machine, is now adapted to mining and tunnelling with advantage; and one of those machines is employed in an open quarry, doing its work well and with economy. The legislature of Massachusetts have asked General Haupt to take charge of the Hosaic Tunnel. Mr. Lowe's boring-machine is reported on as doing good work in Australia. We have consequently three machines competing with each other, and proving their relative values under different circumstances. We hope to see those machines employed ere long in our mines, to relieve the miners from the most trying part of their labour.

10. MINERALOGY.

Is it desirable that the mineralogist should cast aside all those longestablished formula by which he expresses the chemical composition of his mineral-species, and introduce in their stead a new set of formulæ, written in accordance with the advanced views of our modern chemists? Such is the question which Professor von Kobell discusses in a short but interesting paper "On Typical and Empirical Formulæ in Mineralogy. Typical formula, we need hardly say, are those in which certain compounds (such as hydrochloric acid, water, and ammonia) are taken as general types, from which other bodies may be derived by replacing their constituents, according to definite laws, by other elements or by groups of elements called radicals. To illustrate the application of this typetheory to express the constitution of minerals, our author selects the double silicate of potash and alumina, called leucite. The composition of this species we are accustomed to represent by the following formula:

KO, Si O+ Al, 0, 3 Si O,.

But behold the aspect which our formula assumes when written on the type-theory:

༠། ༈༙

It may be necessary to remind those of our readers who have not kept pace with the advance of modern chemistry, that such an expression simply means that the mineral in question may be regarded as formed on the water-type, and that the 24 atoms of

* Journal für praktische Chemie,' 1868, p. 159.

hydrogen in 12 molecules of water (H,O) have been replaced by 4 atoms of tetratomic silicon, 1 atom of hexatomic aluminium, and 2 atoms of monatomic potassium. But although this mode of representing the constitution of chemical compounds has been of eminent service in organic chemistry, it would seem, even from this single illustration, that it is by no means of equal value in mineral chemistry.

From this consideration of typical formula, we turn to the second question discussed in Von Kobell's paper. At the present time the mineralogist endeavours to express the manner in which the constituent elements may be grouped together in any given mineral, by what is termed a rational formula. Many chemists, however, would have us confess our ignorance of this mode of grouping, and would simply write the elements side by side, without regard to the manner in which they may be associated: such formulæ are said to be empirical. Thus, the antimonial sulphide of lead called plagionite, has a rational formula, as follows:-4 Pb S+3 Sb S.; an expression which plainly shows that the mineral is composed of 4 molecules of galena and 3 of antimonite. The would-be innovator objects, however, to this theory, and gives us therefore an empirical formula written in this fashion: Pb. Sb, S.

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From such examples as these, Von Kobell concludes that there is no necessity, at present, for supplanting our old-fashioned expressions either by typical or by empirical formula-a conclusion by no means distasteful to so conservative a creature as the mineralogist. Agates, I think, of all stones, confess most of their past history.' Such are the words of Mr. Ruskin in his pleasing little work, The Ethics of the Dust;' and under this belief he has, of late, set himself the task of studying their history, and interpreting it to the readers of the 'Geological Magazine.'* In one paper he describes a group of agate-like structures which he calls "Dipartite Jaspers," and in a second communication notices the class of "Folded Agates," while he hints that other papers are forthcoming on "Mural Agates" and "Involute Agates." Certainly the most attractive features of these articles are the admirable tinted engravings by which they are illustrated.

It has always been a moot-point whether the peculiar markings observable in the so-called moss-agates and Mocha stones are truly of organic origin. As bearing upon this point, we call attention to a subject recently brought before the Chemical Society by Mr. W. C. Roberts.† Certain specimens of colloid silica prepared in Graham's dialyser, and evaporated in air, exhibited singular den

*

Geological Magazine,' April, 1868, p. 156; May, p. 208.

+ Chemical News,' April 10, 1868, p. 175; April 24, p. 195.

dritic forms which, under the microscope, were found to consist of radiating fibres having a cellular structure. These were evidently low vegetable organisms developed from spores which were deposited from the atmosphere, since similar specimens dried in vacuo were destitute of such appearances. It is possible, then, that vegetable life may be developed in siliceous solutions during solidification.

Mr. David Forbes has published the second part of his "Researches in British Mineralogy." In this paper he describes the occurrence of a sulphide of iron and nickel-probably a nickelliferous pyrrhotine-near Inverary Castle, in Argyleshire, and also at the Craigmuir nickel-mine, near Inverary. Our author calls attention to the tendency of nickel to associate itself with pyrrhotine or magnetic pyrites; whilst the allied metal, cobalt, prefers association with the ordinary iron pyrites. The same paper contains a notice of an arsenio-sulphide of nickel, referred to the species Gersdorffite, also found in the Craigmuir nickel-mine. An abstract of both the first and second parts of Mr. Forbes's "Researches" will be found in the 'Geological Magazine.'t

The exceedingly rare arseniate of copper called Cornwallite has been lately examined by Professor Church, who shows that the mineral contains only two equivalents of combined water, instead of five, as hitherto supposed. Its amended formula is thus given,‡ using of course the new equivalents:

Cu, 2 As O., 2 Cu H, O,, aq.

At length mineralogists are beginning to recognize the value of the microscope as an aid in their investigations. Herr Zirkel, whose name must be familiar to every geologist in connection with his admirable 'Petrographie,' has recently laid before the German Geological Society his researches "On the Microscopic Structure of Leucite, and the Composition of Leucite-bearing Rocks."§ Many crystals of this mineral exhibit, on section, a number of included glass-like particles and acicular bodies, either accumulated in the centre or symmetrically distributed around the margin of the crystal. The use of polarized light reveals a beautiful system of alternate dark and light lines, bearing a relation to the micro-lamellar structure of the mineral.

In a paper on the Basaltic Rocks of the Lower Main Valley, Herr Hornstein describes a new mineral to be called Nigrescite. It occurs in the anamesite of Steinheim near Hanau, and may pos

*Philosophical Magazine,' No. 236, p. 171.

May, 1868, p. 222.

'Chemical News,' April 10, p. 175.

Zeitschrift d. Deutsch. Geolog. Gesell.' Bd. xx., Hft. 1, p. 97.

Zeitsch. d. Deutsch. Geol. Gesell.' Bd. xix., p. 342; Neues Jahrb. f. Mine

ralogie,' 1868, Heft 2, p. 202.

sibly be only an altered form of olivine. Its composition is thus given :

Professor Hermann has again directed his attention to the study of the rare mineral Columbite.* He shows that the metal tantalium is present in this mineral in the state of tantalic acid (Ta, O), and may therefore be replaced by the corresponding acids of niobium and ilmenium. Hence he establishes for columbite the general formula, RO, R, O,, where RO represents the protoxides of iron and manganese, whilst R. O, represents tantalic, niobic, and ilmenic acids.

The Swedish mineralogist, Igelström, describes a new species from the iron mines of Långban, in Wermland.† From the manner in which it is disseminated through the matrix, he proposes to call it Kataspilite. It may perhaps turn out to be an altered variety of cordierite, with which it agrees in crystalline form. Its composition will be seen from the following analysis :--

An elaborate study of the optical characters of the minerals Harmotome and Wöhlerite has led M. Des Cloiseaux to the conclusion that the crystalline forms of these species must be referred to the oblique system, and not to the rhombic system, as previously imagined.‡

Professor Rammelsberg has been engaged in investigating the chemical composition of prehnite, talc, steatite, and chlorite; but his researches are not of general interest.§

On the 30th January of the present year a remarkable shower of meteoric stones fell at Sielce and Gostkow, near Pultusk, in Poland. Several of these stones are now in the British Museum. Externally

*Journ. f. prakt. Chemie,' 1868, p. 127.

† 'Neues Jahrb. f. Mineral,' 1868, Heft 2, p. 203.

'Proc. Roy. Soc., vol. xvi., No. 101, p. 319; 'Phil. Mag.,' June, 1868, p. 461. Zeitschr. d. Deutsch. Geol. Gesell.,' Bd. xx., p. 79, 82.

they are covered with a dull dark-coloured crust, whilst internally they exhibit a bluish-grey colour, somewhat resembling the wellknown meteorites of L'Aigle, in France.*

In spite of the value and variety of our British minerals, we have hitherto been without any work treating specially of their geographical distribution. Mr. Hall has therefore rendered a service to our science by collecting and arranging the principal mineral localities in Britain, and publishing them in the shape of a Directory.' The topographical portion of the work is preceded by an alphabetical list of our 246 British species and sub-species, showing the percentage composition of each. The localities are arranged under their respective counties, and when possible the geological position of each mineral is noticed. Nothing would be easier, were we so disposed, than to point out numerous omissions and errors; but we refrain from doing this, under the belief that it would be wrong to seek perfection in the first edition of a work of reference of this character.

The continuation of Kenngott's 'Forschungen,' noticed in the Chronicles of last quarter, has since been published in the shape of a bulky octavo,§ and the compiler turns out to be Dr. Kenngott himself.

Dr. Schrauf, of Vienna, has lately given us the second volume of his elaborate work on Physical Mineralogy,|| the earlier volume of which has already been noticed in this Journal. T

Tridymite is the name which Vom Rath proposes for a new Mexican mineral which promises to become of considerable interest; but as only a short preliminary notice has yet been published, we defer our description until we are in possession of further details.**

11. PHYSICS.

AFTER a long series of experiments, Baron von Liebig has finally adopted the following process for silvering glass for optical purposes. The solutions employed are:-I. One part of fused argentic nitrate dissolved in 10 of water; II. (a) Commercial nitric acid, free from

6

'Poggendorf's Annalen,' 1868, No. 2, p. 351; Geol. Mag., May, p. 248. The Mineralogist's Directory; or a Guide to the principal Mineral Localities in the United Kingdom of Great Britain and Ireland. By Townsend M. Hall, F.G.S.. London: 1868. 8vo, pp. 168.

↑ P. 256.

Uebersicht der Resultate Mineralogischer Forschungen in den Jahren. 1862-65,' entworfen von Dr. Adolf Kenngott. Leipzig: 1868. 8vo, pp. 482. 'Lehrbuch der physikalischen Mineralogie, von Dr. Albrecht Schrauf. II. Band. Lehrbuch der angewandten Physik der Krystalle.' Vienna; 1868. 8vo, pp. 426.

Quart. Journ. Sc., vol. iii., p. 293.

** 'Pogg. Ann.,' 1868, No. 3, p. 507; Geol. Mag.,' June, p. 281.