362 Proceedings of the Royal Irkh Academy. 



tlie G-eological Survey ilaps, sheets 43 and -55, so excellently show, 

 faults were at the same time produced, which enabled the ancient 

 crystalline mass to assert itself ahove the denuded Carhoniferous 

 limestone as a " horst." 



Those who have hitherto examined the gneiss of the ridge do not 

 seem to have greatly concerned themselves with its mode of origin, 

 llr. G. H. Kinahan- classes the gneiss of the Ox ]^onntains, with other 

 western gneisses, as a highly altered sedimentary series. In dealing 

 with snch rocks in Gralway, he speaks- of schists that graduate into 

 " metamorphie granite and granitoid gneiss " ; even when he states 

 that "rocks of the older groups are absorbed into the granite and 

 gneiss," it appears that we must not read into these words the 

 modem view that the granite is intrusive and is responsible for much 

 of the metamorphism. The words " changed into gneiss or granite" 

 occur later, and radicate the prevalent attitude of the Irish surveyors 

 twenty years ago. !Mr. E. T. Hardman's''' paper, in the same volume, 

 is a solid contribution to the geology of the Ox Mountains, and deals 

 specially with the north-east poition of the range. The gneiss is 

 clearly regarded as of sedimentary origin, and attention is called for 

 the first time (p. 358) to "a curious band of conglomerate," near 

 Ballydawley Lake, consisting of " a coarse granitoid gneiss, containing 

 lenticular blocks and rounded pebbles of diorite or homblendic rock 

 weathering out on the surface." The importance of these inclusions as 

 indicating some earlier mass of homblendic rocks is duly noticed. 



The mineral notes in Mr. Hardman's paper are somewhat incom- 

 plete, and are subordinate to a very detailed description, by the 

 author and Prof. Hull, of the dyke of serpentine in the valley of 

 Correagh. I venture to question if olivine is disseminated in the 

 gneiss at any point, as is implied on p. 361 ; the granules observed 

 were probably a green pyroxene, like that derived from eclogite in 

 Glennagoolagh. Tery scant justice, on the other hand, is done to 

 garnet, which simply abounds throughout the range. 



The Memoir to Sheet 55 of the Geological Survey of Ireland was 

 written by !Mr. J. E. Kilroe, and was published ia 1885, Simul- 

 taneously Mr. A. B. Wynne's Memoir to Sheets 42 and 43 appeared, 

 which includes the gneissic areas of the Bosses and Manorhamilton. 



1 " Palaeozoic rocks of Galway and elsewhere in Ireland, said to be Laurentians," 

 Sci. Proc. E. Dublin Soc., vol. iii. (1882), p. 348. 



"-Ib'xd., p. 353. 



3 " Ontbe Metamorphie Rocks of Counties Sligo and Leitrim, and the enclosed 

 minerals," ihid., p. 357. 



