cuvier's cataclysms. 59 



natural forces, or mechanical agents, at present constantly 

 but slowly at work in changing the earth's surface : first, 

 rain, which washes down the steep mountain slopes 

 and heaps up debris at their foot; secondly, flowing 

 waters, which carry away this debris and deposit 

 ii as mud in stagnant waters ; thirdly, the sea, whose 

 bieakers gnaw at the steep sea coasts, and throw up 

 " dunes " on the flat sea margins ; finally and fourthly, 

 vdcanos, 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 



