668 



MR. E. E. C0WPEE EEED ON THE 



[Nov. 1900, 



felsite earlier in date than the formation of the faults, 1 but whether 

 it is of the same date as the above-mentioned sheets is difficult 

 to determine. On the farther side of it is a mass of tough greyish 

 felsite-porphyry, not unlike that at Foilnaneena and the Long Rock, 

 and forming most of the small headland by the Wooden Jetty ; but 

 it is pierced and overlain by felsites of more than one type, which 

 are themselves affected by the faults on each side of the block of 

 limestones. 



The relation of the red sandstones, etc. to the igneous rocks is 

 well seen here, one of these felsites ending up abruptly against 

 them ; and a decided unconformity exists between the two series. 2 



In the succession of small coves between this spot and Bunmahon 

 Bay are seen two narrow dyke-like intrusions of felsite-porphyry, 

 with a vertical mass of brecciated material of the same character 

 sandwiched in between them. The enclosing walls are of purplish 

 augite-porphyrite, and are much shattered and baked along the 

 planes of contact. Probably we have here an old felsitic vent (fig. 8). 

 Some apophyses of felsite, most likely connected with the same 

 outburst, pierce the surrounding more basic rocks. 



Fig. 8. — Cove betiveen Knockmahon and Bunmahon. 



A 



4- 4 4 I + 



B B' D C A' A 



^ 4-4 ++/;vV v /M^ Lvi++ .v ] 



4 +4 4/ V v v V 



4 4+4 



4 4 44 



4 + + ,/v v v v h, 

 4 4 4+/"v v vV# 





A = Purplish augite-porphyrite. 

 A' = The same, shattered. 

 B = Dark green felsite-porphyry, in- 

 trusive in A. 

 B' = The same, shattered. 



= Paler green felsite-porphyry, re- 

 sembling B and intrusive in A. 

 D = Pipe of breccia of felsitic mate- 

 rial. 

 E = Vein of andesite intrusive in A. 



It may be mentioned that on the low-lying hummocky ground 

 immediately east of the bridge over the River Mahon, a low cliff 

 of a pale grey felsite-porphyry, rather similar to that just described 

 in the cliffs, is exposed in contact with, and doubtfully later than, 

 a dark-green diabase. 



An extensive development of curious greenish rocks, with dark- 

 green tuffs, and some intrusive veins allied to bostonites, occurs 

 between Bunmahon Village and Bunmahon Head (see pp. 677, 678). 

 None of the ordinary types of felsites have been recognized here 

 on the eastern side of the headland, where the red sandstones and 



1 Quart. Journ. Geol. Soc. vol. lv (1899) p. 738 & fig. 15. 



2 Ibid. vol. liii (1897) p. 281. 



