io Memoirs of the Indian Museum. [Vol,. V, 



throughout the southern part of the lake the water in the middle was of lower specific 

 gravity than that nearer the shores. 



A short series of observations made in November indicates that the conditions 

 in this month did not differ largely from those observed two months earlier, the 

 highest specific gravity (l'ooô) being obtained at the south end of Rambha Bay. 

 Water of appreciable salinity was, however, not so closely restricted to the southern 

 area, for a sample obtained off Kalidai gave a reading of 1*0035 an d others off 

 Barkul of 1003. The flood-water; had somewhat abated, with the result that the 

 level had decreased and the saline water, confined during September at the extreme 

 south, had spread further north. 



It is noteworthy that the rocks on the inner shore of the main area appear to 

 indicate that the water sinks mainly in a series of sudden falls, for, as will be seen 

 from the upper photograph on Plate I, the stone is marked in the dry season with 

 three or four horizontal bands of a superficial nature. The distinct demarcation of 

 these bands is apparently due to the fact that the upper limit of each has indicated 

 the highest water-line for some considerable period, and after a high south-westerly 

 wind we noticed in one case that a band actually represented an area of half-dried 

 alga just left bare by a sudden reduction of level. 



An attempt to discuss in detail the various other agencies that affect the 

 _,, . . , salinity of the lake would be beyond the scope of our 



Effect of winds, tides, etc. . . 



present enquiry and would certainly demand an ex- 

 perience of hydrography and meteorology which neither of us possesses. It has been 

 our object to obtain, so far as was practicable within the limits of a single year, a 

 general idea of the alterations in salinity to which the fauna of the lake is subject and 

 of the more important causes to which these changes are due. 



It is evident that the changes are to a large extent correlated with differences in 

 water-level and that the monsoon floods are by far the most potent of the agencies 

 at work. Other causes must, none the less, have a marked effect Although the 

 rivers at the north bring with them by far the greater part of the fresh water that 

 enters the system, the streams which occur in the monsoon at other points but 

 are for the most part dry during the remainder of the year, must also have some 

 influence on the conditions and during periods of heavy rain surface drainage even 

 from the small watersheds at the southern end must be considerable. 



Unfortunately no precise data are available as to the amount of rain that 

 falls actually on the lake ; in our experience it was decidedly less (in 191 4) than that 

 which fell on the surrounding country. Storms coming up from the south often 

 either followed the hill-ranges to the north-west of the lake, or else split in two before 

 they reached it, one part skirting these hills while the other keeps to seaward, follow- 

 ing the line of sand-hills along the coast. 



An important factor in local changes in salinity is the direction of the wind. 

 Owing probably to the topography of the surrounding country the monsoon currents 

 are to some extent diverted and the prevalent wind throughout the greater part of 

 the year is south-westerly. From this quarter it often blows with considerable 



