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This, however, is limited to the period of geology which gives record of organic life, and not to the earlier astronomical period; nor does it exclude changes in temperature, climate, distribution of seas and lands; nor does it "affirm positively that there may not have been in past ages explosions more violent than that of Krakatoa; lava-streams more extensive than that of Skaptar-Jokul, and earthquakes more powerful than that which uplifted five or six hundred miles of the Pacific coast of South America six or seven feet."
Here and there hang, at an impossible angle, black lava-streams which were powerless to reach the plain: they resembled nothing so much as the gutterings of a candle hardening on the outside of its upright shaft. Evidently they had flowed down the slope in a half fluid state, and had been broken by contraction when cooling.
But although we have no reliably historical record of volcanic action amongst the mountains of the Mont Dôme group, the fact that these are, comparatively, extremely recent will be evident to an observer visiting this district, and this conclusion is based on three principal grounds: first, because of the well-preserved forms of the original craters, though generally composed of very loose material, such as ashes, lapilli, and slag; secondly, because of the freshness of the lava-streams over whose rugged surfaces even a scanty herbage has in some places scarcely found a footing; and thirdly, because the lava from the crater-cones has invaded channels previously occupied by the earlier lavas, or those which had been eroded since the overflow of the great basaltic sheets of Mont Dore.
Small basaltic craters, with hollows at their bases. Albemarle Island; fluid lavas, their composition. Craters of tuff; inclination of their exterior diverging strata, and structure of their interior converging strata. James Island, segment of a small basaltic crater; fluidity and composition of its lava-streams, and of its ejected fragments.
Accompanying the lava-streams are great beds of volcanic agglomerate, which Mr. Scrope considers to have been formed contemporaneously with the lava which they envelop, and to be due to torrents of water tumultuously descending the sides of the volcano at periods of eruption, and bearing down immense volumes of its fragmental ejecta in company with its lava-streams.
They were black mounds, ten or twelve feet in height, piled upon each other in the most varied forms, their bases covered with a broad band of whitish-coloured moss, while the tops were broken into peaks and cones of the most fantastic shapes. These lava-streams seem to date from a recent period, as the masses are somewhat scaly and glazed.
Seeing every height crowned with its crater, and the boundaries of most of the lava-streams still distinct, we are led to believe that within a period geologically recent the unbroken ocean was here spread out. Hence, both in space and time, we seem to be brought somewhat near to that great fact that mystery of mysteries the first appearance of new beings on this earth.
A few years before it had flowed down red-hot. Further up we reached large stretches of rock. Here wild vines and lupines were growing in patches where the lava had decayed into soil. Then came bare slopes with dark hollow and sharp ridges. We walked on old stiff lava-streams. Sometimes we had to plod through piles of coarse, porous cinders.
From the midst of the Atria rises the central cone, formed of cinders, scoriæ, and lava-streams, and fissured along lines radiating from the axis. This cone is very steep, the angle being about 40°-45° from the horizontal, and is formed of loose cindery matter which gives way at every step, and is rather difficult to climb.
Some of this lava, ten years old, as we cross its rugged and black surface presents gaping fissures, showing the mass to be red-hot a few feet from the surface, so slow is the process of cooling. These lava-streams some of them reaching to the sea-coast have issued forth from the Atria at successive periods of eruption.
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