352 



University of California Publications. 



| Geology 



beds are limestone. The thin paper shales, of light green, gray, 

 and white shades, contain nodules and thin layers of what seems 

 to be fine-grained limestone. Some clayey concretions are also 

 found in these shales, and interspersed are interbedded layers 

 of fibrous gypsum and borax minerals, principally colemanite 

 (CaoBgO^ -|- 5 ILO) ; and these minerals also form nodules and 

 lenses. Some of the rock superficially resembles a fine conglom- 

 erate, but it is perhaps more properly regarded as tuffaceous or 

 oolitic. Cross-bedding is frequent in the thicker and harder 

 layers. 



The view is entertained that the Escondido Series mapped 

 by Hershey north of the Mohave River, between Barstow and 

 Daggett, is a portion of the Borate member. There is much 

 lithologic resemblance in the two exposures, which are separated 

 only by a narrow alluviated basin. The strata in both localities 

 rest upon rhyolite and have been subjected to the same amount 

 of deformation and erosion. Northeast of Barstow the beds 

 mapped as Escondido lie upon granite and micaceous schist. 

 The basal beds of the series are composed of heavy breccia and 

 of rather fine arkoses of granite and schist, and of medium fine- 

 grained sandstone. The beds are brown, red, green, and gray 

 in color and dip in a southerly direction. They are cross-bedded. 

 The quartz, granite, schist, and lava boulders at the base are 

 angular to subangular in contour, ranging in size up to a foot 

 or larger. The matrix is mainly made up of disaggregated 

 crystals and of small pieces of lava, although all of the material 

 of the boulders are represented. The lava is acidic, and the 

 schist beneath the contact is very much altered and weathered. 

 The beds are folded into anticlines and synclines. 



North of the Mohave flood-plain, near the road on the north 

 side of the river, limestone and chert beds dip southward. The 

 beds are brown, red, and gray in color and contain veins, cavities, 

 and incrustations of calcite, quartz, and other minerals. Strata 

 of this nature locally outcrop in the Mohave Valley between 

 Barstow and Daggett. 



Structure of the Rosamond Series in the Calico Mountains. — 

 The incompetent strata of the Borate member, or those which 

 bend easily under stress or strain, have been intensely folded 



