282 B. L. CLARK THE MEGAXOS GROUP 



detailed work has shown conclusively that here we ha^e an unconformity, 

 which was the result of crnstal movements of considerable magnitude. 



Briefly stated, it is the writer's conclusion, after studying the uncon- 

 formity mentioned above, together with fairly large collections of fossil 

 invertebrates from both above and below the line of contact, that we have 

 here the evidence of a structural break of more than local importance; 

 that the fauna found above the unconformity in beds associated with the 

 coal strata is t3rpically Tejon in aspect, while the fauna found below is 

 very different from that of the Tejon and comes from beds which ap- 

 parently belong to a distinct epoch of deposition, which has not previously 

 been recognized as such. Thus, formerly only two divisions of the Eocene 

 have been recognized in the region of Mount Diablo, the Martinez (Lower 

 Eocene) and the Tejon (Upper Eocene). The new division, described in 

 this paper, is a part of a series of beds which in this vicinity had previ- 

 ously been considered as being of Tejon age. It is the writer's belief that 

 beds belonging to this epoch of deposition are fairly widespread through- 

 out the State. In some localities in California they have been referred 

 to the Tejon, in others to the Martinez. The beds of the ncAvly recognized 

 epoch of deposition are designated in this paper as the Meganos Group. 



Previous Literature coxcerxixg the Eocexe of the Mount 

 Diablo Quads ax^gle 



It is surprising how little detailed work has been done on the Eocene 

 of the Mount Diablo quadrangle. Only a brief statement concerning this 

 portion of the section in this area was given in the early report of the 

 Geological Survey^ of California. The invertebrate fauna obtained from 

 beds above the coal, which is found in the vicinity of the old mining towns 

 of N"ortonville, Sommerville, and Stewartville, was referred to the Tejon 

 formation. This division was regarded at that time as a part of the 

 Upper Cretaceous (Cretaceous B). A few species were also found in 

 strata below the coal and were referred by Gabb, the paleontologist of the 

 survey, to a horizon intermediate between his Cretaceous A and B — that 

 is, the Martinez. Gabb- described a number of invertebrate species from 

 the beds immediately above the coal strata of this section. 



Turner,^ in a paper entitled the "Geology of Mount Diablo, California," 

 mentioned only very briefly the Eocene section of this area. He included 

 aU of the Eocene in the Tejon. Even up to this time (1891) the Eocene 



1 G. D. Wliitney : Kfport of progress and synopsis of tlio field-work from 1860-1864. 

 Geol. Surv. of California, vol. L 1865, pp. 2:\-:\'2. 



-W. M. Gabb: Paleontology of California, vols. 1 and 2. 1864-1869. 

 3 T. W. Turner : Bull. Geol. Soc. Am., vol. 2, 1891, p. 30,3. 



