40 MANSFIELD: MESOZOIC OF FORT HALL -RESERVATION 



Cephalopods are practically absent in this formation, as they are in 

 the Fort Hall. One specimen only was obtained; it is apparently 

 identical with Pseudosageoceras intermontanum. 



ANKAREH SANDSTONE 



The Ankareh sandstone derives its name from Ankareh Ridge 

 in the Park City mining district of Utah. In its type locality, 

 Big Cottonwood Canyon near Salt Lake City, and as originally 

 described, the formation is called a shale and consists chiefly 

 of clay shale of deep maroon or chocolate color, showing little 

 lamination where fresh but commonly breaking down after ex- 

 posure into thinner-bedded shaly material. It includes also 

 some pale greenish, clayey and sandy and limy strata. 



In the Fort Hall Indian Reservation the beds that occupy this 

 stratigraphic interval are not shales but are somewhat sugary, 

 yellowish to grayish sandstones in beds 1 to 3 inches thick, and 

 in some places more massive beds. They are non-fossiliferous, 

 so far as observed, and weather into smooth depressions or slopes 

 between the more resistant formations on either hand. The sand- 

 stone is generally of uniform character and in some places weath- 

 ers with a pinkish tinge. The base of the sandstone rests with 

 apparent conformity upon the massive and siliceous Portneuf 

 limestone, while the top is overlain by the Higham grit. Thus 

 the formation is in most places clearly defined. 



THE NUGGET SANDSTONE 



The Nugget sandstone as originally described by Veatch 7 in 

 southwestern Wyoming is about 1,900 feet thick and consists of 

 two distinct members, a lower brightly colored red bed member 

 600 feet thick, and an upper light-colored sandstone member. 



In the Fort Hall Indian Reservation there is a considerable 

 variation in the character of the Nugget from that at the type 

 locality. The formation is well developed and may be differen- 

 tiated into several units, at least four of which may readily be 

 mapped. These are (1) the Higham grit member at the base, 



7 Veatch, A. C. IT. S. Geol. Survey Prof. Paper 56: 56. 1907. 



