occupying a trough about half a mile in width, with steep, rocky sides. These facts indicate that at one time the river must have found opportunity to discharge its contents at a level two hundred feet below that of the present lake, while an examination of the material filling up the bottom of the gorge to its present level shows it to be glacialdébris, thus proving that the silting up was accomplished during the Glacial period.

As the water of Lake Erie is for the most part less than one hundred feet in depth, and is nowhere much more than two hundred feet deep, it is clear that the preglacial outlet which drained it down to the level of the rocky bottom of the Cuyahoga River must have destroyed the lake altogether. Hence Ave may be certain that, before the Glacial period, the area now covered by the lake wassimply a broad, shallow valley through which there coursed a single river of great magnitude, with tributary branches occupying deep gorges. Professor J. W. Spencer has shown with great probability that the old line of drainage from Lake Erie passed through the lower part of the valley of Grand River, in Canada, and entered Lake Ontario at its western extremity, and that during the great Ice age this became so completely obstructed with glacialdébrisas to form an impenetrable dam, and to cause the pent-up water to flow through the Niagara Valley, which chanced to furnish the lowest opening.

In speaking of the present area of Lake Erie, however, as being then occupied by a river valley, we do not mean to imply that it was not afterwards greatly modified by glacial erosion; for undoubtedly this was the case, whatever views we may have as to the relative efficiency of ice and water in scooping out lake basins.

In the case of Lake Erie, we need suppose no change of level to account for the erosion of its basin, but only that, since the strata in which it is situated were deposited, time enough had elapsed for a great river to cut a gorge extending from the western end of Lake Ontario through to the present bed of Lake Erie, and that here a great enlargement of the valley was occasioned by the existence of deep beds of soft shale which could easily be worn away by a ramifying system of tributary streams. Rivers acting at present relative levels would be amply sufficient to produce the results which are here manifest.

But in the case of Lakes Ontario, Huron, Michigan, and Superior, whose depths descend considerably below the sea-level, we must suppose that they were, in the main, eroded when the continent was so much elevated that their bottoms were brought above tide-level. The depth of Lake Ontario implies the existence of an outlet more than four hundred feet lower than at present, which, of course, could exist only when the general elevationwas more than four hundred feet greater than now.

The existence of an outlet at that depth seems to be proved also by the fact that at Syracuse, where numerous wells have been sunk to obtain brine for the manufacture of salt, deposits of sand, gravel, and rolled stones, four hundred and fifty feet thick, are penetrated without reaching rock. Since this lies in the basin of Lake Ontario, it follows that if the basin itself has been produced by river erosion, the land must have been of sufficient height to permit an outlet through a valley, or cañon, of the required depth, and this outlet must now be buried beneath the abundant glacialdébristhat covers the region.

Professor Newberry, who has studied the vicinity carefully, is of the opinion that there is ample opportunity for such a line of drainage to have extended through the Mohawk Valley to the Hudson River. But, at Little Falls, a spur of the Adirondack Mountains projects into the valley, and the Archæan rocks over which the river runs are so prominent and continuous that some have thought it impossible for the requisite channel to have ever existed there. Extensive deposits of glacialdébris, however, are found in the vicinity, especially in places some distance to the north, and in Professor Newberry’s opinion the existence of a buried channel around the obstruction upon the north side is by no means improbable.

The preglacial drainage of Lake Huron has not been determined with any great degree of probability. Professor Spencer formerly supposed that it passed from the southern end of the lake through London, in the western part of Ontario, and reached the Erie basin near Port Stanley, and so augmented the volume of the ancient river which eroded the buried cañon from Lake Erie to Lake Ontario. But he now supposes, though the evidence is by no means demonstrative, that the waters of Lake Huron passed into Lake Ontario by means of a channelextending from Georgian Bay to the vicinity of Toronto.

With a fair degree of probability, the basin of Lake Superior is supposed by Professor Newberry to have been joined to that of Lake Michigan by some passage, now buried, considerably to the west of the Strait of Mackinac, and thence to have had an outlet southward from the vicinity of Chicago directly into the Mississippi River. Of this there is considerable evidence furnished by deeply buried channels which have been penetrated by borings in various places in Kankakee, Livingston, and McLean Counties, Illinois; but the whole area extending from Lake Michigan to the Mississippi is so deeply covered with glacialdébristhat the surface of the country gives no satisfactory indication of the exact lines of preglacial drainage.

Some of the most remarkable instances of ancient river channels buried by the glacial deposits have been brought to light in southwestern Ohio, where there has been great activity in boring for gas and oil. At St. Paris, Champaign County, for example, in a locality where the surface of the rock near by was known to be not far below the general level, a boring was begun and continued to a depth of more than five hundred feet without reaching rock, or passing out of glacialdébris.

Many years ago Professor Newberry collected sufficient facts to show that pretty generally the ancient bed of the Ohio River was as much as 150 feet below that over which it now flows. During a continental elevation the erosion had proceeded to that extent, and then the channel had been silted up during the Glacial period with the abundant material carried down by the streams from the glaciated area. One of the evidences of the preglacial depth of the channel of the Ohio was brought to light at Cincinnati, where “gravel and sand have been found to extend to a depth of over one hundred feet belowlow-water mark, and the bottom of the trough has not been reached.” In the valley of Mill Creek, also, “in the suburbs of Cincinnati, gravel and sand were penetrated to the depth of 120 feet below the stream before reaching rock.” But from the general appearance of the channel, Professor J. F. James was led to surmise that a rock bottom extended all the way across the present channel of the Ohio, between Price Hill and Ludlow, Ky., a short distance below Cincinnati, which would preclude the possibility of a preglacial outlet at the depth disclosed in that direction. Mr. Charles J. Bates (who was inspector of the masonry for the Cincinnati Southern Railroad while building the bridge across the Ohio at this point) informs me that Mr. James’s surmise is certainly correct, and that his “in all probability” may be displaced by “certainly,” since the bedded rocks supposed by Professor James to extend across the river a few feet below its present bottom were found by the engineers to be in actual existence.

In looking for an outlet for the waters of the upper Ohio which should permit them to flow off at the low level reached in the channel at Cincinnati, Professor James was led to inspect the valley extending up Mill Creek to the north towards Hamilton, where it joins the Great Miami. The importance of Mill Creek Valley is readily seen in the fact that the canal and the railroads have been able to avoid heavy grades by following it from Cincinnati to Hamilton. As a glance at a map will show, it is also practically but a continuation of the northerly course pursued by the Ohio for twenty miles before reaching Cincinnati. This, therefore, was a natural place in which to look beneath the extensive glacialdébrisfor the buried channel of the ancient Ohio, and here in all probability it has been found. The borings which have been made in Milk Creek Valley north of Cincinnati, show that the bedded rock lies certainly thirty-four feet below the low-water mark of the Ohio just below Cincinnati, whileat Hamilton, twenty-five miles north of Cincinnati, where the valley of the Great Miami is reached, the bedded rock of the valley lies as much as ninety feet below present low-water mark in the Ohio.

Other indications of the greater depth of the preglacial gorge of the Ohio are abundant. “At the junction of the Anderson with the Ohio, in Indiana, a well was sunk ninety-four feet below the level of the Ohio before rock was found.” At Louisville, Ky., the occurrence of falls in the Ohio seemed at first to discredit the theory in question, but Professor Newberry was able to show that the falls at Louisville are produced by the water’s being now compelled to flow over a rocky point projecting from the north side into the old valley, while to the south there is ample opportunity for an old channel to have passed around this point underneath the city on the south side. The lowlands upon which the city stands are made lands, where glacialdébrishas filled up the old channel of the Ohio.

Above Cincinnati the tributaries of the Ohio exhibit the same phenomena. At New Philadelphia, Tuscarawas County, the borings for salt-wells show that the Tuscarawas is running 175 feet above its ancient bed. The Beaver, at the junction of the Mahoning and Shenango, is flowing 150 feet above the bottom of its old trough, as is demonstrated by a large number of oil-wells bored in the vicinity. Oil Creek is shown by the same proofs to run from 75 to 100 feet above its old channel, and that channel had sometimes vertical and even overhanging walls.[CC]

[CC]Geological Survey of Ohio, vol. ii, pp. 13, 14.

The course of preglacial drainage in the upper basin of the Alleghany River is worthy of more particular mention. Mr. Carll, of the Pennsylvania Geological Survey, has adduced plausible reasons for believing that previousto the Glacial period the drainage of the valley of the upper Alleghany north of the neighbourhood of Tidioute, in Warren County, instead of passing southward as now, was collected into one great stream flowing northward through the region of Cassadaga Lake to enter the Lake Erie basin at Dunkirk, N. Y. The evidence is that between Tidioute and Warren the present Alleghany is shallow, and flows over a rocky basin; but from Warren northward along the valley of the Conewango, the bottom of the old trough lies at a considerably lower level, and slopes to the north. Borings show that in thirteen miles the slope of the preglacial floor of Conewango Creek to the north is 136 feet. The actual height above tide of the old valley floor at Fentonville, where the Conewango crosses the New York line, is only 964 feet; while that of the ancient rocky floor of the Alleghany at Great Bend, a few miles south of Warren, was 1,170 feet. Again, going nearer the head-waters of the Alleghany, in the neighbourhood of Salamanca, it is found that the ancient floor of the Alleghany is, at Carrollton, 70 feet lower than the ancient bed of the present stream at Great Bend, about sixty miles to the south; while at Cole’s Spring, in the neighbourhood of Steamburg, Cattaraugus County, N. Y., there has been an accumulation of 315 feet of drift in a preglacial valley whose rocky floor is 155 feet below the ancient rocky floor at Great Bend. Unless there has been a great change in levels, there must, therefore, have been some other outlet than the present for the waters collecting in the drainage basin to the north of Great Bend.[CD]

[CD]For a criticism of Mr. Carll’s views, see an article on Pleistocene Fluvial Planes of Western Pennsylvania, by Mr. Frank Leverett, in American Journal of Science, vol. xlii, pp. 200-212.

While there are numerous superficial indications of buried channels running towards Lake Erie in this region,direct exploration has not been made to confirm these theoretical conclusions. In the opinion of Mr. Carll, Chautauqua Lake did not flow directly to the north, but, passing through a channel nearly coincident with that now occupied by it, joined the northerly flowing stream a few miles northeast from Jamestown.[CE]It is probable, however, that Chautauqua did not then exist as a lake, since the length of preglacial time would have permitted its outlet to wear a continuous channel of great depth corresponding to that known to have existed in the Conewango and upper Alleghany.

[CE]Second Geological Survey of Pennsylvania, vol. iii.

The foregoing are but a few of the innumerable instances where the local lines of drainage have been disturbed, and even permanently changed, by the glacial deposits. Almost every lake in the glaciated region is a witness to this disturbance of the established lines of drainage by glacial action, while in numerous places where lakes do not now exist they have been so recently drained that their shore-lines are readily discernible.

An interesting instance of the recent disappearance of one of these glacial lakes is that of Runaway Pond, in northern Vermont. In the early part of the century the Lamoille River had its source in a small lake in Craftsbury, Orleans County. The sources of the Missisquoi River were upon the same level just to the north, and the owner of a mill privilege upon this latter stream, desiring to increase his power by obtaining access to the water of the lake, began digging a ditch to turn it into the Missisquoi, but no sooner had he loosened the thin rim of compact material which formed the bottom and the sides of the inclosure, than the water began to rush out through the underlying and adjacent quicksands. This almost instantly enlarged the channel, and drained the whole body of water oft 3 in an incredibly short time. As a consequence,the torrent went rushing down through the narrow valley, sweeping everything before it; and nothing but the unsettled condition of the country prevented a disaster like that which occurred in 1889 at Johnstown, Pa. Doubtless there are many other lakes held in position by equally slender natural embankments. Artificial reservoirs are by no means the only sources of such danger.

The buried channel of the old Mississippi River in the vicinity of Minneapolis is another instructive example of the instability of many of the present lines of drainage. The gorge of the Mississippi River extending from Fort Snelling to the Falls of St. Anthony at Minneapolis is of post-glacial origin. One evidence of this is its narrowness when contrasted with the breadth of the valley below Fort Snelling. Below this point the main trough of the Mississippi has a width of from two to eight miles, and the faces of the bluffs on either side show the marks of extreme age. The tributary streams also have had time to wear gorges proportionate to that of the main stream, and the agencies which oxidise and discolor the rocks have had time to produce their full effects. But from Fort Snelling up to Minneapolis, a distance of about seven miles, the gorge is scarcely a quarter of a mile in width, and the faces of the high, steep bluffs on either side are remarkably fresh looking by comparison with those below; while the tributary gorges, of which that of the Minnehaha River is a fair specimen, are very limited in their extent.

Upon looking for the cause of this condition of things we observe that the broad trough of the Mississippi River, which had characterised it all the way below Fort Snelling, continues westward, without interruption, up the valley of the present Minnesota River, and, what seems at first most singular, it does not cease at the sources of the Minnesota, but, through Lake Traverse and Big StoneLake, is continuous with the trough of the Red River of the North.

Fig. 53.—Map of Mississippi River from Fort Snelling to Minneapolis and the vicinity, showing the extent of the recession of the Falls of St. Anthony since the great Ice age. Notice the greater breadth of the valley of the Minnesota River as described in the text (Winchell).

Deferring, however, for a little the explanation of this,we will go back to finish the history of the preglacial channel around the Falls of St. Anthony. As early as the year 1876 Professor N. H. Winchell had collected sufficient evidence from wells, one of which had been sunk to a depth of one hundred and seventy-five feet, to show that the preglacial course of the stream corresponding to the present Mississippi River ran to the west of Minneapolis and of the Falls of Minnehaha, and joined the main valley some distance above Fort Snelling, as shown in the accompanying map.

This condition of things was at one time very painfully brought to the notice of the citizens of Minneapolis. A large part of the wealth of the city at that time consisted of the commercial value of the water-power furnished by the Falls of St. Anthony. To facilitate the discharge of the waste water from their wheels, some mill-owners dug a tunnel through the soft sandstone underlying the limestone strata over which the river falls; but it very soon became apparent that the erosion was proceeding with such rapidity that in a few years the recession of the falls would be carried back to the preglacial channel, when the river would soon scour out the channel and destroy their present source of wealth. The citizens rallied to protect their property, and spent altogether as much as half a million dollars in filling up the holes that had been thoughtlessly made; but so serious was the task that they were finally compelled to appeal for aid to the United States Government. Permanent protection was provided by running a tunnel, some ways back from the falls, completely across the channel, through the soft sandstone underlying the limestone, and filling this up with cement hard enough and compact enough to prevent the further percolation of the water from above.

Ice-Dams.

The foregoing changes in lines of drainage due to the Glacial period were produced by deposits of earthy material in preglacial channels. Another class of temporary but equally interesting changes were produced by the ice itself acting directly as a barrier.

Many such lakes on a small scale are still in existence in various parts of the world. The Merjelen See in Switzerland is a well-known instance. This is a small body of water held back by the great Aletsch Glacier, in a little valley leading to that of the Fiesch Glacier, behind the Eggischorn. At irregular intervals the ice-barrier gives way, and allows the water to rush out in a torrent and flood the valley below. Afterwards the ice closes up again, and the water reaccumulates in preparation for another flood.

Other instances in the Alps are found in the Mattmark See, which fills the portion of the Saas Valley between Monte Rosa and the Rhône. This body of water is held in place by the Allalin Glacier, which here crosses the main valley. The Lac du Combal is held back by the Glacier de Miage at the southern base of Mont Blanc. “A more famous case is that of the Gietroz Glacier in the valley of Bagnes, south of Martigny. In 1818 this lake had grown to be a mile long, and was 700 feet wide and 200 feet deep. An attempt was made to drain it by cutting through the ice, and about half the water was slowly drawn off in this way; but then the barrier broke, and the rest of the lake was emptied in half an hour, causing a dreadful flood in the valley below. In the Tyrol, the Vernagt Glacier has many times caused disastrous floods by its inability to hold up the lake formed behind it. In the northwestern Himalaya, the upper branches of the Indus are sometimes held back in this way. A noted flood occurred in 1835; it advanced twenty-five miles inan hour, and was felt three hundred miles down-stream, destroying all the villages on the lower plain, and strewing the fields with stones, sand, and mud.”[CF]

[CF]Professor William M. Davis in. Proceedings of the Boston Society of Natural History, vol. xxi, pp. 350, 351.

In Greenland such temporary obstructions are frequent, forming lakes of considerable size. Instances occur, in connection with the Jakobshavn and the Frederickshaab Glaciers, and in the North Isortok and Alangordlia Fiords.

Frequently, also, bodies of water of considerable size are found in depressions of the ice itself, even at high levels. I have myself seen them covering more than an acre, and as much as a thousand feet above the sea-level, upon the surface of the Muir Glacier, Alaska. They are reported by Mr. I. C. Russell[CG]of larger size and at still higher elevations upon the glaciers radiating from Mount St. Elias; while the explorers of Greenland mention them of impressive size upon the surface of its continental ice-sheet.

[CG]See National Geographic Magazine, vol. iii, pp. 116-120.

With these facts in mind we can the more readily enter into the description which will now be given of some temporary lakes of vast size which were formed by direct ice-obstructions during portions of the period.

One of the most interesting of these is illustrated upon the accompanying map, which will need little description.

Fig. 54.—Map showing the effect of the glacial dam at Cincinnati (Claypole). (From Transactions of the Edinburgh Geological Society.)

While tracing the boundary-line of the glaciated area in the Mississippi Valley during the summer of 1882, I discovered the existence of unmistakable glacial deposits in Boone County, Kentucky, across the Ohio River, from Cincinnati.[CH]; These deposits were upon the height of land 550 feet above the Ohio River, or nearly 1,000 feet above the sea, which is about the height of the water-shed between the Licking and Kentucky Rivers. As the Ohio River occupies a trough of erosion some hundreds of feet in depth, and extending all the way from this point to the mountains of western Pennsylvania, it would follow that the ice which conveyed boulders across the Ohio River at Cincinnati, and deposited them upon the highlands between the Licking and Kentucky Rivers, would so obstruct the channel of the Ohio as to pond the water back, and hold it up to the level of the lowest pass into the Ohio River farther down. Direct evidences of obstruction by glacial ice appear also for a distance of fifty or sixty miles, extending both ways, from Cincinnati.

[CH]The existence of portions of this evidence had previously been pointed out by Mr. Robert B. Warder and Dr. George Sutton (see Geological Reports of Indiana, 1872 and 1878).

The consequences connected with this state of things are of the most interesting character.

The bottom of the Ohio River at Cincinnati is 432 feet above the sea-level. A dam of 550 feet would raise the water in its rear to a height of 982 feet above tide. This would produce a long, narrow lake, of the width of the eroded trough of the Ohio, submerging the site of Pittsburg to a depth of 281 feet, and creating slack water up the Monongahela nearly to Grafton, West Virginia, and up the Alleghany as far as Oil City. All the tributaries of the Ohio would likewise be filled to this level. The length of this slack-water lake in the main valley, to its termination up either the Alleghany or the Monongahela, was not far from one thousand miles. The conditions were also peculiar in this, that all the northern tributaries rose within the southern margin of the ice-front, which lay at varying distances to the north. Down these there must have poured during the summer months immense torrents of water to strand boulder-laden icebergs on the summits of such high hills as were lower than the level of the dam.

Naturally enough, this hypothesis of a glacial dam at Cincinnati aroused considerable discussion, and led tosome differences of opinion. Professors I. C. White and J. P. Lesley, whose field work has made them perfectly familiar with the upper Ohio and its tributaries, at once supported the theory, with a great number of facts concerning certain high-level terraces along the Alleghany and Monongahela Rivers; while additional facts of the same character have been brought to light by myself and others. In general, it may be said that in numerous places terraces occur at a height so closely corresponding to that of the supposed dam at Cincinnati, that they certainly strongly suggest direct dependence upon it. The upward limit of these terraces in the Monongahela River is 1,065 feet, and they are found in various places in situations which indicate that they were formed in still water of such long standing as would require an obstruction below of considerable permanence.

One of the most decisive cases adduced by Professor White occurs near Morgantown, in West Virginia, of which he gives the following description:

“Owing to the considerable elevation—275 feet—of the fifth terrace above the present river-bed in the vicinity of Morgantown, its deposits are frequently found far inland from the Monongahela, on tributary streams. A very extensive deposit of this kind occurs on a tributary one mile and a half northeast of Morgantown; and the region, which includes three or four square miles, is significantly known as the ‘Flats.’ The elevation of the ‘Flats’ is 275 feet above the river, or 1,065 feet above tide. The deposits on this area consist almost entirely of clays and fine, sandy material, there being very few boulders intermingled. The depth of the deposit is unknown, since a well sunk on the land of Mr. Baker passed through alternate beds of clay, fine sand, and muddy trash, to a depth of sixty-five feet without reaching bed-rock. In some portions of the clays which make up this deposit, the leaves of our common forest-trees are found most beautifully preserved.

“At Clarksburg, where the river unites with Elk Creek, there is a wide stretch of terrace deposits, and the upper limit is there about 1,050 feet above tide, or only 130 feet above low-water (920 feet); while at Weston, forty miles above (by the river), these deposits cease at seventy feet above low water, which is there 985 feet above tide. It will thus be observed that the upper limit of the deposits retains a practical horizontality from Morgantown to Weston, a distance of one hundred miles, since the upper limit has the same elevation above tide (1,045 to 1,065 feet) at every locality.

“These deposits consist of rounded boulders of sandstone, with a large amount of clay, quicksand, and other detrital matter. The country rock in this region consists of the soft shales and limestones of the upper coal-measures, and hence there are many ‘low gaps’ from the head of one little stream to that of another, especially along the immediate region of the river; and in every case the summits of these divides, where they do not exceed an elevation of 1,050 feet above tide, are covered with transported or terrace material; but where the summits go more than a few feet above that level we find no transported material upon them, but simply the decomposed country rock.”

Other noteworthy terraces naturally attributable to the Cincinnati ice-dam are to be found in the valley of the Kanawha, in West Virginia, and one of special significance on the pass between the valleys of the Ohio and Monongahela, west of Clarksburg, West Virginia. According to Professor White, there is at this latter place “a broad, level summit, having an elevation of 1,100 feet, in a gap about 300 feet below the enclosing hills. This gap, or valley, is covered by a deposit of fine clay. The cut through it is about thirty feet, and one can observe the succession of clays of all kinds and of different colours, from yellow on the surface down to the finest white potter’sclay at the level of the railway, where the cut reaches bed-rock, thus proving that the region has been submerged.”[CI]

[CI]Bulletin of the Geological Society of America, vol. i, p. 478.

Another crucial case I have myself described at Bellevue, in the angle of the Ohio and Alleghany Rivers, about five miles below Pittsburg, where the gravel terrace is nearly 300 feet above the river, making it about 1,000 feet above the sea. A significant circumstance connected with this terrace is that not only does its height correspond with that of the supposed obstruction at Cincinnati, but it contains many pebbles of Canadian origin, which could not have got into the valley of the Alleghany before the Glacial period, and could only have reached their present position by being brought down the Alleghany River upon floating ice, or by the ordinary movement of gravel along the margin of a river. Thus this terrace, while corresponding closely with the elevation of those on the Monongahela River, is directly connected with the Glacial period, and furnishes a twofold argument for our theory.

A still stronger case occurs at Beech Flats, at the head of Ohio Brush Creek, in the northwest corner of Pike County, Ohio, where, at an elevation of about 950 feet above the sea, there is an extensive flat-topped terrace just in front of the terminal moraine. This terrace consists of fine loam, such as is derived from the glacial streams, but which must have been deposited in still water. The occurrence of still water at that elevation just in front of the continental ice-sheet is best accounted for by the supposed dam at Cincinnati. Indeed, it is extremely difficult to account for it in any other way.

There are, however, two other methods of attempting to account for the class of facts above cited in support of the ice-dam theory, of which the most plausible is, that inconnection with the Glacial period there was a subsidence of the whole region to an extent of 1,100 feet.

The principal objection heretofore alleged against this supposition is that there are not corresponding signs of still-water action at the same level on the other side of the Alleghany Mountains. This will certainly be fatal to the subsidence theory, if it proves true. But it is possible that sufficient search for such marks has not yet been made on the eastern side of the mountains.

The other theory to account for the facts is, that the terraces adduced in proof of the Cincinnati ice-dam were left by the streams in the slow process of lowering their beds from their former high levels. This is the view advocated by President T. C. Chamberlin. But the freshness of the leaves and fragments of wood, such as were noted by Professor White at Morgantown, and the great extent of fine silt occasionally resting upon the summits of the water-sheds, as described above, near Clarksburg, bear strongly against it. Furthermore, to account for the terrace described at Bellevue, which contains Canadian pebbles, President Chamberlin is compelled to connect the deposit with his hypothetical first Glacial epoch, and to assume that all the erosion of the Alleghany and Monongahela Rivers, and indeed of the whole trough of the Ohio River, took place in the interval between the “first” and the “second” Glacial periods (for he would connect the glacial deposits upon the south side of the river at Cincinnati with the first Glacial epoch)—all of which, it would seem, is an unnecessary demand upon the forces of Nature, when the facts are so easily accounted for by the simple supposition of the dam at Cincinnati.[CJ]

[CJ]See matter discussed more at length in the lee Age, pp. 326-350, 480-500; Bulletin of the United States Geological Survey, No. 58, pp. 76-100; Popular Science Monthly, vol. xlv, pp. 184-199.Per contra, Mr. Frank Leverett, in American Geologist, vol. x, pp. 18-24.

Fig. 55.—Map showing the condition of things when the ice-front had withdrawn about on hundred and twenty miles, and while it still filled the valley of the Mohawk. The outlet was then through the Wabash. Niagara was not yet born (Claypole). (Transactions of the Edinburgh Geological Society.)

We have already described[CK]the various temporary lakes and lines of drainage caused by the direct obstruction of the northward outlets to the basin of the Great Lakes. In connection with the map, it will be unnecessary to do anything more here than add a list of such temporary southern outlets from the Erie-Ontario basin.[CL]The first is at Fort Wayne, Indiana, through a valley connecting the Maumee River basin with that of the Wabash. The channel here is well defined, and the high-level gravel terraces down the Wabash River are a marked characteristic of the valley. The elevation of this col above the sea is 740 feet. Similar temporary lines of drainage existed from the St. Mary’s River to the Great Miami, at an elevation of 942 feet; from the Sandusky River to the Scioto, through the Tymochtee Gap, at an elevation of 912 feet; from Black River to the Killbuck (a tributary of the Muskingum) through the Harrisville Gap, at 911 feet; from the Cuyahoga into the Tuscarawas Valley, through the Akron Gap, at 971 feet; from Grand River into the Mahoning, through the Orwell Gap, 938 feet; from Cattaraugus Creek, N. Y., into the Alleghany Valley through the Dayton Gap, about 1,300 feet; between Conneaut Creek and Shenango River, at Summit Station, 1,141 feet; from the Genesee River, N. Y., into the head-waters of the Canisteo, a branch of the Susquehanna, at Portageville, 1,314 feet; from Seneca Lake to Chemung River, at Horseheads, 879 feet; from Cayuga Lake to the valley of Cayuga Creek, at Spencer, N. Y., 1,000 feet; from Utica, N. Y., into the Chenango Valley at Hamilton, about 900 feet.

[CK]See pp.92seq.,199seq.

[CL]See also accompanying map.

Fig. 56.—Map illustrating a stage in the recession of the ice in Ohio. For a section of the deposit in the bed of this lakelet, seepage 200. The gravel deposits formed at this stage along the outlet into the Tuscarawas River are very clearly marked (Claypole). (Transactions of the Edinburgh Geological Society.)

Perhaps it would have been best to give this list in the reverse order, which would be more nearly chronological, since it is clear that the highest outlets are the oldest. We should then have to mention, after the Fort Wayne outlet, two others at lower levels which are pretty certainly marked by distinct beach ridges upon the south side of Lake Erie. The first was opened when the ice had melted back from the south peninsula of Michigan to the water-shed across from the Shiawassee and Grand Rivers, uncovering a pass which is now 729 feet above the sea. This continued to be the outlet of Lake Erie-Ontario until the ice had further retreated beyond the Strait of Mackinac, when the water would fall to the level of the old outlet from Lake Michigan into the Illinois River, which is a little less than 600 feet, where it would remain until the final opening of the Mohawk River in New York attracted the water in that direction, and lowered the level to that of the pass from Lake Ontario to the Mohawk at Rome.[CM]

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