The Quarterly journal of the Geological Society of London . nd more or less spherical masses ofcalcite occur (see fig. 3, p. 144), the concentric shells of calcite beingseparated by shells of haematite, while in other cases chlorite occursabundantly. 144 MESSRS. C. I. GAEDINER & S. H. REYNOLDS [Feb. 1898, There are a few instances, however, where the gronndmassshows the structure known as * micropoikilitic Mr. AlfredHarker, in his paper on The Gabbro of Carroek Fell, ^ and Mr. ,. Cowper Reed, in his notes on The Geology of the Countryaround Fishguard, ^ notice this structure, the former in
The Quarterly journal of the Geological Society of London . nd more or less spherical masses ofcalcite occur (see fig. 3, p. 144), the concentric shells of calcite beingseparated by shells of haematite, while in other cases chlorite occursabundantly. 144 MESSRS. C. I. GAEDINER & S. H. REYNOLDS [Feb. 1898, There are a few instances, however, where the gronndmassshows the structure known as * micropoikilitic Mr. AlfredHarker, in his paper on The Gabbro of Carroek Fell, ^ and Mr. ,. Cowper Reed, in his notes on The Geology of the Countryaround Fishguard, ^ notice this structure, the former in lavasmetamorphosed by the gabbro, the latter in felsites which he con-siders metamorphosed. In the last-named paper a very full accountof previous notices of this structure, which seems generally tohave been seen in felsitic rocks, is given. On Lambay Island, how-ever, it occurs in andesitic rocks and in the coarse porphyrite. It isto be seen in five of the slides which we have had cut; three of these Fig. 3.— Vesicular andesite from Freshwater r. \ y \ -J X 18. [The rock is very much altered, calcite and otber minerals having come in withthe alteration. In the vesicles the calcite often assumes a sphericalarrangement, as shown in the figure, the spheres of calcite being separatedby spherical shells of haematite.] are from andesites, and two from the coarse porphyrite. Two of theslides from the andesites are cut from rocks close to the junctionwith the limestone at Kiln Point. This rock in a hand-specimen isseen to have an appearance somewhat different from that of the usualfine andesite of the island, being more compact and horny, andthe sections show the alteration of the rhombic pyroxene whichthey contain and of the gronndmass, the small felspars in whichhave to a large extent disappeared, ragged-edged plates of quartzhaving been formed, giving rise to the micropoikilitic structure. 1 Quart. Joum. Geol. Soc. vol. 1 (1894) p. 311. 2 Ibid. vol. li (1895) p. 149. Vol. 5
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