MesozoiG and Camozoic Geology and Paloeontology. 201 



Springs on the North Platte westward toward the Sweet Water moun- 

 tains, and near the divide between the North Platte and Wind river 

 they reach a thickness of 400 feet. From this divide throughout the 

 Wind river valley they occupy the greater portion of the country, and 

 though inclining in the same direction with the older strata the beds 

 do not dip more than from 1 to 5 deg. They differ from the other de- 

 posits in the great predominance of arenaceous sediments, and in the 

 absence of vegetable remains, but they contain fragments of turtles 

 and numerous fresh- water and land shells. The entire thickness of 

 these deposits is estimated at from 1,500 to 2,000 feet. 



The White River Tertiary beds extend southward along the Laramie 

 mountains to Willow Springs, and up the North Platte to Box Elder 

 creek, and beyond in small outliers, showing that much has been re- 

 moved b}' erosion. From the source of Box Elder creek, they extend 

 to the head of Bates Fork, and westward to the Medicine Bow 

 mountains. Tiiese beds for the most part, hold a horizontal position, 

 while those of the lignite age are much disturbed; moreover, their 

 position shows that the}' are of much more recent origin. The White 

 river Tertiarj' deposits are followed by the White river bone beds, 

 which pass up into the Pliocene of Niobrara b}^ a slight physical 

 break, and the latter are lost in t4ie yellow marl or Lacs deposits. 



Meek and Hay den* made a vertical section of the Tertiary rocks 

 of Nebraska, in ascending order as follows : 



1. Wind river deposits, consisting of light gray and ash -colored 

 sandstones, with more or less argillaceous la3-ers. Thickness from 

 1,500 to 2,000 feet. Found in the Wind river' valley and west of the 

 Wind River mountains. 



2. The White River Group, consisting of white and light drab 

 clays, with some beds of sandstone and local slayers of limestone. 

 Thickness 1,000 feet or more. Found on the Bad Lands of White 

 river ; under the Loup river beds, on Niobrara, and across the country 

 to the Platte. Age of the Miocene. 



3. Loup river beds, consisting of fine loose sand, with some layers of 

 limestone. Thickness, 300 to 400 feet. Found on Loup fork of Platte 

 river, and extending north to the Niobrara river, and south an un- 

 known distance. Age of the Pliocene. 



They described from the Wind River Group, in the Wind river 

 vallc}'. Helix veterna, and H. spatiosa^ now Macrocyclis spatiosa. 



* Proc. Acad. Nat. Sci., vol. xii. 



