crases; then come the conglomerates of Valorsine, with their micaceous paste and black slates. At the cascade of Pissevache, we again find petrosiliceous veins; at the cascades of Mieville, we perceive felspar and micaceous rocks. Finally, from Mieville to Evionnaz, the geological chart of France, indicates that the valley intersects the axis of the chain of Brevent. All this system is parallel to the Western Alps.

"If we take account," says the author, "of the result of metamorphic actions, we may group these products (these stratified and altered formations, in the following manner :"1st, The baking of schistose clay into argillaceous or clay slates.

"2d, The conversion of ordinary slates into hard unctuous slates, more or less modified in their colours.

"3d, Complete hardening or semi-fusion, which has caused the slates to pass into a petrosiliceous state.

"4th, Crystallisation into chlorite of the slaty fragments embedded in the veins of quartz.

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5th, Transformation of the clay slates into green slates, more or less felspathic, and very variable in the grain.

"6th, Change of the same rocks into felspathic micaceous slates, or into gneiss more or less porphyritic, in consequence of an imbibition and crystallisation of mica and felspar.

"7th, Lastly, crystallisation of black limestones into white limestones, saccharoidal, or saline, with or without idocrase."

He then proceeds to examine the different changes which the rocks have undergone. It then becomes indispensable to inquire into the nature of the rocks. Now, two kinds here present themselves to him as fundamental, namely, the limestone and clay state. M. Fournet first takes up the latter, the metamorphism of which appears to be more general, more complicated, than that of the limestone, on account of its variety of composition, and its exfoliability,—a circumstance which multiplies the points of contact. What is the composition of clay-slate? What is its constitution? Is it itself a metamorphic rock? These are some of the problems discussed.

According to various analyses, this rock is always formed of from 59 to 70 per cent. silica, from 10 to 23 per cent. of alumina, from 6 to 11 per cent. of oxide of iron, and from 2 to 6 per cent. of water; frequently other bases are added to this composition. "It will be observed from the first," says M. Fournet," that their composition (that of the clay-slates) is homogeneous enough to entitle us to expect to find results sufficiently agreeing between the metamorphism of different localities, and thence also the character of generality which these phenomena present."

The clay-slates are formed, according to the analyses, of hydrosilicates, combined with silicates; and M. Fournet thinks that they owe their origin to clays, which have been converted into clay-slate by calorific effects. In order to prove this, he brings forward different modes of reasoning, one of the most remarkable of which is drawn from the state of the colouring matter of the rocks of the Alps.

This colouring matter is commonly bitumen, which is found decomposed into nearly pure carbon. Indeed, it appears, from numerous examples that, among the Alps, at the contact of the eruptive veins, the bitumen has been often converted into graphite. He has found plates of it in the saccharoidal limestone, associated with the idocrases of the Coupe de Martigny. This fact had already been announced by M. Elie de Beaumont, in his work on the Col du Chardonnet.

But beyond the point of immediate contact, to a distance of a mile or more from the plutonic masses, there may be, in certain cases, a more or less complete conversion of the bitumen into anthracite; and at a distance of several miles, the bitumen is not decomposed. These distances, it will be understood, may vary according to the conducting power of the rocks, the power of the eruptive mass, the number of veins, and, finally, the disposition of the beds. It will be observed, moreover, that the above measures have been taken horizontally, so that they give merely an approximation. However, the result is not less certain, that the whole thickness of the jurassic formation of the interior parts of VOL. XLIII. NO. LXXXV.-JULY 1847.

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the Alps, has felt the influence of a temperature capable of altering the bitumens.

We shall not follow our author in his examination of the properties of slates, such as their colour, their state of molecular aggregation, &c., with the view of finding in them the products of a more or less elevated temperature. We may merely mention, that he compares two analyses, one of a clay slate, the other of a petrosilex; the first made by M. Regnault, the other by Saussure; and that he has found them very nearly identical. The petrosilex may, therefore, proceed from the slate; but the word petrosiler does not well indicate the rock M. Fournet had in view, and he proposes to give to this class of rocks the name of Thermantide, a denomination used by Haüy in a more restricted sense, to indicate rocks altered by non-volcanic fires.

The kaolinic disorganisation which the slates are liable to undergo, like all the plutonic rocks, is still another character which, in the opinion of our author, has been left upon them by the heat to which they have been exposed.

M. Fournet thinks that, in certain cases, the mica is a sign of metamorphism, for the denomination mica does not apply to a definite body; it expresses an equivocal physiognomy, and not settled features; and this body must be formed at the expense of the clay-slate, and by associating the latter with the substances brought by the veins.

It is nearly the same with the tales and chlorites which, in the Alps, form complex and confused rocks by associating with other minerals, as well in respect to their composition as in reference to their situation and origin.

On this occasion, the author reverts to some considerations long previously established by him, relative to some terminological errors which have been introduced in reference to the crystalline slates of the Alps. They are almost always spoken of as tale schists, a name which would lead us to believe in the great superabundance of magnesia, while in this locality they are nothing else than what they are everywhere else, rocks essentially aluminous.

With regard to the modification of the limestone; its change into saccharoidal marble by the action of a high tem

perature, is, no doubt, most remarkable. The author, however, does not stop here; because this transformation has been for a long time demonstrated geologically and chemically; but he considers the formation of garnets, and idocrases, which are developed in the same circumstances as the saccharoidal limestone. In truth, according to the numerous indications given by M. Fournet, almost everywhere this limestone is accompanied with idocrase, and the formation at Martigny is only one proof more of the law to which the formation of this latter mineral is subject.

We know that M. Mitscherlich has obtained garnet artificially, and that idocrase, as well as another crystallization of the same kind, has been found by MM. Hausmann and Bertheir, in smelting-houses. The garnet and idocrase are nothing else, according to many mineralogists, than the same substance appearing under two different forms. However this may be, there is no ground for separating these two species, in respect to their formation. It is evident that they are formed when there are siliceous rocks in presence of calcareous rocks, in suitable circumstances of temperature and pressure.

These considerations, according to M. Fournet, are of interest in regard to the study of metalliferous deposits, by establishing the influence of matalliferous veins on their walls, a study which is of the highest importance with respect to its practical and industrial bearings.*

Some Remarks on the High Temperature in the United Mines. By ROBERT WERE Fox.t

The temperature of some of the deeper parts of the United Mines has long been observed to be remarkably high; and it has greatly increased with the increasing depth of the excavations.

* Biblioth. Univers. de Genev. Supplement, No. 6, p. 203,

† Read, 3d September 1846, to the Royal Cornwall Polytechnic Society.

sea.

Captain Youren, one of the agents of the mine,* informs me, that near the eastern extremity of the deepest level, on the "middle lode," there is a spring or jet of water, discharging about 94 gallons a minute, at the temperature of 1063° Fahrenheit.† This level is about 250 fathoms below the surface, and about 200 fathoms under the level of the The "lode" has an underlie or dip of about 23 feet in a fathom towards the north, and the water flows from its northern or upper wall; whilst from the opposite side, or southern wall of the lode, at the distance of only 3 feet, there is another spring, discharging 30 gallons of water in a minute, at the temperature of 973° Fahr. The air near both these springs was found to be at 104° Fahr.: and "killas" is the only rock which has been seen within 30 fathoms of them. Granite occurs at a considerable distance westward of the place; and two "elvan courses" traverse the mine in nearly the same east and west direction as the lode.

1

I have found that of a pint of the water from the warmer spring contained 15 grains of saline matter, consisting of muriate of lime and common salt, in about equal proportions, with a trace of sulphuric acid, probably combined with lime. In the same quantity of the cooler water, only 10 grains of muriate of lime and common salt were found, the latter in less proportion than the former; and in this water also there was a slight trace of sulphuric acid. In both instances, the water was clear, saline to the taste, and without any metallic salt,

It may, I think, be inferred from the saline contents of these springs, that they have a common origin or source; whilst their high temperatures indicate their having come from a considerable depth, and the quantity of water they discharge, that the lode, or rocks beneath, must be very per

*This mine (for it is one concern) continues to produce abundance of copper ore. It is situated in the parish of Gwennap, about 8 miles to the northward, or almost NNW. of Falmouth, and is several miles from the sea.

† The thermometer employed has been carefully compared with a standard one, and found to be of a degree too high; so that this small amount must be deducted from the results, making them 106.08°, 97·5°, and 104, respectively.