CLAYS, THEIR ORIGIN, COMPOSITION AND VARIETIES. 63 



The beds known as fire clay in the table above, and the sandstone and 

 sandy shale underlying it are what are used for the brick manufacture and 

 the product serves an excellent purpose in the construction of the kilns 

 for the manufacture of pressed brick, in the great factories of Zanesville. 



2. The Ferriferous Limestone Clays. 



This deposit must not be omitted, as it occupies a well-marked place 

 in our series, especially in the southern counties, of our Coal Measures. 

 It underlies the limestone coal of the district named above, having a 

 thickness of two to six feet. It is light-colored, of the plastic variety, and 

 appears to be of fair quality, but no important use is known to have been 

 made of it as yet. As clay industries are developed in the districts in 

 which it occurs, it will no doubt be found able to make some contribution 

 to their supplies. 



3. The Kittanning Clay and Shales. 



Under this head we come to the great clay horizon of the state. Its 

 importance far outweighs that of any other clay seam of our scale. 

 Indeed, it is probably equal, in value, to all other sources of clay in the 

 Coal Measures combined. The geological position cf the Kittanning clay 

 is easily remembered. It belongs between the Ferriferous limestone and 

 the Lower Kittanning coal. Often it fills the entire interval between 

 these well-known beds. In some sections, however, where the interval 

 is unusually expanded, a sandstone occurs and the clay and shale are con- 

 sequently reduced to some extent thereby. In its more important fields 

 it ranges in thickness between eight and thirty feet. In some districts it 

 is merged, with only the interruption of the Lower Kittanning coal seam, 

 into the clays that belong next in the ascending series, viz, those which 

 come in below the middle Kittanning coal. In this case the combined 

 deposits constitute a section measuring not less than fifty feet. The Kit- 

 taning clay horizon proper is seen at its best where it enters the state 

 from Pennsylvania, and again where it leaves the state in its extension 

 into Kentucky. In both of these localities of the Ohio Valley, viz, in 

 Columbiana and Jefferson counties, on the one side, and on the other, in 

 Lawrence county, it shows large volume and excellent quality. In Tus- 

 carawas, Stark and Muskingum counties, also, and, in fact, in the other 

 central counties of the coal field, it is scarcely less developed. 



As a rule, the horizon produces a white plastic clay, almost always 

 of fair quality and, in places, of the highest excellence. The plastic clay 

 is the foundation of the great pottery industries of Eastern Ohio, where 

 it is worked on a very large scale. A second, and even more valuable 

 phase of the clay is found at a few points in Stark, Tuscarawas and 

 Carroll counties. The formation here yields a hard or flint fire clay of 



a a. o. 



