62 2 ■ L. C. SNIDER 



other two limestones are thin, not over 5 feet in thickness. They 

 and the shale between them are very fossiliferous, bryozoa being 

 especially abundant. Exceptionally well-preserved shells of Pro- 

 ductus, and Chonetes as well as screws of Archimedes and speci- 

 mens of other bryozoa weather from the shale in abundance. 

 The Productus is the species which is doubtfully identified with 

 P. infiatus var. color ado ensis Girty, in previous lists in this paper. 

 The Chonetes is a rather large, flat species which is apparently 

 unnamed. Specimens of the same species from Arkansas are in 

 the University of Chicago collection. 



In addition to these forms the following species have been identi- 

 fied from the two lower limestones: Lioclema gracillimum Ulrich, 

 Fenestella cestriensis Ulrich, F. serratula Ulrich, Strehlotrypa nicklesi 

 Ulrich, S. distincta Ulrich, S. major Ulrich, Stenopora tuberculata 

 Prout, Polypora cestriensis Ulrich, Pinnatopora vinei Ulrich(?), 

 Pinnatopora sp., Cystodictya nitida Ulrich, C. cj. lineata Ulrich, 

 Thamniscus furcillatus Ulrich, Productus cestriensis Worthen, 

 Spirifer increhescens Hall, and Spiriferina transversa McChesney. 



Pitkin limestone. — In the Tahlequah quadrangle the Pitkin 

 limestone varies in thickness from about 5 feet to 70 feet. In 

 character it varies from an impure, shaly limestone to a massive 

 blue, crystalline limestone. In the Muskogee quadrangle the 

 thickness of the Pitkin varies little from 50 feet. The formation 

 in this quadrangle consists of light blue to brown, granular, earthy, 

 slightly oolitic strata interbedded with fine textured massive 

 layers. The individual beds vary from thin, platy layers, often 

 separated by thin shale partings, to massive layers 2 feet in thick- 

 ness. In this quadrangle the Pitkin is apparently perfectly con- 

 formable above the Fayetteville and below the Morrow formation 

 of Pennsylvanian age. Indeed, the line between the Pitkin and 

 the Morrow is very difficult to follow, and the separation is usually 

 made on the basis of fossils. From the Muskogee quadrangle 

 north, the Pitkin thins very rapidly and also changes in physical 

 characteristics. The massive, pure limestone phase disappears 

 and the formation becomes argillaceous and ferruginous. Locally 

 the limestone is very sandy. In these localities the beds are thick, 

 and on weathering show intricate cross bedding. Where there 



