!;™k ] The Berkeley Hills. 375 



on the face of the escarpment dip into Frowning Ridge, or north- 

 easterly, at angles which vary from a little less than 30 to over 

 6o°. Abundant evidence of the extrusive nature of the rocks lies 

 before the observer. The parallelism of the rock-sheets over wide 

 areas; the presence of pyroclastic material at different horizons; 

 the zones of red laterite between successive sheets; the intercala- 

 tion of detrital material, such as well-worn pebble beds, between 

 the massive rocks; the glassy character of some of the sheets; 

 the occurrence of vesicular and amygdaloidal structures and of 

 flow structures well developed macroscopically and microscop- 

 ically — all of these characters point to only one conclusion, viz. , 

 that the rock sheets were poured out as surface lavas. At several 

 points the actual contact of the lavas with the associated sedimen- 

 tary rocks may be observed, but in no instance can any alteration 

 of the latter be detected, if we except certain inclusions of lime- 

 stone in the lava which have become crystalline and in which 

 silicates have been developed. The lavas may occasionally be 

 observed to hold inclusions of pebbles, which may reasonably be 

 regarded as incorporated portions of the surface over which it 

 flowed. 



Bcrkcleyau Series, Upper and Lower. — From the fact that sev- 

 eral of the lava sheets have lateritic surfaces, which indicates a 

 long exposure to weathering, and from the further fact that water- 

 worn gravel is to some extent intercalated with the lavas, it is 

 apparent that there were intervals between the successive flows. 

 During these intervals not only would the surface of the lava be 

 subject to decay under the processes of weathering, but the effects 

 of erosion would be manifest in proportion to the duration of the 

 interval; and if the region had been affected by deformation, such 

 disturbance would modify the surface over which the next succeed- 

 ing extravasation of lava flowed. 



In respect to these two considerations, amount of deformation 

 of the region and of erosion to which it was subjected, one of these 

 intervals appears to be of much greater importance than the others; 

 it is, therefore, regarded as one of those important epochs of geo- 

 logical history in which time and work are expressed in other terms 

 than those of accumulation. The entire series of rocks, volcanic 



