150 NORTH UIST. MINERALS. 



ing islands where they have already been described, does 

 not appear. It is not absolutely necessary to imagine 

 masses of trap in the vicinity of every vein ; yet it is 

 not improbable, that, as these are always found predo- 

 minant in the neighbourhood of such masses, the veins 

 which occur throughout this part of the Long Island 

 originate in masses of trap connected perhaps at some 

 distant period with that of Sky, and of which Maddy 

 more and Maddy grisioch are the only visible portions 

 remaining. 



It would be superfluous to describe all the trap veins that 

 occur along the east shore of North Uist. One however 

 of a remarkable structure is to be seen in the little island 

 of Hamersa in Loch Maddy. It is about fifteen or twenty 

 feet in thickness, passing through the gneiss in a position 

 nearly vertical. It is irregular, being split into minute ramifi- 

 cations and thus very much confounded and mixed with the 

 including rock, which is of an uncommon hardness. The 

 weathered surface of this trap vein is studded with the 

 same granite points as the schist of Flota More 

 and Flota Beg. It possesses a degree of toughness 

 scarcely inferior to that of cast iron. When broken it 

 displays a number of minute red spots of a granitic aspect, 

 but bears no resemblance to any of those well known 

 greenstones in which red felspar forms an ingredient. 

 In what respect this hardness and structure depend on 

 the gneiss with which it is so intimately mixed, we can 

 only conjecture. 



Among the mineral substances commonly found in 

 gneiss, North Uist, like the neighbouring islands, abounds 

 in reddish, grey, and white felspar, forming concretions 

 in the granite veins often of very great magnitude. In 

 some of the small islands situated in the entrance of 

 Loch Maddy, it is found of a fawn colour. In one of 

 these, Rilee, there is a considerable bed of opalescent 

 quartz, very much resembling that which occurs in Coll, 

 but more pure. This is occasionally tinged with a slight 



