CHAPTER IV 

 THE LITHOSPHERE 



HAVING briefly considered the atmosphere and hydro- 

 sphere, we will now turn our attention to the solid Earth 

 on which they rest. 



A most cursory examination of the country will 

 suffice to show us that the rocks of which the Earth's 

 surface is made up are not of the same character in all 

 places. They differ one from another in colour, texture, 

 hardness, and in the mode of arrangement of their 

 component parts. 



Broadly speaking, there are three great classes of rocks 

 differentiated from one another by their mode of origin. 



To the first class belong rocks which have cooled 

 from a molten state, such as granite, and the various 

 kinds of lava which are poured out from volcanoes. 

 These are called igneous rocks. 



By their decomposition under the action of frost, 

 rain, wind, and other natural agencies, igneous rocks 

 break down into loose granular material (sand, clay, 

 et cetera), which, carried away by brooks and rivers, is 

 eventually deposited in some lake or in the sea. Such 

 deposits accumulate layer upon layer, and when they 

 become hardened so as to form rocks, the layers are 

 still apparent. From the fact that these rocks owe 



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