688 ME. E. E. COWPEE EEED ON THE [Nov. 1 9OO, 



Small patches of chlorite, grains and rods of magnetite, and 

 secondary quartz occur in the groundmass. 



One of the only other two rocks that can be termed augite - 

 porphyrites occurs on the west side of Bunmahon Head (p. 677). 

 It is of a greenish colour, and looks like a dolerite in the hand- 

 specimen. The groundmass consists of a mass of closely-packed 

 small felspar-laths arranged in subparallel lines of now with inter - 

 sertal grains of fresh augite, a few felspar-phenocrysts of medium 

 size, and a few large perfect crystals of fresh augite. There is very 

 little interstitial material, and not much magnetite. 



The second example (Ballydouane Bay, p. 677) has an abundant 

 cryptocrystalline or nearly isotropic groundmass, with numerous 

 small, decomposed, isolated felspar-laths, small pseudomorphs of 

 chlorite after augite, a few large porphyritic felspar-crystals, and 

 some large irregular phenocrysts of pale augite partly replaced by 

 chlorite. 



Another porphyrite with a glassy almost isotropic groundmass, 

 filled with small scattered microlites of felspar and small irregular 

 patches of chlorite and a few xenoliths, contains also numerous 

 crystals and grains of felspar mostly untwinned and of small size, but 

 no other phenocrysts. This rock is of rather an uncommon type, 

 and occurs in association with the augite-porphyrite of Knock - 

 mahon. A somewhat similar rock from the same locality has its 

 groundmass composed of a pale-greenish almost isotropic material, 

 filled with felspar-crystals of various sizes, but mostly elongated 

 large laths. A little iron-ore in large skeleton-crystals is also 

 present. 



/. Miscellaneous Types. 



The peculiar pale-greenish or violet-grey rock with brownish- 

 yellow blotches which occurs near Doneraile Cove (p. 678) has 

 somewhat the appearance of a felsite in the field, but suggests a 

 keratophyre under the microscope. There is fairly abundant 

 brownish interstitial material between the large laths of felspar 

 which make up the bulk of the rock. This interstitial material 

 contains minute grains of magnetite or ilmenite, and irregular patches 

 of pale chlorite. The felspars are entirely replaced by a finely 

 granular or saussuritic aggregate, and secondary minerals, especially 

 calcite, are abundant. A few large crystals of ilmenite, often 

 changed into leucoxene, are noticeable. The brownish patches 

 enclose and enwrap the felspars, and are distinct from the ground- 

 mass • though they hardly seem definite enough to represent ophitic 

 plates of any mineral. 



The 'greenstone' intruded into the slates in Stradbally Creek 

 (p. 678) is of a peculiar type, for it consists almost entirely of large 

 idiomorphic or nearly idiomorphic felspars with extinction- angles 

 of 12° to 15°. There is no original interstitial material, but the 

 spaces between the felspars are filled up by a pale-greenish chloritic 

 mineral, perhaps representing ophitic augite. There are also a few 

 decomposed skeleton-crystals of ilmenite and grains of epidote. 

 Probably it is a diorite. 



