72 A DESCRIPTION OF THE [Ch. V. 



stone.* At Gott Bay, in the same island, a bluish limestone 

 alternates with the gneiss in a nearly vertical set of irregular 

 beds, of no great extent ; and both of these rocks are traversed 

 by granite-veins. In the island of lona, limestone also 

 occurs ; but, in this case, it is not associated with a true 

 gneiss, but with a slate, intermediate, according to M'Culloch, 

 between gneiss and clay-slate. It appears to be a schistose 

 variety of compact felspar, which, in a massive state, occurs 

 in this slate ; and both of which are connected with and pass 

 into gneiss ; and it may, therefore, be considered as an in- 

 tegrant part of this series of primary slates. This limestone 

 also exists as a large irregular nodule, of about thirty feet in 

 breadth, and more than a hundred yards in length. The 

 texture of this marble is compact, its fracture splintery, and 

 its colour white, often with a slight greenish tinge. In 

 many parts, it is fissile ; more particularly where it approaches 

 the schist, in which it lies : here also it becomes magnesian, 

 and gradually passes into a steatitical calcareous schist, which 

 contains leaves of translucent steatite; also dark-green 

 foliated steatite, accompanied by yellowish-green and dark 

 green noble serpentine. This limestone not only gradually 

 passes into the adjacent schist, but both are contorted, and 

 entangled together in a confused manner.f The masses of 

 primary limestone are, however, much more extensively de- 

 veloped on the mainland ; an interesting example of which, 

 at Glen Tilt, will soon be considered more in detail. 



In many parts of the gneiss of the Western Islands, the 

 quartz so predominates, either in alternating laminse with 

 the other constituents, or in the state of a granular mixture, 

 or even to the exclusion of the other minerals altogether, that 

 it produces regular beds of quartz-rock of various extent. 

 But the most interesting feature of this gneiss is its frequent 

 intersection by granite- veins, which are so abundant, that 

 they are rarely absent for any considerable space. 



* Western Islands of Scotland, vol. i. p. 48. | Idem, pp. 17, 18. 



