Evidence of this [transformation of animals into fossils] is that parts of aquatic animals and perhaps of naval gear are found in rock in hollows on mountains, which water no doubt deposited there enveloped in sticky mud, and which were prevented by coldness and dryness of the stone from petrifying completely. Very striking evidence of this kind is found in the stones of Paris, in which one very often meets round shells the shape of the moon.

It seems wonderful to everyone that sometimes stones are found that have figures of animals inside and outside. For outside they have an outline, and when they are broken open, the shapes of the internal organs are found inside. And Avicenna says that the cause of this is that animals, just as they are, are sometimes changed into stones, and especially [salty] stones. For he says that just as the Earth and Water are material for stones, so animals, too, are material for stones. And in places where a petrifying force is exhaling, they change into their elements and are attacked by the properties of the qualities [hot, cold, moist, dry] which are present in those places, and in the elements in the bodies of such animals are changed into the dominant element, namely Earth mixed with Water; and then the mineralizing power converts [the mixture] into stone, and the parts of the body retain their shape, inside and outside, just as they were before. There are also stones of this sort that are [salty] and frequently not hard; for it must be a strong power which thus transmutes the bodies of animals, and it slightly burns the Earth in the moisture, so it produces a taste of salt.

Mountains have been formed by one [or other] of the causes of the formation of stone, most probably from agglutinative clay which slowly dried and petrified during ages of which we have no record. It seems likely that this habitable world was in former days uninhabitable and, indeed, submerged beneath the ocean. Then, becoming exposed little by little, it petrified in the course of ages.

Of what use are the great number of petrifactions, of different species, shape and form which are dug up by naturalists? Perhaps the collection of such specimens is sheer vanity and inquisitiveness. I do not presume to say; but we find in our mountains the rarest animals, shells, mussels, and corals embalmed in stone, as it were, living specimens of which are now being sought in vain throughout Europe. These stones alone whisper in the midst of general silence.

Pure earth does not petrify, because the predominance of dryness over [i.e. in] the earth endows it not with coherence but rather with crumbliness. In general, stone is formed in two ways only (a) through the hardening of clay, and (b) by the congelation [of waters].