SUBMERGED PLATEAU SURROUNDING CEYLON. 71 



well as on the swell accompanying the monsoons, on each side of 

 the Island. 



Currents. — It would be beyond the scope of these remarks to dis- 

 cuss the ocean currents of the Indian Ocean, the Bay of Bengal, and 

 of the Arabian Sea ; but it is necessary to note that Ceylon lies 

 within touch of all three systems ; and it is probably due to their 

 mingling near these shores that so many perplexities and discord- 

 ances have been recorded by navigators approaching the Island. 



The main oceanic currents alter their path (but not their direction) 

 throughout the year, moving north and south with the sun. The 

 change of monsoon is also occasioned by the same alterations in 

 position of the source of heat, and it is thus convenient to refer to 

 the currents in connection wdth the monsoons, for the changes in 

 each take place, necessarily, at about the same times of year. It 

 seems improbable that one is actually occasioned by the other : the 

 currents by the monsoons, or vice versa. The effect in either case 

 would seem too great for the cause under such a hypothesis. 



The combined general effect on the coast of Ceylon, however 

 caused, is that the currents circulate round the Island in the direc- 

 tion of the hands of a watch during the north-east monsoon period, 

 and contrary to the hands of a watch during the south-west monsoon. 

 At the change of monsoon the currents are variable ; that is, they do 

 not alter suddenly from one direction to the other. 



As regards their rates, the greatest recorded occur off the eastern 

 coast during the months of December and January, and then vary 

 from 1^ to 4 knots. (One knot means one nautical mile per hour.) 

 Off the western coast the current never runs more than about one 

 knot, being strongest in January and August. 



The above statements of the direction and speed of the currents 

 must be taken as very broad ; for, in my own experience, when 

 sounding off the western and southern coasts of the Island, or at 

 anchor (when definite observations for current alone are possible), 

 the surface currents were often found to be of the " wrong " character 

 for the time of year ; andnot only that, but on steaming outwards 

 on a line of soundings from the coast (which necessitates the 

 accurate positioning of the ship by the land every few minutes), 

 two perfectly distinct sets of the current have not infrequently been 

 observed, running in diametrically opposite directions, within a 

 mile or less of one another and parallel to the shore. This has also 

 been reported on the eastern side of Ceylon. 



The plateau probably has a considerable part in producing these 

 results. The actual depth of oceanic and indeed of all currents 

 is still a matter of great controversy ; and such observations as 

 exist for the Indian Ocean and these coasts refer solely to surface 

 currents. It is very possible, and indeed probable, that the lower 

 layers of water are moving with different speeds and directions to 

 that of the surface, actuated by differences of temperature, salinity, 



