This paper describes occurrences of cookeite (not previously recorded as a British species) and hydromuacovite, associated with auriferous pyrite and arsenopyrite, blende, galena, carbonates, and free gold at Ogofau, on the left bank of the river Cothi, half a mile ESE. of Pumpsaint, Carmarthenshire.

The hillside around Ogofau is scarred with opencast workings and trenches reputed to be an 'ancient gold mine' dating back to Roman times. Though the mine is described as 'disused' on the Ordnance Survey map (six-inchcs/mile, Sheet XVII, NW.), these surface workings have been exploited for free gold intermittently within the last fifty years, and recent development work (by the Roman Deep Holdings,Ltd.) from a shaft sunk in 1910 is approaching the producing stage.

One of the most promising uses of X-ray diffraction methods in mineralogy is the study of those minerals which are opaque and whose crystals are extremely minute. Although recent methods of ore examination by reflected polarized light have given valuable information about these substances, their application to soft, powdery materials is extremely difficult, an objection which does not apply to X-ray methods.

Pyrolusite (including polianite).—The present study had for its main objective an attempt to settle, by X-ray examination , the uncertainty existing as to the relationship between polianite and pyrolusite, Work already carried out by St. Johns has suggested that polianite and pyrolusite are identical, since they have the same cell sides as found from powder photographs.

In a recent paper the occurrence was described of a very iron-rich orthorhombic pyroxene in thermally metamorphosed iron-rich rocks in Manchuria. The crystals are commonly 2-5 cm. in length, but some are larger, and they are accompanied by grunerite, small garnets, and disseminated magnetite. Some of these crystals are optically positive, and the following data were obtained on one crystal.

Previous accounts of pumpellyite, a blue-gree n hydrous silicate of calcium and aluminium, are few in number; the first record is that of Palache and Vassar, who described the mineral after a study of the amygdaloidal rocks of the Keweenaw Peninsula. Later Burbank recorded a very similar occurrence in Haiti, West Indies. Again, it was observed as a constituent of veins cutting glaucophaneschists in California by Irving, Vonsen, and Gonyer, and later by Waldmann at Hochlantsch Mount, Styria, in an altered diabase, and from Lake Enare, Finnish Lapland, where it occurred in altered lime-silicate rocks. Pumpellyite was found by Quitzow in diabaseporphyrites and glaueophane-rocks from the Trias of northern Calabria, Italy.

The writer has recently described a small collection of glaucophane- schists from the Diahot valley and the north-east coast of New Caledonia (Jensen, 1936), and four of these contain lawsonite.

Lacroix (1897) has recorded lawsonite from New Caledonia, but the occurrence seems worthy of further mention as in two cases the lawsonite is found to be pseudomorphing plagioclase in doleritic rocks which show a relict ophitic fabric. So far as the writer is aware, such an occurrence of lawsonite pseudomorpbing felspar has not been recorded, though Lacroix figures a glaucophane-schist from Corsica which suggests this structure. The other two lawsonitebearing rocks from New Caledonia seem to have been coarse-grained plutonic rocks and probably never had an ophitic fabric.

The Enoggera 'granite', in which occur the minerals to be described, is situated a few miles to the west of the city of Brisbane, and within the Greater Brisbane area. Deuteric and allied minerals have previously been recorded from quarries in the granite by H. C. Richards and W. H. Bryan, and a specimen is recorded ill the Queensland Mineral Index as 'Heulandite occurring as geodes in granite. Loc. Enoggera.'

The granite itself is very varied in character, and Bryan has recognized two main types, a pink phase and a grey phase. The pink phase approaches an adamellite, while the grey is more granodioritic in character. There is, however, every gradation from one type to the other due to admixture, and this reaches its maximum in a hybrid rock formed presumably by the mingling of the two magmas.