442 



GEOLOGY 



The result would be lateral thrust in the outer parts of the earth, 

 and this thrust would be relieved by the bending and crumpling 

 of the rocks, and by shear. 



That the rocks should have undergone extraordinary meta- 

 morphism under these conditions is natural. It has been demon- 

 strated that massive igneous rocks, by crushing and shearing, have 



Fig. 340. Metamorphic rock, showing foliation distinctly; bank of the 

 Ottawa River. (Ells.) 



been transformed into rocks with a foliated or schistose structure, 

 and it is in the rocks of this era especially that metamorphism of 

 this type is found. It is now believed that the larger part of exist- 

 ing gneisses, as well as a considerable part of existing schists, 

 acquired their foliated structure in this way; but it is to be under- 

 stood that some of the schists and perhaps some of the gneisses 

 arose from clastic formations by other processes of transformation. 

 It is not to be understood that the metamorphism of the Archean 

 rocks was completed during the Archean era. All metamor- 

 phosing processes of subsequent times have affected them. 



