200 WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 



blende, minerals which were not abundant in the ordinary channel 

 sands. The garnets contained in the sand are also well rounded. 

 This bed, which is apparently thin and local, evidently represents dune 

 sand deposition. The sands rounded in stream channels have bright 

 surfaces, while those rounded by wind action generally are dull or 

 show etched or pitted surfaces. The sands of the base of the Lep- 

 tauchenia bed in the Sheep Mountain section, mentioned above, show 

 dull and pitted surfaces, confirming their eolian origin. 



Another excellent example of round-grained dune sand of later 

 age than White River is found in the sand grains of the sand-calcite 

 at Rattlesnake Butte, Washington County. The crystals contain 

 about 37 per cent, calcite, crystallizing as perfect scalenohedrons, and 

 contain perfectly rounded sand grains down to the finest present. 

 The quartz approaches spherical shape, the feldspars are generally 

 larger grains and not quite so well rounded. The pink garnets are 

 round. The green hornblende grains are nearly all elliptical in out- 

 line, prisms with the corners rounded. Zircon appears as fine yellow 

 grains, about one fourth the size of the average quartzes. Round 

 fragments of volcanic glass have also been found in this sand. The 

 surfaces of the grains have a dull or ground-glass appearance due to 

 wind abrasion. 



By a study of part of the White River in eastern Colorado, Mat- 

 thew^- came to the conclusion that the White River was largely of 

 eolian origin. A sample of silt from the Oreodon beds of Lewis 

 Creek, Colorado, in the area investigated by Matthew, was examined 

 by the writer and was found to consist largely of fine dust with 

 much volcanic material (pumice and glass) and some of the quartz 

 grains well rounded. It was evidently mainly of eolian origin. Mat- 

 thew points out that in much of the fossil material from the White 

 River of northeastern Colorado the "hollows in the bones (such as 

 the cellular hollows in the skull . . ., the tympanic bullae . , ., etc.) 

 are still empty, never having been filled by mud or crushed in." ^^ 

 He points out that this could not happen if the bones were fossilized 

 in such a body of water as a lake, as the weight of water and overlying 

 sediment would either fill in the cavity with mud or crush the skull. 



12 Matthew, Am. Naturalist, Vol. 33, 1899, pp. 403-408. 



13 Matthew, Am. Mus. of Nat. Hist. Memoirs, Vol. I., p. 365. 



