PA) ACHeJ 



The Berkeley Hills. 



369 



in the country to the south and to the north of the ridge. This 

 expectation, as we shall see later, is amply realized. 



By connecting the point where we first encounter the fault on 

 the .summit of the ridge with the point where it intersects the 

 Telegraph Canon road, we see that the plane of the fault hades at 

 a small angle to the west. On the assumption that we have to deal 

 with a normal fault, this would indicate that the downthrow of the 

 fault was to the west. This we shall find to be the fact, but as there 

 are considerations which, taken alone, might lead us to think that 

 we had to deal, not with a normal or gravity fault, but with a thrust 

 making the upthrow on the west side, it will be better to defer the 

 discussion of the real nature of the fault till we have become more 

 familiar with the way in which it affects the country to the north 

 and south of Skyline Ridge. It may be simply pointed out that 

 the conditions which we have recognized on Skyline Ridge are in 

 a measure duplicated on the south side of Telegraph Canon. The 

 fault will be referred to as the Canon fault. 



Thickness. — As to the thickness of the formation, since the 

 strata from the fault plane to the upper limit of the formation are 

 practically vertical, and since the section along the ridge is nearly 

 normal to their strike, we have in this horizontal distance a meas- 

 ure of the volume of rocks exposed. This is about 1 ,000 feet. 

 The value thus obtained, however, is only a minimum value for 

 the thickness of the formation, for two reasons: First, because we 

 measure not from the base of the formation but from a fault plane 

 along which a part may have been sheared off in the process of dis- 

 location; and, secondly, as will appear more clearly later, we meas- 

 ure not to the original upper surface of the formation but merely 

 to a surface which has been established by erosion and upon which 

 the next higher formation of rocks rests. A similar estimate for 

 the thickness of these rocks is obtained by a measurement along 

 the Telegraph Canon road where the exposures in the road cuttings 

 are much more satisfactory and practically continuous. 



Gcomorpliic Features. — This belt of cherts and shales forms a 

 prominent feature not only in the geology but also in the geo- 

 morphy of the Berkeley Hills, and is traceable along the strike of 

 the rocks for many miles to the south. In this direction it forms 



