Chapter 3

Fig. 1.—Zermatt Glacier (Agassiz).

Aglacieris a mass of ice so situated and of such size as to have motion in itself. The conditions determining the character and rate of this motion will come up for statement and discussion later. It is sufficient here to say that ice has a capacity of movement similar to that possessed by such plastic substances as cold molasses, wax, tar, or cooling lava.

The limit of a glacier’smotionis determined by the forces which fix the point at which its final melting takes place. This will therefore depend upon both the warmth of the weather and upon the amount of ice. If the ice is abundant, it will move farther into the region of warm temperature than it will if it is limited in supply.

Upon ascending a glacier far enough, one reaches acomparatively motionless part corresponding to the lake out of which a river often flows. Technically this is called thenévé.

Glacial iceis formed from snow where the annual fall is in excess of the melting power of the sun at that point. Through the influence of pressure, such as a boy applies to a snow-ball (but which in thenévé-field arises from the weight of the accumulating mass), the lower strata of thenévéare gradually transformed into ice. This process, is also assisted by the moisture which percolates through the snowy mass, and which is furnished both by the melting of the surface snow and by occasional rains.

The division between thenévéand the glacier proper is not always easily determined. The beginnings of the glacial movement—that is, of the movement of the ice-stream flowing out of thenévé-field—are somewhat like the beginnings of the movement of the water from a great lake into its outlet. Thenévéis the reservoir from which the glacier gets both its supply of ice and the impulse which gives it its first movement. There can not be a glacier without anévé-field, as there can not be a river without a drainage basin. But there may be anévé-field without a glacier—that is, a basin may be partially filled with snow which never melts completely away, while the equilibrium of forces is such that the ice barely reaches to the outlet from which the tongue-like projection (to which the name glacier would be applied) fails to emerge only because of the lack of material.

Fig. 2.—Illustrates the formation of veined structure by pressure at the junction of two branches.

A glacier is characterised by bothveinsandfissures. The veins give it a banded or stratified appearance, blue alternating with lighter-coloured portions of ice. As thesebands are not arranged with any apparent uniformity in the glacier, their explanation has given rise to much discussion. Sometimes the veins are horizontal, sometimes vertical, and at other times at an angle with the line of motion. On close investigation, however, it is found that the veins are always at right angles to the line of greatest pressure. This leads to the conclusion that pressure is the cause of the banded structure. The blue strata in the ice are those from which the particles of air have been expelled by pressure; the lighter portions are those in which the particles are less thoroughly compacted. Snow is but pulverized ice, and differs in colour from the compact mass for the same reason that almost all rocks and minerals change their colour when ground into a powder.

Figs. 3, 4.—Illustrate the formation of marginal fissures and veins.

Fig. 5.—c,c, show fissures and seracs where the glacier moves down the steeper portion of its incline;s,s, show the vertical structure produced by pressure on the gentler slopes.

Thefissures, which, when of large size, are calledcrevasses, are formed in those portions of a glacier where, from some cause, the ice is subjected to slight tension. This occurs especially where, through irregularities in the bottom, the slope of the descent is increased. The ice, then, instead of moving in a continuous stream at the top, cracks open along the line of tension, and wedge-shaped fissures are formed extending from the top down to a greater or less distance, according to the degree of tension. Usually, however, the ice remains continuous in the lowerstrata, and when the slope is diminished the pressure reunites the faces of the fissure, and the surface becomes again comparatively smooth. Where there are extensive areas of tension, the surface of the ice sometimes becomes exceedingly broken, presenting a tangled mass of towers, domes, and pinnacles of ice calledseracs.

Fig. 6.—Section across Glacial Valley, showing old Lateral Moraines.

Like running water, moving ice is a powerful agent intransportingrocks and earthydébrisof all grades of fineness; but, owing to the different consistencies of ice and water, there are great differences in the mode and result of transportation by them. While water can hold in suspension only the very finest material, ice can bear upon its surface rocks of the greatest magnitude, and can roll or shove along under it boulders and pebbles which would be Unaffected except by torrential currents of water. We find, therefore, a great amount of earthy material of all sizes upon the top of a glacier, which has reached it very much asdébrisreaches the bed of a river, namely, by falling down upon it from overhanging cliffs, or by land-slides of greater or less extent. Such material coming into a river would either disappear beneath its surface, or would form a line ofdébrisalong the banks; in both cases awaiting the gradual erosion and transportation which running water is able to effect. But, in case of a glacier, the material rests upon the surface of the ice, and at once begins to partake of its motion, while successive accessions of material keep up the supply at any one point, so as to form a train of boulders and otherdébris, extending below the point as far as the glacial motion continues.

Such a line ofdébrisis called amoraine. When it forms along the edge of the ice, it is called alateralmoraine. It is easy to see that, where glaciers come out from two valleys which are tributary to a larger valley, their inner sides must coalesce below the separating promontory, and the two lateral moraines will become united and will move onward in the middle of the surface of the glacier. Such lines ofdébrisare calledmedialmoraines. These are characteristic of all extensive glaciers formed by the union of tributaries. There is no limit to the number of medial moraines, except in the number of tributaries.

A medial moraine, when of sufficient thickness, protects the ice underneath it from melting; so that the moraine will often appear to be much larger than it really is: what seems to be a ridge of earthy material being in reality a long ridge of ice, thinly covered with earthydébris, sliding down the slanting sides as the ice slowly wastes away Large blocks of stone in the same manner protect the ice from melting underneath, and are found standing on pedestals of ice, often several feet in height. An interesting feature of these blocks is that, when the pedestal fails, the block uniformly falls towards the sun, since that is the side on which the melting has proceeded most rapidly.

If the meteorological forces are so balanced that the foot of a glacier remains at the same place for any great length of time, there must be a great accumulation of earthydébrisat the stationary point, since the motion of the ice is constantly bearing its lines of lateral and medial moraine downwards to be deposited, year by year, at the melting line along the front.

Such accumulations are calledterminalmoraines, and the process of their formation may be seen at the foot of almost any large glacier. The pile of material thus confusedly heaped up in front of some of the larger glaciers of the world is enormous.

The melting away of the lower part of a glacier gives rise also to several other characteristic phenomena. Where the foot of a glacier chances to be on comparatively level land, the terminal moraine often covers a great extent of ice, and protects it from melting for an indefinite period of time. When the ice finally melts away and removes the support from the overlying morainicdébris, this settles down in a very irregular manner, leaving enclosed depressions to which there is no natural outlet. These depressions, from their resemblance to a familiar domestic utensil, are technically known askettle-holes. The terminal moraines of ancient glaciers may often be traced by the relative abundance of these kettle-holes.

The streams of water arising both from the rainfall and from the melting of the ice also produce a peculiar effect about the foot of an extensive glacier. Sometimes these streams cut long, open channels near the end of the glacier, and sweep into it vast quantities of morainic material, which is pushed along by the torrential current, and, after being abraded, rolled, and sorted, is deposited in a delta about its mouth, or left stranded in long lines between the ice-walls which have determined its course. At other times the stream has disappeared far back in the glacier, and plunged into a crevasse (technically called amoulin), whence it flows onwards as a subglacial stream. But in this case the deposits might closely resemble those of the previous description. In both cases, when the ice has finally melted away, peculiar ridge-like deposits of sorted material remain, to mark the temporary line of drainage. These exist abundantly in most regions which have been covered with glacial ice, and are referred to in Scotland askames, in Ireland aseskers, and in Sweden asosars. In this volume we shall call themkames, and the deltas spread out in front of them will be referred to askame-plains.

With this preliminary description of glacial phenomena,we will proceed to give, first, a brief enumeration and description of the ice-fields which are still existing in the world; second, the evidences of the former existence of far more extensive ice-fields; and, third, the relation of the Glacial period to some of the vicissitudes which have attended the life of man in the world.

The geological period of which we shall treat is variously designated by different writers. By some it is simply called the “post-Tertiary,” or “Quaternary”; by others the term “post-Pliocene” is used, to indicate more sharply its distinction from the latter portion of the Tertiary period; by others this nicety of distinction is expressed by the term “Pleistocene.” But, since the whole epoch was peculiarly characterised by the presence of glaciers, which have not even yet wholly disappeared, we may properly refer to it altogether under the descriptive name of “Glacial” period.

CHAPTER II.

EXISTING GLACIERS.

In Europe.—Our specific account of existing glaciers naturally begins with those of the Alps, where Hugi, Charpentier, Agassiz, Forbes, and Guyot, before the middle of this century, first brought clearly to light the reality and nature of glacial motion.

According to Professor Heim, of Zürich, the total area covered by the glaciers and ice-fields of the Alps is upwards of three thousand square kilometres (about eleven hundred square miles). The Swiss Alps alone contain nearly two-thirds of this area. Professor Heim enumerates 1,155 distinct glaciers in the region. Of these, 144 are in France, 78 in Italy, 471 in Switzerland, and 462 in Austria.

Desor describes fourteen principal glacial districts in the Alps, the westernmost of which is that of Mont Pelvoux, in Dauphiny, and the easternmost that in the vicinity of the Gross Glockner, in Carinthia. The most important of the Alpine systems are those which are grouped around Mont Blanc, Monte Rosa, and the Finsteraarhorn, the two former peaks being upwards of fifteen thousand feet in height, and the latter upwards of fourteen thousand. The area covered by glaciers and snow-fields in the Bernese Oberland, of which Finsteraarhorn is the culminating point, is about three hundred and fifty square kilometres (a hundred square miles), and contains the Aletsch Glacier, which is the longest in Europe, extending twenty-one kilometres (about fourteen miles) from thenévé-field to its foot. The Mer de Glace, which descends from Mont Blanc to the valley of Chamounix, has a length of about eight miles below thenévé-field. In all, there are estimated to be twenty-four glaciers in the Alps which are upwards of four miles long, and six which are upwards of eight miles in length. The principal of these are the Mer de Glace, of Chamounix, on Mont Blanc; the Gorner Glacier, near Zermatt, on Monte Rosa; the lower glacier of the Aar, in the Bernese Oberland; and the Aletsch Glacier and Glacier of the Rhône, in Vallais; and the Pasterzen, in Carinthia.

Fig. 7.—Mount Blanc Glacier Region:m, Mer de Glace;g, Du Géant;l, Leschaux;t, Taléfre;B, Bionassay;b, Bosson.

These glaciers adjust themselves to the width of the valleys down which they flow, in some places being a mile or more in width, and at others contracting into much narrower compass. The greatest depth which Agassiz was able directly to measure in the Aar Glacier was two hundred and sixty metres (five hundred and twenty-eight feet), but at another point the depth was estimated by him to be four hundred and sixty metres (or fifteen hundred and eighty-four feet).

The glaciers of the Alps are mostly confined to the northern side and to the higher portions of the mountain-chain, none of them descending below the level of four thousand feet, and all of them varying slightly in extent, from year to year, according as there are changes in the temperature and in the amount of snow-fall.

The Pyrenees, also, still maintain a glacial system, but it is of insignificant importance. This is partly because the altitude is much less than that of the Alps, the culminating point being scarcely more than eleven thousand feet in height. Doubtless, also, it is partly due to the narrowness of the range, which does not provide gathering-places for the snow sufficiently extensive to produce large glaciers. The snow-fall also is less upon the Pyrenees than upon the Alps. As a consequence of all these conditions, the glaciers of the Pyrenees are scarcely morethan stationarynévé-fields lingering upon the north side of the range. The largest of these is near Bagnères de Luchon, and sends down a short, river-like glacier.

In Scandinavia the height of the mountains is also much less than that of the Alps, but the moister climate and the more northern latitude favours the growth of glaciers at a much lower level North of the sixty-second degree of latitude, the plateaus over five thousand feet above the sea pretty generally are gathering-places for glaciers. From the Justedal a snow-field, covering five hundred and eighty square miles, in latitude 62°, twenty-four glaciers push outwards towards the German Sea, the largest of which is five miles long and three-quarters of a mile wide. The Fondalen snow-field, between latitudes 66° and 67°, covers an area about equal to that of the Justedal; but, on account of its more northern position, its glaciers descend through the valleys quite to the ocean-level. The Folgofon snow-field is still farther south, but, though occupying an area of only one hundred square miles, it sends down as many as three glaciers to the sea-level. The total area of the Scandinavian snow-fields is about five thousand square miles.

In Sweden Dr. Svenonius estimates that there are, between latitudes 67° and 6812°, twenty distinct groups of glaciers, covering an area of four hundred square kilometres (one hundred and forty-four square miles), and he numbers upwards of one hundred distinct glaciers of small size.

As is to be expected, the large islands in the Polar Sea north of Europe and Asia are, to a great extent, covered withnévé-fields, and numerous glaciers push out from them to the sea in all directions, discharging their surplus ice as bergs, which float away and cumber the waters with their presence in many distant places.

Fig. 8.—The Svartisen Glacier on the west coast of Norway, just within the Arctic circle, at the head of a fiord ten miles from the ocean. The foot of the Glacier is one mile wide, and a quarter of a mile back from the water. Terminal moraine in front. (Photographed by Dr. L. C. Warner.)

The island of Spitzbergen, in latitude 76° to 81°, is favourably situated for the production of glaciers, by reason both of its high northern latitude, and of its relation to the Gulf Stream, which conveys around to it an excessive amount of moisture, thus ensuring an exceptionally large snow-fall over the island. The mountainous character of the island also favours the concentration of the ice-movement into glaciers of vast size and power. Still, even here, much of the land is free from snow and ice in summer. But upon the northern portion of the island there is an extensive table-land, upwards of two thousand feet above the sea, over which the ice-field is continuous. Four great glaciers here descend to tide-water in Magdalena Bay. The largest of these presents at the front a wall of ice seven thousand feet across and three hundred feet high; but, as the depth of the water is notgreat, few icebergs of large size break off and float away from it.

Nova Zembla, though not in quite so high latitude, has a lower mean temperature upon the coasts than Spitzbergen. Owing to the absence of high lands and mountains, however, it is not covered with perpetual snow, much less with glacial ice, but its level portions are “carpeted with grasses and flowers,” and sustain extensive forests of stunted trees.

Franz-Josef Land, to the north of Nova Zembla, both contains high mountains and supports glaciers of great size. Mr. Payer conducted a sledge party into this land in 1874, and reported that a precipitous wall of glacial ice, “of more than a hundred feet in height, formed the usual edge of the coast.” But the motion of the ice is very slow, and the ice coarse-grained in structure, and it bears a small amount only of morainic material. So low is here the line of perpetual snow, that the smaller islands “are covered with caps of ice, so that a cross-section would exhibit a regular flat segment of ice.” It is interesting to note, also, that “many ice-streams, descending from the highnévéplateau, spread themselves out over the mountain-slopes,” and are not, as in the Alps, confined to definite valleys.

Iceland seems to have been properly named, since a single one of the snow-fields—that of Vatnajoküll, with an extreme elevation of only six thousand feet—is estimated by Helland to cover one hundred and fifty Norwegian square miles (about seven thousand English square miles), while five other ice-fields (the Langjoküll, the Hofsjoküll, the Myrdalsjoküll, the Drangajoküll, and the Glamujoküll) have a combined area of ninety-two Norwegian or about four thousand five hundred English square miles. The glaciers are supposed by Whitney to have been rapidly advancing for some time past.

In Asia.—Notwithstanding its lofty mountains and itsgreat extent of territory lying in high latitudes, glaciers are for two reasons relatively infrequent: 1. The land in the more northern latitudes is low. 2. The dryness of the atmosphere in the interior of the continent is such that it unduly limits the snow-fall. Long before they reach the central plateau of Asia, the currents of air which sweep over the continent from the Indian Ocean have parted with their burdens of moisture, having left them in a snowy mantle upon the southern flanks of the Himalayas. As a result, we have the extensive deserts of the interior, where, on account of the clear atmosphere, there is not snow enough to resist continuously the intense activity of the unobstructed rays of the sun.

In spite of their high latitude and considerable elevation above the sea-level, glaciers are absent from the Ural Mountains, for the range is too narrow to affordnévé-fields of sufficient size to produce glaciers of large extent.

The Caucasus Mountains present more favourable conditions, and for a distance of one hundred and twenty miles near their central portion have an average height of 12,000 feet, with individual peaks rising to a height of 16,000 feet or more; but, owing to their low latitude, the line of perpetual snow scarcely reaches down to the 11,000-foot level. So great are the snow-fields, however, above this height that many glaciers push their way down through the narrow mountain-gorges as far as the 6,000-foot level.

The Himalaya Mountains present many favourable conditions for the development of glaciers of large size. The range is of great extent and height, thus affording ample gathering-places for the snows, while the relation of the mountains to the moisture-laden winds from the Indian Ocean is such that they enjoy the first harvest of the clouds where the interior of Asia gets only the gleanings. As is to be expected, therefore, all the great rivers which coursethrough the plains of Hindustan have their rise in large glaciers far up towards the summits of the northern mountains. The Indus and the Ganges are both glacial streams in their origin, as are their larger tributary branches—the Basha, the Shigar, and the Sutlej. Many of the glaciers in the higher levels of the Himalaya Mountains where these streams rise have a length of from twenty-five to forty miles, and some of them are as much as a mile and a half in width and extend for a long distance, with an inclination as small as one degree and a half or one hundred and thirty-eight feet to a mile.

In the Mustagh range of the western Himalayas there are two adjoining glaciers whose united length is sixty-five miles, and another not far away which is twenty-one miles long and from one to two miles wide in its upper portion. Its lower portion terminates at an altitude of 16,000 feet above tide, where it is three miles wide and two hundred and fifty feet thick.

Oceanica.—-Passing eastward to the islands of the Pacific Ocean, New Zealand is the only one capable of supporting glaciers. Their existence on this island seems the more remarkable because of its low latitude (42° to 45°); but a grand range of mountains rises abruptly from the water on the western coast of the southern island, culminating in Mount Cook, 13,000 feet above the sea, and extending for a distance of about one hundred miles. The extent and height of this chain, coupled with the moisture of the winds, which sweep without obstruction over so many leagues of the tropical Pacific, are specially favourable to the production of ice-fields of great extent. Consequently we find glaciers in abundance, some of which are not inferior in extent to the larger ones of the Alps. The Tasman Glacier, described by Haas, is ten miles long and nearly two miles broad at its termination, “the lower portion for a distance of three miles beingcovered with morainicdetritus.” The Mueller Glacier is about seven miles long and one mile broad in its lower portion.

South America.—In America, existing glaciers are chiefly confined to three principal centres, namely, to the Andes, south of the equator; to the Cordilleras, north of central California; and to Greenland.

In South America, however, the high mountains of Ecuador sustain a few glaciers above the twelve-thousand-foot level. The largest of these are upon the eastern slope of the mountains, giving rise to some of the branches of the Amazon—indeed, on the flanks of Cotopaxi, Chimborazo, and Illinissa there are some glaciers in close proximity to the equator which are fairly comparable in size to those of the Alps.

In Chili, at about latitude 35°, glaciers begin to appear at lower levels, descending beyond the six-thousand-foot line, while south of this both the increasing moisture of the winds and the decreasing average temperature favour the increase of ice-fields and glaciers. Consequently, as Darwin long ago observed, the line of perpetual snow here descends to an increasingly lower level, and glaciers extend down farther and farther towards the sea, until, in Tierra del Fuego, at about latitude 45°, they begin to discharge their frozen contents directly into the tidal inlets. Darwin’s party surveyed a glacier entering the Gulf of Penas in latitude 46° 50’, which was fifteen miles long, and, in one part, seven broad. At Eyre’s Sound, also, in about latitude 48°, they found immense glaciers coming clown to the sea and discharging icebergs of great size, one of which, as they encountered it floating outwards, was estimated to be “at leastone hundred and sixty-eight feet in total height.”

In Tierra del Fuego, where the mountains are only from three thousand to four thousand feet in height and in latitude less than 55°, Darwin reports that "every valleyis filled with streams of ice descending to the sea-coast," and that the inlets penetrated by his party presented miniature likenesses of the polar sea.

Fig. 9.—Floating berg, showing the proportions above and under the water. About seven feet under water to one above.

Antarctic Continent.—Of the so-called Antarctic Continent little is known; but icebergs of great size are frequently encountered up to 58° south latitude, in the direction of Cape Horn, and as far as latitude 33° in the direction of Cape of Good Hope. Nearly all that is known about this continent was discovered by Sir J. C. Ross during the period extending from 1839 to 1843, when, between the parallels of 70° and 78° south latitude, he encountered in his explorations a precipitous mountain coast, rising from seven thousand to ten thousand feet above tide. Through the valleys intervening between the mountain-ranges huge glaciers descended, and “projected in many places several miles into the sea and terminatedin lofty, perpendicular cliffs. In a few places the rocks broke through their icy covering, by which alone we could be assured that land formed the nucleus of this, to appearance, enormous iceberg.”[AG]

[AG]Quoted by Whitney in Climatic Changes, p. 314.

Again, speaking of the region in the vicinity of the lofty volcanoes Terror and Erebus, between ten thousand and twelve thousand feet high, the same navigator says:

“We perceived a low, white line extending from its extreme eastern point, as far as the eye could discern, to the eastward. It presented an extraordinary appearance, gradually increasing in height as we got nearer to it, and proving at length to be a perpendicular cliff of ice, between one hundred and fifty and two hundred feet above the level of the sea, perfectly flat and level at the top, and without any fissures or promontories on its even, seaward face. What was beyond it we could not imagine; for, being much higher than our mast-head, we could not see anything except the summit of a lofty range of mountains extending to the southward as far as the seventy-ninth degree of latitude. These mountains, being the southernmost land hitherto discovered, I felt great satisfaction in naming after Sir Edward Parry.... Whether Parry Mountains again take an easterly trending and form the base to which this extraordinary mass of ice is attached, must be left for future navigators to determine. If there be land to the southward it must be very remote, or of much less elevation than any other part of the coast we have seen, or it would have appeared above the barrier.”

This ice-cliff or barrier was followed by Captain Ross as far as 198° west longitude, and found to preserve very much the same character during the whole of that distance. On the lithographic view of this great ice-sheet given in Ross’s work it is described as “part of the South Polar Barrier, one hundred and eighty feet above the sea-level,one thousand feet thick, and four hundred and fifty miles in length.”

A similar vertical wall of ice was seen by D’Urville, off the coast of Adelie Land. He thus describes it: “Its appearance was astonishing. We perceived a cliff having a uniform elevation of from one hundred to one hundred and fifty feet, forming a long line extending off to the west.... Thus for more than twelve hours we had followed this wall of ice, and found its sides everywhere perfectly vertical and its summit horizontal. Not the smallest irregularity, not the most inconsiderable elevation, broke its uniformity for the twenty leagues of distance which we followed it during the day, although we passed it occasionally at a distance of only two or three miles, so that we could make out with ease its smallest irregularities. Some large pieces of ice were lying along the side of this frozen coast; but, on the whole, there was open sea in the offing.”[AH]

[AH]Whitney’s Climatic Changes, pp. 315, 316.

Fig. 10.—Iceberg in the Antarctic Ocean.

North America.—In North America living glaciersbegin to appear in the Sierra Nevada Mountains, in the vicinity of the Yosemite Park, in central California. Here the conditions necessary for the production of glaciers are favourable, namely, a high altitude, snow-fields of considerable extent, and unobstructed exposure to the moisture-laden currents of air from the Pacific Ocean. Sixteen glaciers of small size have been noted among the summits to the east of the Yosemite; but none of them descend much below the eleven-thousand-foot line, and none of them are over a mile in length. Indeed, they are so small, and their motion is so slight, that it is a question whether or not they are to be classed with true glaciers.

Owing to the comparatively low elevation of the Sierra Nevada north of Tuolumne County, California, no other living glaciers are found until reaching Mount Shasta, in the extreme northern part of the State. This is a volcanic peak, rising fourteen thousand five hundred feet above the sea, and having no peaks within forty miles of it as high as ten thousand feet; yet so abundant is the snow-fall that as many as five glaciers are found upon its northern side, some of them being as much as three miles long and extending as low down as the eight-thousand-foot level. Upon the southern side glaciers are so completely absent that Professor Whitney ascended the mountain and remained in perfect ignorance of its glacial system. In 1870 Mr. Clarence King first discovered and described them on the northern side.

North of California glaciers characterise the Cascade Range in increasing numbers all the way to the Alaskan Peninsula. They are to be found upon Diamond Peak, the Three Sisters, Mount Jefferson, and Mount Hood, in Oregon, and appear in still larger proportions upon the flanks of Mount Rainier (or Tacoma) and Mount Baker, in the State of Washington. The glacier at the head of the White River Valley is upon the north side of Rainier, and is the largest one upon that mountain, reaching down to within five thousand feet of the sea-level, and being ten miles or more in length. All the streams which descend the valleys upon this mountain are charged with the milky-coloured water which betrays their glacial origin.

Fig. 11.—Map of Southeastern Alaska. The arrow-points mark glaciers.

In British Columbia, Glacier Station, upon the Canadian Pacific Railroad, in the Selkirk Mountains, is within half a mile of the handsome Illicilliwaet Glacier, while others of larger size are found at no great distance. The interior farther north is unexplored to so great an extent that little can be definitely said concerning its glacial phenomena. The coast of British Columbia is penetrated by numerous fiords, each of which receives the drainage of a decaying glacier; but none are in sight of the tourist-steamers which thread their way through the intricate network of channels characterising this coast, until the Alaskan boundary is crossed and the mouth of the Stickeen River is passed.

A few miles up from the mouth of the Stickeen, however, glaciers of large size come down to the vicinity of the river, both from the north and from the south, and the attention of tourists is always attracted by the abundant glacial sediment borne into the tide-water by the river itself and discolouring the surface for a long distance beyond the outlet. Northward from this point the tourist is rarely out of sight of ice-fields. The Auk and Patterson Glaciers are the first to come into view, but they do not descend to the water-level. On nearing Holcomb Bay, however, small icebergs begin to appear, heralding the first of the glaciers which descend beyond the water’s edge. Taku Inlet, a little farther north, presents glaciers of great size coming down to the sea-level, while the whole length of Lynn Canal, from Juneau to Chilkat, a distance of eighty miles, is dotted on both sides by conspicuous glaciers and ice-fields.

The Davidson Glacier, near the head of the canal, is one of the most interesting for purposes of study. Itcomes down from an unknown distance in the western interior, bearing two marked medial moraines upon its surface. On nearing tide-level, the valley through which it flows is about three-quarters of a mile in width; but, after emerging from the confinement of the valley, the ice spreads out over a fan-shaped area until the width of its front is nearly three miles. The supply of ice not being sufficient to push the front of the glacier into deep water, equilibrium between the forces of heat and cold is established near the water’s edge. Here, as from year to year the ice melts and deposits its burdens of earthydébris, it has piled up a terminal moraine which rises from two hundred to three hundred feet in height, and is now covered with evergreen trees of considerable size. From Chilkat, at the head of Lynn Canal, to the sources of the Yukon River, the distance is only thirty-five miles, but the intervening mountain-chain is several thousand feet in height and bears numerous glaciers upon its seaward side.

About forty miles west of Lynn Canal, and separated from it by a range of mountains of moderate height, is Glacier Bay, at the head of one of whose inlets is the Muir Glacier, which forms the chief attraction for the great number of tourists that now visit the coast of southeastern Alaska during the summer season. This glacier meets tide-water in latitude 58° 50’, and longitude 136° 40’ west of Greenwich. It received its name from Mr. John Muir, who, in company with Rev. Mr. Young, made a tour of the bay and discovered the glacier in 1879. It was soon found that the bay could be safely navigated by vessels of large size, and from that time on tourists in increasing number have been attracted to the region. Commodious steamers now regularly run close up to the ice-front, and lie-to for several hours, so that the passengers may witness the “calving” of icebergs, and may climb upon the sides of the icy stream and look into itsdeep crevasses and out upon its corrugated and broken surface.

Fig. 12.—Map of Glacier Bay. Alaska, and its surroundings. Arrow-points indicate glaciated area.

The first persons who found it in their way to pay more than a tourist’s visit to this interesting object were Rev. J. L. Patton, Mr. Prentiss Baldwin, and myself, who spent the entire month of August, 1886, encamped at thefoot of the glacier, conducting such observations upon it as weather and equipment permitted. From that time till the summer of 1890 no one else stopped off from the tourist steamers to bestow any special study upon it. But during this latter season Mr. Muir returned to the scene of his discovered wonder, and spent some weeks in exploring the interior of the great ice-field. During the same season, also, Professors H. F. Reid and H. Cushing, with a well-equipped party of young men, spent two months or more in the same field, conducting observations and experiments, of various kinds, relating to the extent, the motion, and the general behaviour of the vast mass of moving ice.

Fig. 13.—Shows central part of the front of Muir Glacier one half mile distant. Near the lower left hand corner the ice is seen one mile distant resting for about one half mile on gravel which it had overrun. The ice is now retreating in the channel. (From photograph.)

The main body of the Muir Glacier occupies a vastamphitheatre, with diameters ranging from thirty to forty miles, and covers an area of about one thousand square miles. From one of the low mountains near its mouth I could count twenty-six tributary glaciers which came together and became confluent in the main stream of ice. Nine medial moraines marked the continued course of as many main branches, which becoming united formed the grand trunk of the glacier. Numerous rocky eminences also projected above the surface of the ice, like islands in the sea, corresponding to what are called “nunataks” in Greenland. The force of the ice against the upper side of these rocky prominences is such as to push it in great masses above the surrounding level, after the analogy of waves which dash themselves into foam against similar obstructions. In front of thenunataksthere is uniformly a depression, like the eddies which appear in the current below obstacles in running water.

Over some portions of the surface of the glacier there is a miniature river system, consisting of a main stream, with numerous tributaries, but all flowing in channels of deep blue ice. Before reaching the front of the glacier, however, each one of these plunges down into a crevasse, ormoulin, to swell the larger current, which may be heard rushing along in an impetuous course hundreds of feet beneath, and far out of sight. The portion of the glacier in which there is the most rapid motion is characterised by innumerable crags and domes and pinnacles of ice, projecting above the general level, whose bases are separated by fissures, extending in many cases more than a hundred feet below the general level. These irregularities result from the combined effect of the differential motion (as illustrated in the diagram onpage 4), and the influence of sunshine and warm air in irregularly melting the unprotected masses. The description given in our introductory chapter of medial moraines and ice-pillars is amply illustrated everywhere upon the surfaceof the Muir Glacier. I measured one block of stone which was twenty feet square and about the same height, standing on a pedestal of ice three or four feet high.

The mountains forming the periphery of this amphitheatre rise to a height of several thousand feet; Mount Fairweather, upon the northwest, from whose flanks probably a portion of the ice comes, being, in fact, more than fifteen thousand feet high. The mouth of the amphitheatre is three miles wide, in a line extending from shoulder to shoulder of the low mountains which guard it. The actual water-front where the ice meets tide-water is one mile and a half.[AI]Here the depth of the inlet is so great that the front of the ice breaks off in icebergs of large size, which float away to be dissolved at their leisure. At the water’s edge the ice presents a perpendicular front of from two hundred and fifty to four hundred feet in height, and the depth of the water in the middle of the inlet immediately in front of the ice is upwards of seven hundred feet; thus giving a total height to the precipitous front of a thousand feet.

[AI]These are the measurements of Professor Reid. In my former volume I have given the dimensions as somewhat smaller.

The formation of icebergs can here be studied to admirable advantage. During the month in which we encamped in the vicinity the process was going on continuously. There was scarcely an interval of fifteen minutes during the whole time in which the air was not rent with the significant boom connected with the “calving” of a berg. Sometimes this was occasioned by the separation of a comparatively small mass of ice from near the top of the precipitous wall, which would fall into the water below with a loud splash. At other times I have seen a column of ice from top to bottom of the precipice split off and fall over into the water, giving rise to great waves, which would lash the shore with foam two miles below.

This manner of the production of icebergs differs from that which has been ordinarily represented in the text-books, but it conforms to the law of glacial motion, which we will describe a little later, namely, that the upper strata of ice move faster than the lower. Hence the tendency is constantly to push the upper strata forwards, so as to produce a perpendicular or even projecting front, after the analogy of the formation of breakers on the shelving shore of a large body of water.

Evidently, however, these masses of ice which break off from above the water do not reach the whole distance to the bottom of the glacier below the water; so that a projecting foot of ice remains extending to an indefinite distance underneath the surface. But at occasional intervals, as the superincumbent masses of ice above the surface fall off and relieve the strata below of their weight, these submerged masses suddenly rise, often shooting up considerably higher than they ultimately remain when coming to rest. The bergs formed by this latter process often bear much earthy material upon them, which is carried away with the floating ice, to be deposited finally wherever the melting chances to take place.

Numerous opportunities are furnished about the front and foot of this vast glacier to observe the manner of the formation ofkames, kettle-holes, and various other irregular forms into which glacialdébrisis accustomed to accumulate. Over portions of the decaying foot of the glacier, which was deeply covered with morainicdébris, the supporting ice is being gradually removed through the influence of subglacial streams or of abandoned tunnels, which permit the air to exert its melting power underneath. In some places where oldmoulinshad existed, the supporting ice is melting away, so that the superincumbent mass of sand, gravel, and boulders is slowly sliding into a common centre, like grain in a hopper. This must produce a conical hill, to remain, after the ice has all meltedaway, a mute witness of the impressive and complicated forces which have been so long in operation for its production.

In other places I have witnessed the formation of a long ridge of gravel by the gradual falling in of the roof of a tunnel which had been occupied by a subglacial stream, and over which there was deposited a great amount of morainic material. As the roof gave way, this was constantly falling to the bottom, where, being exempt from further erosive agencies, it must remain as a gravel ridge or kame.

In other places, still, there were vast masses of ice covering many acres, and buried beneath a great depth of morainic material which had been swept down upon it while joined to the main glacier. In the retreat of the ice, however, these masses had become isolated, and the sand, gravel, and boulders were sliding down the wasting sides and forming long ridges ofdébrisalong the bottom, which, upon the final melting of the ice, will be left as a complicated network of ridges and knolls of gravel, enclosing an equally complicated nest of kettle-holes.

Beyond Cross Sound the Pacific coast is bounded for several hundred miles by the magnificent semicircle of mountains known as the St. Elias Alps, with Mount Crillon at the south, having an elevation of nearly sixteen thousand feet, and St. Elias in the centre, rising to a greater height. Everywhere along this coast, as far as the Alaskan Peninsula, vast glaciers come down from the mountain-sides, and in many cases their precipitous fronts form the shore-line for many miles at a time. Icy Bay, just to the south of Mount St, Elias, is fitly named, on account of the extent of the glaciers emptying into it and the number of icebergs cumbering its waters.

In the summer of 1890 a party, under the lead of Mr. I. C. Russell, of the United States Geological Survey, made an unsuccessful attempt to scale the heights ofMount St. Elias; but the information brought back by them concerning the glaciers of the region amply repaid them for their toil and expense, and consoled them for the failure of their immediate object.

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