PalacheJ 



The Berkeley Hills. 



403 



cated on the map. Its relations to the conglomerate are, however, 

 obscure, and it is doubtfully correlated with the basalt of Gopher 

 Ridge, which it resembles, although it may with equal probability 

 be intrusive. 



Lake Beds and Lavas. — Prior to the faulting which converted 

 the Campari basin into a diastrophic trough, the infilling of the basin 

 by sedimentary deposits was several times interrupted, or rather 

 supplemented, by flows of lava and extravasations of tuff. The 

 proof of this is seen in the sheets of lava and tuff which are inter- 

 leaved with the sedimentary strata in the vicinity of Pie Knob and 

 1 Fog Bluff and in the intervening Wolsey Canon. 



The earliest of these lavas are. those best seen on the lower 

 flanks of Fog Bluff and on Pie Knob. There appear to be at least 

 two flows representing this stage of volcanic activity, which can not 

 be discriminated sufficiently well for separate mapping, so that, 

 although the two rocks are quite different in appearance, they are 

 mapped together as andesite, to which type they may both be 

 referred. The lower is a dark rock, readily decomposed, of open 

 texture and frequently vesicular or amygdaloidal. This rock 

 probably underlies Fog Bluff and occurs as a series of outliers on 

 the lower Campan conglomerate on the slopes south and west of 

 Fog Bluff. 



Above this dark andesite is a light-colored lava which is in 

 marked contrast to the lower rock. Typical specimens are of a 

 light gray to reddish-gray color, compact to porous in texture, and 

 have a strongly-defined flow lamination. The rock is resistant to 

 disintegration, and differential erosion brings it out in bold relief. 

 It is owing to this quality that it has found favor to some extent as 

 a road metal for the streets of Berkeley. The rock is microcrystal- 

 line, and phenocrysts are only occasionally observable. 



The porous varieties of the rock frequently show distinct open- 

 ings along the planes of lamination, and seams and films of hematite 

 and limonite are found in these openings. The absence of the 

 ferro-magnesian silicates is a characteristic of the rock in its 

 macroscopic aspects, the rock being almost wholly feldspaltic. 

 These andesites have a maximum thickness in the Pie Knob section 

 estimated at 180 feet. On the north side of Wolsey Canon they 



