388 ransome: the ray quadrangle 



in the Ray quadrangle has a maximum thickness of at least 

 1000 feet. As its upper limit is a surface of erosion dating in 

 part frcm early Mesozoic time, the limestone was probably at 

 one time much thicker than at present. It is of Carboniferous 

 age. The basal division is about 75 feet thick and forms the 

 lower part of the scarp that in this region is so prevalent a fea- 

 ture of the Carboniferous outcrop. Under the action of erosion 

 this division behaves as a single massive bed, but in reality it 

 is made up of alternating dark and light gray layers, a foot or 

 two thick, which in cliff faces give a banded appearance. This 

 member with a few transitional beds at its top is succeeded by 

 a very massive member, fully 100 feet thick, within which, as 

 exposed in cliffs, there is as a rule scarcely more than a sugges- 

 tion of divisional bedding planes. These two members together 

 constitute the principal cliff-forming part of the Carboniferous 

 limestone. The third division consists of beds generally thinner 

 than those in the other two divisions but not separable from them 

 by any marked lithological distinction. Thin layers of calcare- 

 ous shale separate some of the beds but these are a very subordi- 

 nate part of the formation. 



The beds of the two lower divisions carry many fragments of 

 crinoid stems and less abundant rugose corals, with long-winged 

 spirifers and Rhipidomella. In the upper division appear differ- 

 ent species of Productus and Spirifer, Derbya crassa, Composita 

 suhtilita, and Fusulina. According to Dr. George H. Girty two 

 faunas are represented, one Mississippian and the other early 

 Pennsylvanian. Had it proved practicable to map separately 

 the Mississippian and Pennsylvanian portions of the formation 

 the corresponding names Escabroso limestone and Naco lime- 

 stone, used in the Bisbee quadrangle, might have been appli- 

 cable in the Ray quadrangle. 



By far the greater part of the formation as exposed in the Ray 

 quadrangle belongs to the Mississippian. 



