The refractive indices of this mineral for different wave-lengths were determined by the Abbé-Pulfrich total-reflectometer. The dispersion of the glass hemisphere of the instrument was determined by the aid of a highly polished glass prism, the dispersion of the latter being found by the method of minimum deviation. In order to obtain light of definite wave-length Hilger's wave-length spectrometer was used with a Nernst lamp or an electric arc as the source of illumination.

The crystals to which this paper refers are found at Bail Hill, about three miles north of Sanquhar, in Dumfriesshire. At this locality volcanic rocks of Arenlg age outcrop in the midst of the greywacke of the Southern Uplands. The rocks are mainly lavas, and include some coarse-grained tufts which are composed chiefly of augite- and hornblendeandesites. Ill the andesitic fragments, there arc numerous porphyritic crystals of a black augite, which call be easily separated from the rest of the rock. Isolated crystals of augite and hornblende occur also in the matrix of the tufts. No mention of this occurrence is made in Heddle's 'Mineralogy of Scotland', and apparently the only reference to it in previous literature is the short petrographic description in the Geological Survey Memoir.

The specimen to which this paper refers, is one of a number of minerals from Kurdistan, presented to the Hunterian Museum, in Glasgow University, by Mr. D. Ferguson, to whom I am indebted for the following particulars of the occurrence. The exact locality is the Zarshuran River, in Kurdistan, where a large mineral vein, which has been worked for centuries for orpiment, is found. The country-rock is red sandstone, overlying, unconformably, altered slates and schists, which are intruded by a boss of felspathic granite or syenite. Near the surface the vein-stone is chiefly a kind of calc-sinter, but this disappears as the depth increases and calcite becomes the predominant mineral in the gangue, being associated with some quartz and fluorspar.

In 1912 Mr. N. B. Kinnear, Curator of the Bombay Natural History Society's Museum, brought to me at the British Museum, for identification, a specimen of a supposed meteorite which had been sent to the Bombay Natural History Society by the late General W. Osborn.

General Osborn stated that, in November, 1910, on arrival at his usual winter quarters in the hill station of Kotheir in the Punjab, he visited his friend, the Rajah of Bilaspur, who presented him with a fragment, weighing about a quarter of a pound, of a meteorite which had fallen in daylight at the village of Baroti, in the Bilaspur (Simla) district, one day during the month of September, 1910.

During the summer of 1913 the Royal Ontario Museum of Mineralogy secured a nmnber of samples of ruby-silver from the collection of a deceased mining engineer who had been employed in the Cobalt district. Judging from their association it is presumed that they were obtained from the O'Brien mine. The crystals for the most part are less than two millimeters in length and very few exceed a millimeter in diameter. They are light ruby-red in colour and exceedingly brilliant, and casual inspection suggested that they were proustite. As this mineral had not been described from the Cobalt region, it seemed desirable to confirm this supposition by chemical analysis and crystallographic measurement.

The observation of the striking similarity both in chemical and mineral composition of the Baroti, Wittekrantz, and St. Michel meteorites (see the preceding paper) suggested the idea of testing how far such a close relationship applied to other cbondritic meteoric stones.

The practical identity in chemical composition of different meteoric stones has been often pointed out. For example, A. E. Nordenskiöld showed in the case of the stones of Erxleben, Lixna, Blansko, Ohaba, Pillistfer, Dundrum, Hessle, Orvinio, and Stäilldalen that the percentage chemical compositions differed very slightly if the proportions of the metals, silicon, &c., were considered instead of the oxides.

Up to the present time only one of the several ehildrenite occurrences known has been examined both chemically and crystallographieally. This is the well-known occurrence at the George and Charlotte mine near Tavistock, from which nearly all the specimens seen in collections were obtained. The crystals often attain a dimension of 1 cm., so that material for analysis can be easily obtained free from gangue. Crystals from this locality were analysed by Rammelsberg, Church, and Penfield, and it is on the results obtained by the last-named that the comparatively simple formula for this mineral is based.

About the middle of 1911, I was commissioned to report on a copper mine known as the Umkondo, situated in the south-east of Mashonaland, the eastern province of the territory of Southern Rhodesia. The mine is in a very out-of-the-way spot, about 120 miles from Odzi station, the nearest point on the railway, and to reach it took five days of somewhat rough travelling by cart.

A Word of explanatiou as to the nature of valency-volumes : The existence of the law of valency-volumes involves the conclusion that each chemical atom in a crystal has its own special domain throughout which its influence is predominant as compared with that of any other atom. According to this conception the entire space occupied by the crystal can be regarded as portioned out among its constituent atoms, each atom having a cell allotted to it the boundaries of which consist of points at which the influence of some one or more neighbouring atoms is equal to that of the selected atom; thus no interstices are left between the cells.

In nearly every thin section of a rock containing monoelinic pyroxenes it will be found that one or more crystals twinned on the orthopinacoid (100) are included. In such crystals the twin-plane is marked very clearly by the difference of relative retardation and extinction, and also by the interference-bands if the twin-plane is inclined to the plane of section. For the purposes of the complete optical determination, it is essential for the proposed method that one half of the twin should exhibit the emergence of an optic axis suitable for the determination of the optic axial angle by the Becke method.

Lemme. Dans tout triangle, l'arc x (fig. 1), qui mené du sommet partage la base en deux segments α et β, est donné par

It is only recently that the mineral topaz has been found in any considerable quantity in Canada. Previous to the discovery of the topaz of York County, New Brunswick, in 1911, it was distinctly a rarity among Canadian minerals and had never been found crystallized in any Canadian locality. The above-mentioned district, however, has yielded both the massive and crystallized varieties in fair abundance and some fairly perfect crystals have been obtained for measurement.

In 1906 the present writer gave a brief account of the interesting alluvial diamond field which is situated on the borders of the Somabula Forest in Southern Rhodesia. The area is not of very great economic importance, but it has nevertheless yielded to date about 10,500 carats of diamonds (valued at over £45,000). These are extracted from thick beds of gravel which, as described in the paper referred to, generally consist of well-rounded pebbles in a matrix of sandy clay.

Last winter I enjoyed the good fortune of spending some three months at Zweisimmen in the Bernese Oberland of Switzerland, in order to participate in the winter sports. Happily it proved a fine, cold winter of hard frosts and moderately heavy total snowfall. During such a stay in the crisp, dry cold of a snow-mantled world, the manifold and beautiful forms assumed by snow and ice are set before one in a manner impossible in this relatively warm and moist isle with its fleeting glimpses of true wintry weather.

The mineral adamite (Zns(AsO4)2.Zn(OH)2), discovered by C. Friedel in 1866 on specimens from Chafiarcillo, Chile, has since been found at only two other localities, namely Cape Garonne in France and Laurion in Greece. At the original locality it would appear to be of rare occurrence, since in the literature mention is made of only two specimens.

It was therefore of interest to find in the British Museum collection a good specimen of adamite from Chafiarcillo. This was found amongst the hornsilvers, and the associated adamite had been thought to be fluorite, which indeed, at first glance, with its violet colour and good cleavage, it closely resembles in appearance. The crystals are remarkable by reason of their very strong pleochroism, and as this feature of adamite has previously received no mention it has been thought worthy of placing on record.

Measurements for torbernite have been given by numerous observers; the results are, however, of rather early date, and althoug the values for the ratio a:c are generally in fair agreement with the results here stated, the degree of accuracy of these measurements is not always indicated. Moreover, sevelml minor difficulties arise, add it has been suggested that some of the early descriptions refer to the allied species, zeunerite ; both species are optically uniaxial and possess almost the same axial ratios; they can, however, be distinguished by means of their refractive indices.

In 1912 the writer proposed the name voelckerite (in honour of Dr. John Augustus Voelcker, the well-known English agricultural chemist, who made important contributions to our knowledge of the~ chemistry of apatlte) for the basic calcium phosphate, 3Ca2(PO4)2.CaO , related to apatite. The fact that apatite is often deficient in fluorine and chlorine was proved by Voelcker and by Hoskyns-Abrahall, both of whom gave as the general formula of apatite 3Cas(PO4)2.Ca(F2,C]2,O ) or its equivalent Ca10(PO4)6(F2,Cl2,O ). Carnot also noted the deficiency of chlorine and fluorine in apatite from Tyrol, but he offered no explanation.

In the stereographic projection (fig. 1) ABA'B" is the primitive circle, having the same radius a as the corresponding sphere ; ATA'T" is the circle representing a great circle on the sphere inclined at an angle θ to the plane of the projection ; O and C are the centres of the primitive circle and the circle ATA'T' respectively. CO are joined and projected both ways to meet the circles as shown.

The colour of the well-known iron sulphide, pyrrhotite or pyrrhotine, is given in most treatises on mineralogy as 'bronze-yellow'. Dana calls it ' between bronze-yellow and copper-red ', and also notes that it is 'subject to speedy tarnish'. The accuracy of the last statement will not be doubted by any one who has had much acquaintance with mining operations in districts where pyrrhotite is a common lode mineral, but it does not appear to have been put on record in any scientific publication that the characteristic colour, not very accurately designated 'bronze-yellow', does not seem to be the original one of the unaltered mineral.