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It has more than once happened, that the lava-streams of Etna, in their descent from the crater of eruption, have come to a precipitous wall of rock, over which they have plunged in a cascade similar to that formed by the lava of Vesuvius in 1855, but on a less magnificent scale, as respects the height of the fall.
Subsequently to the formation of the lava-streams above described, and probably after the lapse of a lengthened period, the region of the Haute Loire and Ardèche became the scene of a fresh outburst of volcanic action, during which the surface of the older lavas, or of the fundamental granite, was covered by numerous crater-cones and lava-streams strewn along the banks of the Allier and of the Loire for many miles.
I remember having been much struck with the evidence of denudation, when viewing volcanic islands, which have been worn by the waves and pared all round into perpendicular cliffs of one or two thousand feet in height; for the gentle slope of the lava-streams, due to their formerly liquid state, showed at a glance how far the hard, rocky beds had once extended into the open ocean.
I held my commanding foothold in the sky for two hours, gazing on the glorious landscapes spread maplike around the immense horizon, and tracing the outlines of the ancient lava-streams extending far into the surrounding plains, and the pathways of vanished glaciers of which Shasta had been the center.
During the cretaceo-oolitic period this certainly appears to have been the case at the Puente del Inca, judging from the number of intercalated lava-streams in the lower 3,000 feet of strata; but generally, the volcanic orifices seem at this time to have existed as submarine solfataras, and were certainly quiescent compared with their state during the accumulation of the porphyritic conglomerate formation.
The greatest national sin of Christian times has wrought the greatest national overthrow. The hidden evil of the land, which long smouldered underground, has blazed forth at last like a volcano, bursting in sunder the most solid of human institutions, and pouring the lava-streams of ruin and desolation even to the remotest shores where the spoil of guilt had been partaken.
These points will be better understood when I come to give an account of the several groups; and in doing so I will commence with that of the Cantal. The original crater-cones of this group have entirely disappeared throughout the long ages which have elapsed since the lava-streams issued forth from their internal reservoirs.
I remember having been much struck with the evidence of denudation, when viewing volcanic islands, which have been worn by the waves and pared all round into perpendicular cliffs of one or two thousand feet in height; for the gentle slope of the lava-streams, due to their formerly liquid state, showed at a glance how far the hard, rocky beds had once extended into the open ocean.
The streams are separated from each other by beds of fragmentary brown scoriae, firmly cemented together, and including a few well-rounded pebbles of lava. From their general appearance, I suspect that these lava-streams flowed at an ancient period under the pressure of the sea, when the Atlantic covered the Pampas and washed the eastern foot of the Cordillera.
And now he reached the base of a conical hill, the summit of which seemed to have been split into two parts: and the sinuous tracks of the lava-streams, now cold, and hard, and black, adown its sides, convinced him that this was the volcano, from whose rent crater had poured the bituminous fluid so fatal to the vegetation of that region.
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