100 



Proceedings of the Royal Irish Academy. 



found most useful by the authors of the present paper. They are 

 founded essentially upon palajontological evidence, but, after a little 

 experience, are readily recognizable on purely lithological grounds, 

 and by this means are traceable unchanged through all available 

 exposures. 



Corrycroar Group = Tarannon. 



Undivided. 



Little River Group = Llandovery. 



Lime Hill beds. Slate Quarry beds. 



Mullaghnabuoyah beds. Crocknagargan beds. 



Edenvale beds. 



Deserter eat Group = Ashgillian. 



Upper Timaskea beds. Killey Bridge beds. 



Lower Timaskea beds. Bardahessiagh beds. 



These local names are taken directly from the six-inch Ordnance 

 map of 1856, and are here introduced only for the purpose of reference, 

 and for the avoidance of circumlocution in description. 



We may now consider these various sub-divisions in order, begin- 

 ning with the oldest, and, in so doing, will leave all questions of 

 structure and correlation of the beds to a later stage. 



The Bardahessiagh Beds. 



As indicated in the table, the Bardahessiagh beds form the basal 

 member of the Palaeozoic series. They occur all along the northern 

 edge of the district, where they adjoin the hornblendic and granitic 

 series of the Ulster Highlands, and are brought up again by a sharp 

 fold in the neighbourhood of Killey Bridge. According to the 

 view of the present authors, they must rest with notable discordance 

 and unconformity upon the Highland metamorphic rocks ; but the 

 actual base of the series has never been very well seen, and is not 

 now exposed. The lowest members of the Bardahessiagh beds now 

 observable are the rocks exposed along the Slate Quarry road, just 

 south of Craig Bardahessiagh, and are the coarsest of the series. They 

 consist of almost unweathered felspars and micas, with abundant 

 angular quartz chips, which are embedded in a sort of serpentinous 

 paste such as might well be directly derived from the denudation of the 

 hornblendic series, or of the mica schist country a little further noi'th. 

 Conglomeratic beds — such as are mentioned by Portlock — are now 



