On a Piece of Chalk 99 



was present at the Battle of Hastings. The ancestors of 

 Terebratulina caput serpentis may have been present at 

 a battle of Ichthyosauria in that part of the sea which, 

 when the chalk was forming, flowed over the site of 

 Hastings. While all around has changed, this Terebratu- 5 

 Una 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, 10 

 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 will- 

 ingly rest in facts and immediate causes, but seeks always 

 after a knowledge of the remoter links in the chain of 15 

 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 our- 

 selves how these changes have occurred. And when we 20 

 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- 25 

 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 30 

 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 



