G. F. Becker — Metamorphic Hocks of California. 349 



epoch of the metamorphisra is also clearly proved to be within 

 the earlier portion of the Cretaceous period and probably about 

 the close of the Neocomian.* The most interesting alteration 

 processes to which the sandstones have been subjected are 

 closely similar to those which characterize metamorphic areas 

 elsewhere, consisting chiefly in the metasomatic recrystallization 

 of the sediments to noncrystalline feldspathic rouks carrying 

 ferromagnesian silicates, and in the formation of vast quantities 

 of serpentine. It is also clear on structural and chemical 

 grounds that solutions rising from the underyling shattered 

 granite cooperated in the metamorphism. 



Thus the origin of the sedimentary rocks, their mineralogical 

 character in an unaltered state, their age, the approximate 

 epoch at which they were metamorphosed, and the general 

 character of the conditions of metamorphism, are all known, 

 while the exposures illustrating the' comparatively few more 

 important problems are numberless. I am not aware that 

 metamorphism has ever been studied under conditions so 

 favorable for elucidation. It is unnecessary to say that the 

 material is not exhausted by a single investigation and that 

 much must remain to be done, especially from a chemical 

 standpoint, in the present state of knowledge. It is believed, 

 however, that a solid basis has been obtained for future inquiry, 

 and that the results reached are sufficiently definite to form 

 an important aid in the study of metamorphic areas elsewhere, 

 which present less favorable opportunities for complete investi- 

 gation. f 



Excepting the light cream-colored schists of Miocene age 

 which occupy a narrow strip along the coast of California from 

 the neighborhood of Santa Cruz southward, the rocks of the 

 Coast Ranges where unaltered are mainly sandstones of Cre- 

 taceous and Tertiary age. Sandstones often occur here in 

 practically uninterrupted series of beds many thousands of feet 

 in thickness. The mechanical condition of the accumulation 

 of such vast quantities of sand forms a problem which has not 

 been solved for this area, nor, so far as I am aware, for any 

 similar area elsewhere. The unaltered sandstones of the Coast 



* Notes on the stratigraphy of California by G-. F. Becker, Bull. U. S. Geol. 

 Survey No. 19. Xotes on the Mesozoicand Cenozoic Paleontology of California 

 by C. A. White, Bull. U. S. Geol. Survey No. 15. 



\ As it is nearly or quite impossible for any investigator to free himself wholly 

 from preconceptions, it may not be superfluous to state that in beginning the study 

 of the quicksilver belt I entertained no opinions as to the character or origin of the 

 crystalline and serpentinoid rocks. I was prepared to find the former either 

 eruptive or unaltered crystalline precipitates and entertained no prejudice against 

 regarding the serpentine either as an original deposit or as a product of the altera- 

 tion of olivine. Though I have reached different conclusions as to the occurrences 

 of this area, I do not in the least doubt that every mineral has been produced 

 somewhere in nature by every possible method. 



