LXII INTRODUCTORY REMARKS. 



the Upper Missouri country, in coi sequence of the great numbers and fine 

 state of preservation of its Mammalian and Chelonian remains. For some 

 years previous, reports were brought by parties connected with the American 

 Fur Company of the existence of a remarkably rugged country, known as 

 the Mauvaises Terres, or Bad Lands, on White River, near the Black Hills, 

 in what is now known as the Territory of Dakota ; and it was said that 

 many bones of unknown animals occurred there. The first published account 

 of any of these remains, however, was given by Dr. Prout, of Saint Louis, in 

 the American Journal of Science in 1847. Since that time, very extensive 

 collections altogether have been brought from there by Mr. Culbertson, Dr. 

 Evans, and later by Dr. Hayden and the writer, who visited these localities 

 in 1853 on an expedition sent by Professor Hall. Dr. Hayden has also 

 since the latter date visited the Bad Lands on his own account, and brought 

 back extensive collections of vertebrate remains. All of these collections 

 have been ably investigated and described by Dr. Leidy, partly in Dr. Owen's 

 Report on the United States Geological Survey of Wisconsin, Iowa, and Min- 

 nesota, published by the United States Government in 1852, and partly in 

 a quarto memoir published by the Smithsonian Institution in 1853, entitled 

 "The Ancient Fauna of Nebraska"; and also in various smaller papers. • Dr. 

 Leidy refers this group to the age of the Miocene of Europe. 



The area occupied by the Bad Lands proper is not very extensive, 

 being probably not more than sixty miles in length by twenty-five to thirty 

 in breadth, ranging nearly in a northeasterly and southwesterly direction. 

 The maximum thickness of the formation has been estimated at about 1,000 

 feet. The material composing the beds mainly consists of indurated clays 

 and grits, subject to soften when wet ; and the whole -has been weathered 

 into extraordinary naked hills and castellated peaks, so as to present very 

 remarkable scenery. These beds contrast strongly with those of the Fort 

 Union group, being generally whitish or light drab in color, and entirely 

 destitute of lignite, as well as usually of carbonaceous matter in any form. 

 Where seen resting upon the Fort Union group, they are found to be uncon- 

 formable to the same. The following section, taken in descending order by 

 Dr. Hayden, will serve to convey a general idea of the nature of these 

 deposits, and the positions of some of the leading fossils in the same at the 

 typical localities 



