CARBONIFEROUS SYSTEM 431 



I 



massive to thinly lamiaiated in structure, is locally brecciated, and it 

 splits into several beds, some of which give place to shale. At the plaster 

 mill south of Eed Buttes the underlying Satanka red shales contain two 

 beds of gypsum about 25 feet apart. One bed 15 feet thick is now worked, 

 and another one, 10 feet thick, was formerly worked. The limestone is 

 hidden by alluvium in part of the region southwest of Eed Buttes, but 

 an outcrop occurs on Antelope creek, halfway to Eed mountain, which 

 yields the distinctive fossil, Myalina perattenuatus, that occurs north of 

 Laramie. It outcrops again farther southwest, on the west side of Sand 

 creek and in the Eed Mountain region, where there are no underlying 

 Satanka red shales and the limestone lies directly on Casper sandstones. 

 Apparently it is this bed that immediately imderlies the 67-foot gypsum 

 bed in Eed mountain and jaelds the numerous fossils discovered l)y Pro- 

 fessor W. C. Knight. ^^ On the northwest slopes of Eed mountain this 

 limestone appears under the gypsum and, although thin, yields distinctive 

 fossils. 



The Forelle limestone contains fossils in small number throiigliout its 

 course. On the east side of Laramie basin the only species identified is 

 llyalina perattenuata, and this appears to be characteristic. The sup- 

 posed Forelle limestone, lying just below the gypsum, on the northwest 

 slope of Red mountain, afforded Aviculipecten occidentalis. Myalina perat- 

 tenuata, Allerisma terminals, and Schizodus compressus. In the section 

 on the east side of Eed mountain this limestone consists mostly of casts 

 and impressions of fossils which were discovered by Professor Knight in 

 1908.^^ According to Doctor Girty, they comprise the following: 



Solenomya n, sp. Pleuropliorns aff. P. tafft. 



Deltopecten mansantens. Dentalium canna. 



Deltopenten corevanus ? Orthonema ? sp. 



Schizodus meekanus. Mevalima perattenuata. 



This fauna is late Pennsylvanian or possibly equivalent to the lowest 

 limestones in the so-called Permian of Kansas. 



The Forelle limestone is separated on account of the Carboniferous 

 fossils which it contains. If it were not for this evidence, the limestone 

 and underlying Satanka shale might lie regarded as a portion of the 

 Chugwater formation, for near Laramie and Eed Buttes the stratigraphic 

 succession is strongly suggestive of Minnekahta limestone lying on Opeche 

 red shale. The latter limestone occurs on the east side of Laramie moun- 

 tains and in the Black hills, and contains "Permian" fossils in the sense 



' Loc. clt., p. 419. 



