58 THE HISTORY OF CREATION. 
was in one sense, yet in another it became to him the source 
of a very serious error. For as he considered the charac- 
teristic petrifactions of each individual group of strata 
(which had been deposited during one main period of the 
earth’s history) to be entirely different from those of the 
strata lying above or below, and as he erroneously believed 
that one and the same species of animal was never found in 
two succeeding groups of strata, he arrived at the false idea, 
which was accepted as a law by most subsequent naturalists, 
that a series of quite distinct periods of creation had 
succeeded one another. Each period was supposed to have 
had. its special animal and vegetable world, each its peculiar 
specific Fauna and Flora. 
Cuvier imagined that the whole history of the earth’s 
crust, since the time when living creatures had first appeared 
on the surface, must be divided into a number of perfectly 
distinct periods, or divisions of time, and that the individual 
periods must have been separated from one another by 
peculiar revolutions of an unknown nature (cataclysms, or 
catastrophes). Each revolution was followed by the utter 
annihilation of the till then existing animals and plants, and 
after its termination a completely new creation of organic 
forms took place. A new world of animals and plants, 
absolutely and specifically distinct from those of the preced- 
ing historical periods, was called into existence at once, and 
now again peopled the globe for thousands of years, till it 
again perished suddenly in the crash of a new revolution. 
About the nature and causes of these revolutions, Cuvier 
expressly said that no idea could be formed, and that the 
present active forces in nature were not sufficient for their 
explanation. Cuvier points out four active causes as the 
