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.
De Causis Proprietatum Elementorum
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.
Now it must be asked if we can comprehend why comets signify the death of magnates and coming wars, for writers of philosophy say so. The reason is not apparent, since vapor no more rises in a land where a pauper lives than where a rich man resides, whether he be king or someone else. Furthermore, it is evident that a comet has a natural cause not dependent on anything else; so it seems that it has no relation to someone's death or to war. For if it be said that it does relate to war or someone's death, either it does so as a cause or effect or sign.
The beaver is an animal which has feet like those of a goose for swimming and front teeth like a dog, since it frequently walks on land. It is called the castor from 'castration,' but not because it castrates itself as Isodore says, but because it is especially sought for castration purposes. As has been ascertained frequently in our regions, it is false that when it is bothered by a hunter, it castrates itself with its teeth and hurls its musk [castoreum] away and that if one has been castrated on another occasion by a hunter, it raises itself up and shows that it lacks its musk.
To say that there is a soul in stones simply in order to account for their production is unsatisfactory: for their production is not like the reproduction of living plants, and of animals which have senses. For all these we see reproducing their own species from their own seeds; and a stone does not do this at all. We never see stones reproduced from stones; ... because a stone seems to have no reproductive power at all.
Albertus [Magnus] ... debased the doctrine of Aristotle with the itch of the chemists flowing with the bloody flux of quicksilver and the stench of sulphur.
Georgius Agricola in De Orta et Causis Subterraneorum