SILURIAN OUTCROPS 397 



Nelson county, along Rolling fork. In Tennessee, the most northern 

 exposures on the same side of the anticline occur about 7 miles west 

 of Lafayette, in Macon county ; north of Bledsoe, in the eastern part of 

 Sumner county ; and south of South Tunnel, in the same county. The 

 distance between these points in Tennessee and the locality in Kentucky 

 is 75 miles. 



Within 75 miles the lithological features of formations may often 

 change. Indeed, considerable variations are sometimes noticed within 

 comparatively short distances. For instance, within 14 miles, on passing 

 from the southern to the northern end of Bullitt county, in Kentucky, 

 the Clinton changes from a white to a salmon-brown limestone. Within 

 a distance of 15 miles, along the line separating Ripley and Jennings 

 counties, in Indiana, the lower half of the main Osgood clay section is 

 replaced by indurated clay, and the upper half by thin limestone layers. 

 In the area under investigation, in Tennessee, the Osgood changes from 

 a soft, thin bedded clay, at Bledsoe, to an indurated clay, at South Tun- 

 nel ; the upper part is an impure limestone at Baker Station, and farther 

 southwest almost the entire bed becomes an impure limestone. 



There is, however, a remarkable similarity in the characteristics shown 

 by the most southern Silurian exposures in Kentucky and the most 

 northern outcrops in Tennessee. This similarity extends even to the 

 minor subdivisions of the group. 



SUBDIVISIONS OF THE SILURIAN 



In comparing lithological features of different localities it is con- 

 venient to refer to the different subdivisions by distinguishing names. 

 For this purpose various names were proposed in two recent reports of 

 the geological survey of Indiana,^ and the same names will be used in 

 the present paper. Since the Tennessee area is geographically distinct 

 from the Ohio, Indiana, and Kentuck}^ area of outcrop, a second series 

 of names is here proposed, referring to t3^pical exposures in Tennessee, 

 but the names taken from Tennessee localities will not appear in the 

 following pages (see pages 407 and 421) : 



Indiana and Kentucky names. Tennessee names. 



Louisville limestone. Bledsoe limestone "] 



Waldron shalv clay. Newsom shaly clay | pi-ff 



Laurel limestone. Whites Bend limestone.. ) ^ , .„ ' omion 



Osgood shalv clay. South Tannel bed }■ '^^niei viiK 



Clinton limestone. Baker limestone '. . J ^^^^^sione. 



J 



SILURIAN SECTIONS AT SOUTH TUNNEL AND BLEDSOE 



The most accessible of the Silurian sections in northern Tennessee is 

 that along the Louisville and Nashville railroad, near South Tunnel, 



* Tweuty-first and Twenty-second. 



