348 ARRAN. GEOLOGY. GRANITE. 



produce a new, or prolong an old fissure, are unavailing ; 

 the rock breaking before the wedge or chisel in the ordi- 

 nary and irregular manner. 



The occasional schistose structure of granite has been 

 remarked by foreign geologists, although it seems to have 

 excited no particular attention. As before suggested, 

 it may possibly tend to illustrate the question respecting 

 the stratification of granite, concerning which some remarks 

 have already been offered. 



In Glen Sannox, (to select that as the most conspicuous 

 example,) the rock extends in large thick plates only, inca- 

 pable of a more minute schistose division, if we may judge 

 so from the absence of specimens similar to those now 

 described. But in Glen Catcol it presents the same 

 thickly laminar disposition, descending, in a gradual man- 

 ner, through a thinner laminated, down to a schistose 

 structure. Here then is a regular gradation of that, which, 

 through all its variations, must be considered as an 

 example of the concretionary structure ; and it confirms 

 the opinion before held out, that the extended and flat 

 beds of granite, wherever they may occur, are of an 

 analogous nature, and unconnected with the laws that 

 produce stratification. With regard however to the 

 schistose exfoliation of granite, there is another explana- 

 tion to be offered, which will more properly be considered 

 at a future opportunity. But it does not apparently 

 affect this argument; since, even if the schistose speci- 

 mens of Glen Catcol be admitted to have proceeded from 

 the species of exfoliation here alluded to, the gradual 

 diminution in thickness of those laminae which are not 

 schistose, and the want of that persistence and regularity 

 of disposition which attends real strata, leave it in its 

 original force. 



The mineral characters of the granites of Arran are 

 in most cases different from those which prevail through- 

 out the greater number of these rocks in other parts of 

 Scotland. But it is useless to attempt a description of 



