54 GEOLOGY OF OHIO. 



times seen to consist of bundles of minute rods, crowded close together, 

 while the soft clay lacks this feature altogether, or contains only frag- 

 ments of these rods. The difference between the two groups of clays 

 does not depend on the amount of alumina nor on the impurities they 

 contain, as a superficial examination might lead us to conclude. What- 

 ever the explanation may prove to be, the line of demarkation between 

 them is clear and well defined. 



None of the plastic underclays of the state, so far as known, show 

 the high quality which would justify the application of the term "fire 

 clay" to them; but they are all universally known by this name and it 

 seems a hopeless attempt to restrict the term to its true signification. 



2. Potter's Clay. — Between the plastic underclays of the state that 

 are called fire clays and the clays that are known as potter's clays, there 

 is no difference whatever. The names are strictly interchangeable in 

 common use. When potteries are drawing their supplies from them, 

 they are likely to be named in accordance with the fact; but otherwise 

 they are known under the former designation. As a rule, however, the 

 most characteristic clays of this division are decidely inferior in composi- 

 tion to the fire clays. They contain large proportions of the fluxing 

 elements and always show a high degree of plasticity. The last named 

 quality it obviously an essential one and governs all the rest. The clays 

 of this division are used not only in stoneware, but also to a considerable 

 extent in sewer pipe, fire-proofing, flue linings, paving blocks and orna- 

 mental brick. 



3. Brick Clay.. — The last of the divisions made in the rough classi- 

 fication that has here been attempted, comprises a large variety of clays 

 and shales, which are more or less used in the manufacture of sewer pipe, 

 paving blocks and common building brick. It includes all the coarser 

 forms of clay and the numerous varieties differ so widely among them- 

 selves that no definition can be given beyond the simple statement that 

 all contain more or less silicate of alumina in their composition. 



SECTION II. 



The Clay Deposits op Ohio. 



To understand the distribution of the clays in Ohio, we must acquaint 

 ourselves with the geological scale in the state, and of the areas covered 

 by its several formations. All the varieties of argillaceous deposits that 

 have been enumerated in the preceding section, so far as they have pres- 

 ent or prospective economic value, viz : shales, brick clays, potters' clays 

 and fire claj-s, will be included in this review. 



