OF THE UPPER MISSOURI. fe 
often discolors the banks of the river. At the Great Bend, a local variation occurs in No. 
4, near the summit of the hills. It is a seam two to six feet in thickness, of very fine light 
buff-colored clay, containing no fossils, and is visible only for a few miles. 
After passing the mouth of Great Shyenne river, a slight change occurs in the lithologi- 
cal character of the upper portion of this formation, thence to the Moreau river it ex- 
hibits a laminated or shaly structure, and a dark silvery or leaden gray color. These cha- 
racters are seen on the Moreau river eighty miles above its mouth, also at Sage creck near 
the Bad Lands. 
After dipping beneath the water-level of the Missouri, between Grand and Cannon-ball 
rivers, this formation again rises to the surface near Quaking Asp river, in longitude 109°, 
by a reversed inclination of the strata. Its first appearance is in a little tributary of the 
Missouri, and is seen only for about a hundred yards, yet presenting its peculiar characters. 
Thirty miles below the mouth of Milk river it is revealed by the reverse dip above re- 
ferred to, for the first time along the Missouri, after leaving a point near Cannon-ball 
river, under the northern portion of the great lignite Tertiary basin. It here has a thick- 
ness exposed of forty to sixty feet, presenting the same general character as at the Great 
Bend. It contains numerous flat masses of rock arranged in horizontal layers in the ex- 
posure, with a few fossils. Just below the mouth of Porcupine river, there is a high 
range of bluffs, presenting a good exposure of this bed, containing fine argillo-calcareous 
concretions, fully laden with organic remains of the genera Ammonites, Baculites, Inocera- 
mus, &c. I notice that the Inocerami seem to have existed in vast numbers to the exclu- 
sion of other forms. No. 4 continues to attain a greater thickness as we ascend the 
Missouri, until we come in the vicinity of Round butte, where we find it to be two hun- 
dred to two hundred and fifty feet. Here it is overlaid bya ferruginous sand-bed, com- 
posed in part of immense ledges of concretionary sandstone. No fossils were observed in 
it, yet I think it is the upper portion of No. 5, or a transition bed between the Cretaceous 
and ‘Tertiary. Below the mouth of Mussel-shell river, as well as above, indeed wherever 
this formation is exposed in this region, its peculiar fossils are found in great abundance. 
Near the mouth of Mussel-shell river, I found an Jnoceramus fifteen inches long and 
ground to the depth of five or six inches, and is used by the traders in their culinary operations as a substitute for 
saleratus. Dr. Hayes of Boston made an analysis of an impure specimen obtained near Fort Benton, in Gov. 
Stevens’s expedition, with the following result : 
Moisture=3.20. 
Sulphate of lime=5.60. 
100 parts. Sulphate of alumina and iron==3.25, 
Sulphate of soda=43.40. 
Insoluble sand=44.00. 
