CHAPTER II. 



THE LAURENTIAN EOCKS* 



As we descend in deptli and time into tlie earth's 

 crust, after passing through nearly all the vast series 

 of strata constituting the monuments of geological 

 history, we at length reach the Eozoic or Laurentian 

 rocks, 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 supposed 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 consider- 

 able heights, and form the highlands separating the 



* Dana has recently proposed the term " Archcsan," on the 

 ground that some of these rocks are as yet unfossiliferous 

 but as the oldest known part of them contains fossils, there 

 seems no need for this new name. 



