Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/267

Rh or accident. While one party asserted that a regular process had been carried on for the purpose of making a solid wall, the other supposed that these walls might have been originally constructed of stone and wood united, and that accidental fire, or the attack of an enemy, had destroyed the compound structure, producing in consequence the vitrification now to be traced in them. Mr. Williams and Mr. Fraser Tytler are the most conspicuous leaders on each side.

It seemed to me that light might be thrown on the question, by examining with mineralogical accuracy the substances of which these structures were composed, and noting the changes which each had undergone from the operation of the fire, and also by observing whence the stones had been derived which were used in them; and that the question of accident or design might be illustrated by examining in the laboratory the degree of heat necessary to produce the requisite appearances in the stones which actually exist in these structures.

In the present more diffused state of mineralogical and geological knowledge, it is unnecessary to refute the notion of their volcanic origin in a paper addressed to a Society like this. For the purpose of the ordinary spectator, that refutation may be trusted to the increasing progress of natural knowledge.

The hill of Dun Mac Sniochain, which lies in the plain, now supposed by some to be the site of the ancient Beregonium, has been long noticed as the seat of one of these extinguished volcanoes. Having seen specimens of pumice and lava (as they were called) collected from it, I was glad to have an opportunity of investigating a very accessible specimen of what I concluded to be a vitrified fort. Such it proved.

The drawing, pl. 2. fig. 1, which accompanies this paper, contains

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