174 Scientific Proceedings, Royal Dublin Society. 



general, there are two systems of " grain," at right angles to each 

 other ; and under such circumstances the stones can be split into 

 rectangular blocks, or else slabs, of from a few inches to several 

 feet in their various dimensions. Stones of this class are nearly 

 always capable of long and heavy bearings, while they can 

 always be dressed on any face. On the other hand, granites of 

 solely metamorphic origin seldom have a regular " grain." If there 

 be a "grain" it is always along, and never across, the planes of 

 foliation ; and such granites are unsatisfactory for fine cut -stone 

 purposes, as they dress only on one face. But as they are hard, 

 durable stones, and can usually be raised in large sizes, they are 

 admirably suited for heavy work, where permanency rather than 

 finish is required. To this general rule there is an exception, as 

 some of the rocks, originally intrusive granite, and afterwards 

 foliated by subsequent metamorphic action, seem to retain, more 

 or less in their new state, their original " grain." The granitic 

 gneiss, which is considered to be the most durable of all the stones 

 that have been used in New York city, appears to belong to 

 this class of metamorphosed intrusive granite ; as do also the 

 granites along the margin of the Slieve Croob intrude, Co. Down, 

 and certain granites in the Castlebar and Lough Conn district, 

 Co. Mayo. 



The relations between the Irish granitic gneiss, or foliated 

 granites, and their associated schists, are at present only partially 

 understood. 



The granites due to metamorphic action, whether called 

 " foliated granite," " granitic gneiss," or " gneiss," in Iar-Con- 

 naught, Co. Gralway, and in the barony of Kilmacrenan, Co. 

 Donegal, are in no place intruded into the associated schists. It is 

 therefore evident that they must be adjuncts of the schists, and 

 not rocks that were intruded into the schists. In these portions of 

 those counties there are, however, associated with the tracts of 

 metamorphic granitic rocks and schists, newer granites that have 

 been undoubtedly intruded subsequently to the formation of the 

 metamorphic granites and their associated schists. 



At the extreme south of the barony of Boylagh, with the 

 adjoining part of Banagh, Co. Donegal, in the Lough Conn 

 district, Co. Mayo, in the Slieve Crook district, Co. Down, 

 and in south-east Ireland (Leinster granite range) the relations 



