54 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



shales. In Tehama County, the shales are said to dip 

 steeply away from a mass of serpentine at their base, which 

 has evidently been a disturbing agent. H. W. Fairbanks 

 has repeatedly spoken of serpentine cutting the Knoxville 

 shales in the southern Coast Ranges, as near San Luis 

 Obispo and other neighboring points. Dr. J. P. Smith 

 states that he has observed serpentine intrusive in the 

 Aucc/Za-heanng shales on the Whitney ranch, some miles 

 southwest of Gilro}^ Santa Clara County. 



Exactly similar relations are found in connection with 

 strata of the same age at Riddles, Oregon, where a belt of 

 Cretaceous rocks five miles in length is bordered on the 

 west by serpentine and peridotite. It is thus seen that 

 from San Luis Obispo County northward far into Oregon 

 the Knoxville is everywhere penetrated and disturbed by 

 dikes and masses of serpentine and accompanying perido- 

 tites; and it is exactly from this Coast Range region in 

 which serpentine is common that the Horsetown strata are 

 entirely absent. (Turner, 1891, map opposite p. 383.) 



At many places in this same region Chico beds are also 

 found in contact with the serpentine; but it has not been 

 stated that they have ever shown evidences of having 

 been even slightly altered or disturbed by the peridotites. 

 Indeed, quite the contrary is usually the case, as Fairbanks 

 has already stated. 



4. The Chico Overlap. 



This serpentine intruded country does not form a narrow 

 strip bordering the basin of the Great Valley, but it extends 

 from that basin westward, frequently to the ocean. It is 

 many miles in width, and extends from the southern portion 

 of California northward far into Oregon. In the latitude 

 of southern Mendocino County this intrusion has thrown 

 the Horsetown entirely out of the series in the Coast 

 Ranges west of the Great Valley, while Chico strata are 

 found upon both sides of the peridotite belt, at Wallala, 

 upon the seaboard and in the Sacramento Valley. The 

 position of these Wallala beds, which have been classed as 



