350 G. F. Becker — Metamorphic Rocks of California. 



ranges are very much alike whatever their age, the Tejon 

 (Eocene) beds however are of a much lighter color than the 

 Chico (late Cretaceous) or the Miocene rocks. The Chico 

 again is usually more indurated than the Miocene. While the 

 Knoxville (Neocomian) sandstones, where unaltered, closely 

 resemble those of later periods, no case is known in which 

 unaltered Knoxville beds are not intimately associated with 

 greatly disturbed and metamorphosed rocks of the same age, 

 so that there is no difficulty in discrimination when once it is 

 established, that the epoch of violent upheaval and metamor- 

 phism followed soon after the close of the Knoxville. This 

 fact I have already proved.* 



Field study showed that the Coast Ranges are probably 

 everywhere underlain by granite. The microscopic examin- 

 ations have given this inference unexpectedly strong confirma- 

 tion, for though on structural grounds it appears certain that 

 a portion of the later sandstones were formed at the expense of 

 earlier arenaceous beds, they all exhibit unmistakable evidence 

 of granitic origin. They are thus so similar that they may be 

 discussed together lithologically. The microscope shows that 

 the main constituents are quartz fragments with abundant 

 fluid inclusions, and in other respects entirely resembling the 

 quartzes of the underlying granite, orthoclase and the same 

 plagioclases found in the granite. Biotite in foils deformed by 

 the pressure of the adjoining grains is not infrequent, and 

 decomposition products traceable to this mineral are common. 

 Clastic grains of hornblende exactly like that in the granite 

 are tolerably common. Apatite, titanite, zircon, tourmaline, 

 rutile and epidote, also occur. The only clastic constituent 

 not directly referable to the granite consists of black scales, 

 which are sparsely disseminated in some localities, and which 

 resemble in some cases fragments of carbonaceous shale, while 

 in others they suggest plant remains. The proportion of 

 quartz in the sandstones is as a matter of course greater than 

 in the granite. The grains are commonly rounded like ordinary 

 beach sand, but are sometimes extremely sharp. The cement 

 is largely calcite. The sandstones are subject to the ordinary 

 decomposition known as weathering, by which the ferromag- 

 nesian silicates are in part converted to chlorite and in part to 

 a ferruginous cement. 



Sharply defined limits cannot be drawn between the various 

 metamorphosed rocks of the Coast Ranges; they pass over into 

 one another by degrees. For purposes of description, how- 

 ever, it is desirable to consider certain types as distinct. The 

 divisions which appear to satisfy best both their field occur- 

 rence and their microscopical character are as follows : Par- 



* Bull. U. S. Geol. Survey, No. 19. 



