LIMESTONES OF WESTERN TENNESSEE 559 



limestone, 6 inches 'Ci\\cV,cox\\.2im\x\g Bilobites biloba; and clay, 22 

 inches thick. Only the lower part of the Louisville bed, 5 feet 

 8 inches thick, is exposed. It consists of massive limestone 

 overlaid unconformably by a layer of chert, 8 inches thick. At 

 the large quarries between Riverside and Mannie this layer of 

 chert is overlaid by phosphatic nodules, some of them 4 inches 

 long, followed by brown sandstone, 8 inches thick, containing 

 traces of fish remains. 



The coarse, cross-bedded, ferruginous limestone identified as 

 Clinton contains recognizable Silurian fossils only at the top. 

 The possibility therefore exists that further research may prove 

 the greater part of this rock to be of Ordovician age, although 

 for the present it is regarded as equivalent to the Clinton. 



The section at Iron City, just north of the state line of Ala- 

 bama, closely resembles that at Riverside. The best exposures 

 occur directly north of the town, at Cedar Point, along the 

 western side of the railroad branch to Pinckney. The top of the 

 Mannie clay is exposed at various points at the level of the rail- 

 road. The total thickness is unknown, but probably exceeds 16 

 feet, this being the distance of the exposures above the creek. 

 The coarse-bedded ferruginous limestone, 2^ feet thick, was 

 formerly extensively mined. It is overlaid by cherty rock, vary- 

 ing from 2 to 12 inches in thickness, and containing species of 

 Silurian fossils identical with those in the upper part of the Clinton 

 bed at Riverside. The coarse-bedded rock at Cedar Point con- 

 tains very few recognizable fossils, and the few found belong 

 apparently to new species. For the present it is referred to the 

 Clinton, the cherty bed at the top being regarded as its summit. 

 The Clinton is overlaid by soft, red, clayey limestone, 3 feet 

 thick, weathering back, and referred to the Osgood horizon. 

 Above this is more solid limestone, 23 feet thick, referred to the 

 Laurel horizon. In general it is white, but within 3 or 4 feet of 

 the base it is usually more or less strongly tinged with red. The 

 Waldron bed is 3 feet thick, and as at Riverside consists, in 

 ascending order, of clay, i foot thick ; white crumbling limestone, 

 5 inches thick; and clay, 18 inches thick. Only the lower part 

 of the Louisville bed, 19 feet thick, is present. It consists of 



