418 N. H. DARTOK PALEOZOIC AND MESOZOIC OF AVYOMING 



On the northeast slope of Eattlesnake mountains the Tensleep sand- 

 stone is separated from the Chngwater red beds by bnf£ shale and thin 

 layers of pure limestone which probably represent the Embar formation. 

 The only trace of this formation observed in the region eastward is in the 

 local anticline just west of DiflBculty post-office, where the Tensleep sand- 

 stone is overlain by 250 feet of yellow shales and limestones strongly sug- 

 gestive of the Embar formation in the Owl Creek mountains. 



Fossils and age. — ^The massive limestone member of the Embar forma- 

 tion is very fossiliferous, especially in the walls of Bighorn canyon south 

 of Thermopolis, but, so far as observed, there is only one mollusk, identi- 

 fied by Dr G. H. Girty as Spiriferina pulchra. This form is believed to 

 characterize a horizon Just below the so-called Permo-carboniferous of the 

 Wasatch Mountain region, and, as Doctor Girty coi'relates the latter with 

 the Permian of the Grand Canyon section, the occurrence of these fossils 

 in the Embar limestone suggests that this formation is equivalent to the 

 iipper Aubre}- limestone of northern Arizona. A fenestelloid which could 

 not be determined specifically also occurs in this limestone. 



The fossils obtained by Mr Woodruff on the slope of the Wind Eiver 

 mountains on head of Sage creek were found by Dr G. H. Girty to be 

 Spiriferina pulchra, Seminula subtilita, Aviculipecten aff. eruelcensis, 

 Stenopora sp., Polypora sp., Derbya ? sp., and a sponge. From ledges 

 west of Lander there were obtained Spiriferina pulchra, Spirifer aff. cam- 

 eratus, and Productus nevadensis ?. 



According to Doctor Girty, "The Embar limestone has a very different 

 fauna from the Kansas Permian, but it may be equivalent to it or even 

 later. The fauna is not related to Guadaloupian. It occurs in Utah just 

 below Permo-Carboniferous and is known also in Idaho and Nevada." 



CASPER FORMATION 



Name and general relations. — The name Casper formation is proposed 

 for the limestones and sandstones constituting the greater part of the 

 sedimentary rocks in the Casper and Laramie mountains. These rocks 

 represent the southeastward extension of the Amsden and Tensleep for- 

 mations, but are so changed in character and indefinite in stratigraphic 

 limits that correlation is not desirable and a new name is required. The 

 Casper formation lies on pre-Cambrian rocks in the greater part of the 

 area, but possibly to the north the basal sandstone represents an atten- 

 uated eastern extension of the Deadwood formation, and in eastern Car- 

 bon and Natrona counties there may also be a small amoimt of Madison 

 limestone at the base, but at present there is no evidence on which to 

 separate these. . The plane on which the formation lies rises to the south, 



