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successful, so that the smallest pieces of this stone are extremely dear."*

This is truly surprising; and affords a further proof, if necessary, that the ingenious writers of France, with their clear heads and universal talents, never think it a duty, though it be indispensable, to read preceding accounts, that they may not repeat what is already well known; nor, above all, want the necessary knowledge of their subject. For to write on any science, without a complete knowledge of what has been already done, can in few instances contribute to its real advancement, which ought to be the chief end of every publication. The glacier of Miage, where so many beautiful varieties of this rock occur, cannot exceed two French leagues, or six British miles, from the little town of Cormayeur, on the river Doire; a distance surely not invincible for sledges or other conveyances: and any man of common enterprise might soon disperse these beautiful stones all over Europe. The fact is, that the passage of Saussure had totally escaped notice; and at present is only known to M. Sage, and a few other mineralogists, to whom it was indicated by the author. It must not be forgotten that, in whatever

• Brard, ii. 287.

direction the Miagite be cut, the nodules appear the same, so that the globular form is complete. It is also observable that Laet, a writer of the seventeenth century, has quoted a preceding author, Imperati, to this effect: "I must not pass in silence a very remarkable kind of marble, and hitherto undescribed, if I am not deceived. It is brought from an island in the gulf of Genoa, called Monte Cristo; and its colour is a greenish white, but it is all marked with black equidistant lines. It is extremely hard, and very rare, so that we have only small fragments."* He then gives a print, which corresponds with one of the rocks described by Saussure. The Tiegererz of the Germans, which ought rather to be styled Leoparderz, being spotted, not striped, with black, may also belong to this stone. Saussure had been aware of these instances, he would perhaps have argued that in his grand debacle these stones had been rolled from the pre-eminent height of Mont Blanc to the islands of Corsica and Monte Cristo, before the formation of the Mediterranean Sea.

If

Laet De Gemmis et Lapidibus, 1647, 8vo. p. 167. Imperati informs us that, in his time, all the stones used in architecture were called marbles; while those employed in personal decoration were styled gems.

[blocks in formation]

ful stone only found in the ruins of Rome, the Nero e Bianco, falsely called a granite.

NOME II. NIOLITE.

Faujas, in his late interesting work of geology, is the first who has described this singular rock, of which he has also published a coloured plate*.

Description. His general description is that the base or ground

consists of compact felspar, or felsite, of a brown colour, marbled with red; containing large spherical kernels of a flesh-coloured felspar, disposed in unequal rays or petals compressed upon each other, and diverging from the centre to the circumference. M. Rampasse, who brought

* Paris, 1809, 8vo. ii. 245.

many specimens from Corsica, said he found them at the foot of Monte Pertusato, one of the dependencies of the chain of Niolo; which, with its valley, has been long since celebrated by Dolomieu for the variety and beauty of its lithology.

"The ground of this beautiful rock is of a deep brown, with numerous little spots of a yellowish red, which have a pretty effect. They penetrate the whole thickness of this stone, and probably arise from the oxydation of the iron, which abounds in the base of the rock; but this state of oxydation has little injured its hardness, and does not prevent the stone from receiving a tolerable polish.

"Amidst this ground spherical bodies appear; some being an inch, an inch and a half, and even three inches in diameter. Many are perfectly round, others oblong, and they are placed near each other, having the aspect of balls or geods, solid in the interior, and strictly embraced by the base, as if formed when the latter was soft.

"But in this sort of explication we might fall into the same error as Daubenton, when he wished to apply this system of formation to the ocular granitel of Corsica; which, like this rock, is only the result of a particular mode of crystal

lisation, of which numerous examples occur in the rocks and stonęs.

"To distinguish perfectly the interior organisation of these balls, and discover the manner in which they have been formed, it is necessary to cut, with iron wire and emery, some plates off the rock, so as to reach if possible the centre of the balls. They must then be slightly, but not highly, polished; the former being preferable for this kind of rock, as it renders its lineaments more clear and distinct. It is then evidently seen that the interior of these balls is solid, composed of compact felspar or felsite, of a white tinged with rose-colour, disposed in rays, or rather petals*; being flat imperfect crystals, ter minating in sharp points, and diverging from the centre to the circumference. An envelope, about a line in thickness, of a lighter felsite, surrounds the globules; and, when divided by the saw, this envelope presents a circular line, which encloses and circumscribes each disk, serving as a kind of frame. The flowers thus displayed then produce a beautiful effect; and if it were possible to obtain large pieces of this rock, to saw in the form of a table, or turn in

Petalum means a thin plate; and was originally transferred from metals to the leaves of flowers in botany.

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