CUVIER’S CATACLYSMS. 59 
natural forces, or mechanical agents, at present constantly 
but slowly at work in changing the earth’s surface: first, 
vain, which washes down the steep mountain slopes 
and heapes up débris at their foot; secondly, flowing 
waters, which carry away this débris and deposit 
it as mud in stagnant waters; thirdly, the sea, whose 
breakers gnaw at the steep sea coasts, and throw up 
“dunes” on the flat sea margins; finally and fourthly, 
volcanos, which break through and heave up the strata of 
the earth’s hardened crust, and pile up and scatter about the 
products of their eruptions. Whilst Cuvier recognizes the 
constant slow transformation of the present surface of the 
earth by these four mighty causes, he asserts at the same 
time that they would not have sufficed to effect the 
revolutions of the remote ages, and that the anatomical 
structure of the’ earth’s surface cannot be explained by 
the necessary action of those mechanical agents: the great 
and marvellous revolutions of the whole earth’s surface 
must, according to him, have been rather the effects of very 
peculiar causes, completely unknown to us; the usual thread 
of development was broken by them, and the course of 
nature altered. 
These views Cuvier explained in a special work “On the 
Revolutions of the Earth’s Surface, and the Changes which 
they have wrought in the Animal World.” They were 
maintained, and generally accepted for a long time, and be- 
came the greatest obstacle to the development of a natural 
history of the creation. For if such all-destructive revolu- 
tions had actually occurred, of course a continuity of the 
development of species, a connecting thread in the organic 
history of the earth, could not be admitted at all, and we 
? 
