TKUTIAUIES. . J 35 



establishing the Cretaceous age of these rocks, though indecisive of the 

 portion of tliis formation to whicli they should he referred. The above 

 comprise all the instances detinitelv known in which the age of the silicifled 

 and serpentinized meramorphic rocks is directly determinable by paleonto- 

 logical evidence. Mr. Gabb also found AiiceUa along Puta Creek, Lake 

 County. This stream runs through a region chiefly occupied by highly 

 metamorphosed rocks, and, were the exact locality known, it would probably 

 fiuMiish another instance of transition. 



Besides the rocks referred to above, the Coast Ranges include others 

 wliich have been subjected to more or less complete alteration.- Thus, 

 along the shore of Carmelo Bay, Miocene schists have been locally chancred 

 to a cindery mass, as if by the action of heat ; but these rocks bear no 

 resemblance to the serpentinized and silicifled material just described. 

 More or less complete induration is common, even in the most recent rocks 

 of the coast, and oxidation and impregnations with calcite and gypsum 

 occur abundantly in rocks of all ages. In the Arroyo de la Penitencia, 

 above Alum Rock, near San Jose, there is also an area of altered Miocene 

 sandstones referred to by Professor Whitney.^ The rock here is much 

 indurated and is full of veins of calcite. No objection can be made to its 

 description as metamorphic by Professor Whitney ; but it is not serpentin- 

 ized and silicifled and does not partake of the characteristics so strongly 

 marked in the highly metamorphosed rocks of the Knoxville group. On 

 the other hand, there are plenty of rocks of this group no more altered than 

 the Miocene of the Arro}'0 de la Penitencia and some areas still less modi- 

 fied. The Tertiary of the Arroyo has been subjected to influences seem- 

 ingly identical with those which have aff"ected portions of the Knoxville 

 beds, but not to those which have produced in the older strata the charac- 

 teristic serpentinization and siliciflcation. 



Professor Whitney also refers twice" to altered beds in the San Fran- 

 cisquito Pass, which, indeed, is to the south of the Coast Ranges as usually 

 deflned. In the first reference he states that "this belt of metamorphic is 

 referred by us to the Cretaceous formation from general analogy rather 



' Geol. Survey California, Geology, vol. 1, p. 51. 



'2 Ibid., p. 195; The Auriferous Gravels: Mem. Mus. Comp. ZoiJl. Harvard Coll., vol. ti, Xo. 1, lrt80> 

 p. If. 



