South Dakota School of Mines 41 



Wyoming, is lithologically and faunally divisable into two easily 

 distinguishable horizons, namely, the Monroe Creek beds, below, 

 and the Harrison beds above. 



The Monroe Creek Beds. The Monroe Creek beds, Hatcher 

 states, are well shown in the northern face of Pine Ridge at the 

 mouth of Monroe Creek Canyon, five miles north of Harrison, 

 where they overlie the Gering sandstones, and are composed of 

 300 feet of very light colored, fine-grained, not very hard, but 

 firm and massive sandstones. The thickness decreases rapidly 

 to the east and increases to the west. The beds are generally 

 non-fossiliferous, though remains of Promerycochoerus are 

 found in it, hence the name Promerycochoerus zone. 



The Harrison Beds. The Harrison beds receive their name 

 from Harrison, in the vicinity of which town the beds are well 

 exposed. As stated by Hatcher, they are composed of about 

 200 feet of fine-grained, rather incoherent sandstones, permeat- 

 ed by great numbers of siliceous tubes arranged vertically rather 

 than horizontally. They are further characterized by the pres- 

 ence, often in great abundance, of those peculiar and interesting, 

 but as yet not well understood, fossils known as Daemonelix, 

 ( hence called Daemonelix beds by Barbour, who first studied 

 than), and by a considerable variety of fossil mammals belong- 

 ing to characteristic Miocene genera.* 



Later investigation has shown that in some places the di- 

 vision is not readily made on lithologic features alone, but that 

 the formation can in all places be separated faunistically into 

 lower and upper levels as indicated. The following section by 





Figure 7 — Diagrammatic section of the Arikaree on the Nebraska-Wyoming 

 line west of Harrison. After Osborn modified from Peterson, 1906-09. 



*Hatcner, J. B. Origin of the Oligocene and Miocene Deposits of 

 the Great Plains. Am. Phil. Soc, Proc. Vol. 41, 1902, p. 117,. 



