OCEANOGRAPHICAL AND FISHERIES RESEARCH IN INDIA 295 



the Danish Dana Expeditions (1920-22) and the Dutch SneUius Expedi- 

 tion (1929), and to a smaller extent by traverses made by other survey 

 ships. 



John Murray Expedition 



The third phase in the progress of Indian Oceanography relates to 

 the period covered by the John Murray Expedition to the Indian 

 Ocean on the research vessel "MABAHISS" led by Sewell. The region 

 especially chosen was the Arabian Sea, to the west of Maldive and Lac- 

 cadive Archipelago, in continuation of the "INVESTIGATOR" work. 

 The expedition was able to confirm some of the findings of the Dana 

 on the submarine contours and it brought evidence of the presence of 

 submarine ridges running parallel to the Rift Valley system. The 

 changes in the distribution of fauna in regions of the Arabian Sea were 

 also clearly shown by the work of the John Murray Expedition, and a 

 noteworthy discovery was made of the existence of large azoic areas off 

 Arabia probably connected with petroleum formation. The results ob- 

 tained by the John Murray Expedition have been dealt with in various 

 volumes which have already come out, but the principal findings have 

 been dealt with by Sewell in various papers. 



Features of the Indian Ocean 



Our present knowledge of the Indian Ocean has been summarized 

 by Schott (1935), Sewell (1937), and Sverdrup et al. (1950). The 

 fact that oceanographic information relating to the Indian Ocean is 

 imperfect has been often stressed and with more intensive work it is 

 possible that some of the concepts now current may require modification. 

 This is especially so for that part of the Indian Ocean south of the 

 Equator. The Northern part of the ocean is broadly divided into the 

 Arabian Sea and the Bay of Bengal, each with further geographical 

 sub-divisions. The topography of the Arabian Sea is characterized by 

 the existence of a long series of submarine ranges, the Carlesberg Ridge 

 beginning from the region of the island of Socotra and Gape Gardafui 

 and extending to the southeast along the Chagos Archipelago and fur- 

 ther south to the Island of Rodriguez. To the southwest of the Carles- 

 berg Ridge and lying parallel to it lies the Mascarane Bank covering 

 the Islands of Seychelles and Mauritius together with a series of reefs. 

 To the north, the Carlesberg Ridge is continued by a different forma- 

 tion in the direction of Arabia and the Gulf of Oman; this ridge which 

 is considered as the submarine continuation of the Kirthar Range of 

 Sind is the Murray Ridge. The geology of these ridges and the sea 

 floor require much further study before their origin could be established 



