Vol. 4] "Weaver. — Palaeontology of the Martinez Group. 107 



The average thickness of the Martinez formation is about two 

 thousand feet. On the north side of the straits it is much less. 

 The section representing Martinez beds at Army Point railroad 

 station has a thickness of about eighteen hundred feet. The 

 Tejon above is nearly twelve hundred feet in thickness. In 

 southern Lake County the Eocene is much thicker than at Mar- 

 tinez. The Martinez appears to be represented by at least 

 twenty-five hundred feet of strata, and the Tejon by a volume 

 nearly as great. 



The Martinez beds are for the most part composed of thick 

 bedded sandstones containing large quantities of glaueonite, and 

 alternating with these are considerable beds of shale. The shales 

 are, however, not often seen, as they break down and do not 

 show on the surface. In general the sandstones prevail. They 

 vary somewhat in texture, and are sometimes cross-bedded. They 

 generally have a grayish color, in contrast to the red Tejon. 

 They are soft and break down easily. The variations in character 

 are such as to distinguish upper and lower sections of the forma- 

 tion. 



In the section at Army Point the lower two-thirds of the 

 series is composed entirely of soft, thick bedded, light colored 

 sandstones, while the upper third is made up of alternating beds 

 of sandstone, varying in thickness from a few inches to several 

 feet. They are more compact and more resistant to erosion than 

 the lower portion of the series. The upper third of this series is 

 fossiliferous. In the region about LoAver Lake the same condi- 

 tions prevail, except that the lower portion of the series is not 

 entirely composed of thick bedded sandstones, but contains alter- 

 nating layers of conglomerate, sandstone and shale, with a few 

 beds of clay. Glaueonite is very abundant. The fact that the 

 deposits are so largely glauconitic is evidence that they were 

 slowly deposited, and that the depth at which sedimentation took 

 place was moderate. 



Although there is no angular unconformity between the Chico 

 and Martinez or the Martinez and Tejon, yet there exists a well 

 marked faunal distinction. The fauna occurring in the Martinez 

 beds is distinct, both from that above and below. Only four 

 species range down into the Chico, and seven into the Tejon 



