THE 



QUARTERLY JOURNAL 



OF 



THE GEOLOGICAL SOCIETY OF LONDON. 



Vol. LXV. 



1. The Geological Interpretation of the Earth - Movements 

 associated with, the Calieornian Earthquake of April 18th, 

 1906. By Richard Dixon Oldham, E.G.S. (Read December 

 2nd, 1908.) 



The Californian earthquake of 1906 was accompanied by very 

 considerable displacements of the ground along a great fault-line, 

 which has been traced for a distance of about 200 miles from its 

 southern extremity to the point where it finally passes out under the 

 sea. As several stations of the principal triangulation lay within 

 the disturbed area, the Government of the United States decided to 

 repeat the observations over this area, and determine with accuracy 

 the present positions of the points previously fixed. The result of 

 this work has been issued, with most commendable promptness, as 

 an Appendix 1 to the Report of the Coast & Geodetic Survey for 

 1907, and the results seem of such importance, from the light 

 thrown on the nature of the earth-movements which gave rise to 

 this earthquake, that I have thought it desirable to make a detailed 

 study of them from the geological point of view. 



The area covered by the observations is not co-extensive with, but 

 covers the most important part of, the seismic area ; it extends from 

 near Monterey, in the south, to Point Arena, in the north, and 

 within this area all the points fixed by the triangulation which was 

 carried out at various times between 1851 and 1899 were again 

 fixed after the earthquake of 1906. 



When the results came to be worked out, it was found that 

 wherever triangulation of earlier date than about 1868 was 

 connected up with triangulation of later date, the positions of the 



1 ' The Earth-Movements in the Californian Earthquake of 1906 ' by John 



F. Hayford, Inspector of Geodetic Work, & A. L. Baldwin, Computer, Coast 



& Geodetic Survey. Washington, 1908. [Reprinted in the Report of the State 



Earthquake Investigation Commission. Carnegie Institution, Washington, 1908.] 



Q. J. G. S. No. 257. b 



