336 Rejmrts and Proceedings — Geological Society of London. 



marine origin, mixed with mineral detritus from adjacent liills. 

 The rocks can hardly be older than Pliocene ; and there is nothing 

 in the general character of their organic remains which is incon- 

 sistent with a still more recent date. The tests of some of the 

 foraminifera have been filled with limonitic substances or with the 

 yellow, brown, or green varieties of glauconite. Six specimens are 

 described in detail, and lists of the contained foraminifera given. 

 In one instance the granules are all invested with a thin, dark 

 layer, which seems to be the first stage towards an oolitic structure. 

 A note is appended on the foraminiferal wind-borne sands of Dog's 

 Bay (Galway), discovered by Welch. 



3. " On Ceylon Eocks and Graphite." By A. K. Coomara Swamy, 

 F.G.S. 



Ceylon is surrounded by raised beaches, and has been elevated in 

 recent geological times ; fluviatile deposits also occur : the gems for 

 which Ceylon is famous are obtained from gravels in the Katnapura 

 district. With the exception of these recent deposits, the island 

 probably consists entirely of ancient crystalline rocks. Pyroxene- 

 granulites are recorded from several localities ; they are dark in 

 colour and greasy in lustre. Foliation is not evident, but it may 

 appear in thin slices. The minerals most frequently present are 

 augite or hypersthene, or both, plagioclase (usually labradorite), 

 orthoclase-microperthite, garnet, quartz, amphibole, magnetite, apatite, 

 zircon, and biotite — the pyroxene and felspar alone being essential 

 constituents. Varieties approach gabbro and eclogite. The texture 

 is granulitic or granular. Centric structures are very characteristic, 

 probably resulting from the corrosion of garnets. Normal granulites 

 are white or grey, and usually contain red garnets. The minerals 

 are quartz, orthoclase- and microcline-microperthite, plagioclase, and 

 garnet ; biotite, magnetite, ilmenite, apatite, and zircon are often 

 present ; and the texture is granulitic. Microcline-gneiss, sometimes 

 with hornblende, occurs in conical hills, originating the term domoid 

 gneiss employed by Professor Walther. The minerals include 

 orthoclase- and microcline-microperthite, quartz, plagioclase, biotite, 

 pyroxene, amphibole, pyrite, magnetite, apatite, and zircon. 

 Anorthosite-gneiss, gneissic granite, and pegmatite are also described. 

 Dark diorites (containing amphibole, plagioclase, quartz, pyroxene, 

 biotite, magnetite, apatite, and zircon), dolerite, hornblende-gabbro, 

 and ophitic quartz-norite are also present. The white, crystalline 

 limestones usually contain pale mica and blue apatite ; sometimes 

 also colourless pyroxene. Banded scapolite- and wollastonite-bearing 

 rocks are found at Galle. Certain rocks, apparently vein-products, 

 are also described, which contain quartz and calcite micrographically 

 intergrown. 



Graphite occurs chiefly in branching veins in igneous rocks, which 

 at Ragedara are granulites and pyroxene-granulites. The relations 

 to the matrix are described, and are held to favour the idea of the 

 deposition of the mineral as a sublimation - product (Walther), or 

 from the decomposition of liquid hydrocarbons (Diersche). Analyses 

 of several of the minerals, including manganhedenbergite, are given; 

 and a bibliography of the geology of the island is appended. 



