Ch. V.] PRIMARY SCHISTOSE ROCKS. 73 



In composition, the granite of these veins cannot sometimes 

 be distinguished from ordinary granite ; more generally, 

 however, it possesses a distinct character, consisting chiefly in 

 the larger size and more decided crystallization of its con- 

 stituent parts ; and occasionally, the mica and hornblende 

 being absent, it gives rise to that peculiar variety called 

 graphic granite. These veins are infinitely various in size, 

 and in the number and intricacy of their ramifications. At 

 times they intersect each other, so as to produce even a 

 reticulation of the general surface, their intersections being 

 sometimes attended with shiftings of the veins, while at other 

 times, they cross each other without any disturbance. In 

 some kinds of gneiss, they are so abundant as nearly to ex- 

 clude the basis altogether, so that the mass presents little else 

 than a congeries of veins. An instance of this occurs in the 

 Flannan Isles, but the most remarkable one is to be seen on 

 the mainland, between Loch Laxford and Cape Wrath, where 

 the gneiss and hornblende-schist, in angular pieces, are 

 entangled among the veins, resembling a variegated marble ; 

 and these fragment-like portions do not form a twentieth part 

 of the whole mass, whilst one set of veins is intersected by a 

 second and third, of different textures. The granite-veins are 

 most abundant, and most intricately arranged, in the granitic 

 gneiss ; whilst, in the regular schistose variety, they are gene- 

 rally disposed in laminae, which are parallel with the beds, and 

 alternate therewith, as is well exhibited in the island of Coll. 

 This parallelism sometimes continues for a considerable dis- 

 tance ; at others, it is only for a short space, and the veins, 

 quitting their even course, become either thicker or thinner, 

 and cut through the laminae. It is also worthy of remark, 

 that lumps of granite, apparently independent of veins, are 

 often imbedded in the gneiss : these differ much in size, and 

 when they are large, they commonly give out branches or 

 veins, which diverge in a very capricious manner, cross- 

 ing and uniting with each other, so as to produce a most 

 intricate reticulation. These granitic veins not only intersect 



