66 SEA FISHERIES 



south-westerly direction, approaches the surface, and 

 blossoms into an archipelago, which is none other than 

 the Azores. It once more plunges into the depths, still 

 continuing in a south-westerly direction, until it arrives 

 within two or three hundred miles of the Brazilian coast. 

 It then changes its course, running in a south-easterly 

 direction as far as Ascencion, of which it forms the frame- 

 work. Finally it runs as far south as Tristan d'Acunha. 

 I will call this ridge the "Central Atlantic ridge." The 

 third is the "Wyville Thomson ridge." It starts from 

 the bluffs of the south-eastern portion of Iceland. In a 

 straight unbroken line it stretches to the Faroe Islands, 

 where, changing its direction, it turns to the south and 

 terminates in the north-western point of Scotland. The 

 Icelandic mountain is thus the starting-point of three 

 great ranges of submarine mountains. 



The Central Atlantic range is covered with volcanic 

 debris. The Wyville Thomson range is perhaps of the 

 same nature. Murray, however, believes it to be the 

 remains of an ancient moraine, on account of the great 

 number of glacial imprints which he has found on the 

 rocks of the formation. It plays a part of the first im- 

 portance in the distribution of temperature. Thus, at 

 the same depth of 800 fathoms, the waters on the north- 

 eastern side of the range have a temperature of 30*2 

 Fahr., while on the south-western side the temperature 

 is never less than 39*2. 



In the space enclosed by the roots of the three ranges 

 the Icelandic mountain rises in an abrupt slope from a 

 depth of 1,000 fathoms. The first step coincides with the 

 5oo-fathom line. The second step, which is less abrupt, 

 is 1,800 feet in height, or 300 fathoms. The third step 

 is 600 feet high, or 100 fathoms, which gives a depth of 

 100 fathoms. As it completely surrounds the island with 



