364 University of California Publications in Geology [Vol. 10 



posed upon the latter. A considerable portion of the country just 

 east of the Haywards fault was covered with detritus and then 

 elevated, the uplift giving rise to the present stream system. 



As near as can be judged, at least a branch of the old stream flowed 

 out through Arroyo Viejo Creek during the last stages of its existence. 

 There must have been a large amount of detrital material deposited 

 on the lower hillslopes at the advent of the present erosional cycle. 

 This material has been largely if not all covered by recent alluvium. 

 The former stream system probably represents the period in which 

 the San Antonio formation was deposited. Material similar to that 

 in the San Antonio formation covers a considerable area of the Knox- 

 ville just north of Lake Chabot. The material here, however, contains 

 many large boulders, which at some places are imbedded in the finer 

 alluvium ; it is the finer alluvium that is similar to the San Antonio. 



GEOLOGICAL HISTOEY 



The portion of the Berkeley Hills here considered is composed of 

 several kinds of rocks, both igneous and sedimentary. The oldest of 

 these, comprising sandstone, conglomerate, quartzite, radiolarian chert, 

 serpentenized peridotite, diabase, ellipsoidal basalt, and glaucophane 

 schist, compose the Franciscan group. 3 Upon this group the lower 

 Cretaceous or Knoxville formation rests unconformably. It is pre- 

 vailingly a fine-grained arenaceous and carbonaceous shale having a 

 thickness of several hundred feet. As has been pointed out, 4 the shale 

 contains no coarse sand or conglomerate at its base, which would signify 

 a slowly transgressing sea. The lack of this coarse material would seem 

 to indicate that the surface of the Franciscan must have been reduced 

 to low relief and submerged rapidly. 



Upon the Knoxville shale rests the Chico or upper Cretaceous. 

 The Oakland conglomerate at the base of the Chico ranges in thickness 

 from 100 feet near Temescal Lake to perhaps 800 or 900 feet east of 

 Leona Heights ; near Lake Chabot it reaches a thickness of 1000 to 

 1200 feet; but it is probably not thicker than 1000 feet near the 

 southern end of the Haywards quadrangle. The upper portion of the 

 Chico is composed of sandstone and shale many thousand feet thick. 



The apparent conformity of the Oakland conglomerate and the 

 Knoxville is an interesting point connected with the geologic history 



s Op. tit., p. 4. 

 * Op. tit., p. 8. 



