MATERIALS COMPOSING THE LAND 



253 



GRANITE 



Igneous rock formed deep below the 

 surface of the earth. 



The igneow rocks are 

 those which have solidi- 

 fied from a melted con- 

 dition. They may have 

 solidified deep down 

 within the crust, or on 

 the surface, or some- 

 where between the 

 depths and the surface. 

 If these rocks cooled 

 slowly, they will have a 

 crystalline structure, as 

 in granite, and if very rapidly, a glassy structure, as in 

 obsidian. Their structure can vary anywhere between 



these two extremes. 

 A common dark 

 colored variety of 

 this kind of rock is 

 called basalt. There 

 are many varieties 

 of igneous rocks, but 

 they need not be 

 considered here. 



The sedimentary 

 rocks are those that 

 are made by deposi- 

 tion in water. When 

 rocks are worn away 

 into fragments and 

 these fragments are 



FOSSIL-BEARING LIMESTONE deposited in water 



A sedimentary rock formed from sea shells. they will, under cer- 



