CHAP, x.] CONTINUITY OF THE CHALK. 495 



most cephalopods and all pteropods, heteropods, and 

 other surface living animals of high type, even to 

 their extinction. By oscillations of 500 feet up or 

 down, the great mass of gasteropods, and all reef- 

 building corals, would be forced to emigrate, would 

 become modified, or would be destroyed, and another 

 hundred fathoms would exterminate the greater num- 

 ber of bivalves ; while elevations and depressions to 

 ten times that amount might only slightly affect the 

 region of brachiopods, echinoderms, and sponges. 



After a careful consideration of the results of recent 

 investigations, we are strengthened in our confidence 

 in the truth of the opinion which we previously held, 

 that the various groups of fossils characterizing the 

 tertiary beds of Europe and North America represent 

 the constantly altering fauna of the shallower por- 

 tions of an ocean whose depths are still occupied by 

 a deposit which has been accumulating continuously 

 from the period of the pre-tertiary chalk, and w r hich 

 perpetuates with much modification the pre-tertiary 

 chalk fauna. I do not see that this view militates in 

 the least against the " reasoning and classification" of 

 that geology which we have learned from Sir Charles 

 Lyell ; our dredgings only show that these abysses of 

 the ocean abysses which Sir Charles Lyell admits in 

 the passage quoted above, to have outlasted on account 

 of their depth a succession of geological epochs are 

 inhabited by a special deep-sea fauna, possibly as persis- 

 tent in its general features as the abysses themselves. 

 I have said at the beginning of this chapter, that I 

 believe the doctrine of the 'continuity of the chalk, 5 

 as understood by those who first suggested it, now 

 meets with very general acceptance ; and in evidence 



