AGE AND KELATIOXS OF COAST RANGES. 77 



Dr Becker, while lie has held that the granite and crystalline lime- 

 stone may he older, has said that the upheaval hetween the Knoxville 

 and Chico was the first distinctly traceable movement in the Coast ranges ; 

 and, farther i'*^ 



"The earliest dcternnnal)lc p(3rtion of the Coast ranges must then he considered 

 as due to the same disturl)ance which added the gold belt proper to the Sierra 

 Nevada." 



H. W. Turner,t in a recent article reviewing the proposition advanced 

 by the writer for the pre-Cretaceous age of the metamorphic rocks of the 

 Coast ranges, offers the following hypotheses : 



"1. That the granite, gneiss and metamorphic limestone of the Gavilan range 

 and similar area elsewhere in the Coast ranges are Paleozoic and probably Car- 

 boniferous in age. 



"2. That the phthanites, hardened sandstones and diabase are earlier than the 

 Knoxville beds. 



"3. That the serpentine, gabbro, and perhaps the glaucophane-schist, which is 

 frequently associated with the serpentine, are post-Knoxville in age." 



AGE OF COAST RAXGES AS COMPARED WITH THAT OF THE SIERRA NEVADA. 



As compared with the Sierra Nevada, the Coast ranges have univer- 

 sally been considered the younger. Dr Trask, however, regarded the 

 granite as of thesame age as that of the Sierra Nevada. The references 

 in geologic literature all give emphasis to the views of a great age for the 

 Sierra Nevada and a comparatively recent date for the upheaval of the 

 Coast ranges. Nearl}^ all investigators have recognized the presence of 

 granitic rocks ; yet they have generally been considered of small extent 

 and to have played an insignificant part in the development of the sys- 

 tem. A great age for the granitic rocks has been postulated by some, 

 while others have considered them younger than the Miocene. This 

 almost universal opinion as to the age of the Coast ranges must be based 

 on some prominent geologic fact, and that undoubtedly is the great de- 

 velopment of the middle Tertiary in the region south of San Francisco; 

 and while Cretaceous as well as older uncrystalline rocks are present, 

 they have not been distinguished from each other, and by some not even 

 separated from the Tertiary. 



PHYSICAL AND GEOLOGIC RELATION TO THE SIERRA NEVADA. 



The chief difficulty in making an exact definition of the Coast ranges 

 lies in the fact of the intimate geologic and structural relation to otlier 

 mountain ranges, both north and south. Both Trask and Marcou in- 



* Quicksilver Deposits of the Pticific Slope, p. 211. 

 t American Geologist, vol. xi. p. 324. 



