4i SOUTHERN CALIFCXRNIA GEOLOGY 



at all true that either the great shocks or small 

 shocks affecting a particular locality ... are separ- 

 ated one from the other by a regular or approximately 

 regular interval ; and it is not true that the immediate 

 danger is past when a great shock has wrought its 

 havoc; and yet I am prone to believe that the rhyth- 

 mic principal does hold a place in the mechanism of 

 earthquakes." 



". . . . And if it were possible to group the shocks 

 according to place of origin it might be found that each 

 earthquake center has its orderly law of sequence. 

 But while the existence of such a systematic arrange- 

 ment seems within the range of possibility I regard 

 it as altogether outside the field of probability and I 

 feel sure that any attempt to discriminate rhythmic 

 series on numerical grounds without any other basis 

 for classification would prove unprofitable." 



"The hypothesis of alternation between parts of 

 any district is being tested — but the verdict belongs 

 to the future. Hypothesis of precipitation by acces- 

 sory forces, which are in a large part periodic and 

 foreknown, has a good status and is being developed 

 on the statistical side. It promises to make the time 

 of prediction more precise if ever the approximate 

 time shall be obtained by other means . . . The hy- 

 pothesis of an intelligible prelude has only been 

 broached and the manner of testing it is not yet in 

 sight ... In a word, the determination of danger-dis- 

 tricts and danger-spots belongs to the indefinite future. 

 . . . K the places of peril are definitely known, wise 

 construction will take all necessary precautions and the 

 earthquake-proof house will not only insure itself but 

 will practically insure its inmates." 



