Some two years since the authors received from East Cornwall examples of a erystallised mineral presenting features dissimilar to those of any species previously known to them, but presumably referable to Dufrenite. The specimens obtained were from the central part of a narrow neck of "dead ground" (compact ferruginous quartz rock) connecting the much broader E. and W. continuations of a lode, yielding respectively copper and tin ores.

The freshest crystals have a vitreous lustre, and vary in colour from almost black to a light apple-green, their sections, however, being of a yellow brown to yellow. Where, as commonly, some superficial chemical change has taken place—seemingly into limonite—the colour is from red to brown or yellowish brown.

This mineral occurs plentifully, though finely disseminated, in the veins of auriferous quartz in the Lydenburg district of the Transvaal. These veins are often capped by a "gossan" of brown hvematite, crystalline, amorphous, or at times pseudomorphous after iron pyrites; a good deal of similar brown hæmatite occurs also throughout the veins themselves. The Bismutite is disseminated irregularly through the veins, and also occurs in small pockets in the ferruginous gossan; it is from the latter source that the mineral was obtained for the subjoined description and analysis.

It is amorphous, pulverulent; colour greenish yellow to lemon-yellow, more rarely brownish yellow; opaque (feebly translucent, with waxy lustre under the microscope); its hardness appears to be about 8, but cannot well be determined on account of its pulverulent character. Specific gravity 6.86.

The mineral Leucite has for so long a period been considered as one of the most remarkable examples of limited distribution both in space and time, that the discovery in Australia of a rock largely composed of this mineral, by Mr. T. W. Edgeworth David, F.G.S., of the Geological Survey of New South Wales, is one that appears deserving of being at once placed upon record.

Leucite-crystals, under the head of "white garnet," or "white schorls," appear to have been known from a very early period ; and, indeed, the fine examples from Somma could scarcely fail to attract the attention of the older mineralogists. Subsequently it was found that the mineral occurs in other parts of Italy, and especially the neighbourhood of Rome, as well as at the Laacher See and the Kaiserstuhl.

The rock-like mineral, known as Agalmatolite, derives its name from the Greek word aγuλμa, an image. It has also received the trivial name of Pagodite from Pagoda ; it having been long used by the Chinese as the substance from which they carve their images and pagodas.

The earlier mineralogists confined the above names to hydrated silicates of alumina and potash, doubtless a product of the decomposition, or alteration, of orthoclase felspar ; an intermediate stage in its conversion into the kaolin which is so abundant in the Celestial Empire.

Jameson, Phillips, Allan, Nicol, and all the fathers of mineralogy, admitted no other substance under the name. Nicol, who was a thoroughly well-read mineralogist, writes : “Many substances are named Agalmatolite which are really distinct;” and he clearly defines the species, which he makes the same as that called Agalmatolite in the present communication.

The specimens to which this note refers were obtained from a precipitous cliff at the north-west end of Loch Maree, Ross-shire, called Creag Mhôr Thollie. The mineral occurs on the 1,000 ft. contour to tile east or loch side of the Creag, and is in quantity.

The specimen which is the subject of the present note is a magnificent piece of Proustite from Chañarcilio, Chili, which has been recently acquired for the British Museum. It is a mass of lustrous crystals, measuring about 3 inches by 2½ inches, and nearly 3 inches in height.

The specimen has a peculiar cockscomb appearance, due partly to the habit of the crystals and partly to the way in which they are grouped ; the lower part consists of Proustite, interpenetrated by a little minutely crystalline white Calcite, which on one side of the specimen extends partly over the crystals in the form of darker coloured acute rhombohedra.

In the last Number of the Society's Journal I described some crystals of apatite (francolite variety) from St. Just district of Western Cornwall; I have now to bring to the notice of the members some very fine beautiful crystals of this same mineral which I have received from Mr. Henson.

In point of beauty and lustre they far surpass any of the apatites that have yet been found in England.

The crystals are in the form of hexagonal prisms, doubly terminated with basal planes and narrow pyramid planes; colour pale bluish green, translucent with strong vitreous lustre.

They vary in size from a pin's head to half-an-inch across.

In my previous papers on this subject I have detailed various localities in which the mineral Diatomite has been found. Since the dates on which my papers were read various other localities have been discovered for the mineral, and I now beg to lay the details before the Society. The new samples are four in number, and are from—

1. 1.—Golspie, Sutherlandshire.

2. 2.—Loeh Osabhat, Tolsta, Lewes.

3. 3.—Auchnerran, Aberdeenshire.

4. 4.—Presswhin, Aberdeenshire.

A fifth sample of a nodular mass from the Diatomite of Loch Kinnord, Aberdeenshire, has been analysed, and the results are included in this paper.

The discovery by my friend, Mr. Dick, of zircon, rutile, tourmaline, cyanite, &c., in the Hampstead and other sands, and also the necessities of a work in which I am engaged, have induced me within the last few weeks to turn my attention in a somewhat systematic manner to the sedimentary rocks, and especially to the clays. At present I have examined only eight or nine samples of clays, but I have already come across a fact which I trust will be thought of sufficient interest to justify this communication. In examining the clays the method I adopt differs from that followed by Thurach in his classic investigations, " Ueber das vorkommen mikroskopischer Zirkone und Titan-Mineralien in den Gesteinen, only in one respect. I examine the washings which are removed by his process.

The great similarity which exists in the crystallographie and optical constants, cleavage, and absence of twinning in the isomorphous rhombic sulphates is especially marked in Barytes and Celestine, but though the combination of forms is sometimes the same, yet up to the present time a marked individuality has bees perceived in Celestine crystals which has made it easy to recognise the one mineral from the other.

The crystals of Celestine from near Bristol in the red marl, those associated with sulphur from Sicily, or the large flat more or less bluish tabular crystals from Strontian Island, Lake Erie, are varieties which are seldom if ever mistaken for Barytes.

The tin from the Straits Settlements has hitherto been solely derived from the alluvial deposits, and is consequently in the form of alluvial or "stream" tin—each grain of Cassiterite being separate, and in many cases so considerably water-worn as to afford evidence of its having been washed down for a considerable distance; the angles of the grains having given place to smooth surfaces during their deposition.

The largest grains occur on the tops of some of the hills, with a diminution in size noticeable with distance from the hills.

In the following pages we propose to give a short description of the recent discovery of diatomite in Skye. The portion of ground that has been explored for the deposit lies at the north end of the Island, and forms the estate of Colonel Fraser, of Kilmuir. The area is about 58 square miles, and within these limits the diatomite has been found in large quantities at two localities. As the situation of these and the conditions under which the deposition took place are in both eases very different, they will be described separately.

The not unfrequent occurrence of the variety of Calcite, containing Carbonate of Lead and known as "Plumbo-calcite," at the Leadhills district, suggested that an examination of some of the ordinary Calcites from this locality, for Lead, might be of interest. The specimens for this examination were most kindly put at my disposal by Dr. Wilson. All of them were ordinary Calcites, none consisting of the recognised Plumbo-calcite.

The clays appear under many widely different aspects, and from one point of view must be studied as rocks. There are rock-masses alike of clay and of serpentine, both the result of important metamorphic processes. The basis, however, of most—probably of all—clays appears to be a substance of definite composition and well-marked characters, as much entitled to specific mineral rank as allophane or serpentine, or perhaps opal. In this paper I propose to consider clay as a rock and as a mineral.

During the course of an inquiry into the nature and extent of the less known iron ore deposits of Scotland undertaken in connection with a paper to be communicated to the Society of Antiquaries of Scotland during the Winter Session 1886-87, I have been led to consieler certain masses of Bog Iron Ore which are distributed somewhat widely over the less cultivated portions of the country. The present communication deals only with the north-westerly portion of Ross-shire, and most of the localities are within the parish of Gairloch.

In a paper read before this Society on June 16th, 1885, Mr. Wallace drew attention to this mineral as being found at Loch Bhruithaich, and stated that it was obtained incrusting Barytes.

The mineral is clear, beautifully crystalline, with a tendency to a bluish tinge of colour, and very friable.

If the planes of a crystal be replaced by lines drawn perpendicular to them through a point the intersection of the sheaf of lines so formed with the plane of the paper is the Gnomonic Projection of the crystal; each face being represented by a point and each zone by a line joining two such points. This projection, which has been frequently used and fully described, has generally been employed to represent the symmetrical disposition of the faces, the plane of the figure being a plane of symmetry.

But the practical value of the projection is best seen when it is used either as a graphic representation of the forms of a mineral, or as a method of drawing a perspective figure of any part of a crystal.

In my previous communication I drew attention to an impure variety of Agalmatolite found on Creag Mhôr Thollie, and which contained an excess of silica. A similar body was referred to in connection with Mr. Hamilton Bell's paper on "New Localities for Agalmatolite" as having been obtained from Ballater Pass. In connection with the material obtained at Creag Mhôr Thollie, I expressed the opinion that the agalmatolitie mineral had been formed in the presence of an excess of silica which had become combined with the other ingredients, forming what I then termed a "Siliceous Agalmatolite."

During the past summer I have again had an opportunity of examining the Creag, and towards the northmost end found very large masses of the pure mineral.