The Rogers Gap Fauna of Central Kentucky 109 



THE ROGERS GAP FAUNA OF CENTRAL KENTUCKY 



By Aug. F. Foerste 



Subdivisions of the Lexington or Trenton limestone. 



In Central Kentucky, the series of strata included in the Lex- 

 ington limestone long have been regarded as the approximate equiv- 

 alent of the Trenton of New York. The basal part of the Lex- 

 ington is composed of coarse grained limestone, forming the 

 Curdsville member, and containing the fauna known from the cri- 

 noid and cystid zones of the lower Trenton in Ontario, in Canada. 

 This is overlaid by a very fine-grained, hard limestone, interbedded 

 with clay. On chemical analysis, this limestone proves to contain 

 a considerable quantity of silica. It corresponds to the Hermitage 

 of central Tennessee. The immediately overlying part of the Tren- 

 ton consists of more or less argillaceous limestone, frequently 

 weathering into small, irregular fragments. In this part of the 

 section Prasopora simiilatrix, the "chocolate drop" bryozoan, is 

 abundant. 'It forms the JV ilmore mtmhev of the Trenton. Above 

 the Wilmore is found a coarse-grained limestone, often forming 

 massive outcrops, identified by L^rich as equivalent to the Bigby 

 of central Tenessee. The next part of the Trenton section con- 

 sists of very fine-grained, argillaceous-appearing limestone, which, 

 on chemical analysis, is found to be a siliceous limestone. This 

 is the Bvachiospongia and Strobilospougia horizon. At and just 

 below this level, Dinorthis ulrichi, Strophomena vicina, and Platy- 

 strophia colbiensis make their first appearance. For this siliceous 

 limestone, usually only five to ten feet thick. Prof. Arthur AI. 

 jNIiller has proposed the name Brannon. In the railroad cut south 

 of Brannon station this siliceous limestone forms most of the cut, 

 resting upon the top of the Bigby, containing Stromatoceriuiii and 

 Strophomena vicina. In the eastern part of central Kentucky, the 

 Brannon limestone often is more or less cherty, and forms the 

 characteristic part of the Flanagan chert horizon, of ^larius 

 Campbell. 



The strata immediately above the Brannon member consist of 

 coarse-grained limestone, often forming large, massive outcrops, 



