40 MINERAL RESOURCES OF ALABAMA. 



Of the above analyses, Numbers I and 2 are from Paleozoic 

 formations; Numbers 3 to n, inclusive, are from the Lower 

 Cretaceous, (Tuscaloosa), and 12 is from the Tertiary, and 

 they have been selected from a great number to illustrate the 

 wide distribution of clays of economic value. 



Clays and Shales for Portland Cement Making. Under the 

 head of Cement Resources, we have given a number of analyses 

 of clays adapted to use in cement making, and add here several 

 others. 



These clays, like the preceding, are widely distributed, as 

 may be seen from the localities given, and they are from a 

 great variety of geological formations. 



Analyses of a few shales from the Coal Measures are also ap- 

 pended as being very likely to come into use in this connection, 

 not only because of the fitness of the chemical composition, but 

 also on account of their proximity to the Trenton and Lower 

 Carboniferous limestones and to the mines of coal. 



While the composition of the limestone which is to be used in 

 the cement manufacture, varies in the different formations, and 

 will in a measure determine the character of the clay which will 

 be suitable to mix with it, yet there are certain limits within 

 which the composition of the clay must fall in order to adapt it 

 to the rotary kiln in the burning of the cement. Ordinarily a 

 clay will give good results which contains as nearly as possible 

 60 per cent, of silica and about one-third as much, or less, of 

 alumina and iron oxides, the smaller the proportion of iron the 

 better. The clay should not contain more than 2 per cent, of 

 magnesia and as little sulphur as may be. (D. Fall.) 



