62 GENERAL DISCUSSION OF CLAYS. 



kaolin has been reached the filling in of the pit is 

 begun, the crib work removed from the bottom up- 

 ward as the filling proceeds. If there is any overbur- 

 den this is used for filling in the pit, and as soon as pit 

 is worked out a new one can be sunk in the same 

 manner right next to it. In this way the whole vein is 

 worked out, and if the deposit is large, several pits 

 may be sunk at the same time to increase the output 

 of the mine.* 



Hydraulic mining has been tried with some success 

 in some very sandy loose-grained kaolins, but it would 

 not work in any of the deposits in Alabama, which the 

 writer has thus far examined. The method to state it 

 briefly, consists in washing the clay down into the 

 bottom of the pit whence it is sucked up by means of 

 a pump and discharged into washing trough from the 

 conveying pipe, it being sometimes necessary to have 

 a scraper to stir or loosen up the clay in order to per- 

 mit its being drawn up more easily. This is a cheap 

 and rapid methed where it can be employed, but most 

 kaolins are too dense and not sandy enough to allow 

 of its being used. 



THE WASHING OF KAOLINS. 



As has already been stated, most kaolins have to be 

 washed before shipment, and one of two methods may 

 be employed, i. e. washing in tanks or troughing. 

 With the first method or that of washing in tanks, the 

 kaolin is thrown into large circular tubs filled with 

 water, in which it is stirred up by means of revolving 

 arms and the clay lumps thereby disintegrated. By 

 this treatment the fine kaolinite particles as well as 

 very fine grains of mica, feldspar, and quartz remain 



*F. Biep, Clay Deposits and Clay Industry in North Carol'na Bullettn No. 13. 

 N. C. Geol. Surv., p. 54. 



