By examining these vitrifiable matters, we find only a few sea shells there, and those not placed in beds, but dispersed about as if thrown there by chance. For example, I have never seen them in free-stone; that stone which is very plenty in certain places, is only composed of sandy parts, which are re-united, and are only met with in sandy soils; and the quarries of it are generally in peaked hills and in divided eminences. We may work these quarries in all directions, and if they are in large beds, they are much farther from each other than in quarries of calcinable stone or marble. Blocks of free-stone may be cut of all dimensions and in all directions, although it is difficult to work,
it nevertheless has but a degree of hardness sufficient to resist powerful strokes without splitting; for friction easily reduces it into sand, excepting certain black pieces found therein, and which are so very hard, that the best files cannot touch them. Rock is vitrifiable as free-stone, and of the same nature, only it is harder and the parts more connected. This also contains many hard pieces, as may easily be remarked on the summits of high mountains, which cut and tear the shoes of travellers. This rocky stone, which is found at the top of high mountains, and which I look upon as a kind of granite, contains a great quantity of talky leaves, and is so hard as not to be worked but by an infinite deal of labour.
I have narrowly examined these sharp pieces which are found in free-stone and rock, and have discovered it to be a metallic matter, melted and calcined by a very violent fire, and which perfectly resembles certain substances thrown out by the volcanos, of which I saw a great quantity when I was in Italy, where the people called them Schiarri. They are very heavy black masses, on which neither water nor the file can make any impression, and the matter
of which is different from that of the lava; for this is a kind of glass, whereas the other appears to be more metallic than vitreous. The sharp pieces in free-stone, and rock, resemble greatly the first matter, which seems still to prove that all these matters have been formerly liquified by fire.
We sometimes see on the upper parts of mountains, a prodigious quantity of blocks of this mixed rock; their position is so irregular that they appear to have been thrown there by chance, and it might be thought they had fallen from some neighbouring height, if the places where they are found were not raised above the other parts. But their vitrifiable nature, and their angular and square figures, like those of free-stone, discover them to be of one common origin. Thus in the great beds of vitrifiable sand, blocks of free-stone and rock are formed, whose figures and situations do not exactly follow the horizontal position of these strata. The rain, by degrees, carried away from the summits of the hills and mountains the sand which at first covered them, and then began to furrow and cut those hills into the spaces which are found between
the nucleus in free-stone, as the hills of Fontainbleau are intersected. Each hilly point answers to a nucleus in a quarry of free-stone, and each interval has been excavated and loosened by the rain, which has caused the sand, they at first contained, to flow into the vallies; so likewise the highest mountains, whose summits are composed of rocks, and terminated by these angular blocks of granite, have formerly been covered with vitrifiable sand, and the rain having carried away the sand which covered them, they remained on the tops of the mountains in the position they were formed. These blocks generally present points; they increase in size in proportion as they descend; one block often rests upon another, the second upon a third, and so on, leaving irregular intervals between them: and as in time the rain washed away all the sand which covered these different parts on the top of the high mountains, they would remain naked, forming larger or lesser points; and this is the origin of the peaks or horns of mountains.
For supposing, as it is easy to prove by the marine productions we find there, that the chain of the Alps was formerly covered by the sea, and that above this chain there was a great
thickness of vitrifiable sand, which rendered the whole mountains a flat and level country. In this depth of sand, there would necessarily be formed granite, free-stone, flint, and all matters which take their origin and figure in sand, nearly in a similar manner to that of the crystallisation of salts. These blocks once formed would support their original positions, after the rains and torrents had carried away the sand which surrounded them, and being left bare formed all those peaks or pointed eminences we see in so many places. This is also the origin of those high and detached rocks found in China and other countries, as in Ireland, where they are called the Devil's stones, and whose formation as well as that of the peaks of mountains, had hitherto appeared so difficult to explain; nevertheless the explanation which I have given is so natural, that it directly presents itself to the mind of those who examine these objects, and I must here quote what Father Tatre says, "From Yanchu-in-yen, we came to Hoytcheou, and on the road met with something particular, rocks of an extraordinary height, of the shape of a large square tower, and situate in the midst of vast plains: I cannot account for it, unless by supposing
they were formerly mountains, from which the rain having washed away the earth that surrounded them, thus left the rocks entirely bare. What strengthens this conjecture is, that we saw some which, towards the base, are still covered with earth to a considerable height."
The summits of the highest mountains are composed of rocks, of granite, free-stone, and other hard and vitrifiable matters, and this often as deep as two or three hundred fathoms; below which we often meet with quarries of marble, or hard stone, filled with fossil-shells, and whose matter is calcinable; as may be remarked at Great Chartreuse, in Dauphiny, and on Mount Cenis, where the stone and marble, which contains shells, are some hundred fathoms below the summits, points and peaks of high mountains; although these stones are more than a thousand fathom above the level of the sea. Thus mountains, whereon we see points or peaks, are generally vitrifiable rock, and those whose summits are flat, mostly contain marble and hard stones filled with marine productions. It is the same with respect to hills, for those containing granite, or free-stone, are mostly intersected with points, eminences, cavities, depths, and small intermediate valleys; on