Development of Animal Organization. 215 
microscopic species, some Infusoria and Algw, which belong to 
the present creation are found likewise in very old strata, as in 
those of the Carboniferous or even of the Silurian eroup*. 
There are two suppositions we can make respecting the manner 
ef the extinction of species in the history of the earth. We can 
ascribe that extinction to a change of external conditions, by 
the influence of which the life of the organisms was affected, and 
by whose continued action the species, formed for other condi- 
tions, diminished in number, and sooner or later perished alto- 
gether ; or we can ascribe the fact to the sudden action of some 
violent revolutions on the globe, by which plants and animals 
were destroyed. The latter explanation formerly predominated; 
the assumption of a general cataclysm, by which the inhabited 
earth was destroyed, led easily and almost unavoidably to this 
belief. The more extended knowledge of facts showed after- 
wards that a deluge recorded in human history could not explain 
the great diversity of fossil remains which were found in the 
strata of mountains; and the hypothesis was modified by the 
assumption of several geological cataclysms, by which, durmg 
the modelling and remodelling of the earth, various generations 
of plants and animals perished, and were imbedded in the de- 
posits of the watert. In our time the explanation is generally 
given up; but it seems that some writers go too far by an entire 
denial of lesser or much more sudden revolutions, which were 
natural consequences of the upheaving of volcanos and of chains 
of plutonic mountains. 
- That there was a succession of new species of plants and ani- 
mals, a repetition of distinct creations, is, as I have already said, 
a conception which seems not so favourable to acceptance. 
There is nothing, indeed, in actual observation of the present 
order of nature that can be comparéd to this new creation. 
Almost daily, it is true, some formerly unknown species of 
plants or animals is registered in our catalogues; but there is 
no more reason to think that they are really new than to believe 
that the New World was upheaved from the ocean at a later 
period than Europe because its discovery was only made in the 
15th century. There is, however, a power of evidence which 
cannot be annihilated by our doubts or by the difficulty of un- 
derstanding the facts; and, in our researches on natural objects 
and phenomena, it is not fair to ask what we can explain before 
we see what we are obliged to admit by the authority of obser- 
_ * Microgeologie. Das Erden- und Felsen-schaffende Wirken, &c. Leip- 
aig, 1854, fol. S. xiv. 
+ Cuvier; for instance, speaks often of such “catastrophes et révolu- 
tions subites,” in his famous and always remarkable ‘ Discours sur les 
Révolutions de‘la Surface du Globe.’ 
