The specimen of cordierite-gneiss under notice was collected by Mr. T. N. Muthuswami (Assistant Professor of Geology, Presidency College, Madras) in a quarry at Ganguvarpatti in the Madura district. On examining tliin sections of the rock, he found that many of the cordierite crystals were optically positive, and, thinking that the mineral might be worth further investigation, he sent a specimen of the rock to me. The investigation was carried out ill the Geological Department of the Imperial College of Science and Technology, and my thanks are due to Professor W. W. Watts and Dr. J. W. Evans for their kindness in affording me facilities for this work and also to Dr. H. H. Thomas, of H.M. Geological Survey, for his kindness in placing Fedorov's universal stage at my disposal for the measurement of the optic axial angle.

On the basis of field relationships, the main types of the Dartmoor granite can be referred to four stages of intrusion, the sequence being from relatively basic to thoroughly acid.

To this sequence is closely related an increase in the content of tourmaline and in the extent to which autopneumatolysis (with tourmalinization) was effective before solidification of the rock was complete.

Autopneumatolysis is well displayed by many minor intrusions referred to the latest stage. Such an intrusive rock is reddened more or less uniformly throughout its entire mass, and volatile constituents exhaled from its margin have reddened a contact-zone of the grey granite into which it is intrusive.

In September 1923 a visit to the lead-mining district of Holywell, Flintshire, so closely associated with the name of Thomas Pennant, was organized by Mr. Campbell Smith in order to examine the abandoned workings with a view to collecting specimens. The occurrence of the ores has been described in detail by Sir Aubrey Strahan and Mr. Bernard Smith, and reference to many mineral localities, mentioned by Pennant, is made by Mr. Campbell Smith (loc. cit.).

The commoner specimens collected consist of ruby-blende (Talargoch mine), botryoidal and pseudomorphous calamine ZnCO3 (Milwr mine), orange and reddish-mauve fluor with bitumen and blende (Bryn-gwiog mine).

Calcite also occurs abundantly in veins and cavities throughout the limestone, the crystals usually consisting of large modified obtuse rhombohedra.

Recently H. E. Merwin employed an improved immersion method for determining refractive indices to identify certain salts of the system Fe2O3–SO3–H2O. In the present paper is described an application of the principle of his method to the determination of plagioclases in cleavage-flakes.

The material which is the subject of the present note was presented to the British Museum (Natural History) in November 1923, by Captain Eric C. Palmer, of the Styrian Jade Company, Bernstein, Burgenland, Austria. Bernstein is situated 92 kilometres south of Vienna, on the present borders of Styria and Upper Austria, and 22 kilometres west of the frontier town of Guns. Previous to the Treaty of Versailles, Bernstein was in Hungary, Comitat Vas (Eisenburg). Its Hungarian name is Borostytánkő.

In 1854, Johann Cžjžek, in a paper entitled ‘Das Rosaliengebirge und der Wechsel in Niederösterreich’, had described the geology of the district, and given some account of the rocks, including a description of the occurrence at Bernstein of serpentine in the midst of an area of hornblende-schists, chlorite-schists, and gneiss.

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.

A Fine set of loose crystals of felspar from Mt. Erebus was collected by Mr. F. Debenham on the British Antarctic (‘Terra Nova’) Expedition in 1910, and was acquired by the British Museum (Natural History) with the collection of rocks obtained on that voyage. These crystals are found in great profusion on the crater slopes, and their occurrence has been briefly described by David and Priestley, who referred to them as anorthoclase. On ascending the inclined floor of the second crater they saw ‘that the covering of snow became thinner until it almost entirely disappeared, being replaced by a surface formed of crystals of anorthoclase felspar from half an inch to four inches in length’.

Short biographical notices of persons interested in scientific mineralogy have been given in this Magazine since 1876. In the last volume these were more systematically collected together and indexed for convenience of reference and permanent record. For a continuation of this series the various details have been collected and filed during the past three years. I have to thank several foreign correspondents for kindly supplying some of the less readily accessible information; in particular, Professor P. N. Chirvinsky, of Novocherkassk in the Don region.

The present list includes 55 haines, for 49 of which dates of birth and death, or ages, are here recorded. Including these with the 254 previously recorded in this Magazine, the total is 308 lives for which ages are known. The average age for these 303 lives of mineralogists is 64 years.

The occurrence of brookite aud anatase within the limits of the Dartmoor granite exposure was first indicated by a sample of stream-sand taken two years ago below the bridge at Dartmeet–a locality which is noteworthy for sands rich ill these and other accessory minerals of the Dartmoor granite.

Anatase, either alone or associated with brookite in small amounts, was found in a majority of the sands taken the following year at selected points along (1) the Plym River, between Cadover Bridge and Hatter Tor, (2) the East Dart and the West Dart, upstream from Dartmeet, (3) the West Webburn, upstream from Ponsworthy, (4) the East Webburn, upstream from Lizwell Meet, and (5) minor streams in the Hamel Down-Bonehill Down area. Rutile proved to be a rare mineral, liable to be overlooked in a residue containing brown cassiterite, from which it cannot readily be distinguished except by microchemical means.

The isomorphous relationships for organic compounds are not so simple as they sometimes are for inorganic. Very often a series of chemically similar orgallic substances does not show any apparent trace of crystallographic similarity. It appears that the introduction of further groups into the molecule may cause the crystal-system to change in a manner which cannot be predicted. Thus, glyoxalinc-4(or 5)- sulphonic acid is tetragonal, whilst 4(or 5)-bromoglyoxaline-5(or 4)- sulphonic acid is monoclinic; the introduction of a methyl group into the 2 position gives rise to an orthorhombic crystal, whilst the introduction of the same group into the 1 position leaves the crystal-system unchanged. In some cases it has been found that evell though the crystal-system is changed, there still remains a very close similarity between corresponding angles in the different substances.

That dolomite (CaCO3 . MgCO3) on being heated behaves as though it were a mixture of the two carbonates by dissociating in two distinct stages, appears to be the widely accepted opinion. Thus it is staled (Mem. Geol. Survey, Special Reports on Min. Resources, London, 1920, vol. 16, ‘Refractory Minerals’, p. 102) ‘On calcination, dolomite undergoes a progressive dissociation which may be considered chemically as covering two distinct stages. The first effect of rising temperature is the expulsion of carbon dioxide from the magnesium carbonate contained in the dolomite and the formation of a mixture of magnesium oxide and calcium carbonate, accompanied by a considerable reduction in volume… . Complete calcination results in the expulsion of the remaining carbon dioxide, a still further reduction in volume, and the production of a dense crystalline aggregate of magnesium and calcium oxides.’

The Meldon aplite is a small intrusion lying to the north-west of the Dartmoor granite about two miles south-west of Okehampton. Its microscopic characters were investigated by Sir Jethro Teall, whilst the geology of the district, with petrological accounts of the aplite and its associated rocks, has been fully dealt with by R. H. Worth, who notes the presence of felspar, quartz, mica, tourmaline, topaz, apafite, fluor-spar, montmorillonite, and axlnite.

Tyuyamunite from Tyuya-Muyun was established as a mineral species by K. A. Nenadkevich in 1912. It is closely allied to carnotite, differing from this in containing calcium in place of potassium, and also, according to W. F. Hillebrand, in the degree of hydration. On this account the mineral has been also known as calciocarnotite.

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.

Calcium formate, (HCOO)2Ca, is soluble in cold water, from which it crystallizes by slow evaporation. Groth gives the following data concerning the crystals of this substance :

The molecular weight is 130.1. No definite cleavage has been observed, nor does twinning occur. There seems to have been some difference of opinion regarding the degree of symmetry. Originally the crystals were described as orthorhombic (holohedral) by J. C. Heusser in 1851, and this was followed by V. von Lung (1858) and A. Schrauf (1861). Later, however, Plathan claimed to have observed unsymmetrical etch-figures which would prove the crystal to be bisphenoidal (like the strontium, barium, and lead formates), but Wagner found only etch-figures in accordance with what would be expected from bipyramidal symmetry.

At the November (1923) meeting of the Society I gave an account of a new find of euclase of peculiar habit and of native platinum from the gold and diamond washings in British Guiana. The occurrence of platinum being a new record for that country, the announcement was naturally received there with some interest—but also with some scepticism. Mr. J. C. Menzies, by whom the platinum was found, has been accused of ‘salting’ the locality, or, alternatively, doubt has been cast on the correctness of my determination. The euclase aggregates, thought by Mr. Menzies to be fossils, could certainly not have been used by him for ‘salting’; and as the platinum (together with some small, silvery scales of mica) came with these, I have no reason to doubt his bona tides. I am also quite satisfied with the correctness of my determination of the material as platinum, as set out in detail on p. 191 of this volume.

Thin sections afford a very inadequate basis for the determimation of thc accessory minerals present in the Dartmoor granite, and they are of little or no value for assessing the relative proportions of these minerals. A recognizable cryst'd of zircon, for example, is rarely seen iu thin sections of this granite, and uutil zircons were isolated in quantity from the crushed rock, stream-sands, &c., one type of zircon was not detected.

Pentaerythritol tetranitrate, C(CH2ONO2)4, is an interesting compound structurally, since there is, in the molecule, a carbon atom with foul' like groups (–CH2ONO2) attached to it. The molecule is therefore of the type CX4. It was hoped that an examination of the crystals by means of X-rays would show how far the molecule retains its form and symmetry in the crystalline state ; also that some light would be thrown on the configuration of the nitro- (–NO2) group, especially the equivalence or otherwise of the two oxygen atoms of the group—a question which it has not yet been found possible to settle by chemical methods.

In this paper is described an apparently hitherto scientifically unnoticed mode of alteration of olivine-dolerite in the intrusive sill at Ible near Matlock.

The igneous rocks of Derbyshire, locally called ‘toadstones’, constitute a well-known basic series of both contemporaneous and intrusive rocks. They comprise lava-flows, sills, a few thin dikes, agglomerates, and tufts. All occur in beds of Lower Carhoniferous age, and are confined to the upper half of the known thickness of the Carboniferous Limestone, with, in the south of the county, the overlying Limestone Shales. They have been described, in recent years, by Sir A. Geikie (‘Ancient Volcanoes of Great Britain’, 1897, vol. 2); II. H. Arnold-Bemrose (Quart. Journ. Geol. Sot., 1894, vol. 50, pp. 603-644; 1907, vol. 63, p. 241, et seq.); and H. C. Sargent (ibid., 1918, vol. 73, pp. 11-25).

The existence of rotatory polarization is comparatively easy to detect in isotropic crystals and in uniaxial crystals in the direction of the optic axis ; but in a biaxial crystal the problem presents far greater difficulties, since in general the rotatory polarization is obscured by the double refraction. The possibility of its existence in a biaxial crystal was denied by É. Mallard (Traité de Cristallographie, 1884, vol. 2, p. 818). However, the persistence of rotatory polarization in a quartz crystal , made biaxial by pressure, brought this conclusion into doubt. Later work, both experimental and theoretical, by H. C. Pocklington (Phil. Mag., 1901, ser. 6, vol. 2, p. 861) established its presence in certain biaxial crystals.