60 GENERAL DISCUSSION OF CLAYS. 



slaked under the influence of weathering. In some 

 localities this mellowed outcrop may be only a few 

 feet thick, but in many it is of sufficient volume to sup- 

 ply a small brick yard, without the necessity of at- 

 tacking the fresh shale beneath. 



MINING OF CLAYS*- 



Clays, when soft and plastic, are mostly dug with 

 pick and shovel, loaded on wheel-barrows, carts or cars 

 and hauled to the works. If the deposit is broad and 

 shallow the clay is usually dug at any convenieait 

 point; often any overlying sand or other useless ma- 

 terial has been first removed and used for filling in or 

 some other purpose. 



If the bank is located on ,the hillside, and has con- 

 siderable height, it is worked out in broad steps, the 

 object of this being to prevent the bank from sliding 

 in wet weather. 



When tlie bank is near the works, wheel-barrows or 

 carts can be used to haul the clay, but far distances, 

 over 600 feet, it pays to lay tracks and use cars, haul- 

 ed either by horse or steam power. 



Underground methods of mining are only used in 

 case the amount of overlying material is very great. 

 It is cliiefly used for shale deposits. 



Steam shovels are employed for sandy clays or soft 

 shales at some localities in the United States, but 

 most shales are mined by blasting, and the fragments 

 thus loosened are sent to the works. 



Where the clay is rough, and the face of the bank 

 12 or 15 feet high, a plan often followed is to under- 

 mine it by picking at the base, and then inserting 

 large wooden wedges at the top. This brings down 



*Thi8 does not include the mining of kaolin, which is treated separatelr. 



