146 ELEMENTS OF BIOLOGY. 



and does not apply in any manner that admits of being 

 traced to early geological epochs. The general result of 

 this law is, that existing zoological provinces are in some 

 cases older than the species by which they are now char- 

 acterised. 



The vertical 01 /^^z/^)''^'^^^^''^^'^ distribution of animals relates 

 to the limits of depth within which each marine species is 

 confined. In many cases it is found that marine animals 

 occupy definite bathymetrical zones, existence being impos- 

 sible, or at any rate difficult, at depths greater or less than 

 those comprised within the limits of the zone which each 

 inhabits. In accordance with the facts at that time known, 

 naturalists formerly accepted the following four bathymetrical 

 zones, as being characterised each by its peculiar fauna : — 



T. The Littoral zone, or the tract between tide-marks. 



2. The Laminarian zone, from low water to 15 fathoms. 



3. The Coralline zone, from 15 to 50 fathoms. 



4. The Deep-sea coral zone, from 50 to 100 fathoms or 

 more. 



Beyond a depth of something between 100 and 200 fa- 

 thoms it was formerly believed that marine life did not ex- 

 tend. Recent researches, however, especially those by Drs 

 Carpenter and Wyville Thomson and Mr Gwyn Jeffreys, 

 have greatly modified the above generalisation, and have led 

 to the establishment of conclusions of the greatest import- 

 ance and interest. The value of the Littoral zone, or the 

 tract between tide-marks, as a marine province, has not been 

 aftected by these discoveries, but the importance of the 

 others has been greatly reduced ; and we might well adopt 

 the views of Mr Gwyn Jeffreys, and consider that there are 

 but two chief bathymetrical zones, the littoral and the sub- 

 marifte. 



The next important point which has been brought to 

 light is, that life extends to all depths in the ocean, marine 

 animals having been dredged in abundance from a depth 

 of 2300 fathoms, or not far short of three miles. If, there- 



