458 N. H. BARTON PALEOZOIC AND MESOZOIC OF WYOMING 



teristic of the iipper portion of tlie Benton in a wide area of the Eocky 

 Mountain and Great Plains provinces. 



The Niobrara chalky beds contain large numbers of Ostrea congesta. 

 In sandstone high in the Benton, on Muddy creek south of Big Muddy, 

 Inoceravius fragilis and Cardium paupereulina occur in abundance. In 

 Wind Eiver basin, in the vicinity of Dry creek and farther west toward 

 the base of Black mountain, the top sandstone of the Colorado formation 

 is highly fossiliferous, containing the following species, which have been 

 identified by Mr T. W. Stanton: Ostrea coalvillensis Meek, Ostrea san- 

 nionis White, Anomia sp., Pecten sp., Inoceramus erectus Meek, Gervillia 

 sp. ci.,G. propleura Meek, Cardium curtum M. and H., Cardium sp., Ana- 

 tina ? sp., Turritella spironema Meek ?, and Baculites compressus Say. 

 Mr Stanton states that they belong to a faunule that occurs in the 

 upper part of the section at Coalville, Utah, and is also found in western 

 Wyoming occupying tlie stratigraphic position of the Niobrara or not far 

 above it. At no great distance above the sandstone occur distinctive 

 Pierre fossils. 



MONTANA FORMATION 



Occurrence and general relations. — The Montana formation underlies 

 large areas in Wyoming, mainly in the many wide synclines between the 

 larger uplifts. It is extensively overlain by formations wliich have been 

 termed Laramie and Port Union and widely overlapped l)y various Ter- 

 tiary deposits. In central Wyoming it outcrops along the east slope of 

 Wind Eiver uplift east of longitude 109°, along- the south side of Owl 

 Creek uplift between Muddy and Dry creeks, across the south side of 

 Bighorn basin, along the north side of the Eattlesnake Mountain uplift, 

 in a broad belt extending through Casper to and down the South Powder 

 valley, in the basins between Casper and Aleova, along the south side of 

 Shirley hills, along the Muddy Creek-j\Iedicine Bow basin, in a large por- 

 tion of Laramie basin, and at intervals along the east side of Laramie 

 mountains from Chugwater creek to Crow creek. The lower rocks for 

 2,500 feet or more present all the characters of Pierre shale. They are 

 overlain by sandstones, shales, and local coal measures representing the 

 Mesa Verde, Lewis, and Fox Hills formations. The upper division occurs 

 in the Wind Eiver and Laramie basins, in a small area north of Freezeout 

 hills, and in the broad basin which extends far to the east and northeast 

 from Casper and Douglas. Both divisions appear also on Horse, Lodge- 

 pole, and Crow creeks east of Laramie mountains, which indicates that 

 they underlie the Tertiary deposits for some distance under the Great 

 Plains. 



