METAMORPHIG ROCKS. 293 



Pre-Cretaceous; but, even if this could be sliown, it is evident that tliey 

 must have sliared in the disturbance whicli accompanied the metamorphism 

 of tlie Knoxville beds at Jft. Diabhi to tlie nortliwest and at San Luis 

 Obispo to tlie south. 



An immense area of serpentine exists to the southwest of the New 

 Idria district, only an edge of which is included in the map. In thi.s, as 

 in some other respects, there is a close analogy between New Idria and the 

 area surrounding the Redington mine. Partially serpentinized rocks are 

 common, and the descriptions of the transitions from sandstone to serpen- 

 tine given in the chapter on the Knoxville district would apply without 

 change to occurrences observed in this district. Professor Whitney here 

 saw masses of serpentine consisting of radially arranged fibers in concentric 

 layers, which he also considered as showing the unquestionably inetamor- 

 phic origin of the mineral. 



Shales are also largely represented here among the metamorphic rocks, 

 and at Venado Peak argillaceous rocks of this description pass over by 

 gradual transitions into })hthanites. Some of the shales are so little altered 

 that fossils might have been preserved in them, but prolonged and earnest 

 search failed to reveal even a fragment of a shell. Similar rocks devoid of 

 fossils are provokingly frequent in the Coast Ranges. AiiceUa was evidently 

 a gregarious mollusk, and where specimens are found they are sometimes 

 very abundant; but, though these animals lived on both sand}' and niudd}- 

 bottoms, the localities in which they flourished .seem to have been few. 



The metamorphic rocks have been dislocated in the most violent man- 

 ner; indeed, the greater part of the mass was crushed at the time of the 

 metamorphism to a small rubble. This is the case throughout the entire 

 quicksilver belt and renders it utterly impossible to plot any sections of 

 the metamorphic strata. I had hoped, by taking very numerous dips in the 

 metamorphic area, to determine at least a prevailing system in the strati- 

 graphit'al arrangement of the mass, for such a system might very well 

 exist in spite of a large amount of comminution. Hundreds of dips were 

 accordingly measured all over the metamorphic area, but without any 

 result. No fortuitous distribution of directions could have been less ac- 

 cordant The position of the .serpentine belt, however, and observations 



