THEORIES OF THE CAUSES OF FAULTING 197 



terial which wore away as the block rose to its present 

 position. Thus the block, as we now see it must repre- 

 sent a total upward movement of at least forty-two 

 miles. 



THE HORIZONTAL MOVEMENTS 

 It has been alleged that horizontal, or drifting move- 

 ments, have taken place on a large scale throughout 

 various parts of the earth, as has been set forth in 

 Wegener's recent and much discussed book on "The 

 Origin of Continents and Oceans." Great, drifting 

 movements of this kind have taken place in California 

 in times past, and may probably be slowly continuing 

 at present, but certainly not at the great rate which 

 prophets of earthquake disaster would have us believe. 

 The causes of these drifting movements are not posi- 

 tively known, but it was long ago suggested^ (before 

 the theory of isostasy was advanced) that they might 

 be the result of a lag in the movements of some of the 

 larger continents in comparison to that of the smaller 

 ones. 



RENEWAL OF MOVEMENT ALONG OLD 

 FAULT LINES 

 There is much evidence that, while fault lines may 

 have originated and had their maximum movement 

 in some one particular epoch, renewal or repetition of 

 movements along the line may have taken place in one 

 or several later epochs, or even have continued in less- 

 ening degree into the present time. Noble has shown 

 some tine examples of such renewals of movement 

 along fault lines of great antiquity in the region of 



"Emerson, B. K. The Tetrahedral Earth and Zone of the Inter-continental 

 Seas. Proc. Geological Society of America (Vol. 11, 1900), 



