CHAPTER II. 



CLAYS AND CEMENT. 



The industries which in the near future bid fair to rival in 

 importance that of Iron Making, are those connected with the 

 utilization of our vast resources of clay and of cement materials, 

 and these come appropriately next to be described. 



KAOLINS, CLAYS AND SHALES. 



Many accumulations of clay-like materials, are the insoluble 

 residues left from the decomposition of other minerals and 

 rocks, and when such clays have not been removed far from 

 their parent rocks they are known as residual clays. Some of 

 the purest of clays, i. e., kaolins, are of this kind, resulting from 

 the decomposition of feldspars, and on the other hand residual 

 clays left after decomposition of limestones and of many cry- 

 stalline rocks, are among the most impure of the clav kind. 



Any .of these residual clays, from the pure kaolins to the 

 heterogenous mixtures left from limestones, etc., may, bv the 

 action of running water, be taken up and redeposited in secon- 

 dary positions, becoming thus sedimentary clays. In this re- 

 moval from one place to another, much of the contaminating 

 material may be separated from the clayey matters, and in this 

 way the secondary deposits may occasionally be freer from for- 

 eign admixtures than the original residual mass. But, a- i 

 rule, the opposite is the case, and the more a mass of clay has 

 been subjected to transportation and redeposition, the more 

 likely it is to take up and incorporate impurities of all sorts. 



KAOLINS. 



If we use this term to designate only the residual material 

 from the decomposition of feldspars, the kaolins are in Ala- 



