116 SOUTHERN CALIFORNIA GEOLOGY 



of the same lamentable lack of interest that has until 

 recently allowed all of the desert southwest to remain 

 terra incognita, we have no knowledge of details of 

 these faults beyond the international line. Neverthe- 

 less, these continuations have bearings upon the earth- 

 quake question in Southern California, for it is em- 

 phatically and decidedly wrong to speak of them as 

 having their southern termini here. 



NATURE OF THE DISPLACEMENTS 



The movement which takes place along a fault line 

 results in what is called "displacement." These dis- 

 placements often aggregate thousands of feet and have 

 accumulated through vast periods of time. 



The displacements along the master fault lines are 

 largely in vertical directions, varying but slightly from 

 the perpendicular, but there are conspicuous examples 

 of gigantic displacements of other kinds, in which the 

 movement was horizontal-drifting or over-thrusting 

 (where one end of the faulted block is pushed over 

 the other) . 



MOVEMENTS ALONG FAULT LINES 



Movements along fault lines may be continuous 

 through great lengths of time, and practically unob- 

 servable. It is improper to look upon the great fault 

 scarps, often thousands of feet in height, as records 

 of a series of earthquake disturbances, for the blocks 

 may have moved upwards without a jar, just as slow 

 movements of this kind may be observed along active 

 lines of faulting in mines of today. 



Movements along fault lines may also be sudden 

 and intermittent in kind, and they may occur locally 



