OF THE UPPER MISSOURI. 93 
a greater or less extent over the prairie, resting upon Cretaceous formation No. 5 of the 
vertical section. At Long lake the Lignite Tertiary begins to assume considerable impor- 
tance. On the left side of the Missouri from a series of denuded hills we have the follow- 
ing section of strata in descending order. 
Feet. 
1. Yellow and drab arenaceous grit, . é é 4 i : : ‘ ‘ F 4 . 20 to 30 
2. Impure lignite, 0 j é 4 : ° : E : 0 : 0 . : : o I 
3. Gray arenaceous grit, indurated, contains a small portion of clay, also vertebrate remains, as Compsemys 
victus, Lmys obscurus, Trionyx, &e.,  . : : : : ‘ : : F A : . 40 
4, Impure lignite of a reddish color, with somewhat the character of a carbonaceous clay, . E : . 4 
5. Rather fine-grained gray silicious grit, with a slight admixture of clay, contains great numbers of dull red 
argillaceous concretions, fragments of turtles mentioned in bed 3, and the bones of a huge deinosaurian, 
described by Dr. Leidy as Thespesius occidentalis, . ; 5 < : c . : - 30 to 50 
The lowest bed of the above section rests directly upon the well-known Cretaceous 
formation No. 5 of the vertical section. Bed 5 is the same yellow sandstone seen near 
Fort Clark, which there contains so many freshwater and estuary shells. On the Square 
hills, thirty miles below Fort Clark, it becomes a heavy-bedded, coarse-grained, ferrugin- 
ous sandstone, containing Faludina, Melania Nebrascensis, M. Warrenana, and Corbula 
mactriformis. 
Near Apple creek on the Missouri, in a bank cut by the river, we have the following 
section of beds in descending order. 
Feet. 
1. Deep yellow grit, with some clay, caps the hills. 
2. Yellow sand, passing down into a gray and dark gray grit, . : 3 : : : ° 3 . 40 
3. Impure lignite, with a shaly structure, . 3 : ; : : : 0 : c : eel 
4. Drab indurated arenaceous clay, . c 2 . 
5. Impure lignite; 2 feet. First appearance of lignite immediately along the river. 
6. Gray and dark gray grit, . ° Bee fe : : : . 3 : o 5 . : . 80 
Underneath the Tertiary bed 6 comes a layer of yellow arenaceous and argillaceous grit, 
containing several species of Pectunculus, Fusus, &c. This is undoubtedly the upper por- 
tion of No. 5 of vertical section, though its fossils all have a peculiar Tertiary aspect. 
Indeed all the mollusca from formation No. 5 approximate so closely to well-known Ter- 
tiary forms, that I am inclined to consider it a transition or bed of passage from the 
Cretaceous to the Tertiary epoch. 
At Fort Clark we have a bed of lignite, two feet in thickness exposed, presenting its 
usual characters. 
1. Ferruginous sandstone, 30 to 40 feet. Near the base of the sandstone is a seam eighteen inches in thick- 
ness, composed of shell-marl, with fine specimens of Puludina, Melania, Corbula, &e. These shells are 
