In the mountains of Verona the red marble is found all mixed with
cockle shells turned into stone; some of them have been filled at
the mouth with the cement which is the substance of the stone; and
in some parts they have remained separate from the mass of the rock
which enclosed them, because the outer covering of the shell had
interposed and had not allowed them to unite with it; while in other
places this cement had petrified those which were old and almost
stripped the outer skin.