WORK IN PALAIONTOLOGY 127 
sils are extinct species, and that the earth has passed 
through a general catastrophe (wx bouleversement unt- 
versel) 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 (douleversement) 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 re- 
spects its production and everything which constitutes 
itsdomain. I have already elsewhere said what should 
be thought of this so-called universal overturning of 
the globe; I return to fossils. 
“Tt is very true that, of the great quantity of fossil 
shells gathered in the different countries of the earth, 
there are yet but avery small number of species whose 
living or marine analogues are known. Nevertheless, 
although this number may be very small, which no 
one will deny, it is enough to suppress the universality 
announced in the proposition cited above 
“Tt is well to remark that among the fossil shells 
whose marine or living analogues are not known, there 
are many which have a form. closely allied to shells of 
the same genera known to be now living in the sea. 
However, they differ more or less, and cannot be rig- 
orously regarded as the same species as those known 
to be living, since they do not perfectly resemble 
them. These are, it is said,-extinct species: 
“Tam convinced that it is possible never to find, 
among fresh or marine shells, any shells perfectly sim- 
ilar to the fossil shells of which I have just spoken. I 
believe I know the reason; I proceed to succinctly 
indicate, and I hope that it will then be seen, that al- 
