Vol. 55.] BEDDED EOCKS OP COUNTY WATER:^0ED. 763 



Gltptooystis sp. 



This form, from Stage 3 of the Tramore Limestone Series, was 

 previously ^ compared by me with Gl. Logani (Billings), but the 

 examination of more material shows that this was an error. 



The angular spaces between the strong ribs radiating from the 

 elevated centre of the conical plate to the angles are occupied by 

 regular radiating rows of minute granules separated by fine linear 

 striae parallel to the ribs. This peculiar ornamentation is particu- 

 larly well seen in an external cast of a six-sided plate bearing half 

 a pore-rhomb with the characters rather of Gl. gigantea (Leucht.)^ 

 than of Gl. perinigera. 



MoNTiCFLiPORA (Diploteypa) peteopolitan-a, Pander. 



Characteristic of Stage C in Eussia.^ Abundant iii Stages 1 & 2 

 of the Tramore Limestones. Milne-Edwards & Haime ^ described 

 it from these at Tramore, Knockmahon, and Ballydouane. 



y. Petrological Notes on the Contempoeaneous 



YOLCANIC EoCKS. 



The mode and place of occurrence of these rocks have been 

 described above, and it will have been noticed that all are of a 

 felsitic character. Microscopically they show some interesting 

 features. Perlitic and nodular structures are not uncommon. 

 Thus, at Eaheen, near the top of the bedded series, a light grey tough 

 felsite (see fig. 1, D, p. 722) [6 w] is found to be traversed by well- 

 marked perlitic cracks filled with clear transparent material, and 

 small ragged crystals and microlites of felspar are observable with 

 minute, circular, clear spots in the groundmass. With crossed 

 nicols, the groundmass is seen to be cryptocrystalline and almost 

 isotropic in parts ; but it is mainly composed of innumerable 

 microspherulites closely packed together and giving a black cross. 

 In the perlitic cracks they are especially distinct and sharp, 

 and these, at any rate, must be regarded as secondary in origin. 

 Some nests and veins of angular grains of clear non-spherulitic 

 quartz also are visible, and the few small felspar-microlites are 

 arranged in parallel lines of flow. There are a few small, twinned, 

 lath-shaped crystals of plagioelase-felspar with very low angles of 

 extinction, which probably are oligoclase. 



The pale grey felsite [7 w] underlying this (fig. 1, E, p. 722) 

 shows perlitic structure with great distinctness on weathered 



1 Geol. Mag. 1897, p. 511. 



2 Schmidt, Mem. Acad. Imp. Sci. St. Petersb. ser. 7, vol. xxi (1874) No. 11, 

 p.23&pl. ii, figs. 11 &12. 



3 Dybowski, ' Die Chateticlce d. Ostbalt. Silur-Form.' 1877, p. 24, & pi. i, 

 figs. 4 & 5 ; Nicholson, ' Struct. & Affinities of the Genus MonticuUpora,' 1881 [ 

 p. 156 ; Eoemer & Freeh, ' Leth. Geognost.' pt. i (1880-1897) p. 473 & pi. iii, 

 figs- 1 a-h. 



^ Monogr. Palaeont. Soc. ' Bi-it. Foss. Corals,' 1854, p. 264, & references to 

 foreign literature. 



3d 2 



