Although the mineral spinel belongs to an isomorphous group, and in the simple formula MgO.Al2O3 a both Mg and A1 are susceptible to isomorphous replacement, yet in the transparent varieties oI gem quality there is, as a rule, very little deviation from the type composition, and the physical properties are moderately constant. In fact, one may say that the only considerable replacement hitherto recorded in spinels used as gemstones is by ferrous iron in the variety known as ceylonite or pleonaste, which is black and opaque even when 7 or 8 % of FeO is present, the end-member of this series being hercynite, FeO.Al2O3, with 41% ferrous oxide.

The purpose of this paper is to draw attention to certain transparent blue spinels from the gem gravels of Ceylon, the physical properties of which differ quite strikingly from those of the normal spinels, from which they are indistinguishable in appearance, magnesium being replaced in this instance not by ferrous iron but by zinc.

The behaviour of the zeolites on dehydration, and their capacity for absorbing other gases and vapours in place of the water removed, have formed the subject of numerous investigations, qualitative and quantitative, of various degrees of accuracy. In only a few cases have attempts been made to fit an equation to the experimental data. Of these equations, those proposed by O. Weigel, G. F. Hüttig, and O. Schmidt are quite inadequate, as is readily seen by a trial with the more extensive data now available. On the other hand, E. Rabinowitsch derived an equation which proved capable Of reproducing the experimental data and is very similar to the equation now proposed, but derived in a quite different way.

In 1911 Dr. W. B. Wright briefly described the felspathized quartzite blocks in the hornblendite of Port Easdale, Kiloran Bay, Colonsay, Hebrides. He showed that the exposures provide a conclusive demonstration that the action of hornblendite magma on quartzite xenoliths was to convert them to alkali-felspar and quartz, so that in the final stage ‘one can recognize in numerous angular and rounded patches of felspathic material, without visible xenolithic core, the ghosts of former masses of quartzite’.

Our knowledge of the rare rock type eulysite (A. J. Erdmann, 1846) comes almost wholly from Swedish occurrences amt hitherto no examples have been recognized from Britain. It is therefore of interest to place on record a new Occurrence of eulysites and related rocks from among Lewisian rocks of the Glenelg area, Scotland.

The rocks shortly to be described come from the vicinity of Totaig on Loch Duich between Totaig and Letterfearn, little more than half a mile from the first described occurrence of eclogite in Britain. These eulysitic rocks crop out on the hillside immediately south-west of Druideig Lodge. About 200 yards south-west of the lodge coarse garnet-paragneisses form outcrops associated with grunerite- and cummingtonite-garnet-gneisses, and a similar interbanded association is found at higher levels.

In a paper entitled 'Hornfelses from Kenidjack, Cornwall' 1 the nature and origin of the rock types characterized by anthophyllite and cummingtonite occurring in the aureole of the Land's End granite were discussed.

Since these rocks were 'investigated in 1928 the writer has extended his study of them both in the field and in the laboratory, with the result that further light on the origin of these rock types has been obtained. It is the purpose of these notes to examine in more detail the evidence which is considered to add to their understanding. In the Kenidiack paper the petrography of the rocks was described at some length and in the present paper petrographic data will be given only in so far as they supplement the previous account, which may be consulted for a detailed statement.

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.

In the following list of 36 lives, with a range in ages frdm 56 to 89, the average age is 71.0 years. The average of 460 lives noticed in this Magazine since 1877 is 65.9 years ; and in the six numbers of this series since 1919 there has been a gradual and steady increase from 63.6 to 71.0.

Particulars respecting Czech, Italian, Japanese, and Russian subjects have been kindly supplied by Professors F. Slavlk, G. R. Levi, R. Ōhashi, and Mr. S. I. Tomkeieff respectively, and to these colleagues I express my thanks.

A. De Schulten published a crystallographic and optical investigation of the bismuth oxyhalides in 1900. He succeeded in preparing minute square plates capped with pyramidal planes, but evidently the difficulties of manipulation prevented the measurement of interfacial angles. He did, however, record a negative uniaxial figure observed in a direction perpendicular to the plane of the square plates of all three salts BiOCl, BiOBr, and BiOI. The present work was undertaken to extend A. de Schulten's observations, to measure the axial ratios, and to determine the crystal-structure.

Towards the close of the Carboniferous period in Britain, igneous activity, which had been prominent from time to time throughout the system, broke out afresh in a new form affecting a large area of the country between the Moray Firth and the River Tees. This activity was entirely, hypabyssal in character, the intrusions consisting of basic dikes and sills belonging without exception to the tholeiite magma-type of Dr. W. Q. Kennedy and W. Wahl. Those in the north of England include the famous Whin Sill and have been studied in great detail, particularly by Professor A. Holmes and by Dr. J. A. Smythe. The same cannot be said of their Scottish representatives. They possess, indeed, an abundant literature and several excellent publications deal with the intrusions of limited areas, but there is no connected account of them as a whole. Many districts, in fact, appear to have escaped investigation almost completely.

A small specimen (McGregor Museum, no. 4465) labelled ' Bismuth ore' was sent to me in 1932 by Miss M. Wilman, Curator of the McGregor Museum, Kimberley, for identification. It had been presented to the Museum by Mr. M. Caplan, a store-keeper of Steinkopf. The majority of bismuth-bearing minerals from Namaqualand come from a number of spots in the neighbourhood of the water-hole known as Jackals Water, which is situated 18 miles NNE. of the village of Steinkopf. Reference has already been made to this locality in a previous paper. The exact locality of this specimen is a pegmatite outcrop in granite-gneiss about a mile and a half south of the Noumaas trigonometrical beacon which is situated some 13 miles north-west of Jackals Water to the west of the Viool's Drift road. The specimen was picked up on the surface, being obviously of eluvial origin.

It is now more than sixty years since Tschermak first published his classical paper on the relationship between the pyroxenes and amphiboles, but, in spite of our greatly increased knowledge of these important rock-forming minerals, many of the problems concerning their constitution and genesis remain unsolved. In particular, the nature of the conditions which determine whether a pyroxene or an amphibole will separate from a crystallizing magma are imperfectly understood, although the point is one of very considerable petrological significance. Much fuller information is necessary, particularly with regard to the relationship between the composition of the ferromagnesian minerals and the rocks in which they occur. The present paper merely represents a preliminary attempt to correlate the available chemical evidence and to determine what other possible factors might influence the character of the ferromagnesian crystallization.

Fluorite is by no means a common mineral in Scotland, and Scottish specimens, with the exception of those from Craigmuschat quarry, Gourock, Renfrewshire, arc very rarely to be seen in collections. In the following notes an account is given of some of the more remarkable occurrences visited by the writer in the summer of 1934. Others recorded by M. F. Heddle were also visited and are mentioned, although they no longer yield specimens.

Aconspicuous feature of all published diagrams, showing the results of the determination of a number of plagioclase felspars by the Fedorov method, is the pronounced scattering of the poles. They lie not only on the curves of the determinative stereogram, but on either side of them, and, in fact, occupy a belt, varying in different instances, and in different positions along the length of the same curve, from 3 to 8 mm. in width. These belts usually contain, but are not symmetrically disposed to, the curves.

The occurrence in basic lavas of quartz xenocrysts and xenoliths and the various types of reaction phenomena which they exhibit have been well described by Lacroix (1893, pp. 17-48). The modified quartz is often surrounded by a zone of pyroxene granules or prisms and on the inner side of this zone the quartz may be replaced by glass, both peripherally and through an anastomosing system of vein-like channels. The glass may be clear or charged with gas inclusions; some examples contain minute quartz-pseudomorphs after tridymite, while in others microliths of alkali-felspar occur. In the basanitoid of Hirzstein, Hesse, nepheline occurs around quartz in place of the usual vitreous shell (Fromm, 1891, pp. 58, 65, and 70). Despite these observations, it seems to have been tacitly supposed that the glass is a more or less hydrous variety of vitreous silica.

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.

Very little reformation can now be gathered about a remarkable shower of meteoric stones that fell many years ago in a remote district in south-west Queensland. Only a few scraps of information have appeared in print, and these are largely contradictory. However, some very tangible evidence arrived unexpectedly at the British Museum in 1935 in the form of a remarkable collection of 102 complete meteoric stones with a total weight of 107¾lb. This material had been in the possession of Mr. Benjamin Dunstan, formerly Government Geologist of Queensland, who had been collecting information of the fall with a view to writing up an account for publication. This unfortunately he never did, and much of the information is now lost. The specimens were offered to the British Museum by his widow, but they came along quite casually as an appendix to a collection of fossils.