Some Zermatt Guides (Joseph Taugwalder and his brother) made, on a recent excursion up one of the mountains (Pollux ?) in the neighbourhood, the discovery of some very interesting crystals of idocrase and red garnet.

The idocrase crystals are of a dark sherry eolour, and are developed in simple forms, the prism-planes m{110}, a{100}, and the base c{001}, being well developed. The edges [cm] are truncated by narrow planes u{111}, and at the corners small planes i{312} are sometimes found. The prism planes are deeply striated, and at the same time the c plane shows more or less coarse squares, which sometimes seem to belong to independent crystals. The sides of the square are parallel to the a {100} faces. The crystals have, therefore, much the character of a bundle of thin pyramidal crystals united together in parallel positions.

The number of localities at which glaucophane has been discovered is still comparatively small, so that it may be of interest to add another and to describe the microscopic structure of a rock in which this interesting variety of hornblende occurs.

The carriage road between Vertex and St. "Vincent in the Val d' Aoste mounts along the left bank of the Dora Baltea, which, in one part, often called the defile of Mont Jovet, is scarped and craggy. The steepest part of the ascent is between the hamlets of Berrioz and Nus (?). I was walking up this, one day in July 1885, in company with my friend the Rev. E. Hill, F.G.S., when my eye fell upon a rock, which I at once reeognised as a variety of eclogite, composed chiefly of small reddish garnets and dull-green hornblende. We secured specimens, though with considerable difficulty, for the rock was very tough ; made a few observations and passed on.

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.

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.

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.

The ores which I have the honour to submit for your inspection were collected by me in Chili. They consist of numerous compounds of copper, silver, gold, &c., and represent the very varied minerals obtained in that country.

Besides the primary metal there is usually at least one secondary body of value present.

The proportion in which this secondary metal—I mean secondary as regards quantity—is present in metallic ores does not seem to be a mere chance affair, but seems to follow some law. My attention was directed to this matter by the silver ores from the district of “Lomas Bayas” near Copiapó. These ores contain gold in a certain proportion, not in relation to the gross weight of the ore but to the contents in silver.

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.

Since many of the minerals grouped as hydrocarbon compounds in Dana's Mineralogy have become extensively exploited for their commercial uses, allied questions in chemical geology and in their classification have bulked largely in scientific discussion. Thus their place as rocks or minerals in petrology has been mooted; for it is difficult to make out definite chemical composition or crystallographic form in many of the materials of the group now used for heating, lighting or paving. Notably the question, What is coal ? has not been authoritatively removed from the range of scientific controversy―though the supply of the mineral which occasioned the great trial Gillespie v. Russel, nearly thirty years ago, was, until last year, considered exhausted. Diligently bored for to its exact position inthe Scottish carboniferous series of rocks, no trace of it has been found except in its limited basin of four miles area or so around Torbanehill, Linlithgowshire.

Professor Bonney has described, in the British Association Report for 1885, the rock specimens brought from Kilima-njaro by Mr. H. Johnston, and has called attention to the peculiar form of the felspar crystals which are porphyritieally developed in a rock referred by him to augite-andesite. It is at his suggestion that a more detailed account of these crystals is here attempted.

They are of a brown to yellowish-brown colour, full of cavities, and considerably weathered, and are so much rounded that it is impossible to determine their nature with certainty by means of the hand goniometer. They sometimes attain a length of 85 mm.

Every student of crystals is aware how frequently they fall short of the ideal perfection which theory ascribes to them. With regard to the development of the simple forms, the irregularities are most prominent on the crystals which are subject to certain laws of symmetry. In consequence of the differences of size presented on the same crystal by planes belonging to the same form, the most manifold distortions ensue, resulting at one time in the imitation of forms of a lower degree of symmetry, at another in the complete absence of symmetry. Moreover, as long as the faces constituting the distorted form remain the same, i.e. as long as the cause of the distortion is without influence on the development of the combination, so long will the angles of inclination of the circumscribing elements of the individual remain the same, and thus the degree of symmetry can be determined by measurement of the crystal notwithstanding the distortion.

I obtained this summer a most beautiful variety of fluor spar, which was raised from the 145 fathom level of the Holmbush Mine. It is of a transparent azure-blue colour, and shows well marked fluorescent phenomena, though not so strongly as that of Weardale, Cumberland.

Some of the specimens are deep blue in one part and limpid like glass in another ; it was found that while the deeply coloured part was strongly fluorescent the limpid part had little or no effect upon the refrangibility of the light passed through it.

At the conclusion of my term of office it is a great pleasure to me to be able to congratulate the Society on the condition of its finances. This, three years since, caused some of us no little anxiety ; now, thanks to the efficient management of our Honorary Secretary, we can look forward to the future with confidence.

The proportion of actual carbon varies much in different samples. Some portions are stated to have analysed as high as 75 per cent., but, as will be noticed from the figures given below, the carbon may be much lower.

The gradual decline in the production of copper from the mines of Cornwall and the consequent diminution of their number renders any discovery of a rare copper mineral an object of interest to all mineralogists.

Owing to the exhaustion of all the upper deposits, those products of decomposition—the beautiful arseniates and phosphates, &c. which adorn the cases of our national collection and those of private collections—are getting more and more scarce, and perhaps in the near future, so far as Cornwall is concerned, we shall have to rely for illustrations entirely on its past productions.