66 GEOLOGY OF OHIO. 



quality scarcely inferior to the best clays of the country. This phase is 

 ,known under the name of the Mineral Point clay. It is largely worked 

 and manufactured at the village of this name, and at Canal Dover, as well, 

 and the products have an excellent name in all markets, for their refrac- 

 tory quality. 



Analyses of the Mineral Point clay have been often published. A 

 single one will be quoted here, fairly representing the formation. (Lord) 

 The figures show a clay of great excellence. 



Combined silica 35.39 



Alumina 31.84 



Combined water 11.68 



Percentage kaolinite base 78.91 



Free silica 17.13 



Titanic acid '. 1.68 



Sandy material (total) t 18.81 



Susquioxide of, iron 0.67 ■ 



Lime 0.50 



Magnesia 0.19 



Potash 0.59 



Of the ordinary phase of the deposit, viz., the white plastic variety, 

 abundant analyses are at hand, but it is hard to find any one that can be 

 called thoroughly representative. In the discussion of clays in manufac- 

 tures in a succeeding chapter, numerous analyses will be found. The 

 products of this horizon are used on a great scale in the finer pottery 

 manufacture for saggers, also in part for the manufacture of Rockingham 

 and yellow ware; and, lower still in the scale of value, for stoneware. 

 These clays are a main dependence of great sewer-pipe factories, and also 

 are sometimes used in making fire-brick of ordinary quality. An enor- 

 mous amount is now being turned to account in the manufacture of pav- 

 ing brick. By reason of the uses and adaptations above named, the Kit- 

 tanning clay seems certain to hold for all time to come the first place in 

 our clay horizons. 



4. The Middle Kittanning Clay. 



As already stated, this stratum is in some instances merged into the 

 Kittanning clay proper, but it deserves a name and place of its own in 

 our scale. At one locality, viz., Oak Hill, Jackson county, it yields a 

 "No. 1," or hard fire clay, and is there made the basis of an important 

 fire-brick manufacture. It carries in many of its outcrops, nodules of iron 

 ore, which interfere to some extent with its availability as a source of clay 

 for manufactures. No peculiarities of composition can be claimed for it, 

 according to present knowledge, but it reinforces in an important way, 

 the deposits of the horizon already described, which directly underlie it 



