1921] Lawson: The Mohility of the Coast Ranges of California 439 



1908 to 1912, when j\Ir. Tucker was in South America. The values 

 tabulated are the averages by quarter years, as near as possible, and 

 the number of nights in each quarter during which observations were 

 made averages seventeen. The results have been corrected for the 

 revised refractions adopted at Lick Observatory and for the variation 

 of latitude. 



I have taken these vaUies and plotted them on coordinates in 

 figure 1, B. It is apparent from an inspection of the figure that, not- 

 withstanding the variations in the values, there is in general a fairly 

 steady increase in the latitude from 1893 to 1903. This increase is 

 expressed in the mean line A-B. It amounts to 0'/4 in ten years, or 

 at the I'ate of O'.'Ol or 1.24 meters per year. 



Between 1903.60 and 1903.92 there is an exceptionally large drop 

 of 0'.'63 in the value for the latitude. In this interval occurred the 

 earthquake of August 2, 1903, which was rather severe at the Lick 

 Observatory. It seems not improbable that the rather large drop in 

 the value of latitude may be due to a shift of the ground at the time 

 of this earthquake. The values for latitiide since 1903.60 clearly fall 

 into a grouping distinct from the grouping of the values for the period 

 preceding that date. The mean expression for the values, as indicated 

 by the line C-Z>, is, however, not so satisfactory as the line A-B, owing 

 largely to the interval of no observations from 1908 to 1912. This line 

 rises from 1903 to 1915. but at a less rapid rate than the rise of the 

 line A-B. The rate of increase of the value for latitude for this 

 period is 0'.'022 or .70 meters per year. Beyond 1915 the data are 

 insufficient for the determination of a mean position. It is interesting 

 to note that there is no indication of sudden change of position at the 

 time of the slip on the San Andreas fault in 1906. 



The rate of increase of latitude of Lick Observatory on either side 

 of 1903.6 is much greater than that at Ukiah, and there may be doubt 

 as to the true value of the rate, owing to the fact that the lines A-B 

 and C-D each represent the mean position of a series of points which 

 depart notably and irregularly from the adopted mean. There can, 

 however, be no doubt as to the general significance of the observations, 

 particularly between 1893 and 1903. They accord with those of Ukiah 

 in pointing to a northerly creep of the region. The increase of latitude 

 both at Ukiah and Mount Hamilton, taken together with the legitimate 

 deductions that may be made, in the light of the rebound theory, from 

 the results of the geodetic surveys in the intervening territory, seems 

 to establish the fact of a northerly creep of the Middle Coast Ranges. 



