144 GNEISS. COMPACT FELSPAR. 



Thus also the quantity and intricacy of the contortions 

 in any mass, are almost always proportional to the pre- 

 valence of the veins; while, when absent, the rock is 

 never more disturbed than micaceous schist, which is 

 but occasionally subject to this irregularity. Hence the 

 contortions are nearly limited to the granitic variety, 

 since it is in this that the veins abound. 



In some cases, the granite veins are so abundant as 

 nearly to exclude the original rock, so that the mass 

 presents little else than a congeries of veins. Of the 

 instances of this nature described in the account of the 

 Western Isles, the most striking is that of Cape Rath. 

 Here, the hornblende schist and gneiss are broken into 

 pieces and entangled among the veins, as the secondary 

 strata are in the trap of Sky, but with infinitely greater 

 intricacy, so as to resemble a red and white veined 

 marble with imbedded fragments of black. These do 

 not seem to form a twentieth part of the whole mass; 

 the progress of the different veins, and their effects in 

 producing the disturbance, being as distinct as in an 

 ordinary hand specimen : while it is most important 

 in geological philosophy to remark, that the intricacy 

 of the ramifications, an,d the intersection of one set of 

 veins by a second and a third, of different textures, 

 prove a succession of granitic eruptions at several pe- 

 riods ; and that the absolute resemblance of the whole 

 to the parallel cases of trap veins successively intruding 

 among strata, can leave no question in the mind of any 

 man capable of seeing and reasoning, that there is but 

 one theory for granite and for trap. He who declares 

 his doubts, in such a case, is the suicidal betrayer of his 

 own calibre of mind. The appearances are, in fact not 

 merely similar or analogous, but identical. 



The last cirsumstance of importance as to these 

 vein's is, that they do not exist where gneiss alternates 



