30 Scientific Proceedings, Royal Dublin Society. 



adjuncts of tHe gneiss ; second, granite intruded into these rocks, 

 and sheared along with them ; third and fourth, two distinct 

 granites intruded after the shearing ; and fifth, a much more recent 

 invasion. The lateness of the last appears from the facts, already 

 pointed out, that the dykes and courses of elvan and porphyries 

 from the laccoliths run continuously in the northern portion of 

 the barony of Kilmacrenan without being affected by any of the 

 upthrusting, and rarely by any of the faulting to which the 

 associated country rocks have been subjected/ 



That the strata from the base of the Oreat quartzite upwards 

 to the Barnhill grit series are of a much newer age than the 

 " Kilmacrenans " is self-evident, as the latter were contorted, meta- 

 morphosed, and denuded prior to the Later Rocks accumulating 

 over them. 



As to the age of the Later Rocks (from the Grreat quartzite to 

 the Barnhill grit series) it may be suggested that they are the 

 equivalents of the Lower Ordovieian. The rocks of the higher 

 group {Manorcunningham series) are still undetermined as to age. 

 These MuUaghsawnites and their associated slates, in the barony 

 of Raphoe evidently lie unconformably on the Older Period Rocks ; 

 but in the barony of Inishowen they overlap much more recent 

 rocks [Killygarvan volcanic series). This overlap, as seen in the hill 

 to the south and south-east of Buncrana, may be due to upthrust- 

 ing ; but I suspect it is in part, at least, due to a second hiatus or 

 unconformability. 



The MuUaghsaivnites are pebbly sandstones or schistose rocks, 

 containing quartz and feldspathic grains from the size of shot to 

 that of large peas. Usually the grains are quartz, but in some 

 places these are in a great measure feldspathic. Very similar rocks 

 occur in the Upper Ordovicians {Slate series) of Cos. Clare and 

 Tipperary, while they also occur in the supposed metamorphosed 

 Ordovicians in the hill immediately south of Westport, Co. Mayo. 

 In Mid-Scotland, especially in Perthshire, in rocks also supposed 

 to be sub-metamorphosed Ordovicians, similar pebbly rocks are 

 said to be of glacial origin ; for what reason it is hard to conceive, 

 as no modern accumulations, due to any ice, have any characters 



^ The above conclusions I came to from field observations. I learn, however, from 

 Dr. Hyland that, after microscopical and chemical investigation, hie has arrived at a 

 classification which is very similar to, if not identical with,"'mine. 



