64 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



io erosion has produced a marked effect upon the contours of the vallevs, 

 causmg, in some instances, notable constrictions, as shown below. 



This formation constitutes part of the Knobstoiie of Indiana. The 

 name Knobstone, there as well as in Kentuck)?-, arises from the topographic 

 features resulting from its persistence as a protective capping on the sum- 

 mits of the ridges and hills. The knobs of southern Indiana rise abruptly 

 3U0 feet or more above the shale lowland to the east. 



Above the Logan conglomerate there is a local development of hme- 

 stone in south-central Ohio, which was classified by Prof. E. B. Andrews, 

 from a study of fossils, as an equivalent of the Chester limestone of Illinois 

 and Missouri, or the latest of the Eocarboniferous series. It is known as 

 the Maxville limestone, from a locality in Perry County, and is probably 

 best displayed on Jonathan Creek in Muskingum County. It has a thick- 

 ness of only a few feet and the outcrops are mainly on valley slopes. 



Pottsville, or Conglomerate Coal Measures. TllC SerieS of formatioUS iu whicll tlie 



coal seams are embraced are found in a large basin extending from northern 

 Pennsylvania and northeastern Ohio southward to eastern Temiessee. Tlie 

 Ohio River traverses the northern half from Pittsburg, Pa., to Marietta, 

 Ohio, below which it bears toward the western margin of the basin and 

 leaves it a short distance above Portsmouth, Ohio. The area covered by 

 these formations in Ohio is estimated by Orton to be about 10,000 square 

 miles, or about one-fourth the area of the State. Pennsylvania and West 

 Virginia each have an area about as extensive as that of Ohio. A few 

 square miles in southwestern New York, chiefl)' in the portion of Catta- 

 raugus County south of the AUeglieny River, fall within the limits of this 

 basin. By reason of being in a basin which was in process of filling, the 

 lowest members appear on the Borders, while the highest are found in its 

 interior portion. 



At the base of these formations there is found a series of conglomerates 

 and sandstones with thin beds of sliale and limestone, and with local 

 developments of coal, to which the general name Conglomerate group lias 

 been applied. In the Pennsylvania reports it has the names Serai con- 

 glomerate and Pottsville conglomerate, and constitutes No. XII of the rock 

 series of that State. 



Allegheny, or Lower Productive Coal Measures. NeXt aboVe tllC SCricS of COUgloiUerateS 



and sandstones just discussed come the Lower Productive Coal Measures, 

 which have a thickness aboiit as great as the entire Conglomerate group. 



