S2 The Badland Formations of the Black Hills (Region 



materials consist largely of conglomerates and gravels inter- 

 stratified with beds of sand and clay and occasionally impure 

 fullers earth, similar to that of the Titanotherium beds else- 

 where. The gravels and conglomerates contain many pebbles, 

 cobbles., and even boulders of considerable size derived from the 

 nearby older rocks, both sedimentary and igneous. The thick- 

 ness ranges up to 200 feet or more. Near Missouri Buttes, 

 west of the main Bear Lodge uplift, the material is usually a 

 fine, massive, creamy white calcareous clay with thin bands 

 or bunches of argillaceous limestone. The deposits here are 

 known to be twenty or thirty feet thick and there is some indi- 

 cation that the thickness at the very base of the buttes on the 

 northwest side may reach more than one hundred feet. All of 

 these Bear Lodge beds, evidently of Tertiary age, are provision- 

 ally classed as Oligocene, but it should be borne in mind that 

 not being continuously connected with deposits of known age 

 elsewhere, and no fossils having been found in them, their exact 

 horizon has not been certainly established. 



A little deposit not well known, but of much interest, found 

 near Lead City by Prof. Jenney about 1879 or I B8o, deserves 

 particular mention. This deposit does not outcrop at the sur- 

 face, but was found in a prospect shaft about one-half mile 

 southeast of Lead, at an elevation of 5,200 feet. The full extent 

 of the deposit could not be determined, but it lies in a deep basin 

 or channel eroded in the Algonkian slates, the latter outcropping 

 on all sides within a radius of half a mile. Fortunately three 

 nearly perfect skulls were found in the light-colored sandy clay 

 beds penetrated by the shaft and these were all determined by 

 Prof. Marsh as belonging to the species Oreodon culbertsoni. 

 At a later time remains were found in light colored clay exca- 

 vated in a tunnel not far from the shaft mentioned, and these' 

 were identified by F. A. Lucas as being the jawbone of a small 

 Mesohippus and the skull and jaw of Ischyromys typus. All 

 of these fossils indicate Oligocene beds similar to those of the 

 Big Badlands. 



The Tertiary deposits of the central and southern Hills 

 within and near the main uplift, have been studied mainly by 

 Mr. N. H. Darton. He identifies them as being of Oligocene 

 age and has summarized their general character as follows : 



"The deposits of the White River group (Oligocene) ex- 

 hibit considerable diversity of composition. The principal 

 material is a' porous, crumbling clay of pale flesh color when dry, 



