In a paper read before the Mineralogical Society on April 10, 1894, describing the details of the analysis of a meteoric stone which had been found at Makariwa in New Zealand, attention was called by the present author to the fact that the operation of extracting the nickel-iron by mercuric solution from the material separated from the powdered stone by the magnet was scarcely a terminable one; for even the twelfth extraction by means of a solution of mercuric ammonium chloride evidently contained an appreciable amount of colouring matter, while the colour of the extract indicated an increase in the proportion of the nickel. ‘It was clear that one or other constituent of the attracted material was being only slowly dissolved, and that it was practically useless to push the operation farther.

One of the most important and striking properties of isomorphous substances is their capacity for forming microscopically homogeneous mixed crystals, the physical properties of which are, as Retgers has especially shown, intermediate between the properties of the constituents. With the great majority of isomorphous substances the mixed crystals can be obtained in all proportions, but with others the miscibility is limited.

The first case of restricted miscibility was discovered by Retgers in potassium phosphate (mol. vo1.=58.25) and ammonium phosphate (64.17) crystallizing in the tetragonal system ; he did not determine the exact proportions which each salt can take up of the other, but estimated them to be about 20 per cent. each way.

When investigating the morphology of crystals, such as those of schwartzembergite, which are so rounded or striated as to afford no definite reflections of the object-slit of the goniometer, the author found most serviceable a camera lucida which could be attached to the eye-piece of the telescope of the goniometer, and thus used for the direct drawing upon paper of the ‘light-figures’ given by the crystals, the ordinary signal being replaced by a pin-hole. The cap of the eye-piece in use is unscrewed and the camera lucida is fixed to the tube by means of four clamping screws.

Mr. T. V. Barker has lately shown that the parallel growth of isostructural substances upon one another is conditioned by similarity of molecular volume. This very important conclusion invites further investigation from this new point of view, and Professor H. A. Miers suggested to me, while working in his laboratory last summer, that I should make experiments on the parallel growth of sodium nitrate on the pseudo-rhombohedral mineral barytocalcite.

The first experiments, which were made on crystals of barytocalcite in the Oxford collection, were unsuccessful, the crystals employed being small and somewhat impure. Later, I received, from the Museum of Practical Geology in London, some very good and perfectly pure crystals of barytocalcite from Blagilt, near Alston, in Cumberland.

A Sample of supposed ‘vegetable asbestos’ obtained in the west of the province of Süchwan, China, was forwarded in 1907 by Mr. J. H. Bristow, the British Consul at Chungking. It was later reported by Mr. H. Phillips, the British Consul at Chungking, that the so-called ‘vegetable’ asbestos previously mentioned ‘is found in crevices between rocks in the districts of Lei Po T'ing and P'ing Shang Hsien, in the prefecture of Sui-fu.’ The author has recently been informed that it occurs along the length of the Yangtse-kiang generally, from Sui-fu to the Huili-chou neighbourhood—i.e., along the Süchwan-Yunnan border on the outskirts of the Man Tzu country.

In a single homogeneous crystal the physical character of parallel lines are everywhere the same, and it may be justifiably assumed that the orientation of the crystal-structure is constant throughout. Compound crystals, however, occur in which the orientation of the crystal-structure is different in different parts although they consist of the same substance.

This difference of orientation may either be original or result from the action of mechanical forces on the crystal-structure. I shall in the first place assume that the former is the case.

Early in 1909 a small quantity of fine sand was brought to the writer from a big Chinese-owned mine at Rotan Dahan, in the district of Kinta, the leading tin-producing district of Perak and, indeed, of any of the Federated States. The sand was a concentrate, and had been obtained in the final washing of the rough tin-ore concentrates, whereby the heavier impurities, generally referred to locally as ‘amang’, are separated from the cassiterite. In this case, however, the Chinese miner found that there was a reddish mineral present which he could not separate from the cassiterite. This proved to be native copper, and the mode of occurrence is of sufficient interest to watTant a brief description of this and other samples of ore from the same mine and an adjoining mine working on the same deposit.

In ‘Nature’ of May 31, 1906, the senior author gave a preliminary account of a new Vesuvian mineral, which he had found amongst the products of the eruption of April 1906, and for which he proposed tile name chlormanganokalite. It was described as a hydrous chloride of manganese and potassium, occurring as deliquescent crystals apparently rhombohedral in form. A few days later, on June 5, 1906, Professor A. Laeroix described, before the French Academy of Sciences, a Vesuvian mineral which he thought must be identical with chlormanganokalite : he stated it to be an anhydrous chloride of manganese, potassium, and sodium, and he determined the deliquescent crystals to be monoclinic and psehdo-rhombohedral. In a later paper, Professor Lacroix rightly insists upon this identity.

During recent years a considerable industry has grown up at Paris in the synthetical manufacture of corundum for jewellery purposes by means of the process devised by Professor A. Verneuil. In place of the fragments of natural ruby used in previous attempts, ammoniumalum is the material employed. After careful preparation to free it from potash and other impurities, it is ground to a powder and placed in a sieve at the top of the oxygen tube of an inverted blowpipe. The sieve is tapped by a hammer at regular intervals, and uniformity is in this simple way produced in the amount of powder that falls; the necessary adjustment is effected by varying the height through which the hammer falls. To minimize the cost of production, a few alterations have been made in the original apparatus.

The continuation of the mapping of the aureole of metamorphism round the Bodmin Moor granite has led to the discovery of fresh occurrences of idocrase, developed in the altered, impure limestones. The failure to find this mineral hitherto is now clearly due to the former absence of artificial openings in suitable localities, for the mineral has so far not been found in recognizable form in natural exposures, owing to the rapidity with which these calcareous rocks decompose.

Altered calcareous rocks containing idocrase in considerable abundance have recently been laid open in a small quarry on the west side of the stream at Tvenuth Mill, which is about 400 yards south of the granite margin in the well-known Caradon area.

The question of the system to which perovskite should be referred, and the explanation of the discrepancy between its form and optical-properties, have been the subject of much discussion among crystallograpbers ever since the discovery by Des Cloizeaux, in 1858, of the double refraction of crystals of calciam titanate from Zermatt, having the same composition as the crystals of cubic form from the Ural Mountains, to which the name perovskite had been given by G. Rose in 1889.

Until quite recently, in spite of its characteristic features, andalusite had not been met with in the younger detrital rocks of Britain ; a few years ago, however, I remarked on its relative abundance in the older Pliocene sands of St. Erth and St. Agnes in the west of Cornwall. Its presence in these deposits, in which it is associated with pink garnet and cyanite, is easily explained by the close proximity of the areas of deposition to the metamorphic aureoles of the west of England granitemasses, in which andalusite of identical character is exceedingly common. It also occurs in fair quantity in the Pliocene sands of Lenham in Kent accompanied by cyanite, and together with cyanite and garnet in the Red and Norwich Crags and the Chillesford Beds in the east of England.

Having had occasion recently to draw the twins of calcite, I noticed the advantage of the twin-axes being all placed in the plane of the paper. The representation of the rhombohedron which results from this condition is so unsatisfactory that, obvious as the idea must have been to all crystal draughtsmen, few, if any, seem to have tested the utility of the projection. I desire to point out a few of its advantages.

It is usual to divide axes of rotatory symmetry into those of the first and those of the second sort. In the former a crystal is brought into coincidence by a rotation through a certain angle round the axis and in the latter by such a rotation followed by a reflection about (or, as I prefer to say, a reversal relatively to) the plane at right angles to the axis. In 1906 Mr. H. Hilton proposed to define an axis of rotatory symmetry of the second sort as one in which the rotation was followed by an inversion about (reversal relatively to) a point, and he showed that his proposal would, if adopted, simplify the definition of the crystallographic classes.

The mining village of New Brancepeth, in the parish of Brandon and Byshottles, is situated in the Durham coalfield at a distance of four miles to the west of the city of Durham. One of the faults which intersect the sandstones, shales, and coal-seams (the Harvey, Busty, and Brockwell seams) of the Coal Measures at this place has, at its eastern end, an east to west direction with a downthrow of 120 feet and a hade of 20° to the south. Along this portion of its course the fault is of the nature of a fissure-vein, with a width varying from a few inches to 16 feet. The material filling the vein consists mainly of barytes. In places, especially where the walls of the vein are of sandstone, the pure white, massive barytes extends throughout from one sharply-defined cheek to the other.

In October 1907 two mineral-specimens were sent for investigation to the Mineral Department of the British Museum by Mr R. T. Hancock, of Cardiff, who had brought them back from South Africa. On examination they proved to contain patches of olivine and troilite and particles of nickeliferous iron, and appeared therefore to be of meteoric origin. According to Mr. Hancock two ‘boulders’ of similar material had been found, 100 yards apart and a foot below the surface, in gravel near Simondium Station on the Paarl to French Hock line, Cape Colony. These ‘boulders’, which were as much as a foot in diameter, were broken up into small fragments by the finders, who supposed the bright particles of metallic iron exposed on the fractured surfaces to be silver.

When mounted for measurement on the goniometer, the faces of the perovskite crystals described in the preceding paper yield, owing to the complex lamellated structure, a confused mass of images of the signal which cannot be analysed by the ordinary methods (such as using a lens in front of the eyepiece or shading portions of the face with a screen held in the hand), on account of the number and extremely small size of the reflecting surfaces. The apparatus described below was designed to give the means of identifying with certainty the image reflected from any given portion of such a face, and has been found to answer this purpose satisfactorily.

The mineral strüverite occurs as a rare accessory constituent of the pegmatite which is found in large detrital masses in the neighbourhood of Craveggia (Val Vigezzo, northern Piedmont), namely on the Piano dei Lavonchi and in other localities on the eastern slope of the mountain across which runs the road from Vasca to the Alp Marco. In this pegmatite Professor G. Spezia in 1882 noted the occurrence of beryl, and two years later Professor G. Strüver that of columbite, a mineral which had not hitherto been found in the Alps. Still later, notices of other rare minerals from the pegmatiie were published by Professor A. Piccini and Professor A. Cossa.

The change suggested relates mainly to the representation of the faces below the plane of projection. I propose that every face below that plane shall be represented by the same point as a parallel face above it.

If the two parallel faces are equivalent they will both be indicated by the same circular dot (accompanied, if desired, by the indices of either face). If they are not equivalent and only one be present, it will be represented by a plus sign (+) if it be above the plane of projection, and by a minus sign with a dot in the centre (-) if below it. If both are present but not equivalent, the double sign (±) will be used.

Vernadsky has pointed out that in certain cases a twin-crystal appears to be a more stable form than the simple polyhedron, as proved by Scacchi's observation that twins sometimes exceed in magnitude and regularity simple crystals growing in the same solution. He suggests that an explanation can be found in the fact that the surfaceenergy may be tess for a twin than for a simple crystal of the same volume. The suggestion is a valuable one, but Vernadsky applies no quantitative test to his theory.