14 ON THE GEOLOGY AND NATURAL HISTORY 
tains the freshwater shells near Pinau’s spring, though holding a higher geological posi- 
tion. Indistinct traces of shells and abundant remains of fishes, as scales, vertebrae, &c., 
were observed on the surface of tabular masses. It seems to form the upper part of gray 
sandstone bed E of the general section, and to vary much in its lithological characters in 
different localities, presenting every variety, from a translucent chalcedony to a fine-grained 
sandstone or compact limestone, and furnishing those chalcedonic masses which meet the 
eye of the traveller so often on the surface of this formation, having the appearance of 
erratic blocks. Further from the river and capping the hills, are beds of yellow and 
yellowish gray calcareous grit, undoubtedly of Pliocene age, containing numerous fragments 
of the jaws and finely preserved bones of the Mastodon and Elephant. As we pass up 
the Niobrara the gray sandstone bed assumes a variety of characters, sometimes forming a 
coarse conglomerate, then an aggregate of granular quartz cemented with calcareous matter. 
Lithological changes are constantly occurring in the Upper Tertiary beds. About fifty 
miles up the Niobrara from the point where we struck it (Aug. 10th), the Pliocene beds 
cease to appear, and the whole country is occupied by the Miocene formations D and K 
of the general section. 
August 14th. On the distant hills saw large layers of a fine-grained arenaceous lime- 
stone, forming a bed ten to fifteen feet in thickness. At this locality we find in bed E, 
alternations of reddish flesh-colored grit and light ash-colored clay with layers of concre- 
tionary sandstone and limestone. Fifty miles above our camp of August 10th, a new bed 
arises above the water level of the river, composed of a flesh-colored calcareous grit with 
a reddish tinge. Sometimes it is a light yellow calcareous marl, and the eroded material 
gives a reddish yellow tint to the whole surface of the country. It seems to pass up quite 
gradually into the sandstone above. The remains of an animal allied to the Oreodon, 
named by Dr. Leidy, Meycochoerus proprius, were collected from this bed at this locality. 
August 15th. One of the most characteristic and picturesque instances of the castel- 
lated appearance of the Bad Lands on the Niobrara, is seen near our camp. At this point 
the thickness of bed D is one hundred and twenty-four feet above the river. It has the 
same general lithological character as in the White river valley, where a much greater 
thickness is exposed, It contains many layers of silico-calcareous concretions, sometimes 
forming large ledges, which break into irregular fragments on exposure. The more inco- 
herent material has much the color and composition of the turtle bed on Bear creek, but 
contains less aluminous matter. 
Leaving the Niobrara for Fort Laramie we observe at Spoonhill creek the conglomerate 
composing a large portion of bed E, giving a very rugged appearance to the scenery. It 
consists of angular and water-worn pebbles of every variety and color, from the granitic 
and metamorphic rocks of the Black hills and other mountainous portions, varying in size 
