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Updated: May 14, 2025
This conclusion accords with the highly scoriaceous condition of all the rock on it, appearing to be of subaerial formation: and this is important, as there are some beds of calcareous matter near its summit, which might, at a hasty glance, have been mistaken for a submarine deposit.
It is interesting to trace the changes produced by the heat of the overlying lava, on the friable mass, which in parts has been converted into a crystalline limestone, and in other parts into a compact spotted stone Where the lime has been caught up by the scoriaceous fragments of the lower surface of the stream, it is converted into groups of beautifully radiated fibres resembling arragonite.
Their surfaces are rough, and fissured with branching cracks; their internal structure is either irregularly scoriaceous and compact, or it presents a symmetrical and very curious appearance. Its size was about that of a man's head. The whole interior is coarsely cellular; the cells averaging in diameter about the tenth of an inch; but nearer the outside they gradually decrease in size.
At one place there was a low pyramid less than ten feet in height. To its top led a flight of rude stone steps. Among the ruins we found a number of broken stone dishes, rudely carved out of soft, highly porous, scoriaceous lava. The dishes must have been hard to keep clean!
The whole region had been the stage of great volcanic activity, and the monticules of scoriaceous rock, the broad plains excavated with deep pools that reflected their dismal, untenanted borders in the black depths of unruffled water, spoke of meteorological conditions long prolonged and intense. It was a weird, strange place, silent and dead.
In a pile of successive sheets of lava each flow may be distinguished and its thickness measured; for the surface of each sheet is glassy and scoriaceous, while beneath its upper portions the lava of each flow is more dense and stony.
At the distance of fifty yards from a second level-topped patch of lava, but of much smaller size, I found an irregular circular group of masses of cemented, scoriaceous breccia, about six feet in height, which doubtless had once formed the point of eruption.
The Governor, Francesco Valenza, having manned a boat, rowed out towards the fiery column, and on arriving found it to consist of black scoriaceous bombs, which were being hurled into the air to a height of nearly thirty yards; some of them burst in the air, others, discharging steam, ran hissing over the water; many of them were very hot, some even red-hot.
Both varieties include a few scattered fragments, large and small, of dark- coloured scoriaceous rocks, the cells of some of which are partially filled with the white earthy stone; they likewise include some huge blocks of a cellular porphyry.
The same lava, for example, may be glassy, or scoriaceous, or stony, or porphyritic, according to the more or less rapid rate at which it cools. It would be easy to multiply examples and authorities to prove the gradation of the Plutonic into the trap rocks.
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