tropical seas, was precipitated to form almost universal snow-fields and glaciers; certainly very favorable conditions for the production of many of the phenomena which characterized the Glacial period. It must be remembered, however, that this theory presupposes barriers established not only across the North Atlantic and Pacific Oceans, but in the southern hemisphere as well—for this also had its Ice period—barriers connecting the widely-separated promontories of Cape Horn, Cape of Good Hope, and the islands of the East Indian Archipelago; also that, simultaneously with the existence of such barriers, the tropical lands were depressed, and the sea spread its sediments over much of what is in the present age terra firma.
In reviewing the theory proposed by Lyell and Dana, I have been impressed with the conviction that if the physical geography of the northern and southern hemispheres had been either alternately or simultaneously such as this theory requires, we should find some evidence of it, apart from the inscriptions made by glaciers nearer the equator than any now exist. In the search for such evidence, however, I have not only failed to find it, but have, as it seems to me, found other things which go far to disprove the theory.
In order to fully state the case, it will be necessary to review several chapters in geological history, and compare the preceding and also the succeeding age with that in which the climate of Greenland came as far south as New York.
The results of such comparisons may be given as follows:
I. It is known to most students of geology that, during the Tertiary age, the climate of all the arctic regions was warm-temperate. A luxuriant forest then covered Greenland, and all the northern portion of this continent; such a forest as could only flourish in a climate as mild as that of our Middle and Southern States.[1]
According to the Lyellian hypothesis this should have been a period of great depression of arctic, and elevation of tropical lands; but we have proof that such was not the case. On the contrary, the land area at the north was broader then than now, while in the tropics it was narrower.
It can be shown, too, that land-connection then existed in northern latitudes between Europe and America, and also between America and Asia. The Atlantic bridge stretched from Greenland to Iceland, thence to the Hebrides and Scotland, which was then part of the
- ↑ It has been suggested that the warmth of the Tertiary climate was simply the effect of the residual heat of a globe cooling from incandescence, but many facts disprove this. For example, the fossil plants found in our Lower Cretaceous rocks in Central North America indicate a temperate climate in latitude 35° to 40° in the Cretaceous age. The coal-flora, too, and the beds of coal, indicate a moist, equable, and warm but not hot climate in the Carboniferous age, millions of years before the Tertiary, and 3,000 miles farther south than localities where magnolias, tulip-trees, and deciduous cypresses, grew in the latter age. Some learned and cautious geologists even assert that there have been several Ice periods, one as far back as the Devonian.
