Some Salient Points in the Science of the Earth

by Sir John William Dawson

We have in America ancient periods of cold as well as of warmth. I have elsewhere referred to the boulder conglomerates of the Huronian, of the early Lower Silurian, and of the Millstone grit period of the Carboniferous; but I have not ventured to affirm that either of these periods was comparable in its cold with the later glacial age, still less with that imaginary age of continental glaciation, assumed by the more extreme theorists. We know that these ancient conglomerates were produced by floating ice, and this at periods when in areas not very remote, temperate floras and faunas could flourish. The glacial periods of our old continent occurred in times when the surface of the submerged land was opened up to the northern currents drifting over it mud and sand and stones, and rendering nugatory, in so far, at least, as the bottom of the sea was concerned, the effects of the superficial warm streams. Some of these beds are also peculiar to the eastern margin of the continent, and indicate ice drift along the Atlantic coast much as at present, while conditions of greater warmth existed in the interior. Even in the more recent glacial age, while the mountains were covered with snow, and the low lands submerged under a sea laden with ice, there were interior tracts in somewhat high latitudes of America in which hardy forest trees and herbaceous plants flourished abundantly, and these were by no means exceptional "interglacial" periods. Thus we can prove that from the remote Huronian period to the Tertiary, the American land occupied the same position as at present, and that its changes were merely changes of relative level, as compared with the sea; but which so influenced the ocean currents as to cause great vicissitudes of climate.

Uniformitarian geologists have recently been taunted with a willingness to assume great and frequent elevations and submergences of continents, as if this were contrary to their principle. But rational uniformitarianism allows us to use any cause of whose operation in the past there is good geological evidence, and Lyell himself was perfectly aware of this.

While no geologists can fail to appreciate the evidence of the power of geographical change in affecting climatal change, and the fact that such change has occurred at various geological periods, there are some, and especially those who take extreme views as to the latest period of cold climate, who doubt its sufficiency to account for all the phenomena observed. It is instructive, however, to notice that some of the ablest of these, in default of other probable causes, are driven to fall back either on agencies of a wholly improbable character, or to give up the problem as insoluble. Two recent examples of this deserve citation.

The late Dr. Newmayr, of Vienna, a veteran physical geographer, in an able discussion of the climates of past ages, one of his last scientific papers, has fallen back on the hypothesis of a change in the position of the poles.[181] His failure to account for ancient climates by other causes evidently, however, depends on an inadequate conception of the effects of geographical changes, along with serious misconceptions as to the distribution of plants and the characters of vegetation at different periods. These points we shall have to discuss in subsequent pages.

[181] Society for Dissemination of Natural Science. Vienna, January, 1889.

In an address before the American Association, in 1886, Dr. Chamberlain, one of the ablest American authorities on the Glacial period, makes the following remarks as to the causes of the Pleistocene cold:—

"If we turn to the broader speculations respecting the origin of the Glacial epoch, we find our wealth little increased. We have on hand practically the same old stock of hypotheses, all badly damaged by the deluge of recent facts. The earlier theory of northern elevation has been rendered practically valueless; and the various astronomical hypotheses seem to be the worse for the increased knowledge of the distribution of the ancient ice sheet. Even the ingenious theory of Croll becomes increasingly unsatisfactory as the phenomena are developed into fuller appreciation. The more we consider the asymmetry of the ice distribution in latitude and longitude, and its disparity in elevation, the more difficult it becomes to explain the phenomena upon any astronomical basis. If we were at liberty to disregard the considerations forced upon us by physicists and astronomers, and permit ourselves simply to follow freely the apparent leadings of the phenomena, it appears at this hour as though we should be led upon an old and forbidden trail,—the hypothesis of a wandering pole. It is admitted that there is a vera causa in elevations and depressions of the earth's crust, but it is held inadequate. It is admitted that the apparent changes of latitude shown by the determinations of European and American observatories are remarkable, but their trustworthiness is challenged. Were there no barriers against free hypotheses in this direction, glacial phenomena could apparently find adequate explanation; but debarred—as we doubtless should consider ourselves to be at present—from this resource, our hypotheses remain inharmonious with the facts, and the riddle remains unsolved."

It should be observed here that the unsolved "riddle" is that of a continental ice sheet. This, as we have already seen, is probably insoluble in any way, but fortunately needs no solution, being merely imaginary. If we adopt a moderate view as to the actual conditions of the Pleistocene, the geographical theory will be found quite sufficient to account for the facts.

Let it be observed here also, in connection with the above thoughtful and frank avowal of one of the ablest of American glacialists, that the geographical theory provides for that "asymmetry "'or irregular distribution of glacial deposits to which he refers; since, at every stage of continental elevation and depression, there must have been local changes of circumstances; and the same inequality of temperature in identical latitudes which we observe at present must have existed, probably in a greater degree, in the Glacial age.

The sufficiency of the Lyellian theory to account for the facts, in so far as plants are concerned, may, indeed, be inferred from the course of the isothermal lines at present. The south end of Greenland is on the latitude of Christiania, in Norway, on the one hand, and of Fort Liard, in the Peace River region, on the other; and while Greenland is clad in ice and snow, wheat and other grains, and the ordinary trees of temperate climates, grow at the latter places. It is evident, therefore, that only exceptionally unfavourable circumstances prevent the Greenland area from still possessing a temperate flora, and these unfavourable circumstances possibly tell even on the localities with which we have compared it. Further, the mouth of the McKenzie River is in the same latitude with Disco, near which are some of the most celebrated localities of fossil Cretaceous and Tertiary plants. Yet the mouth of the McKenzie River enjoys a much more favourable climate, and has a much more abundant flora than Disco. If North Greenland were submerged, and low land reaching to the south terminated at Disco, and if from any cause either the cold currents of Baffin's Bay were arrested, or additional warm water thrown into the North Atlantic by the Gulf Stream, there is nothing to prevent a mean temperature of 45° Fahrenheit from prevailing at Disco; and the estimate ordinarily formed of the requirements of its extinct floras is 50°, which is probably above, rather than below, the actual temperature required.