Rock-stone and granate are one and the same substance, but I have used both denominations, because there are many persons who make two different species of them. It is the same with respect to flints and free-stone in large pieces; I look on them as kinds of granate, and I call them large flints, because they are disposed like calcinable stone in strata, and to distinguish them from the flints and free-stone in small masses, and the round flints which have no regular quarries, and whose beds have a certain extent; these are of a modern formation, and have not the same origin as the flints and free-stone in large lumps, which are disposed in regular strata.
I understand by the term slate, not only the blue, which all the world knows, but white, grey, and red slate: these bodies are generally met with below laminated clay, and have every appearance of being nothing more than clay hardened in this strata. Pit coal and jet are matters which also belong to clay, and are commonly under slate. By the word tuffa, I understood not only the common pumice which appears full of holes, and, as I may say, organized, but all the beds of stone made by the sediment of running waters, all the stalactites,
incrustations, and all kinds of stone that dissolve by fire. It is no ways doubtful that these matters are not modern, and that they every day grow. Tuffa is only a mass of lapidific matter in which we perceive no distinct strata: this matter is disposed generally in small hollow cylinders, irregularly grouped and formed by waters dropt at the foot of mountains, or on the slope of hills, which contain beds of marl or soft and calcareous earth; these cylinders, which make one of the specific characters of this kind of tuffa, is either oblique or vertical according to the direction of the streams or water which form them. These sort of spurious quarries have no continuation; their extent is very confined, and proportionate to the height of the mountains which furnish them with the matter of their growth. The tuffa every day receiving lapidific juices, those small cylindrical columns, between which intervals are left, close at last, and the whole becomes one compact body, but never acquires the hardness of stone, and is what Agricola terms Marga tofocea fistulosa. In this tuffa are generally found impressions of leaves, trees, and plants, like those which grow in the environs: terrestrial shells also are often met with, but never any of the
marine kind. The tuffa is certainly therefore a new matter, which must be ranked with stalactites, incrustations, &c. all these new matters are kinds of spurious stones, formed at the expence of the rest, but which never arrive at true petrification.
Crystal, precious stones, and all those which have a regular figure, even small flints formed by concentrical beds, whether found in perpendicular cavities of rocks, or elsewhere, are only exudations of large flints, or concrete juices of the like matters, and are therefore spurious stones, and real stalactites of flint or rock.
Shells are never found either in rock, granate, or free-stone, although they are often met with in vitrifiable sand, from which these matters derive their origin; this seems to prove that sand cannot unite to form free-stone or rock but when it is pure, and that if it is mixed with shells or substances of other kinds, which are heterogeneous to it, its union is prevented. I have observed the little pebbles which are often found in beds of sand mixed with shells, but never found any shell therein: these pebbles are real concretions of free-stone formed in the sand in the places where it is not
mixed with heterogeneous matters which oppose the formation of larger masses.
We have before observed, that at Amsterdam, which is a very low country, sea shells were found at 100 feet below the earth, and at Marly-la-Ville, six miles from Paris, at 75 feet; we likewise meet with the same at the bottom of mines, and in banks of rocks, beneath a height of stone 50, 100, 200, and 1000 feet thick, as is apparent in the Alps and Pyrennees, where, in the lower beds, shells and other marine productions are constantly found. But to proceed in order, we find shells on the mountains of Spain, France, and England; in all the marble quarries of Flanders, in the mountains of Gueldres, in all hills around Paris, Burgundy, and Champagne; in one word, in every place where the basis of the soil is not free-stone or tuffa; and in most of these places there are more shells than other matters in the substance of the stones. By shells, I mean not only the wrecks of shell-fish, but those of crustaceous animals, the bristles of sea hedge-hogs, and all productions of the sea insects, as coral, madrepores, astroites, &c. We may easily be convinced by inspection, that in most calculable stones and marble, there is so
great a quantity of these marine productions that they appear to surpass the matter which unites them.
But let us proceed; we meet with these marine productions even on the tops of the highest mountains; for example, on Mount Cenis, in the mountains of Genes, in the Apennines, and in most of the stone and marble quarries in Italy; also in the stones of the most ancient edifices of the Romans; in the mountains of Tirol; in the centre of Italy, on the summits of Mount Paterne, near Bologna; in the hills of Calabria; in many parts of Germany and Hungary, and generally in all the high parts of Europe[233:A].