WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 187 



of the Pierre shale. The lower part of the Titanotherium beds con- 

 sists of blue and lavender clays made up entirely of reworked Pierre 

 shale and affording calcareous nodules with cone-in-cone structure 

 containing remanie Pierre shale fossils.^ This lower zone is dis- 

 cussed below in connection with ground water circulation. The 

 channels and limestone lenses are so numerous and, apparently, local 

 that their stratigraphic positions have not been indicated in the gen- 

 eralized section. 



2. Oreodon-Metamynodon Beds. — (a) Wall of the Badlands sec- 

 tion. The Oreodon or Middle White River series as generally de- 

 veloped consists essentially of clays with local limestone lenses, inter- 

 rupted by channels of coarse sandstone containing Metamynodon. 

 In the " Wall of the Badlands " section near Interior (Fig. i, A) they 

 are divided into: (a) lower zone of rusty nodules and clays; (&) 

 intermediate clay zone; (c) upper zone of nodules, more generally 

 greenish than rusty; {d) upper clay zone. (See Plate II, Fig. 2.) 

 The upper zone of nodules as here developed is absent in the Big 

 Badlands and the same term is there applied to a thin caliche zone 

 which is remarkably persistent over at least 200 square miles and may 

 extend farther yet, but does not occur, or has not been identified, in 

 the Interior section. 



{h) Big Badlands section (Fig. i, C). The base of the Oreodon 

 beds in the Big Badlands is defined by discontinuous thin bands or 

 lenses of silicified limestone or chert, ranging where present from two 

 inches to one foot thick. This division plane was mentioned bj 

 Darton* when he first defined the Chadron and Brule formations. 

 Where the limestones are absent the line of change in the weathering 

 between the Oreodon and Titanotherium beds is used for the contact 

 plane. The profiles developed on the Oreodon clays, as a rule, have 

 steep slopes and a more angular appearance, while the Titanotherium 

 beds weather with gentler slopes and more rounded surfaces. Plates 

 I. and II. bring out this contrast clearly. 



In the same area, the lower zone of rusty nodules, or so-called Tur- 



tle-Oreodon layer or " red layer," is defined by Sinclair^ as beginning 



3 Science, Vol. 19, p. 254, 1904. 



* Professional Paper, 32, U. S. G. S., p. 71. 



5 Prog, of the Amer. Philos. Soc, Vol. 40, 1921, pp. 457-466. 



