Notices of Memoirs — O. H. Kinahan. 483 



I. — Geological Suevet of Ireland. 



Explanation to accompany Sheet 95 of the Map of the Geological Sui'vey of 

 Ireland, including the country around Headford and Oughterard, illustrating parts of 

 the counties of Galway and Mayo. By G. H. Kinahan, and J. Nolan, 1870. 

 8vo. pp. 71. 



THE authors first draw attention to the Physical Geography of 

 the area. A considerable portion of it is occupied by Lough 

 Oorrib, the second largest sheet of fresh- water in Ireland. This is 

 only twenty feet above the mean sea-level in Galway Bay. The 

 southern portion of Lough Mask enters the map at the north-west, 

 its surface is thirty-six feet higher than that of Lough Corrib, into 

 which it flows by subterranean passages. The "rock basins" in 

 which these lakes lie, present appearances which suggest their having 

 been excavated at the same time, and by similar denuding agents.^ 



The area is in general hilly, the highest point, Benlevy, reaches 

 1,370 feet. The rivers in the low country east of the lakes were 

 formerly, for a great part, subterranean, but some years since arti- 

 ficial cuts were opened that now carry off the greater part of the 

 drainage, although in no case has the water ceased to flow in the 

 subterranean channels. 



The formations noticed in the area under consideration consist of : — 



Alluvium, Bog, and other superficial coverings. 



Drift or Glacial deposits. 



Carboniferous Limestone. 



Carboniferous Sandstone. 



Upper Llandovery. 

 Igneous and metamoi-phic rocks are also met with. The former 

 include Greenstone, Hornblende rock, Felstone, and intrusive 

 Granite ; the latter comprise Quartzites, Gneiss, Crystalline Lime- 

 stone, Schist, and Serpentine. 



The authors^ give a brief general description of the rocks, and 

 then proceed to describe in detail the geological structure of the 

 country, dividing it for convenience into four districts, namely, the 

 Oughterard district, the Headford and Cong district, the island in 

 Lough Corrib, and the Benley and Kilbride district. The drift and 

 other superficial deposits are noticed in a separate section, and after 

 them the Mines and Mineral Localities. 



The Irish Granite has been divided by the Eev. Prof. Haughton 

 into two distinct classes — intrusive and non-intrusive. All the 

 granite in this area seems to be intrusive, it is termed the " Oughter- 

 ard Granite," from its being so largely developed in the neighbour- 

 hood of that town. Its usual constituents are quartz, orthoclase, 

 white and black mica, and frequently iron-pyrites. It is occasionally 

 traversed by mineral lodes, particularly lead lodes. 



1 See paper by G. H. Kinahan " On the Formation of the ' Rock-basin ' of Lough 

 Corrib," Geological Magazine, Vol. III., 1866, p. 489. 



^ The parts furnished by both authors are specified in the ' Explanation.' The 

 country was surveyed chiefly by Mr. Kinahan. 



