Carlile. 



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CRETACEOUS SYSTEM 457 



Section of Benton Formation West of Horse Greek Station, Wyoming 



Feet 



f Black shale (overlain by Niobrara limestone) 10 



Sandstone and sandy shale 20 



Gray shale, with concretions containing Prionotropis 



near top 200 



Greenhorn. . .^. Sandy limestone with Inoceramus laMatus % 



r Shale, dark and fissile below 350 



Hard shale and thin-bedded, fine-grained, hard sand- 

 stone, weathering light gray ; many fish scales 



(Mowry beds) 80 



Dark shale : 30 



Hard, coarse sandstone, massive 25 



Dark shales, fissile to soft, on Cloverly sandstone 150 



Graneros. 



Total 865y4 



Some of these measurements are uncertain, owing to talus or crushing. 



Near North fork of Horse creek the top member is 15 feet of slabby 

 gray sandstone with some sliale, lying on 20 feet of shale with oval con- 

 cretions. The Greenhorn limestone layer is about 1 foot thick, l)ut 

 yielded no fossils. In this vicinity the Mowry beds lie 500 feet below the 

 Niobrara and grade down into 30 feet of black shale. The latter is under- 

 lain by 25 feet of fine-grained, hard' white sandstone separated from the 

 Cloverly by 200 feet of black fissile shale. This lower sandstone is con- 

 spicuous in ridges south, east, and north of Iron Mountain station, where 

 it is 25 feet thick and lies on 125 feet of dark shale. Above it are 50 feet 

 of dark shale, grading into j\Iowry beds. The Niobrara formation ap- 

 pears extensively at intervals from Lodgepole creek to Chugwater creek, 

 east of Laramie mountains. A small outcrop occurs on Crow creek. 

 "West of Horse Creek station it is 375 feet thick and consists of limestone 

 and limy shales, with a massive bed of limestone at the base containing 

 Inoceramus deformis. Another bed of limestone occurs near the middle, 

 while at the top are impure shaly limestones which weather to a bright 

 yellow color. Slabby aggregates of Ostrea congpsta occur in many of the 

 beds, and this fossil also occurs disseminated in some of the layers. Near 

 North fork of Horse creek the formation is 400 feet thick. 



Fossils. — The principal fossils of the Benton formation are the very 

 numerous fisli scales in the ]\Iowry beds and molluscan remains and sau- 

 rian and fish bones and teeth, which occur at various horizons. In the 

 upper sandstone, near the foot of Jelm mountain, Avere found Inoceramus 

 fragilis, together with fish teeth apparently of Ptychodus and Lamna. 

 The upper sandstone also contains Prionocyclus, a fossil which is charac- 



