1912] Louderback: Pseudost ratification 27 



oxides of iron, which occasionally act as a cement of minor im- 

 portance. The chief role is played by opaline silica, as the 

 following tests indicate. 



Boiling or long standing in contact with concentrated hydro- 

 chloric acid turns the rock white and yields a ferruginous solu- 

 tion, accompanied by a slight superficial disintegration, a few 

 of the surface grains becoming disconnected from the mass and 

 settling to the bottom of the liquid. This disintegration action 

 is probably due to physical action, however, more than to the 

 freeing of grains by the solution of the cement. 



Boiling with hydrofluoric acid quickly disintegrates this mass ; 

 the grains fall apart and we have a clear sand as a residue. 



A similar boiling with potassium hydroxide solution com- 

 pletely disintegrates the rock into a ferruginous sand, if a yellow 

 or brown specimen be used, or, if it be one previously leached by 

 hydrochloric acid, a clean white sand results. 



A preparation of the sandstone cleared by hydrochloric acid 

 treatment shows distinctly under the microscope the amorphous 

 coating on and between many of the grains, and a crushing of 

 the grains between slide glasses disconnects some of the coating, 

 which shows the characteristics of opaline silica. 



The usually ochreous-colored coatings or separation laminae 

 that are often found where distinct separable layers or laminae 

 occur are in like manner determined to consist chiefly of 

 amorphous hydrous silica, colored with ferric hydroxides, and 

 including minute crystal fragments much smaller than the 

 average grain of sandstone, but evidently derived from it 

 mechanically. 



Sand pendants. — In a few places where the pseudostrata 

 were undermined by erosion or caving, small sand pendants and 

 mammillations were observed. These vary from slight just notice- 

 able protuberances up to pendants ten or more centimeters in 

 length. They may be roughly cylindrical, with various irregular 

 cross-sections, or, in the shorter ones, conical. 



These all have a central core of whitish, dull, opaque, porous 

 opal, similar to that of the white veinlets described above, and 

 usually showing a distinct concentric structure. The axial por- 

 tion of the concentric structure may be hollow. The outer 



