ROCKS GRANITE LIMESTONE. 195 



LESSON XLV. 



ROCKS GRANITE LIME-STONE FREE-STONE 



SLATE CLAY SALT. 



MOUNTAINS and hills are, in general, masses of 

 rock of various kinds. Some of these tower to 

 great heights, being many thousand feet above the 

 level of the sea. One kind of rock called granite 

 is very hard, and of this some of the highest moun- 

 tains are composed. The hardness and toughness 

 of granite has caused it to be used for laying down 

 roads, as it lasts much longer than other kinds of 

 stone: the pavement, the curb-stones, and the car- 

 riage-ways in London are, in most instances, of this 

 rock, which has been brought chiefly from Scotland. 

 The Astor House in New York is entirely built 

 of it, and some of our public buildings are also of 

 the same substance. Granite takes a fine polish, 

 and is difficult to break. 



Lime-stone forms many mountainous ranges in 

 England, as in Derbyshire, Somersetshire, and 

 Yorkshire. This kind of rock often contains lead 

 ore, and is quite full of fossil remains, so much so, 

 indeed, that it would seem to be almost entirely 

 composed of them, principally the shells of mollus- 

 cous animals. This stone, when burnt in a kiln 

 with coal, becomes lime, which is largely used in 

 agriculture, for spreading over the ground, and 



