s 



ILLUSTRATIONS OF THE 



k 



whin, it exifts both in veins and in tabular 

 maffes, having, no doubt, an origin limilar ta 

 that which has juft been defcribed. Porphyrjy 



culiarity of being rarely 



however, has the -p: 

 found in any but the primary (Irata ; it feems 

 to be the whinllone of the old world, or at leail 

 that which is of higheft antiquity in the prefent. 

 It no-where, 1 believe, affumes a columnar, or 

 bafaltic appearance, of any regularity ; but this 



is alfo true of many other varieties of whin, of 

 all, indeed, except the' moft compad and ho- 



Thefe differences are not fo con- 



mogeneous. 



liderable as to require our entering into any 

 particular detail concerning the natural hiilorj 

 of this foffil. 



3. Granite, 



77. The term Granite is ufed by Dr Hutton 

 to fignify an aggregate ftone, in which quartz, 

 felti|)af and mica are found dillind: from one 

 another, and not difpofed in layers. The addf- 

 tion of hornblend, fchorl, or garnet, to the three 

 ingredients jull mentioned, is not undcrltood to 

 alter the genus of the ftone, but only to confti- 

 tute a fpecific difference, which it is the bufinefs 

 of lithology to mark by fome appropriate cha- 



radter, annexed to the generic name of granite. 



The 



