40 The Badland Formations of the Black Hills Region 



clearly differentiated only in the Big Badlands. Elsewhere the 

 lilhologic conditions do not generally serve to indicate their 

 presence, hence if they occur outside of the Big Badlands, the de- 

 termination of their areal distribution must in a large measure 

 await the study of the paleontologist. The total thickness of 

 the beds, including with them the Leptauchenia clays, is approx- 

 imately 150 to 175 feet. 



THE ARIKAREE FORMATION 



The Arikaree formation, first designated as such by Darton, 

 receives its name from the Arikaree Indians, who were at one 

 time identified with the area in which it is most largely de- 

 veloped. Its greatest development is in Pine Ridge and south- 

 ward. It lies uncomformably on the Brule and in places over- 

 laps the margins of that formation. 



The Arikaree is largely a soft sandstone, varying in color 

 from white to light gray. Calcareous concretions occur through- 

 out the formation in abundance. They are usually of cylindrical 

 form and are often more or less connected into irregular sheets. 

 It is to this feature especially that the Pine Ridge escarpment 

 and other prominent topographic features of that part of the 

 country are due. For the manner of development of these con- 

 cretionary forms, the reader is referred to the discussion of con- 

 cretions and sand-calcite crystals elsewhere in this paper. 



The Arikaree has not been carefully defined for all the area 

 where it has been found, and owing to the variable nature of the 

 formation in different localities a number of terms in this con- 

 nection need to be referred to and defined. Darton in his studies 

 iv western Nebraska some years ago, differentiated certain sands 

 and sandstones, lying below the typical Arikaree deposits, as 

 the Gering formation. These* sands and sandstones are not very 

 abundantly developed within the area covered by the Black Hills 

 map, but are of importance farther south. More recent study 

 seems to show that much of this material is little more than 

 non-continuous river sandstones and conglomerates that traverse 

 the lower Arikaree clays and occupy in places irregular chan- 

 nels in the partly eroded upper Brule formation, the relation to 

 the Arikaree clays being in such places much as that of the 

 Titanotherium, Metamynodon and Protoceras sandstones to the 

 clays in which they severally occur. The general tendency at 

 present seems to be to consider them as a special depositional 

 phase of the lower part of the Arikaree. According to Hatcher, 

 the Arikaree in Sioux County, Nebraska, and Converse County, 



