PART FIVE 



THEORIES OF THE CAUSES OF FAULTING 



Why did all of these great earth features of which I 

 write, exist — the faults, their rectilinearity and direc- 

 tions of trends, the great flextures, the successions of 

 belts and other striking characteristics? What forces 

 made them; Why, when and how? Truly these are 

 large questions to try to answer in a limited pamph- 

 let ; in fact, hard to answer at all. 



All movements of the earth crust are included by 

 geologists under the formidable word "diastrophism." 

 Let us briefly state what is known of diastrophism and 

 its causes. 



THE CONTRACTIONAL THEORY 



We will still find it stated in most text books that 

 the greater inequalities of the surface were produced 

 by the contraction of the earth's center or interior by 

 cooling. This is known as the contractional theory. 

 It has so far failed to explain the great fault displace- 

 ments of Southern California and the Pacific Coast in 

 general, so different from the folded Appalachian 

 structures of the Atlantic side and of the Alps Region, 

 whose folded conditions gave rise to the contractional 

 theory. 



