SILURIAN SECTIONS 399 



(figure 1, locality 4), about ten miles south of the Kentucky border. 

 The railroad passes through two tunnels south of the station. The 

 farther end of the second tunnel is five-eighths of a mile south of the 

 station. 



One hundred and fifty feet south of this tunnel the top of the Chat- 

 tanooga Black shale is visible at the side of the railroad track. A rail- 

 road cut, one-seventh of a mile south of the tunnel, shows the lower 

 part of this shale, and a second cut, one-third of a mile south of the 

 same point, exposes its full thickness. At a third railroad cut, half a 

 mile south of the tunnel, the Chattanooga shale (Devonian) rests on 

 the Waldron shale (Silurian). From this point the Silurian section 

 (figure 3) extends for a distance of about four-fifths of a mile along the 

 railroad track. The strata are met in descending order. 



The Waldron shale is onl}^ 5 feet thick at the cut mentioned (plate 

 35, figures 1 and 2). It weathers to a soft clay and contains very few 

 fossils. Although it presents all the lithological appearances of the 

 Waldron shale, as seen in Kentucky, its paleontological identity is 

 better established b}^ exposures farther southwest, preeminently b}^ 

 those at Newsom, 40 miles distant. 



Beneath the Waldron shale lies the Laurel limestone (plate 35, figure 

 2), forming the main body of the cut. It is 28 feet thick. The stone is 

 white and heavy bedded and, elsewhere in Tennessee, is frequently 

 quarried as a building rock. At the top of the Laurel limestone, for a 

 thickness of 2 to 3 inches, the rock is distinctly oolitic. The same 

 oolitic phase is shown at the top of the Laurel limestone in many parts 

 of Nelson and Bullitt counties, in Kentuck3^ Both in Kentucky and 

 in Tennessee the top of the limestone, especially the oolitic laj^er, con- 

 tains fossils which also occur, but in greater abundance, in the Waldron 

 shale. At South Tunnel, Whilfieldella nitida occurs in the oolitic layer. 

 Orthoceras amycus is found near the middle of the Laurel limestone. 

 Pisocrinus gemmiforinis is common near the base. This fossil is 

 especially abundant at a fourth railroad cut, south of the semaphore 

 electric signal, three-fourths of a mile from the tunnel (plate 36, 

 figures 1 and 2). The base of the formation is here a crinoidal limestone. 

 In Indiana and northern Kentucky, Pisocrinus gemmiformis occurs 

 abundantly, both in the base of the Laurel limestone and in the lime- 

 stone la3^ers placed at the top of the Osgood beds. Farther south it be- 

 comes difficult to determine where to draw the line between the limestone 

 layers belonging to the Laurel and those referred to the top of the 

 Osgood beds. In Tennessee it is impossible to make such a separation, 

 and here all of tlie limestone section is referred to the Laurel. 



In the cut south of the semaphore signal, already mentioned, the 



