Kinahan — On Granite and Met amorphic Rocks. 193 



years, some of these stones Lave been suggested as good for "paving- 

 setts." They work readily, as they split squarely and easily ; but 

 most of those that have been tried seem to have a soapy quality 

 (steatitic) which is detrimental, as they would be slippery if 

 subjected to traffic. [ Vide papers on Irish Arenaceous Bocks, vol. v., 

 p. 507, and ante, p. 6.] In Howth, Saggart, and other places 

 quarries have been opened to supply road metal to Dublin, the 

 Townships, and the local roads. 



In the neighbourhood of Balbriggan are many intrudes of 

 whinstone, some of which Jukes considered to be specially suitable 

 for paviug-setts. 



Gneisses and Schists. 



Gneiss, is nearly, if not altogether, absent from the Co. Dublin. 

 On the margins of the granite intrude there is in places a thin 

 coating, having a gneissoid appearance. It is scarcely, however, a 

 typical gneiss, the foliation being rather of a platy structure, in- 

 troduced in the outer crust of the granite. 



The schists are various, both here and in the adjoining portion 

 of the Co. Wicklow. They may be either metamorphosed igneous 

 or sedimentary rocks. If they were originally felstones they are 

 now felsitilyte (felsite-schist), or felspathic micalytes ; but if origin- 

 ally eurytes or whinstones, they are now, nearly always, some 

 variety of hornblendyte. 



[" The thick courses of euryte and whinstone, as already mentioned, 'have usually a 

 compact rib margined by schist. This is, generally, not the case with felstone courses ; 

 although it has been recorded as occurring in the Co. Galway. Some of the metamor- 

 phosed felstone courses in that country, near the town of Galway, are a granitic rock 

 along the margins, but have a felstone or porphyry rib." (g.s.m.) ] 



In the schist districts this rock is extensively used for general 

 purposes, especially the micalyte. It affords good serviceable 

 stones, very durable ; but some are unsightly, as they become by 

 weathering "iron-masked." Micalytes ought to be used much more 

 than they are, in sea-walls and piers ; because when they can 

 be raised as rough flags in large, or even fair sizes, if they are 

 pitched, not built, in courses in the walls, no wave can work them 

 out ; while if the walls are left rough enough on the face, waves 

 cannot rise so well on them, as they would otherwise do. 



