ERUPTIVES AND KLAMATH MOUNTAIN ROCKS. 89 



these occurrences have resulted from the metaniorphism of a crystalHne 

 rock. One strong argument in favor of its eruptive origin is the marked 

 contrast between the small dike-like masses and the enclosing rock, which 

 is often only slightly metamorphosed. In the San Onofre range, in San 

 Diego county, is a breccia containing many fragments of glaucopliane- 

 schist, among which can be noted transitions to a massive crystalline 

 rock. 



Alteration an Obstacle to Identification. — Thegreat numbers of intrusives 

 in the pre-Cretaceous series, both dikes and surface flows, have been 

 studied only in places. They are generally much decomposed, so much 

 so that it is often difficult in the field to distinguish them from the sedi- 

 mentary rocks. In many cases the original minerals have entirely dis- 

 a])peared, and their places have been taken by secondary ones. They 

 have, of course, participated in the distortion to which the ])re-Cretaceous 

 series has been subjected. The most of them certainly antedate the 

 Cretaceous. 



ROCKS OF THE KLAMATH MOUNTAINS. 



Characteristics and Relation to Rocks of other Localities. — All the evidence 

 thus far gathered tends to show that no sharp lines can be drawn on 

 lithologic grounds between the older rocks of the central Coast ranges 

 and those ranges included under the term Klamath mountains. Strati- 

 graphically those of the Klamath mountains are older. The silicious 

 metaniorphism of the central Coast ranges has been noted in many places 

 in Trinity county and southern Siskiyou. There was also noted as 

 accompanying it a disturbed and broken condition of the strata. These 

 features were not prominent east of the north and south line of the 

 Trinity mountains. 



In a general way there might be two divisions made of the Klamath 

 mountains — the eastern portion, in which the rocks resemble those of 

 the Sierra Nevada and are comparatively regular in strike and dip, and 

 the western, in which the rocks resemble those of the Coast ranges and 

 luive been mashed together rather than folded. 



Tlie Nonconformity beneath the Knoxville. — The nonconformity of the 

 rocks of the Klamath mountains beneath the Shasta-Chico series is too 

 well substantiated by the work of Mr Diller to need any further proofs. 

 He says : * 



"The same unconfonnity extends southwestward by way of Redding, Horse- 

 town and Ono alonj.' the western side of the Sacramento valley into Tehama county, 

 California." 



That unconformity traced by Mr Diller, with all its marked features, 



* Bull. Geol. Sue. Am., vol. iv, p. 221. 



