SOUTH UIST. GEOLOGY. 97 



exhibit on close examination the same appearances which 

 in a more limited manner occur in Barra, Gia, and 

 Hellesa. Here the magnitude of the trap veins and the 

 extent of surface exposed render the junction more 

 extensive and the disturbance much more striking. I 

 have already detailed the nature of these junctions so 

 minutely that it is unnecessary to repeat it. But in 

 this place may be seen very perfectly the conglomerated 

 nature of portions of the trap vein. This is a matter 

 of considerable difficulty to explain, since, as far as I yet 

 know, the trap conglomerates have been invariably found 

 forming portions of masses, or else entire beds. The 

 conglomerated substance consists in some places of frag- 

 ments of trap imbedded in a trap basis, while in others 

 the imbedded masses are of gneiss and granite. As the 

 cliffs are of very difficult access, I do not speak very 

 decidedly respecting the latter variety, as it may be a 

 fallacy arising from the intermixture of fragments of 

 the original rock with minute reticulating veins. The 

 basalt of this vein acquires by the action of the sea on 

 its surface a dark green colour. Where it has been 

 subjected to atmospheric action only, it is cavernous 

 and scoriform, resembling very much some varieties of 

 iron slag; and it is invested with a black sooty powder 

 in those cavities which are protected from the rain. 



The bottoms of these cliffs are coated with spongia 

 papillaris, and various other marine productions. 



All the hills which skirt Loch Eynort are of gneiss, 

 and among them the varieties which contain hornblende 

 predominate. Its disposition is equally irregular as at 

 Loch Boisdale, and veins of granite are equally rare. 

 Among them are seen concretions of a very dark grey 

 felspar, and similarly large ones of common hornblende. 

 Quartz is of rare occurrence. Nothing indeed can be 

 imagined more tiresome to a geologist than the perpetual 

 and almost unvarying recurrence of gneiss, which forms 

 the lowest as it rises to the highest parts of this cheer- 



VOL. i. H 



