202 WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 



diffuse cementation of the clays by colloidal silica in the vicinity of 

 chalcedony veins is occasionally noticed, rapidly wearing the edge off 

 the chisel used in the preparation of a specimen. 



In many places the basal titanotherium beds contain a series of 

 about 30 feet of clay of blue, lavender, and pink colors when fresh, 

 weathering to a limonite brown and hematite red. This clay is clearly 

 derived from a reworking of the Pierre shale material and even con- 

 tains Pierre shale fossils, as Baculites, Inoceramus, etc., which are 

 remanie or redeposited as first reported by Loomis.^* In places 

 where this series is absent, the silts or sands resting directly on the 

 Pierre shale are almost always colored a bright pink color, and on 

 examination the clay particles are seen to be strongly colored by the 

 red oxide of iron. 



The uniform presence of these iron-colored beds at the base of 

 the more or less pervious Titanotherium beds and directly above the 

 impervious Pierre shales is evidently a case of iron dissolved out of 

 the White River series and redeposited and concentrated at the limit 

 of downward circulation along the Pierre shale contact. 



VII. Conclusions Drawn from the Lithogenetic Evidence. 



From the evidence above presented one can draw a fairly good 

 picture of the physiographic conditions at the time of the deposition 

 of the White River beds. 



The country was very level, with a gradual slope away from the 

 Black Hills uplift, as evidenced by a slight initial southeast and 

 easterly dip of the beds. The Black Hills were probably still being 

 elevated, but already were sufficiently high and eroded to furnish 

 clastic material from the pre-Cambrian central core. 



Fairly sluggish streams meandered across the plain in shallow 

 channels and frequently spread widely out upon the plain when in 

 flood, depositing thin sheets of fine silt. Gradually increasing vol- 

 canic action in the Cordilleran region and perhaps in the northern 

 Black Hills furnished a growing supplement to the clastic material 

 from the hills, until in the Leptauchenia stage this source became 

 predominant. It is possible that the statements of Ransome, Schu- 

 chert, and others that the Oligocene represents a lull in the uplift and 



1* Science, Vol. 19, p. 254. 



