98 ON THE GEOLOGY AND NATURAL HISTORY 
SECTION OF TERTIARY BEDS NEAR O’FALLON’S CREEK, ON THE YELLOWSTONE. 
Feet 
1. Yellowish flesh-colored marl. The upper portion of the bed is a rather coarse-grained reddish sandstone, = 
with many large Unios, too imperfect to characterize, ‘ ‘ ‘ : ‘ ; . - 20 to 30 
2. Reddish drab indurated clay, . ‘ “ : ‘ > ‘ ' , : : ; . . 
3. Dark drab indurated clay, ‘ . ‘ . ‘ae ee . : ‘ , ; ; . 80 
Earthy lignite, 2 inches, 
Dark drab indurated clay, 4 inches, 
Impure lignite, 2 inches, . 
4. Yellow clay with concretions, 2 feet, in all, over ‘ : 3 ; : 3 ; ; ean 
Impure lignite, 2 inches, . 
Carbonaceous clay, 3 inches, 
Impure lignite, 2 inches, . 
5. Dark drab indurated arenaceous clay, ; : : i : ‘ ‘ : ; : ; : oo? 
6. Lignite, quite pure, 18 inches. 
7. Deep yellow ferruginous grit, contains a few shells, as Paludina, Corbula, &c., and impressions of leaves, 25 
Lignite, quite pure, 18 inches. 
8. Very dark carbonaceous clay, . . : : ‘ ‘ . Q ; : ; - 8 told 
Lignite of good quality, 2 feet. 
9. Light gray sand, reaching to water’s edge at this point, though reposing on Cretaceous formation No. 4a 
few miles below, exposed, . : : ee ‘ ‘ : . : : : . 80 to 40 
In bed 9 of the above local section we find numerous argillo-calcareous concretions, 
containing distinct impressions of leaves of dicotyledonous trees, Smilax, Acer, Ulmus, 
&c. I think this bed holds the same position as the lowest sand-bed seen on Moreau 
river near Thunder hill and on Cherry creek. Plants and shells are found to some extent 
in all the strata of clay, especially near the lignite beds. Bed 8, a few miles down the 
river, becomes a solid stratum of lignite, seven feet in thickness, and is the largest bed of 
this material seen on the river. After passing the mouth of Powder river it diminishes in 
thickness and becomes more impure, and thus continues to the mouth of Big Horn river, 
the limit of my observations. I have no doubt, however, that, like the same beds on the 
Missouri, the Tertiary beds soon disappear on the high hills (the strata dipping toward 
the east apparently), and give place to formations of older date. In the summer of 1854, 
I received from intelligent traders, specimens of Inoceramus and Ammonites from a locality 
near Clark’s fork, a branch of the Yellowstone, which is on the same parallel with Mus- 
sel-shell river, where the well-known Cretaceous formation No. 4 reaches its largest de- 
velopment on the Missouri. 
Throughout the region of the Yellowstone, silicified wood is found in the greatest 
abundance, so that many portions have been called by the trappers “petrified forests.” 
There is everywhere evidence of an exceedingly luxuriant growth of timber. during the 
Tertiary period. 
The spontaneous ignition of the lignite beds, and its influence on the contiguous strata, 
