In a previous paper two well-known crystalline compounds, sodiumpotassium tartrate, XaKC4H4O6. 4H2O, and sodium-ammonium tartrate, Na(NH4)C4H4O6.4H2O, were described, and it was therein shown how, in the crystals obtained by mixing these two isomorphous substances in any proportion, the dispersions of the ojjtic axes in the freshly prepared crystals were incompatible with orthorhombic symmetry. The crystals have been frequently measured and found to be orthorhombic bisphenoidal in external symmetry and this has been further confirmed by the author's measurements. A. full description of all the various dispersions to be found in the orthorhombic and monoclinic systems may be obtained from any text-book of crystallography, but in the following pages two of these are specially important.

The occurrence of chloritic minerals as infillings of vesicular cavities in volcanic rocks is very common in rocks of all geological ages. Numerous chlorites have been described and analysed, but their classification and nomenclature are complicated by the fact that, as in the case with other hydrous alumino-silicates such as zeolites and clay minerals, the chloiites present a great variety of chemical compounds, usually of indefinite composition.

Six analyses of berthierite from various localities are quoted by Dana and show a varying composition. The analyses correspond approximately to the formulae FeS.Sb2S3, 3FeS.2Sb2S3, and 3FeS.4Sb2S3. It is considered by Dana that the variation is probably due to the impurity of the analysed material and that the composition of berthierite is probably FeS. Sb2S3. This view is supported by the examination and analysis of a specimen of berthierite from Xullarnanna, 18 miles north of Inverell, Now South Wales.

The specimen was kindly lent by Mr. G. W. Card, Curator of the Mining Museum, Sydney, for comparison with certain minerals under investigation, and measured approximately l x l x O-7 cm. It was sliced and one portion was polished for examination under the reflecting microscope while the other portion was used for the chemical analysis.

From an examination of thin sections of specimens in the British Museum (Natural History) labelled Cobija and Lampa and also from a consideration of the present distribution of these meteorites in the British Museum and in the Ward-Coonley collection in the Field Museum of Natural History, Chicago, Dr. G. T. Prior thought that there was strong evidence in favour of their identity. In his 'Catalogue of Meteorites' (1923, p. 95) ho states with reference to the Lampa stone: 'Except that it is more oxidized, in characters it is very similar to Cobija, and may be identical with it since the information as to locality was obtained not from H. A. Ward but indirectly from the School of Mines, Santiago.' Dr. Prior subsequently handed me these meteorites for a chemical examination.

A very fine and unusual crystal of sperrylite, recently presented by Mr. G. H. Beatty of Johannesburg to the mineral collection of the British Museum, came from a new adit on the Tweefontein farm (no. 1083), about 10 miles NNW. of Potgietersrust, Waterberg district, Transvaal. It had been found embedded in copper-stained limonite in crush-zones of banded ironstone underlying norite. The limonite matrix is presumably an alteration-product of sulphides (pyrrhotine, pentlandite, and chalcopyrite). The banded ironstone is an altered sediment belonging to the dolomite series, and is penetrated by apophyses from the basic margin of the Bushveld igneous complex.