132 NOKTH-CAROLINA GEOLOGICAL SUKVKV. 



CHAPTER XL 



(lay. Characteristics of a good clay. Composition of fine clays. Com 

 position of a clay upon Bogue Sound. 



99. Clay, though rarely, if ever, a constituent part of a 

 vegetable, is still an important substance in matters pertain 

 ing to agriculture. It is one of the most important substances 

 in construction. It is also employed largely in the manufac 

 ture of articles indispensable in the economy of the house 

 hold, and is the principle material employed in the draining 

 tile. 



Clays differ widely from each other; some are fusible; 

 others are very refractory in the fire, or scarcely fusible bv 

 the highest heat of a furnace. For certain purposes, the re 

 fractory clays are indispensable. For lining stoves and fur 

 naces, this property should exist in an eminent degree. For 

 household utensils, it is not necessary the clay should be 

 highly refractory in the ftre. As different properties are re 

 quired for the different uses to which clay is to be put, it is 

 desirable that the adapteduess of clay for a special purpose 

 should be determined by methods which are within the reach 

 of every intelligent individual; at least that good clay may 

 be determined by some simple and easy experiment. 



In the first place, good clay is homogeneous ; it is free from 

 lumps, stones and other foreign matter. In the second place, 

 it should have an unctuous feel ; this property implies tena 

 city, and an ability to mould readily and retain forms and 

 shapes which is given to it by working. 



In the third place it should contain sand. Too much sand 

 destroys cohesion, but a certain proportion of sand imparts to 

 clay an ability to dry or season. Bricks, tiles and all utensils 

 must dry through before they can be burned, else they will 

 crack when exposed to the heat of the kiln. Excess of sand 

 renders moulded clav weak and unfit for handling: ; its tena- 



m 



