1032 OYSTERS, AND ALL ABOUT THEM. 



and with the results of a most extensive series of dredinnir 



o O 



operations before him, Sir Wyville Thomson concluded 

 that " there is a direct movement of cold water from the 

 Spitzbergen Sea into the North Sea." (d) The North 

 Sea slopes to the north, becoming gradually shallower 

 towards the south. There is great abundance of animal 

 life in the Arctic regions, and great abundance of Arctic 

 types of life in the deep water in the neighbourhood of 

 the Shetland Islands, (ej The influence of the indraught 

 of cold water from the north becomes less and less appa- 

 rent as we proceed southward towards the shallower waters 

 between Scotland and Denmark. By the time w r e reach 

 the Dogger bank the northern fauna has entirely disap- 

 peared. On the western side of the British Islands, how- 

 ever, northern species are to be found down to and beyond 

 the southern limit of the British area. For this reason 

 Sir Wyville Thomson suspected that the water of the Gulf 

 Stream amalgamated, before touching these islands, with a 

 portion of the northern water. ( f ' J .... 



Let us next consider the effects of temperature. 

 Currents are an agency in the distribution of temperature 

 as well as of animal forms. Warm water has a fauna of its 

 own, cold water another and entirely distinct fauna. The 

 former, as we have seen, is brought to these shores by the 

 Gulf Stream ; the latter by the great submarine indraught 

 from the Arctic regions. The surface temperature of the 



(d) " Depths of the Sea," p. 112. 



(e) See Reports of British Association, 1862-68. Reports by Mr. 

 Gwyn Jeffreys, Rev. A. M. Norman, &c. 



( f ) The Currents, Temperatures, and Physical Conditions of the 

 Sea, in relation to Reproduction, Growth, and Migrations of Fish. 

 By W. Watt. (Prize Essays issued in connection with the Great 

 International Fisheries Exhibition, London. 1883. William Clowes 

 and Sons.) 



