GEOLOGY OF THE ATLANTIC OCEAN. 187 



ity and colonizing power of which, as Hooker has well shown, the 

 Scandinavian flora is the best modern type, spreading itself to the 

 south. A very similar distribution of land and water in the Creta- 

 ceous age gave a warm and equable climate in those portions of North 

 America not submerged, and coincided with the appearance of the 

 multitude of broad-leaved trees of modern types introduced in the 

 early and middle Cretaceous, and which prepared the way for the 

 mammalian life of the Eocene. 



We may take a still later instance from the second continental 

 period of the later Pleistocene or early modern, when there would seem 

 to have been a partial or entire closure of the North Atlantic against 

 the Arctic ice, and wide extensions seaward of the European and 

 American land, with possibly considerable tracts of land in the vicin- 

 ity of the equator, while the Mediterranean and the Gulf of Mexico 

 were deep inland lakes. The effect of such conditions on the climates 

 of the northern hemisphere must have been prodigious, and their inves- 

 tigation is rendered all the more interesting because it would seem 

 that this continental period of the post-glacial age was that in which 

 man made his first acquaintance with tbe coasts of the Atlantic, and 

 possibly made his way across its waters. We haA*e in America ancient 

 periods of cold, as well as of warmth. 



I have elsewhere referred to the bowlder conglomerates of the Huro- 

 nian, of the Cambrian and Ordovician, of the millstone-grit period of 

 the Carboniferous and of the early Permian ; but would not venture 

 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 certain of .the more extreme theorists. These 

 ancient conglomerates were probably produced by floating ice, and 

 this at periods when in ai-eas not very remote temperate floras and fau- 

 nas 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 cur- 

 rents, drifting over it mud and sand and stones, and rendering nuga- 

 tory, 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-drifts 

 along the Atlantic coast in the same manner as at present, while con- 

 ditions of greater warmth existed in the interior. Even in the more 

 recent glacial age, while the mountains were covered with snow, and 

 the lowlands submerged under a sea laden with ice, there were inte- 

 rior tracts in somewhat high latitudes of America in which hardy for- 

 est-trees and herbaceous plants flourished abundantly ; and these were 

 by no means exceptional " interglacial " periods. Thus we can show 

 that, while from the remote Huronian period to the Tertiary the Ameri- 

 can land occupied the same position as at present, and while its changes 

 were merely changes of relative level as compared with the sea, these 



