246 Scientific Proceedings, Royal Dublin Society. 



FERMANAGH. 



In the north-west part of this county, near Belleek and 

 Pettigoe, there is a small tract of metamorphic rocks, probably 

 equivalents of the Arenig or Cambrian, coming- in from Co. Donegal. 

 These rocks, like those of the Slieve Gallion district, Co. Tyrone, 

 are very much altered, and there are in them some interesting 

 varieties of hornblende rock. 



There are large dykes of whinstone in the Carboniferous and 

 Silurian rocks, while in the latter, near the bounds of Co. Tyrone, 

 there are also eurytes, more or less similar to those in that county. 

 These rocks are not made use of, except to a small extent for road 

 metal- {T. Plunkett.) 



ANTRIM. 



Overlying the greater part of this county are the well-known 

 extensive sheets of Eocene (?) basalt and doleryte, and their 

 associated agglomerates, conglomerates, and other tuffs, with, in 

 places, intrudes of trachyte and granitic rocks (granitone and 

 nevadyte). 



In the neighbourhood of Carrick-a-rede there seems to have 

 been one of the principal volcanic centres, the remains of the old 

 volcano being still more or less visible, consisting of large masses of 

 agglomerate, conglomerate, and more or less fine tuffs, cut up and 

 displaced by numerous dykes and other intrudes of basalt, dole- 

 ryte, and more crystalline rocks. 



Slemish is considered by Traill to have been a volcanic vent. 

 " It forms a bold ridge, 3000 feet long and about 1000 feet wide, 

 which rises abruptly from 300 feet to an altitude of 1437 feet. It 

 is an intrusive mass of dark, greenish blue, crystalline doleryte." 

 In numerous places the sheets were due to fissure eruptions, the 

 dyke that now fills the fissure merging into the sheet. This can 

 be well seen at the iron mines in Gienarm. 



Another well-marked volcanic centre was Tardree. Here, 

 however, the adjuncts of the outburst were principally acidic 

 rocks {trachytes and nevaclytes), on which, in places, are lying 



