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Updated: April 30, 2025
We ought not, however, to suppose, in hardly any instance, that the whole body of matter, forming a volcanic island, has been erupted at the level, on which it now stands: the number of dikes, which seem invariably to intersect the interior parts of every volcano, show, on the principles explained by M. Elie de Beaumont, that the whole mass has been uplifted and fissured.
In a volcano, molten rock from a region deep below, which we may call its reservoir, ascends through a pipe or fissure to the surface. The materials erupted may be spread over vast areas, or, as is commonly the case, may accumulate about the opening, forming a conical pile known as the volcanic cone.
The Chevalier de Dolomieu supposes these rocks to have been erupted lavas, originally containing cavities; and that these cavities in the solid rock had been afterwards filled and crystallised, by means of infiltration, with the different substances which are found variously concreted and crystallised within the solid rocks.
The basalt, which is one of the igneous rocks, has been erupted into the coal-seam in a state of fusion, and the heat contained in it has been sufficient to cause the disentanglement of the gases, the extraction of which from the coal brings about the condition of anthracite and graphite. The mention of graphite brings us to the next stage.
I made my way by tortuous walking round the erupted masses of lava, and also by portions of the lava streams, which, on losing their original fluidity, had become piled up and contorted into gigantic masses. At the extreme edges of the flow, where the lava had become viscid, these folds and contortions were very remarkable.
It has even been supposed to form part of a crater; but so far is this from having been the case, that the summit of Flagstaff Hill once formed the lower extremity of a sheet of lava and ashes, which were erupted from the central, crateriform ridge.
This is the cause of the difference between those erupted lavas, and our whin-stone, toad-stone, and the Swedish trap, which may be termed subterraneous lava. The visible effects of those different operations may now be mentioned.
Jago, where the horizontally upraised, calcareous stratum dips into the sea, directly beneath a cone of subsequently erupted lava.
"More tourist, maybe," Hassan offered. Rick looked around. In the echoing chamber it was hard to tell the direction from which the footsteps were coming, and whether it was one person or many. Hassan was probably right, he thought. It was late enough in the day for tourists to be arriving. And on the heels of the thought, Arabs erupted from the entrance through which they had come!
It is a remarkable fact that all the many small islands, lying far from any continent, in the Pacific, Indian, and Atlantic Oceans, with the exception of the Seychelles and this little point of rock, are, I believe, composed either of coral or of erupted matter.
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