138 GEOLOGY OF OHIO. 



admixture of some more fusible clay. It also seems likely that there is 

 a decided difference in the thermal qualities of the shales and fire clays 

 which their analyses and oxygen ratios fail to show. 



It cannot be stated as a fact or even a theory of well established 

 likelihood that such a fact exists, but if such were the fact it would 

 explain a number of questions which are very difficult to answer or 

 explain. 



If the theory concerning the role of iron in clays, as part of the 

 hydrous silicate base of the clay, be true, then these shales in which this 

 condition is best shown will depend on the thermal qualities of an iron- 

 alumina silicate, about which as a separate ingredient or mineral we know 

 nothing. The fire clays of the river district contain their iron largely 

 as granular iron oxide and sulphide, in which the iron acts directly as a 

 flux from the beginning and is to be classed as such. 



The actual temperature used in burning these two classes of clay 

 throws little light on the problem. 



The following measurements were made in kilns of sewer pipe and 

 paving brick which were at the highest temperature and just ready to 

 finish the burning: 



1. The A. O.Jones Co., Fire clay and Shales mixture 1,860 



2. The Logan Fire clay Co., Fire clay and Shales mixture 1,712 



3. The Massillon F. B. & S. Co., Fire clay and Shales mixturel 1,890 



4. The Nelsonville Sewer Pipe Co., Fire clay 1,920 



5. The Canton & Malvern Paving Brick Co., Pure Fire clay 1,920 



6. The Crown Sewer Pipe Co., J Shales J Fireclay 1,820 



7. W. B. Harris &Bros., Shales and Drift clay 1,800 



8. The Canton Brick Co.. Shales only 1,800 



9. The Hill Sewer Pipe Co., Sandy Shales 1,920 



10. Akron Sewer Pipe Co., Sandy Shales 1,900 



11. The Buckeye Sewer Pipe Co., Sandy Shales 1,875 



Average 1^60 



In this table, the quality and appearance of the mixture used is very 

 much alike in Nos. 1, 2, 3 whose temperatures are 1,860, 1,712, 1,890 

 respectively. 



The qualities of 4 and 5 are very sinilar and both show the same 

 temperature, 1,920. 



The shales used at numbers 7 and 8 are not especially similar in 

 appearance, the temperatures coincide at 1,800. 



The shales at 9, 10, 11 are similar in composition except that the 

 clay used, at 9 was more croppy and sandy than usual and showed the 

 effect in its fire qualities. 



Whether this suggestion as to the part that iron plays be the true 

 reason or not, suffice it to say that there is not the difference of temper- 

 ature or duration of exposure in that temperature which the difference in 

 the average analyses or oxygen ratios would lead us to expect. 



