MODE V, GRANITE. 197 



STRUCTURE III. VEINED. 



Saussure has described this rock with such 

 accuracy and precision, and has himself so distin- 

 guished it from gneiss, that it is surprising it 

 should since have been referred to the latter. In 

 gneiss the veins of mica run parallel through the 

 rock, which regularly splits in their direction. In 

 veined granite the seams of mica are irregular, 

 and terminate abruptly in various directions, being 

 met by the solid rock. 



Saussure discusses, 1726, the differences be- 

 tween gneiss and his veined granite. In the latter 

 the elements are interlaced among each other; 

 while in gneiss there are fine leaves of pure mica, 

 which alternate with leaves composed of quartz 

 and felspar. 



He mentions, 1799? an extent of more than 

 four leagues and a half of veined granite in hori- 

 zontal beds : and, 1 802, veined granite in double 

 zigzag, sometimes between other beds in right 

 lines, which proves, according to Saussure, that it 

 is the effect of crystallisation. That veined in zig- 

 zag is of a very fine kind, the quartz being scarcely 

 distinguishable, while the beautiful white veins 

 appear to be entirely composed of granular fel- 

 spar, resembling a small-grained marble. The 



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