554 CENOZOIC TIME — MAMMALIAN AGE. 



perature zone, the coldest of the ocean, descends now on the coast 

 into the Gulf of St. Lawrence ; so that the depression could only- 

 have given greater extension to the waters. The zones of oceanic 

 temperature in the Middle Post-tertiary period approximated, 

 therefore, to those of the present day. 



(2.) Temperature of the air. — A cold oceanic temperature and a 

 warm climate may be in close proximity ; the chart referred to 

 gives an example of this on the coast of Peru (see p. 43). Hence 

 we have to look to other facts than those from oceanic species to 

 determine the climate of the epoch. The depression of the land 

 over the north would of itself be a cause of a warmer climate than 

 the present (p. 45) ; and this inference is sustained by the life over 

 the land. The facts on this point are stated beyond. 



One of the earliest effects of the subsidence would have been the 

 melting of the glaciers of the Glacial epoch. This would have made 

 a vast flow of waters over the continent through all the valleys 

 which had been in process of excavation, and it would have filled 

 them with sand, gravel, or earth, making each, when the land had 

 reached its lowest depression, a vast plain of alluvium through 

 which the stream would have run in its narrow channel, except in 

 its times of floods, when it may have spread over its whole breadth. 

 And while the glaciers were disappearing, many a stream or lake 

 would have existed to stratify the drift (p. 549) and cause denudation 

 in elevated places where now there are no running waters within 

 scores of miles. 



3. TERRACE EPOCH. 



The Terrace epoch belongs in part, at least, to the age of Man, 

 being, as has been stated on p. 535, a transition epoch. But the 

 relations, both geographical and zoological, which it bears to the 

 Post-tertiary are such that its general characteristics are most con- 

 veniently stated in this place. 



Distribution and origin of the Terraces in North America. 



The sea-beaches and river-flats of the Champlain epoch are at the 

 present time elevated beaches and plains ; and the heights of many 

 of them are already given on pages 549-552. The time when they 

 were raised, and became terraces along the rivers, lakes, and sea- 

 coast, corresponds to the Terrace epoch ; and during the process 

 other parallel terraces were formed. These proofs of elevation are 

 coextensive with the breadth of the continent, as is evident from 

 the account of them under the Champlain epoch. 



