GENERALIZATIONS CONCERNING EARTHQUAKES 59 



vations were made. This deflection of the vertical is 

 obtained from the difference in the longitudes deter- 

 mined by astronomic positions and by triangulation. 

 Where Laplace azimuths are available, the triangula- 

 tion can be held rigid in direction. Without such sta- 

 tions, there is a swerving of the areas of triangulation 

 from their true course. 



In order that the western half of the United States 

 might have its triangulation of the requisite strength, 

 a number of Laplace stations were established in Cali- 

 fornia, during and just after the triangulation observa- 

 tions were made. These Laplace observations were 

 available for the readjustment of the triangulation 

 done some years ago. 



The new triangulation was extended to the eastward 

 of the stations Mt. Lola and Round Top, on the crests 

 of the Sierra Nevadas, to stations in central Nevada. 

 A comparison of the angles in the new work and the 

 old and of the geographic positions of several stations 

 indicates very clearly that there has been no shifting 

 in position of the stations Mt. Lola and Round Top 

 and those to the eastward. The triangulation stations 

 to the eastward of Cuyamaca and San Jacinto, extend- 

 ing to the Colorado River, were reoccupied in the last 

 few years. The original observations across Southern 

 California were made about 1910. The comparison of 

 the angles and positions between the new and old work 

 for that triangulation across Southern California indi- 

 cates conclusively that no earth movements had oc- 

 curred in that region or, at any rate, that there was no 

 relative movement among the stations involved. 



Since no changes were indicated in geographic posi- 

 tions to the eastward of Mt. Lola and Round Top and of 



