THE DAWN OF LIFE 97 



geological time. Now, however, we have announcements to be 

 referred to in the sequel of other organisms discovered in the 

 so-called Archaean rocks ; and it is not improbable that these 

 will rapidly increase. The discussion of its claims has also 

 raised questions and introduced new points, certain, if properly 

 entered into, to be fruitful of interesting and valuable thought, 

 and to form a good introduction to the history of life in con- 

 nection with geology. 



As we descend in depth and time into the earth's crust, 

 after passing through nearly all the vast series of strata consti- 

 tuting the monuments of geological history, we at length reach 

 the Eozoic or Laurentian rocks, 1 deepest and oldest of all the 

 formations known to the geologist, and more thoroughly altered 

 or metamorphosed by heat and heated moisture than any 

 others. These rocks, at one time known as Azoic, being sup- 

 posed destitute of all remains of living things, but now more 

 properly Eozoic, are those in which the first bright streaks of 

 the dawn of life make their appearance. 



The name Laurentian, given originally to the Canadian 

 development of these rocks by Sir William Logan, but now 

 applied to them throughout the world, is derived from a range 

 of hills lying north of the St. Lawrence valley, which the old 

 French geographers named the Laurentides. In these hills 

 the harder rocks of this old formation rise to considerable 

 heights, and form the highlands separating the 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 anywhere 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. Upheaved in the folding of the 

 earth's crust into high and rugged ridges, they have either re- 

 1 Otherwise named " Archrean." 



