c,8 The Badland Formations of the Black Hills Region 



The total thickness of the formation within the Big Bad- 

 lands is approximately 180 feet. Hatcher and others subdivide 

 the formation in that locality as follows: Lower, 50 feet; Mid- 

 dle, 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 forma- 

 tion, outcrops chiefly in the Big Badlands and along the north- 

 ward facing escarpment of Pine Ridge. As now commonly un- 

 derstood, it may for the Big Badlands be best considered under 

 its two subdivisions, namely, the Oreodon Beds, constituting the 

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



The Oreodon Beds. The Oreodon beds, so named because 

 of the abundant remains of Oreodons found in them, are made 

 up chiefly of massive arenaceous clays, lenticular sandstones, and 

 thin layers of nodules. A particular feature of the beds is the 

 color banding. The general color is a gray or faint yellow, but 

 this is often much obliterated by horizontal bands showing some 

 shade of pink, red or brown. They are present in greater or less- 

 prominence over large areas, particularly in the Big Badlands,, 

 and in places become a rather striking feature. Their thickness- 

 varies from an inch or less to occasionally several feet. Some- 

 times they are repeated in rapid succession without great con- 

 trasts in color. More often a few bands stand out with 

 prominence, especially if moistened by recent rains and, seen 

 from some commanding point, may be traced for long distances. 



The sandstones being of a lenticular nature are often absent 

 or of little consequence, but in many localities they reach con- 

 siderable thicknesses. One series near the middle of the bed 

 is of particular importance. It reaches in the Big Badlands a 

 thickness of twenty feet or more, and according to Wormian, 

 covers an area approximately twelve miles in length and a mile 

 or a mile and a half in width. It contains fossil remains in 

 abundance of the ancestral rhinoceros, Metamynodon, hence is 

 commonly known as the Metamynodon sandstone. 



Of the nodular layers, one just above the Metamynodon* 

 sandstone is of paramount importance. For description of this 

 I quote from Mr. Wortman : "There is one layer found in the 

 Oreodon Beds which is highly characteristic and is perhaps more 

 constant and widely distributed than any other single stratum 



