26 REroRT— 1886. 



lar distribution of land and water in the Cretaceons age gave a warm and 

 equc jle 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 Pleisto- 

 cene 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 exten- 

 sions seaward of the European and American land, with possibly consider- 

 able tracts of land in the vicinity of the equator, while the Mediterranean 

 and the Gulf of Mexico were deep inland lakes.' The effect of such con- 

 ditions on the climates of the northern hemisphere must have been pro- 

 digious, and their investigation is rendered all the more interesting be- 

 cause it would seem that this continental period of the post-Glacial age 

 was that in which man made his first acquaintance with the coasts of the 

 Atlantic, and possibly made his way across its waters. 



We have in America anci'mt periods of cold as well as of warmth. I 

 have elsewhere referred to the boulder conglomerates of the Huronian, 

 of the Cambrian and Ordovician, of the Mill ?-grit period of the Car- 

 boniferous and of the early Permian ; but v^ Ad not venture to aflSrm 

 that either of these periods was comparable in its cold with the later 

 glacial age, still less with that imaginary age of contmentar glaciation 

 assumed by certain of the more extreme theorists.* These ancient con- 

 glomerates were probably produced by floating ice, and this at period i 

 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 ic 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-dfift along the Atlantic 

 coast in the same manner 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 lowlands sub- 

 merged under a sea laden with ice, there were interior tracts in some- 

 what high latitudes of America in which hardy forest trees and her- 

 baceous plants flourished abundantly ; and these were by iiu means 

 exceptional * interglacial * periods. Thus we can show that while from 

 the remote Huronian period to the Tertiary the Amencan land occupied 

 the same position as at present, and while its changes were merely 

 changes of telative level as compared with the sea, these have so in- 

 fluenced the ocean currents as to cause great vicissitudes of climate. 



Without entering on any detailed discussion of that last and greatest 



• Da^kins, Popular Science Monthly, 187S. 



* Notes on Post-Pliocene of Canada. Pre- Cambrian Oaloiers, Qeol. Mag., 1880. 



