134 



Proceedings of the Royal IrkJi Academij. 



the striking similarity of the rocks at Erris Head to those at Cape 

 Wrath in Sutherland was also recognized.^ A group of rocks in the 

 extreme west of Achill Island, consisting of micaceous and graphitic 

 schists, limestone, &c., was then also taken to be of Archaean Age, and 

 to have formed the ancient floor of the younger or Dalradian meta- 

 morphic series, commencing with the conglomerates and quartzite of 

 Croaghaun Hill.^ This hill rises steeply upward from^the hollow near 

 Achill Head, where the schists, &c., are seen, and is sharply truncated 

 by imposing cliffs of remarkable grandeur overlooking the Atlantic 

 westward. 



The Director-General further made traverses in 1892 of the Ox 

 Mountain chain with Messrs. McHenry and Watts, I, too, accompany- 

 ing them, by Foxford and Lough Talt to Ballina. The traverses 

 issued in decisions upon two important points, viz. : — 



{a) That the range north-eastward from Castlebar to Manor- 

 hamilton consisted of Archaean granites and granulites. 



{V) That a line observed on previous traverses running northward 

 from near Castlebar, and apparently an unconformable boundary, 

 should be taken as a base-line of the Dalradian series. ^ 



Mr. McHenry had previously noted that the rocks of the Ox Moun- 

 tain range near CoUooney were of igneous origin, though now trans- 

 formed into gneisses,* which are usually much gnarled and contorted ; 

 and the observations proved to be of valuable aid in the interpretation of 

 the geology of this ancient ridge. Limestones and epidiorites are 

 included in the gneisses and granites near Lough Talt ; and these 

 appeared to me, during the traverse, to correspond to similar inclusions 

 in the Donegal granites, which in 1884^ were decided to be more recent 

 than the Dalradian schists. 



1 Transactions of the Eoy. Dub. Society, vol. i., 1877-1883, pp. 252, 253, 

 by Ed. Hull, ll.d., f.r.s., Director of the Geological Survey of Ireland. He also 

 published his views about the same time in "Nature," 1881, pp. 81, 82 ; and 

 at the British Association meeting of 1881. Mr. G. H. Kinahan, too, in 1881 

 (Geolog. Magazine, Sept.) referred to the occurrence of these in the above- 

 mentioned areas; and later, in a paper read January 15, 1891, before the Edin- 

 Geo. Soc. he made reference to the discussion on these rocks. 



^ See " Recent Researches into the Origin and Age of the Highlands of Scot- 

 land and West of Ireland," by Sir A. Geikie, ll.d., f.r.s., Proc. Roy. Institution 

 of Great Britain, vol. xii., Part III., No. 82, pp. 528, et seq. 



2 Annual Report of the Geological Survey and Museum of Practical Geology for 

 year ending December 31st, 1892, Appendix E, p. 267. 



* Described in some detail in a Paper read before the Royal Irish Academy. 

 Proceedings, vol. xxiv., sec. B., Part 4, p. 371. 



^ Explanatory Memoir of Sheets 3, 4, 5, 9, *S:c., p. 54. 



