224 Scientific Proceedings, Royal Dublin Society. 



intrusions of diabase (?), while in the different groups of strata there 

 are intrudes and dykes of melaphyre (Carboniferous ?) dolerytes and 

 basalts (probably Cainozoic). Peculiar rocks that weather easily, 

 forming great roads or ravines, with perpendicular sides, are probably 

 the roots of the interbedded Silurian whinstones. These rocks are 

 not sought after ; yet the friable whins should make good fertilizers, 

 especially if used as top-dressing on the boggj r , mountain slopes. 



In N.W. Mayo there are whinstones of different ages. The 

 Tertiary Dolerytes and Basalts occur very frequently ; for the most 

 part as dykes in the granitic and metamorphic rocks, but sometimes 

 in the Carboniferous. They vary in character and in composition. 

 In the Carboniferous Limestone, a little northward of Killala, there 

 is an intrude of a very coarsely crystalline doleryte, which is partly 

 ophytic. It polishes well, but unfortunately it generally contains 

 a quantity of iron, which comes out under the influence of the 

 weather. As it rises, however, in large blocks, and is very hard, it 

 ought to be suitable for sea-walls, piers, and such like rough 

 work. 



In the Little Cannavar Island, Lough Corrib, there is an 

 intrude of actinolite and tremolite rocks, which should be capable 

 of being economically used in the manufacture of black glass. 



[This trade is almost totally neglected in Ireland. At the Artizans' Exhibition 

 in Dublin in 1885, tbere were exhibited black glass bottles made from tremolite rocks 

 from Co. Antrim. This, however, does not seem to have been turned to much account. 

 There would be a fine opening for bottle works in Galway, the materials being close at 

 hand.] 



Hornblende and Ophite Rocks. — These are sometimes metamor- 

 phosed whinstones ; sometimes they are root-rocks and other in- 

 trusions, allied to basic elvan or granitone. None of those found in 

 this territory have as yet been utilized for ornamental purposes ; 

 yet it is very possible that suitable stones might be procured, more 

 or less in connexion with the Ophyte, in the following localities. 



Co. Galway. In connexion with the two tracts of Ophyte near 

 Lough Ballard and a short distance east of it, in the wild tract 

 westward of Roundstone. 



About half-a-mile south-west of Bunowen Castle, near the north 

 shore of Gralway Bay. 



To the south and south-east of Glendollagh, or Lough Garroman, 

 in the tract of hornblende-rock. 



