CHAP, v.] GENERAL CONCLVSIONS. 289 



Atlantic. Along this line, wliicli may be said to indicate the 

 limit between the Atlantic and the Southern Sea, the forms 

 which are specially abyssal, and which are most nearly related 

 to extinct chalk or older tertiary species, are certainly more 

 fully developed and more numerous than they are in any part 

 of the Atlantic " gulf." 



It may not be out of place, before leaving this subject, to give 

 a brief preliminary sketch of the distribution of the groups of 

 marine organisms which inhabit the depths of the sea ; or, lead- 

 ing a pelagic existence, contribute by the subsidence of their 

 hard parts after death to the formation of submarine deposits. 

 This is a subject which must be much more fully discussed 

 when the species have been determined, and the new forms de- 

 scribed ; but we have already perhaps sufficient material for a 

 general outline. 



Ko plants live, so far as we know, at great depths in the sea ; 

 and it is in all probability essentially inconsistent w^ith their nat- 



