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University of California. 



[Vol. 2. 



the heave and the dip of the strata, the throw of the fault may be 

 calculated. The throw of the fault, where it dislocates the amygda- 

 loidal andesite, thus estimated is not more than 150 feet, although 

 the heave is nearly 500 feet. This fault not only traverses this 

 limb of the dominant syncline of the Berkeley Hills, but also the 

 subordinate flexures of the lower portion of the San Pablo slope, 

 as is indicated on the map, and is in part responsible for the some- 

 what complicated appearance of the map in this region. 



There is also a slight dislocation of the strata on the summit of 

 Frowning Ridge just north of the Summit Pass, and also evidence 

 of faulting at the lower end of Spoon Gulch, and as these are in the 

 same general line as the dislocation on the San Pablo slope, they 

 may be regarded as part of the same general fault, and they have 

 been so indicated on the map. It is to be noted, however, that the 

 downthrow of the fault on Frowning Ridge is on the east side of 

 the fault, whereas, as we have just seen, the downthrow on the San 

 Pablo slope is on the west side. This of course tends to cast doubt 

 upon the supposition that the two dislocations occur upon the same 

 fault plane; but it is believed that within the limits of the move, 

 ment there might easily be sufficient inequality of displacement to 

 allow of such a discrepancy. 



Intrusive Dolerite. — -On the north side of Orinda Hill and in the 

 vicinity of Tumbling Brook there are indicated upon the map 

 some areas of dolerite. Although the relations of this rock to the 

 Orindan formation can not be made out as clearly as could be 

 desired, yet the fact that their distribution shows them to be dis- 

 cordant to the adjacent rocks, and that they appear at different 

 horizons, indicates that they are intrusive masses. The rather 

 coarse holocrystalline character of the rock and its petrographical 

 identity with a clearly-marked dyke in a part of this same field 

 beyond the limits of the map, support this conclusion. 



THE CAMPAN SERIES. 



Limits of Basin. — The Berkeleyan series, although representing 

 in its accumulation of varied sedimentary and volcanic rocks, in the 

 recognizable intervals of non-accumulation between these, and in 

 the deformation of series as a whole, a long and important epoch 



