FORMATIONS OF THE HARTVILLE UPLIFT 409 



base a white to pinkish conglomeratic quartzite lying on a relatively 

 smooth surface of Algonkian schists and granites. The thickness ranges 

 from about 75 feet to 200 feet, the smaller amount being due mainly to 

 the removal of upper members by erosion prior to the deposition of the 

 overlying formation. The following fossils, which are Mississippian in 

 age, were determined by Dr G. H. Girty : 



Eumetria verneuiliana f Sem inula subquadrata. 



Product as gallailnensis. Spirifer cf. Keokuk. 



Productus Isevicosta. Spirifer striatus var. madisonensis. 



Productus semireliculatus ? Zaphrentis sp. 



Pugnax sp. 



It is believed that this formation represents the attenuated and eroded 

 southern extension of the Pahasapa and Little Horn limestones of the 

 region north. 



HARTVILLE FORMATION 



This formation consists of a thick mass of limestone, having at the 

 base a characteristic deposit of brownish red quartzite from 50 to 100 

 feet thick, lying on the irregularly eroded surface of the Guernsey for- 

 mation. The erosion separating these two formations represents a por- 

 tion of earlier Carboniferous times. The limestones contain sandy beds, 

 some sandy admixture, and occasional thin layers of shale. They are 

 fine grained and compact, generally of light gray color, and at some 

 horizons there are thin sheets of chert and chert nodules. The sand- 

 stones are medium fine grained, with calcareous cement, and occur 

 mostly in beds less than 10 feet thick, although locally they are thicker. 

 The formation is most extensively exposed in the deep canyon of North 

 Platte river above Guernsey. The following Pennsylvanian fossils were 

 obtained from between 300 and 500 feet above the base of the formation 

 in the canyon of Platte river : 



Ambocoeliaf sp. Productus sequicostatus. 



Archseocidaris spines. Productus cf. inflatus. 



Aviculopecten occidentalis. Productus pratlentianus. 



Derbya crassa. Productus punctatus. 



Ruomphalus sp. Productus ser.iireticulatus. 



Fusilina cylindrica. Seminula subtilita. 

 Marglnifera splendens f . Spirifer rockymontanus. 

 Orthothetes (or Derbya) . 



From the lower portion of the formation there were obtained several 

 of the Lower Carboniferous (Mississippian) species found in the Guern- 

 sey formation, so that the lower beds represent products of deposition of 



