Lamarck drew his supplies of tertiary shells from the tertiary beds situated within a radius of from twenty-five to thirty miles from the centre of Paris, and chiefly from the village of Grignon, about ten miles west of Paris, beyond Versailles, and still a rich collecting ground for the students of the Museum and Sorbonne. He acknowledges the aid received from Defrance,[81] who had already collected at Grignon five hundred species of fossil shells, three-fourths of which, he says, had not then been described. Lamarck's first essay ("_Sur les fossiles_") on fossils in general was published at the end of his _Système des Animaux sans Vertèbres_ (pp. 401-411), in 1801, a year before the publication of the _Hydrogéologie_. "I give the name _fossils_," he says, "to remains of living beings, changed by their long sojourn in the earth or under water, but whose forms and structure are still recognizable. "From this point of view, the bones of vertebrate animals and the remains of testaceous molluscs, of certain crustacea, of many echinoderms, coral polyps, when after having been for a long time buried in the earth or hidden under the sea, will have undergone an alteration which, while changing their substance, has nevertheless destroyed neither their forms, their figures, nor the special features of their structures." He goes on to say that the animal parts having been destroyed, the shell remains, being composed of calcareous matter. This shell, then, has lost its lustre, its colors, and often even its nacre, if it had any; and in this altered condition it is usually entirely white. In some cases where the shells have remained for a long period buried in a mud of some particular color, the shell receives the same color. "In France, the fossil shells of Courtagnon near Reims, Grignon near Versailles, of what was formerly Touraine, etc., are almost all still in this calcareous state, having more or less completely lost their animal parts--namely, their lustre, their peculiar colors, and their nacre. "Other fossils have undergone such an alteration that not only have they lost their animal portion, but their substance has been changed into a silicious matter. I give to this second kind of fossil the name of _silicious fossils_, and examples of this kind are the different oysters ('des ostracites'), many terebratulæ ('des terebratulites'), trigoniæ, ammonites, echinites, encrinites, etc. "The fossils of which I have just spoken are in part buried in the earth, and others lie scattered over its surface. They occur in all the exposed parts of our globe, in the middle even of the largest continents, and, what is very remarkable, they occur on mountains up to very considerable altitudes. In many places the fossils buried in the earth form banks extending several leagues in length."[82]