Malott: The "A'merican Bottoms" Region 19 



of Archimedes, the latter usually in larger numbers than 

 occur in any other Chester limestone of Indiana. In the 

 ''American Bottoms" region it is usually overlaid by a few 

 feet of green shales where it is not cut out by the discon- 

 formity between the Mississippian and the Pennsylvanian. 

 Toward the extreme southern end of the state, it is succeeded 

 by a persistent sandstone of the Chester Series. This sand- 

 stone is not found north of the French Lick region. The 

 Golconda limestone takes its name from Golconda, on the 

 Ohio River in southern Illinois, where the limestone and 

 shale are upwards of 80 feet in thickness.^ In the ''American 

 Bottoms" region there are nowhere more than 10 feet of lime- 

 stone, and frequently much less. It is of little importance 

 physiographically in this region. V\^here it appears in the 

 accompanying shales above the Cypress sandstone, it has been 

 included on the map under the convention used for the Cypress 

 and other contiguous strata beneath the Pennsylvanian con- 

 tact. The single symbol has been used because the discon- 

 formity is so marked that the Pennsylvanian strata are found 

 in several places resting on beds well down in the Cypress, 

 the Golconda formation having been entirely removed by the 

 erosion preceding the deposition of the later strata. The 

 stratigraphic column shown on the right of the geologic map 

 indicates at what levels the disconformity may occur in the 

 region. 



The Pemisylvaiiian Strata. The Pennsylvanian strata ex- 

 posed in the "American Bottoms" region belong exclusively 

 to the lower part of the Pottsville, and are composed for the 

 most part of coarse, gritty sandstone with some associated 

 sandy shales and intercalated thin coal seams. 



The Mansfield Sandstone. The Mansfield sandstone is the 

 name given to the massive, cross-bedded sandstone at the 

 base of the Pennsylvanian rocks of Indiana. Frequently the 

 lower portion is represented by sandy shales which may con- 

 tain a thin seam of coal. The disconformity referred to in 

 the preceding paragraph allows the Mansfield sandstone or 

 its corresponding shale to begin at various horizons from 

 the middle of the Cypress sandstone up to a level perhaps 60 

 feet higher. In the latter case the Golconda limestone and 



■* Charles Butts, Mississippian Series in Western Kentucky. KoitucI: u Gcoloc/ical 

 Survey. 1917. 



