THE DAWN OF LIFE 



o 



she shrunk and wrinkled since those 

 youthful days when the Laurentian rocks 

 were her outer covering. 



I cannot describe such rocks, but their 

 names, as given in the section, Fig. 2, 

 will tell something to those who have 

 any knowledge of the older crystalline 

 materials of the earth's crust. To those 

 who have not, I would advise a visit to 

 some cliff on the lower St. Lawrence, or 

 the Hebridean coasts, or the shore of 

 Norway, where the old hard crystalline 

 and gnarled beds present their sharp 

 edges to the ever raging sea, and show 

 their endless alternations of various kinds 

 and colours of strata, often diversified 

 with veins and nests of crystalline 

 minerals. He who has seen and studied 

 such a section of Laurentian rock cannot 

 forget it. 



The elaborate stratigraphical work of 

 Sir William Logan has proved that these 

 old crystalline rocks are bedded or 

 stratified, and that they must have been 

 deposited in succession by some process 

 of aqueous action. They have, however, 

 through geological ages of vast duration 

 been subjected to pressure and chemical 

 action, which have, as stated in a pre- 

 vious chapter, much modified their struc- 

 ture, while it is also certain that they 

 must have differed originally from the 

 sands, clays and other materials laid 

 down in the sea in later times. 

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