26 University of California Publications in Geology [Vol.7 



what different case. It shows a structure that a number of 

 men have taken to be an anticline, although the strata on both 

 sides have not the same appearance. On the left can be seen 

 the original stratification, on the right the pseudostratification. 

 The original stratification does not show itself to the eye in the 

 right hand part of the exposure even upon careful examination. 

 The more indurated pseudostratum appears to be cross-bedded. 

 The vertical parallel columnoid appearance of the layer under 

 the pseudo-crossbedded stratum is simply a channeling of the 

 surface of the uncemented sand, in part by dripping water, 

 chiefly by the action of falling sand particles dislodged by various 

 agents or blown by the wind. 



Cement of indurated layers. — Some of the indurated layers 

 are grayish white, others yellowish or brownish, and many show 

 in part a color banding, or irregular color blotches suggesting 

 concretionary deposition of cement. Small white or yellowish 

 veinlets of secondary deposition are occasionally found, and the 

 minor layers (and laminae) are often separated by coatings 

 which vary from one-half to three millimeters in thickness, and 

 may be brown or yellow or almost white. 



The first material examined was that of the white veinlets, as 

 they were presumably of the purest and most easily separable 

 secondary substance. It is dull opaque white and rather porous 

 and has the appearance often presented by secondary crusts of 

 calcium carbonate or dull sinter. 



This material is insoluble in hydrochloric acid, infusible 

 before the blowpipe where it sinters and gives up water, easily 

 soluble in hydrofluoric acid with little or no residue, and fuses 

 with soda to a clear glass. Under the microscope it is chiefly 

 amorphous with a showing here and there of anomalous double 

 refraction. These properties, combined with the refractive index, 

 determine it to be amorphous hydrous silica — opal. 



The general cement which has indurated pseudostrata and 

 pseudolaminae is essentially of the same nature in all of the 

 samples examined. The amount of carbonate material is very 

 slight or absent — practically negligible. The ochreous yellow or 

 brown rocks, the predominant types, owe their color to hydrous 



