igo$. C01.E. — Rece7it Irish Geology 3 



evidence of stratification, despite the conversion of its argil- 

 laceous members into mica-scliist and its basic igneous 

 members into epidiorite. The author minimises the alleged 

 importance of pressure-metamorphism in the production of 

 the gneiss of Boylagh, and regards that rock as essentially 

 due to the flow of granite along the planes of parting in the 

 folded Dalradian series. Incidentall}^ it may be observed that 

 the intrusion of this granite is held to be connected (p. 204) 

 with the Caledonian earth-movements. Since the author, in 

 his earlier paper, recognised certain composite gneisses in 

 Tyrone and Southern Donegal as probably of Archaean age, 

 it may be asked whether he is now prepared to reconsider 

 the matter, and to bring all these gneissoid granites into line 

 as Caledonian. This may be possible in the County of 

 Donegal, but would be a difficult matter in Tyrone, where the 

 Slieve Gallion granite is known to be pre-Devonian, and yet 

 cuts an already consolidated and ancient gneiss. 



THE "gre;e;n rocks of the^ pomkrov area irt 



TYRONE). 



Sir A. Geikie (Discussion on a paper on Forfarshire, by Mf. 

 G. Barrow, in Quart. Jown. Geol. Soc. Lo7idoft, vol. Ivii., 1901, 

 p. 344) again called attention to the green igneous rocks and 

 cherts that bound the gneissic axis of Tyrone ; he now 

 regarded these as Silurian, and their accurate reading as 

 likely '• to remove some of the difficulties which stiil stand in 

 the way of a satisfactory interpretation of the geological 

 history of the structure and metamorphism of the Highlands 

 of Scotland." 



In consequence, Mr. G. Barrow, m 1902, visited the district 

 in Ireland thus indicated, and is disposed to correlate the 

 green rocks with his Forfarshire series, but to place the 

 whole as pre-Silurian and probably Archaean. His pre- 

 liminary paper was read before the British Association in 

 Belfast (see J^ish Naturalist, 1902, p. 277). The tuff's of 

 Beagh-beg and Creggan, once regarded by Sir A. Geikie as 

 Archaean, and subsequently as of Arenig age, may thus prove, 



after all, to be of the most venerable antiquity. 



A 2 



