] 56 Froceedings of the Royal Irish Academy. 



grained gray porphyritic f elstone 1 5 feet wide, has originated a cave 

 with a blowing hole at its inner extremity. The erosion within has 

 been so extended as to form a natural bridge, so that the roof of the 

 former cave forms a natural bridge over the narrow inlet to the space 

 withia as represented in the wood-cut (fig. 17)." 



(p. 87.) — '■^ Fanacl District {Biorite andEpidiorite). — Commencing at 

 the northern part of Panad Head, we find an irregular mass of dark- 

 bluish evenly crystalline diorite, forming a small boss. South of this 

 boss at Bonnaweelmore, another large mass of finely crystalline diorite 

 extends from the shore inland, apparently bedded in the quartzites, 

 seen in cliff section. Along this coast there are several fine sea- 

 staeks formed of these rocks, notably that of Stookmore, or Brown 

 George, inside S willy Beg." 



(p. 88.) — "From Illanmore to Lee Point, numerous dykes and 

 irregular masses of diorite occur, sometimes following the bedding of 

 the rocks, and at others crossing it. They are all of a dark greenish 

 coloiu' with varying degrees of crystallization. At the ' Seven 

 Arches ' several dykes of diorite occur, weathering freely, but the 

 ' Arches ' are formed by the weathering of the quartzites along joint 

 planes and planes of bedding." 



(p. 89.) — " From Ardbune Point in Caffard Bay, a well-defined 

 diorite dyke averaging 400 feet in width, can be traced almost con- 

 tinuously in a south-east direction, from the eastern to the western 

 shores of Mulroy waters. It forms the elevated peak called Cashel 

 Fort, 496 feet, a striking feature in the landscape." 



(p. 93.) — '•'• Sorn Head. — The diorite of Horn Head occupies a 

 considerable area of the more rugged portions of the promontory. 

 Sections in the cliffs, which from the coast line show that this rock 

 has been to a large extent intruded between the beds of quartzite 

 among which it can be traced in dark bands, varying in thickness and 

 confortuing in general direction to the lines of outcrop. In cases 

 where it has crossed the bedding horizontally, or nearly so, and the 

 upper portion of the quartzite has been denuded away, the diorite 

 appears in section as a cap resting on the truncated portion below. 

 South of Traglish Point the diorite ranges up among the quartzite beds 

 to the top of the cliff, a height of about 600 feet in a mass, 60 or 70 feet 

 in width." 



(p. 97.) — " Bloody Foreland District. — A very conspicuous dyke of 

 columnar dolerite 4 yards wide cuts tkrough the schists west of 

 Cui'ran's Point (Sheet 9), where it is shifted for a distance of 25 yards 

 by a fault. It appears again to the north-west, penetrating both the 



