168 Proceedings of the Royal Irish Academy. 



iiorth.-east face is broken by a precipitous rift or chasm, wbicb. extends 

 to within a few hiinch'ed feet of its snnnnit, and runs down nearly to 

 the sea cliff. From this out to the extreme west point of the island, 

 viz. , A chill Head, the surface of the country consists of only high hills- 

 and elevated boggy plateaux, culminating in the mountain called 

 Croaghaun, whose summit towers nearly vertically over the Atlantic, 

 at a height of 2192 feet. This mountain is sheared off by an 

 enormous precipice of nearly 2000 feet, running from top to bottom of 

 its north-west face, and forming an almost perpendicular wall to the 

 sea." 



(p. 9.) — '■'■Acliillleg Island. — One and a half miles long by one 

 mile wide is an elevated tract of land, lying about half a mile from 

 the main island. Three hundred feet up the sharply inclined flank of 

 the south-east face of this high ground are found large perched blocks 

 of red sandstone, more than a ton in weight, in a condition of unstable 

 equilibrium. Achillbeg is bisected by a broad, sandy, east and west 

 cut, or passage, running parallel to the passage that divides the two 

 islands, and the three eastern and western valleys, occurring at 

 intervals of two miles each, going north on the mainland. The above 

 passage is nearly on a level with the sea, which has evidently swept 

 through it ; its direction coincides with that of the joint planes and of 

 the numerous eastern and western faults." 



(p. 12.) — " Starting from the north-east end of the island, viz. 

 Eidge Point ; the ridge is due to the hard siliceous nature of the 

 schists, backed up on the least weathered side, by a strip of still 

 harder quartzite. On the west side of this the sea has encroached 

 along the line of strike, leaving exposures of the harder portions of 

 rock here and there. jS^orth of Doogort the coast-line is most irregular, 

 the rock being soft and easily decomposed, and also cut by numerous 

 faults. The bold sea-cliffs at the base of Slievemore, standing out in 

 a semUune, are composed of a hard quartz-schist. From Dirk to 

 Armagh the coast-line is recessed at right angles to itself. Here the 

 rocks are not less hard, but we have a sudden change of dip along a 

 northern and southern fault at Dirk, and the change in the outline is 

 probably due to jointing, by which the rocks are much cut up. This 

 increased excavation is due also to the reversed dip. From this point 

 the seaboard projects outwards until it terminates on the north-west 

 point of Gubroenacoragh, composed of hard quartzose schists. The 

 flanking cliffs on the north and west coasts of this tableland, being of 

 felspathic or micaceous schists, have been more rapidly cut away 

 along the parallel jointings, which running north-north-west at 



