I08 RELICS OF PRIMEVAL LIFE 



in short, experienced the changes known to geologists 

 by the formidable word metamorphism, whereby they 

 have lost the more obvious characters of ordinary 

 aqueous deposits, and have assumed new and strange 

 forms. Dr. Adams, of Montreal, has taken the pains 

 to collect a number of chemical analyses of the 

 gneisses and schists or crystalline slates of the 

 Grenville series, and finds that, however unlike to 

 more modern shales and clays, they have substan- 

 tially the same chemical composition. Now if they 

 were originally such shales and clays, it has happened 

 to them that the ingredients of the clays have 

 rearranged themselves in new forms and become 

 crystalline. We are familiar in a small way with 

 such changes when brick clay, over-heated in the 

 kiln, becomes fused into slag or vitrified ; and if 

 such slag were allowed to cool very slowly, it would 

 present different kinds of crystalline minerals. We 

 actually see changes of this kind in the substance 

 of bricks which have been long exposed to intense 

 heat in the walls of furnaces. Now in the crust 

 of the earth, very old rocks, buried under newer 

 deposits, and exposed to the heat of the interior 

 molten rocks, experience such changes on a great 

 scale ; and there is one kind of influence present in 



