430 N. H. DARTON PALEOZOIC AND MESOZOIC OF WYOMING 



Correlation. — From the general composition and stratigraphic relations 

 of the Casper formation, it is believed to represent the Amsden and Ten- 

 sleep formations of the Bighorn and Wind River regions, the Minnelusa 

 formation of the Black hills, or the Hartville limestone of the Hartville 

 uplift, but the precise stratigraphic equivalency and limits are not appar- 

 ent. The persistent red shale, which appears in the basal portion of the 

 formation in the northwestern portion of Albany county and rises still 

 higher to the northwestward, dou.btless represents the basal member of 

 the Amsden formation, and if this is the case the underlying limestone is 

 j\Iadison, which can be separated by future detailed field work in Carbon 

 and Natrona counties and perhaps also in Converse county. Although 

 the upper member of the Casper formation is a massive buS to white 

 sandstone, supposed to represent the Tensleep sandstone, this is not every- 

 where separable from the underlying members, notably in the region south 

 of the latitude of Laramie. As the lower portion of the Amsden forma- 

 tion is ]\Iississippian, the lower part of the Casper formation also extends 

 into that division, at least in the region north of the canyon of Laramie 

 river through Laramie mountains. As there is overlap of the higher 

 beds to the south, it is probable that at the latitude of Laramie, and even 

 for some distance farther north, the Casper formation is entirely of Penn- 

 sylvanian age. 



FORELLE LIMESTONE AND SATANKA SHALE 



In the vicinity of Laramie the limestones and sandstones of Casper for- 

 mation are succeeded by about 200 to 232 feet of red shale capped by a 

 thin but conspicuous and persistent bed of limestone. For these the 

 names of Forelle limestone and Satanka shale are proposed, from stations 

 on the railroad a few miles south of Laramie. 



The Forelle limestone outcrops along the west slope of Laramie moun- 

 tains from about 5 miles south of Eed Buttes to Howell, and apparently 

 also at Boswell spring, 23 miles east of Medicine Bow. It varies in 

 thiclmess from 4 to 20 feet, and gives rise to a low ridge separated from 

 the main slope by a shallow valley excavated in 200 feet or more of 

 Satanka red shale which underlies the limestone. The outcrop is a short 

 distance west of the great springs 2 miles east of Laramie, and it crosses 

 the railroad at Forelle and Eed Buttes. In places the limestone is fossil- 

 iferous. Locally it becomes gypsiferous and southeast of Laramie a 10- 

 foot bed of g3^psum occurs in the red shales a short distance below it. In 

 the railroad cut just south of Forelle, Avhere the limestone is well exposed, 

 it is heavily bedded, quite pure, and nearly 20 feet thick. To the south, 

 near Eed Buttes and beyond, the rock becomes gypsiferous, varies from 



