GRANITE. 89 



same hypotheses make it important to remark, that in 

 Shetland, where there oceurs a red micaceous granite, 

 together with one containing hornblende, and passing 

 into basalt, the latter is the oldest, since it is pene- 

 trated by veins of the former. This fact proves the anti- 

 quity of those granites which, from their resemblance 

 to trap, might be esteemed comparatively modern: 

 and also, that the mineral composition is no test of 

 antiquity, as has been said. The latest granite here, 

 is that termed " genuine old granite" by the Germanic 

 teachers of what they did not know. Whatever there- 

 fore may be the fact, we cannot at present determine 

 the age of any granite, except where this occurrence 

 takes place ; since the supposed proofs from mineral 

 composition are worthless : whence the term genuine 

 granite is only admissible as a distinction for mine- 

 ralogists. 



Granite is one of the most universal rocks, forming 

 some of the highest and most remarkable chains of 

 mountains ; being thus the most elevated, in absolute 

 position, as it is supposed to be the lowest in a geolo- 

 gical one. It is not however limited to such hi^h 

 chains as the Himalya or the Alps, or even to the 

 much lower ridges of Britain ; since it also occupies 

 many extensive tracts of comparatively level land. 

 Hence it presents that diversity of picturesque outline 

 formerly noticed ; and if this variety sometimes results 

 from disintegration^ the same effects arise from its na- 

 tural disposition. *In these cases, it forms tracts of 

 various extent, though often constituting single moun- 

 tains, or groups, or ridges, far separated from any 

 analogous mass ; as it sometimes also occupies places 

 so small as not to be easily discovered. That difficulty 

 is much increased where it is surrounded by gneiss, 

 as in Scotland, where such insulated masses frequently * 



