ENVIRONMENT, PAST AND PRESENT 71 



period of glaciatlon. The same is in all probability 

 true of north America. 



A close examination of the map will reveal that 

 at no time did the ice-sheets cover the whole of 

 Alaska or the Canadian arctic islands. What con- 

 ditions may have been lijce here during the ice-ages 

 it is, perhaps, difficult to surmise with any assur- 

 ance ; but we know that even at the height of glacia- 

 tion, plants of various kinds existed on these areas. 

 That being the case, the presence of insect-life may 

 be taken for granted, the more so since insects were 

 known to be abundant during the interglacial 

 periods. In other words this region was probably 

 able to support at least certain forms of summer 

 bird-life right through the ice-ages. Yet even so 

 it would, of course, prove birdless if inaccessible. 

 There remained, however, the ocean border on the 

 west of the mountains, no doubt an open road 

 throughout the period of glaciation. There is also 

 considerable evidence that, during the Wisconsin 

 age at least, there remained a lane from Alberta 

 north, on the east side of the mountains, which was 

 only partly glaciated, with open lakes and marshes 

 in summer, which may have provided food and a 

 migratory path to the north. Geese, various ducks 

 and a number of shore-birds may thus very well 

 have continued to breed in the far north even at 



