192 Tertiary. 



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. 



5. Bed E. — Usuall}^ a coarse-grained sandstone, sometimes heaA^y 

 bedded and compact; sometimes loose and incoherent^ and varying 

 much in different 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 1st, 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 ; 5th, 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. It is 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. 



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 rivei', 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 600 feel. 



Prof. G. C. Swallow* referred a formation made up of clays and 



* Proc. Am. Ass. Ad. Sci. 



