NATURAL SCIENCES OF PHILADELPHIA. 
151 
^ of the vertical section. The distant hills, on either side of the river, are 
covered with a considerable thickness of Pliocene and Post Pliocene beds. 
Near the mouth of North Branch the following section of the strata, in' de- 
scending order, were observed : 
d. — Yellowish brown laminated argillaceous grit ; effervesces briskly with muri- 
atic acid. - 
c. — Similar to the bed above, but of a deeper color, more compact, containing 
a greater per cent, of clay, with numerous calcareous concretions dis- 
seminated through it, ----- - 70 to 100 feet. 
b. — Light brown clay, filled with fine whitish particles like magnesia. 70 feet. 
a. — Gray, coarse sand, forming a heavy bedded sandstone, reaches 
to the waters edge, - - 30 feet. 
In the upper beds of the above local section, fragments of Mammalian and 
Chelonian remains were found, and all but the lower bed, which is bed E of the 
vertical section, are Pliocene. Lt. Warren explored the North Branch thirty 
miles above its mouth, and met with a similar series of beds, containingthe same 
organic remains. Above the mouth of North Branch, bed a of the local section 
appears, in the form of large ledges of light gray arenaceous limestone, filled with 
silicified tubes like the stems of plants, and seeds resembling cherry stones 
In the Pliocene beds, on the distant hills, when exposed by erosion, I found 
numerous fragments of bones and teeth of Hipparion, Cervus, &c. 
About Ion. 99° we enter the desolate region of the Sand Hills. I measured the 
heighth of these hills at one locality and found them to be two hundred and 
thirty feet above the bed of Loup Fork, and composed of Pliocene beds as a 
base, then a thin bed of Post Pliocene marl, overlaid by a great thickness of 
loose incoherent sand and gravel, derived from the erosion of the different Ter- 
tiary beds. The whole country from the head of Loup Fork presents a similar 
character, consisting of movable sand hills, the true Tertiary beds being very 
seldom exposed. On the South Branch, the stream cuts though the following 
Pliocene strata. 
c — Yellowish brown grit, containing Ilastodon micificus^ (Leidy.) 
b — White chalky stratum, charged with fresh water and land shells of the 
genera Helix, Flanorbis, Limnea, &c., probably identical with recent 
species, __________ 3 feet. 
a — Heavy bedded gray sandstone, - - - - - 8 tO 10 feet. 
From the head of Loup Fork to the Niobrara river the whole country is 
covered with this superficial deposit of sand, which is blown by the wind into 
ridges and high conical hills, rendering travelling quite difficult. On reaching 
the Niobrara we find bed E quite well developed, also a full series of the Pliocene 
beds filled with Mammalian remains. Passing up the Niobrara about fifty miles, 
the Pliocene strata gradually disappear, and the whole country is occupied by 
the Upper Miocene beds U and D. A Butte near this point affords a fine detailed 
section of the gray sandstone bed which, measured from the base, with a 
pocket level, I found to be one hundred and sixty-six feet in heighth. It is 
composed mostly of a gray coarse grit, sometimes quite incoherent, containing 
many layers of concretionary sandstone. On the summit is a thin bed of 
shelving limestone similar to that containing organic remains at Pinau's spring, 
though probably not holding the same geological position. Indistinct traces 
of freshwater shells and numerous remains of fishes, scales, vertebrae, &c., 
were visible in the tabular masses. It seems to form the upper portion of 
bed E, and to vary much in its character in different localities. It presents 
every variety from a translucent chalcedony to a fine grained sandstone or com- 
pact limestone, and furnishes those chalcedonic masses which meet the eye of 
the traveller so often and have the appearance of erratic blocks. Farther from 
the river, and holding a higher position than the summit of the Butte, are thin 
beds of yellow and yellowish gray calcareous grit undoubtedly of Pliocene 
age, containing numerous fragments of teeth and finely preserved bones of the 
Uastodon and Elephant. As we pass up the river the gray sandstone bed E 
presents a great variety of lithological characters. Sometimes it forms a coarse 
1858.] 
