The mineral to be described in the following pages was found hy Mr. J. L. Popham in 1910 at Bwana Mkubwa, Northern Rhodesia, and was sent by him to Mr. A. E. V. Zealley, at that time Curator of the Rhodesia Museum, Bulawayo. Investigations conducted by one of us (A. M. M.) in Bulawayo showed that the mineral occurred as definite, though minute, orthorhombic crystals and that it consisted in the main of copper and phosphoric acid, but that it differed in many respects from the known hydrated copper phosphates such as libethenite, tngilitc, dihydrite, or pseudomalachite.

Whilst some atention has in the past been devoted to the question of the properties of natural glasses, very little has been done to indicate the interrelations of the properties determined. In the case of tile natural volcanic glasses, this is unfortullately only too evident from a study of the standard text-books. A determination of such properties as density, refractivity, ttud chemical composition, and the interrelations of these for particular glasses, is rarely to be found in the literature. The chief contribution to this subject is due to Stark, who has examined the refringence of a large number of volcanic glasses. Unfortunately, there is no record of the density of these rocks, and the interrelation of these remained unknown.

In 1879 the late Dr. C. O. Trechmann described in the pages of this Magazine some orthorhombic crystals from Cornish tin furnaces, which from the analyses of the late Mr. J. H. Collins were stated to be metallic tin. Shortly afterwards Baron Foullon described similar crystals from tin furnaces in Bohemia, arriving at the same results, and thus apparently confirming the observations of the previous authors. At a later date, in 1898, Dr. W. P. Headden analysed crystals of similar appearance, also from Cornish tin furnaces, which he found to be stannous sulphide (SnS), hut he stated that these crystals were monoclinic.

The Upper Triassic sediments are assumed to have contained concentrated solutions, which caused, or contributed to, their dehydration and contraction. The contraction of a colloidal mass results in the production of tension planes, and unless compensated by settlement, rupture finally ensues. Relief of pressure by rupture may bring the sohtions into the labile state, when innumerable closely-spaced centres of crystallization will be set up. The crystals, fed by vertically diffusing solutions, grow vertically, so long as contraction and feeding continue. When, at length, contraction attains its limit, further growth is resisted, and the stresses set up, transmitted to the central parting, produce bending and other pressure effects in the veins.

There exists a bewildering variety of notations for the thirty-two classes of crystal-symmetry and for the 230 groups of symmetry-movements which control the arrangements of atoms building up a crystalline medium. The notation which has found most favour has been that of Schoenflies's ' Krystallsysteme und Krystallstructur ' (1891). This was followed in Hilton's ' Mathematical Crystallography ' (1903) (see the second column of the table given below), and more recently in Niggli's 'Geometrische Kristallographie des Diskontinuums' (1919).

The first broad grouping of meteorites was into irons and stones according as they consisted mainly of nickeliferous iron or of silicates. These were the two main divisions of the first really serviceable classification as applied by Gustav Rose in 1862-4 to the collection of meteorites in the, University Museum of Berlin. In this classification the division of meteoric irons included as separate groups the pallasites and the mesosiderites, in which nickel-iron "rod silicates are present in about equal amounts; and the meteo~fic stones were for the first time split up into chondrites, or stones containing those curious rounded grains (chondrules) peculiar to meteorites, and non-Chondritic stones, which were divided according to mineralogical composition into the groups of eucrites, howardites, &c., still largely recognized.

On Saturday, September 18, 1902, at 10.30 a.m. (Irish time), a stone coming from the sky struck the earth (let. 54° 88' 20" N., long. 6° 12' 10" W. of Greenwich) at a farm, belonging to Mr. Andrew Walker, situated in the district termed Crossbill, a mile to the north of the village of Crumlin, in which there is a station of the same name on the line of railway between Lisburn and Antrim. The place of fall is 3½ miles east of Lough Neagh, the largest lake in the British Isles, and I2 miles almost due west of Belfast, in which city nearly two thousand members of the British Association were then assembled for the annual meeting (September 10-17).

Various authors have discussed the problem how to determine the position of the optic axes of a biaxial crystal when the extinction-angles on n different faces have been observed. It has been proved that a unique solution is possible when n = 1, 2, or 4, according as the crystal is orthorhombic, monoclinic, or triclinic. It is assumed (and will be assumed in this paper) that the n faces have general positious. The result is uot true, if one or more of the faces has a specialized position. For instance, the extinction-angle ou a face of an orthorhombic crystal which is parallel to an axis of symmetry will obviously not suffice to determine the position of the optic axes.

A description is given of the occurrence of gearksutite under novel conditions, viz. in Cretaceous greensand, at Gingin in Western Australia. Some additions are made to the previously known physical and chemical properties of the mineral and a new suggestion is put forward as to its constitution. Its genesis is discussed and theories put forward to account for its origin under the previously known and newly discovered conditions.

The mineral here described was exhibited at the meeting of the Iron and Steel Institute held on May 6, 1920, in illustration of a paper by Mr. J. F. Wilson, who found that slags yielding these crystals had a composition approximating to the orthosilicate ratio. The slag was obtained from a metal-mixer ladle of about ten tons capacity, and consisted of a network of interlacing rhombie prisms, from which the mother-liquor had withdrawn, leaving material on which it has been possible to make fairly accurate measurements. Mr. Wilson very kindly arranged to place at the disposal of the present authors the specimen on which this account is based.

The specimens which form the subject of the present notes were contained ill a collection of minerals formed by the late Mr. Alfred Fox, of Falmouth, and which was acquired by myself in 1909. According to an old label with them, they are described as 'Murio-carbonate of lead taken up the 4th March, 1846, flora the wreck of the fire-shlp Firebrand, which was burnt in Falmouth Harbour about the year 1780. They were found under the lead pump, most of which appeared to be melted and mixed with charcoal.'

The fall of this meteorite, which took place at 1.15 p.m. on December 8, 1917, was witnessed by many people over a large area. The circumstances were investigated immediately by Mr. Henry Coates who has given in a paper already published full and accurate details of the appearance of the meteorite as it described its path, the direction in which it travelled, and the noise caused by its explosion. Fragments were recovered at four different localities lying on a line running from South Corston in Forfarshire north-westwards for about six miles to Easter Essendy in Perthshire, and the following table gives the particulars of the weights and localities of the various pieces.

The apparatus here described was designed in the first instance to provide a means for the rapid preparation and accurate adjustment of the liquid mixtures now commonly used for mineral determinatiom For this purpose refractometers of the Pulfrich type are inconvenient, not only on account of the risk of error due to the complicated centring of the prism or hemisphere and scales, but also because the transfer of a drop of liquid to the refracting surface renders the determination especially liable to errors arising from temperatm'e variation, from contamination of the drop, and from evaporation. Ful%her, in the preparation of liquid mixtures the frequent transference of small quantities to a refractometer is the source of much inconvenience.

Present industrial conditions have tbrccd the engineering trades of the country to adopt methods of mass production, in order to cope with increases in the cost of raw materials and labour. Specialized trades such as the manufacture of scientific instruments are unable to develop quite on these lines, partly because of the limited demands for their goods, and partly because each job is largely an individual one. In the microscope trade much has been done by systematic shop organization, and at the same time an approach is made to mass production by considerably reducing the number of models made, and standardizing the remainder. Naturally the large models for special work have been most affected.

The quantitative distribution of igneous rocks has recently assumed a place of importance in petrogenic discussions. This is due largely to the influence of Daly, who made a survey of the areal distribution of rock types as shown by their outcrops on published maps, and reached the well-known conclusion that intrusions are overwhelmingly granitic in composition, and that extrusions arc largely basaltic. If further research should firmly establish this result, it will unquestionably be a fact of the first order of importance of which any general theory of petrogenesis must take cognizance.