The new crystalline compound triphenyl-bismuthine dichloride, described crystallographically by Mr. G. Greenwood (Min. Mag., 1923, vol. 20, p. 123), possesses the remarkable property of exhibiting crossed axial-plane dispersion of the rhombic ‘brookite’ type and circular polarization. For purposes of comparison, the author prepared specimens of the mixed Seiguette salts, which also exhibit crossed axial-plane dispersion together with circular polarization. The Seignette salts, sodium-potassium tartrate and sodium-ammonium tartrato, crystallize each with four molecules of water ill the bisphenoidal class of the rhombic system. They are truly isomorphous and form a continuous series of mixtures. The acute bisectrix for sodium-ammonium tartrate is normal to (001)and for sodium-potassium tartrate normal to (100). For all proportions of mixture containing 5 % and over of sodium-ammonium tartrate, the acute bisectrix is normal to (001).

In April 1909 a paper on artificial reproduction of meteoric structure in alloys of iron aud carbon was read by the author before the Russian Mineralogical Society. In that paper special reference was made to the work of Sorby, who, to cite his own words, for ‘more than twenty years … commenced to carefully study the microscopical structure of iron and steel in order, if possible, to throw light on the origin of meteoric iron’. A brief survey of the work of Stodart and Faraday, of Osmond, Rinne, and Berwerth was also given and, subsequently, the structure of a carbon-steel containing 0.55 % carbon with perfectly developed Widmanstätten figures was described.

The euclase here described is not only from a new locality, but it represents an entirely new type of habit for this rare mineral, which is occasionally used as a gem-stone. The crystal aggregates present a strange resemblance to fossils, and fossils not having been found in British Guiana they were submitted to the Geology Department of the British Museum by Mr. R. P. Stewart of Georgetown, Demerara. They had been found by Mr. J. C. Menzies whilst engaged in washing for gold and diamonds in the neighbourhcod of the Kaieteur gorge on the Potaro river, a left tributary of the Essequibo. Both of these gentlemen have interested themselves in the matter and have kindly sent further material for examination.

Pisolitic ironstones occur at various localities in North Wales, at about the horizon of Nemagraptus gracilis. The rocks have undergone considerable folding and the hard ironstones are often faulted and in many cases deformed. Greenstone dikes frequently intersect the beds, usually with little visible alteration of the ore, though the ironstones are generally hardened, with incipient re-crystallization of the chamosite. At Pen-y-rallt iron mine, situated half a mile east of Llanfrothen church near Penrhyndreudraeth in Merionethshire, a steeply inclined pisolitic ironstone bed rests upon a mass of igneous rock; and here the alteration of the ore is in a more advanced stage, for the ironstone is in places seamed with roughly parallel asbestiform veins (up to 1 inch) which contain a brittle dark-brown mineral strongly resembling biotite ; the centre of the vein is sometimes filled with chalybite.

It has long been recognized that if specific gravity determinations are to be accurate to a unit or two of the third decimal place corrections must be applied for the error due to the circumstances (i) that the weighings are made in air instead of in a vacuum, and (ii) that the temperature at which the determinations are made usually differs considerably from the standard temperature of 4° C.