30 
ON THE GEOLOGY AND NATURAL HISTORY 
The Titanotherium bed varies much in its lithological characters in different localities. 
The layer of gray sandstone is sometimes two to four feet in thickness, 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 pebbles and sand, two to six inches in thickness, passing up into a fine ferruginous 
grit containing small plates of mica, weathering to a light gray color; then a band of 
pinkish gritty clay six inches in thickness, passing up into an ash-colored clay, which has 
also alternate arenaceous layers. The pinkish band is quite persistent, and being exposed 
wherever the T. bed is worn through, marks with a great deal of precision the base of the 
Tertiary. The surface in many places is covered with well-waterworn pebbles varying in 
size from a granule of quartz to a rounded boulder eighteen inches in diameter, though the 
pebbles are mostly small, representing all the varieties of metamorphic rocks with fragments 
of silicified wood, rounded masses of limestone and flint, and indistinct organic remains, so 
that the surface of No. 5, when the T. bed is eroded away, is paved with these stones. 
Sometimes the pebbly bed is twenty feet in thickness. The turtle bed above does not seem 
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 indicated the line of separation 
at this locality between the turtle bed and the overlying stratum by a layer of very porous 
argillaceous sandstone of a dull brown or drab color. The turtle bed contains much more 
sand at this point 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 thick¬ 
ness of asli-colored clay. Disseminated all through the bed in every direction are thin 
seams of silex in the form of chalcedony. A few organic remains were obtained, mostly of 
Oreoclon and Rhinoceros. 
On the right or east side of the Shyenne as we proceed toward White river, the Creta¬ 
ceous bed No. 5 presents some peculiarities which are worthy of notice. We have, first, 
No. 4, black clay, laminated, gradually passing up into a dark brown clay; then a deep 
ferruginous color; then a dull purplish hue, with red iron rust seams, half an inch to an 
inch in thickness, passing up into a deep yellow arenaceous clay; lastly, a brown clay, un¬ 
derlying the Titanotherium bed. I have been thus minute in describing these beds from 
the fact that, although a long period must have elapsed after the close of the Cretaceous, 
and prior to the deposition of the Tertiary, the transition to the Tertiary epoch from the 
Cretaceous does not seem to be marked by any conspicuous physical break, but by a gradual 
change of sediments. We know, however, from observations at other localities that the 
Cretaceous surface was more or less subjected to erosion prior to the. deposition of the 
Tertiary beds of this region. 
