36 CLAYS AND CLAY INDUSTRY. 



tough, the material is sometimes loosened by means of a blast, 

 but more often by undermining or falling. This is done by 

 digging a narrow cut into the bank at its base, and then driving 

 in a line of wedges on top, one or two feet from the edge. In 

 this manner large masses weighing many tons are pried off and 

 break in falling (Plate VII, Fig. i, and XVI, Fig. i). 



Haulage. — If the distance from the bank to works or shipping 

 point is short, wheelbarrows or one-horse carts (Plate VII, Fig. 

 i) are used, but, if a longer haulage is necessary, it is more 

 economical to lay light tracks and haul the clay in cars drawn 

 by horses or small engines. The latter method is much used 

 around South River, Sayreville, Keasbey, Lorillard, Wood- 

 mansie and Winslow Junction, Steam, haulage (Plate VII, 

 Fig. 2) is economical for a distance of perhaps not less than 

 1,000 feet, and provided the locomotive is kept constantly em- 

 ployed. 



Shale mining. — There are only two localities in this State, 

 Port Murray, Warren County, and Kingsland, Bergen County, 

 where shale is being mined (PL LVI, Fig. 1) for clay products. 

 The shale generally has to be loosened by blasting, and can then 

 be loaded, into' cars and hauled to the works. Many soft shales 

 can, however, be easily excavated with a steam shovel. 



PREPARATION OP CLAY POR MARKET. 



Unless clay is to be used for higher grades of ware, it rarely 

 requires much preparation to make it marketable, for, since the 

 impurities in clay often run in streaks or beds, they can be 

 avoided in mining. Large concretions, pyrite nodules and lumps 

 of lignite are often picked out by hand and thrown to one side. 

 Where the impurities are present in a finely divided form and 

 distributed throughout the clay, screening or hand picking may 

 be ineffective, and washing is necessary. In New Jersey, this 

 is practiced only in the case of ball clays, which are commonly 

 prepared from a No. 1 fire clay. 



Washing. — The method of washing most commonly adopted 

 is the troughing method, in which the clay, after being stirred up 

 and disintegrated with water, is washed into a long trough 



