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Other extinct animals accompany the Mastodon giganteus in the post-glacial deposits of the United States, and this, taken with the fact that so few of the mollusca, even of the commencement of the cold period, differ from species now living is important, as refuting the hypothesis, for which some have contended, that the intensity of the glacial cold annihilated all the species in temperate and arctic latitudes.
Now these historic ditches and root bowls occur in all the present Sequoia groves and forests, but as far as I have observed, not the faintest vestige of one presents itself outside of them. We therefore conclude that the area covered by Sequoia has not been diminished during the last eight or ten thousand years, and probably not at all in post-glacial times. Is the species verging to extinction?
The summit is now a mass of ruins, and all the finer striations have been effaced from the flanks by post-glacial weathering, while the irregularity of its lavas as regards susceptibility to erosion, and the disturbance caused by inter- and post-glacial eruptions, have obscured or obliterated those heavier characters of the glacial record found so clearly inscribed upon the granite pages of the high Sierra between latitude 36 degrees 30 minutes and 39 degrees.
These square-topped hills ended at a common level, showing that they were not the result of an upheaval, but were the remains of the original stratification formations left standing after the scooping action of the post-glacial floods had ceased. Some of them looked like ruined walls of castles ancient as hills, on whose massive tops time had sown sturdy oaks and cedars.
But still more interesting and significant are the glacial phenomena displayed hereabouts. All this exuberant tree, bush, and herbaceous vegetation, cultivated or wild, is growing upon moraine beds outspread by waters that issued from the ancient glaciers at the time of their recession, and scarcely at all moved or in any way modified by post-glacial agencies.
The chronological relations of the human and glacial periods were frequently alluded to in the last chapter, and the sections obtained near Bedford, and at Hoxne, in Suffolk, and a general view of the Norfolk cliffs, have taught us that the earliest signs of Man's appearance in the British isles, hitherto detected, are of post-glacial date.
However, Prestwich has some "facts" as well as prepossessions, such as "the rapid advance of the glaciers of Greenland," which does not accord with the generalization from the Swiss glaciers; and the quicker erosion of river valleys, due to a greater rainfall; facts which, however, are met by "a minute description of the successive changes by which in post-glacial time the Mersey valley and estuary were brought into their present condition, with an estimate of the time they may have required;" which is "in round numbers 60,000 years," as opposed to Prestwich's 10,000 or 8,000.
But although all the observed phenomena bearing on the post-glacial history of this colossal tree point to the conclusion that it never was more widely distributed on the Sierra since the close of the glacial epoch; that its present forests are scarcely past prime, if, indeed, they have reached prime; that the post-glacial day of the species is probably not half done; yet, when from a wider outlook the vast antiquity of the genus is considered, and its ancient richness in species and individuals, comparing our Sierra Giant and Sequoia sempervirens of the Coast Range, the only other living species of sequoia, with the twelve fossil species already discovered and described by Heer and Lesquereux, some of which flourished over vast areas in the Arctic regions and in Europe and our own territories, during tertiary and cretaceous times then, indeed, it becomes plain that our two surviving species, restricted to narrow belts within the limits of California, are mere remnants of the genus, both as to species and individuals, and that they may be verging to extinction.
That his home is in the south, that he is closely related with the men of the African and Arabian grasslands, and that he was among the first post-glacial explorers of the Atlantic seaboard, is admitted. More doubt arises as to the extent to which he penetrated from these southern and western bases into the heart of peninsular Europe.
The primitive people, who co-existed with the elephant and rhinoceros in the valley of the Ouse at Bedford, and who made use of flint tools of the Amiens type, certainly inhabited part of England which had already emerged from the waters of the glacial sea and the fabricators of the flint tools of Hoxne, in Suffolk, were also, as we have seen, post-glacial.
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