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 terebratulae ('des terebratulites'), trigoniae, 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] Conchologists, he says, did not care to collect or study fossil shells, because they had lost their lustre, colors, and beauty, and they were rejected from collections on this account as "dead" and uninteresting.
"But," he adds, "since attention has been drawn to the fact that these fossils are extremely valuable _monuments_ for the study of the revolutions which have taken place in different regions of the earth, and of the changes which the beings living there have themselves successively undergone (in my lectures I have always insisted on these considerations), consequently the search for and study of fossils have excited special interest, and are now the objects of the greatest interest to naturalists." Lamarck then combats the views of several naturalists, undoubtedly referring to Cuvier, that the fossils are extinct species, and that the earth has passed through a general catastrophe (_un bouleversement universel_) with the result that a multitude of species of animals and plants were consequently absolutely lost or destroyed, and remarks in the following telling and somewhat derisive language: "A universal catastrophe (_bouleversement_) which necessarily regulates nothing, mixes up and disperses everything, is a very convenient way to solve the problem for those naturalists who wish to explain everything, and who do not take the trouble to observe and investigate the course followed by nature as respects its production and everything which constitutes its domain.