MINING AND PREPARATION OF CLAYS. 61 



a large mass at once, the fall serving to break it up. 

 While effective, this method is often attended with 

 danger. 



MINING OF KAOLIN. 



Kaolin is usually sufficiently soft in nature to be 

 mined by means of the pick and shovel. In some por- 

 tions of the beds near Valley Head streaks of halloy- 

 site are found in the clay, which are quite .hard, but 

 they are of such a limited extent as not to cause much 

 extra trouble. If the deposit is deep, narrow, or in- 

 terbedded with other formations which are too thick 

 to be removed by stripping, or if again the kaolin does 

 not run regular in its composition, it is often advisable 

 to follow the better portions of the bed, or the narrow 

 vein if it is such, by means of shaft, levels, or slopes. 

 These sometimes have to be timbered, at other times, 

 as at Valley Head, they do not. 



In the case of deposits which are large and broad, 

 it is most economical to operate them as quarry work- 

 ings or open pits, digging out the material and loading 

 it on the cars or wheel-barrows which convey it to 

 the washing plant. If a pit is large and broad the 

 sides, instead of being dug out vertically, should be 

 left in benches to prevent the washing down of the 

 bank. 



In North Carolina, where most of the kaolin depo- 

 sits are vein formations whose depth is comparatively 

 great as compared with their width, the method ad- 

 opted is to sink a circular pit in the kaolin about 25 

 feet in diameter. As the pit proceeds in depth it is 

 lined with crib work of wood, and this lining is ex- 

 tended to the full depth of the pit, which varies from 

 50 to 100 or even 120 feet. When the bottom of the 



