THE DAWN OF LIFE IOI 



she shrunk and wrinkled since those ^ ^ 



youthful days when the Laurentian rocks 



were her outer covering. o 



I cannot describe such rocks, but their c - 

 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 <g MB 



the Hebridean coasts, or the shore of 

 Norway, where the old hard crystalline jjf 

 and gnarled beds present their sharp 'g |a * J 



edges to the ever raging sea, and show %o. HI -I 



their endless alternations of various kinds | 

 and colours of strata, often diversified 

 with veins and nests of crystalline ^ g s 



minerals. He who has seen and studied I ** IJ 



a sSm g O 



such a section of Laurentian rock cannot *, 1 *:fl^ 



The elaborate stratigraphical work of Jg 



Sir William Logan has proved that these g < 



old crystalline rocks are bedded or 3 



stratified, and that they must have been ^ m| a J 



deposited in succession by some process ig ^ ^ 



of aqueous action. They have, however, |g ^ 



through geological ages of vast duration 



been subjected to pressure and chemical o 



action, which have, as stated in a pre- % 



vious chapter, much modified their struc- I. , 



ture, while it is also certain that they ^ ^ 



must have differed originally from the '!___ J|| "^ 

 sands, clays and other materials laid 

 down in the sea in later times. 



a 



