13 



disappearance of tins mollusc. The inner or landward portion 

 of the lake now harbours no species of molluscs except small 

 gastropods which live along the water's edge ; what exist else- 

 where (Ostrea, Mactra, and Area rhomhea are examples) live 

 within a radius of some two to three miles from the bar where 

 the salinity of the water is better maintained and dry age of the 

 lake le?s extreme. 



The final phase will probably be characterised by the 

 complete canalisation of the lake and the gradual reclamation 

 of all the area not utilised for drainage and flood channels and 

 traffic waterways. 



Depths of water and periodic closure of the bar. — As men- 

 tioned above I ran a large number of lines of soundings across 

 the lake, and for reference append details * of the more 

 important. 



During the period of inspection ( August) the sea bar was 

 open and the levels subject to a limited tidal influence averag- 

 ing a difference of about one foot between high and low tides. 

 So far as possible the soundings were made at half-tide and 

 may therefore be taken as representing the mean level of 

 the lake under normal tidal conditions, and when no flood 

 water is pouring in. 



Omitting the dredged boat-channel maintained by the canal 

 authorities along the east side of Pulicat island, the only 

 section of the lake with depths of one-fathom and upwards is 

 the narrow channel which extends westwards from the vicinity 

 of the bar and separates Karimanal from Pulicat. Off the 

 south end of Karimanal, depths up to 14 feet are obtained. 

 -From this point the channel curves to the north hugging the 

 Karimanal side at first and then bends west till about midway 

 between the Karimanal shores and Annamalaicheri. Here the 

 greatest depth becomes reduced to 5f feet. Further north 

 this channel, becoming further reduced in depth, widens 

 very extensively to form a great area to the west, south . and 

 south-east of Irakam carrying depths varying between 4 and 

 if feet. 



Between Venadu island and Tada (west shore of lake), the 

 deeper water does not run to more than three feet, while east 

 of Venadu, 1 J to 2 feet of water is carried practically tie whole 

 way across to the east shore, Zonangipalayam and neighbour- 

 hood. The northern and main section of the lake thus forms 

 two well marked divisions, (a) an eastern, characterised by 

 such shallowness of water as to permit of no traffic worth 



* Omitted for the present. 



