WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 185 



tion. Hatcher was among the first to suggest the possibility of a 

 flood-plain of fluviatile origin instead of lacustrine, and evidence in 

 recent years has been accumulating which supports his hypothesis. 

 We are now able to recognize river-channel, fresh-water pond, sheet- 

 flood, and eolian elements in the series. In the present investigation 

 the writer has endeavored to draw from the lithologic characteristics 

 of the sediments the sources of the material, the methods of transpor- 

 tation and deposition, and the physiographic and climatic conditions 

 under which the White River faunas lived and evolved. 



II. Generalized Section of the Big Badlands. 



To make the stratigraphic relations of the various types of sedi- 

 ments more clear, a generalized columnar section of the Big Badlands 

 is presented in Figure i, C, correlated with a section of the Oreodon 

 beds from the Wall of the Badlands near Interior, about 40 miles to 

 the east, and with Wortman's 1893^ section, which has been generally 

 used as the standard section for the district and is now somewhat in 

 need of revision. The datum plane of correlation used is the top of 

 the lower zone of rusty nodules or " Red Layer," as defined below. 

 The stratigraphic elements of the White River series may be briefly 

 indicated as follows : 



I. Titanotherium Beds. — This zone consists of clay beds with 

 numerous large sandstone channels. Thin limestone lenses are fre- 

 quent throughout, but caliche zones are rare or absent. The subdivi- 

 sion of the Titanotherium beds into Upper, Middle, and Lower zones 

 in Wortman's section is based on the supposed zonal distribution of 

 titanotheres presenting different stages of horn development, as 

 worked out by Hatcher.^ A corresponding stratigraphic or lithologic 

 subdivision has not yet been recognized and it is doubtful whether 

 such will ever be possible. The thickness of the Titanotherium beds 

 in the sections measured by our expeditions varies from no to 132 

 feet, which is somewhat less than Wortman's figure of 180 feet, 

 though there are doubtless thicker sections than those measured by 

 the writer, for the Titanotherium beds vary greatly in thickness from 

 point to point, resting as they do on the very irregular erosion surface 



1 Am. Mus. Bull, 5, 1893, pp. 98-9. 

 '^ Am. Naturalist, March, 1893. 



