SOUTH DAKOTA SCHOOL OF MINES 39 



of fullers' earth, but generally they contain more or less 

 sand. In most of the beds little cementing material is pres- 

 ent, although the clays are often quite compact. Occasion- 

 ally 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 de- 

 gree of compactness, from loose beds of sand to the most 

 solid sandstones. They are composed of quartz, feldspar, 

 and mica, and are evidently of granitic origin. When soli- 

 dified the cementing substance is carbonate of lime. 



"The conglomerates, like the sandstones, are not con- 

 stant, are of very limited vertical extent, never more than a 

 few feet thick. They are usually quite hard, being firmly 

 held together 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."* 



The total thickness of the formation within the Big 

 Badlands is approximately 180 feet. Hatcher and others 

 subdivide the formation in that locality as follows : Lower, 

 50 feet; Middle, 100 feet; Upper, 30 feet. The sub-divisions 

 are based on the nature of the Titanotheres found at the 

 various horizons. Along Pine Ridge the formation is much 

 thinner. Darton gives it as approximately 30 to 60 feet. 



THE BRULE FORMATION 



The Brule formation, like the underlying Chadron for- 

 mation, outcrops chiefly in the Big Badlands and along the 

 northward facing escarpment of Pine Ridge. As now com- 

 monly understood, it may for the Big Badlands be best con- 

 sidered under its two subdivisions, namely, the Oreodon 

 Beds, constituting the lower part, and the Protoceras Beds, 

 constituting the upper part. 



♦Hatcher, J. B. The Titanotherium Beds. Am. Nat., Vol. 27, 

 1893, pp. 204-221. 



