2.12 Froceedings of the Royal Irish Academy. 



Carbane rises on the south-east of this metamorphosed area, and 

 consists of granite, which penetrates the shale. On the southern slope 

 of the hill the contacts are excellently seen. The granite is a pale 

 pink aplitic rock, consisting almost entirely of pink orthoclase, larger 

 and less decomposed colourless microcline, and quartz. Its specific 

 gravity is 2-59. J^ear any large inclusions of schist, and near the 

 junction generally, it becomes darkened and gneissose ; but even the 

 uncontaminated specimens show a delicate foliation, especially on their 

 weathered surfaces. Specimens intermediate in structure between 

 the darkened granite and those which exhibit distinct veins of aplite 

 penetrating schist are only intelligible when their relations are followed 

 out in the field. The schist, which is here not much more than a dark 

 micaceous shale or phyllite, occurs in situ, dipping south-east, about 

 midway between the road from Glenties and the summit of Carbane. 

 The granite not only invades «t, but is so worked up in it that crystals 

 of quartz and microcline lie as white oval specks in a dark ground of 

 phyllite, which flows round them. Tongues of granite shade off into 

 mixed rocks of the most diverse character — here into a schist which 

 has become set porphyritically with constituents from the granite ; here 

 into a fine-grained composite gneiss, in which the former sediment is 

 represented by delicate waving sheets of biotite, with aplite layers, 

 less than 0*5 mm. thick, between them. Hence the same contact- 

 zone gives us granulitic biotite-gneisses, and rocks that, by themselves, 

 might be regarded as felspathic ash-beds. The more uniformly inter- 

 mingled masses show the same type of darkened granite as in the 

 dome of Ardara, and occasionally obvioiis flecks of schist indicate the 

 origin of the darkening. The composite rock, in a handsome specimen 

 specially examined, has a specific gravity of 2-73, and is seen under 

 the microscope to contain bent and streaky groups of biotite and yellow 

 epidote, cauglit up between the constituents of the normal granite. 

 Sphene, a common accompaniment of such contact-action, occurs 

 freely. Some subsequent pressure -effects are traceable, in the pro- 

 duction of mylonitic envelopes about certain felspars, and the alter- 

 ation of quartz crystals to granular aggregates ; but, both in the field and 

 in the section, the actual intermingling is seen to be due to igneous flow. 

 We pass by gradations from this rock to those which resemble felspa- 

 thic ash, and see under the microscope how an excess of sedimentary 

 material and a deficiency in granite has produced this extreme compo- 

 site type. (PI. II., fig. 2). Earth-pressures no doubt assisted the pene- 

 tration of the gxanite-magma into the schist ; as usually happens, the 

 igneous rock followed, but did not originate, the upheaval, and its 



