EUAS OF METAMOIII'IIISM. 187 



Similarity of litliological and physical character may, I think, be 

 given too much weight in geological diagnosis. I cannot conceive, for 

 example, that any degree of similarity between the rocks of California and 

 those of Switzerland should properly be considered as even tending to 

 prove the age of cither.^ I go further, and refuse to regard the metamor- 

 phism of the rocks of Butte County as necessarily contemporaneous with 

 that of the strata of Napa County, in spite of external similarity. On the 

 other hand, within properly limited areas, observations show tliat the same 

 fauna is associated with similar rocks; while, if it were impracticable to 

 draw any conclusions as to age except where the rock is fossiliferous or 

 where absolute continuity with fossiliferous localities uninterrupted by 

 fiiults could be proved, geological mapping would be impossible. In Cali- 

 fornia great use can be made of resemblances. Thus the Tejon strata of 

 Nev/ Idria are mostly heavy-bedded sandstones of a peculiarly light color, 

 which there distinguishes them from the tawny Chico sandstones. Both 

 are fossiliferous there, as also near Mt. Diablo, where, at a distance of 125 

 miles from New Idria, they preserve the same external characteristics. 

 Similarlv, the Knoxville beds of Knoxville and Mt. Diablo are externally 

 indistinguishable, and in their typical development, even when unaltered, 

 very different from most of the later rocks. 



Strata older than tlie Knoxville period may nevertheless be included 

 in the metamorphic series and may have undergone upheaval and meta- 

 morphism at the same date. Tiiere is also a possibility that older rocks not 

 only exist, but were metamor[)hosed before the deposition of the Knoxville, 

 so that the metamorphic areas in contact with the Wallala beds on the coast 

 and with the Chico strata at New Idria may conceivably be earlier than 

 the Knoxville, Even this hypothesis, which, in the absence of any evi- 

 dence tending to establish it, seems rather strained, would have no effect 

 on the principal conclusions drawn in this chapter, unless it could also be 



' The resemblance between the Miocene sandstones and the Molasse of Switzerland was advanced 

 by Mr. Jnles Marcon Hoc. cit.) as an evidence of the Tertiary age of the California rocks. That the 

 resemblance exists I can testify from observation. To me it indicates only that the California Miocene 

 and the Molasse were both deposited near the shore of land areas largely composed of Archiean rocks. 

 Mr. Marcon attribntes to ignorance of lithology my failure to appreciate it as an indication of age, and 

 he regrets that " a competent person has not been selected for the study of the Tertiarics of Califor- 

 nia" (American Geological Classification and Nomenclature, 1888, p. 52). I am very sorry that my 

 work produces so bad an impression on this veteran geologist. 



