216 SOUTHERN CALTFOtRNIA GEOLOGY 



110 other view was possible in the absence of ap- 

 propriate data. Recently, however, English^ and 

 Noble- have presented some valuable data on the sub- 

 ject. 



Although my interpretations are confessedly im- 

 perfect, it seems to me that at least some of the 

 fault-belts herein described may be the records of 

 distinctly separate, structural unities of a sequence of 

 movements of different epochs. There are many rea- 

 sons for believing that such a sequence exists and 

 will ultimately be more clearly defined. Although 

 the classification presented has been studied by the 

 writer for many years, he does not by any means con- 

 sider his conclusions as final. 



Many of the great master, scarp-making faults 

 are of Pleistocene age, but movements along them 

 may have been revivals of those initiated in re- 

 motely previous epochs and may be continuing in some 

 instances into the present time. 



Faulting, in some instances, may have originated 

 along lines of earth weakness or along sea borders 

 which existed in remote geologic times, although the 

 immediate expressions as now visible are the effects of 

 revived movements of later times. 



Besides the light thrown upon the age of the fault- 

 ing by aid of physiography, there are two other lines 

 of evidence whereby the ages of fault systems may 

 be determined. One of these is by ascertaining the 

 age of the latest strata cut through by them. The 

 other is evidence afforded by their intersections with 

 one another. 



'Bull. 768, U. S. Geological Survey, 192. 

 -Carnegie Institution Bull., 1926. 



