CHAP. I.] INTRODUCTION. 1 7 



of peculiar creatures are few, yet sufficient to give a 

 marked character to it, whilst the other portions of its 

 population are derived from the higher zones, and 

 must be regarded as colonists. As we descend deeper 

 and deeper in this region, its inhabitants become more 

 and more modified, and fewer and fewer, indicating 

 our approach towards an abyss where life is either 

 extinguished, or exhibits but a few sparks to mark 

 its lingering presence." ' 



Eorbes pointed out that the groups of animals having 

 their maximum development in these several zones 

 are thoroughly characteristic, and that groups of 

 representative forms occupy the same zones all over 

 the world, so that on examining an assemblage of 

 marine animals from any locality, it is easy to tell 

 from what zone of depth they have been procured. 

 At all periods of the earth's history, there has been 

 the same clear definition of zones of depth, and fossil 

 animals from any particular zone are in some sense 

 representative of the fauna of the corresponding zone 

 at the present day. We can, therefore, usually tell 

 Avith tolerable certainty to which zone of depth a par- 

 ticular assemblage of fossils is to be referred. 



Although we must now greatly modify our views 

 with regard to the extent and fauna of the zone of 

 deep-sea corals, and give up all" idea of a zero of 

 animal life, still we must regard Forbes' investiga- 

 tion into the bathymetrical distribution of animals 

 as marking a great advance on previous knowledge. 

 His experience was much wider than that of any 

 other naturalist of his time ; the practical difficulties 

 in the way of testing his conclusions Avere great, and 



' Edward Foi'bes, Natural History of the European Seas, p. 26. 



C 



