292 



The National Geographic Magazine 



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it was destined to play in the commercial 

 development of the Pacific and the 

 Orient. 



PROBABLY IN NO PART OF THE WORLD HAS 



THE LAND BEEN SO ACTIVE IN 



RECENT TIMES 



The general connection between the 

 geological history that has just been 

 briefly summarized and the earthquakes 

 so prevalent in California is clear and 

 unmistakable. We have seen that the 

 record of the rocks shows that through 

 long geological periods the land has oscil- 

 lated up and down in a startling manner. 

 Probably in no part of the world have 

 the processes of upheaval and subsidence, 

 folding and faulting, and erosion and 

 sedimentation been, as a whole, so in- 

 tensely active in the same period of later 

 geological time. Moreover, the general 

 activity and rapidity of geomorphic de- 

 velopment have continued up to the pres- 

 ent day. The region thus amply fulfills 

 the conditions under which tectonic 

 earthquakes arise. It is in unstable 

 equilibrium, and it is cut by long north- 

 northwest faults into narrow blocks 

 which are in turn traversed by many 

 minor dislocations. Under the operation 

 of the unknown forces of elevation and 

 subsidence, stresses are set up which 

 finally overcome the adhesion of the op- 

 posing walls of one or more of the fault 

 fissures, an abrupt slip of a few inches or 

 a few feet takes place, and an earthquake 

 results. The region extending for some 

 hundreds of miles north and south of the 

 Bay of San Francisco may be considered 

 as particularly susceptible to shocks on 

 account of the number and magnitude of 

 the faults, the evidence that these furnish 

 of very recent slipping, and the marked 

 recent subsidence in the vicinity of the 

 Golden Gate. We may now turn from 

 the geological record to the recent dis- 

 aster. 



SUMMARY OF DAMAGE 



The apparent facts with reference to 

 the San Francisco earthquake of April 

 18, 1906, as gleaned from the daily pa- 

 pers, are as follows : 



