SUBMERGED PLATEAU SURROUNDING CEYLON. 16 



The deep sea mud off the plateau of Ceylon has a greenish colora- 

 tion, which Mr. M. Kelway Bamber, F.I.C., F.C.S., pronounces to be 

 organic in nature, dissolving out in hot alcohol, and leaving an 

 amorphous green colour on evaporation, easily soluble again in 

 alcohol. Mr. Kelway Bamber has kindly undertaken a chemical 

 analysis of this mud, and the results are given in the Note accom- 

 panying this paper. 



It is noticeable that the area in which occurs what I hav6 termed 

 " green mud " is the deep water outside the plateau, whilst on the 

 plateau we found only brown sand, broken shells, and occasionally 

 broken coral, always in very small quantities. This would seem to 

 point to the probability of currents existing along the bottom over 

 the surface of the plateau, preventing the accumulation of soft 

 material composed of light particles, such as is represented by the 

 " green mud " of the greater depths. When at anchor in 12 fathoms 

 on the easternmost of the three small banks off Mount Lavinia, a 

 diver from the ship procured a specimen of the bottom for investi- 

 gation. He reported the surface to be flat, smooth, and hard, with- 

 out sand or any loose material lying on it. The specimen, which 

 had to be levered up from its position with an iron bar, consiats 

 of coral, which Dr. Willey informs me to be Porites coated with 

 nuUipore in places. 



The green colour above noticed is usually associated in bottom 

 specimens with " terrigenous " material, and is found only on 

 continental slopes. On reaching true oceanic depths the deposits 

 are almost invariably coloured gray, or pale brown (except in the 

 cases of recent volcanic upheavals). 



More extended collection of specimens round the outside of the 

 plateau will, no doubt, produce the correct reasons for the occur- 

 rence of the green coloured deposit, and also the outside limits at 

 which it is found from the coast, but since the material is not of a 

 properly constituted " oceanic " colour, but rather " terrigenous," 

 we may suppose that its greenness is due to the finer washings of the 

 detritus from the rivers, which, held in suspension for a considerable 

 period in the sea water by reason of their lightness, have been 

 carried by the surface current over the edge of the plateau and not 

 deposited until deep water has been reached ; while the coarser and 

 heavier particles have remained behind to be acted on by bottom 

 currents near the land and on the plateau. These conjectures refer 

 solely to the southern and western surroundings of the Island, no 

 specimens having yet been obtained elsewhere. 



III. — The Coast Line of Ceylon. 



I do not know whether the considerations which I now propose 

 to set forth have been previously advocated, but while dealing with 

 the plateau, the currents, and swell, I should like to point out an 

 effect on the coasts of the Island, which is probably due to these 



