THE DAWN OP LIFE. 



St. Lawrence valley from the great plain fronting on 

 Hudson's Bay and the Arctic Sea. At first sight it 

 may seem strange that rocks so ancient should any- 

 where appear at the surface, especially on the tops of 

 hills ; but this is a necessary result of the mode of 

 formation of our continents. The most ancient 

 sediments deposited in the sea were those first 

 elevated into land, and first altered and hardened 

 by heat. Upheaved in the folding of the earth's 

 crust into high and rugged ridges, they have either 

 remained uncovered with newer sediments, or have 

 had such as were deposited on them washed away; 

 and being of a hard and resisting nature, they have 

 remained comparatively unworn when rocks much 

 more modern have been swept off by denuding 

 agencies. 



But the exposure of the old Laurentian skeleton of 

 mother earth is not confined to the Laurentide Hills, 

 though these have given the formation its name. The 

 same ancient rocks appear in the Adirondack moun- 

 tains of New York, and in the patches which afc 

 lower levels protrude from beneath the newer for- 

 mations along the American coast from Newfoundland 

 to Maryland. The older gneisses of Norway, Sweden, 

 and the Hebrides, of Bavaria and Bohemia, belong to 

 the same age, and it is not unlikely that similar rocks 

 in many other parts of the old continent will be found 

 to be of as great antiquity. In no part of the world, 

 however, are the Laurentian rocks more extensively 

 distributed or better known than in North America ; 



