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eruption generally forms one of these mountains. As the great crater of Ætna itself is raised to such an enormous height above the lower regions of the mountain, it is not impossible, that the internal fire raging for a vent, even round the base, and no doubt vastly below it, should be carried to the height of twelve or thirteen thousand feet, for probably so high is the summit of Ætna. It has therefore generally happened, that after shaking the mountain and its neighbourhood for some time, it at last bursts open its sides, and this is called an eruption. At first it only sends forth a thick smoke and showers of ashes, that lay waste the adjacent country: These are soon followed by red hot stones, and rocks of a great size, thrown to an immense height in the air. The fall of these stones, together with the quantities of ashes discharged at the same time at last form the spherical and conical mountains I have mentioned. Sometimes this process is finished in the course of a few days, sometimes it lasts for months, which was the case in the great eruption 1669. In that case, the mountain formed is of a great size; some of them are not less than seven or eight miles round and upwards of 1000 feet in perpendicular height; others are not more than two or three miles round, and 3 or 400 feet high.
