FORMATIONS OF 



T II E 



MAUVAISES TEHEES. 



195 



afforded to him by the Fur Company, both in passing rapidly from point to point, 

 on the river, and afterwards in procuring the means of land travel, which he other- 

 wise could not have obtained, and by which he finally reached that most curious 

 unexplored region, the country of the " Bad Lands" (Mauvaises Terres), lying high 

 up on White River ; a locality which seemed likely, above all others, to furnish 

 satisfactory information regarding the precise character and age of the tertiary 

 deposits of the Upper Missouri country. 



The following is the substance of Mr. Evans's Report : 



After having first struck, near the mouth of the Ayoway, the cretaceous forma- 

 tion, possessing the lithological character as described in Nicollet's Report, he 

 traced it, with some local variations in its beds, in a northwest direction, to a point 

 on the Missouri, three hundred miles below the Yellowstone, and one hundred 

 and thirty miles west from Fort Pierre. 



In the Fox Hills, which form the dividing ridge between the Cheyenne and Morean 

 Rivers, as indicated on the small map, he found the upper members of this forma- 

 tion particularly characterized by a species of Oucullcea, allied to, but not identical 

 with, C. transversa (see Table VII. Fig. 1) ; by Ammonites NicoUett'd (Table VIII. 

 Fig. 1) ; by Ammonites Conradi (?) (Table VIII. Figs. 2 and 3) ; by Scapldtes nodosus 

 (Table VIII. Fig. 4) ; by Ammonites lenticidaris (Table VIII. Fig. 5), some speci- 

 mens of which attain a diameter of thirteen inches ; and by portions of other Ammo- 

 nites, some, perhaps, identical with A. placenta, of De Kay, and which appear 

 occasionally to have attained the size of a small carriage-wheel. 



On Sage Creek, a southern branch of the Cheyenne, Inocerami are very abundant, 

 some of unusual dimensions. The most remarkable are, /. Bambini (?) , I. mytiloides (?) 

 (Table VII. Fig. 3), a species occurring in the chalk formation of Westphalia ; and 

 a very large species belonging to the same genus, probably an undescribed species, 

 measuring upwards of nine inches in length and six in breadth. Along with these 

 are several species of Bacidites, usually in disjointed pieces. 



At the Great Bend of the Missouri, in addition to several of the same Ammonites 

 and Baculites, occur Inoceramus cripsii, and Ammonites apalus, a new species (Table 

 VIII. Fig. 6). 



At Grand River, where there is much selenite in the rocks, a small species of 

 Inoceramus prevails. 



At most of these localities, and especially on Sage Creek, the Ammonites and other 

 fossils form the nucleus of argillaceous and ferruginous septaria, which lie strewn 

 on the surface, or scattered in the beds of the streams ; the soft, argillo-calcareous 

 matrix having been washed from around them. Some of these possess the character 

 of ironstones; others have the property of hydraulic cement. The fossils are 

 mostly procured by breaking up these septaria, which are of very irregular frac- 

 ture ; and it is therefore difficult to obtain them entire. 



The shelly matter of the fossils usually presents all the appearance of the original 

 nacre, often reflecting, at the same time, the most brilliant iridescent hues. 



Below Fort Clark, the great lignite formation first shows itself in the banks of 

 the Missouri. It was traced to a point twenty miles below the Yellowstone. 



One of the thickest and most valuable beds of coal observed by Mr. Evans, occurs 



