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Updated: May 29, 2025
This regular disposition of lithoid basaltic lava and feldsparry vitreous lava is analogous to the phenomena of all trappean mountains; it reminds us of those phonolites lying in very ancient basalts, those close mixtures of augite and feldspar which cover the hills of wacke or porous amygdaloids: but why are the porphyritic or feldsparry lavas of the Peak found only on the summit of the volcano?
"What is this molten matter composed of which is burning under our feet?" "The same substances which we see around us granite, porphyry, and basalts, which are called igneous or Vulcanian rocks, as contrasted with the Neptunean rocks, such as gypsum or lime, clay and sandstone, the agglomeration of which is attributed to water.
Volcanoes of earlier date than the sandstone and calcareous rocks have been for ages extinguished; those which are yet in activity are in general surrounded only with breccias and modern tufas; but nothing hinders us from admitting, that the archipelago of the Canaries may exhibit some real rocks of secondary formation, if we recollect that subterranean fires have been there rekindled in the midst of a system of basalts and very ancient lavas.
Our friendly stream not only turned to the north, but afterwards to north-east and east-north-east; and though I had not succeeded in leaving it from Reedy Brook not having been able to cross the lava streams of the basaltic table land I now concluded, from the nature of the pebbles, and sands of the creek which we had crossed last, that the basalts and lavas had ceased, and that a passage to the westward would be practicable.
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