ix.] ON A PIECE OF CHALK. 199 



site of Hastings. While all around has changed, this 

 Terebratulina has peacefully propagated its species from 

 generation to generation, and stands to this day, as a 

 living testimony to the continuity of the present with 

 the past history of the globe. 



Up to this moment I have stated, so far as I know, 

 nothing but well-authenticated facts, and the immediate 

 conclusions which they force upon the mind. 



But the mind is so constituted that it does not 

 willingly rest in facts and immediate causes, but seeks 

 always after a knowledge of the remoter links in the 

 chain of causation. 



Taking the many changes of any given spot of the 

 earth s surface, from sea to land and from land to sea, 

 as an established fact, we cannot refrain from asking 

 ourselves how these changes have occurred. And when 

 we have explained them — as they must be explained 

 — by the alternate slow movements of elevation 

 and depression which have affected the crust of the 

 earth, we go still further back, and ask, Why these 

 movements ? 



I am not certain that any one can give you a satis- 

 factory answer to that question. Assuredly I cannot. 

 All that can be said, for certain, is, that such movements 

 are part of the ordinary course of nature, inasmuch as 

 they are going on at the present time. Direct proof 

 may be given, that some parts of the land of the 

 northern hemisphere are at this moment insensibly rising 

 and others insensibly sinking ; and there is indirect, but 

 perfectly satisfactory, proof, that an enormous area now 

 covered by the Pacific has been deepened thousands of 

 feet, since the present inhabitants of that sea came into 

 existence. 



Thus there is not a shadow of a reason for believing 



