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seem properly to belong to the composition of 

 rocks, and the other comprising those which 

 appear to be merely incidental. Such mineral 

 substances must, in these cases, be considered as 

 being accidentally accumulated in particular 

 places in those rocks which are their natural 

 repositories. 



Catalogue of the Minerals which enter into the 

 Composition of Rocks. 



INDURATED CLAY. 



This is a substance of great importance in 

 the composition of rocks ; forming the whole of 

 some, and a principal portion of many others. 

 The chief variations which it presents are in 

 the degree of induration, and in the massive or 

 schistose nature of its structure. It is here un- 

 derstood to comprise the softest substances found 

 in the rocks of the trap family, and the hardest, 

 which constitutes jasper and siliceous schist. 



CLINKSTONE. 



This substance forms simple rocks, and is 



