SILURIAN SECTIONS 40l 



At South Tunnel the top of the Ordovician (plate 37, figure 1), which 

 is a thick bedded limestone, presents a peculiar contorted appearance. 

 Similar exposures of this rock occur at Whites Bend (plate 39, figure 

 1 ; figure 1, locality 8). 



The section at South Tunnel includes only the lower half of the Wal- 

 dron clay shale, and the Louisville limestone is entirely absent. The 

 Louisville limestone is, however, well exposed at Bledsoe, 14 miles east- 

 ward. Along the railroad cut, above Sam Fleming's house, about a 

 mile north of Bledsoe (plate 37, figure 2 ; figure 1, locality 3), the Chat- 

 tanooga Black shale (Devonian) rests upon limestone. The 5 feet of 

 limestone at the top of the section are white and crinoidal. The lime- 

 stone below the level of the railroad track is fine grained and has been 

 so much weathered that it is all more or less tinged with brown. Many 

 of the courses are quite soft and weather aw^ay rapidly. 



Nine feet below the Black shale and 1 foot above the railroad track 

 Conchidium knappi was found. The same fossil is common 19 and 22J 

 feet below the Black shale. It is characteristic of the Louisville lime- 

 stone horizon in Indiana and Kentucky. At the quarries east of Louis- 

 ville, along Beargrass creek, it occurs above what is there called the 

 " blue ledge." In the Bledsoe section Pentamerus oblongus is found on 

 the hillside opposite C. F. Hedge's house, in the lower part of the Louis- 

 ville limestone. Although cited in New York from the Clinton lime- 

 stone, along the western side of the Cincinnati anticline it has so far 

 been discovered only in the Louisville horizon. In fact, it is fairly 

 common at this horizon, between Louisville and Charlestown. along the 

 Ohio river, and at Clermont, in southern Bullitt countj^, Kentucky. 

 The fossils occurring in the Louisville horizon at Bledsoe are enumerated 

 later. 



LITHOLOGICAL CHARACTER AND THICKNESS OF TENNESSEE SILURIAN 



FORMATIONS * 



Explanation of the section. — While the various subdivisions of Silurian 

 age recognized in Indiana and Kentucky can be readily identified in 

 northern Tennessee, several of them change so much on being followed 

 south westward that they can be traced through central and southern 

 Tennessee only with difficulty. This is especially true of the Clinton 

 limestone and the Osgood clay shale. 



The following notes will make the accompanying drawings more in- 

 telligible. In the first set of sections of Silurian strata accompanying 

 this paper (figure 3) the sections have been so arranged as to place the 

 top of the Osgood bed at the same level, the intention being to indicate 

 the variation in thickness of the various formations on following them 



