Popular Science Monthly/Volume 14/November 1878/The Ice Age II
|THE ICE AGE.|
By L. P. GRATACAP, Ph. B.
SOME months ago we described very rapidly the principal features of that widely-extended and enigmatical formation known as the Drift, and in conclusion indicated an intention to consider the views of geologists as to its cause, and in particular illustrate the paramount claims to our acceptance of the so-called Glacial Theory. In this paper those hypotheses are given, accompanied by a proof of the manifest power of existing ice-streams, thus offering the most striking argument for their colossal potency in times when their size and duration were factors in their influence, fully commensurate with the continental ravages we attribute to them.
A great variety of theories have been submitted to the world as possible explanations of the appearances we have reviewed, and, though we cannot occupy ourselves with their discussion, it may be interesting, from their singularity and number, to enumerate such as have arisen.
First is the theory of Deluc, who supposed the erratics to have been thrown upward in the air by the same force that elevated the mountains, and that in their promiscuous descent they rolled and tumbled everywhere.
Second in order is the hypothesis of De Buch and Escher, who imagined that an immense deluge swept the bowlders along its surging course, and landed these blocks upon the acclivities of mountains, through the stupendous impetus they had acquired in its midst.
Third is the presumption of many that they are the wreck of a mantle of rocks of similar kinds which once covered the surface, and by different agencies have been tossed into alignments, heaped into hills, or left undisturbed upon the mountains.
Fourth, Dolomieu supposed that the summits of the Alps, and those of the Jura Mountains, were formerly connected by a regular incline, down which the masses of rock rolled, so that bowlders from the Alps got perched upon the Jura, and that during subsequent convulsions the ground sunk and assumed its present form.
Fifth, Venturi suggested very early the aid of ice, as glaciers and floating ice, to explain their transportation.
Sixth, a view, received by several, regarded the Jura range to have been once a level plain at the feet of the Alps, and that, when it had become strewed with bowlders, torn by frost and torrents from the latter, it was elevated into a line of hills carrying up its old accumulations.
Seventh, M. de Buch, developing the first theory, thought that the erratics were a conscience of the elevation of the Alps posterior to the deposition of the Tertiary,
Eighth, the Noachian deluge was burdened with the responsibility of their dispersion.
Ninth, glacial action, as explained by Prof. Agassiz.
Tenth, ancient alluvial action, identical in nature with that known at present.
Eleventh, action, by its tractile strength, of the receding waters of the ocean, as mountain-chains were successively upheaved above its surface.
Twelfth, elevation of the arctic seas, which caused a flow of water from the polar regions, transporting ice loaded with rocks and gravel southward.
Fourteenth, an explanation of the phenomena in the United States, viz., a drainage of a vast inland sea through the valleys of the St. Lawrence, Hudson, Susquehanna, Ohio, etc., accompanied or followed by a débâcle of ice and drift from the north.
Fifteenth, a change in the axis of rotation of the earth.
Sixteenth, collision with a comet, which extraordinary jolt loosened the rocks, and rattled them from the mountain-peaks to the adjacent plains.
Seventeenth, shrinkage of the earth, increased velocity of rotation, and consequent rush of arctic waters to the equator, carrying bowlders.
In the above enumeration some theories will be observed to have only a local application, and were originated at a time when the dispersion of bowlders was not known to have so universal a character. Of these seventeen hypotheses we believe it would be impossible to insist seriously upon more than two classes: those which attribute the phenomena to the action of water, and those which enlist the agency of ice either as glaciers or icebergs, or both. A slight inquiry into the nature of aqueous erosion must instantly discredit those views which rely upon its efficacy, and relegate them with the rest to unqualified rejection.
Water, though supplied in torrents so tremendous as to transport the enormous bowlders which are now found scattered so far from their origin, would toss and tumble these masses over the subjacent rock, breaking, fracturing, and denting the latter, but never impressing it with deep, straight furrows for miles, or scoring it with delicate and reticulating striæ.
Again, the numerous pebbles and stones which are found upon and through the topmost soils, in gravel-beds and sand-heaps, would have been smoothly rounded like beach-worn agates, and not, as they really are, tattooed and etched with fine lines running the length of the stone. In the grooves of the rock, and in the fine lines of the pebbles, we have evidence of a body firmly held upon the engraved surface, and passed along with undeviating directness and irresistible power. Prof. Agassiz has traced these flutings upon the rocks of Maine for miles, up hill and down dale, across rivers disappearing upon one side, and reappearing upon the other; and it is beyond possibility to have a plunging torrent of water, charged with stones and rocks, pursue such continuous and definite traces over the hardest rock. More than that, the action of water has been recorded alongside of these very grooves, both in this country and the Alps, as if to invite attention to the opposite character of the two inscriptions. The original traces are firm, direct rulings, and the water-marks beneath them, as in rocky troughs, are waving lines and cracks of denudation following the relative softness of the rock.
Untenable as this theory is, after such considerations, it seems more inadequate when we remember that this element was to transport for leagues masses weighing hundreds and thousands of tons, and to raise them to almost inaccessible altitudes, to arrange them in long succession across intervening slopes. We find, on the contrary, that moderate sized bowlders have sunk to the bottoms of streams, which have removed the soil and lighter material upon which they rested, allowing them, otherwise undisturbed, to sink almost vertically to their beds. Lastly, the high mounds and "horsebacks" associated with this era, composed of unassorted gravel, pebbles, bowlders, and clay, would have been arranged in superimposed layers. Their present composition is almost irrefragable evidence that water had no part in their construction.
On the other hand, the demonstration of the adequacy of the glacial theory to account for these phenomena is found only in a study of those glacial effects which are contemporaneous, or have been witnessed within the memory of man. By establishing an exact accordance between these latter, wherever examined, and the indications of erosion and transportation wide-spread over the continents, we prove the identity of both, and legitimately conclude that the agency in each case was the same.
And let us select the Alps, as the first field for our explorations, renowned for the phalanx of illustrious minds who have studied this subject there, and famous as embracing those districts where the presence of traveled blocks first aroused inquiry, and their significance gave birth to the theory we are testing.
The Alps cover with their various arms, encircling ranges and subordinate elevations, all Switzerland; her lakes are nestled within their valleys, her rivers spring from their frigid slopes, her cities rest upon the débris of their attrition, while the strange and romantic loveliness which surrounds their fields of ice cover it as with a garment of imperishable beauty. The Alps are the result of gigantic upheavals, probably conducted through ages, which succeeded each other throughout the Tertiary age, and were continental in their extent. The Pyrenees, the Julian Alps, the Balkans, the Apennines, and Corsica, were elevated in this series of vast perturbations, a long range of towering mountains whose influence upon physical and social development has been as marked as the revolution it signalized in the world's topography.Europe, which had worn the flora of America, then lost it, and the sassafras, liriodendron, maple, and magnolia, failing to survive the climatic changes which intervened, yielded before the gradual growth of distinctively European species.
The Alps, after passing up along the eastern boundary of Piedmont, irregularly in long, deep bends and winding arches, run east and west, gathering upon their flanks innumerable lesser ranges, and knots of mountains, or in places subdividing into new and splendid lines of peaks which, diverging to the north, afterward unite with the parent chain or melt into the plain of Germany, through successive steps. A great congeries of intermingling and twisting ranges communicates the original disturbance over Switzerland, and the radiate lines of agitation may be traced southward upon the plains of Piedmont, through the Apennines into Italy, and by the Illyrian Alps into Dalmatia. The Alps inclose valleys and plateaus; their highest summits are scored by deep gulches which descend their sides; and broad crevices, ravines, and passes, ramify along their slopes. Into these troughs, far above the snow-line, fed by confluent furrows, the snows of winter have collected, and heaped up layer upon layer accumulated to great depths. The water of the melted surface percolating through these subjacent films, an increasing pressure has solidified them to a semi-icy state. Slowly in these deep fields of snow, by pressure, by alternate thawing and melting, the molecular condition of the mass undergoes a change, and becomes compacted into crystalline ice. Before this change is consummated, the mass of snow, ice, and congealing water, is called the nève. Thus formed, there emerge from these upper reservoirs vast sheets of ice which pass down between cliffs and crags, winding over rocky beds, and through the avenues of least resistance, sometimes fusing together into solid seas amid the mountains, elsewhere stealing in sinuous and gleaming currents to the plains beneath. These solid masses, fastened like inexorable wedges into the mountain-clefts, possess motion, moving like a river, faster at the top than at the bottom, in the centre than along the sides, and in curves fastest upon the long curve; they, like rivers, also perform the offices of transportation and erosion. Long lines of fragments, detached by frost or avalanche, cover their surfaces in medial and lateral moraines, whose collected masses are poured over the glacier's extremity, where in stream or river it ends its course. Immense heaps of débris thus indicate, at the mountain's foot, the accumulated waste of its substance through the years of the glacier's slow and perpetual advance, and also record, as they lie beyond the present wall of the glacier, the past periods of its greatest extension. They grind the beds they pass over, the walls of their stony vaults are polished and inscribed, and the bowlders brought in contact with their stupendous powers of attrition are rubbed into brilliant surfaces and scored with rigid lines. Thus advancing, crevassed, convulsed, and rent into gaping chasms, loaded with blocks of stone, the glaciers are grinding down the everlasting hills and lowering the proud summits of their birthplace to the plain. Imagine half a hemisphere covered by a universal glacier whose powers of abrasion and transportation are proportionately enlarged: will not the appearances we are attempting to explain be adequately accounted for by so tremendous an agent? Let us turn to contemporaneous glaciers of the Alps and elsewhere for an answer. In mentioning characteristic instances of glacial action the glaciers are referred to by name only, as our space does not permit their reference to appropriate groups. The Glacier des Bois, as it projects its frozen tongue like a crystal wedge within the valley of Chamouni, reveals the mass of débris it has dragged down with it from the sides of Mont Blanc, in a high and rocky moraine over whose eminence the glacier pours its broken and shattered columns. In 1820 this glacier reached its frigid finger among the cultivated fields of neighboring villages, and in its slow retreat left an enormous bowlder perched upon a slope, and tracts of fragments spread in stony desolation up to the doors of the threatened hamlets. The Glacier of Tacconay has similarly withdrawn to its recesses, but strewed along the path of its former progress groups of bowlders which reach beyond the Arne. The rocks about are polished and furrowed, hillocks have been moulded into roches moutonnées, and upon their summits huge blocks deposited.
Seven thousand feet above the sea, upon the Col de Bellevue, erratic blocks are found, where no tidal force could ever have brought them, and these mingle with the present moraine of the Glacier de Bionassay, so that, as Forbes remarks, "it is impossible to say where the erratic phenomenon ends and where the glacial phenomenon begins." The Glacier de Miage, with its wild and ruffled surface breaking in cataracts of splendor down its steep defile, by its unceasing attrition upon the mountainside, and its perpetual transport of bowlders, has piled up, far out in the valley it occupies, a long and high slope of gravel and rocks, whose impervious sides dammed up the allée blanche and formed Lac Combal. So immense became the accumulations of débris that they consolidated into an impregnable hill, around whose base the glacier poured its divided stream. The Glacier la Brenna in 1767 was much contracted, while in 1831 new accretions caused it to reach out and attack with such vigor a promontory in its path as to shatter it with fissures, and compel the removal of a chapel upon its crest. Upon this same glacier Principal Forbes has observed the very act of glaciation, its method and effects. One side of the ice was exposed and found by him thickly set with nodules, pieces of granite as large as cherries, and protuberances of stone, while beneath this armed surface lay the limestone, over which it had just passed, with its face finely lined and graven in the direction of the glacier's motion. This glacier, now shrunken from its former imposing magnitude, once erected below its present terminus moraines of enormous size, while in its retreat it paved the land, predestined to sterility, with thickly-scattered fragments. On the west bank of the Mer de Glace, two hundred and forty feet above the present level of the glacial débris, traveled rocks lie in morainic alignments, and the bed-rock is scratched and abraded, indicating an ancient margin of the glacier in days when its frigid tide was swollen by greater additions and more favorable climates.
The distinction between aqueous action upon the rocks and mechanical abrasion is easily understood, and their presence readily distinguished. Forbes observed a face of limestone marked with grooves many yards in length, and, nearly horizontal above them, he found the marks produced by flowing water charged with fragments. The latter were blunt, irregular, and blotchy, having no continuity, and strikingly contrasted with the straight rulings below them. Furthermore, the memorable flood of water which devastated the valley of Bagnes, a mass over five hundred million cubic feet in volume, which swept up bridges and houses, snapped trees asunder, and transplanted a colony of buildings, was yet unable with all its Titanic violence to move large bowlders which it encountered even through inconsiderable distances.
In our glance over the glacial fields of to-day, leaving the inferences from those facts mentioned to be drawn themselves, let us briefly inspect the frozen valleys and important ice-streams of Norway. The backbone of the Scandinavian peninsula lies in Norway, reaching from Drontheim to the North Cape in the long neck of the Kiölen Mountains. This chain attains in places an elevation of six thousand feet, and again stoops to less than two thousand, receding at times from the shore-line, and again pushing out upon the ocean, till, as in the Loffoden Islands, many of its conspicuous summits stand insulated among its billows. North of latitude 68° north the range "scatters," and finally sinks into slight and timid heights or gradually disappears. South of Drontheim this central axis unfolds and deliquesces into a series of separate lines of elevation, forming the wide expansion of Southern Norway which, thickened and braced by ridges of crystalline rock, held back the force of the North Sea, and bore the searching pressure of the northern glacier, when in a single and enormous surface it invaded Europe. This southern extension of the Norwegian highlands has less height than the narrow fork which enters the north, and is really a succession of tablelands interrupted by occasional peaks, or narrow and precipitous valleys. These level floors, barren and monotonous, constitute over forty per cent, of the surface, reducing the available land for cultivation, roughly estimated, to less than eleven per cent. The coast of Norway along its entire extent is deeply penetrated by a complex system of fiords, long channels which wind in almost inextricable detail amid its highlands and at the base of its loftiest summits. Running for miles inland, and connected with the labyrinth of straits which fimbriate the shores and break the outlines with detached islands, these wonderful expanses expose the most bewitching and lovely scenery which Norway boasts. Glacier, snow-capped mountain, green fields verdant under cultivation, villages, and dizzy cliffs, are exquisitely blended into a diversified panorama of sublimity and beauty.
The glaciers of Norway are not so imposing, so numerous, or so accessible, as those of the Alps. The peaks are frequently too isolated and too steep, the valleys too shallow and too small, and the stretches of table-land too frequent, to permit the best exhibition of glacial forms; yet the accumulations of snow are very formidable. The snow-fields of Justedals Bracen, which feed several glaciers, the largest of which is only one-seventh the size of the Aletsch glacier in the Alps, stretch for fifty miles upon one range, and cover an area of four hundred square miles. Sognefield and Ymesfield form imperfect reservoirs of snow, and generate only inferior though numerous ice-streams, falling off their declivities through abrupt and narrow passes. The Fondalen Mountains and the Borgefield both release glacial currents, in some instances impinging their icy barriers upon the sea, but all subordinate in interest.
Sulitelma, the highest mountain within the arctic circle, occupies a conspicuous centre of glacial activity. It dominates over an extensive region of elevated and snowy ranges, and distributes its frigid emissions on either side to Lapland or to Norway. The peaks of the Loffoden Islands reach above the snow-line, but no adequate footing is afforded for the formation of glaciers, though the islands of Ringvadsö and Kraagen contain glaciers, which in the first instance have pushed their moraines to the water's edge. If we now examine the actual evidence of glacial action, we shall find it analogous to that we have witnessed in the Alps, except that it is perhaps less emphatic. The slaty rock of Norway fails to retain the erosive markings of the ice plough, and has lost frequently its graven surface through frost. Again, the more characteristic traces must be found upon the steep slopes and narrowed exits of the snow-fields, and these are not always readily approached.
Along Drontheim Fiord, and in many localities over the shore and bays, the roches moutonnées appear repeatedly, and at Sognefiord the hard conglomerate, rounded into these huge knobs, is graven with channels and grooves. At Moranger Fiord the impressions increase in distinctness as we approach the glacial ridges which overhang it. The Bandhuus Glacier at one time extended to the sea, and the mingled heap of rocks it pushed before it now lies, a crescent of desolation, in its old path. One hundred years ago, by local traditions, the Suphelle Glacier, among the Justedals glaciers, extended across the entire valley into which it now debouches, and a series of recent moraines indicates its retreat. About 3,600 feet in front of the Krondal and Nygaard glaciers, terminal moraines, unmistakably modern, are seen, while the evidence of their erosive action is found in the increasing definiteness of the rocky striations as we advance over the land last scored toward the glacier, this same track being sown with bowlders and pebbles, relics of their past ravages. Two hundred feet above the Nygaard, on the face of the cliff, we can read, as legibly as we do the record of the fallen tide, the annals of its past increase; and local tradition, stories of destruction, removal of villages and houses, corroborate this ocular examination. In short, in Norway, as in the Alps, the characteristics of glacial denudation, as seen in the forces now at work, appear to perpetuate the memory of agencies which, on a magnificent scale, operated upon continents.
Turning our eyes from the picturesque surprises of the Scandinavian cliffs and streams, let us fix them upon the multitudinous slopes and the confused outlines of the Himalaya Mountains, as they rise to the plains of Thibet, and read their lesson. Here we shall encounter the same arctic currents cleaving the fissures
"Of vales more wild and mountains more sublime."
Upon their surface we see the same long avenues of bowlders, fed in their tedious course from every faltering cliff or frost-riven peak, and their ancient channels indelibly indicated in the disordered débris of rocks and pebbles filched from quarries leagues away.
The Himalaya Mountains mark the northern frontier of India, and form the most important section of that long axis of elevation which reaches from the Bosporus to the Pacific, and separates, as a similar girdle does in Europe, the northern plains and table-land from the low peninsulas and milder districts of the south. The Himalayas ascend to the grandest heights, and in their sublime elevation crown the continental water-shed with earth's most stupendous peaks. Their passes are little lower than Mont Blanc; their roads are dizzy shelves encircling more tremendous cliffs, or swinging jhúlas spanning frightful gorges, whose depths seem lost in the bowels of the earth. "There, far above the habitation of man, no living thing exists, no sound is heard, the very echo of the traveler's footsteps startles him in the awful solitude and silence that reigns in these august dwellings of everlasting snow." Deep ravines penetrate between imposing groups of inaccessible mountains, torrents hew out their tortuous courses over precipitous slopes, and the gathered influx of innumerable lines of drainage gives rise to the Indus, Ganges, and Brahmapootra, great and sacred streams whose head-waters here pursue their rocky and dangerous descent to the plains of India. Between the higher ranges nestle the fertile valleys of Nepaul, Bootan, and Assam, themselves high table-lands upon the declivity of the snowy peaks; and to the east, beneath the alternate shadows of the Hindoo-Koosh and the Himalayas, reposes the fragrant vale of Cashmere.
As we approach the mountains we traverse three distinct regions: the green "Tarai," marshy and insalubrious; the middle country, a belt of wooded land, arid and with a porous soil; and lastly, at 10,000 feet, the dry and unhealthy marais. The nucleal range we find is beset with numerous branches, whose long axes stretch out in waving and complicated lines from the central ridge, lie furcating and multiplying like tree-limbs as they embank the rivers, or surround occasional basins, into whose fruitful beauty the traveler peers. Clay slate, very micaceous, and passing into sandstone with interstratified limestone, forms the lithological basis of the mountains, and through the passes ramifying veins of quartz and granite. The tertiary formation extends up the valleys and laps over the foot-hills. The ascent now becomes strewed with erratic blocks, and angular bowlders of granite occur far removed from their origin, while ravines and stream-beds are picturesquely strewed with transported masses. At times the accumulation of bowlders becomes so extensive as to choke the valleys, or rise in confused piles and in unstable equilibrium for a hundred feet above the brawling streams which pass between them. The valley of the Shayuk is filled with these bowlders; and, after its waters unite with the Indus, their swollen floods pour through a narrow channel beneath enormous heaps of angular fragments. Again, about Iskardo, two banks of bowlders project upon the valley forty to fifty feet high; in fact, along the Indus immense tracts are covered with granitic masses; they lie over the alluvial land, intermixed indeed with it, and form natural features from their size. The valley of the Thawar is fairly blocked at one end by the collection of bowlders, and long hills are composed of such débris. For almost a day's journey on the mountain-sides, west of Pok, limestone blocks occur in great numbers, transported from indeterminate distances, as no limestone occurs here in situ. A glacier occurs upon the Parang Pass, not of large proportions, which, wedged between the mountains, ruggedly advances, carrying limestone bowlders, and terminating three miles from the head of the pass in a steep precipice one hundred feet high, where its final burdens are discharged down the mountain. Snow-beds or small glaciers are of constant occurrence at the heads of the ravines, and the cool water-brooks which traverse the slopes spring from their melting edges. In Butna Valley the traveler passes for two miles among huge bowlders, then crosses a moraine, and finally reaches a plain encircled by lofty mountains, some of which reveal resplendent pyramids of snow which "bind" into a glacier, filling the head of the valley. Its Surface is obscured by masses of rock and gravel, and beyond its present limits similar proofs of its ravages lie in bewildering confusion. From the valley of Nubbra the traveler beholds the encircling peaks brilliant and luminous in the blaze of countless snow-fields, while icy currents, confluent in larger glaciers, stream from the distant heights. One of these, approached through avenues of bowlders, is half a mile wide, and black with a coverlid of stones and dirt. Neighboring ravines conceal kindred masses whose extremities retire from terminal heaps of bowlders, landmarks of their former expansion. The magnificent glaciers north of Sassar are conspicuous and famous. The large glacier passes down the mountain-side, ploughing a deep furrow through an alluvial plain and plunging into the Shayuk River, whose waters eddy and boil from underneath it. Two moraines accompany it, one of enormous blocks and sixty feet high, outside of its present shrunken area, formed in the glacier's former strength, and a smaller one upon it. In furrows, fifteen and twenty feet deep, upon its surface are sunk strings of rocks imbedded in the icy matrix, and released in occasional showers from its terminal cliffs upon a talus of fragments thus accumulated. In the Shigri Valley and at Zanskar, enormous glaciers are gathered together in companies. Some are literally buried beneath the extraordinary heaps of rocks and detached slabs which are caught upon them from shattered cliff and stony avalanche. They work their way underground, while grass and flowers decorate the desolate covering which conceals them. The valleys of Thibet show unmistakably the past presence of extensive glaciers. Moraines and traveled blocks reach low down into them, often three thousand feet lower than the existing termini of the glaciers.
If, leaving the inhospitable terraces of Thibet and the sublime and unrivaled summits of the Himalayas, we traverse the ice-covered tableland of Greenland, we shall encounter the same phenomena as those we have examined in the Alps, in Norway, and in India, but so magnified in extent as to become continental, and in a measure reconstruct the picture of a world hidden beneath a universal mer de glace. Greenland stretches down from those vast and unexplored regions, whose limits encircle the pole, in a broad wedge-like peninsula, deeply fissured by fiords and bays, its margins abruptly rising in mural precipices, and bearing upon its bosom the oppression of an illimitable glacier. From Cape Farewell, where Greenland rises amid a group of rocky islands, to more than 1,300 miles northward, and far beyond, where no human step has trod, a rigid sea of ice sweeps its appalling and silent surface. The ice piled up upon central axes forces itself outward in vast sheets and icy currents to the shore. This universal exudation of ice makes an ice-wall many hundred feet high along the coast, an impressive feature in that northern land, and a solemn token of the desolation it protects. At its foot a shelf of ice projects into the water, in places a smooth table, but more frequently tossed in the wild commotion of confused hummocks straining and grinding together, urged by the resistless impetus of the arctic tides.
From the wide central area descend numerous glaciers upon both the eastern and western coasts, and fimbriate by slow erosion the rockbound land. Thus carved, in the long succession of ages, deep fiords penetrate the country, walled by lofty and inaccessible precipices, and terminating at the feet of ice-tongues which protrude their burdens of rock, gravel, mud, and soil, into their waters. In places these deposits shallow the water to great distances; and far from shore, rounded rocks, transported from interior highlands, project their polished summits above the waves. Bowlders of green-stone and syenite, rounded by friction and brought from remote localities, are scattered over wide districts. Again, upon the ice-foot which fringes the base of the cliffs, bowlders, tons in weight, are found, dislodged by frosts from the rocks above, and composed of magnesian limestone and inferior sandstones, while elsewhere long backs of rocks are seen abraded and furrowed by ice-floes and glaciers.
The glaciers occur at the indentations of the shore-line and where the cliffs decline, affording them approach to the waters. Here breaking into gigantic fragments, each one a towering iceberg, or slowly melting in the warmer waters of the sea, they constantly waste away, and are as constantly replenished from the inexhaustible and overflowing reservoirs they have left. The great conduit from the inland sea is the Humboldt Glacier, which extends its glassy wall, 300 feet high, along the deepest water for sixty miles, pouring out incalculable volumes of ice, laden and penetrated with bowlders, trophies of its resistless march from hidden and unknown recesses. Kane's Northumberland Glacier, interesting from the apparent viscosity of the ice, reaches from the interior to the coast unbroken, even when subjected to most unequal and various descents, by any fracture, while in many places "it could be seen exuding its way over the very crest of the rocks, and hanging down in huge stalactites seventy or one hundred feet long." This glacier carried enormous measures of earth, gravel, and rubbish. The Great Glacier is rifted in long shelves, which at a distance seem pressed together, the intermediate crevasses appearing as lines above one another. As the motion conspicuous in every part of this glacier successively brings these detached walls to the seas, they are floated away in trains of icebergs, over whose sides pour streams of water, to be lost in cavities, while torrents gush down their faces, sculpturing the ice with the facile mimicry of towers, minarets, and spires. Bowlders polished and channeled rocks, submarine moraines, abraded and excavated cliffs, are met with everywhere, and Kane counted forty-one ledges, old beaches marking the recession of the sea, which in their succession led from the granitic nucleus, formerly the coast-wall, to the present shore—all typical features of the landscape where glaciers and ice-caps are no longer found. The scenic effects in Greenland are wonderful in the extreme. Appalling cliffs rise in barren and frigid splendor from the broken floors of hummocks, and the peripheral ice-foot; their summits, corroded by frost, discharge bowlders and débris upon the ice beneath, while icebergs in towering and fantastic glory, crowd the shallowing bays, or press along the coast in weird processions, marshaled by the shriek of the cracking floes, the crush of their own dismantled pinnacles, or the thunder of distant avalanches.
Again, turning our eyes to warmer latitudes, let us direct our explorations to New Zealand, and learn the corroborative testimony it offers for this great theory. On the South Islands of New Zealand glaciers rest among the high recesses of its western mountains, upon Mount Cook, Mount Tasman, and neighboring summits, while a glacier from Mount Tyndall, at an elevation of 4,000 feet, gives birth to the river Clyde, where its abrupt termination rears an icy wall 1,300 feet long and 120 feet high. The Francis Joseph Glacier from Mount Tasman descends to within 705 feet of the sea-level, exhibiting the characteristics of all known glaciers. These massive streams are carving with remorseless energy the solid rocks, and transporting in their course the trophies of their labor. Yet, strong and magnificent as they now appear, they are but the ghosts of those former seas which swept from peak to wave, and piled upon the flanks of the mountains and the depressions of the coast the huge moraines and the transported bowlders which appear on every hand. These heaps of débris and congeries of rocky fragments lie in the direct extension of the present glaciers, and indicate most strikingly their origin. Lake-basins and narrow fiords created by the erosion of prehistoric ice are universal; and Lake Wakatipu, by the most indisputable proofs, has been thus dug out of the living rock—1,400 feet deep—itself but the shrunken outline of a previous sheet of water that reached into the rock-worn valley below it. Even now the glaciers of Mount Carnslaw, the brief remains of former arctic glories, now retreated beyond the thermal influences of the lowland, emit two rattling streams, turbid with the ground powder of the rocks, which, depositing their silt at the upper extremity of Lake Wakatipu, are obliterating in made land the testimony of past ravages.
Passing in one broad stride to the opposite, the eastern margins of the Pacific, we find amid the savage and inhospitable Cordilleras of Patagonia new glaciers, and around and beneath them memorials of a grander reign than that they now engross. Immense bowlders of basalt, sixty-seven miles distant from the nearest mountain, pebbles of porphyry, fragments of granite and slate, border the Santa Cruz River, impede its course, and lie broadcast upon the plain which rises 1,100 feet above its bed. From the encircling shores of Beagle Channel, glaciers born upon the lofty slopes and granitic peaks 4,000 and 5,000 feet above the sea, push their frozen lengths into the sea, which is shaken into waves as successive ruptures into the ice launch mimic icebergs upon its surface. "Almost every arm of the sea," writes Darwin, "which penetrates to the interior higher chain, not only in Terra del Fuego but on the coast for 650 miles northward, is terminated by tremendous and astonishing-glaciers." Old channels, now dry by the elevation of the land, are diversified with groups of traveled blocks, and the bowlders, so well known, from the distant Andes, lying upon the island of Chiloe, are further indications of an action in the past identical with that exerted at present.
In conclusion, without rehearsing the evidence drawn from the Pyrenees or the Caucasus, where glaciers still exist, we see in the northern and southern hemispheres the imposing remains of primitive areas of ice which in a more congenial era projected their confluent and inter-mingling branches over vast regions of the earth, where, as they have retreated, they have left irrefragable evidence of their power. We have observed the same processes at work, the same results produced, the same methods utilized, in the world about us, and the clearest analogy compels us to accept a theory which ascribes the morainic débris piled up in hills and islands, the engraved rocks, the excavated basins, and the rounded slopes, to an identical though vastly-magnified cause in times only within the ken of Geology in its retrospective glance of ages.
- No. I. was published in The Popular Science Monthly for January, 1878.