92 ON THE GEOLOGY AND NATURAL HISTORY 
OE Oe eed 28 CMS A a 
VII. Tertiary Basins oF THE Upper Missouri. 
This system occupies so extended a geographical area in the Northwest, that it forms 
a most important feature in its geology. As far as it is now understood on the Upper 
Missouri it may be separated into two distinct divisions or basins, exhibiting well-marked 
lithological differences and containing organic remains peculiar to each. 
Ist. Great Lignite Tertiary Basin, commencing near the mouth of Cannon-ball river 
and extending along the Missouri nearly to the mouth of the Mussel-shell, a distance of 
about six hundred miles. I have traced this formation up the Yellowstone to the mouth 
of Big Horn river, a distance of three hundred miles. Its limits have not been ascer- 
tained with accuracy, in several directions. 
2d. Les Mauvaises Terres, or Tertiary basin of White river, which, with its outliers, in- 
cluding the sandhills and Pliocene beds, occupy an area of from four hundred to five hun- 
dred miles from east to west, and four hundred to six hundred miles from north to south. 
Exact limits not yet ascertained. 
Ist. Great Lignite Tertiury Basin. 
This great basin occupies an immense geographical area, and when thoroughly explored 
will undoubtedly be found the largest freshwater deposit in our country. Indeed the 
wide extent of country which it underlies, its influence on the external features of the 
country, the character and abundance of its organic remains, render it a matter of the 
highest interest to determine its exact age and its true relation to other Tertiary deposits. 
It has been known since the time of Lewis and Clarke that a deposit containing lignite, 
&c., existed on the Upper Missouri. Reports of a similar nature have been given to us 
by other travellers since that time, but no details of its lithological characters, no collec- 
tion of its fossils, or other information that would enable us to determine its age or extent. 
The collections which have been already secured by the writer from this great deposit, 
show most conclusively that it possesses the mixed character of an estuary and freshwater 
formation, and its fossil flora indicates its age to be probably of the Miocene Tertiary.* 
We will now give a few of the details of its geology, together with some views in regard 
to its economical value to the country. 
In ascending the Missouri river we meet with outliers of this deposit between Grand 
and Cannon-ball rivers, near lat. 46°, in the form of denuded hills. These are scattered to 
* The lower portion, at least, is probably Eocene. 
