KiLKOE — 'Silurian and Metamorphic Rochs. 



137 



Dalradian system. As previously stated, I do not discuss whether 

 this latter should be termed Archaean ; neither do I attempt here to 

 fix the position of the Dalradian with reference to the Cambrian or 

 Ordivician system. 



The Director-General, in his summary of the work done in 1894, 

 mentions that Mr. McHenry also came to the conclusion that the 

 supposed Archaean rocks of Connemara penetrate the mica-schists, 

 limestones, and quartzites of that region. He had " collected a body 

 of evidence which disproves the existence of any Archaean rocks, at 

 least within the area examined."^ 



From the foregoing it will be seen that we cannot now deal with 

 the Dalradian rocks as a series built up from a recognizable base ; it 

 has, however, been possible to reduce the congeries of strata repre- 

 sented on the published maps to such order as justifies my speaking 

 of it as a system, consisting of well-established members. These, in 

 broad outline, are mica-schist with fine and coarse cleaved grits below, 

 and a quartzite group above, with an intermediate zone containing 

 black schist, limestone, and pebbly (or conglomeratic) beds, which 

 thickens generally westward to an important deposit. The system 

 is identical with that established in Western Donegal, even to the fact 

 tbat the conglomeratic or boulder-deposit assumes large proportions 

 westward, as on tlie coast to the west of Slieve League ; and the 

 system is traceable throughout Korth-West Mayo and West Galway, 

 often with reversal of dips, attendant upon remarkable over-foldings 

 and dislocations. The three members of the intermediate series, or 

 zone, are not always recognizable together ; the limestone is fairly 

 persistent, and, having been noticed at several new points, it has 

 supplied an important means of locating the zone, where the quartzite 

 and schist series are not to be seen in close proximity in the generally 

 obscure ground of Korth Mayo. The pebbles in the boulder-deposit 

 may be in places few and small ; sometimes they are of very large 



1 Ann. Report of the Geo. Sur. and Museum of Pract. Geo., for year ending 

 December 31st, 1904, Appendix E, p. 290. The condusions thus reached 

 by Mr. McHenry in Galway, and by me in Mayo (1892-93), possess considerable 

 significance, in view of the universally-conceded lithological similarity and 

 geographical resemblances of our rocks to those in Sutherland. Nor is the 

 significance at all diminished by the fact that recognized Archaean gneiss seems to 

 penetrate mica-schist, graphite, dolomite, and quartzite at Lough Carron 

 and Gairloch (Ancient Volcanoes of Great Britain, vol. i., p. 115). Is there any 

 good reason for supposing that these clastic rocks are not of Dalradian Age, and 

 that the gneisses which penetrate them are not, like our own, of subsequent date .- 



