WORK IN PALEZONTOLOGY 126 
in general was published at the end of his Systeme 
des Animaux sans Vertcbres (pp. 401-411), in 1801, 
a year before the publication of the AHydrogéologie. 
~ h sive 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 cal- 
careous 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 
