Basin of the Southern Ocean. 23 



The Basin of the Southern Ocean, — This ocean, which 

 makes the circuit of the world along the parallel of lat. 60° S., in 

 length equal to half the circumference of the Earth at the 

 Equator, may be considered as occupying the space between 

 the Antarctic Circle and the parallel of lat. 40° S. Owing to the 

 limited number of soundings as yet obtained within its limits, 

 we can only form a general idea of the distribution of its depths. 



The boundary-line of the fortieth parallel, which separates 

 the Southern Ocean from the Pacific, Atlantic, and Indian 

 Oceans, is occupied, as has been shown in the previous pages, 

 alternately by areas of depression, with depths ranging from 

 2500 to nearly 3000 fathoms, and by areas of elevation, or sub- 

 marine plateaux, approaching to within 1 500 fathoms of the sea 

 surface. On the side of the Pacific, we have the deep area 

 explored by the " Gazelle " stretching up towards the Samoan 

 Islands, and the submerged plateau between Tahiti and Pata- 

 gonia. On the side of the Atlantic, we find the southern end of 

 the central Atlantic plateau, with the island of Tristan d'Acunha 

 and Gough Island, flanked on the east and west by the deep 

 areas explored by H.M.S. " Challenger." Upon the limit of the 

 Indian Ocean, we observe what may be called the Kerguelen 

 plateau, extending from Marion and Prince Edward Islands to 

 St. Paul and Amsterdam Islands, as proved by the soundings 

 both of the " Challenger " and of the " Gazelle," and the deep 

 area, an extension of the main basin of the Indian Ocean, which 

 passes to the southward of Australia and New Zealand, as 

 established by the soundings of the officers of both ships. The 

 plateaux on the border of the Atlantic and Indian Oceans may 

 turn out to be mere extensions of the Antarctic plateau, whilst 

 the deep areas leading to the three oceanic basins may be con- 

 sidered, in accordance with the observed bottom-temperatures, 

 as the main channels by which the cold water of the Antarctic 

 region flows northward into the Pacific, Atlantic, and Indian 



