1868.] 



on Deep-sea Dredgings. 



189 



would be very desirable to. ascertain whether the minimum temperature is 

 that of the bottom (a point of fundamental importance as regards the dis- 

 tribution of Animal life), or whether it is that of some intermediate stratum. 

 The deep-sea Sounding-apparatus with which we were provided only al- 

 lowed the attachment of the Thermometers to the extremity of the line ; 

 and it is possible, of coarse, that their minimum may represent, not the 

 temperature of the sea-bottom, but that of some higher stratum. Inde- 

 pendently, however, of the physical improbability (for the reason already 

 stated) that Sea-water at 32° should overlie water of any higher temperature, 

 which would be specifically lighter than itself, we have the evidence afforded 

 by our Sounding in 170 fathoms (§ 13) within the cold area, that the tem- 

 perature descends progressively with the depth ; at first (as elsewhere ob- 

 served) more rapidly, afterwards more slowly. And as this shallow bank 

 is of very limited extent, and the bottom in its neighbourhood must 

 become rapidly deeper, a careful examination of the bottom-temperature of 

 its inclined sides at different depths would furnish satisfactory data on this 

 point. 



IV. A general comparison of the Faunae of the different localities which 

 we had the opportunity of examining seems to warrant the conclusion that 

 the distribution of the Animal life of the seas beyond the Littoral zone* is 

 more closely related to the temperature of the water than to its depth. The 

 predominance of North British types, not merely on the southern but on the 

 northern side of the deep valley which separates the Faroe Banks from the 

 coast of Scotland, and in the warm area of the valley itself, the slight admixture 

 of exclusively Scandinavian or Boreal forms even as far north as the Faroe 

 Islands, the larger admixture of these on the shallow bank in the concurrent, 

 the still greater proportion of Boreal forms in the deeper and yet colder waters 

 of that current, and (in most striking contrast with this) the presence of 

 forms hitherto known only as inhabitants of the warmer temperate seas at the 

 like depth in the warm area not many miles off, — all indicate the intimacy of 

 the relationship between Geographical distribution and Temperature. The 

 existence of Boreal types in the midst of an area whose surface-temperature 

 is 52° [11°-1 Cent.], and whose bottom-temperature, even at 500 fathoms' 

 [914 metres] depth, is generally 47° or 48° [8°'3 or 8°-8 Cent.], is obviously 

 a phenomenon parallel to the occurrence of Alpine plants at a high eleva- 

 tion on mountains within the tropics ; and as every Botanist would regard 

 such occurrence as having no relation to elevation 'per se } but only to eleva- 



* The distribution of marine Animal life in the Littoral zone is affected by a great 

 number of conditions, which place it in altogether a different category from that of the 

 deeper seas. I am very glad to find our views on this point in harmony with those of 

 my friend Mr. J. Gwyn Jeffreys. " The bathymetrical zones have been too much 

 divided by Eisso and subsequent authors. There are two principal zones, littoral and 

 submarine ; the nature of the habitat and the supply of food influence the residence 

 and migration of animals, not the comparative depth of water."-— Annals of Natural 

 History, 4th ser. vol. ii. (1868) p. 303. 



p 2 



