South Dakota School of Mines 2 7 



•steps taken in building up the classification. The table given in- 

 dicates in concise form the results of the combined effort on the 

 part of many investigators, and while some adjustment must still 

 be made, particularly in the Miocene, it may perhaps in the main 

 be taken as final. I have endeavored in this manner to put the 

 chief facts in convenient analytical form for the student and the 

 layman and at the same time have endeavored to see that brevity 

 has not interfered in any material way with the rights or prefer- 

 ence of any one, who by his careful study may have been instru- 

 mental in developing the separation and correlation of the forma- 

 tions as we now know them. Differentiation of the formations 

 has been confined chiefly to the country southeast, south and 

 southwest of the main Black Hills uplift. Farther north the de- 

 posits have been mostly eroded away, fossils are less abundant, 

 and little determinative work has been possible. 



The v general stratigraphic relation of the formations to the 

 closely related deposits found elsewhere in the west, is well 

 shown in Figure 5 from Osborn's book, "Evolution of Mam- 

 malian Molar Teeth," 1907. 



NATURE OF THE DEPOSITS 



The geology of the northern part of the area represented on 

 the accompanying map has not been fully studied, but recon- 

 naissance trips by various geologists have served' to indicate the 

 general features. The fullest and most detailed account of the 

 conditions in northwestern South Dakota is given by Prof. 

 Todd, who spent two months in the region in 1895. 



The badland formations in this part of the state and in the 

 more immediate localities across the line in Montana and North 

 Dakota are restricted to the , higher buttes. Those in South 

 Dakota known to be capped by Tertiary materials are : Short 

 Pine Hills, Cave Hills, Slim Buttes, Haystack Butte, Castle 

 Pock Butte, and Deers Ears Butte. It is possible that future 

 study will disclose others. 



The following observations are among those made by Prof. 

 Todd: Short Pine Hills show approximately 285 feet of the 

 Tertiary, the upper 260 feet being a fine grained white sand- 

 stone, with many small concretions. This is underlain by a 

 stratum twenty-five feet thick, mostly concealed, but apparently 

 a soft clay. Deers Ears, approximately thirty miles to the 

 southeast, retains only six or eight feet, and this is a coarse 

 gray conglomerate. About the same distance to the northeast 



