188 WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 



with the algal limestone or chert band at the base of the Oreodon beds 

 and continuing upward from 29. to 43 feet (varying with the locality), 

 generally overlain by a more greenish clay or nodule-bearing horizon 

 much poorer in fossils than is the red layer. The red layer consists 

 of pinkish clay with rusty-brown caliche nodules in fairly regular 

 bands or irregularly distributed. In the Indian Creek sections usu- 

 ally from one to three nodule-bearing horizons are found in it, while 

 in parts of Corral Draw as many as ten levels of nodules may occur. 

 Elsewhere, as on Cain Creek, six miles east of Scenic, nodules are 

 locally absent over large areas, and the whole lower Oreodon series 

 consists of clays. As it is often impossible to tell at what part 

 of the lower zone the nodules are developed it has been found that 

 the upper layer discussed at greater length in the paragraph following 

 makes a better datum plane than the lower zone. Both of these zones 

 are very fossiliferous and the intervening clays from the upper nodu- 

 lar level to the base of the Oreodon beds have also produced many 

 important fossils. Professor Sinclair's paper on the " Turtle-Ore- 

 odon layer or ' red layer,' a Contribution to the Stratigraphy of the 

 White River Oligocene," which has just appeared, discusses primarily 

 the lower nodular zone, and reference may be made to it for further 

 details. 



The upper level of rusty nodules is six inches to one foot thick 

 and 80 feet, more or less, above the base of the Oreodon beds, or 40 

 to 60 feet above the top of the Lower nodular zone, the variation be- 

 ing due to changes in the thickness of the latter. As mentioned above, 

 this thin zone of nodules is so widely distributed over the area of the 

 Big Badlands that it makes the best datum plane in the whole series 

 of the Oreodon beds. It has been clearly recognized at points sep- 

 arated by 25 miles (Arnold's Ranch district, 12 miles southeast of 

 Scenic and Battle Creek Canyon, 30 miles southwest of Scenic) and 

 may be found to have a still wider distribution. 



The channels which cut the lower zone of rusty nodules are char- 

 acterized by the presence of the large aquatic rhinoceros, Metamyno- 

 don, and are therefore called Metamynodon sandstones. They cut 

 the Oreodon clays at various levels, but are most numerous between 

 the upper level of rusty nodules and the base of the Oreodon beds. 

 The stratigraphic position of six of these channels is shown in Fig. i, 



