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The New Zealand Evangelist

Geology and Chronology.—Mount Etna

page 251

Geology and Chronology.—Mount Etna.

Under these circumstances I naturally felt a desire to verify an observation reported to Brydone on the authority of the Canon Recupero, which might render us suspicious of the correctness of our received chronologies. This writer, after giving an instance of a lava, the date of which he says goes back to the time of the second Punic war, proceeds to state that at Aci Reale we see seven such beds superimposed, one on the other, each of which has its surface completely decomposed and converted into rich vegetable mould.

Now, if a single bed of lava, he say, has continued more than 2000 years without experiencing this alteration, what a lapse of time raust it have required to reduce seven successive beds of the same material into a state of such a complete decomposition?

The following is the passage to which I refer:—“Near to a vault, which is now thirty feet below ground, and has probably been a burial place, there is a draw-well where there are several strata of lavas, with earth to a considerable thickness over the surface of each stratum. Recupero has made use of this is an argument to prove the antiquity of the eruptions of the volcano. For if it requires two thousand years, or upwards, to form but a scanty soil on the surface of a lava, there must have been more than that space of time betwixt each of the eruptions which have formed these strata.

But what shall we say of a pit they sunk near to Jaci of a great depth? They pierced through seven distinct lavas, one under the other, the surfaces of which were parellel, and most of them covered with a thick bed of rich earth. “Now,” says he, “the eruption which formed the lowest of these lavas, if we may be allowed to reason from analogy, must have flowed from the mountain at least 14,000 years ago. Recupero tells me he is exceedingly embarrased by these discoveries, in writing the history of the mountain; that Moses hangs like a dead weight upon him, and blunts all his zeal for enquiry, for he really has not the conscience to make his mountain so young as that prophet makes the world. The bishop, who is strenuously orthodox—for it's an excellent see—has already warned him to be on his guard, and not pretend to be a better historian than Moses, nor to presume any thing that may, in the smallest degree, be deemed contradictory to his sacred authority.” —(Brydone's Tour in Sicily, vol. i. p. 140.)

Although I have no reason to doubt that Brydone received from Reenpero the observation on which he grounds his inferences, it seems most probable that the remarks appended were in reality his own, though he thought to give them more zest, by putting them into the mouth of the Canon, whose scientific knowledge it was his aim to exalt at the expense of his orthordoxy.

The fact nevertheles reported by Brydone, obtained a currency proportionate to the popularity which his work enjoyed; and the mode in which the conclusion drawn from it had generally been page 252 combated, was by reference to the great variableness as to the period which a bed of lava will take to undergo decomposition. Thus even Spallanzani, though he visited Sicily, seems to have contented himself with pointing out instances in which newer beds of lava have taken the start of older ones in their progress toward cultivation, a circumstance now explained by the fact that lava, like basalt, is not in general a homogeneous body, but in reality is made up of an intimate mixture of at least two minerals in different proportions, which are unequally affected by decomposing agencies.

Supposing therefore the fact mentioned by Brydone to be unquestionable, I was not a little surprised when on visiting the celebrated spot adverted to, I found the beds of vegetable mould, which proved, according to that author, the degree to which the decomposition of the lava had extended, to be in reality nothing more nor less than layers of a ferruginous tuff, formed probably at the very period of the flowing of the lava, and originating perhaps from a shower of ashes that immediately succeeded its eruption.

It seems also very doubtful whether these beds have resulted from the operations of Mount Etna, at least in modern times; for if we examine their characters, we shall find them sufficiently distinguished by greater compactness and a stony aspect from modern lavas, whilst the general correspondence in mineralogical characters that exist between them all affords a strong presumption of their having been produced about the same period.

But it is useless to multiply proofs of the fallacy of Mr Bry-done's statement, and the only circumstance that need surprise us is, that so many years should have elapsed, without any traveller having visited the spot with the view of ascertaining the correctness of his observations.