One of the Mouths of the Fairweather Ice-Sheet, in the recently discovered Glacier Bay to the north of Cross Sound, Southeastern Alaska
The monuments of the glaciation of the regions about Bering Sea and the northern shores of Siberia and Alaska are in general much broken and obscured on account of the intensity of the action of the agents of destruction in these low, moist regions, together with the perishable character of the rocks of which most of the monuments consist. Lofty headlands, once covered with clear glacial inscriptions, have been undermined and cast down in loose, draggled taluses, while others, in a dim, ruinous condition, with most of their surface records effaced, are rapidly giving way to the weather. The moraines, also, and the grooved, scratched, and polished surfaces are much blurred and wasted, while glaciated areas of great extent are not open to observation at all, being covered by the shallow waters of Bering Sea and the Arctic Ocean, and buried beneath sediments and coarse detritus which has been weathered from the higher grounds, or deposited by the ice itself when it was being melted and withdrawn towards the close of the main glacial period. But amid this general waste and obscurity a few legible fragments, favorably situated here and there, have escaped destruction--patches of polished and striated surfaces in a fair state of preservation, with moraines of local glaciers that have not been exposed to the heavier forms of water or avalanche action. And had these fading vestiges perished altogether, yet would not the observer be left without a sure guide, for there are other monuments of ice action in all glaciated regions that are almost indestructible, enduring for tens of thousands of years after those simpler traces that we have been considering have vanished. These are the material of moraines, though scattered, washed, crumbled, and reformed over and over again; and the sculpture and configuration of the landscape in general, cañons, valleys, mountains, ridges, roches moutonnées with forms and correlations specifically glacial. These, also, it is true, suffer incessant waste, being constantly written upon by other agents; yet, because the glacial characters are formed on so colossal a scale of magnitude, they continue to stand out free and clear through every after inscription whether of the torrent, the avalanche, or universal eroding atmosphere; opening grand and comprehensive views of the vanished ice, and the geographical and topographical changes effected by its action in the form of local and distinct glaciers. River-like, they flowed from the mountains to the sea, and, as a broad, undulating mantle, crawled over all the landscape through unnumbered centuries; crushed and ground and spread soil-beds; fashioned the features of mountain and plain; extended the domain of the sea; separated continents; dotted new coasts with islands, fringed them with deep inreaching fiords, and impressed their peculiar style of sculpture on all the regions over which they passed.
A general exploration of the mountain ranges of the Pacific Coast shows that there are about sixty-five small residual glaciers on the Sierra Nevada of California, between latitude 36° 30' and 39°, distributed singly or in small groups on the north sides of the highest peaks at an elevation of about eleven to twelve thousand feet above the level of the sea, representatives of the grand glaciers that once covered all the range. More than two thirds of these lie between latitude 37° and 38°, and form the highest sources of the San Joaquin, Tuolumne, Merced, and Owens Rivers.
Mount Shasta, near the northern boundary of California, has a few shrinking glacier remnants, the largest about three miles in length. We find that, to the north of California, groups of active glaciers still exist on all the highest mountains--Mounts Jefferson, Adams, Saint Helens, Hood, Rainier, Baker, and others. Of these Mount Rainier is the highest and iciest. Its summit is fairly capped with ice, and eight glaciers, from seven to fifteen miles long, radiate from it as a center and form the sources of the principal streams. The lowest descends to about thirty-five hundred feet above sea level, pouring a stream opaque with glacial mud into the head of Puget Sound.
On through British Columbia and southeastern Alaska the broad sustained mountain chain extending along the coast is generally glacier-bearing. The upper branches of nearly every one of the main canons are occupied by glaciers, which gradually increase in size and descend lower until the lofty region between Mount Fairweather and Mount St. Elias is reached, where a considerable number discharge into the waters of the ocean.
This is the region of greatest glacial abundance on the continent. To the northward from here the glaciers gradually diminish in size and depth and melt at higher levels until the latitude of about 62° is reached, beyond which few, if any, glaciers remain in existence, the ground being comparatively low and the annual snowfall light.
Between latitude 56° and 60° there are probably more than five thousand glaciers, great and small, hundreds of the largest size, descending through the forests nearly to the level of the sea, though, as far as I know after a pretty thorough exploration of the region, not more than twenty-five discharge into the sea.
All the long, high-walled fiords into which these great glaciers of the first class flow are of course crowded with icebergs of every conceivable form, which are detached at intervals of a few minutes. But these are small as compared with those of Greenland, and only a few escape from the intricate labyrinth of channels, with which this portion of the coast is fringed, into the open sea. Nearly all of them are washed and drifted back and forth in the fiords by wind and tide until finally melted by sunshine and the copious warm rains of summer.
The southmost of the glaciers that reach the sea occupies a narrow fiord about twenty miles to the northwest of the mouth of the Stikine River, in latitude 56° 50'. It is called "Hutli" [Now known as Le Conte Glacier; also the Bay into which it discharges. Both were so named in 1887 by Lieutenant-Commander Charles M. Thomas, U.S.N., presumably in honor of Joseph Le Conte, the well-known California geologist. "Hutli" is the Tlingit Indian name for the mythical bird which produces thunder by the flapping of its wings. The word, therefore, means "The Thunderer."] by the natives, from the noise made by the icebergs in rising and falling from the inflowing glacier. About one degree farther north there are four of these complete glaciers at the heads of branches of Holkham Bay, at the head of Taku Inlet one, and at the head and around the sides of a bay [Now known as Glacier Bay.] trending in a general northerly direction from Cross Sound, first explored by myself in 1879, there are no less than five of these complete glaciers reaching tide-water, the largest of which, the Muir, is of colossal size, having upwards of two hundred tributaries and a width of trunk below the confluence of the main tributaries of three to twenty-five miles. Between the west side of this icy bay and the ocean all the ground, high and low, with the exception of the summits of the mountain peaks, is covered by a mantle of ice from one to three thousand feet thick, which discharges to the eastward and westward through many distinct mouths.
One of the Mouths of the Fairweather Ice-Sheet, in the recently discovered Glacier Bay to the north of Cross Sound, Southeastern Alaska
This ice-sheet, together with the multitude of distinct glaciers that load the lofty mountains of the coast, evidently once formed part of one grand, continuous ice-sheet that flowed over all the region hereabouts, extending southward as far as the Straits of Juan de Fuca, for all the islands of the Alexander Archipelago, great and small, as well as the headlands and promontories of the mainland, are seen to have forms of greatest strength with reference to the action of a vast press of oversweeping ice, and their surfaces have a smooth, rounded, overrubbed appearance, generally free from angles. The canals, channels, straits, passages, sounds, etc., between the islands--a marvelous labyrinth--manifest in their forms and trends and general characteristics the same subordination to the grinding action of a continuous ice-sheet, and they differ from the islands, as to their origin, only in being portions of the general pre-glacial margin of the continent, more deeply eroded, and, therefore, covered with the ocean waters, which flowed into them as the ice was melted out of them.
That the dominion of the sea is being extended over the land by the wearing away of its shores is well known. But in these northern regions the coast rocks have been so short a time exposed to wave-action that they are but little wasted as yet, the extension of the sea affected by its own action in post-glacial time in this region being probably less than the millionth part of that affected by glacial action during the last glacial period.
Traces of the ancient glaciers made during the period of greater extension abound on the California Sierra as far south as latitude 36°. Even the most evanescent of them, the polished surfaces, are still found, in a marvelously perfect state of preservation, on the upper half of the middle portion of the range. They occur in irregular patches, some of which are several acres in extent, and, though they have been subjected to the weather with all its storms for thousands of years, their mechanical excellence is such that they reflect the sunbeams like glass, and attract the attention of every observer.
The most perfect of these shining pavements lie at an elevation of about seven to eight thousand feet above the level of the sea, where the rock is close-grained, siliceous granite. Small fading patches may be found at from three to five thousand feet elevation on the driest and most enduring portions of vertical walls, where there is protection from the drip and friction of water; also, on compact swelling bosses partially protected by a covering of boulders.
On the north half of the Sierra the striated and polished surfaces are rarely found, not only because this portion of the chain is lower, but on account of the surface rocks being chiefly porous lavas subject to rapid waste. The moraines, also, though well preserved on the south half of the range, seem to be nearly wanting over a considerable portion of the north half, but the material of which they were composed is found in abundance, scattered and disintegrated, until its glacial origin is not obvious to the unskilled observer.
A similar blurred condition of the superficial records obtains throughout most of Oregon, Washington, British Columbia, and Alaska, due in great part to the action of excessive moisture. Even in southeastern Alaska, where the most extensive glaciers still exist, the more evanescent of the traces of their former greater extension, though comparatively recent, are more obscure than those of the ancient glaciers of California, where the climate is drier and the rocks more resisting. We are prepared, therefore, to find the finer lines of the glacial record dim or obliterated altogether in the Arctic regions, where the ground is mostly low and the action of frost and moisture specially destructive.
The Aleutian chain of islands sweeps westward in a regular curve, about a thousand miles long, from the Alaska Peninsula toward Kamchatka, nearly uniting the American and Asiatic continents. A very short geological time ago, just before the coming on of the glacial winter, the union of the two continents was probably complete. The entire chain appears to be simply a degraded portion of the North Pacific pre-glacial coast mountains, with its foot-hills and lowest portions of the connecting ridges between the peaks a few feet under water, the submerged ridges forming the passes between the islands as they exist today, while the broad plain to the north of the chain is now covered by the shallow waters of Bering Sea.
Now the evidence seems everywhere complete that this segregating degradation has been effected almost wholly by glacial action. Yet, strange to say, it is held by most observers who have made brief visits to different portions of the chain that each island is a distinct volcanic upheaval, but little changed since the period of emergence from the sea, an impression made no doubt by the volcanic character of most of the rocks, ancient and recent, of which they are composed, and by the many extinct or feebly active volcanoes occurring here and there along the summits of the highest masses. But, on the contrary, all the evidence we have seen goes to show that the amount of glacial denudation these rocks have undergone is very great, so great that, with the exception of the recent craters, almost every existing feature is distinctly glacial. The comparatively featureless pre-glacial rocks have been heavily sculptured and fashioned into the endless variety they now present of peak and ridge, valley and fiord and clustering islets, harmoniously correlated in accordance with glacial law.
King Island
Granite Rocks on the South Side of St. Lawrence Island,
showing Effects of Oversweeping Action of Ice-Sheet
On Mount Makushin [Muir probably adopted current estimates of the altitude of this volcano. Gannett's Altitudes in Alaska (1900) gives the elevation as 5474 feet, and the United States Coast and Geodetic Survey Map, No. 8860 (1916), as 5691 feet.]. Whose summit reaches an elevation of about nine thousand feet above the sea, several small glaciers still exist, while others yet smaller may be hidden in the basins of other mountains not yet explored. The summit of Makushin, at the time my observations were made, was capped with heavy clouds, and from beneath these the glaciers were seen descending imposingly into the open sunshine to within a thousand or fifteen hundred feet of the sea level, the largest perhaps about six miles in length. After the clouds cleared away the summit was seen to be heavily capped with ice, leaving only the crumbling edges of the dividing ridges and subordinate peaks free. The lower slopes of the mountain and the wide valleys proceeding from the glaciers present testimony of every kind to show that these glaciers now lingering on the summit once flowed directly into the sea. The adjacent mountains, though now mostly free from ice, are covered with glacial markings, extending over all the low grounds about their bases and the shores of the fiords, and over many of the rocks now under water. But besides this evidence of recent local glacial abundance, we find traces of far grander glacial conditions on the heavily abraded rocks along the shores of the passes separating the islands, and also in the low wide valleys extending in a direction parallel with the passes across the islands, indicating the movement of a vast ice-sheet from the north over the ground now covered by Bering Sea.
The amount of degradation this island region has undergone is only partially manifested by the crumbling, sharpened condition of the ridges and peaks, the abraded surfaces that have been overswept, and by the extent of the valleys and fiords, and the gaps between the mountains and islands.
That these valleys, fiords, forges, and gaps, great and small, like those of the Sierra, are not a result of local subsidences and upheavals, but of the removal of the material that once filled them, is shown by the broken condition and the similarity of the physical structure and composition of their contiguous sides, just as the correspondence between the tiers of masonry on either side of a broken gap in a wall shows that the missing blocks required to fill it up have been removed.
The chief agents of erosion and transportation are water and ice, each being regarded as the more influential by different observers, though the phenomena to which they give rise are widely different. All geologists recognize the fact that glaciers wear away the rocks over which they move, but great vagueness prevails as to the size of the fragments of erosion, and the way they are detached and removed; and if possible still greater vague vagueness prevails as to the forms and characteristics in general of the mountains, hills, rocks, valleys, etc., resulting from this erosion.
Towards the end of summer, when the snow is melted from the lower portions of the glaciers, particles of dust and sand may be seen scattered over their surfaces, together with angular masses of rocks, derived from the shattered storm-beaten cliffs above their fountains. The separation of these masses, which vary greatly in size, is due only in part to the action of the glacier, though they are all transported on its surface like floating drift on a river, and deposited together in moraines. The winds supply a portion of the sand and dust, some of the larger fragments are set free by the action of frost, rains, and general weathering agents, considerable quantities are swept down in avalanches of snow where the inclination of the slopes is favorable to their action, and shaken down by earthquake shocks, while the glacier itself plays an important part in the production of these superficial effects by undermining the cliffs from whence the fragments fall.
But in all moraines boulders and small dust particles may be recognized that have not been thus derived from the weathered cliffs and dividing ridges projecting above the glaciers, but from the rocks past which and over which the glaciers flow. The streams which drain glaciers are always turbid with finely ground mud particles worn off the bed-rocks by a sliding motion, accompanied by great pressure, giving rise to polished surfaces, and keeping up a waste that never for a moment ceases while the glacier exists; and besides these small particles boulders are found that may be traced to their origin in the bottoms or sides of the channels. Accordingly, an abrupt transition is discovered from the polished and plain portions of the channels to the more or less angular and fractured portions, showing that glaciers degrade the rocks over which they pass in at least two different ways, by grinding them into mud, and by crushing, breaking, and splitting them into a coarse detritus of chips and boulders, the forms and sizes of which are in great part determined by the divisional planes the rocks possess, and the intensity and direction of application of the force brought to bear on them. The quantity of this coarser material remaining in the channels along the lines of dispersal, and the probable rate of movement of the glaciers that quarried and transported it, form data from which some approximation to the rate of this method of degradation may be reached.
The amount of influence exerted on the Aleutian region by running water in its various forms, and by the winds, avalanches, and the atmosphere in degrading and fashioning the surface subsequent to the melting of the ice, is as yet scarcely more appreciable than it is in the upper middle portion of the Sierra; for, besides being much feebler in their action, the time during which the region has been exposed to their influence is comparatively short.
On the other hand, the quantity of material quarried and carried away by the force of ice, in the process of bringing the region into its present condition, can hardly be overestimated; for, with the exception of the recent volcanic cones, almost every noticeable feature, great and small, has evidently been ground down into the form of greatest strength in relation to the stress of oversweeping floods of ice. And that these present features are not the pre-glacial features merely smoothed and polished and otherwise superficially altered, but an entirely new set sculptured from a surface comparatively featureless, is manifested by the relationship existing between the spaces that separate them and the glacier fountains. The greater the valley or hollow of any sort, the greater the snow-collecting basin above it whence flowed the ice that created it, not a fiord or valley being found here or on any portion of the Pacific coast that does not conduct to fountains of vanished or residual glaciers corresponding with it in size and position as cause and effect.
And, furthermore, that the courses of the present valleys were not determined by the streams of water now occupying them, nor by pre-glacial streams, but by the glaciers of the last or of some former glacial period, is shown by the fact that the directions of the trends of all these valleys, however variable, are resultants of the forces of the main trunk glaciers that filled them and their inflowing tributary glaciers, the wriggling fortuitous trends of valleys formed by the action of water being essentially different from those formed by ice; and therefore not liable to be confounded with them. Neither can we suppose pre-existing fissures or local subsidences to have exercised any primary determining influence, there being no conceivable coincidence between the trends of fissures and subsidences and the specific trends of ice-created valleys and basins in general, nor between the position and direction of extension of these hypothetical fissures, subsidences, and foldings and the positions of ice-fountains.
Volcanic Cones on St. Lawrence Island
Bed of Small Residual Glacier on St. Lawrence Island
Herald Island
The Pribilof Islands, St. Paul, St. George, Walrus, and Otter, appear in general views from the sea as mere storm-beaten remnants of a once continuous land, wasted into bluffs around their shores by the action of the waves, all their upper surfaces being planed down by a heavy oversweeping ice-sheet, slightly roughened here and there with low ridges and hillocks that alternate with shallow valleys. None of their features, as far as I could discover without opportunity for close observation, showed any trace of local glaciation or of volcanic action subsequent to the period of universal glaciation.
St. Lawrence Island, the largest in Bering Sea, is situated at a distance of about one hundred and twenty miles off the mouths of the Yukon, and forty miles from the nearest point on the coast of Siberia. It is about a hundred miles long from east to west, fifteen miles in average width, and is chiefly composed of various kinds of granite, slate, and lava.
The highest portion along the middle is diversified with groups of volcanic cones, some of which are of considerable size and clearly post-glacial in age, presenting well-defined craters and regular slopes down to the base, though I saw no evidence of their having poured forth extensive streams of molten lava over the adjacent rocks since the close of the glacial period; for, with the exception of the ground occupied by the cones, all the surface is marked with glacial inscriptions of the most telling kind--moraines, erratic boulders, roches moutonnées, in great abundance and variety as to size, and alternating ridges and valleys with wide U-shaped cross-sections, and with nearly parallel trends across the island in a general north to south direction, some of them extending from shore to shore, and all showing subordination to the grinding, furrowing action of a broad oversweeping ice-sheet.
Some of the widest gap-like valleys have been eroded nearly to the level of the sea, indicating that if the ice action had gone on much longer the present single island would have been eroded into a group of small ones; or the entire mass of the island would have been degraded beneath the sea level, obliterating it from the landscape to be in part restored perhaps by the antagonistic elevating volcanic action. The action of local glaciers has been comparatively light hereabouts, not enough greatly to obscure or interrupt the overmastering effects of the ice-sheet, though they have given marked character to the sculpture of some of the higher portions of the island.
The two Diomede Islands and Fairway Rock are mostly residual masses of granite brought into relief and separated from one another and from the general mass of the continent, by the action of ice in removing the missing material, while the islands remain because of superior resistance offered to the universal degrading force. That they are remnants of a once continuous land now separated by Bering Strait is indicated by the relative condition of the sides of the islands and of the contiguous shoulders of the continents, East Cape and Cape Prince of Wales, while the general configuration of the islands shows that they have been subjected to a glaciation of the most comprehensive kind, leaving them as roches moutonnées on a grand scale.
West Diomede Island (from the North)
East Cape (from the South)
I discovered traces of local glaciation on the largest of the three, but the effects produced by this cause are comparatively slight, while the action of excessive moisture in the form of almost constant fogs and rains throughout the summer months, combined with frost and thaw, has effected a considerable amount of denudation, manifested by groups of crumbling pinnacles occurring here and there on the summits.
Sledge, King, and Herald Islands are evidently of similar origin, displaying the same glacial traces, and varying chiefly in the amount of post-glacial waste they have suffered, and in the consequent degree of clearness of the testimony they present. During our visit to Herald Island an exceptionally favorable opportunity offered as to the time of year, state of the weather, etc., for observation.
Kellett, who first discovered this island and landed on it under adverse circumstances, describes it as an inaccessible rock. The sides are indeed precipitous in the main, but mountaineers would find many slopes and gullies by which the summit could be easily attained. We landed on the southwest side, opposite the mouth of a small valley, the bed of a vanished glacier. A short gully which conducts from the water's edge to the mouth of the valley proper is very steep, and at the time of our visit was blocked with compacted snow, in which steps had to be cut, but beyond this no difficulty was encountered, the ice having graded a fine broad way to the summit. Thence following the highest ground nearly to the northwestern extremity, we obtained views of most of the surface. The highest point is about twelve hundred feet above the sea, about a mile and a half from the northwest end of the island, and four and a half miles from the southeast. This makes the island about six miles long, the average width being about two miles.
Near the middle of the island there is a low gap, where the width is only about half a mile, and the height of the summit of this portion of the water-shed between the two sides is only about two hundred and fifty feet. The entire island as far as seen is a mass of granite, with the exception of a patch of metamorphic slates near the middle, which no doubt owes its existence, with so considerable a height, to the superior resistance it offered to the degrading action of ice, traces of which are presented in the general moutonnée form of the island, and in the smooth parallel ridges and valleys trending north and south. These evidently have not been determined as to size, form, position, or the direction of their trends by subsidences, upheavals, foldings, or any structural peculiarity of the rocks in which they have been eroded, but simply by the mechanical force of an oversweeping ice-sheet.
The effects of local glaciers are seen in short valleys of considerable depth as compared with the area from which their fountain snows were derived. We noticed four of these valleys that had been occupied by residual glaciers; and on the hardest and most enduring of the upswelling rock bosses several patches of the ancient scored and polished surface were discovered, still in a good state of preservation. That these local glaciers have but recently vanished is indicated by the raw appearance of the surface of their beds, while one small glacier remnant occupying a sheltered hollow and possessing a well-characterized terminal moraine seems to be still feebly active in the last stage of decadence. This small granite island, standing solitary in the Polar Ocean, we regard as one of the most interesting and significant of the monuments of geographical change effected by general glaciation.
Overswept Glacial Valleys and Ridges on
Saint Lawrence Island
Bed of Local Glacier, Saint Lawrence Island
Our stay on Wrangell Land was too short to admit of more than a hasty examination of a few square miles of surface near the eastern extremity. The rock here is a close-grained clay slate, cleaving freely into thin flakes, with occasional compact metamorphic masses rising above the general surface or forming cliffs along the shore. The soil about the banks of a river of considerable size, that enters the ocean here, has evidently been derived in the main from the underlying slates, indicating a rapid weathering of the surface. A few small deposits of moraine material were discovered containing traveled boulders of quartz and granite, no doubt from the mountains in which the river takes its rise, while the valley now occupied by the river manifests its glacial origin in its form and trends, the small portion in the middle eroded by the river itself being clearly distinguished by its abrupt angular sides, which contrast sharply with the glacial outlines.
In general views obtained in sailing along its southern coast the phenomena presented seemed essentially the same as have been described elsewhere--hills, valleys, and sculptured peaks, testifying in all their main trends and contours to the action of ice. A range of mountains of moderate height extends from one extremity of the island to the other, a distance of about sixty-five miles, the highest point as measured by Lieutenant Berry being twenty-five hundred feet above the sea.
All the coast region of Siberia that came under our observation, from the Gulf of Anadir to North Cape, presents traces in great abundance and variety of universal as well as local glaciation. Between Plover and St. Lawrence Bays, where the mountains attain their greatest elevation and where local glaciation has been heaviest, the coast is lacerated with deep fiords, on the lofty granite walls of which the glacial records are in many places well preserved, and offer evidence that could hardly be overlooked by the most careless observer.
Our first general views of this region were obtained on June 7, when it was yet winter, and the landscape was covered with snow down to the water's edge. After several days of storm the clouds lifted, exposing the heavily abraded fronts of outstanding cliffs; then the smooth overswept ridges and slopes at the base of the mountains came in sight, and one angular peak after another, until a continuous range forty to fifty miles long could be seen from one standpoint. Many of the peaks are fluted with the narrow channels of avalanches, and hollowed with névé amphitheaters of great beauty of form, while long withdrawing fiords and valleys may be traced back into the recesses of the highest groups, once the beds of glaciers that flowed in imposing ranks to the sea.
Plover Bay, which I examined in detail, may be taken as a good representative of the fiords of this portion of the coast. The walls rise to an average height of about two thousand feet, and present a severely desolate and bedraggled appearance, owing to the crumbling condition of the rocks, which in most places are being rapidly disintegrated, loading the slopes with loose, shifting detritus whenever the angle is low enough to allow it to come to rest. When examined closely, however, this loose material is found to be of no great depth. The solid rock comes to the surface in many places, and on the most enduring portions rounded glaciated surfaces are still found grooved, scratched, and polished in small patches from the sea-level up to a height of a thousand feet or more.
Large taluses with their bases under the water occur on both sides of the fiord in front of the side cañons that partially separate the main mountain masses that form the walls. These taluses are composed in great part of moraine material, brought down by avalanches of snow from the terminal moraines of small vanished glaciers that lay at a height of from one to five thousand feet, in recesses where the snow accumulated from the surrounding slopes, and where sheltered from the direct action of the sun the glaciers lingered longest. These recent moraines are formed of several concentric masses shoved together, showing that the glaciers to which they belonged melted and receded gradually with slight fluctuations of level and rate of decadence, in accordance with conditions of snow-fall, temperature, etc., like those of lower latitudes.
When the main central glacier that filled this fiord was in its prime as a distinct glacier it measured about thirty miles in length and from five to six miles in width, and was from two to three thousand feet in depth. It then had at least five main tributaries, which, as the trunk melted, became independent glaciers; and, again, as the trunks of these main tributaries melted, their smaller tributaries, numbering about seventy-five, and from less than a mile to several miles in length, became separate glaciers and lingered probably for centuries in the high, cool fountains. These also, as far as we have seen, have vanished, though possibly some wasting remnant may still exist in the highest and best-protected recesses about the head of the fiord.
Along the coast, a distance of fifteen or twenty miles to the eastward and southward of the mouth of Metchigme Bay, interesting deposits occur of roughly stratified glacial detritus in the form of sand, gravel and boulders. They rise from the shore in raw, wave-washed bluffs about forty feet high and extend to the base of the mountains as a gently inclined plain, with a width in some places of two or three miles. Similar morainal deposits were also observed on the American coast at Golofnin Bay, Kotzebue Sound, Cape Prince of Wales, and elsewhere. At Cape Prince of Wales the formation rises in successive well-defined terraces.
The peninsula, the extremity of which forms East Cape, trends nearly in an easterly direction from the mainland, and consequently occupies a telling position with reference to ice moving from the northward. I was therefore eager to examine it to see what testimony it might have to offer. We landed during favorable weather on the south side at a small Eskimo village built on a rough moraine, and pushed on direct to the summit of the watershed, from which good general views of nearly all the surface of the peninsula were obtained.
The dividing ridge along the high eastern portion is traversed by a telling series of parallel grooves and small valleys trending north and south approximately, the curves on the north commencing nearly at the water's edge, while the south side is more or less precipitous. The culminating point of the elevated eastern portion of the peninsula is about twenty-five hundred feet high, and has been cut from the mainland and added as another island to the Diomede group, the wide gap of low ground connecting it with the adjacent mountainous portion of the mainland being only a few feet above tide-water. Out in the midst of this low, flat region smooth upswelling roches moutonnées were discovered here and there like groups of small islands, with trends and contours emphatically glacial, all telling the action of a universal abrading ice-sheet moving southward.
Near the Southwest Extremity of Saint Lawrence Island,
illustrating Effects of Ice-Sheet
Overswept Mountains, with Parallel Valleys and Ridges,
from Twenty Miles northwest of East Cape
Hence along the coast to Cape North, which is the limit of our observations in this direction, the same class of ice phenomena was discovered--moraine material, washed and re-formed, moutonnée masses of the harder rocks standing like islands in the low, mossy tundra, and traveled boulders and pebbles lying stranded on the summits of rocky headlands.
These enduring monuments are particularly abundant and significant in the neighborhood of Cape Wankarem, where the granite is more compact and resisting than is commonly found in the Arctic regions we have visited, and consequently has longer retained the more evanescent of the glacial markings. Cape Wankarem is a narrow, flat-topped, residual mass of this enduring granite, on the summit of which two patches of the original polished surface were discovered that still retains the fine striae and many erratic boulders of slate, quartz, and various kinds of lava, which, from the configuration and geographical position of the cape with reference to the surrounding region, could not have been brought to their present resting-places by any local glacier.
Cape Serdzakamen is another of these residual island masses, brought into relief by general glacial denudation, manifesting its origin in every feature, and corroborating the testimony given at Cape Wankarem and elsewhere in the most emphatic manner.
All the sections of the tundra seen either on the Siberian or Alaskan coast lead towards the conclusion that the ground is glacial, re-formed under the action of running water derived in broad, shallow currents from the melting, receding edge of the ice-sheet, and also in some measure from ice left on the high lands after the main ice-sheet had been withdrawn; for these low, flat deposits differ in no particular of form or composition that we have been able to detect from those still in process of formation in front of the large receding glaciers of southeastern Alaska. On many of the so-called "mud-flats" extending from the snouts of glaciers that have receded a few miles from the shore, mosses and lichens and other kinds of tundra vegetation are being gradually acquired, and when thus clothed these patches of tundra are not to be distinguished from the extensive deposits about the shores of the Arctic regions.
The phenomena observed on the American coast from St. Michael to Point Barrow differ in no essential particular from those which have been described on the opposite shores of Siberia. Moraines more or less wasted, and re-formations of moraine material, smooth overswept ridges with glacial trends and the corresponding valleys, roches moutorinées, and the fountain amphitheaters of local glaciers were observed almost everywhere on the mountainous portions of the coast, though in general more deeply weathered, owing mainly to the occurrence of less resisting rocks, limestones, sandstones, porous lavas, etc.
A number of well-characterized moraines so situated with reference to topographical conditions as to have escaped destructive washing were noticed near Cape Lisburne, and moraine deposits of great extent at Kotzebue Sound and Golofnin Bay, of which many fine sections were exposed. At the latter locality, judging from the comparatively fresh appearance of the rock surfaces and deposits around the head of the bay, and the height and extent of the ice-fountains, the glacier that discharged here was probably the last to vanish from the American shore of Bering Sea.
As to the thickness attained by the ice-sheet over the regions that we have been examining during the period of greatest glacial development, we have seen that it passed heavily over the islands of Bering Sea and the adjacent mountains on either side, especially at East Cape and Cape Prince of Wales, at a height of twenty-five hundred feet or more above the bottom of Bering Sea and Strait, the average depth of water here being about a hundred and fifty feet. And though the lowest portion of the land beneath the ice may have been degraded to a considerable depth subsequent to the time when these highest portions were left bare, on the other hand the level of the ice must have been considerably higher than the summits over which it passed, inasmuch as they give evidence of having been heavily abraded. It appears, therefore, that the thickness of the general northern ice-sheet throughout a considerable portion of its history was not less than twenty-five hundred feet, and probably more, over the northern portion of the region now covered by Bering Sea and part of the Arctic Ocean.
In view of this colossal ice-flood grinding on throughout the hundreds of thousands of years of the glacial period, the excavation of the shallow basins of Bering Sea and Strait and the Arctic Ocean must be taken as only a small part of the erosion effected; for so shallow are these waters, were the tallest sequoias planted on the bottom where soundings have been made, their tops would rise in most places a hundred feet or more above the surface. The Plover Bay glacier, as we have shown, eroded the granite in the formation of its channel to a depth of not less than two thousand feet, and the amount of erosion effected by the ice-sheet was probably much greater.
It appears, therefore, in summing up the results of our observations along the North Pacific and Arctic coasts:--
We are now better prepared to read the changes that have taken place on the Sierra, and fortunately, as we have already seen, nowhere is the glacial record clearer.