218 GEOLOGY OF OHIO 



possible without the use of fire resisting brick, and no other form of 

 clay working would be possible if it were not for fire proof kilns. 



In a word, while making refractory materials has not had the expan- 

 sion and development of some of the cruder forms of clay working, it is 

 par excellence the most impottant use to which clay can be put. 



Taken as a whole, this industry in Ohio is not in as healthy a con- 

 dition as could be wished; many of the fire brick factories have 

 deserted their original business to enter into the temporarily more 

 profitable manufacture of paving materials, and but few new factories 

 for the manufacture of fire brick have been built in the last decade. 



The reason for this is probably due to the over expansion which 

 prevailed some ten years ago. The iron business, on which, above 

 others, the firebrick business depends, has been constantly improving 

 in its metallurgical work, so that while less furnaces are in operation 

 year by year, and that while for one new furnace built about five old ones 

 are dismantled, the production of iron increases nevertheless as the 

 demand justifies it. Also, the introduction of new processes and new 

 refractory materials in both iron and steel making are combining to cut 

 down the demand or the product of former 3^ears. 



Notwithstanding these facts many of the well located firebrick 

 plants of the state show a gratifying advance in prosperity in the last 

 decade. 



The Clays. — The native cla3 T s, suitable to manufacture of refractory 

 materials, are of two classes : 



1st. The Flint Clays. 



2d. The Plastic Fireclays. 



Flint clays are the ma n standby of the refractory material trade of 

 Ohio and Pennsylvania. As has been mentioned in the preliminary 

 discussion of the general properties of clay, flint clays are a lusus natures 

 which scientific men find it very hard to explain. In composition, the 

 best of them are practically pure kaolins but other flint clays are found 

 which are the counterpart of the common plastic fire clays of the state in 

 chemical anah'sis, and still show the typical flint clay structure to its best 

 advantage. And furthermore, flint clays have now been encountered 

 which retain the flinty structure in connection with the most impure 

 chemical character and an absence of any high refractory qualities. 



The main and essential feature which distinguishes the flint clays 

 from others is their almost complete lack of plasticity. Flint clays do 

 exist which are apparently a connecting link between the strictly non- 

 plastic and the common hard plastic clays, and such clays by use of 

 severe physical treatment become somewhat plastic. 



But, it is claimed by those who use the best grade of flint claj^s that 

 no amount of grinding and kneading with water will make a true flint 

 clay any more plastic than a sand rock would become under similar con- 

 ditions. One or two dealers in flint clays have asserted their ability to 



