196 LIME-STONE CLAY SALT. 



when slaked or thrown into water, it becomes hot, 

 and crumbles into a white powder, of which mor- 

 tar is made, and the whitewash with which many 

 of our rooms are washed. The different kinds of 

 marbles are lime-stone. Many beautiful kinds are 

 found in the United States, but the finest and best 

 are imported from Italy and Sicily. 



The most useful stones for building are free- 

 stone and sand-stone. Granite, which is the most 

 durable, is so difficult to work, that it is very ex- 

 pensive ; but the Portland-stone is soft when taken 

 out of the quarry or stone pit, and may be cut 

 very easily, by a saw, into blocks of a proper size; 

 when it has been exposed some time to the air it 

 hardens. 



Clay is found lying in vast beds under the soil 

 of many countries. It is generally stiff, somewhat 

 tenacious, and capable, by the addition of a little 

 water, of being moulded into a variety of shapes. 

 Clay is of very great utility. Bricks, so much 

 used for building houses, are made of it. 



All kinds of earthenware are made from a clay 

 called potters'-clay. England is particularly fa- 

 mous for her manufacture of pots, and one large 

 district in Staffordshire is named the Potteries, 

 from its being almost covered with works devoted 

 to this purpose. 



Common salt, which is of such importance to 

 us, as a seasoning for our food, and in many of 

 the arts, is found either dissolved in water, as in 

 salt springs and sea-water, or in solid masses, as 



