T1IK ARCHKAN ROCKS 



319 



Fitf- 2<;.|. Metamorphic rock, showing foliation distinctly; bank of the Ottawa 

 Kivrr. ( Klls.) 



as well as a considerable part of existing schists, got their foliated 

 structure in this way; but it is to be understood that some of the 

 schi>ts and perhaps some of the gneisses arose from sedimentary 

 formations in other ways. It is not to be understood that the 

 tnetamorphism of the Archean rocks was completed during the 

 Archean era. The metamorphosing processes of subsequent times 

 have affected them. 



It would be difficult to obtain an exaggerated idea of the com- 

 plexity of the rocks which has caused this system to be called a, 

 "complex." It consists in some places of rocks which are mainly 

 massive (igneous intrusions); in other places, of rocks which are 

 mainly gneissic (chiefly meta-igneous) ; and in still others, of rocks 

 (largely mcta-igneous and subordinately meta-sedimentary) in 

 which a schistose structure predominates. Furthermore, the rocks 

 of each of these structural types have a wide range in composition, 

 from acid on the one hand to basic on the other. Rocks of all these 

 eludes an- intimately associated locally, and any one may pre- 

 dominate over the others. In places the rocks of the several struc- 



