INDIAN MARINE SURVEYS. 23 



The bar of the Dhumra river was found also to have altered 

 considerably since 1882. 



In March 1885 an examination was made by the " Investigator " 

 of the curious submarine ravine called the Swatch-of-no-ground, 

 south of the Sundarbans. It was found to have an average breadth 

 of nine miles, with a floor of from 600 to 400 fathoms depth, and 

 inclined sides of soft mud of about 1 in 4. The mouths and sands 

 of ttie whole delta of the Sundarbans converge to throw their ebbing 

 waters towards the Swatch, and one suggestion has been that the 

 eddy caused by these waters meeting has tended for many ages to 

 prevent the mud held in suspension from settling over the central cleft, 

 and thus the banks on either side have grown seaward while the 

 Swatch has retained its original depth. 



The result of the 1884-5 season's work of the Marine Survey of 

 India was 11 charts and plans, including one of the entrance to the 

 Rajpuri river by a boat's party, under Lieutenant E. Helby, E.N. 

 The " Investigator " ran also over 4,500 linear miles of soundings. In 

 the department of zoological and botanical work the general expe- 

 rience of Commander Carpenter, R.N., and Lieutenant Channer, R.N., 

 who had both served on board H.M.S. " Challenger," proved most 

 valuable. Under the supervision of Mr. G. M. Giles, M.B., F.R.C.S., 

 who acted as surgeon-naturalist, some interesting hauls from 

 deep-sea trawling were made, though the appliances had been 

 long disused, and the microscope was one of very old-fashioned 

 construction. 



On the whole the season of 1884-85 had been one of fair weather, 

 and the outcome of work was larger than during any previous 

 year. 



In March 1885, the " Investigator " left the Sunderbuns and 

 carried a line of soundings to Kyauk-pyu in Arakan, where a survey 

 of that port was commenced and finished in April. Seven deep-sea 

 soundings were taken diagonally across the Bay of Bengal, on the same 

 line but between the soundings taken by Commander Dawson in 

 December 1883, and thus a complete section of the bay was obtained, 

 the average distance between the casts being 70 miles. The surface 

 temperature averaged 86 0, 5 ; that of the abysmal regions of the 

 open ocean is universally low, the mean temperature of the sea 

 bottom being everywhere about 36° in very deep water, this being 

 the temperature of greatest density. 



