South Dakota School of Mines 55 



may often be traced as greatly elongated lenses extending out 

 toward or even far beyond the center of the region which the 

 lake was supposed to have occupied. They are in general more 

 -abundant and coarser near the higher western border, but even 

 here the fine clays often greatly predominate. Ordinarily coarse 

 materials cannot be carried in quantity far within the borders 

 of standing water nor can large deposits of fine clays be depos- 

 ited near the margin. If the badland materials are lake deposits 

 they indicate frequent and abnormal changes in the lake level. 

 If they are river and lagoon deposits they indicate simply the 

 change of course of a stream meandering on its flood plain. The 

 trend of the coarser deposits is irregular, but there is a general 

 •convergence to the east and southeast so that in the area of the 

 Big Badlands southeast of the Black Hills the sandstones and 

 •conglomerates are finer and less frequent and are generally 

 wider and thicker than in the higher regions to the west and 

 northwest. Mr. Hatcher indicates this in an excellent way by 

 illustration from the Black Hills region. 



"Taking the Protoeeras sandstones as the most favorable 

 -example, owing to the greater extent to which they have been 

 -exposed by the subsequent erosion of the overlying sediments, 

 they are seen to extend as a series of narrow elongated lenses 

 from the Cheyenne and White River divide for several miles to 

 the southward of the last-mentioned stream, where they pass 

 Ibeneath more recent deposits. Throughout their entire extent 

 they exhibit frequent examples of cross-bedding, while the sands 

 become finer and the channels fewer in number and broader and 

 deeper as one goes southward toward and across the White 

 River. That they have been removed by erosion over consid- 

 erable areas lying between their present limits and the Black 

 Hills is evident. At the summit of the Cheyenne and White 

 River divide there are several of these sandstone lenses at ap- 

 proximately the same horizon. These bear many evidences of 

 having been in the channels of small streams or rivers pertain- 

 ing to a single drainage system, which had its source somewhere 

 in the present region of the Black Hills and was tributary to a 

 much larger river coming from the southwest. These sand- 

 stone lenses appear to converge and unite as one proceeds to- 

 ward W T hite River, like the tributaries of a stream."* 



Fourth, the lowest beds in their contact with the Cretaceous 

 and older rocks beneath show little or none of the depositional 



*Proc. Am. Phil. Soc, Vol. 41, 1902. pp. 122-123, 



