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CHAP. VI. 



On the general Distribution of the Materials which 

 constitute the Earth. 



THE superficial parts of the earth, which are all to 

 which we can have access, whether hy observation or 

 inference, are formed of indurated and of loose ma- 

 terials; the first constituting rocks, and the latter 

 being the various alluvial substances which, no less 

 than the former, are objects of geological investigation. 

 In the following chapters, the various details, whether of 

 a general or of a particular nature, namely, those which 

 relate to the substances themselves, and those which have 

 a reference to the constitution of the globe, the origin 

 of these materials, and the various revolutions they 

 have undergone, will be considered in the several points 

 of view which may appear necessary. The object of 

 the present is to give a sketch of the most remarkable 

 distinctions among rocks, and of their general distri- 

 bution as constituent parts of the earth. 



Observation has shown that rocks may be divided 

 into unstratified and stratified: or into those, of which 

 the forms are irregular, and those which are disposed 

 in successive beds, maintaining a general parallelism, 

 for, at least, certain spaces. To these must be added, 

 veins, which intersect all rocks; and those repositories 

 of earthy and metallic minerals in a mixed or confused 

 state, which occupy similar situations. 



The unstratified rocks often form the highest ridges 

 and summits of mountains, constituting the apparent 



