158 J. Nolan — Metamorphic and Intrusive Rocks of Tyrone. 



class, while immediately at the bridge is typical granite. At all 

 these places the rock has the same general character of a coarse 

 quartzose mass with pink felspar and green mica, except that to the 

 north the base is felspathic, while to the south it is siliceous, and 

 has tbe granular character of granite. Similar observations were 

 made in a quarry a little east of this, and in some other localities, 

 particularly at Slieve Gallion, where several sections exhibit this 

 change from porphyry into granite. 



At the summit of Glenarudden Mountain, the porphyry is 

 succeeded by a rock having a compact base of a greenish or greyish 

 colour, with, occasionally, spots of red or flesh-coloured felspar, and 

 a little diffused hornblende. Towards the north this latter mineral 

 increases in quantity, and quartz appears; giving place, however, to a 

 rock devoid of that mineral, and in which the hornblende is replaced 

 by pyroxene, with some serpentine. This, again, is succeeded by and 

 passes into the same kind of compact felspathic green rock, and 

 ultimately into the porphyry. In the vicinity, at a stream called the 

 "White Water, the latter rock has a decided schistose character, 

 approximating it more closely to the nature of a metamorphic than 

 of an intrusive igneous rock. 



Another remarkable variety may be seen at Carrickmore, at the 

 Glebe of Athenree, and at some other localities in the adjoining 

 little glen of Tremogue. This is a finely-crystalline mixture of 

 quartz and felspar, with a small proportion of mica, some of which 

 is talcose-looking, though for the most part it occurs in small white 

 silvery scales, probably lepidolite. It is described by Portlock as a 

 granite, though it may perhaps be more properly classed among 

 the elvanites. As the exposures of this rock occur on a regular 

 line bearing north-eastwards, it might at first appear to be an 

 intrusive dyke in the metamorphic rocks, but this view is not borne 

 out by an examination of its relations to those rocks. At the 

 several localities where sections were observed, they seem to 

 graduate into each other, the dark-green micro-crystalline horn- 

 blendic rock becoming felspathic and light-coloured, in the vicinity 

 of the elvanite, passing insensibly into it, though in one place it 

 seems to penetrate it as a dyke. It is impossible to say whether the 

 elvanite might not have been originally a bed of fine quartzose grit, 

 or perhaps an intrusive dyke in the old sedimentary rocks, fused in 

 with them when the whole series were metamorphosed. 



The granite of this district is very variable in composition. In 

 general, it contains the same minerals as the porphyry, but in some 

 places the mica is replaced by talc or chlorite. Of secondary 

 minerals, carbonate of lime is the most prevalent, and at Limehill, 

 near Pomeroy, it occurs in such quantity, that in one part the 

 quartz altogether disappears, and the resultant is a curious mixture 

 of pink felspar and carbonate of lime : so that it has been burned, 

 though with little success, for agricultural purposes. 



Changes from the granite into the green hornblendic rocks, 

 through syenite, have already been noticed. Hornblende, indeed, 

 is pretty generally disseminated through the granite, and in some 



