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verted into lime: for some of the noblest monuments of Greece have been used for this purpose by the barbarous Turks; and a temple or statue of Diana has been turned into cement, for the voluptuous apartments of a Haram. It is also conceived by antiquaries, that some of the finest monuments of ancient Rome perished in this manner during the middle ages.

It must not be forgotten that stones apparently hard, are sometimes more subject to decay than those of a softer contexture. The pyramids of Egypt have suffered little degradation, though constructed with a soft calcareous konite. The Roman Pharos, at Dover, remains almost entire, though built with a soft stalactitic tufa, found in abundance on the shores of several rivers; for example, the Tees, in the north of England. The transportation of this stone from a distance, seems to evince that there was some reason for giving it a preference; and as it is coralloid in its structure, it was perhaps justly conceived that it would emit the moisture with the same ease as it was received, and hence be little subject to decomposition. The conjecture, if such, was certainly verified by the event. From this, and numerous other examples, it may be inferred that the ancient architects observed, with a most scrutinizing eye, the nature and the structure of the stone which they employed; an important circumstance which has not met with due consideration among the moderns.

The same considerations are also of the greatest importance in private buildings, where stone is abundant and in general request; and the product of any new quarry should be put to several tests, and severely examined, before it be brought into use. The example of the houses of Malta, mentioned by Mr. Kirwan, is a striking lesson of this kind; and some modern buildings in Scotland are more decayed than the ancient. If iron, clay, or even perhaps

some magnesian mixtures, be much in termingled, the stone is apt to become carious. But the magnesian rocks in gemeral are little subject to decay; and serpentine, resisting moisture by its unc-. tuous nature, forms some of the boldest summits and promontories. It was, perhaps, this consideration which induced the preference of ollite, or potstone, in the construction of the Duke. of Argyle's noble mansion at Inverary.

Domain XII.-Volcanic.

The volcanic rocks may be said, with the German mineralogists, to be of the most modern formation, as every new eruption of about one hundred and fifty volcanoes scattered over the face of the . globe, must produce new rocks of this description. That there are also vol canoes at the bottom of the sea, we know, from the ejection of new islands in the seas of Greece; and, in the Atlantic near Iceland, and the Azores. It may therefore be considered as a most rational conclusion, that, as the ocean occupies two-thirds of this globe, numerous volcanoes may exist at such depths, that their effects are wholly unperceivable. Dolomieu seems to have demonstrated that the matter, which supplies the prodigious eruptions of volcanoes, must lie at an immense depth beneath the crust of the earth. This position may be argued, 1. from the surprising extent of earthquakes, felt from Lisbon to Scotland, a space of 15 degrees, or about 1000 British miles. 2. From the prodigious quantity of matter ejected in the course of ages; from the comparatively small craters of Etna, for example, whole mountains, may territories have issued; which, if drawn from a space near the surface, the mountain inust long since have sunk into its own abysses. 3. From the nature of the lava, which, in some instances, has burst through the superincumbent masses of granite, itself regarded as the fundamental rock.

[END OF THE THIRTY-THIRD VOLUME.]

GENERAL

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