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deposited advocated to in centred the elevatideposit of pa England oriemediately preche wide-spread the South
deposited by him in the Geological Society's Library. The principal view advocated is, that the “ entire valley-system of the East of England originated in centres of arc-like or curvilinear disturbance, which immediately preceded the elevation of the bed of the sea from which was deposited the wide-spread deposit of Boulder-clay forming the latest of the Glacial beds of the South of England." We are glad to see that Mr. Wood now recognizes the ambiguity of the terms Upper Drift, Middle Drift, &c., which we pointed out in noticing a former paper of his, and has substituted for them the terms Upper Glacial clay, Middle Glacial beds, &c. Many other points of interest are also discussed, especially the relations of the Thames valley-gravel, the Brick-earth deposits, &c., for which we must refer our readers to the paper itself.
On December 1st the Society published a bulky Supplement number, the description of which we must reserve for our next Chronicle.
9. MINERALOGY, MINING, AND METALLURGY.
MINERALOGY. Among British mineralogists no one has latterly been more active, whether in laboratory work or in literary work, than Mr. David Forbes, F.R.S. Without referring to his writings on Chemical Geology, which, however, are full of interest to the mineralogist, it will be sufficient in this place to call attention to his purely mineralogical work. In introducing the first part of his “Researches on British Mineralogy,"* Mr. Forbes takes occasion to contrast the present backward state of the science in this country with the honourable position which it occupied in the early part of this century. The chemist now-a-days is attracted by the organic branch of his science rather than by mineral chemistry, while the geologist is usually allured by palæontological research; and hence but few labourers enter the field of Mineralogy. To correct this state of things, and to develop a wholesome taste for the study, Forbes protests against the too-prevalent notion that Mineralogy is occupied exclusively with the dry enumeration of species, and with the description of their physical characters and chemical composition. Taking a higher stand-point, he maintains that minerals should properly be studied with reference to their mode of occurrence, origin, paragenesis, and especially the relations of their associated rocks. When thus prosecuted, the study cannot fail to prove a valuable aid both to the geologist in his examination of rock-masses in the field, and to the miner in his investigation of the
* • Philosophical Magazine, Nov., 1867, p. 329.
laws of mineral deposits. As an illustration of these advanced views, our author refers to his own researches which, although confessedly imperfect, tend to the remarkable conclusion that, in eruptive rocks, most minerals present themselves under similar conditions, accompanied by the same associated minerals, and in rocks of corresponding geological age. Hence he believes that certain minerals may serve to identify contemporaneous outbursts of eruptive rocks, in the same way that fossils serve to determine the age of sedimentary deposits. When, as often happens, the same mineral occurs in rocks of different age, he finds that in each situation it is marked by distinctive characters of its own, either physical or chemical. Thus, mica is distributed through rocks varying widely both in character and age; but while in granite it usually occurs as muscovite or potash-mica, in limestone and serpentine it appears as phlogopite or magnesia-mica, in zirconsyenite as astrophyllite or titaniferous mica, and in volcanic rocks as biotite. Generalizations of this kind are sufficient to show that the field of labour which Mineralogy affords is after all not so unattractive as many are inclined to think. As an earnest that the author himself is willing to bear a fair share of the work, he gives us a paper devoted chiefly to a notice of British Gold. Although public attention has from time to time been directed to the occurrence of gold in this country, and considerable excitement has been aroused by the recent workings in North Wales, * no analysis of British Gold has hitherto been recorded. Mr. Forbes has therefore visited the Welsh mines, and has analyzed specimens from the celebrated Clogau lode with the following results :
0:32 074 Loss . . .
The metal from this mine is therefore an alloy of gold and silver, closely agreeing with the formula—Au. Ag. After fully describing the character of the lode in which it occurs, Mr. Forbes discusses the probable age of the gold. He has already classified all known auriferous veins in two great groups, the older or granitic, which were formed at some time between the Silurian and the Carboniferous period, and the newer or dioritic, probably of Cretaceous age: it is to the former of these classes that the author is inclined to refer the gold-veins of North Wales.
* See a paper in this Journal on “ British Gold with especial reference to tho Gold Mines of Merionethshire, by Robert Hunt, F.R.S.," vol. ii., p. 635.
Mr. Forbes has also analyzed some Welsh stream-gold from the river Mawddach, about eight miles above Dolgelly. The metal yielded 84:89 per cent. of gold, and 13.99 of silver.
In the “Rowley Rag," a well-known basaltic rock from the South Staffordshire coal-field, the same chemist has detected minute grains of a black mineral, which, on analysis, proved to be Titano ferrite, or titanate of iron, having the following composition :
. 34.28 Oxide of iron.
Titanic acid .
ture de nestruction the progresiune, France countryme
Mr. Forbes brings his paper to a conclusion by noticing a newlydiscovered silver ore from the Foxdale mines in the Isle of Man. This ore, which contains 13 per cent. of silver, occurs in sufficient quantity to form an object of considerable commercial importance. The mineral is an argentiferous fahlerz, such as the Germans would call Weissgiltigerz, but which the author describes under the rarely used name of Polytelite.
Among the recent reports on the advancement of French literature and science, published under the direction of the Minister of Public Instruction, it comes within our province to notice only the “Report on the Progress of Mineralogy," drawn up by M. Delafosse * By giving a résumé of nearly all the mineralogical work which has been conducted in France within the last quarter of a century, the reporter shows that his countrymen, led by such men as Dufrénoy and Descloiseaux, have played a part in the advancement of our science by no means discreditable to the fatherland of Haüy and De l'Isle.
Those who love to speculate on the ultimate constitution of matter, and to study the recondite laws of crystallogeny, will find much to interest them in an essay on the “Molecular Constitution and Growth of Crystals,” recently published by Dr. Adolph Knop, of the Polytechnic School of Carlsruhe.fi
It is well known that certain varieties of sandstone enjoy to a limited extent the curious property of flexibility. Such flexible sandstone-known to the mineralogist as Itacolumite-is usually found in association with the diamond, and, so far as our knowledge at present extends, appears to be restricted to the mining districts of Brazil and the Ural Mountains, to the neighbourhood of Delhi in India, and to the gold-bearing States of Georgia and North Carolina. As itacolumite always contains more or less disseminated talc or mica, its flexibility has usually been referred to the presence of these elastic scales. This opinion has, however, been lately
* • Rapport sur les progrès de la Minéralogie.' Paris, 1867. 4to. pp. 97.
+ Molekularconstitution und Wachsthuin der Krystalle. Leipzig, 1867. 8vo. Pp. 96. 48 woodcuts.
opposed by Dr. Wetherill, whose observations show that while the micaceous or talcose mineral determines the cleavage of the rock, it bears no relation whatever to its flexibility. “This flexibility,” says the doctor, “is due to small and innumerable ball-and-socket joints.” The grains of silica composing the sandstone, instead of cohering into one uniform mass, are arranged in definite groups separated from one another by intervening cavities; and when the projections of one cluster engage in the corresponding cavities of a neighbouring group, there is produced an articulated structure, permitting motion within certain limits. By experiment the author has found that grains of sand, if saturated with petroleum, will cohere into groups separated by such intervening cavities; and hence, applying this fact, he conceives that the very gradual removal of the hydrocarbon might be attended with the separation of crystallized carbon in the form of diamond. As the jointed structure is quite characteristic of flexible sandstone, the author proposes to introduce the term Articulite-apparently a needless multiplication of synonymes since the mineral is already well-known as Itacolumite.*
Rarely does the mineralogist meet with a crystal presenting that perfect symmetry of form which the laws of crystallography demand. As a rule crystals are more or less distorted, the appearances presented by such irregularities being in many cases extremely deceptive. Some curious examples of such monstrosities have lately been described by Dr. Scharff, in a paper “On Deformed Crystals of Rock Salt.” | Instead of the six faces of the cube being all equally developed, certain faces were drawn out in some crystals and depressed in others, thus giving rise on the one hand to prismatic forms and on the other to tabular crystals. Moreover, the angles of the cube occasionally deviated from right angles—an irregularity giving a rhombohedral aspect to the crystal. In all cases, however, the true form was easily discoverable by the cubic cleavage.
In a specimen of Wolfram from Auvergne, Dr. Phipson has detected the presence of Columbite. When the mineral is attacked by aqua regia the wolfram is dissolved, leaving an insoluble residue, which consists of angular fragments of a black non-magnetic substance having the composition of Columbite. I
Some curious numerical relations between the atomic constitution of a mineral and the symmetry of its crystalline form have recently
* " Experiments on Itacolumite (Articulite), with the Explanation of its Flexibility and its Relation to the Formation of the Diamond."-Silliman's American Journal,' xliv., No. 130, p. 61.
+ Ueber missbildete Steinsalz-Krystalle.' Leonhard und Geinitz's Jahrbuch, 1867. Heft vi., p. 670.
I “Sur la présence du Columbite dans le Wolfram.”—Comptes Rendus,' 1867, No. 10, p. 419.
been worked out by the American mineralogist, Professor Dana.* Hitherto we have been unable to explain why a given substance should crystallize in a certain definite system in preference to any other; why, for example, a piece of tin-stone should invariably crystallize in forms belonging to the tetragonal system rather than in those of the other crystallographic groups. Dana shows that this symmetry of form is immediately connected with the chemical constitution of the mineral. Taking, as an example, this tetragonal or pyramidal system, we may remind the reader that the solids belonging to this order are bounded by 4, 8, or 16 sides; and hence the symmetry of the forms is characterized by the number 4, or a multiple of 4. Now it is found that in most minerals belonging to this system the number of atoms of the electro-negative or non-metallic element is in like manner 4, or a multiple or submaltiple of that number. Hence a piece of tin-stone crystallizes in tetragonal forms, in virtue of its constitution as a binoxide, Sn 0.; the number of atoms of the electro-negative oxygen being 2, a submultiple of 4. So again, zircon, wulfenite, scheelite, and schee-litine, are all tetragonal species, each containing 4 atoms of oxygen, their formule being respectively-Zr 0, Si 0,; Pb O, MO,; Ca 0, WO,; and Pb O, WOg: or, combining the oxygen of the acid with that of the base, according to the fashion of modern chemists, their composition may be expressed by the following formulæ, which more clearly show the 4 atoms of the element in question—Zr SO, Pb MO,, Ca WO., and Pb WO..
Turning to the hexagonal or rhombohedral system, we find the relations to be equally curious. The symmetry of this system is related to the number 6; its prisms, pyramids, and other forms, being bounded by 3, 6, 12, or 24 sides. Here the number of atoms of the electro-negative element is consequently 3, or a multiple of 3. Thus, the sapphire and the ruby_varieties of crystallized alumina -assume hexagonal forms, since alumina is a sesquioxide containing 3 atoms of oxygen, Al, Og. In like manner specular iron-ore is hexagonal, being a sesquioxide of iron, Fe, 03. The same is the case with the large class of rhombohedral carbonates, including those of lime, magnesia, and the protoxides of iron, manganese, and zinc; forming the species known respectively as calcite, magnesite, chalybite, diallogite, and calamine (CaCO, Mg CO2, FeCO MnCO3, Zn CO2.)
While the professor thus establishes his position with regard to the tetragonal and hexagonal systems, he is by no means so happy in his attempts to deal with the other orders. In the cubic system the number of atoms of the electro-negative element appears to be
* "On a Connection between Crystalline Form and Chemical Composition, with some Inferences therefrom."-Silliman's Journal,' xliv., No. 130, P. 89; Phil. Mag.,' p. 178.