and colours of strata often diversi- 



THE LAURENTIAN ROCKS. 13 



with great beds of triclinic felspar, 

 especially of that peculiar variety 



known as labradorite, or Labrador ^ 



felspar, and which sometimes by its 

 wonderful iridescent play of colours 



becomes a beautiful ornamental ^ 



stone. ; ls 



I cannot describe such rocks, js 



but their names will tell something ^ 



to those who have any knowledge 



of the older crystalline materials '1 



of the earth's crust. To those who , 



have not, I would advise a visit 1 



to some cliff on the lower St. Law- ^ 



rence, or the Hebridean coasts, or o 



the shore of Norway, where the ^ 



old hard crystalline and gnarled d 



beds present their sharp edges to ' Z 



the ever raging sea, and show their 



endless alternations of various kinds 3 





^ 



5 





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- . g 

 rentian series are in that state d|^ 

 known to geologists as metamor- ^^ 

 phic. They were once sandstones, 

 clays, and limestones, such as ^ 



