4 Cincinnati Society of Natural History. 
fine-grained sandstone, and containing comparatively few organic re- 
mains. Found on the Niobrara and Platte rivers; well developed in 
the region of Fort Laramie, and in the valley of White river; and con- 
Spicuous, and composing the main part of the dividing ridge between 
White and Niobrara rivers. Thickness, 350 to 400 feet. 
0. Bed H.—Usually a coarse-grained sandstone, sometimes heavy | 
bedded and compact; sometimes loose and incoherent, and varying 
much indifferent localities. It forms immense masses of conglomerate, 
and contains layers of tabular limestone, with indistinct organic re- 
mains, and a few mammalian remains, in a fragmentary condition. It 
passes gradually into the bed below. It is most fully developed along 
the upper portion of Niobrara river, and in the region around Fort 
Laramie. It is seen also on White river, and on Grindstone hills. 
Thickness from 180 to 200 feet. 
The Pliocene consists of ist, dark gray or brown sand, loose, in- 
coherent, with remains of mastodon and elephant ; 2d, sand and gravel, 
incoherent; 3d, yellowish-white grit, with many calcareous, arenaceous 
concretions ; 4th, gray sand with a greenish tinge, which contains the 
greater part of the organic remains; Sth, deep  yellowish-red 
arenaceous marl; 6th, yellowish-gray grit, sometimes quite calcareous, 
with numerous layers of concretionary limestone, from two to six 
inches in thickness, containing fresh water.and land shells, closely 
allied, and perhaps identical with living species, which belong to the 
genera, Succinea, Limnea, Paludina and Helix. It contains also, much 
wood of coniferous character. It covers a very large area on Loup Fork, 
from the mouth of North Branch to the source of Loup Fork, and 
occurs in the Platte valley. Itis most fully developed on the Niobrara 
river, and extends from the mouth of Turtle river three hundred miles 
up the Niobrara. It occurs on Bijou hills, and Medicine hills, and is 
thinly represented in the valley of White river. Thickness from 300 
to 400 feet. A . 
The Post-pliocene consists of yellow, silicious marl, similar in its 
character to the loess of the Rhine, passing down into variegated indu- 
rated clays, and brown and yellow fine grits. It contains the remains 
of extinct quadrupeds, mingled with those identical with recent ones, 
and a few mollusca, mostly identical with recent species. It is most 
fully developed along the Missouri river, from the mouth of the Nio- 
brara to St. Joseph, and occurs in the Platte valley and on the Loup 
Fork. Thickness from 300 to 500 feet, 
' Prof. G. C. Swallow* referred a formation made up of clays and 
* Proc. Am. Ass. Ad. Sci. 
