CHARACTER OF SILURIAN FORMATIONS 407 



fore, in northern Tennessee and in Kentucky and southern Indiana the 

 Osgood bed forms a well marked horizon, south of the Cumberland river, 

 especially south of the Harpeth river, it can be recognized only when 

 followed from outcrop to outcrop, or studied in connection with the 

 fossils found in the Laurel limestone above and the Clinton limestone 

 below. South of Harpeth river, where the Clinton-Osgood-Laurel beds 

 form practically a single lithological unit, the name Centerville limestone 

 may prove convenient as a general name for this series (figure 3). 



Constancy of Laurel limestone. — As compared with the Clinton limestone 

 and Osgood bed, the Laurel limestone is constant in character, both in 

 thickness and in lithological appearance. It is a whitish limestone, at 

 some localities slightly blotched with red. Almost all the Silurian quar- 

 ries at present operated in Indiana, except those at Utica and Charles- 

 town Landing (Louisville limestone), along the Ohio river, belong to this 

 horizon. The numerous quarries east of Clermont, in Bullitt county, 

 Kentucky, are in the Laurel limestone. The quarries along Beargrass 

 creek, east of Louisville, are the only important Silurian quarries known 

 in western Kentucky which belong to another horizon, the Louisville 

 limestone. In Tennessee the Laurel limestone could be quarried at 

 South Tunnel (locality 4). It was formerly extensively quarried at Baker 

 (locality 6) and west of Whites Bend (locality 7). It is at present actively 

 operated at various points west of Newsom (localities 11, 12), and local 

 quarries are opened at Linton (locality 15) and at Centerville (locality 26). 



Constancy of Waldron shale. — The Waldron clay shale is another re- 

 markably constant bed. North of Decatur county, in Indiana, it changes 

 into a limestone horizon. From Waldron, in Indiana, southward to 

 Newsom (plate 39, figure 2; figure 1, locality 12), in Tennessee, it con- 

 sists of shaly clay, sometimes interbedded with a little thin limestone. 

 It is very fossiliferous at numerous points in Indiana; at most localities 

 in Kentucky it is nearly barren or contains only a small fauna, and this 

 is also true of most localities in Tennessee ; but at Whites Bend it is 

 fairly supplied with fossils, and at Newsom it contains a rich fauna, 

 rivalling the best localities in Indiana. Its thickness usually varies in 

 the neighborhood of 8 feet, but along Duck river its thickness does not 

 appear to exceed 4 feet. It has so far not been identified farther south 

 or west in Tennessee than Montgomery's mill (locality 27). 



Constancy of Louisville limestone. — East of Louisville, along Beargrass 

 creek, the Louisville formation is a whitish limestone. All of the lime- 

 stone is quarried, although some of the layers are rather soft and seem to 

 weather readily. Where long exposed the softer rock has disintegrated 

 so that the section seems to consist of fairly hard limestone layers sepa- 

 rated by more or less covered intervals. 



