CAUSES OF THE COLD OF THE ICE PERIOD. 283 



tropical seas, was precipitated to form almost universal snow-fields 

 and o-laciers; 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 bar- 

 riers 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 bar- 

 riers, the tropical lands were depressed, and the sea spread its sedi- 

 ments 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 evi- 

 dence 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 

 Reveral 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 



1 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 mile9 

 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. 



