160 Archdeacon Verschoyle on the Geology of the North Coast of 



In Erris, behind the vicarage at Tarmoncarra, the rock is well exposed in the 

 cliffs. The strata range north-west and south-east^ and though when considered 

 t»enerally, the gneiss appears to lie above the mica slate, and below the quartz 

 rock, yet when examined in detail, frequent alternations and transitions are ob- 

 servablCj even in the space of a few perches ; so that it is only from an inspec- 

 tion of the whole deposit, its nature and character can be determined. For 

 instance, at Annagh, the south headland of Port-na-Frankagh (French Port), 

 mica predominates, and the gneiss approaches in aspect to mica slate, while the 

 north point presents gneiss, distinctly marked, abounding in red felspar, with 

 black mica; and more northward, near Scotch Port, it is studded with garnets, 

 and the mica coalesces into small feathery crystals, while the felspar has dimi- 

 nished into fine grains, detectable only by a magnifier. Proceeding along 

 the shore, hornblende gradually becomes a component, and even occasionally 

 the predominant ingredient, and sometimes the mica slate contains crystals of 

 sahlite. Between Scotch Port and Donamoe is, however, a sudden change. 

 A narrow fault or fissure, scarcely a foot Avide, filled with a clayey breccia, 

 apparently derived from the detritus of hornblende and gneiss, and ranging in 

 an easterly direction, cuts through all these beds, having on the south the horn- 

 blende schist, and on the north, mica slate, perfectly distinct, and containing 

 those peculiar plumose concretions of mica, alluded to above. From this sud- 

 den variation, we may conclude, that an elevation has taken place at the north 

 side of the fault, produced, probably, by the same operation which erupted the 

 dykes parallel to it ; and that the mica slate and gneiss of Port-na-Frankagh, or 

 French Port, are here forced up to the surface ; the coast rising once more into 

 mica slate cliffs, in which the mica again diminishing and the felspar reappear- 

 ing, the rock passes into gneiss. Oxydulous iron in laminae is met with here, 

 accompanied by druses of felspar crystallized in oblique rhomboidal prisms. 

 From this point mica again predominates, and Donamoe consists of mica slate. 

 Proceeding to the northward, the mica and the felspar decrease gradually, 

 and the beds pass into quartz rock, which, towards Erris Head, as already 

 detailed, exclusively constitutes the sea cliffs. In the eastern part of the district, 

 at MuUi-na-Shee, below which the road from Coolany to Tyreragh passes, the 

 same transition from quartz rock to mica slate is seen, the latter containing an 

 unusual ingredient, in small crystals of asbestos disseminated through the mass, 

 and accompanied by minute prisms of felspar ; schorl and calcareous spar also 

 sometimes occur. The beds under these abound with garnets. The entire 

 series, from the conglomerate to the mica slate, dips about 15° or 20° to the 

 south-east, which is the general inclination of the strata in the Ox Mountains. 



