CLAYS, THEIR ORIGIN, COMPOSITION AND VARIETIES. 59 



These figures show a deposit approaching absolute purity, and attest 

 the very great value' of the clay. Unfortunately the deposits of this seam 

 in Ohio are few in number, and they are also capricious to a high degree, 

 even within the narrow limits in which they are represented at all. 



The clay deposits of Ohio that have now been described, with the 

 exception of the one last named, would scarcely enter into the account of 

 the practical clay working of the state as at present carried on. We 

 should be told in making this review that we had not yet reached the 

 clays of the geological columns; that the latter are all to be found, with 

 the single exception noted above, at a higher level in our series than our 

 examinations have yet covered. As far as general use is concerned, 

 this is entirely true. The coal measures of the state at the level to which 

 we have now come in our review, are also the clay measures of the state. 

 Every coal seam is normally underlaid by a bed of clay. Further, it is 

 often overlaid as well by clay or shale. Sometimes the coal fails to appear 

 where it is due and clay may occupy the place that belongs to it. The 

 thin coal-measure limestones, in like manner, often rest on clay or are 

 covered by such deposits after the fashion of coal seams. It thus results 

 that we find argillaceous deposits by the score, through the entire series 

 of the Conglomerate group and the Coal Measures proper, including the 

 Barren Measures. A brief catalogue of the principal horizons, so far as 

 the latter are known, will now be given. 



13. The Carboniferous Conglomerate Group. 



As is well known to all students of our geology this group em- 

 braces several great sandstones and conglomerates, four or five coal seams, 

 some of them of wide range and one, at least, of considerable economic 

 value, two thin but persistent limestones, three or four iron ore seams, 

 and a half dozen argillaceous deposits that are severally known as fire 

 clays and shales. The order of the Conglomerate group is as follows: 



Tionesta sandstone. 

 Tionesta coal. 

 Tionesta clay and shale. • 

 Upper Mercer ore. 

 Upper Mercer limestone. 

 Upper Mercer coal. 

 Upper Mercer fire clay. 

 Lower Mercer iron ore. 

 Lower Mercer limestone. 

 Lower Mercer fire clay. 

 Massillon sandstone (upper). 

 Quakertown coal. 

 Quakertown shales. 

 Massillon sandstone (lower). 

 Sharon shales. 

 Sharon coal. 

 Sharon clay. 

 Sharon conglomerate. 



