506 



LOCAL SECTIONS 



Louisville, and in the glades of Decatur County, Tennessee. The rock is highly 

 magnesian, and assumes a cellular character from the presence of the casts of corals. 

 Higher up the hill, twenty-two feet above the river-level, the rocks are quarried for 

 burning into lime, and though still magnesian, they seem to afford a tolerable lime. 

 They repose on the strata above-mentioned, and contain Leptwna depressa, and Tere- 

 hratula reticularis (small variety) . 



In a small creek about half a mile above Le Claire the rocks have a considerable 

 local dip to the northwest, and the following section is exposed : 



Feet. 



1. Thick-bedded magnesian limestone, with casts of MurcMsonia, Pleuroto- 



maria, Favosites GotMandica , and Orthoceratites, ... 15 



2. Massive magnesian limestone, with Pentamerus galeatus (?), casts of 



Lituites and Lucina, Favosites GotMandica, a large Gyrtoceras and 



a small Orthis, ....... 20 



3. Broken magnesian limestone, made up almost of casts of a small globose 



Terebratula. 



4. Bed containing Orthis caualis (?), ..... 6 



5. Thin layers, without fossils. 



6. Bed containing Orthis canal is (?), ..... 20 



7. Thin shaly layers, without fossils. 



At Le Claire, the rocks are seen a little above the water-level, containing nume- 

 rous casts of a Pentamerus (probably P. Galeatus); and Terebratula Wilsoni was 

 found in rocks taken from the foundation of a house thirty-five feet above the river. 



Two miles below Le Claire, and opposite Smith's Island, the rocks contain Favo- 

 sites Gofhlandica, Gorgonia, or Fenestella, and casts of columns of Orinoidea. 



Just below this locality, opposite Smith's Island, the first exposures of sandstones, 

 shales, and argillaceous iron ore of the coal-measures, make their appearance, abutting 

 and even resting immediately on the above magnesian limestone of the Upper Silurian 

 date.* The sandstone which forms the lower part of the section is ash-coloured, 

 with small cavities filled with carbonaceous matter ; above this lie the shales, with 

 argillaceous iron interstratified ; the latter sometimes in flattened nodules, con- 

 taining impressions of Lepidodendron. The thickness of these strata is above fifty- 

 five feet. Below this, the magnesian limestones of Upper Silurian date reappear at 

 several points before they are finally lost to view under the waters of the Mississippi ; 

 once, a quarter of a mile below the first carboniferous exposure, where they attain a 

 height of six feet above the water-level, and again, a few hundred yards lower down, 

 in perpendicular walls, fifty-eight feet high, with a dip of 26° to the north-northeast. 

 No limestone could be discovered here referable either to the Carboniferous or De- 

 vonian systems. Magnesian limestones of Upper Silurian date are again seen 

 about one mile below Smith's Island ; thence they gradually decline, and are soon 

 lost to view. Near Hampton, the carboniferous sandstones and shales again 



* From Le Claire to this point, the stratified rocks support a deposit of loose sandy loam, imbedding 

 immense numbers of Unios and other genera of fluviatile shells, which would afford an excellent mineral 

 manure. This shell loam seems to be of considerable extent, and is usually reached, even some distance 

 back from the river, after penetrating the soil. 



