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CHAP. X. 



On the Characters and Disposition of unstratified 

 Rocks and Veins. 



THE unstratified rocks are far less numerous than 

 the stratified, and they have all been comprised, in 

 the present arrangement, under two general heads. 

 Granite forms one of these ; and, to the other, the 

 term Trap has been applied ; with some latitude, it 

 must be owned, but to avoid the necessity of invent- 

 ing a new one. Under these two heads, in the twenty- 

 fourth and thirty-ninth chapters, and in the Classifica- 

 tion of Rocks, will be found all the minuter particulars 

 which it was not necessary to introduce into this very 

 general view. 



Of the Extent and Places of the unstratified Rocks. 



Though the unstratified rocks form but a small 

 part of those which are visible to us, there is reason to 

 imagine, that at depths to which we have not pene- 

 trated, they occupy a much greater extent than would 

 be suspected on a superficial view. Conjectures have 

 been offered respecting the proportion of space which 

 granite fills at the surface ; but no measurement has 

 been given ; nor has any thing been done towards 

 answering this question as it relates to the later unstra- 

 tified substances. In fact, these vary so much in 

 different countries, that if any worthy object were to 

 be gained by that knowledge, it could still only be 

 done after the whole surface of the globe should have 



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