418 University of California Publications. [Geology 



and therefore it was presumable that blocks of the earth's crust 

 were not shifted as a whole. Fortunately accurate geodetic 

 surveys had been made throughout this region many years ago, 

 and the Commission appealed to Mr. 0. H. Tittman, Superin- 

 tendent of the United States Coast and Geodetic Survey, to 

 repeat the surveys and to determine the true displacements of 

 the various stations of the surveys. Mr. Tittman realized the 

 importance of this, and the work was carried out under the 

 immediate direction of Messrs. Hayford and Baldwin. The 

 results were published in detail in the report of the Commission, 

 and we shall merely summarize them here. 



The earlier surveys can be divided into two groups : I, those 

 made between 1851 and 1866 ; II, those between 1874 and 1892. 

 The survey after the earthquake (III) was made in 1906-7. 

 The surveys extend from Mt. Diablo, thirty-three miles east of 

 the fault-line, to the Farallon Lighthouse, twenty-three miles 

 west of it, as shown in the map, figure 1. 



All the surveys are connected through the common points 

 Mt. Diablo and Mocha on the inner Coast Range, and the line 

 between them, which is practically parallel with the fault-line. 

 Dr. Hayford has shown that this line either has not moved at all, 

 or has moved parallel with itself without changing its length ; 

 for astronomical observations at the times of the surveys show 

 differences in its direction of only a small fraction of a second 

 of arc — that is, within the limits of error of the surveys ; and 

 the distances of various points from it measured at right angles 

 to its direction do not show a systematic change depending on 

 their distances, which proves that it has substantially preserved 

 its length without change. Although there is no evidence that 

 this line has moved as a whole, evidence that it has not is also 

 lacking; but fortunately for our purposes this is unimportant, 

 as we are considering only relative displacements. 



Survey II covers very well the region north of San Francisco, 

 and in combination with survey III brings out clearly the dis- 

 placement of a number of stations between the dates of these 

 surveys. Without going into details the following table sum- 

 marizes the displacements (which are practically parallel with 

 the fault-line) undergone by the best determined points. 



