ITS EXTENT AND ITS MARINE FAUNA. 23 



Thomson and Sir John Murray, is known as the Wyville 

 Thomson Eidge. This ridge is a most important factor in the 

 distribution of life. Its biological influence is of necessity very 

 great. The so-called Grulf Stream, flowing north with a depth of 

 500 to 700 fathoms, is interrupted in its progress. Meeting with 

 this ridge it can only overflow it with a depth of 200 to 300 

 fathoms, and while it influences the whole of the ocean to the 

 bottom south of the ridge, so that the bottom temperature here 

 at 500 to 600 fathoms is 45° to 46° Fahr., north of the ridge it 

 has no influence in the Faroe Channel below the depth which it 

 has in passing over the ridge, and the bottom temperature falls 

 to 29° or 31° Fahr. Thus geographically we here find the 

 Atlantic Ocean with Atlantic temperature on the north bounded 

 by the Wyville Thomson Ridge, while just north of this the 

 Faroe Channel is found to be a southern tongue of the Arctic 

 Ocean, with the temperature which belongs to that ocean. Such 

 differences cannot but affect the conditions of life, and we 

 find that many southern species reach the Wyville Thomson 

 Ridge, but ai'e absent in the Faroe Channel, while Arctic species 

 ai'e met with in the latter which ai*e absent in the former. The 

 Wyville Thomson Ridge, therefore, must be taken to be the limit 

 both of the Atlantic Ocean and of the British fauna ; while 

 the Faroe Channel, both geographically and zoologically, must be 

 assigned to the Faroe Islands. 



Professor Edward Forbes divided the European marine fauna 

 into Provinces. Of these Provinces we are concerned with that 

 which he named the Celtic. This, as defined by him, extended 

 from Cape Finisterre in the south to Denmark in the north, 

 and included the Baltic, except its northern shores. Thus it 

 embraced our islands, except the Shetland Islands, which he 

 transferred to the Boreal Province. 



Our present knowledge of the fauna of the Bay of Biscay 

 at one extremity, and of the Shetland Seas at the other, would 

 make it seem desirable that Ushant, instead of Cape Finisterre, 

 should be the southern boundary, while the seas of Shetland 

 should be removed from the Boreal Province into the Celtic. 



But just as the British Islands intervene between the north 

 and south portions of the European Sea, so their fauna in 

 the south partakes of characteristic animals which have their 

 home in the Lusitanian and Mediterranean Seas, and in the 

 north the fauna is intermingled with species of northern or 

 Arctic origin. 



I now pass to some peculiar conditions which aft'ect those 



