THE DAWN OF LIFE IOI 



she shrunk and wrinkled since those ^ ^ 



youthful days when the Laurentian rocks |_J 



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 ^ vjn * 



some cliff on the lower St. Lawrence, or *j Nn w 



<^ 



the Hebridean coasts, or the shore of 



Norway, where the old hard crystalline 'ft 



and gnarled beds present their sharp 's <* ~* o 



edges to the ever raging sea, and show , iH ~ 



their endless alternations of various kinds g 



and colours of strata, often diversified 



with veins and nests of crystalline ^ g s 



minerals. He who has seen and studied ^ 1 * | J 



such a section of Laurentian rock cannot ^ 



The elaborate stratigraphical work of ,3 



Sir William Logan has proved that these g 



old crystalline rocks are bedded or S 



stratified, and that they must have been J Hl| " J 



deposited in succession by some process 't5 



of aqueous action. They have, however, g 



through geological ages of vast duration 



been subjected to pressure and chemical . 



action, which have, as stated in a pre- j> 



vious chapter, much modified their struc- I , ^ 



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. > 1~~||| ^ 



6 5: " 



