Viewing page 187 of 285

This transcription has been completed. Contact us with corrections.

[[2 pages]]
64 ANNUAL REGISTER
[[2 columns]]

Over the stratum of pumice and burnt matter that covers Pompeii, there is a stratum of good mould, of the thickness of about two feet and more in some parts, in which vines flourish, except in some particular spots of this vineyard, where they are subject to be blasted by a foul vapour or mofete, as it is called here, that rises from beneath the burnt matter. The abovementioned shower of pumice stones, according to my observations, extended beyond Castel-a-mare (near which spot the ancient town of Stabia also lies buried under them), and covered a tract of country not less than thirty miles in circumference. It was at Stabia that Pliny the elder lost his life, and this shower of pumice stones is well described in the younger Pliny's letter. Little of the matter has issued from Vesuvius since that time, has reached these parts: but I must observe that the pavement of the streets of Pompeii is of lava; nay, under the foundation of the town, there is a deep stratum of lava and burnt matter. These circumstances, with many others that will be related hereafter, prove, beyond a doubt, that there have been eruptions of Vesuvius previous to that of the year 79, which is the first recorded by history.
The growth of soil by time is easily accounted for; and who, that has visited ruins of ancient edifices, has not often seen a flourishing shrub, in a good soil, upon the top of an old wall? I have remarked many such on the most considerable ruins at Rome and elsewhere. But from the soil which has grown over the barren pumice that covers Pompeii, I was enabled to make a curious observation. Upon ex- 5|
|amining the cuts and hollow ways made by currents of water in the neighbourhood of Vesuvius and of other volcanos, I had remarked that there lay frequently a stratum of rich soil, of more or less depth, between the matter produced by the explosion of succeeding eruptions; and I was naturally led to think that such a stratum had grown in the same manner as the one abovementioned over the pumice of Pompeii. Where the stratum of good soil was thick, it was evident to me that many years had elapsed between one eruption and that which succeeded it. I do not pretend to say that a just estimate can be formed of the great age of volcanos from this observation, but some sort of calculation might be made; for instance, should an explosion of pumice cover again the spot under which Pompeii is buried, the stratum of rich soil abovementioned would certainly lie between two beds of pumice; and if a like accident had happened a thousand years ago, the stratum of rich soil would as certainly have wanted much of its present thickness, as the rotting of vegetables, manure, &c. is ever increasing a cultivated soil. Whenever I find them a succession of different strata of pumice and burnt matter like that which covers Pompeii, intermixed with strata of rich soil, of greater or less depth, I hope I may be allowed reasonably to conclude, that the whole has been the production of a long series of eruptions occasioned by subterraneous fire. By the size and weight of the pumice, and fragments of burnt erupted matter in these strata, it is easy to trace them up to their source, which I have done more than once in the neighbour-|

[[top of page]]
For the YEAR 1772. 65
[[2 columns]]

|neighbourhood of Puzzole, where explosions have been frequent. The gradual decrease in the size and quantity of the erupted matter in the stratum abovementioned, from Pompeii to Castel-a-Mare, is very visible: at Pompeii, as I said before, I have found them of eight pounds weight, when at Castel-a-Mare the largest do not weigh an ounce.
The matter which covers the ancient town of Herculaneum, is not the produce of one eruption only; for there are evident marks that the matter of six eruptions has taken its course over that which lies immediately above the town, and was the cause of its destruction. These strata are either of lava or burnt matter, with veins of good soil between them. The stratum of erupted matter that immediately covers the town, and with which the theatre and most of the houses were filled, is not of that foul vitrified matter, called lava, but of a sort of soft stone, composed of pumice, ashes, and burnt matter. It is exactly of the same nature with what is called here in Naples stone; the Italians distinguish it by the name of tufa, and it is in general use for building. Its colour is usually that of our free-stone, but sometimes tinged with grey, green, and yellow; and the pumice stones, with which it ever abounds, are sometimes large and sometimes small: it varies likewise in its degrees of solidity.
The chief article in the composition of this tufa seems to me to be, that fine burnt material, which is called puzzolane, whose binding|
|quality and utility by way of cement are mentioned by Vitruvius, and which is to be met with only in countries that have been subject to subterraneous fires. It is, I believe, a sort of lime prepared by nature. This, mixed with water, great or small pumice stones, fragments of lava, and burnt matter, may naturally be supposed to harden into a stone of this kind; and, as water frequently attends eruptions of fire, as will be seen in the accounts I shall give of formation of the new mountain near Puzzole, I am convinced that the first matter that issued from Vesuvius, and covered Herculaneum, was in the state of liquid mud. A circumstance strongly favouring my opinion is, that, about two years ago, I saw the head of an antique statue dug out of this matter within the theatre of Herculaneum; the impression of its face remains to this day in the tufa, and might serve as a mould for a cast in plaister of Paris, being as perfect as any mould I ever saw. As much may be inferred from the exact resemblance of this matter, or tufa, which immediately covers Herculaneum, to all the tufa's of which the high grounds of Naples and its neighbourhood are composed; I detached a piece of it sticking to, and incorporated with, the painted stucco of the inside of the theatre of Herculaneum, and shall send it for your inspection*. It is very different, as you will see, from the vitrified matter called lava, by which it has been generally thought that Herculaneum was destroyed. The village of Resina and some villas stand|

[[bottom of page]]
* This piece is now in the Museum of the Royal Society, together with many other specimens, mentioned in this and in the following letter. M.M. VOL. XV. F at

Transcription Notes:
---------- Reopened for Editing 2023-05-13 14:02:31 ---------- Reopened for Editing 2023-05-13 18:38:48 ---------- Reopened for Editing 2023-05-13 19:26:23 ---------- Reopened for Editing 2023-05-13 19:02:25 ---------- Reopened for Editing 2023-05-13 23:27:47