Sir John William Dawson

THE GREAT ICE AGE.

S

Scientific superstitions, understanding by this name the reception of hypotheses of prominent men, and using these as fetishes to be worshipped and to be employed in miraculous works, are scarcely less common in our time than superstitions of another kind were in darker ages. One of these which has been dominant for a long time in geology, and has scarcely yet run its course, is that of the Great Ice Age, with its accompaniments of Continental Glaciers and Polar Ice Cap. The cause of this it is not difficult to discern. The covering of till, gravel and travelled boulders which encumbers the surface of the northern hemisphere from the Arctic regions more than half way to the equator, had long been a puzzle to geologists, and this was increased rather than diminished when the doctrine of appeal to recent causes on the principle of uniformity became current. It was seen that it was necessary to invoke the action of ice in some form to account for these deposits, and it was at the same time perceived that there was much evidence to prove that between the warm climate of the early Tertiary and the more subdued mildness of the modern time there had intervened a period of unusual and extreme cold. In this state of affairs attention was attracted to the Alpine glaciers. Their movement, their erosion of surfaces, their heaping up of moraines bearing some resemblance to the widely extended boulder deposits, their former greater extension, as indicated by old moraines at lower levels than those in process of formation, were noted. Here was a modern cause capable of explaining all the phenomena. Men's minds were taken by storm, and as always happens in the case of new and important discoveries, the agency of glaciers was pushed at once far beyond the possibilities of their action under any known physical or climatal laws. This exaggerated idea of the action of land ice in the form of glaciers is not yet exploded, more especially in the United States, where official sanction has been given to it by the Geological Survey, and where it has been introduced even into school and college text-books. It affords also a telling bit of scientific sensationalism, which can scarcely be resisted by a certain class of popular writers. America has also afforded greater facilities for extreme theories of this kind, owing to the wide and uninterrupted distribution of glacial deposits, and the more simple and less broken character of its great internal plateau, while the influence of great leading minds, like those of the elder Agassiz and of Dana, naturally held sway over the younger geologists. Fortunately Canada, which possesses the larger and more northern half of the North American continent; though numerically inferior, and therefore overborne in the discussion, has, in the main, remained steadfast to facts rather than to specious theories, and has been confirmed in this position by the clearer testimony of nature in a region where many of the features of the glacial age still persist.[156]

[156] I may refer here to the recent researches of Dr. G. M. Dawson, Mr. R. Chalmers, Mr. McConnell and Dr. Ells.

The writer of these pages has, ever since the publication of the first edition of his "Acadian Geology,"[157] steadily resisted the more extreme views of glaciation, and has opposed the southward progress of the great continental glacier. Though, figuratively speaking, overborne and pressed back in the course of its extension, he has now, like those primitive men who are imagined in the post-glacial age to have followed up the retreat of the ice, the pleasure of seeing the once formidable continental glacier broken up into great local glaciers on the mountain ranges separated by intervening areas of submergence.

[157] 1855.

The questions relating to this subject are too numerous and varied for treatment here. The question of the causes of the great lowering of temperature in the glacial age I shall leave for consideration in the next chapter, and merely state here that I believe changes of distribution of sea and land and of ocean currents are sufficient to account for all the refrigeration of which there is good evidence. I content myself with a comparison of the glacial phenomena of Mont Blanc and of the Gulf of St. Lawrence from my own observation,[158] and some general deductions as to glacier possibilities.

[158] Published in 1867.

A scientific voyager carries with him a species of questioning peculiar to himself. Not content with vacantly gazing at the sea, scrutinizing his fellow passengers, noting the changes of the weather and the length of the day's run, he recognises in the sea one of the great features of the earth, and questions it daily as to its present and its past The present features of the sea include much of surpassing interest, but the questions which relate to its origin and early history are still more attractive. Some of these questions are likely to interest a voyager from Canada entering the Atlantic by one of its greatest tributaries, the St. Lawrence.

In doing so, we approach the ocean not at a right angle, but along a line only slightly inclined to its western side, and we find ourselves in a broad estuary or trough, having on its north-western side rugged hills of old crystalline rocks, the Laurentian, ridged up in great folds or earth waves parallel to the river. On the south-east or right-hand side we have a lower barrier of earth waves composed of sedimentary rocks somewhat later in date, but still geologically very ancient. We are thus introduced to a remarkable feature of the west side of the North Atlantic, namely, that its border is made up of very old rocks folded into mountain ridges thrown up at an ancient period, and approximately parallel to the coast. The Lower St. Lawrence occupies a furrow between two of these ridges.

Here, however, a more modern feature attracts our attention. The sides of the bounding hills are cut in a succession of terraces, rising one above another from the level of the sea to a height of 500 feet or more, capped with long ranges of the white houses and barns of the Canadian habitants, and furnishing level lines for the "concession roads" which run along the coast. These terraces are really old sea margins indicating the stages of the elevation of the land out of the sea immediately before the modern period. On these terraces, and in the clays and sands which form the plateaus extending in some places in front of them, are sea shells of the same kinds with those now living in the Gulf of St. Lawrence, and occasionally we find bones of whales which have been stranded on the old beaches.

These terraces are, of course, indications of change of level in very modern times. They show that in what we call the Pleistocene age the land was lower than at present, and we shall find that in the Lower St. Lawrence there is evidence of a depression extending to over 1,000 feet, carrying the sea far up the valley, so that sea shells are found in the clays as far up as Kingston and Ottawa, and stranded skeletons of whales as far west as Smith's Falls, in Ontario.

If we examine the shores more minutely, we shall find all along the south coast a belt of boulders which are often as much as eight to ten feet in diameter, and consist largely of rocks found only in the hills of the northern coast, more than thirty miles distant, from which they must have been drifted to their present position. This boulder belt, which extends from the lowest tide mark about fifty feet or more upward, is sometimes piled in ridges and sometimes flattened out into a rude pavement. It is a product of the modern field ice, which, attaining a great thickness in winter, has boulders frozen into its bottom, and floating up and down with the tide, deposits these on the shore. At Little Metis, two hundred miles below Quebec, where I have a summer residence, I have from year to year cleared a passage through the boulder belt for bathing and for launching boats, and nearly every spring I find that boulders have been thrown into the cleared space by the ice, while one can notice from year to year differences in the position of very large boulders.

If we pass inland from the shore belt of boulders, we shall find similar appearances on the inland terraces at various heights, up to at least 400 feet. These are inland boulder belts belonging to old shores now elevated. Like the modern boulder belt these inland belts and patches consist partly of Laurentian rocks from the North Shore, partly of sandstones and conglomerates in place near to their present sites. In some places the stones are smaller than those of the present beach, in other places of gigantic size. These boulders lie not only on the bare rock striated in places with ice grooves pointing to the north-north-east; but on the old till or boulder clay, which also abounds with boulders, and which is more ancient than the superficial boulder drift. Locally we find here and there masses of fossiliferous limestone which must have been derived from the high ground to the south of the St. Lawrence, and which have been borne northward either by drift ice or by local glaciers.

If now we study the polished and scored surfaces of rocks in the St. Lawrence valley and the bounding hills, we shall find that while the former testify to a great movement of ice and boulders up the river from the north-east, the latter show evident signs of the movement of local glaciers down the valleys of the Laurentide hills to the south, and on the continuation of the Appalachians south of the river similar evidence of the movement of land ice to the north. Thus we have evidence of the combined action of local glaciers and floating ice. To add to all this, we can find on the flat tops of the hard sandstone boulders on the beach the scratches made by the ice of last winter, often in the same north-easterly direction with those of the Pleistocene time.

In addition to the ice formed in winter in the St. Lawrence itself, the snow-clad hills of Greenland send down to the sea great glaciers, which in the bays and fiords of that inhospitable region form at their extremities huge cliffs of everlasting ice, and annually "calve," as the seamen say, or give off a great progeny of ice islands, which, slowly drifted to the southward by the arctic current, pass along the American coast, diffusing a cold and bleak atmosphere, until they melt in the warm waters of the Gulf Stream. Many of these bergs enter the Straits of Belle-Isle, for the Arctic current clings closely to the coast, and a part of it seems to be deflected into the Gulf of St. Lawrence through this passage, carrying with it many large bergs. The voyager passing through this strait in clear weather may see numbers of these ice islands glistening in snowy whiteness, or showing deep green cliffs and pinnacles—sometimes with layers of earthy matter and stones, or dotted with numerous sea birds, which rest upon them when gorged with the food afforded by shoals of fish and others marine animals which haunt these cold seas. In early summer the bergs are massive in form, often with flat tops, but as the summer advances they become eroded by the sun and warm winds, till they present the most grotesque forms of rude towers and spires rising from broad foundations little elevated above the water.

Mr. Vaughan, late superintendent of the Lighthouse at Belle-Isle, has kept a register of icebergs for several years. He states that for ten which enter the straits, fifty drift to the southward, and that most of those which enter pass inward on the north side of the island, drift toward the western end of the straits, and then pass out on the south side of the island, so that the straits seem to be merely a sort of eddy in the course of the bergs. The number in the straits varies much in different seasons of the year. The greatest number are seen in spring, especially in May and June; and toward autumn and in the winter very few remain. Those which remain until autumn are reduced to mere skeletons; but if they survive until winter, they again grow in dimensions, owing to the accumulations upon them of snow and new ice. Those that we saw early in July were large and massive in their proportions. The few that remained when we returned in September were smaller in size, and cut into fantastic and toppling pinnacles. Vaughan records that on the 30th of May, 1858, he counted in the Straits of Belle-Isle 496 bergs, the least of them sixty feet in height, some of them half a mile long and 200 feet high. Only one-eighth of the volume of floating ice appears above water, and many of these great bergs may thus touch the ground in a depth of thirty fathoms or more, so that if we imagine four hundred of them moving up and down under the influence of the current, oscillating slowly with the motion of the sea, and grinding on the rocks and stone-covered bottom at all depths from the centre of the channel, we may form some conception of the effects of these huge polishers of the sea floor.

Of the bergs which pass outside of the straits, many ground on the banks off Belle-Isle. Vaughan has seen a hundred large bergs aground at one time on the banks, and they ground on various parts of the banks of Newfoundland, and all along the coast of that island. As they are borne by the deep-seated cold current, and are scarcely at all affected by the wind, they move somewhat uniformly in a direction from north-east to south-west, and when they touch the bottom, the striation or grooving which they produce must be in that direction.

In passing through the straits in July, I have seen great numbers of bergs, some low and flat-topped, with perpendicular sides, others convex or roof-shaped, like great tents pitched on the sea; others rounded in outline or rising into towers and pinnacles. Most of them were of a pure dead white, like loaf sugar, shaded with pale bluish green in the great rents and recent fractures. One of them seemed as if it had grounded and then overturned, presenting a flat and scored surface covered with sand and earthy matter.

At present we wish to regard the icebergs of Belle-Isle in their character of geological agents. Viewed in this aspect, they are in the first place parts of the cosmical arrangements for equalizing temperature, and for dispersing the great accumulations of ice in the Arctic regions, which might otherwise unsettle the climatic and even the static equilibrium of our globe, as they are believed by some imaginative physicists and geologists to have done in the so-called glacial period. If the ice islands in the Atlantic, like lumps of ice in a pitcher of water, chill our climate in spring, they are at the same time agents in preventing a still more serious secular chilling which might result from the growth without limit of the Arctic snow and ice. They are also constantly employed in wearing down the Arctic land, and aided by the great northern current from Davis's Straits, in scattering stones, boulders and sand over the banks along the American coast. Incidentally to this work, they smooth and level the higher parts of the sea bottom, and mark it with furrows and striÆ indicative of the direction of their own motion.

When we examine a chart of the American coast, and observe the deep channel and hollow submarine valleys of the Arctic current, and the sandbanks which extend parallel to this channel from the great bank of Newfoundland to Cape Cod, we cannot avoid the conclusion that the Arctic current and its ice have great power both of excavation and deposition. On the one hand, deep hollows are cut out where the current flows over the bottom, and on the other, great banks are heaped up where the ice thaws and the force of the current is abated. I have been much struck with the worn and abraded appearance of stones and dead shells taken up from the banks off the American coast, and am convinced that an erosive power comparable to that of a river carrying sand over its bed, and materially aided by the grinding action of ice, is constantly in action under the waters of the Arctic current.[159] The unequal pressure resulting from this deposition and abrasion is not improbably connected with the slight earthquakes experienced in Eastern America, and also with the slow depression of the coast; and if we go back to that earliest of all geological periods when the Laurentian rocks of Sir Wm. Logan, constituting the Labrador coast and the Laurentide Hills, were alone above water, we may even attribute in no small degree to the Arctic current of that old time the heaping up of those thousands of feet of deposits which now constitute the great range of the Alleghany and Appalachian mountains, and form the breast bone of the American continent. In those ancient times also large stones were floated southward, and enter into the composition of very old conglomerates.

[159] At the time when this was written I had only studied stones brought up accidentally by fishermen and others from the banks of Newfoundland and elsewhere. At a later date Murray of the Challenger has given more ample material. He states that the bottom in the Labrador current, 100 miles from land, was found to be blue mud with 60 per cent, of sand and stones; and mentions a block of syenite weighing 490 lbs. taken up in 1,340 fathoms, and stones and pebbles of quartzite, limestone, dolomite, mica schist and serpentine, one of which was glaciated. This is the modern boulder clay produced by Greenland glaciers and the field ice of Baffin's Bay and the Labrador coast.

But such large speculations might soon carry us far from Belle-Isle, and to bring us back to the American coast and to the domain of common things, we may note that a vast variety of marine life exists in the cold waters of the Arctic current, and that this is one of the reasons of the great and valuable fisheries of Labrador, Newfoundland and Nova Scotia, regions in which the sea thus becomes the harvest field of much of the human population. On the Arctic current and its ice also floats to the southward the game of the sealers of St. John and the whalers of GaspÉ.

We may now proceed to connect these statements as to the distribution of icebergs, with the glaciated condition of our continents, with the remarkable fact that the same effects now produced by the ice and the Arctic current in the Strait of Belle-Isle and the deep-current channel off the American coast, are visible all over the North American and European land north of forty degrees of latitude, and that there is evidence that the St. Lawrence valley itself was once a gigantic Belle-Isle, in which thousands of bergs worked perhaps for thousands of years, grinding and striating its rocks, cutting out its deeper parts, and heaping up in it quantities of northern dÉbris. Out of this fact of the so-called glaciated condition of the surface of our continents has, however, arisen one of the great controversies of modern geology. While all admit the action of ice in distributing and arranging the materials which constitute the last coating which has been laid upon the surface of our continents, some maintain that land glaciers have done the work, others, that sea-borne ice has been the main agent employed. As in some other controversies, the truth seems to lie between the extremes. Glaciers are slow, inactive, and limited in their sphere. Floating ice is locomotive and far-travelled, extending its action to great distances from its sources. So far, the advantages are in favour of the flotation. But the work which the glacier does is done thoroughly, and, time and facilities being given, it may be done over wide areas. Again, the iceberg is the child of the glacier, and therefore the agency of the one is indirectly that of the other. Thus, in any view we must plough with both of these geological oxen, and the controversy becomes like that old one of the Neptunists and Plutonists, which has been settled by admitting both water and heat to have been instrumental in the formation of rocks.

In the midst of these controversies a geologist resident in Great Britain or Canada should have some certain doctrine as to the question whether at that period, geologically recent, which we call the Pleistocene period, the land was raised to a great height above the sea, and covered like Greenland with a mantle of perpetual ice, or whether it was, like the strait of Belle-Isle and the banks of Newfoundland, under water, and annually ground over by icebergs, or whether, as now seems more probable, it was in part composed of elevated ridges covered with snow and sending down glaciers, and partly depressed under the level of ice-laden straits and seas.

A great advocate of the glacier* theory has said that we cannot properly appreciate his view without exploring thoroughly the present glaciers of Greenland and ascertaining their effects. This I have not had opportunity to do, but I have endeavoured to do the next best thing by passing as rapidly as possible from the icebergs of Belle-Isle to the glaciers of Mont Blanc, and by asking the question whether Canada was in the Pleistocene period like the present Belle-Isle or the present Mont Blanc, or whether it partook of the character of both? and taking advantage of these two most salient points in order to elicit a reply.

Transporting ourselves, then, to the monarch of the Alps, let us suppose we stand upon the Flegere, a spur of the mountains fronting Mont Blanc, and commanding a view of the entire group. From this point the western end of the range presents the rounded summit of Mont Blanc proper, flanked by the lower eminences of the Dome and Aiguille de GoutÉ, which rise from a broad and uneven plateau of nevÉ or hard snow, sending down to the plain two great glaciers or streams of ice, the Bossons and Tacony glaciers. Eastward of Mont Blanc the nevÉ or snow plateau is penetrated by a series of sharp points of rock or aiguilles, which stretch along in a row of serried peaks, and then give place to a deep notch, through which flows the greatest of all the glaciers of this side of Mont Blanc, the celebrated Mer de Glace, directly in front of our standpoint. To the left of this is another mass of aiguilles, culminating in the Aiguille Verte. This second group of needles descends into the long and narrow Glacier of Argentiere, and beyond this we see in the distance the Glacier and Aiguille de Tour. As seen from this point, it is evident that the whole system of the Mont Blanc glaciers originates in a vast mantle of snow capping the ridge of the chain, and extending about twenty miles in length, with a breadth of about five miles. This mass of snow being above the limits of perpetual frost, would go on increasing from year to year, except so far as it might be diminished by the fall of avalanches from its sides, were it not that its plasticity is sufficient to enable the frozen mass to glide slowly down the valleys, changing in its progress into an icy stream, which, descending to the plain, melts at its base and discharges itself in a torrent of white muddy water. The Mont Blanc chain sends forth about a dozen of large glaciers of this kind, besides many smaller ones. Crossing the valley of Chamouni, and ascending the Montanvert to a height of about 6,000 feet, let us look more particularly at one of these glaciers, the Mer de Glace. It is a long valley with steep sides, about half a mile wide, and filled with ice, which presents a general level or slightly inclined surface, traversed with innumerable transverse cracks or crevasses, penetrating apparently to the bottom of the glacier, and with slippery sloping edges of moist ice threatening at every step to plunge the traveller into the depths below. Still the treacherous surface is daily crossed by parties of travellers, apparently without any accident. The whole of the ice is moving steadily along the slope on which it rests, at the rate of eight to ten inches daily—the rate of motion is less in winter and greater in summer; and farther down, where the glacier goes by the name of the Glacier du Bois, and descends a steeper slope, its rapidity is greater; and at the same time by the opening of immense crevasses its surface projects in fantastic ridges and pinnacles. The movements and changes in the ice of these glaciers are in truth very remarkable, and show a mobility and plasticity which at first sight we should not have been prepared to expect in a solid like ice.[160] The crevasses become open or closed, curved upwards or downwards, perpendicular or inclined, according to the surface upon which the glacier is moving, and the whole mass is crushed upward or flattens out, its particles evidently moving on each other with much the same result as would take place in a mass of thick mud similarly moving. On the surface of the ice there are a few boulders and many stones, and in places these accumulate in long irregular bands indicating the lines of junction of the minor ice streams coming in from above to join the main glacier. At the sides are two great mounds of rubbish, much higher than the present surface of the glacier. They are called the lateral moraines, and consist of boulders, stones, gravel and sand, confusedly intermingled, and for the most part retaining their sharp angles. This mass of rubbish is moved downward by the glacier, and with the stones constituting the central moraine, is discharged at the lower end, accumulating there in the mass of detritus known as the terminal moraine.

Glaciers have been termed rivers of ice; but there is one respect in which they differ remarkably from rivers. They are broad above and narrow below, or rather, their width above corresponds to the drainage area of a river. This is well seen in a map of the Mer de Glace. From its termination in the Glacier du Bois to the top of the Mer de Glace proper, a distance of about three and a half miles, its breadth does not exceed half a mile, but above this point it spreads out into three great glaciers, the Geant, the Du Chaud, and the Talefre, the aggregate width of which is six or seven miles. The snow and ice of a large interior table-land or series of wide valleys are thus emptied into one narrow ravine, and pour their whole accumulations through the Mer de Glace. Leaving, however, the many interesting phenomena connected with the motion of glaciers, and which have been so well interpreted by Saussure, Agassiz, Forbes, Hopkins, Tyndall, and others, we may consider their effects on the mountain valleys in which they operate.

1. They carry quantities of dÉbris from the hill tops and mountain valleys downward into the plains. From every peak, cliff and ridge the frost and thaw are constantly loosening stones and other matters which are swept by avalanches to the surface of the glacier, and constitute lateral moraines. When two or more glaciers unite into one, these become medial moraines, and at length are spread over and through the whole mass of the ice. Eventually all this material, including stones of immense size, as well as fine sand and mud, is deposited in the terminal moraine, or carried off by the streams.

2. They are mills for grinding and triturating rock. The pieces of rock in the moraine are, in the course of their movement, crushed against one another and the sides of the valley, and are cracked and ground as if in a crushing mill. Further the stones on the surface of the glacier are ever falling into crevasses, and thus reach the bottom of the ice, where they are further ground one against another and the floor of rock. In the movement of the glacier these stones seem in some cases to come again to the surface, and their remains are finally discharged in the terminal moraine, which is the waste-heap of this great mill: The fine material which has been produced, the flour of the mill, so to speak, becomes diffused in the water which is constantly flowing from beneath the glacier, and for this reason all the streams flowing from glaciers are turbid with whitish sand and mud.

The Arve, which drains the glaciers of the north side of Mont Blanc, carries its burden of mud into the Rhone, which sweeps it, with the similar material of many other Alpine streams, into the Mediterranean, to aid in filling up the bottom of that sea, whose blue waters it discolours for miles from the shore, and to increase its own ever-enlarging delta, which encroaches on the sea at the rate of about half a mile per century. The upper waters of the Rhone, laden with similar material, are filling up the Lake of Geneva; and the great deposit of "loess" in the alluvial plain of the Rhine, about which Gaul and German have contended since the dawn of European history, is of similar origin. The mass of material which has thus been carried off from the Alps, would suffice to build up a great mountain chain. Thus, by the action of ice and water—

Many observers who have commented on these facts have taken it for granted that the mud thus sent off from glaciers, and which is so much greater in amount than the matter remaining in their moraines, must be ground from the bottom of the glacier valleys, and hence have attributed to these glaciers great power of cutting out and deepening their valleys. But this is evidently an error, just as it would be an error to suppose the flour of a grist mill ground out of the mill stones. Glaciers, it is true, groove and striate and polish the rocks over which they move, and especially those of projecting points and slight elevations in their beds; but the material which they grind up is principally derived from the exposed frost-bitten rocks above them, and the rocky floor under the glacier is merely the nether mill stone against which those loose stones are crushed. The glaciers, in short, can scarcely be regarded as cutting agents at all, in so far as the sides and bottoms of their beds are concerned, and in the valleys which the old glaciers have abandoned, it is evident that the torrents which have succeeded them have far greater cutting power.

The glaciers have their periods of advance and of recession. A series of wet and cool summers causes them to advance and encroach on the plains, pushing before them their moraines, and even forests and human habitations. In dry and warm summers they shrink and recede. Such changes seem to have occurred in bygone times on a gigantic scale. All the valleys below the present glaciers present traces of former glacier action. Even the Jura mountains seem at one time to have had glaciers. Large blocks from the Alps have been carried across the intervening valley and lodged at great heights, on the slopes of the Jura, leading the majority of the Swiss and Italian geologists to believe that even this great valley and the basin of Lake Leman were once filled with glacier ice. But, unless we can suppose that the Alps were then vastly higher than at present, this seems scarcely to be physically possible, and it seems more likely that the conditions were just the reverse of those supposed, namely, that the low land was submerged, and that the valley of Lake Leman was a strait like Belle-Isle, traversed by powerful currents and receiving icebergs from both Jurassic and Alpine glaciers, and probably from farther north. One or other supposition is required to account for the appearances, which may be explained on either view. The European hills may have been higher and colder, and changes of level elsewhere may have combined with this to give a cold climate with moisture; or a great submergence may have left the hills as islands, and may have so reduced the temperature by the influx of arctic currents and ice, as to enable the Alpine glaciers to descend to the level of the sea. Now, we have evidence of such submergence in the beds of sea-shells and travelled boulders scattered over Europe, while we also have evidence of contemporaneous glaciers, in their traces on the hills of Wales and Scotland and elsewhere, where they do not now occur.

I have long maintained that in America all the observed facts imply a climate no colder than that which would have resulted from the subsidence which we know to have occurred in the temperate latitudes in the Pleistocene period, and though I would not desire to speak so positively about Europe, I confess to a strong impression that the same is the case there, and that the casing of glacier ice imagined by many geologists, as well as the various hypotheses which have been devised to account for it, and to avoid the mechanical, meteorological, and astronomical difficulties attending it, are alike gratuitous and chimerical, as not being at all required to account for observed facts, and being contradictory, when carefully considered, to known physical laws as well as geological phenomena.[161]

Carrying with me a knowledge of the phenomena of the glacial drift as they exist in North America, and of the modern ice drift on its shores, I was continually asking myself the question To what extent do the phenomena of glacier drift and erosion resemble these? and standing on the moraine of the Bosson glacier, which struck me as more like boulder clay than anything else I saw in the Alps, with the exception of some recent avalanches, I jotted down what appeared to me to be the most important points of difference. They stand thus:—

1. Glaciers heap up their dÉbris in abrupt ridges. Floating ice sometimes does this, but more usually spreads its load in a more or less uniform sheet.[162]

2. The material of moraines is all local. Floating ice carries its deposits often to great distances from their sources.

3. The stones carried by glaciers are mostly angular, except where they have been acted on by torrents. Those moved by floating ice are more often rounded, being acted on by the waves and by the abrading action of sand drifted by currents.

4. In the marine glacial deposits mud is mixed with stones and boulders. In the case of land glaciers, most of this mud is carried off by streams and deposited elsewhere.

5. The deposits from floating ice may contain marine shells. Those of glaciers cannot, except where, as in Greenland and Spitzbergen, glaciers push their moraines out into the sea.

6. It is of the nature of glaciers to flow in the deepest ravines they can find, and such ravines drain the ice of extensive areas of mountain land. Floating ice, on the contrary, acts with greatest ease on flat surfaces or slight elevations in the sea bottom.

7. Glaciers must descend slopes and must be backed by large supplies of perennial snow. Floating ice acts independently, and being water-borne may work up slopes and on level surfaces.

8. Glaciers striate the sides and bottoms of their ravines very unequally, acting with great force and effect only on those places where their weight impinges most heavily. Floating ice, on the contrary, being carried by constant currents and over comparatively flat surfaces, must striate and grind more regularly over large areas, and with less reference to local inequalities of surface.

9. The direction of the striÆ and grooves produced by glaciers depends on the direction of valleys. That of floating ice, on the contrary, depends upon the direction of marine currents, which is not determined by the outline of the surface, but is influenced by the large and wide depressions of the sea bottom.

10. When subsidence of the land is in progress, floating ice may carry boulders from lower to higher levels. Glaciers cannot do this under any circumstances, though in their progress they may leave blocks perched on the tops of peaks and ridges.

I believe that in all these points of difference the boulder clay and drift on the lower lands of Canada and other parts of North America, correspond rather with the action of floating ice than of land ice; though certainly with glaciers on such land as existed at the different stages of the submergence, and these glaciers drifting stones and earthy matter in different directions from higher land toward the sea. More especially is this the case in the character of the striated surfaces, the bedded distribution of the deposits, the transport of material up the natural slope, the presence of marine shells, and the mechanical and chemical characters of the boulder clay. In short, those who regard the Canadian boulder clay as a glacier deposit, can only do so by overlooking essential points of difference between it and modern accumulations of this kind.

I would wish it here to be distinctly understood, that I do not doubt that at the time of the greatest Pleistocene submergence of Eastern America, at which time I believe the greater part of the boulder clay was formed, and the more important striation effected, the higher hills then standing as islands would be capped with perpetual snow, and through a great part of the year surrounded with heavy field and barrier ice, and that in those hills there might be glaciers of greater or less extent. Further, it should be understood that I regard the boulder clays of the St. Lawrence valley as of different ages, ranging from those of the early Pleistocene to that now forming in the Gulf of St. Lawrence; and that during these periods great changes of level occurred. Further, that this boulder clay shows in every place where I have been able to examine it, evidence of subaqueous accumulation, in the presence of marine shells or in the unweathered state of the rocks and minerals enclosed in it; conditions which, in my view, preclude any reference of it to glacier action, except possibly in some cases to that of glaciers stretching from the land over the margin of the sea, and forming under water a deposit equivalent in character to the bone glaciare of the bottom of the Swiss glaciers. But such a deposit must have been local, and would not be easily distinguishable from the marine boulder clay. It is of some interest to compare Canadian deposits with those of Scotland,[163] which in character and relations so closely resemble those of Canada; but I confess several of the facts lead me to infer that much of what has been regarded as of subaËrial origin in that country must really be marine, though whether deposited by icebergs or by the fronts of glaciers terminating in the sea, I do not pretend to determine.[164] It must, however, be observed that the antecedent probability of a glaciated condition is much greater in the case of Scotland than in that of Canada, from the high northern latitude of the former, its hilly and maritime character, and the fact that its present exemption from glaciers is due to what may be termed exceptional and accidental geographical conditions; more especially to the distribution of the waters of the Gulf Stream, which might be changed by a comparatively small subsidence in Central America. To assume the former existence of glaciers in a country in north latitude 56°, and with its highest hills, under the present exceptionally favourable conditions, snow-capped during most of the year, is a very different thing from assuming a covering of continental ice over wide plains more than ten degrees farther south, and in which, even under very unfavourable geographical accidents, no snow can endure the summer sun, even in mountains several thousand feet high. Were the plains of North America submerged and invaded by the cold arctic currents, the Gulf Stream being at the same time turned into the Pacific, the temperature of the remaining North American land would be greatly diminished; but under these circumstances the climate of Scotland would necessarily be reduced to the same condition with that of South Greenland or Northern Labrador. As we know such a submergence of America to have occurred in the Pleistocene period, it does not seem necessary to have recourse to any other cause for either side of the Atlantic. It would, however, be a very interesting point to determine, whether in the Pleistocene period the greatest submergence of America coincided with the greatest submergence of Europe, or otherwise. It is quite possible that more accurate information on this point might remove some present difficulties. I think it much to be desired that the many able observers now engaged on the Pleistocene of Europe, would at least keep before their minds the probable effects of the geographical conditions above referred to, and inquire whether a due consideration of these would not allow them to dispense altogether with the somewhat extravagant theories of glaciation now agitated.

The preceding pages give the substance of my conclusions of twenty-four years ago. I give those of to-day from a paper of 1891,[165] relating to Eastern Canada only:—

These conclusions have, in my judgment, been confirmed, and their bearing extended, more especially by the researches of Mr. Chalmers, who has shown in the most convincing way that glaciers proceeding from local centres along with sea-borne ice, may have been the agents in glaciating surfaces and transporting boulders in Nova Scotia and New Brunswick. Taken in connection with the observations of Dr. Dawson and Mr. McConnell in the Cordillera region of the west, and those of Dr. Bell, Dr. Ells, Mr. Low, and others in the Laurentian country north of the St. Lawrence, and in the Province of Quebec, we may now be said to know that there was not, even at the height of the glacial refrigeration of America, a continental ice sheet, but rather several distinct centres of ice action,—one in the Cordillera of the West, one on the Laurentian V-shaped axis, and one on the Appalachians, with subordinate centres on isolated masses like the Adirondacks, and at certain periods even on minor hills like those of Nova Scotia. It would further seem that, in the west at least, elevation of the mountain ridges coincided with depression of the plains. In Newfoundland also, it would appear from the observations of Captain Kerr, with which those of Mr. Murray are in harmony,[166] though they have been differently interpreted, that the gathering ground of ice was in the interior of the island, and that glaciers moved thence to the coasts, but principally to the east coast, as was natural from the conformation of the land and the greater supply of moisture from the Atlantic.

The labours of Murray in Newfoundland, of Matthew, Chalmers, Bailey, and others, in Nova Scotia and New Brunswick, have considerably enlarged our knowledge of Pleistocene fossils, showing, however, that the marine fauna is the same with that of the beds of like age in the St. Lawrence valley, and with the existing fauna of the Labrador coast and colder portions of the Gulf and River St. Lawrence, as ascertained by Prickard, Whiteaves, and the writer. It would seem that throughout this region, the 60 feet and the 600 feet terraces were the most important with reference to these marine remains, and that their chief repository is in the Upper Leda Clay, a marine deposit intermediate between the Lower and Upper boulder drift, and corresponding to the interglacial beds of the interior of America.

The general conditions of the period may be thus summarized:—

In this district, and the eastern part of North America generally, it is, I think, universally admitted that the later Pliocene period was one of continental elevation, and probably of temperate climate. The evidence of this is too well known to require re-statement here. It is also evident, from the raised beaches holding marine shells, extending to elevations of 600 feet, and from drift boulders reaching to a far greater height, that extensive submergence occurred in the middle and later Pleistocene. This was the age of the beds I have named the Leda clays and Saxicava sands, found at heights of 600 feet above the sea in the St. Lawrence valley, nearly as far west as Lake Ontario.

It is reasonable to conclude that the till or boulder clay, under the Leda clay, belongs to the earliest period of probably gradual subsidence, accompanied with a severe climate, and with snow and glaciers on all the higher grounds, sending glaciated stones into the sea. This deduction agrees with the marine shells, polyzoa, and cirripedes found in the boulder deposits on the lower St. Lawrence, with the unoxidized character of the mass, which proves subaqueous deposition, with the fact that it contains soft boulders, which would have crumbled if exposed to the air, with its limitation to the lower levels and absence on the hillsides, and with the prevalent direction of striation and boulder drift from the north-east.[167]

All these indications coincide with the conditions of the modern boulder drift on the lower St. Lawrence and in the Arctic regions, where the great belts and ridges of boulders accumulated by the coast ice would, if the coast were sinking, climb upward and be filled in with mud, forming a continuous sheet of boulder deposit similar to that which has accumulated and is accumulating on the shores of Smith's Sound and elsewhere in the Arctic, and which, like the older boulder clay, is known to contain both marine shells and driftwood.[168]

The conditions of the deposit of "till" diminished in intensity as the subsidence continued. The gathering ground of local glaciers was lessened, the ice was no longer limited to narrow sounds, but had a wider scope, as well as a freer drift to the southward, and the climate seems to have been improved. The clays deposited had few boulders and many marine shells, and to the west and north there were land-producing plants akin to those of the temperate regions; and in places only slightly elevated above the water, peaty deposits accumulated. The shells of the Leda clay indicate depths of less than 100 fathoms. The numerous Foraminifera, so far as have been observed, belong to this range, and I have never seen in this clay the assemblage of foraminiferal forms now dredged from 200 to 300 fathoms in the Gulf of St. Lawrence.

I infer that the subsidence of the Leda clay period and of the interglacial beds of Ontario belongs to the time of the sea beaches from 450 to 600 feet in height, which are so marked and extensive as to indicate a period of repose. In this period there were marine conditions in the lower and middle St. Lawrence and in the Ottawa valley, and swamps and lakes on the upper Ottawa and the western end of Lake Ontario. It is quite probable, nay, certain, that during this interglacial period re-elevation had set in, since the upper Leda clay and the Saxicava sand indicate shallowing water, and during this re-elevation the plant-covered surface would extend to lower levels.

This, however, must have been followed by a second subsidence, since the water-worn gravels and loose, far-travelled boulders of the later drift rose to heights never reached by the till or the Leda clay, and attained to the tops of the highest hills of the St. Lawrence valley, 1,200 feet in height, and elsewhere to still greater elevations. This second boulder drift must have been wholly marine, and probably not of long duration. It shows no evidence of colder climate than that now prevalent, nor of extensive glaciers on the mountains; and it was followed by a paroxysmal elevation in successive stages till the land attained even more than its present height, as subsidence is known to have been proceeding in modern times.

I am quite aware that the above sequence and the causes assumed are somewhat different from those held by many geologists with reference to regions south of Canada; but must hold that they are the only rational conclusions which can be propounded with reference to the facts observed from the parallel of 45° to the Arctic Ocean.

My own observations have been chiefly in the eastern part of North America. My son, Dr. G. M. Dawson, has much more ably and thoroughly explored those of the west; and after describing the immense Cordilleran ice mass which extended for a length of 1,200 miles along the mountains of British Columbia and discharged large glaciers to the north, as well as to the west and south, and stating his reasons for believing in that differential elevation and depression which caused the greatest height of the mountains to coincide with the greatest depression of the plains, and vice versÂ, and showing the Cordilleran glacier must have been separated by a water area from that of the Laurentide hills on the east, thus concludes:—

"It is now distinctly known, as the result of work done under the auspices of the Geological Survey of Canada, and more particularly of observations by the writer and his colleagues, Messrs. McConnell and Tyrrell, that the extreme margins of the western and eastern glaciated areas of the continent barely overlap, and then only to a very limited extent, while the two great centres of dispersion were entirely distinct. For numerous reasons which cannot be here entered into, the writer does not consider it probable, or even possible, that the great confluent glacier of the north-eastern part of the continent extended at any time far into the area of the great plains; but erratics and drift derived from this ice mass did so extend, and are found between the 49th and 50th parallels, stranded on the surface of moraines produced by the large local glaciers of the Rocky Mountains. Recognising, however, the essential separateness of the western and eastern confluent ice masses, and the fact that it is no longer appropriate to designate one of these the "continental glacier," the writer ventures to propose that the eastern mer de glace may appropriately be named the great Laurentide glacier, while its western fellow is known as the "Cordilleran glacier." It may be added that there is good evidence to show that both the Laurentide and Cordilleran glaciers discharged into open water to the north."

These conclusions, based on a large induction of facts applying to a very large area of the North American Continent, coincide with my own observations in the east, and with the inferences deducible from the present condition of Greenland and Arctic America.

When extreme glacialists point to Greenland and ask us to believe that in the Glacial age the whole continent of North America, as far south as the latitude of 40°, was covered with a continuous glacier, having a wide front, and thousands of feet thick, we may well ask, first, what evidence there is that Greenland or even the Antarctic continent is at present in such a condition; and, secondly, whether there exists a possibility that the interior of a great continent could ever receive so large an amount of precipitation as that required. So far as present knowledge exists, it is certain that the meteorologist and the physicist must answer both questions in the negative. In short, perpetual snow and glaciers must be local, and cannot be continental, because of the vast amount of evaporation and condensation required. These can only be possible where comparatively Warm seas supply moisture to cold and elevated land, and this supply cannot, in the nature of things, penetrate far inland. The actual condition of interior Asia and interior America in the higher northern latitudes affords positive proof of this. In a state of partial submergence of our northern continents, we can readily imagine glaciation by the combined action of local glaciers and great ice floes; but in whatever way the phenomena of the boulder clay and of the so-called "terminal moraines" are to be accounted for, the theory of a continuous continental glacier must be given up.

The great interior plain of western Canada, between the Laurentian axis on the east and the Rocky Mountains on the west, is seven hundred miles in breadth, and is covered with glacial drift, presenting one of the greatest examples of this deposit in the world. Proceeding eastward from the base of the Rocky Mountains, the surface, at first more than 4,000 feet above the sea level, descends by successive steps to 2,500 feet, and is based on Cretaceous and Laramie rocks, covered with boulder clay and sand, in some places from one hundred to two hundred feet in depth, and filling up pre-existing hollows, though itself sometimes piled into ridges. Near the Rocky Mountains the bottom of the drift consists of gravel not glaciated. This extends to about one hundred miles east of the mountains, and must have been swept by water out of their valleys. The boulder clay resting on this deposit is largely made up of local dÉbris, in so far as its paste is concerned. It contains many glaciated boulders and stones from the Laurentian region to the east, and also smaller pebbles from the Rocky Mountains, so that at the time of its formation there must have been driftage of large stones for seven hundred miles or more from the east, and of smaller stones from a less distance on the west. The former kind of material extends to the base of the mountains, and to a height of more than 4,000 feet. One boulder is mentioned as being 42 × 40 × 20 feet in dimensions. The highest Laurentian boulders seen were at an elevation of 4,660 feet on the base of the Rocky Mountains. The boulder clay, when thick, can be seen to be rudely stratified, and at one place includes beds of laminated clay with compressed peat, similar to the forest beds described by Worthen and Andrews in Illinois, and the so-called interglacial beds described by Hinde on Lake Ontario. The leaf beds on the Ottawa river, and the drift trunks found in the boulder clay of Manitoba, belong to the same category, and indicate in the midst of the Glacial period many forest oases far to the north, having a temperate rather than an arctic flora. In the valleys of the Rocky Mountains opening on these plains there are evidences of large local glaciers now extinct, and similar evidences exist on the Laurentian highlands on the east. A recent paper of Dr. G. M. Dawson on the PalÆography of the Rocky Mountains illustrates in a most convincing manner the changes which have occurred in the Cordillera of North America, and the differential elevation and depression which have affected its climate in the later geological periods.[169]

Perhaps the most remarkable feature of the western drift region is that immense series of ridges of drift piled against an escarpment of Laramie and Cretaceous rocks, at an elevation of about 2,500 feet, and known as the "Missouri Coteau." It is in some places 30 miles broad and 180 feet in height above the plain at its foot, and extends north and south for a great distance: being, in fact, the northern extension of those great ridges of drift which have been traced south of the great lakes, and through Pennsylvania and New Jersey, and which figure on the geological maps as the edge of the continental glacier—an explanation obviously inapplicable in those western regions where they attain their greatest development. It is plain that in the north it marks the western limit of the deep-water of a glacial sea, which at some periods extended much farther west, perhaps with a greater proportionate depression in going westward, and on which heavy ice from the Laurentian districts on the east was wafted south-westward by the arctic currents, while lighter ice from the Rocky Mountains was being borne eastward from these mountains by the prevailing westerly winds. We thus have in the west, on a very wide scale, the same phenomena of varying submergence, cold currents, great ice floes and local glaciers producing icebergs, to which I have attributed the boulder clay and upper boulder drift of eastern Canada. In short, we arrive at the conclusion that there never has been a continental glacier, properly so called, but that in the extreme Glacial period there have been great centres of snow and glacial action, in the Cordillera of the west, in the Laurentian plateau of the north, and in the northern Appalachians, and the Adirondacks, while the lower lands have been either submerged, or enjoying a climate habitable by hardy animals and plants.

The till or boulder clay has been called a "ground moraine," but there are really no Alpine moraines at all corresponding to it. On the other hand, it is more or less stratified, often rests on soft materials which glaciers would have swept away, sometimes contains marine shells, or passes into marine clays in its horizontal extension, and invariably in its embedded boulders and its paste, shows an unoxidized condition, which could not have existed if it had been a subaËrial deposit. When the Canadian till is excavated and exposed to the air, it assumes a brown colour, owing to oxidation of its iron, and many of its stones and boulders break up and disintegrate under the action of air and frost. These are unequivocal signs of a subaqueous deposit. Here and there we find associated with it, and especially near the bottom and at the top, indications of powerful water action, as if of land torrents acting at particular elevations of the land, or heavy surf and ice action on coasts, and the attempts to explain these by glacial streams have been far from successful. A singular objection sometimes raised against the subaqueous origin of the till is its general want of marine remains; but this is by no means universal, and it is well known that coarse conglomerates of all ages are generally destitute of fossils, except in their pebbles, and it is further to be observed that the conditions of an ice-laden sea are not those most favourable for the extension of marine life, and that the period of time covered by the glacial age must have been short, compared with that represented by some of the older formations.

It follows from all this that the great "continental moraine," which the United States Geological Survey has now "delineated for several thousand miles extending from the Atlantic to the Pacific," cannot be a glacier moraine, but must be, like its great continuation northward, the Missouri coteau, a margin of sea drift, and that we must explain the whole of the drift of the American continent by the supposition, first, of a period of elevation of the hills and subsidence of the valleys in which there were great accumulations of snow on the Western Cordillera; the Laurentian axis, and the Appalachians and Adirondacks radiating in every direction from these points, while minor areas of radiation may have temporarily existed on smaller elevations: that this was followed by a period of more equal level, in which parts of the low grounds were clothed with a temperate flora, the "Interglacial period" so called, succeeded by a second great depression, in which the high level boulders of the second boulder drift were wafted to great distances by floating ice.

The late Prof. Alexander Winchell, a man who did not hesitate to express his convictions, thus bears similar testimony:—"There has been no continental glacier. There has been no uniform southerly movement of glacier masses. There has been no persistent declivity as a sine qua non, down which glacier movements have taken place. The continuity of the supposed continental glacier was interrupted in the regions of the dry and treeless plains of the west; and in the interior and Pacific belts of the continent within the United States, ancient glaciation was restricted to the elevated slopes."[170] He might have added that the St. Lawrence valley was submerged and received the ends of Appalachian and Adirondack glaciers on the south-east, and those of Laurentide glaciers on the north-west.

[170] Nov., 1890.