244 CEYLON MARINE BIOLOGICAL REPORTS. 



Tlio fftlleu beacon and tl\c tanks marking tlie shoal buoy position have been examined on several 

 occasions by one of us in a diving dress for evidence of bottom movement. The tanks liave remained 

 exposed to successive monsoons at least during the last twenty years, and there has been no segregation 

 or piling up of sand. The three remaining tanks are as empty as when first examined two years ago, 

 and stand on the bottom witli no piUng up of sand or evidence of scour such as might be expected. 

 But the sand is heavily ridged. 



Tlio slioal rises verj- abruptly on the west from 9 to 4 fathoms, giving rise to a confused sea during 

 the south-west monsoon, which breaks at times. So thathcre, if anywhere, one would expect evidence of 

 bottom movement. The tanks, however, remain empty as when first examined, and stand on the bottom 

 free from segregating sand. So that it appears that the ridging of the sand is due to vertical and not 

 horizontal disturbance. 



The preceding facts indicate some of tlie reasons wliich lead us to the conclusion that bottom 

 currents do not exist on the pearl banks under lease, neither during the north-east or the south-west 

 monsoon. 



Inspection work is often commenced late in October, before the south-west monsoon has subsided. 

 At such a time the bottom layer of water is invariably turbid. The cause of this turbidity has been 

 microscopically examined, and has been repeatedly proved to be due to the disintegrated remains of sea- 

 weed and Caulerpas. The turbidity renders it almost impossible for divers to see, but it subsides gradually 

 as the north-east monsoon begins. This condition of the bottom water is by no means an entirely 

 unhealthy condition, for it provides extensive organic material for oysters to feed upon. 



It has been suggested using a Nanson's currentometer for observations on the bottom currents 

 during the south-west monsoon. Such a meter however would, we believe, in any case only give the 

 rate of the current, and not the direction, or the varying directions. The utter impossibihty of mooring 

 such a meter on the banks during the south-west monsoon wiU, however, be apparent to any one who 

 is famiUar -vnth the conditions in the gulf during this monsoon. 



In addition to the preceding data, a further 927 bottles in all were liberated during 1907, 1908, 

 and 1910. The results therefrom have, however, been discarded. Li the majority of cases the place 

 where they were liberated is not kno'on. In otlier instances they were liberated between the monsoons, 

 when no definite result can be expected; whilst tlie balance includes bottles liberated at unsuitable 

 places, or under unsuitable conditions. 



The returns quoted in Part III., "Ceylon Marine Biological Reports," are not included in 

 this report. 



The following table gives topographical returns and percentages : — 



South-west Monsoon. 

 BolUes liberated north of Tallaicillu Point (inshore), 1908 and 1909. — Bottles liberated went ashore and 

 form part of the 927 discarded. 



Bottles liberated south of Tallaivillu Point, 1910. — Liberated, 60; recovered, 49; percentage, 81 "6 

 per cent. 



Bottles liberated between Colombo and Tuticorin, 7970.— Liberated, 505 ; recovered, 242 ; percentage, 48 

 per cent, (practically). 



Total number of bottles liberated on tlie above positions, 1908 and 1910. — Liberated, 565 ; recovered, 291 ; 

 percentage, 51 '5 per cent. 



North-east Monsoon. 

 Bottles liberated north of Tallaivillu Point, 1907, 1908, 1909, and J9i0.— Liberated, 284 ; recovered, 48 ; 

 percentage, 17 per cent, (practically). 



Bottles liberated between Colombo and Tuticorin, 1909. — Liberated, 74 ; recovered, 12 ; percentage, 16" 2 

 per cent. 



Total number of bottles liberated on the above positions, 1907, 1908, 1909, and 1910. — Liberated, 358 ; 

 recovered, 60 j percentage, 17 per cent, (practically). 



Abstract. 

 Total number of bottles liberated .. .. .. 1,853 



Total number of bottles discarded 

 Total number of bottles liberated at all stations dnrmg both monsoons 

 Total number of bottles returned during both monsoons . . 

 Percentage returned over both monsoons 



927 



923 



351 



38- 1 



