346 University of California Publications. [Geology 



The lower member of yellowish-brown beds has in places 

 layers of coarser angular granitic boulders. A typical layer 

 of the finer breccia, which occurs interbedded with the still finer 

 material which makes up the greater mass of this lower portion, 

 contains angular particles up to four inches in diameter of 

 granitic rock and red, white, and brown lavas, with a coarse, 

 gritty matrix of disaggregated fragments of quartz, feldspar, 

 and mica. Some of the lava particles are porphyritic, with 

 phenocrysts of orthoclase, mica, and quartz. Aside from this 

 rhyolite, there are lavas of other composition. 



The fossiliferous tuff member outcrops in the very middle 

 of the Barstow syncline where the topmost exposed layer, of a 

 light gray fine conglomerate, contains many isolated mammalian 

 bones. It is underlain here by the uppermost beds of the resist- 

 ant breccia member, the whole being faulted on both sides against 

 lower beds of the resistant breccia member. The chief exposures 

 of the fossiliferous member are found at the western end of 

 the outcrop of the Rosamond Series in the Barstow locality, 

 where the strata are folded into a syncline and displaced by 

 several strike faults. The general aspect of the beds may be 

 seen in the accompanying illustrations (pis. 36b and 37a). 



The organic remains found comprise ungulate and carniv- 

 orous mammals of plains-living cursorial types, several species 

 of fresh-water gasteropods, and a few fragments of silicified 

 and lignitized wood. 



Structure of the Rosamond Series in the Barstow Locality. — 

 The general structure in this locality is synclinal (pi. 37b) and 



N 10 



Fig. 1. North-south section through the. center of the minor axis of 

 the Barstow syncline. Not drawn to scale, but the length of the section 

 is approximately three miles. (1) Basin alluvium. (2) Basic andesite or 

 acid basalt. (3) Basal breccia member. (4) Fine ashy and shaly tuff 

 member. (5) Resistant breccia member. (6) Lowermost beds of fossil- 

 iferous tuff member. (7) Coarse granodiorite breccia, separated from 

 (8) by an unconformity. (8) Tuff-breccia member. (9) Granodiorite. 

 (10) Unconformable mantle of alluvial debris, dipping toward basin at 

 a uniform angle of 2°. 



