NATURAL SCIENCES OE PHILADELPHIA. 
155 
around the Black Hills. I am inclined to the opinion, however, that prior to 
the convulsion that upheaved the fossiliferous rocks, only the Cretaceous "beds 
Nos. 4 and 5 were exposed in any portion of this region. 
Along the Shyenne River, No. 4 contains most finely preserved fossils in the 
greatest abundance. Large Ammonites, two to three feet in diameter, still 
preserving their original pearly lustre, Scaphites, Baculites, Ostrea, &c. Ascend- 
ing the valley of Sage Creek, we pass over the Cretaceous beds for the first five 
miles, which contain an abundance of fossils similar to those found on the 
Shyenne. We then meet with the lowest bed of the great Tertiary Basin of 
White River, resting conformably upon Cretaceous strata, which appear to be 
a blending of Nos. 4 and 5. We have, first, the dark clays of No. 4, then the 
yellowish brown, gritty shale of No. 5, with numerous ferruginous concretions ; 
then the Titanotherium bed which sets regularly upon No. 5, and exhibits its 
highest development in the valleys of Sage and Bear Creeks. It is here com- 
posed, 1st, of a band of argillaceous grit weathering to a pink color, two feet in 
thickness, passing up into an ash colored plastic clay with a greenish tinge, 
full of chalcedony and calcareous concretions, altogether 50 to 80 feet in thick- 
ness ; then a light gray calcareous grit upon which rests the Turtle Bed. A 
considerable deposit of drift consisting of water-worn bowlders, and loose sand 
and gravel, is distributed over the surface of the Bad Lands to a greater or less 
extent. 
Proceeding up the valley of the Shyenne, we see only the Cretaceous beds 
Nos. 4 and 5, until we pass the mouth of Bear Creek, when the Tertiary makes 
its appearance, crossing the Shyenne and stretching off toward the base of 
the Black Hills in long ridges or isolated Buttes. The belt of Tertiary on the 
left side of the Shyenne is about thirty miles in width. A section fifteen miles 
above the mouth of Bear Creek, on the Shyenne, presents the following char- 
acters. 
c. — Light gray indurated clay, 6 feet. 
b. — Seam of gray sandstone, 18 inches. 
«• — Ash-colored plastic clay with a greenish tinge, and a pinkish band of fine 
grit at the base, ; 30 feet. 
The Titanotherium Bed varies much in its lithological characters in different 
localities. The layer of gray sandstone is sometimes two to four feet in thick- 
ness, composed of an aggregate of water-worn pebbles, with granular quartz, 
and small particles of mica, forming somewhat conspicuous ledges. On the 
western side of the Shyenne, the Titanotherium bed presents the following 
characters proceeding upward from No. 5 : First, alternate seams of small peb- 
bles and loose sand, two to six inches in thickness, passing up into a fine 
ferruginous grit, containing small scales of mica, weathering to a light gray 
color, then a band of pinkish gritty clay, six inches in thickness, passing up 
into ash-colored clay which has also alternate gritty layers. The pink band if 
quite persistent, and being exposed whenever the Titanotherium Bed is worn 
through, marks with a good degree of precision the base of the Tertiary. The 
surface in many places is covered with water-worn pebbles, varying in size from 
an eighth of an inch to eighteen inches in diameter, though mostly small, and 
representing all the varieties of metamorphosed rocks, with rounded masses of 
lime and flint rock, fossil wood, &c., so that No. 5, when the Titanotherium Bed 
is eroded away, is paved with this loose material. The Turtle Bed alone does not 
s«em to be so marked in its character here as at Bear Creek. It weathers to a light 
yellow color and passes almost insensibly into the bed above. I have marked 
the line of separation at this locality, between the Turtle bed and the one over- 
lying it, by a layer of very porous argillaceous sandstone of a dull brown or 
drab color. The Turtle bed contains much more sand than at Bear Creek, and 
the upper portion consists of alternate layers of calcareous concretions and 
indurated argillaceous grit with one band, eight feet in thickness, of ash-colored 
clay. Disseminated through the bed in every direction, are thin seams of chal- 
1858.] 
