GRANITE. 99 



mentSjto note the peculiar interest of these changes; while 

 they resemble those which take place in the argil- 

 laceous sandstones and the shales when in contact 

 with trap. Similarly, the stratified limestones become 

 amorphous ; while their texture also undergoes a 

 change from the earthy to the crystalline, when pure, 

 as, when originally impure, they become cherty sub- 

 stances, or else perfect cherts. A change not less re- 

 markable occurs in Glen Tilt, where the limestone in 

 the vicinity of the granite is interleaved with cherty 

 laminae ; while it is easy to see that it has been pro- 

 duced from a bed consisting of alternating laminae of 

 limestone and schist ; the latter having been indurated 

 -to its present nature, while the calcareous portion has 

 remained comparatively unchanged. All these re- 

 markable appearances, which I long ago described, 

 abound in Scotland ; and they have all been recently 

 confirmed by foreign geologists ; the last by Ramond, 

 in the Pyrenees. 



If there is little more to remark respecting the 

 Theory of Granite, than what is deducible from this 

 chapter and that on the unstratified rocks, a few 

 points still demand notice, while I presume I can now 

 trust to the reader for combining the whole. Re- 

 specting its successive productions, there ought, a 

 priori to be a sufficient number to account for the 

 first great revolutions of the earth, and also for that 

 original rock whence the first primary strata were 

 produced. There are at least three traceable through 

 successions of veins ; but I shall hereafter show, that 

 quoad hoc, the older porphyries and granites are iden- 

 tical, while not essentially differing in composition. 

 Geologists, reasoning as usual, even where they admit 

 the igneous theory of this rock, persist also in ima- 

 gining tKat all the visible granites must have been 



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