1921] Laivson: The Mobility of the Coast Eanges of California 459 



1865. The dominance of the southerly component suggests the disten- 

 sion of the region for which Rothpletz and AVood have proposed 

 independent and different explanations. 



In considering the geodetic data available for this region I shall 

 continue to apply the elastic rebound theory and shall adopt the 

 hypothesis that the results observed here are due to the operation of 

 the same fundamental causes as in the region to the north of the 

 Golden Gate. That is to say, I shall endeavor to show that the 

 ascertained facts of displacement may be the consequence of the same 

 northerly strain creep, due to subcrustal flow, as that which affected 

 the region farther north, and that distension, in the sense of Rothpletz 

 and Wood, may therefore be only apparent and not real. 



The movement of 1868. — Before taking up this discussion, however, 

 I will state what appears to me to be the nature of the movement which 

 caused the earthquake of 1868, since this conception will enter into the 

 discussion as an essential hypothesis. The evidence as to what actually 

 happened in 1868 in the way of earth movement is scant and unsatis- 

 factory. It is certain that the Haywards fault opened as a gaping 

 fissure at intervals for at least twenty miles southeastward from San 

 Leandro. At some places it stayed open and had to be bridged.^^ At 

 other places it was sounded with a string and plummet but the bottom 

 could not be reached. This open crack was not a feature of the 

 alluvium at the base of the hills but was found in the rock of the hill 

 slopes. There was no fault slip on the fissure, and the displacement of 

 a few inches which affected fences, and which occurred slowly after 

 the earthquake, is clearly referable to later adjustments, necessitated 

 by the lack of support for the walls of the fissure. The Haywards 

 fault thus behaved very differently in 1868 from the San Andreas 

 fault in 1906. The open fissure is significant not of differential dis- 

 placement as a relief from shear strain, but of relief from tension. It 

 seems to prove conclusively that there was no northerly displacement 

 of the valley of San Francisco Bay at the time of the shock, for in this 

 event the crack would not have opened. 



It appears, moreover, that the earth wave which was generated by 

 the displacement of the earth's crust moved from north to south. 

 Captain Peterson while in the vicinity of Robert's Landing heard a 

 great rumble off across the fields towards San Leandro (i.e., to the 

 north). lie looked quickly in that direction, and over a mile away 



15 Op. cit., p. 444. 

 19 Op. cit., p. 441. 



