360 PEECT SLADEJN^ TRUST EXPEDITION, 



The 1000-fathoras contour follows closely the coast-line of the land-masses and of 

 the island-groups. The area between 1000 and 2000 fathoms forms a fairly wide zone 

 round the different island-groups and along the east coast of Africa, and a compara- 

 tively narrow zone along the coasts of the Sunda Islands and of Australia in the east. 

 The greater part of the Arabian Sea and of the Bay of Bengal is included in this area, 

 and tliere is a wide expanse between Tasmania and the Antarctic Continent which 

 gradually becomes narrower towards the west, as well as a large tract extending from 

 latitude 30° to 55° S., from which rise the islands of Prince Edward, Crozet, Kerguelen, 

 McDonald, Heard, St. Paul, and Amsterdam ; other small isolated areas occur in 

 different parts of the ocean. 



As shown by the above table, by far the greatest portion of the Indian Ocean (58 per 

 cent.) has a depth of between 2000 and 3000 fathoms, this area being interrupted only by 

 the isolated shallower areas already mentioned and by the areas exceeding 3000 fathoms 

 in depth, to which the term " deeps " has been limited. 



Deeps. — There are four deeps lying entirely in the Indian Ocean, and one lying half in 

 the Atlantic and half in the Indian Ocean. The last-mentioned, the Ross Deep, is foimded 

 on seven soundings of over 3000 fathoms taken by the ' Valdivia ' in 1898-99, and that 

 part of it which lies in the Indian Ocean, extending from long. 20° E. to about 52° E., 

 is estimated to cover an area of about 613,000 square miles. 



The Jeffreys Deep lies off the south-western coast of the continent of Australia, and 

 is estimated to cover an area of about 198,000 square miles. It is based on twelve 

 soundings, eight of which are wide apart in the southern part of the deep, the other 

 four being much closer together at the northern end. There is thus a long stretch 

 where no depths have been recorded, and future soundings may show that what is now 

 regarded as one continuous deep may be interrupted by shallower areas. 



The Wharton Deep, extending from the Tropic of Capricorn northwards to lat. 10° S., 

 and from long. 91° E, to about 118° E., is estimated to cover an area of about 852,000 

 square miles. It is based on twenty-five soundings, about half of which were taken by 

 the ' Sherard Osborn ' in 1900, and it contains the two deepest soundings yet found 

 in the Indian Ocean, viz. 3828 and 3703 fathoms, taken by the German ship ' Planet,' 

 in what the Germans call the " Sunda Graben." 



The Maclear Deep, based on four soundings, two on the southern and two on the 

 northern side of lat. 10' S., lies to the north of Wharton Deep, and is estimated to 

 cover an area of about 62,000 square miles. 



A fourth area, the Enterprise Deep, is based on a single sounding in 3097 fathoms 

 taken by IJ.S.S. ' Enterprise ' in 1883 in lat. 4° 14' S., 99° 50' E. In this region there 

 are numerous soundings in 2600 and 2700 fathoms, so that the area covered by more 

 than 3000 fathoms must be comparatively very small, probably about 1000 square miles. 



Notwithstanding the numerous soundings hitherto recorded in the Indian Ocean, 

 there still remain certain tracts of the ocean calling for futher investigation. Eor 

 instance, in the Arabian Sea north of lat. 10° N. there are still areas east and west of 

 long. 63° E. that might with advantage be more extensively surveyed, and in the 

 southern part of the Mozambique Channel the soundings lie nearer to the African than 

 to the Madagascar coast. 



