Whilst we have no lack of literature on the geology of the volcanic district of Auvergne-of which the excellent works of Scrope and Lecoq may be cited as conspicuous examples-there has hitherto been but little written on the mineralogical, chemical, and microscopic structure of the many and varied rocks of that country. It is true that a few of these rocks have been carefully described in the memoirs of Kosmann and of Zirkel, but it has been left for Dr. Lasaulx, of Bonn, to offer us the results of a systematic course of "Petrographic Studies on the Volcanic Rocks of Auvergne. The first part only has yet appeared, and this is devoted to a description of certain of the Auvergne lavas, so that we must look to the continuation of the memoir for a notice of the basalts, trachytes, melaphyres, and phonolites of this interesting locality.

10. MINING AND METALLURGY.

MINING.

THE Completed returns of the mineral produce of the United Kingdom for the year 1868 have been published in the 'Mineral Statistics.' The following are the results:

Total value of the Minerals produced in the United Kingdom £33,637,558

*Leonhard und Bronn's 'Jahrbuch,' No. vi., 1869, p. 641.

+ Calculated at the actual cost of raising, before any charges for movement are added.

ABSOLUTE TOTAL VALUE of the METAL and COAL, with other MINERALS (not including Slates, Lime, Building Stones, or Common Clays), produced in 1868.

£

..

Value of the Metals produced from the Mines of the
United Kingdom

..

15,736,416 25,785,289

Other Minerals, not smelted, including Salt, Barytes,

&C.,
&c.

2,003,819

£43,525,524

For two years the sad depression of Cornish mining has been the reiterated complaint. This happily has given place to great activity. The tin mines of Cornwall were never producing more tin than at present, and the prices are such as enable most of the mines to give a good dividend, after paying all the working expenses. The long celebrated Bearhaven mines, in Ireland, which produced (in 1868) 3837 tons of copper ore, are about to change hands, and will for the future be worked by the Mining Company of Ireland.

A variety of experiments have of late years been made in our mines and quarries with explosive compounds of various kinds, with very varied degrees of success. Attention is now called to "Poudre d'ammoniaque," which has created quite a sensation in some of the Continental mines. The following extracts will convey nearly all the information, of value, at present available.

The Militai-Wochenr-Blatt,' of Berlin, says :-"Some time ago. the proprietors of the powder manufactory of Nora-Gyttorp took out a patent in Sweden for the invention of the 'poudre d'ammoniaque, a substance only employed hitherto in a few mining districts, and which seems to be completely unknown elsewhere. Its explosive power may be compared to that of nitro-glycerine, and, consequently, surpasses that of dynamite. It will not explode with a flame or with sparks, but explodes by a powerful blow with a hammer. Chambers charged with this powder have been burst by means of a cartouche of ordinary powder. One of the useful and

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important properties of this new powder is that it does not require to be heated in cold weather, whilst it is necessary first to heat nitro-glycerine and dynamite, which operation has caused many accidents. According to the information we have received, the "poudre d'ammoniaque" was invented by Norbin, the chemist. The Journal of German Public Works' contains extracts from the report of the Prussian architect, Steenke, amongst which are the following remarks concerning poudre d'ammoniaque :-" Experiments have been made by attaching a lamp to a pendulum, and causing it to oscillate. Powder, gun-cotton, nitro-glycerine, and dynamite ignited the moment the flame passed beneath them, but poudre d'ammoniaque only commenced to burn when the flame had touched it twenty times.

"Making experiments to ascertain the pressure requisite to explode it, it was found that, with the instrument employed, explosion followed when the weight descended from 4.5 ft. to 5.5 ft. with powder, 1 6 ft. to 2.25 ft. with nitro-glycerine, 3 ft. to 3-3 ft. with dynamite, and from 13 125 ft. to 14.2 ft. with poudre d'ammoniaque.'

The production of gold in Australasia, according to the quarterly returns issued by Mr. R. Brough Smyth for Victoria, and the reports from other quarters, continues to be almost as large as ever.

The quantity of gold exported from Victoria to the 10th of September was 1,145,170 ounces, of which 154,075 ounces were from New Zealand. Very remarkable things are said of the gold fields of the latter place. Some of the quartz, broken from the reefs, or veins, have yielded in recent crushings 30 per cent. of gold. Mr. R. Brough Smyth's book on gold mining will be noticed hereafter.

The want of scientific knowledge amongst our miners is shown in a curious way by some statements which have lately appeared in The Mining Journal' on "The Prosperity of Mexico." The

Correspondent" informs us that some curious stones have been discovered at Tula del Hidalgo, "which present a great variety of appearances, and each face has received, and is constantly receiving, the landscape in front of it, by means of a colour so perfect, that I believe that art itself cannot produce such relative exactness." Again, we are told, "The faces which begin to receive the first impressions only present the images of the nearest trees with a wonderful perfection and beauty; those that have been in one position for a long time without variation present the complete landscape within the visible horizon, and even the most distant mountains by which it is limited." We perceive in this description a great want of the habit of observation, and a considerable display of Our Correspondent's" fancy. It will be evident to every one, possessing the slightest knowledge of Mineralogy, that the stones

so vividly described are only examples of that mimic vegetation often so beautifully displayed in stones by the oxide of manganese. Those arborescent forms and shaded outlines will be familiar to many who have visited the heights of Clifton, where the "landscape marble," as it is called, is nicely polished and sold to the many visitors to that delightful locality.

'La Houille,' a French journal devoted to the colliery interests of France is, from, the excellence of many of the articles contained in it, commanding a considerable amount of attention. It has recently given some notices of experiments made by MM. Rouille and Co., on producing a light for mines by atmospheric air, impregnated with petroleum vapour by being passed through the more volatile of the coal-shale oils, or other hydro-carbons. We refer to this only to condemn it. In the first place, the introduction of volatile hydro-carbon vapour into a coal mine is only adding another to the many dangers by which the coal miner is surrounded; and in the second place, the process has been long known, often tried, and it has always failed; because the vapour of the petroleum is speedily deposited from the air, and at a comparatively short distance from the reservoir the air ceases to be inflammable.

Our Colliery Guardian' calls attention to the "Lighting of Mines" with common gas, by an apparatus devised by Messrs. Church and Co. We are told that the light is produced by the combustion of a mixture of ordinary carburetted hydrogen gas with atmospheric air in certain proportions, and that from the manner in which the combined fluids are consumed no flame is produced. We have not seen this lamp. We do not know how the mixture of air and gas is burnt; we presume from the description given that we have a modification of the well-known Oxyhydrogen Lampsomething of either the Bude-light, or the Drummond-light type. This, however, we do know, that the statement that "no flame is produced" is one which cannot be maintained; and while it tends to deceive those who are not familiar with the laws of combustion, it may prove highly dangerous, by leading the unwary to make experiments in explosive atmospheres, under the idea that where there is no flame there can be no ignition of the surrounding gases. That the flame may not have the character of the ordinary flame of a gas-burner may be true; but the very description given proves that a flame of great intensity is produced by the combustion of the mixed gases.

At the Hayle Foundry, in Cornwall, there have been some experimental trials of a system of pneumatic stamps, which have been witnessed by a large number of practical miners, who are most favourably impressed with the results. The following brief description will, we believe, convey a sufficiently clear idea of the general principles of this machine:

The battery with which the experiment was tried consisted of six heads, all working in one coffer, contained in a strong cast-iron framing; the crank-axle running in two plummer-blocks, carried on top of side frames, which are 62 inches apart; and the height from ground to centre of axle, 110 inches; the total weight, including everything, 8 tons. The difficulty to overcome was to give a long and variable stroke of head, with a short and constant throw of crank; this, however, has been accomplished, as with forging hammers, in the following manner :-The upper end of the cylinder is bored, to receive the piston, to a depth of 14 inches; the pistonrod plays air-tight through the cylinder cover, which is screwed metal to metal on the cylinder. The working barrel of cylinder is pierced with two sets of small holes, for the ingress and egress of air, discharging the air behind the piston after it has been once used as an elastic cushion. Suppose the head to be set in motion with the crank in a horizontal position, the piston being in the middle, vertically of the working barrel of cylinder, and midway between the two sets of air-holes referred to. As the crank and attached piston rise, the air is compressed between the piston and cylinder cover, and the cylinder, with stamp-head attached, is forced upwards. When in rapid motion, the elasticity of the compressed air between the piston and cover flings the cylinder, with head, some inches above the range, due to the motion of the crank; on the descent of the piston below the bottom set of holes in the cylinder, the air is compressed in a similar manner, and the cylinder is forced down by the compressed air between the piston and cylinder bottom, until the stamp-head strikes the ore in a coffer-trough; thus, whether the quantity of ore be large or small, the blow is always effective.

At the last meeting of the Midland Institute of Mining Engineers, a discussion took place on the paper read by Mr. A. Lupton, in August last, "On the Use of Hydraulic Machines for Breaking down Coal:

On first introducing the subject, Mr. Lupton, with the aid of a number of diagrams, gave the results of several experiments which he made for the purpose of testing the value of the hydraulic machines, including those of Mr. Grafton Jones, Mr. Bidder, and Mr. Chubb. The machine of Mr. Grafton Jones, the principle of which consists in driving a wedge by means of a hydraulic press between two blocks of steel which are rendered incapable of any but lateral movement, by tension-bars connecting them with the press, was tested at the Shipley Colliery, in Derbyshire, where the bed of coal is worked on the long wall system in banks from 80 to 100 yards in length, the coal being 4 ft. 7 in. thick. As much work could be done by it and two men, Mr. Lupton said, in from two to three hours, and as much coal got, as would take two men by the ordinary method from one-and-a-half to two days.