WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 197 



portant elements in the formation of the caliche nodular levels. The 

 part which climate played in the color-banding of the Oreodon clays 

 has not yet been determined. 



The clays making up the nodular layers resemble the normal clays 

 very closely. They contain very finely divided silt from the decom- 

 position of the feldspars of the Black Hills, and small angular frag- 

 ments of quartz of a size smaller than the lower limit of rounding by 

 water. Flakes of brown mica are frequently seen. Fragments of 

 pumice and volcanic glass were recognized in all samples studied and 

 sometimes make up an appreciable per cent, of the total clastic mate- 

 rial. These were wind-carried and water-laid, as demonstrated by 

 the marked horizontal bedding of the nodular layers and the absence 

 of cross-bedding. 



Volcanic Ash Beds. 



The Leptauchenia beds consist largely of a well-consolidated white 

 fine-grained rock, which weathers with a marked vertical columnar 

 appearance, giving rise to sheer cliffs up to 200 feet high. This 

 seems to consist very largely of volcanic glass and pumice. The 

 pumice shows numerous capillary tubes in parallel arrangement which 

 are sometimes deformed by flowage (indicated by strain polarization). 

 There are also throughout the mass long hair-like needles with capil- 

 lary tubes in the center resembling superficially Pele's hair. With 

 the material of volcanic derivation there are also small fragments of 

 mineral matter of the texture of silts. The grains are not rounded 

 and are mostly too small to be rounded by water. Quartz and biotite 

 are the most common of these mineral fragments, and feldspars and 

 tourmalines were also recognized. A sample of the sand from the 

 White Ash layer, division (b) oi the beds as described above, which 

 contains about 90 per cent, glass or pumice fragments, was analyzed 

 by Professor A. H. Phillips, of Princeton University, with the fol- 

 lowing result : 



Si02 68.21 MgO 1. 13 



Ti02 0.32 K2O 441 



AInOs 10.97 NasO 313 



Fe.Os 2.89 P2O5 none 



FeO 0.13 H20>iio° S-Oi 



MnO 0.12 H20<iio° 305 



CaO 1.08 



100.45 



