168 Geological Society. 



marine origin, mixed with mineral detritus from adjacent hills. 

 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 (Gal way), discovered by Welch. 



3. ' On Ceylon Rocks and Graphite.' By A. K. Coomara-Swamy. 



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

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

 which Ceylon is famous are obtained from gravels in the Ratnapura 

 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, mag- 

 netite, 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 Prof. Walther. The minerals include ortho- 

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

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

 orthosite-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). Ana- 

 lyses of several of the minerals, including mangan-hedenbergite, are 

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



