34 CLAYS AND CLAY INDUSTRY. 



The clay is dug by a gouge spade, which differs from an 

 ordinary spade in having a curved or semicylindrical blade, as 

 well as a tread on its upper edge, to aid the digger in forcing it 

 into the tough clay. A lump of clay dug by the pitman is 

 termed a spit, and in taking out the material it is customary to 

 dig over the area of the bottom of the pit to the depth of a spade 

 and then begin a new spit. The thickness of any bed of clay, 

 therefore, is always judged in spits. 



Where a pit is dug so deep that it is not possible for the 

 workman to throw or lift the lumps to* the surface of the ground,, 

 a platform may be built in the pit, halfway up its side, or else 

 the clay is loaded into buckets (PI. VI) and hoisted to' the sur- 

 face by means of a derrick operated by steam-power or horse- 

 power. As soon as a pit is worked out, a new one is begun 

 next to it, but a wall of clay, i to 2 feet thick, is commonly left 

 between the two. When the second pit is done, as much as 

 possible of this wall is removed. A platform of planking is laid 

 on one side of the pit on the ground, and the clay thrown upon 

 this, the different grades being kept separate. 



When the clay lies above the ground or road level, there is 

 less trouble with water, and it is not necessary to work the clay 

 in pits, although the general system of working forward in a 

 succession of pit-like excavations or recesses is followed. In 

 such banks, the cart or car is backed against the face of the 

 excavation and the clay thrown into it. 



Unless a number of pits are being dug at the same time, the- 

 output of any cne deposit or of any one grade is necessarily- 

 small, since five or six different kinds are sometimes obtained 

 from one pit. It would alsoi seem that by this method any one 

 grade of clay might show greater variation than if the excava- 

 tion were more extended, for the reason that since clay beds 

 are liable to horizontal variation, the material extracted from 

 one pit might be different from that taken from another farther 

 on. Against this we may, of course, argue that the clays from 

 different pits get mixed up on the storage pile. 



As these pits are small, and the time required for sinking 

 one, viz., two or three days, is not very great, but little water 

 runs into them, although, in some, much water comes from sand 



