104 MR. GARDINER AND PROF. REYNOLDS ON THE [June I914, 



5. The Ordovician and Silurian Bocks of the Lough Naeooey 

 Area (County Gal way). By Charles Irving Gardiner, 

 M.A., F.G.S., and Prof. Sidney Hugh Reynolds, M.A., 

 Sc.D., F.G.S. (Bead January 7th, 1914.) 



[Plates XVI & XVII.] 



Contents. 



Page 



I. Introduction 104 



II. The Sedimentary and Volcanic Arenig Bocks 105 



(a) The Spilites (Pillow-Lavas). 



(b) The Sedimentary and Pyroclastic Bocks. 



III. The Mweelrea Grits and Conglomerates (Llandeilo) . . . 109 



IV. The Silurian Bocks 109 



V. Field-Belations of the Intrusive Igneous Bocks 112 



(a) The Felsites. 



(6) The Labradorite-Porphyrite. 



(c) The Lime-Bostonite. 



(d) The Dolerites. 



VI. Petrographical Details 115 



VII. Comparison of the Bocks of the Kilbride, Lough 



Nafooey, and Killary Areas ; and Conclusions 116 



I. Introduction. 



The area with which this paper deals is a direct continuation of 

 the Kilbride area (described by us in 1912), froni which it is only 

 separated by the Finny River. It forms a tract measuring about 

 4 miles in length, and about a mile and a half in width. It is 

 bounded on the north by Lough Nafooey, on the north-east by the 

 Finny River, and on the south-east by the inlet of Lough Mask 

 known as Kilbride Bay. On the south and west the boundaries 

 are not determined by any well-marked features. 



Geographically the area forms a ridge, rising to its highest 

 points in the hills known as Curraghrevagh (1615 feet) and 

 Benbeg (1788 feet). There is a steep northward descent from 

 this lofty ridge to Lough Nafooey, while the southern descent is 

 more gradual. A second and lower ridge diverges from the main 

 one to the south of Red Island (see map, PL XVII), and extends 

 north-eastwards towards the Finny River. Between these two 

 ridges is a valley occupied by two streams, which join and flow 

 into the Finny River: we propose to call this Two- Stream 

 Valley. 



Little has been written about this area, the only detailed account 

 being in the Memoir of the Geological Survey of Ireland to accom- 

 pany Sheet 94, published in 1878 ; but references to it are to 

 be found in the Summary of Progress of the Geological Survey 

 for 1896, p. 49. 



