148 /. BURR TYRRELL 



Hudson Bay. The contour lines here shown are respectively 

 600, 1500, and 3000 feet above the sea, and from the 3000 feet 

 contour line the surface has an average slope of a little less than 

 three feet to the mile. This slope is of course not quite regular, 

 being broken by hills and valleys, and occasionally the country 

 rises for some considerable distance in the opposite direction, 

 but on the whole the general decline is very well marked, and 

 no high mountains break the general monotony of the landscape. 



In the more northern portion of the region are the treeless 

 plains, or "Barren Lands," extensive level or undulating grassy 

 plains, with a mean summer temperature below 50 F., and with 

 a frozen subsoil which prevents the growth of trees. South of 

 this is the great forest region, the home of the chief fur-bearing 

 animals of Canada, and still farther south are the plains or 

 prairies, which many of you will probably cross on the transcon- 

 tinental railways after the close of this meeting. 



It would be beyond the scope of this paper to discuss the 

 question of rainfall, but suffice it to say that the humidity of the 

 atmosphere decreases from the seacoast inland, and while the 

 Barren Lands are kept constantly wet by fogs and drizzling 

 rains, the air over the prairies is very dry, and licks up rapidly 

 any moisture that may be lying on the surface of the ground. 



As you will see from the handbooks prepared for the use of 

 the members of the association, the northeastern part of this 

 region is underlain by crumpled and distorted Archaean rocks, 

 whose surface has, even in pre-Cambrian times, been reduced to 

 an undulating plain, with very slightly accentuated contours. 

 On each side of this elongated area, or low central ridge, of 

 highly altered Archaean rocks, are flat-lying limestones, sand- 

 stones, and shales, varying in age from the Cambrian up to the 

 Tertiary, and separated by several erosion intervals, which, with 

 the water-deposited strata, would indicate a gradual rising and 

 lowering of the land along a line parallel to the present Archaean 

 outcrop. From a study of the Rocky Mountains, and the moun- 

 tainous region of British Columbia, 1 Dr. Dawson has shown rea- 



1 On the Later Physiographical Geology of the Rocky Mountain Region in Can- 



