678 ME. E. E. COWPEE EEED ON THE [Nov. I9OO, 



The rock which crosses the head of Stradbally Creek is a 

 diorite of a type not met with elsewhere along the coast. It 

 forms a large irregular intrusive sheet piercing the black slates, and 

 is later than the period when they received their cleavage. 



There is a peculiar intrusive rock near Tramore traversing the 

 bedded felsites immediately north of Doneraile Cove. It is 

 lilac-grey to greenish-grey, with small irregular yellow patches, 

 and rings under the hammer like a felsite. Prom the hand- 

 specimen its true nature cannot be determined, but the microscope 

 (see p. 688) throws some light on its characters. A variety of 

 this rock, forming part of the same mass, shows small, irregularly- 

 oval, yellowish-green spots enclosing a darker centre. This intrusive 

 mass appears to be earlier than the diabase-sheet previously described, 

 but it is pierced by some of the smaller intrusive veins. 



The Bunmahon Bock and its associated dark-green tuffs 

 form most of the cliffs on the western side of Bunmahon Bay. 

 It is a dark-green, tough, compact rock, not at all decomposed, but 

 showing small patches of bright greenish-yellow epidote and a 

 granular fracture. The felspars of the groundmass are distinctly 

 visible on a freshly broken surface, embedded in the dark greenish- 

 grey matrix. Various faults and planes of crushing traverse it, 

 and intrusive sheets of a dark-green compact rock of a bostonitic 

 type (p. 683), and some other dark green felsitic dykes or veins 

 pierce it. The cliffs a few yards to the west consist of fine com- 

 pacted tuffs, and these are pierced by intrusions of a peculiar type 

 of greenish-grey felsitic rock, one dyke of which forms a conspicuous 

 Hying buttress. The site of the vent from which the clastic 

 materials were ejected is found on the foreshore, being indicated 

 by an assemblage of fragments, large and small, of the surround- 

 ing solid rocks. Coarse green tuffs of this character compose the 

 cliffs and foreshore up to the faulted mass of Old Bed Sandstone 

 and on the west side of it. 1 The outpouring of the Bunmahon Bock 

 and tuffs was certainly prior to the veins, dykes, and sheets which 

 penetrate them, and also to the Old Bed Sandstone. 



III. Peteological Notes. 



a. The Felsites. 



It has been noticed by several geologists that there is more than 

 one type of felsite, both chemically and microscopically, in this 

 area. Thus Dr. Hatch 2 mentions the analyses given by Haughton 3 

 and J. Arthur Phillips, 4 and remarks upon their different characters, 

 describing at the same time two other felsites of which he tabulates 

 analyses. One of the latter, called a potash-felsite, was 

 found at a locality 1 mile west of Great Newtown Head, and it 

 is suggested that it represents a devitrified pitchstone. The other 



1 Quart. Journ. Geol. Soc. vol. liii (1897) p. 280. 



2 Geol. Mag. 1889, p. 546. 3 Trans. Eoy. Irish Acad. vol. xxiii (1859) p. 615. 

 4 Phil. Mag. vol. xxxix (1870) pp. 13-14 ; Geol. Mag. 1889, p. 288. 





