16 



GEOLOGY OF THE TERTIARY FORMATIONS OF 



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SITBDIVISIONS. 



1st. Dark gray or brown sand, 

 loose, incoherent with remains of 

 Mastodon, Elephant, &c. 2d. Sand 

 and gravel incoherent. 3d. Yel- 

 lowish-white grit, with many calca- 

 reous, arenaceous concretions. 4th. 

 Gray sand with a greenish tinge ; 

 contains the greater part of the or- 

 ganic remains. 5th. Deep yellow- 

 ish-red arenaceous marl. 6th. Yel- 

 lowish-gray grit, sometimes quite 

 calcareous, with numerous layers 

 of concretionary limestone from 

 two to six inches in thickness, con- 

 taining fresh-water and land shells, 

 Succinea, Idmncea, Paludina, He- 

 lix, &c., closely allied and perhajis 

 identical with living species; also 

 much wood of a coniferous charac- 

 ter. 



LOCALITIES, 



Covers a very large area on 

 Loup Fork from the mouth of 

 North Branch to source of 

 Loup Fork ; also in the Platte 

 Valley. Most fully developed 

 on the Niobrara River, ex- 

 tending from the mouth of 

 Turtle River three hundred 

 miles up the Niobrara. Also 

 on Bijou Hills and Medicine 

 Hills. Thinly represented in 

 the valley of White River. 



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Usually a coarse-grained sand- 

 stone, sometimes heavy-bedded and 

 compact, sometimes loose and inco- 

 herent ; varies much in different 

 localities. Forms immense masses 

 of conglomerate, also contains lay- 

 ers of tabular limestone with indis- 

 tinct organic remains. Very few 

 mammalian remains detected, and 

 those in a fragmentary condition. 

 Passes gradually into the bed be- 

 low. 



Most fully develoj^ed along 

 the upper portion of Niobrara 

 River, and in the region 

 around Fort Laramie. Seen 

 also on White River and on 

 Grindstone Hills. 



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