588 ^V. A. TAEE OOLITES IX SHALE AXD THEIR ORIGIN 



show that the upper portion at least is Triassic. Their conchisious are 

 based ou rej^tilian and amphibian remains found in a member of this 

 upper portion. Williston has given the name Popo Agie to this fossil- 

 bearing member.* 



It is this fossiliferous member that is discussed in this paper, as it is 

 oolitic, in considerable part at least. Branson has described these beds,^ 

 and although the writer has studied them in the field, the following notes 

 regarding them are based on Bransons description, as he has studied 

 them along the entire front of the TTind River Range. 



The thickness of the beds vary, ranging from less than 20 to more than 

 60 feet. In the main, this member is a sandy shale. The upper bed is 



FiGUBE 1. — ?\ot]ula)- stiijftiiif of ooJitir- sliale after Weatherinfj 



massive, ranging up to 15 feet in thickness, and "consists of nodules of 

 purplish, argillaceous sandstone." Branson suggests that the massive 

 character of this bed may be due to the destruction of the bedding planes 

 through the exposure of the beds and the alternate development and 

 filling of sun-cracks, as described by Barrell.^ The color of the Popo 

 Agie beds shows a remarkable variation, ranging through shades of green, 

 red, brown, yellow, purj^le, and tan, "with occasionally white beds and 

 now and then carbonaceous bands. Xot infrequently included fossil bones 

 are black, owing to carbonization.'' The beds are fine-grained through- 

 out, and much of the formation is decidedly oolitic. The amount of the 



< Ibid. 



^ E. B. Branson : Origin of tbe Red Beds in western Wyoming. Bull. Geol. Soc. Am., 

 vol. 26, 1015, pp. 217-230. 



6 Joseph Barren : Bull. Geol. Soc. Am., vol. 23. 1912, p. 426. 



