THE LAURENTIAN EOCKS. 



with great beds of triclinic felspar, 

 especially of that peculiar variety 

 known as labradorite, or Labrador 

 felspar, and wbicli sometimes by its 

 wonderful iridescent play of colours 

 becomes a beautiful ornamental 

 stone. 



I cannot describe such rocks, 

 but their names 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. Law- 

 rence, 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 diversi- 

 fied with veins and nests of crystal- 

 line minerals. He who has seen 

 and studied such a section of Lau- 

 rentian rock cannot forget it. 



All the constituents of the Lau- 

 rentian series are in that state 

 known to geologists as metamor- 

 phic. They were once sandstones, 

 clays, and limestones, such as 



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