GNEISS. 145 



with extensive strata of clay-slate, quartz rock, or mi- 

 caceous schist ; and this leads me to enquire into the 

 philosophy of the appearances in question. They 

 who have called these veins contemporaneous, are 

 of those who write phrases without ideas ; and they 

 who have supposed them independent of granitic con- 

 nected masses, have wanted industry or capacity to 

 examine them. I have traced these veins to their 

 parent masses wherever a mass existed ; and where 

 they cannot thus he followed, it is hecause the funda- 

 mental granite is out of sight and reach. If the uni- 

 versal inference is not safe, it may be asked what and 

 whence is a granite vein. Let me also remark, that 

 in numerous parts of Scotland, where the leading 

 masses of gneiss are' schistose, evenly stratified, and 

 scarcely ever traversed by granite veins, they become 

 contorted and irregular as they approach the granite ; 

 assuming also the granitic character, and becoming 

 intersected by veins, numerous in proportion to the 

 vicinity of the mass. The conclusion is almost too 

 obvious to require being stated ; and it implies the 

 most essential part of the theory of gneiss. The 

 fluid granite has invaded the aqueous stratum as far 

 as its influence could reach, and, thus far, has filled it 

 with veins, disturbed its regularity, and generated in 

 it a new mineral character, often absolutely confounded 

 with its own. And if the more remote beds, and 

 those alternating with other rocks, are not thus affect- 

 ed, it is not only that it has acted less on those, but 

 that if it had equally affected them, they never could 

 have existed, or would have been all granitic and 

 venous gneiss. Thus are its varieties of character, 

 even to its absolute transition into granite, explained. 

 Though the general facts have formerly been stated, 

 it is necessary to mention, as part of the history of 



VOL. II. J, 



