MUERAY— DEPTH AND MARINE DEPOSITS. 



350 



Depth. 



Area of Indian Ocean. — Looking upon tlie Indian Ocean as extending from the 

 Bay of Bengal and Arabian Sea as far south as the Antarctic Continent between the 

 longitudes of the Cape of Good Hope and of Tasmania, the total water surface is 

 estimated to cover about 27,600,000 square miles. 



Up to the year 1889 the number of soundings recorded in depths over 1000 fathoms 

 was 415 *, the greater portion of which lay in the north-west part oP the ocean, distri- 

 buted in depth as follows : — 



Between 1000 and 2000 fathoms .... 248 soundings. 



.... 158 

 9 



415 



The number shown in the chart accompanying this paper in depths excseding 1000 

 fathoms is 878 — more than double the previous number, viz : — • 



Between 1000 and 2000 fathoms . . . 

 ,, 2000 and 3000 „ ... 



2000 and 3000 

 Over 3000 fathoms . . 



420 soundings. 

 410 



Over 3000 fathoms 



48 



878 



The total number of soundings taken, however, exceeds the number shown on the 

 chart, for where soundings are crowded together only a small selection may be laid down 

 on a map of this scale. 



The depths of the Indian Ocean are represented on the map (Plate 22). The shallowest 

 zone indicating depths less than 100 fathoms is left white, while the deeper zones are 

 shown by varying shades of blue colour, each succeeding zone being indicated by pro- 

 gressively darker shades of blue; thus the palest shade of blue is used for depths 

 between 100 and 500 fathoms, the second shade for depths between 500 and 1000 

 fathoms, the third shade for depths between 1000 and 2000 fathoms, the fourth shade 

 for depths between 2000 and 3000 fathoms, and the fifth shade for depths between 

 3000 and 4000 fathoms. Depths exceeding 4000 fathoms have not been recorded in 

 the Indian Ocean. In the upper right-hand corner of the map a purplish shade will be 

 noticed in one or two places in the north-west Pacific Ocean, where depths exceeding 

 4000 and 5000 fathoms have been recorded. 



The following are approximately the areas between the consecutive contour-lines, 

 drawn in at intervals of 1000 fathoms, and the percentage of each of these areas 

 respectively to the whole Indian Ocean : — 



Square miles. Percentage. 



Less than 1000 fathoms 1,958,000 7 



Between 1000 and 2000 fathoms 8,014,000 29 



Between 2000 and 3000 fathoms 15,902,000 58 



Over 3000 fathoms 1,726,000 6 



27,600,000 



100 



» Scott. Geogr. Mag., vol. v. p. 405 (1889). 



