JANTJAKY 8, 1915] 



SCIENCE 



53 



tiary the region was a lowland of gentle 

 relief cut down like the Sierra Nevada to 

 a peneplain, but later it was raised as per- 

 haps the great valley sank, and became a 

 prominent mountain group. 



THE COAST BANGE OF CALIFORNIA 



The coast range of California lacks the 

 wealth of precious metals found in the 

 Sierra Nevada, and for that reason until 

 recently it has not received so much atten- 

 tion from geologists. But the discovery of 

 oil and its development has greatly stimu- 

 lated research in that field. Only a few 

 districts have been surveyed in detail and 

 published, but much general reconnaissance 

 has been done. "What we know of the com- 

 position, structure and history of the range 

 has been admirably summarized by A. C. 

 Lawson and Ealph Arnold. Their sum- 

 maries have recently been discussed in a 

 most helpful critical way by Ransome, who 

 is himself familiar with portions of the 

 region. 



The coast range of California, according 

 to Lawson, extends from the Mexican 

 boundary to near the mouth of Klamath 

 River, with a length of about 720 miles, a 

 width ranging from 40 to 60 miles, and a 

 general trend of N. 30° W. 



At the northern end Lawson includes the 

 South Fork Mountain in the coast range, 

 but it seems to me that the great fault on 

 the western slope of South Fork Moun- 

 tain is the delimiting feature and keeps the 

 South Fork Mountain and Yallo Bally in 

 the Klamath group. 



The coast range is regarded by some, and 

 Ransome among them, as ending on the 

 south at the headwaters of Santa Maria 

 River where the Tehachapi range joins the 

 southern terminus of the coast range to the 

 Sierra Nevada. 



South of the Santa Maria River is a 

 group of ridges including the San Rafael, 



Santa Barbara, Santa Ynez, San Gabriel, 

 San Bernardino and other ranges, which, 

 although not strictly parallel, have a gen- 

 eral trend nearly east and west. These 

 ranges embrace the Los Angeles country 

 and have been most appropriately referred 

 to by Ransome as the Sierra de Los Angeles. 



The coast range throughout is composed 

 of a succession of parallel ridges which, 

 south from San Francisco to Santa Maria 

 River, trend about N. 43° W., while in the 

 northern portion of the range the trend is 

 N. 26° W., giving an average course of 

 N. 30° W. for this portion of the range. 

 Everywhere the course of the ridges is 

 more or less oblique to the coast line, which 

 is made up of a series of zigzags that Law- 

 son regards as probably due to faulting 

 parallel and transverse to the ridges, thus 

 cutting them oE on the shore and affording 

 excellent exposures of the composition and 

 structure of the range. 



The coast range of California is com- 

 posed chiefly of Mesozoic and Tertiary 

 rocks, with some that are older, as well as 

 a considerable portion that belong to the 

 Pleistocene. The oldest rocks are marble, 

 quartzite, mica and hornblende schists like 

 those of the Klamath Mountains and Sierra 

 Nevada. They appear mainly as inclu- 

 sions in the granitic rocks which form the 

 concealed basement of the coast range and 

 upon which was deposited unconformably 

 the Franciscan formation, a complex suc- 

 cession composed in the main of strongly 

 indurated sandstone with subordinate quan- 

 tities of shale and conglomerate, a consider- 

 able part of radiolarian chert and foramin- 

 iferal limestone. In the upper part of the 

 formation are interbedded lavas, and the 

 whole is intruded by peridotite and basalt. 

 A thick series (29,000 feet) of shales, sand- 

 stones and conglomerate of Cretaceous age 

 follow unconformably on the crushed Fran- 

 ciscan and are succeeded by an extensive 



