294 THE ICE AGE IN CANADA. 



seen in the Leda clay the assemblage of foraminiferal 

 forms now dredged from 200 to 300 fathoms in the Gulf 

 of St. Lawrence. 



6. I infer that the subsidence of the Leda clay period 

 and of the interglacial beds of Ontario belongs to the 

 time of the sea beaches from 450 to 600 feet in height, 

 which are so marked and extensive as to indicate a period 

 of repose. In this period there were marine conditions 

 in the lower and middle St. Lawrence and in the Ottawa 

 valley, and swamps and lakes on the upper Ottawa and 

 the western end of Lake Ontario ; and it was at this time 

 that the plants described in previous pages occupied the 

 country. It is quite probable, nay, certain, that during 

 this interglacial period re-elevation had set in, since the 

 upper Leda clay and the Saxicava sand indicate shallowing 

 water, and during this re-elevation the plant-covered 

 surface would extend to lower levels. 



7. This, however, must have been followed by a second 

 subsidence, since the water-worn gravels and loose, far- 

 travelled boulders of the later drift rose to heights never 

 reached by the till or the Leda clay, and attained to the 

 tops of the highest hills of the St. Lawrence valley, 1,200 

 feet in height, and elsewhere to still greater elevations. 

 This second boulder drift must have been wholly marine, 

 and probably not of long duration. It shows little 

 evidence of colder climate than that now prevalent, nor 

 of extensive glaciers on the mountains; arid it was 

 followed by a paroxysmal elevation in successive stages 

 till the land attained even more than its present height, 

 as subsidence is known to have been proceeding in modern 

 times. 



8. For the region between the great lakes and the 

 Rocky mountains and for the Pacific coast the sequence 



