ADDITIONS to the Article, Of Caverns, Vol. I. p. 442.

Of Caverns formed by the Primitive Fire.

IN my theory of the Earth, I mentioned on|ly two kinds of caverns, the one produced by the fire of volcano's, and the other by the motion of subterraneous waters. Those two species of caverns are not situated at great depths. They are even new, when compared with those vast cavities, which were formed at the time the globe first assumed a solid form; for, at this pe|riod, all the supersicial eminences and hollows, and all the cavities in the interior parts of the earth, especially near the surface, were produced. Several of those caverns produced by the primi|tive sire, after being supported for some time, have afterwards split by cooling, which diminish|es the volume of every kind of matter; these would soon fall in, and, by their sinking, form basins or reservoirs for the sea, into which the waters, formerly much elevated above this level, ran, and abandoned the lands which they origi|nally Page  223 covered. It is more than probable, that a certain number of these ancient caverns still subsist in the interior parts of the globe, and by their sinking may produce similar effects, and give rise to new receptacles to the waters. In this case, they will partly abandon the basin which they now occupy, and run, by their na|tural propensity, into these lower places. For example, we find beds of sea shells in the Pyren|nees 1500 fathoms above the present level of the ocean. Hence it is certain, that the waters, when these shells were formed, rose 1500 fa|thoms higher than they do at present. But, when the caverns, which supported the lands that are now the bed of the Atlantic ocean, sunk, the waters which covered the Pyrennees and the whole of Europe would run with rapi|dity into these reservoirs, and, of course, leave uncovered all the lands in this part of the world. The same revolution would extend to every o|ther country. The waters appear to have ne|ver reached the summits of the highest moun|tains; because they exhibit no relicks of marine productions, and no sufficient marks of a long abode of the waters. However, as some of the matters of which they are composed, though all of the vitrescent kind, seem to have derived their solidity and consistence from the interven|tion and cement of water, and as they appear to have been formed, as already remarked, in Page  224 the masses of sand, or glass dust, which former|ly lay on the peaks of mountains, but which, in the progress of time, have been carried down to their bottoms by the rains, we cannot pro|nounce positively, that the waters of the sea ne|ver stood higher than the places where shells are now found: The waters have perhaps stood much higher, even before their temperature permitted the existence of shells. The greatest height reached by the universal ocean is to us un|known. But we know that the waters were ele|vated from 1500 or 2000 fathoms above their present level; since shells are found in the Pyrennees at 1500 hundred fathoms, and in the Cordelieres at 2000.

If all the peaks of mountains were formed of solid glass, or of other matters immediately pro|duced by fire, it would be unnecessary to have recourse to the abode of the waters, or to any other cause, in order to conceive how they as|sumed their consistence. But most peaks of mountains seem to be composed of matters, which, though vitrifiable, have acquired their so|lidity by the intervention of water. We cannot, therefore, determine whether their consistence is solely owing to the primitive fire, or whe|ther the intervention and cement of water were not requisite to complete the operation of fire, and to bestow on these vitrifiable masses the qualities which they possess. Besides, this supposition Page  225 prevents not the primitive fire, which at first produced the greatest inequalities on the globe, from being the chief cause of those chains of mountains that traverse its surface, and particu|larly of their cores or nuclei; but the contours of these same mountains have perhaps been dis|posed and fashioned by the waters at a subse|quent period; for it is upon these contours, and at certain heights, that shells and other produc|tions of the sea are found.

To acquire a clear notion of the ancient ca|verns formed by the primitive fire, we must suppose the globe to be deprived of all its wa|ters, and of all the matters which cover its sur|face, to the depth of ten or twelve hundred feet. By removing in idea this external bed of earth and water, the globe will present to us the form it possessed about the time of its first con|solidation. The whole mass was composed of vitreous rock, or, if you will, of melted glass; and this matter, in cooling and acquiring con|sistence, produced, like all other melted bodies, eminences, depressions, and cavities, upon the whole surface of the globe. These internal ca|vities formed by fire, are the primitive caverns, and they are more numerous in the southern than in the northern regions; because the rota|tory motion, which elevated the equatorial re|gions before consolidation, likewise produced the greatest derangement of the matter, and, by Page  226 retarding the consolidation, would concur with the action of the fire in giving rise to a greater number of inequalities in this than in any other part of the globe. The waters coming from the Po•es could not approach those burning re|gions before they cooled. The vaults which supported these regions having successively fal|len in, the surface sunk and broke in a thousand places. For this reason, the greatest inequali|tie of the globe are found in the equatorial re|gions: There the primitive caverns are more numerous than in any other part of the earth. They are likewise more profound, i. e. perhaps five or six leagues deep; because the matter of the globe, while in a liquid state, was agitated to that depth by the motion of rotation. But all the caverns in high mountains derive not their origin from the operation of primitive fire. Those alone which are deeply situated below the mountains can be ascribed to this cause. The more exterior and more elevated have been form|ed, as already remarked, by the operation of secondary causes. Hence the globe, deprived of its waters and the matters transported by them, would present to us a surface much more irregular than it appears with the aid of this co|vering. The great chains of mountains and their peaks and ridges, have not now the ap|pearance of half of their real height. The whole are att•••ed by their bases to a vitrifiable Page  227 rock, and are of the same nature. Thus we should reckon three species of caverns produced by Nature: The first by the force of the primi|tive fire; the second by the action of water; and the third by that of subterraneous fires: Each of these caverns, though different in their origin, may be distinguished by examining the matters they contain, or by which they are sur|rounded.