June, 1921] Steel Molding Sand in Ohio 251 



THE POTTSVILLE FORMATION. 



Since the Pottsville is the basal formation of the Penn- 

 sylvanian rocks, its Hne of outcrop Hes along the junction of 

 the Pennsylvanian and Mississippian systems. It is shown 

 in detail on the Geologic Map of Ohio for 1920, and in a general 

 way in Map I of this article. As there sketched it enters 

 Ohio in Trumbull County, extends north nearly to Lake Erie, 

 thence west of south to the Ohio River, which it reaches in 

 Lawrence County. 



The Pottsville formation, which has a thickness of about 

 225 feet in Ohio, consists of conglomerate, sandstone, shale, 

 coal, clay, limestone and flint. The following section shows 

 the principal members of the formation. 



Homewood sandstone 



Tionesta or No. 3b coal 

 Upper Mercer limestone, flint and iron ore 



Bedford coal 

 Shales 



Upper Mercer or Webster Block or No. 3a coal 

 Lower Mercer limestone and iron ore 



Lower Mercer or No. 3 coal 

 Upper Massillon sandstone 



Quakertown or No. 2 coal 

 Clay and shale 

 Lower Massillon sandstone 



Sharon or No. 1 coal 

 Sharon conglomerate 



THE SHARON CONGLOMERATE. 



The Sharon conglomerate, the basal member of the Potts- 

 ville, is the main source of steel molding sand in Ohio. While 

 called conglomerate, it varies greatly in its physical makeup 

 and may be conglomerate, coarse sandstone or shale. 



Where the rock is conglomeratic the pebbles are of quartz 

 which vary in size from a small fraction of an inch up to three 

 inches or even more. The color is usually of light shades. In 

 places pink is common. Near the top of the rock, buff is the 

 characteristic color, while below, light gray is the usual shade. 

 In places dark brown patches, due to iron, were noted. The 

 pebbles are well rounded and have smooth surfaces, which 

 suggest abrasion, due to water action. The characteristic 

 shape is oval. The proportion and size of pebbles vary rapidly 



