236 Scientific Proceedings, Royal Dublin Society. 



[These obliquely foliated granites are very similar in appearance to the felsitic 

 quartzytes and sandstones among the schists and other rocks. The quartzytes, sand- 

 stones, and said granites all occur in irregular beds, and the oblique foliation in each is 

 of the same character, while' the constituents of the quartzytes and sandstones are 

 such as would easily change into those of the granites. At the south entrance of 

 Barnesbeg and elsewhere, there are rocks which it is difficult to say whether they ought 

 to be classed as quartzyte or granite. All these circumstances have led me to believe 

 that most, if not all, of the obliquely foliated granites were originally sandstones which 

 have passed through the stage of quartzytes into their present condition. Others of 

 the metamorphic granites are in mass, or in massive courses similar, respectively, to 

 the intrudes and courses of the hornblende rocks and the Donegalyte, in the schists and 

 allied rocks. This may lead us to suppose that they were originally intrudes of exotic 

 rocks into the derivate rocks with which they are now associated. 



In Ireland, as has been mentioned in the Introduction (ante, p. 173), there is 

 generally more or less freedom from systems of ' ' grain ' ' or parallel splitting planes in 

 all the granites of metamorphic origin : this, however, is not so noticeable in Donegal 

 as elsewhere, as some of the metamorphic granites split remarkably well. Those, for 

 instance, at Barnesbeg are reported by the stonecutters as " kind, plugging easily in 

 all directions, durable, of good colour, yielding large and square scantlings, and capable 

 of long and heavy bearings." (/. M'Fadden.)'] 



Matin. At the north extremity of Inishowen there is here 

 quartzose gneiss with subdinate nricalytes and hornblendytes 

 {Metamorphosed Cambrian (?) ), which, to the southward, are overlaid 

 unconforrnably by quartzites (Ordovicians(?)). The typical gneiss to 

 the westward is remarkable, as the foliation therein is horizontal. 

 The quartzitic gneiss is all more or less flaggy, and suitable for 

 building purposes, and some veins of it for flags. The locality is 

 very inaccessible, and the stones have only been used for local 

 purposes, and in the building of the Telegraph Station for the 

 Trans- Atlantic Shipping. 



Elvans and Felstones. 



Courses and dykes of these rocks are well exposed in the neigh- 

 bourhoods of Falcarragh, Dunfanaghy, Eosscuill, and other places 

 in the north of Donegal, as also in some localities in the south of 

 the county, while generally they are not common elsewhere. In 

 some of the exposures there are nice-looking stones ; but they are 

 very little sought after, and no quarry of note seems to have been 

 opened in any of them. 



As is usually the case elsewhere, the stones of this class do not 

 appear to be capable of producing blocks of as large or long scant- 



