GENERAL REMARKS ON GNEISS. 219 



respecting those beds of gneiss which alternate with 

 other rocks, such as clay slate ; these, as far as I 

 have observed, never containing veins. In some va- 

 rieties of gneiss they are so abundant as nearly to 

 exclude the original rock, so that the mass presents 

 little else than a congeries of veins. An instance of 

 this nature occurs in the Flannan isles, but the most 

 striking are to be seen on the north west coast 

 between Loch Laxford and Cape Wrath. The latter 

 spot is no less remarkable for its picturesque grandeur 

 than for the perfect manner in which it displays this 

 circumstance ; the cliffs being free from lichens and 

 unaltered by the weather, so that all the parts are as 

 visible as in an artificial section. The hornblende schist 

 and the gneiss are broken into pieces and entangled 

 among the veins in the same manner as the stratified 

 rocks are in the trap of Sky ;* but with infinitely 

 greater intricacy, so as rather to resemble a red and 

 white veined marble with imbedded fragments of black. 

 These fragments do not seem to form a twentieth part 

 of the whole mass ; while the progress of the different 

 veins, and their effects in producing the disturbance, 

 are as distinct as in an ordinary hand specimen. If the 

 intricacy of the ramifications, and the intersection of 

 one set of veins by a second and a third of different 

 textures, present an argument in favour of a succession 

 of these at several periods, there is here no want of 

 such evidence. I have only to regret that I cannot 

 give a correct view instead of the very slender sketch 

 subjoined : the limits of the plates do not admit of a 

 more perfect representation^ 



Whether these granite veins are connected with masses 



* It is not easy to admit the arguments derived from these ap- 

 pearances in favour of the igneous origin of trap and refuse them in 

 the instance of granite. There is in trutli no difference in the cases 

 but that which arises from the difference of the materials engaged. 



t PI. XXXI. fig. 1. 



