202 EVOLUTION IN THE PAST 



States long buried gradually reappeared ; and in course 

 of time vast tracts of Canada were relieved of their load. 



What has been said about Europe at the time of the ice 

 retreat applies more or less to North America. Great floods 

 followed more destructive, perhaps, to animal life than had 

 been the gradual extension of the ice-sheet. The Missouri and 

 Mississippi Rivers, with vastly widened courses, must have 

 fairly plunged along. New lakes were formed in many parts 

 of the country ; and desolated scenes were slowly clothed 

 with a northward-bound scrub vegetation of arctic character. 

 Forests, in time, began to form in favoured districts ; and a 

 general trend of animal life set in from the congested southern 

 areas. 



In course of time so genial did the climate become that 

 mastodons roamed over the northern States, and even entered 

 Canada. Mastodons had become extinct in the old world in 

 Pliocene times ; and they are not known anywhere after the 

 Pleistocene. Many of them were ending their days in America 

 somewhat ingloriously wandering into boggy lands (ap- 

 parently in search of salt), and perishing after vain efforts to 

 extricate themselves. Mammoths, by this time, must have 

 wandered far away north. 



There is no satisfactory evidence that man was in North 

 America in pre-glacial times. Nor is it certainly known that he 

 was there during or even soon after the glaciation. Imple- 

 ments, apparently palaeolithic, have been exhumed ; but 

 there is no general consensus of opinion as to the date of the 

 beds in which they have been found. Indeed, it is affirmed 

 by some authorities that these so-called palaeoliths are the 

 refuse flakes of well-finished implements made by Indians in 

 much later times. But whatever be the true date of the 

 relics, the human race was probably represented in Europe 

 much earlier than in North America. 



SOUTH South America was also visited with an exceptional amount 

 AMERICA of ice ; but this may have been later in the Period than the 

 time of the great northern glaciation. In the region of the 

 Andes the valleys were blocked with ice. There was also 

 an ice-invasion from the far south, but this did not extend 

 north of Patagonia. The ice, however, never seems to- 



