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Updated: May 24, 2025
The ancient submarine orifices whence the porphyries and their fragments were ejected having been arranged in a band, like most still active volcanoes, accounts for the thickness, the narrowness, and linear extension of this formation.
The peculiar gallstone-yellow variety was common, but less numerous than at Port S. Julian, where it formed nearly one-third of the mass of the gravel; the remaining part there consisting of pale grey and greenish porphyries with many crystals of feldspar.
This land, probably islands, must have been mainly formed of porphyries, with some mica-slate, whence the quartz was derived, and with some red sandstone and jaspery rocks.
Next, around the whole runs a pattern of different kinds of stone let into the marble with a beautiful and well-varied arrangement of variegated marbles and rare stones, such as serpentines, porphyries, and jaspers.
The feldsparry lavas of the Peak, of a much less black tinge than those of Arso in the island of Ischia, whiten at the edge of the crater from the effect of the acid vapours; but internally they are not found to be colourless like that of the feldsparry lavas of the Solfatara at Naples, which perfectly resemble the trappean porphyries at the foot of Chimborazo.
The threat was enough to raise a howl from the Egyptian; but this Porphyries soon put a stop to, and Sachepris, with perfect veracity, told her tale of all that had happened till Herse's return to the vessel.
On all sides the borders of this highland area are deeply grooved by numberless streams flowing in narrow gorges. Against its nucleus of very ancient granites and porphyries the Ozark series of magnesian limestone was laid down. Then the area occupied by these rocks was elevated, and around its margins were deposited successively the other members of the Paleozoic.
The earlier eruptions seem to have been chiefly granitic, though this must not be understood in too wide a sense, since there are granite formations even as late as the Tertiary period; those of the middle periods were mostly porphyries and basalts; while in the more recent ones, lavas predominate.
The clay-slate is in many parts capped by a thick mass of fragments of the same rock, firmly recemented; and both together have been injected and broken up by very numerous hillocks, ranging north and south, of lilac, white, dark and salmon- coloured porphyries: one steep, now denuded, hillock of porphyry had its face as distinctly impressed with the angles of a fragmentary mass of the slate, with some of the points still remaining embedded, as sealing-wax could be by a seal.
Parts pass into a very pale green, semi- porcellanic stone. Ninthly: red or brown coarse conglomerate, three or four hundred feet thick, formed chiefly of pebbles of porphyries, with volcanic particles, in an arenaceous, non-calcareous, fusible basis: the upper two feet are arenaceous without any pebbles.
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