214 Proceedings of the Royal Irish Academy. 



The microscopic evidence, in fact, sustains to the full the broader 

 evidence in the field. The handsome red granite of a portion of 

 Cartane, with flakes of mica-schist in it at intervals, passes clearly into 

 darkened gneissic types along its margin. The more we study the rela- 

 tions of the granite and the Dalradian series in Boylagh, the more 

 influence we may ascribe to the structure of the latter, prior to its 

 invasion by the granite. Even vrhere not already foliated by the 

 earth-movements which reared successive mountain-chains, even where 

 it remained as little altered as in " the Rock " at Glenties, the sedi- 

 mentary series provided surfaces for the penetration of the granite, 

 and the previous structure of the country originated that of the 

 banded gneiss. 



j\Ir. Kilroe^ has ali-eady laid stress on the metamorphosed condition 

 of the strata in Boylagh prior to tlie intrusion of the granite. I 

 cannot lielp thinking, in considering the modifications of this igneous 

 mass, that too great importance has been attached to the dynamic 

 action which followed on its consolidation, and too little to the con- 

 tact-phenomena and interpenetration, of which Carbane serves as so 

 typical an example. 



I^ ■ — The Maegin' of the Granite fkom Eaxnt to Deekjbeg Hill. 



In the southern half of Sheet 15 of the Geological Survey Hap, 

 Mr. Kilroe has represented in remarkable detail the intrusive and 

 serrated margin of the granite, where it invades the Dalradian series 

 near the mouth of the Gweebarra. Limestones, diorites, quartzites, 

 and schists are, as it were, dovetailed into the granite across four 

 miles of country. North of the Gweebarra Eiver, their strike is 

 fairly parallel to the granite-margin; but on the south side their- 

 -outcrops swing round to the north-east, and are crossed at right angles 

 by the igneous rock. The prominent tongues of the granite, how- 

 ■ever, run out along the strike, and show how potent an influence the 

 lie of the sedimentary rocks exerted on the flow of the invader. 



Mr. Kib'oe- has similarly noted that at Dunlewy, further north, 

 where the granite cuts across the foliation of the Dalradian series, 

 its ofPshoots invade that series, " usually along the strike." Masses 

 are described as having been detached from the metamorphic series, 

 and remaining as bands within the granite. 



1 Mem. S.W. Donegal, p. 30 ; also p. 27. 



- Memoir to Sheets 3. 4, 5. 9, 10, 11, 15, ;ind 16 (1891), p. 71. 



