GENERALIZATIONS CONCERNING EARTHQUAKES 31 



quakes more frequently but of much less intensity than 

 those along the rift, especially when it involves the 

 harder rocks such as granite and the Franciscan and 

 Cretaceous formations." 



If the great stresses arising within the zone of 

 flowage are deep-seated, and directionally far-reaching 

 along the line of weakness as they apparently are, then 

 the nature of the veneer of a surface of sedimentary 

 rocks may soften but not cancel the movement. But 

 this cushioning may be a great protection value, as 

 Mr. Arnold shows. 



GEOLOGICAL FORMATIONS OF LOS ANGELES 

 NOT UNFAVORABLE 



The alluvial formations of this city, especially the old 

 sediments of the Los Angeles river, which underlie the 

 business part of city are well settled, more or less com- 

 pact, and ordinarily dry, unlike the ocean-water-sat- 

 urated alluviates of San Francisco harbor with which 

 they have been erroneously compared. The facts that 

 the oldest houses of the region and the Los Angeles 

 and Santa Barbara Missions are built on such forma- 

 tions and have withstood all historic shakes of the 

 region, sufficiently negates the idea of the instability 

 of its old, alluvial formations. 



DIFFERENCES IN STRUCTURE 

 There is no identity between the fault systems of 

 Northern and Southern California, except in the in- 

 stance of the supposed continuity of the San Andreas 

 Rift from one region to the other, which the path of 

 maximum seismicity is supposed to follow, and which, 

 as I will show, may be a line of several united faults. 

 In Northern California the fault pattern and con- 



