ABSTRACTS OF PAPEES 45 



MOBILITY OP THE COAST RANGES OF CALIFORNIA 

 BY ANDREW C. LAWSON 



(Abstract) 



The paper adduces evidence that the region is moving nortlierly by strain 

 creep, due to a subcrustal current. This strain is relieved from time to time 

 by faulting and the region springs back, causing an earthquake at each slip. 

 The displacements of 1868 and 1906, as determined by the U. S. Coast and 

 Geodetic Survey, may be explained consistently with this conception. The re- 

 bound of 1868 was an expression of relief from longitudinal strain effected by 

 a deep lowly inclined fault with a strike normal to the direction of stress. 

 The rebound of 1906 was a relief from transverse strain on a vertical fault 

 oblique to the direction of stress. 



Eeacl from manuscript. 



CERTAIN MARKED DIFFERENTIAL MOVEMENTS IN THE SAN FRANCISCO 



BAY REGION 



BY GEORGE D. LOUDERBACK 



{■Abstract) 



Brief statement of physiographic contrasts of east and west sides of San 

 Francisco Bay. Evidence of general movements and of differential movements 

 based on consideration of physiographic features, alluvial deposits, and bay 

 deposits, present and former cross-sections of a drowned valley, borings, and 

 core samples of bottom deposits. Brief comparison of recent diastrophic rela- 

 tions of this region with those of Tertiary time. 



Presented without notes. 



Discussion 



Prof. W. H. HoBBs : I am glad that Professor Louderback's paper has been 

 read in connection with Professor Lawson's, for I think that supplies an alter- 

 native, and I believe a truer picture of the type of deformation which took 

 place during the earthquake of 1906. I believe it only fair to say that the 

 Reid theory of that earthquake, indorsed as it is by Lawson, grows out from 

 the notion that the California earthquake was unique, instead of being not 

 essentially diflferent in its nature from others. No attempt was made to fit 

 the Reid theory of strain creep and rebound to other earthquakes. I consider 

 it fair criticism of the studies made by the geologists who studied the earth- 

 quake that they made no adequate survey of the vast field of seismological 

 knowledge already at hand, but, on the contrary, started out as though their 

 own observations were alone of importance. 



Professor IjAwson replied that the first volume of the report on the Cali- 

 fornia earthquake of 1906 sought merely to lay the facts of that quake before 

 the scientific public, and that the second volume brought out the application 

 of a theory that, as far as known, had not theretofore been applied to earth- 

 quakes. 



