82 



NORTH AMERICA 



Siberia ; the reason perhaps being the proximity of the 

 great ice sheet which covers the highlands of Greenland, 

 or even ultimately the climatic conditions of the circum- 

 polar cap. The sub-arctic forest deserves indeed to be 

 termed scattered. Over vast expanses, trees are dotted 

 singly or in clusters, seldom in close formation ; the 

 rivers, however, are fringed on either side by regular 



• 



Fig 24 Spruce forest on a river flat— Canada. Pine-clad slopes 

 and tree limit. 



marginal forests which follow them, as on the Mac- 

 kenzie River, almost to their mouths. The species of 

 conifers may vary from east to west, but the general 

 conditions, aspect, and mode of life are very similar 

 throughout. 



The soil of the north Canadian forest is all of glacial 

 origin: sand, clay, or gravel The irregular surface is 



