SOUTH DAKOTA SCHOOL OF MINES 51 



profound elevation took place and a more active erosion 

 was inaugurated. The history here for a time is not well 

 disclosed but beginning with the Oligocene the conditions 

 become more evident. By that time the streams had be- 

 come sluggish and muddy and by meandering had developed 

 vast flood plains across which they shifted their lazy way 

 and deposited and redeposited the debris obtained from the 

 higher lands to the west- Following the Oligocene there was 

 further uplifting and erosion was correspondingly quick- 

 ened but the general history continued much as before. 



The climate for a considerable time in the history of 

 the deposition seems to have been moist to a marked degree. 

 Later a more arid condition prevailed and it was then that 

 transportation and deposition by wind became a feature of 

 importance. 



The great disturbances in the early part of the Tertiary 

 resulting in the pronounced doming of the Black Hills 

 region and the uplifting of the Eocky Mountain front were 

 accompanied and followed by profound igneous intrusion. 

 The White River region was influenced only in a general 

 way by the disturbances and no volcanic outbursts occurred 

 there. However some of the igneous material within the 

 Rockies and possibly some also in the northern Black Hills 

 connecting with the throats of vigorous volcanoes was from 

 time to time hurled high above the surface. Here favorable 

 winds, catching up the finely divided fragments, bore them 

 far to the eastward and there gently dropped them as thin 

 widespread ashen blankets to become an integral and in- 

 teresting portion of the general badland deposits. 



Subsequent to the Pleiocene the history of the White 

 River badlands is largely one of rapid weathering and 

 vigorous erosion. 



PHYSIOGRAPHIC DEVELOPMENT 



The White River badlands are the result of erosion, 

 controlled in part by climatic conditions and in part by the 

 stratigraphic and lithologic nature of the deposits. There 

 is a too frequent lack of appreciation of the work of com- 

 mon disintegrating and carrying agents and many an in- 

 dividual speculates upon the mighty upheavals and the 

 terrific volcanic forces that to him have produced the won- 

 derful ruggedness of the badlands, when the real work, so 



