The minerals described in this paper were obtained by Mr. Arthur L. Collins last summer, and their mode of occurrence is explained in the accompanying note by him. My description will deal in detail with their crystallographic characters.

The following brief notes on the occurrence of these gems in one of the least known portions of the Siamese ruby fields may prove of interest, as the particular district to which they refer has very rarely, if ever, been visited before by any European, whilst nothing at all has ever been written on the subject as far as I am aware. The notes are chiefly extracts from my journal for the months of May and June 1892, which I venture to present with as little modification as possible, in the belief that a description written on the spot is likely to give a more correct and vivid, even although it be a less highly finished picture of the locality than can be attained by any subsequent elaboration.

The name xanthoconite was given by Breithaupt (1) to a mineral which he found in 1840 associated with proustite upon an old ore-specimen in the collection of the Berg-Akademie at Freiberg. He describes it as occurring in reniform masses with a surface consisting of microscopic crystals, but with a crystalline granular interior.

In the year 1890 Mr. S. L. Penfield described a new copper mineral, to which he gave the name of Spangolite in honour of Mr. Norman Spang, by whom it was first brought to his notice. Of this beautiful mineral only a single specimen was found, and the exact locality has never been ascertained; it belonged to a man living near Tombstone in Arizona, who had gathered together a collection of minerals within a radius of about 200 miles, and it is described by Mr. Penfield as " a rounded mass of impure euprite which was mostly covered with hexagonal crystals of Spangolite associated with a few crystals of azurite and some slender prismatic crystals of a copper mineral containing chlorine, probably atacamite."

It has long been known that several of the felspar-porphyry dykes (Elvans) of the West of Cornwall contain crystals of pinite--apparently pseudomorphous after iolite--as an accessory mineral, and similar crystals occur.in the granite in several places.

In the parish of Breage there are several of these dykes running towards the sea in a south-easterly direction, which are somewhat largely used as road-material. That which reaches the sea at Praa is in places thickly charged with the pinite crystals, and the same in a somewhat less degree may be said of the dyke which passes from the village of Trew through Great Wheal Fortune.

All petrologists who have worked much with the microscope must have felt the want of a system of micro-chemical analysis ar once simple and reliable. Having devoted some time to the study of micro-chemical reactions, I think it may save the time and labour of students who propose to take up the subject if I give them the result of the experience I have gained up to date.

In the early part of this year Mr. W Goodlet, laboratory assistant to Prof. Black, of the Dunedin University, submitted to me for examination a mineral specimen which he had brought from a journey of inspection of the gold fields of the West Coast, Middle Island. It had, so he told me, been broken from a boulder, about 40 lbs. in weight, which was found in the gold drift of a claim at Back Creek near Rimu, Westland, and placed aside by the claim owners as something uncommon, because of its weight and colour.

This rare mineral, the Dufrenoysite of yon Waltershausen and others, crystallising in the cubical system, has been made the subject of careful investigation by several observers, with the result that, up to the present moment, it is doubtful whether the character of its forms is holohedral or hemihedral with inclined faces. Hessenberg found that the mineral crystallised holohedrally, but Groth, confirming Kenngott's view, states that the best crystal in the Strassburg University collection shows a distinctly hemihedral development.

The specimen which is the subject of the present note consists of a group of large rude, reddish crystals of tetrahedral aspect, which in colour, lustre, and general appearance, resemble garnet; they were formerly supposed to be garnet pseudomorphous after some tetrahedral mineral, and the original mineral was presumed to have been fablerz, on account of the size of the crystals, which measure as much as 3 to 5 centimetres across.

The great variation which occurs in the specific gravity of zircons seems to render it possible that the presence of fluid and gas inclusions might, to some extent, account for this. A small, partly red, partly eolourless crystal was selected from a number of others all derived from the Riou Pezzoliou, Expailly, near Le Puy, which, when examined under the microscope, was found to contain numerous inclusions, some with, others without bubbles.

In a former communication to this Society, I have demonstrated that quartz must now be added to the long list of minerals in which a lamellar structure can be set up by mechanical stresses. In that paper, a crystal of smoky quartz was described in which well marked lamellæ could be detected; the relations of these lamellæ to the parts of the crystal which had suffered mechanical deformation and crushing are such as to leave no possibility of doubt that the lamellar structure is not an original but a secondary one; while it is equally clear that the structure has been developed by the action of mechanical forces upon the crystal.

In my paper "On the Micro-chemical Analysis of Rock Making Minerals, '' I noticed the abnormal behaviour of globules of lithium phosphate Li3PO4 + H2O in polarised light; the dark cross which ought to remain fixed when the globule is revolved between crossed nicols, opening up, in some cases, into two hyperbolic branches like those of a biaxial crystal in converging polarised light. I find that similar ano. malous results may be obtained from the globules yielded by other salts; as for example those of the double sulphates of beryllium and potassium (BeSO4K2SO4 + 2H2O), and of lithium and sodium (LiNaSO4).

Probably everyone who has considered the arrangement of the constituents of an aggregate composed of radially grouped fibres has realised that the individual fibres are conical or pyramidal in form, their apices meeting in the centre of the aggregate. In a coarse example of this mode of erystallisation, such as the calcite concretions in the magnesian limestone of Durham, this conical form of the constituent crystals is very easily seen; the cones cleave across, where composed of a cleavable mineral, showing that the particles composing them have the same orientation within the limits of the cone, and that each cone, in fact, is a crystal, bounded ultimately by contact with its neighbours.

Through the kindness of Professor D. Hahn of the South African College, Cape Town, I received, some time since, a series of specimens of fulgurites which were collected in the vicinity of Griquastad.

In this locality Professor Hahn informs me that there is a particular sand hill which is noted among the farmers living in the neighbourhood for the frequency with which it is struck by lightning during thunderstorms.

In the early part of 1890 I noticed in some of the workings of the Torreon Mines, and chiefly on a decomposed ehalcopyrite or in close connection therewith, a greenish-blue to sky-blue lamellar coating about inch in thickness, with sometimes isolated plumose groups of scaly crystals having a pearly lustre. Both appearance and mode of occurrence of the mineral led me to think it a basic sulphate of Copper, probably cyanotriehite, or possibly a new species. Soon afterwards however, it was noticed that when the ore, as sorted for smelting, contained any quantity of the pale blue incrustation the cyanide assay failed to give accurate results in the estimation of copper, and on testing such ore qualitatively for zinc quite an appreciable quantity was found. Want of leisure prevented a more extended examination, but a good many specimens were selected and carefully preserved.

My friend, Mr. A. T. Karslake, sent me recently a pareel of crystals from Ceylon, amongst which was a brown tourmaline showing the very rare face z =, (first recorded by Haüy), on whose existence so much doubt has been thrown. The crystal is about ½ inch across, and about ¼ inch in the direction of the axis, and shows well the hemimorphic development. At the analogous pole are r{100} and z, both largely developed, also o {111}, e {110}, s, .

In the appendix to the paper on the new mineral, baddeleyite, in the last number of the Magazine, Mr. Fletcher proves the identity of that mineral with the brazilite of Husssk, and explains the deviation in specific gravity and the original incorrect determination of the chemical composition of the Brazilian mineral by the supposition that the crystallographic measurements were made on the true mineral, while the specific gravity determination and chemical analysis were made on another, a tantalo-niobate of yttrium associated with it.

In a quartz crystal, slightly over 2¾ inches in length, which has been in my possession for many years, and was stated to come from Derbyshire (possibly Castleton), there is a curious white cirrous inclusion which describes a graceful feather-like curve, and consists of a series of nearly parallel lines of colourless and transparent to opaque snow-white grains, which, under the microscope, are seen to be at times well defined rhombohedra; but for the most part they present the appearance of thorn. bohedra which have been more or less eroded, and they are so ranged in lines that one rhombohedron lies with one pair of faces slightly above or below the corresponding pair of faces of the succeeding rhombohedron, thus giving the line a distinctly serrated edge.

On examining a specimen of manganite from Harzgerode, consisting of iron-black crystals of apparently long-prismatic habit, it was found that they were, in most instances, composed of many individual crystals, the latter ranging from about two to four millimetres in length. As they seem to differ in habit, so far as I know, from the crystals of manganite hitherto described and figured, a short account of them, pending more careful investigation and measurement, may be of interest.