The road was very uneven, rocky, cut up by rivulets from the higher ridges, and in most places only a rude dug-way, with a rocky wall on one side, and a butment of thickly wooded débris steeply descending to a black brawling torrent on the other. But we did not trouble ourselves with the road. The wild beauty of the forest absorbed us on either hand; and we were astonished at the rapid transition which the leaves suddenly took on, from the dry, burnt look, characteristic of the end of the California dry season, to autumnal splendors of red and yellow, hardly rivalled by the numberless varieties of tint in our own October woods. Just as the sun sank out of sight, we reached a lofty commanding ridge, stopped to rest, turned around and saw Shasta looming grandly up out of the valley-twilight, his icy forehead all one mass of gold and ruby fire. It was one of the grandest mountain-sights I ever looked on: such a purple hush over the vast level below us; such colossal broad shadows on the giant's foot; such a wonderful flame on that noble, solitary head, which, but for the unbroken outlines leading up to it out of the twilight, might have been only some loftier cloud catching good-night sun-glimpses at half-way up the firmament. Goodnight from Shasta! Alas, not only to the sun, but to us! We felt a real pang, as we confessed to ourselves that we were now looking upon this noblest and serenest, if not loftiest, of all the mountains in our travel, for the last time in years,—perhaps the last forever. We gazed wistfully till admonished by the deepening twilight; then, as Shasta became a shadow on the horizon, plunged silently into the dense woods again, climbed to the Siskiyou summit, and, descending through almost jetty darkness, were in Oregon.
ICE-PERIOD IN AMERICA.
In the autumn of 1846, six years after my visit to Great Britain in search of glaciers, I sailed for America. When the steamer stopped at Halifax, eager to set foot on the new continent so full of promise for me, I sprang on shore and started at a brisk pace for the heights above the landing. On the first undisturbed ground, after leaving the town, I was met by the familiar signs, the polished surfaces, the furrows and scratches, the line-engraving of the glacier, so well known in the Old World; and I became convinced of what I had already anticipated as the logical sequence of my previous investigations, that here also this great agent had been at work, although it was only after a long residence in America, and repeated investigations of the glacial phenomena in various parts of the country, that I fully understood the universality of its action. A detailed description of these appearances could hardly be more than a monotonous repetition of my statements respecting their existence in other regions; but the peculiar configuration of this continent, as compared with the more mountainous countries of Europe and Asia, has led to some modifications of the same phenomena here, worthy of special notice.
Thus far, the traces of ancient glaciers in America have been studied only east of the Rocky Mountains; little is known of the glaciers still remaining in the high mountain-ranges dividing the eastern part of the continent from California, still less respecting any indications of their former extension. There can be little doubt that such traces exist, and as soon as the so-called parks between Pike's Peak and Long Peak are explored, we may hope for information on this point. Indeed, the investigation may be spoken of as already undertaken; for among the exploring parties now on their way to that region are some intelligent observers who will not fail to make this point a subject of special study. But it is well known that the usual characteristic marks of glaciers extend over the whole surface of the land in the eastern half of the continent, from the Atlantic shores to the States west of the Mississippi, and from the Arctic Sea to the latitude of the Ohio, in its middle course, while within the range of the Alleghanies they stretch as far south as Georgia and Alabama. In no other region where these traces have been observed do they extend over such wide tracts of country in unbroken continuity, this being of course owing to the level character of the land itself.
The continent of North America, east of the Rocky Mountains, is, indeed, an immense uniform plain, intersected from east to west only by the ranges of low hills running in the direction of the St. Lawrence and the Canadian lakes, and from northeast to southwest by the Alleghany range stretching from Alabama to New England, where it trends towards the Canadian hills in the ridges known as the Green and White Mountains. This coast-range has a short slope towards the Atlantic, and a long one in the direction of the great Mississippi valley. With the exception of some higher points of the Alleghany range, the surface of this whole plain is glacier-worn from the Arctic regions to about the fortieth degree of northern latitude, the glacier-marks trending from north to south, with occasional slight inclinations to the east or west, according to the minor inequalities of the surface. There is, however, no decided modification of their general trend in consequence of the range of hills intersecting them at right angles for nearly the whole width of the continent between latitudes forty-six and fifty; indeed, the Canadian, or, as they are sometimes called, the Laurentian Hills, formed a no more powerful barrier to the onward progress of the immense fields of ice covering the continent than did the small hummocks, or roches moutonnées, in the Swiss valleys to the advance of the Alpine glaciers. In fact, these low hills may be considered as a succession of roches moutonnées, trending in a continuous ridge from east to west, over which the masses of northern ice have moved unimpeded to the latitude of the Ohio.
Owing to the absence of high mountain-ranges over this vast expanse of land, the glacial phenomena of America are not grouped about special centres of dispersion, or radiating from them, as in Europe. During the greatest extension of the ice-fields, there were but few prominent peaks rising above them, and dropping here and there huge boulders on their surface, to be transported to great distances without losing their rough angular character. And when the temperature under which these vast frozen masses had been formed rose again, the wasting ice must have yielded first on its southern boundary, gradually and uniformly retreating to the Arctic regions, without breaking up into distinct glacial regions, separated from one another, each with its local distribution of erratic boulders and glacier-marks radiating from circumscribed areas on higher levels, as they occur everywhere in Europe. It is true that there are a few localities within the Alleghany range, on the Green and White Mountains, and in parts of Maine, where it is evident that local glaciers have had a temporary existence; but even throughout this eastern coast-range the elevation of the mountains is so slight, and their trend so uniform in a northeasterly and southwesterly direction through twenty degrees of latitude, that the localization of the phenomena is less marked than in Norway, Great Britain, or Switzerland. In short, the ice of the great glacial period in America moved over the continent as one continuous sheet, overriding nearly all the inequalities of the surface. Thus the peculiar physical character of the country gives a new aspect to the study of glacial evidences here. The polished surfaces stretch continuously over hundreds and hundreds of miles; the rectilinear scratches, grooves, and furrows are unbroken for great distances; the drift spreads in one vast sheet over the whole land, consisting of an indiscriminate medley of clays, sands, gravels, pebbles, boulders of all dimensions, and so uniformly mixed together that it presents hardly any difference in its composition, whether we examine it in New England, New York, Pennsylvania, Ohio, Michigan, Indiana, Illinois, Wisconsin, in Iowa beyond the Mississippi, in the more northern Territories, or in Canada.
In Europe, boulders of large dimensions do not often occur within the drift, but are usually resting above it with their sharp angles and rough surfaces unchanged, having travelled evidently upon the glacier and not under it. But such large boulders, polished and scratched like the smaller pebbles, are to be found everywhere imbedded in American drift, while the angular fragments of rock resting above these triturated masses are comparatively rare.[H] It is evident from this that the ice overtopped the rocky inequalities of the land, and that the detached fragments remaining beneath the icy covering underwent the same action from friction and pressure to which the whole mass of drift was subjected. The distribution of the few angular boulders scattered over the country no doubt began when some of the higher portions of the land had emerged from the mass of snow and ice; and they are most frequent in New England, where the mountain-elevation is greatest.
The mineralogical character of the loose materials forming the American drift leaves no doubt that the whole movement, with the exception of a few local modifications easily accounted for by the lay of the land, was from north to south, all the fragments not belonging to the localities where they occur being readily traced to rocks in situ to the north of their present resting-places. The farther one journeys from their origin, the more extraordinary does the presence of these boulders become. It strikes one strangely to find even in New England fragments of rock from the shores of Lake Superior; but it is still more impressive to meet with masses of northern rock on the prairies of Illinois or Iowa. One may follow these boulders to the fortieth degree of latitude, beyond which they become more and more rare, while the finer drift alone extends farther south.
It is not only, however, by tracking the boulders back to their origin in the North that we ascertain the starting-point of the whole mass; we have another kind of evidence to this effect, already alluded to in the description of the roches moutonnées. Wherever the natural surface of any hill, having a steep southern slope, is exposed, the marks are always found to be very distinct on the northern side and entirely wanting on the southern one, showing, that, as in the case of many of the roches moutonnées in Switzerland, the mass moved up the northern slope, forcing its way against it, grinding and furrowing the northern face of the hill as it moved over it, but bridging the opposite side in its descent without coming into contact with it.[I] This is true, not only of hills, but of much slighter obstacles which presented themselves in the path of the ice. Even pebbles imbedded in masses of pudding-stone, but rising sometimes above the level of the general surface, often have their northern side polished and scratched, while the southern one remains untouched.