From Falkland Islands to Cape of Good Hope. 83 



surface as far north as lat. 15° S., it sinks below that level in 

 lat. 30° S. between Stations 335 and 336 (Table IV.), upon the 

 plateau which divides the western from the eastern half of the 

 South Atlantic — a further proof of the higher temperatures 

 which prevail in the lower strata of the latter as compared with 

 the former. At Station 340, towards Ascension, the isotherm 

 of 2 . 5 C. is already below 1500 fathoms, and its remaining near 

 that level as far as the equator indicates the presence of a large 

 accumulation of warm water in the depths of the eastern half of 

 the South Atlantic between lat. 20° S. and the equator. This 

 circumstance has suggested the existence of a submarine ridge 

 connecting the Central Atlantic plateau with the coast of Africa 

 between the parallels of lat. 20° and 35 S., as shown in the 

 chart of Staff- Commander T. H. Tizard which accompanies 

 No. 7 of the Report on Ocean Soundings, by Captain Frank 

 T. Thomson of H.M.S. " Challenger," and published by 

 the Hydrographic Office. There are indications of the 

 existence of such a ridge or area of elevation furnished by the 

 discovery of several shallow soundings of less than 2000 

 fathoms between the central plateau and the coast of Africa, 

 but the reasons stated above perhaps suffice to explain the 

 presence of higher temperatures in the eastern basin of the 

 South Atlantic, the more so as we observe a similar phenomenon 

 in the North Atlantic. We know, besides, that a current of 

 cold water opposes as effectual an obstacle to the further exten- 

 sion of warmer strata as a- solid barrier formed by a submarine 

 ridge or protuberance of the earth's crust. Further soundings 

 in this region of the South Atlantic will decide this question. 



Section from the Falkland Islands to the Cape of Good 

 Hope (Plate 11, Table VI.). — This section includes the Stations 

 317, 318, 319, and 320, situated between the Falkland Islands 

 and the mouth of the Rio de la Plata, and they were added as 

 belonging to the same thermal area. The section between 



