LUNGA. GEOLOGY. 16\9 



ration have given a passage to the fluid intruding 

 material.* Such appearances are here both frequent 

 and remarkable ; and analogous, if not equally well 

 marked facts, occur in other parts of the Western 

 islands. There is nothing in the mineral character of 

 these veins to call for particular notice ; but I must 

 not omit to mention, that in one instance, a wide vein 

 is found to include in its centre fragments of quartz 

 rock and schist, similar to the surrounding rocks, but 

 broken and twisted in several intricate directions ; an 

 appearance resembling that which occurs in the granite 

 veins of Mull.^ 



Having thus described the structure of this island, 

 it only remains to examine its relations to those which 

 have preceded it in description. It has been shown 

 that the western side of Luing consists of clay slate, 

 arid that the same rock occurs on the east side of 

 Lunga, differing from the former in no respect, either 

 in character or position ; the chief distinction lying in 

 the greater frequency of micaceous schist, which is 

 however not entirely absent in Luing. This alternation 

 becomes more frequent, and the micaceous schist more 

 predominant, as we approach to the quartz rock; an 

 observation that will be confirmed by the examination 

 of Scarba. The eastern side of this island projects 

 far beyond the line of direction which is the common 

 boundary of the clay slate and quartz rock ; and thus, 

 admitting of a much more continuous and extensive 

 succession of the former rock, enables us to trace the 

 diminished frequency of the beds of micaceous schist 

 at a distance from the latter. 



From the final disappearance of the quartz rock at 

 the eastern boundary of both these islands, and from 

 its absence on the opposite shore of Luing, it is a 

 natural conclusion that those parts of the surface 



* i'hite XXI. fig. 2. f P^te XI. fig. 6. 



