OF THE UPPER MISSOURI. 79 
In summing up the extent of country underlaid by this great formation, we find that 
south of the Lignite basin, it occupies an area of two hundred miles in length and one 
hundred in breadth, or twenty thousand square miles. North of the Great Lignite basin, 
commencing at its first appearance near Milk river, we find it covering an area of two 
hundred miles in length and sixty in breadth, or about twelve thousand square miles. I 
have been thus particular in estimating its approximate limits and extent of surface, on 
account of its influence on the future destiny of that region. Wherever this deposit pre- 
vails it renders the country more completely sterile than any other geological formation I 
have seen in the Northwest. We see from the above estimate that it renders barren over 
thirty thousand square miles of the valley of the Missouri. 
The organic remains of this formation are too numerous to mention in detail. The 
lower and upper members appear to be very fossiliferous, while the intervening portion, of 
considerable thickness, contains only a few imperfect specimens of Cephalopoda and the 
bones of Mosasaurus Missouriensis. The strata dip toward the northwest below Fort 
Clark. At the Lower Bend, which seems to be formed of the lower portion of No. 4, 
contains its peculiar fossils in great numbers. They are found in the loose clay or in 
tough argillo-calcareous concretions, and many fine specimens are found along the shore of 
the river at low water. We then have an interval of about two hundred and fifty miles, 
to a point near the mouth of Grand river, wholly occupied by No. 4, in which are only 
the few imperfect specimens of fossils before mentioned. Near the mouth of Grand river 
the upper members yield an abundance of organic remains, many of which are specifically 
identical with those occurring at the Great Bend, with many new and interesting forms. 
At Sage creek and along the Shyenne river above its forks are noted localities for fossils. 
Baculites ave found in great perfection and beauty, Ammonites placenta occur three feet in 
diameter, and a peculiar fossil, having a columnar structure like some forms of coral, Capri- 
nella coraloidea (Hall and Meek), which is known only in this region. On the Yellow- 
stone many new forms are found, mostly belonging to small Acephala and Gasteropoda, 
and the only species of Echinoderm yet known in the Cretaceous rocks of the Northwest 
occurs at this locality. Above Milk river this formation is filled with fossils, revealing, in 
addition to many of the forms occurring in the localities already mentioned, a large 
number of new species, as Gervilia subtortuosa, Ostrea patina, Ammonites Halli, &c. For 
the complete list of the fossils occurring in each formation the reader is referred to the 
catalogue at the close of the remarks on the Cretaceous formations. 
Formation No. 5 of VERTICAL SECTION. 
This very interesting bed, though differing lithologically from the preceding one, con- 
tains many of the same species of fossils. It is worthy, however, of a distinct position in 
