54 SOUTHERN CALIFORNIA GEOLOGY 



preted by Willis to have been "away from the source 

 of pressure" and "consequently to indicate a growing 

 strain from the southwest" — the one whose future 

 release was to produce the great earthquake predicted 

 for Southern California within "from three to ten 

 years. "^ 



From these admittedly questionable data he deduced 

 that the strains supposedly resulting from this great 

 stress, pushing from the south, had been relieved in 

 Northern California by the San Francisco shock of 

 1906, but as further supposed by him, the pres- 

 sure was still active and the strains were still 

 accumulating in Southern California along the line 

 of the San Andreas Rift since the quake of 1857. 

 Upon this latter supposition he reached the deduc- 

 tion] that the next release of strain was due in 

 the latter region. The time factor in his predictions 

 was arrived at by deductions from his concept of a 

 thirty-year cycle of periodicity based on the few and 

 unreliable earthquake data in existence concerning 

 California, as stated. 



Under the impression that the Coast Survey's find- 

 ings as announced in 1924 in Special Publication 106, 

 were true, some few geologists believed in the sub- 

 stance of Dr. Willis's deduction that the strain which 



'In justice to the Coast Survey, as called to my attention by a recent 

 letter from Director Jones cf that organization, it must be said that Special 

 Paper 106 warned the reader that the apparent changes in the position of the 

 stations should not be accepted as positive evidsnce cf earth movements. 



Following is the letter from Director Jones : 



"I should like to call your attention to the statement, in Special Publica- 

 tion No. 106, carrying a warning against accepting the difference in geo- 

 graphic positions shown on the diagrams as being due to earth movements. 

 It was not Icnown at that time whether the changes wei-e due to earth move- 

 ments or to the unavoidable errors of triangulation which had not been rigidly 

 adjusted." 



