South Dakota School of Mines 37 



•outcrop, lying as it does at the base of the high escarpment, 

 passes quickly beneath younger formations and leaves only a 

 long narrow east-west band for observation. In and near the 

 Big Badlands the White and Cheyenne rivers and their tribu- 

 taries have cut deeply into and across the deposits, and there the 

 Chadron is exposed over a large territory. The beds are known 

 to underlie an extensive area of later formations within and be- 

 yond the Black Hills region and are well exposed in the valley 

 ■of North Platte river in western Nebraska, and of South Platte 

 river in northeastern Colorado. 



The formation is made up chiefly of a sandy clay of light 

 •greenish-gray color, with generally coarser sandy materials at 

 or near the bottom, including sometimes deposits of gravel or 

 -conglomerate several feet thick. The beds immediately above 

 the gravels are often of a yellowish, pinkish, reddish, or brown- 

 ish color, and Mr. Darton states that in northwestern Nebraska, 

 near Adelia, the red color is especially prominent. Aside from 

 this the color in the main is a greenish white, the green showing 

 as a very delicate tinge on weathered slopes, but a distinctly 

 deeper olive green in fresh exposures. The clays sometimes 

 partake of the nature of fullers' earth, but generally they con- 

 tain more or less sand. In most of the beds little cementing 

 material is present, although the clays are often quite compact. 

 Occasionally thin persistent bands of knotty, grayish limestone 

 or lime clay concretions are found. These weather to a chalky 

 white, and although seldom prominent individual bands may 

 sometimes be traced over considerable areas. Concerning the 

 sandy layers within the Big Badlands, Hatcher says : 



"The sandstones are never entirely continuous, and never 

 more than a few feet thick. They present every degree of com- 

 pactness, from loose beds of sand to the most solid sandstones. 

 . They are composed of quartz, feldspar, and mica, and are evi- 

 dently of granitic origin. When solidified the cementing sub- 

 stance is carbonate of lime. 



"The conglomerates, like the sandstones, are not constant, 

 are of very limited vertical • extent, never more than a few 

 feet thick. They are usually quite hard, being firmly held to- 

 gether by carbonate of lime. A section of the beds taken at any 

 point and showing the relative position and thickness of the 

 sandstones, clays and conglomerates is of little value, since these 

 vary much at different and quite adjacent localities."* 



♦Hatcher, J. B. The Titanotherium Beds. Am. Nat., Vol. 2 7, 

 1893, p,p. 204-221. 



