420 



University of California Publications. 



[Geology 



Number of 

 points 



Average distance 

 East 



from fault 



West 



Displacement between sur- 

 veys I and II 

 South North 



1 



4.0 miles 







1.8 feet 





3 



2.6 miles 







2.8 feet 





10 



0.9 miles 







4.2 feet 





12 







1.2 miles 





9.7 feet 



7 







3.6 miles 





7.8 feet 



1 







23.0 miles 





4.8 feet 



These displacements are shown graphically in figure 2. 



A — 1 





B 

 G 



— — c 



A 







G 



a a 



R 





 D 





s 



' Mitt* ' 





Fig. 2 



The line A'C represents a line which was straight at the 

 time of the second survey. At the time of the earthquake this 

 line was broken at the fault, and its two parts were separated 

 about 21 feet, taking the positions A"B' and CD'. Three points 

 and the distant Mt. Diablo determine the right-hand curve; two 

 points and the distant Farallon Light House, together with the 

 fact that D'B' must be 21 feet, determine that on the left. In 

 the figure the distance scale is 1000 times the displacement scale 

 because this difference is necessary to show the character of the 

 displacements. The curvature of the lines is extremely small, 

 the radius of curvature being nowhere less than 4000 miles, and 



