438 N. H. DARTON PALEOZOIC AND MESOZOIC OF WYOMING 



These brownish red sandstones with limestone layers in the basal series 

 may possibly represent the Tensleep sandstone, but if so the Minnekahta 

 limestone is absent in overlying red beds. The top member of the Chng- 

 water red beds here is a massive bed of pale red sandstone. 



Fossils and age. — Fossils found at varioxis horizons in limestones in the 

 Chugwater red beds do not afford conclusive evidence as to age. Those 

 in the lower limestones in the Bighorn mountains and other uplifts are 

 believed to be "Permian" in the sense in which the term is used in the 

 Mississippi valley. Many fossils occur in the limestone 150 feet below 

 tlie top of the formation, on the east bank of Bighorn river, 3 miles belcw 

 Thermopolis. According to Dr G. H. Girty, the principal species is 

 Natica lelia, usually considered diagnostic of the Triassic, but probably it 

 is older. BaTceivellia and probably Phleurophorus may also be present, 

 and an aviculipecten occurs, resembling A. curticardinalis, which is char- 

 acteristic of the Permo-Carboniferous of Utah. Doctor Girty is inclined 

 to correlate the fauna with the Permo-Carboniferous of the Wasatch 

 Mountain section. The 150 feet of red shales and sandstones which over- 

 lie this limestone may possibly represent part of the Triassic. In the 

 lower portion of the ChugAvater formation, 10 miles southwest of Casper, 

 a cast of Schisodus wheeleri was found. This form is usually regarded as 

 Pennsylvanian. 



Jurassic Ststem 



sundance formation 



General relations. — The Sundance formation occupies a large area in 

 central Wyoming, but it is absent in the Laramie basin south of Rock 

 river. In Wind Eiver basin it is mostly covered by Tertiary, but it out- 

 crops extensively near Port Washakie, Lander, and Dallas. It appears 

 along both flanks of Owl Creek mountains, on the north slope of Rattle- 

 snake mountains, in southeastern Natrona county, in northeastern Carbon 

 county, in the flexures south of Douglas and east and northeast of Medi- 

 cine Bow, and along the east side of Laramie Mountains from Iron 

 Mountain station to Crow creek. Although there is a long time interval 

 between the Sundance and Chugwater formations, marked erosional un- 

 conformity is rare and in places it is difficult to draw the line between 

 them. This is probably because the first sediments of the upper forma- 

 tion were derived from the one below. The upper limits are similarly ill- 

 defined. There is no discordance in dips of underlying or overlying for- 

 mations. 



Owl Creek uplift. — In the Owl Creek Mountain region the Sundance 

 formation consists of about 200 feet of soft gray sandstones and green 



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