FORMATIONS OF THE MAUVAISES TERRES. 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 Cucullea, allied to, but not identical 
with, C. transversa (see Table VII. Fig. 1) ; by Ammonites Nicollettii (Table VIII. 
Fig. 1); by Ammonites Conradi (2) (Table VIII. Figs. 2 and 3) ; by Scaphites nodosus 
(Table VIII. Fig. 4) ; by Ammonites lenticularis (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, Jnocerami are very abundant, 
some of unusual dimensions. The most remarkable are, 1. Barabini (2), I. mytiloides (?) 
(Table VII. Fig. 3), a species occurring in the chalk formation of Westphalia ; and 
avery 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 Baculites, usually in disjointed pieces. 
At the Great Bend of the Missouri, in addition to several of the same Ammonites 
and Baculites, oceur Jnoceramus cripsii, and Ammonites opalus, 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 
