MINING AND PREPARATION OF CLAYS. 59 



A classification which has been made by Seger, the 

 great German Ceramic Chemist, gives : 



1. Yell o ir burning, containing lime and iron. 



2. Red burning, non-aluminous, ferruginous clays, 

 which are free from lime. 



3. WJtitc ami i/ellow burning. These clays are low 

 both in lime and iron. 



4. White burning, low in iron and high in alumina, 



THE MIXING AND PREPARATION OF CLAYS. 



RPOSPECTING FOR CLAYS. 



Clay deposits are best seen in those regions where 

 rivers and brooks have cut gullies and ravines, the clay 

 showing on the sides of the cut. In such locations the 

 thickness of the deposit and variation in its character 

 vertically are well shown. Similar sections are to be 

 loooked for along railroads. As the beds are apt to 

 wash down it is necessary to clean the surface of the 

 cut before taking any sample for tesiting, and even 

 then great care must be observed to insure the sample 

 being an average one. 



Apart from cuts the presence of clay can often be 

 determined by the character of the vegetation, the na- 

 ture of the soil, or upturned tree roots. 



The outcropping of clay in a ravine should not be 

 depended on alone, but in addition borings should be 

 made to determined the depth and extetnt of the de- 

 posit, and persistance of the different layers if there 

 is a variation in them. 



Shale often forms cliffs or steep slopes, at the base 

 of which there may be a talus of partly weathered 

 fragments and soft clav; in fact the outcrop of a shale 

 deposit may be covered by the clay into which it has 



