8 Memoirs of the Indian Museum. [Voi,. V, 



In February and March, as will be seen from the chart on p. 9, an abrupt 

 change in density was encountered at Mugger-Mukh on the bar that separates the 

 main area from the outer channel — a bar covered at this period by water only some 

 eighteen inches or two feet in depth. The specific gravities in little more than a 

 mile changed from 1-026 to I'Oio. The floods of the previous year's monsoon had 

 not only altogether subsided, but a considerable quantity of salt-water had entered 

 from the Bay of Bengal. The most noteworthy feature of the specific gravities in 

 this large region was that the denser water was accumulated at the south end. 

 The highest readings were obtained at the southern extremity of Rambha Bay and 

 from this point to Nalbano the specific gravities regularly decreased. North of 

 Nalbano, water of greater density was again met with, while the lowest readings 

 were obtained along the north-western shore in the vicinity of Patsahanipur. At 

 this period the specific gravities we obtained ranged from 100675 to roi 150. Owing 

 to the extreme shallowness of the lake we were unable, however, to visit a con- 

 siderable region at the northern end and the comparatively small amount of water 

 that enters from the rivers probably produces specific gravities lower than any we 

 actually recorded. 



Subsidiary observations made in the middle of April at the southern end of the 

 lake seem to indicate that no great change in the conditions had taken place, though 

 the position of the isohalines (as indicated by the lines of equal specific gravities) had 

 probably altered to a certain extent. Samples taken in Rambha Bay and off Break- 

 fast and Chiriya Ids. gave readings identical with those of February ; but off 

 Barkuda the specific gravity was lower (1-00975) and off Maludaikuda higher 

 ( 1 '00975). By July, however, a notable change had occurred and there is little 

 doubt that during May and June a considerable volume of salt water had entered the 

 lake ; the specific gravities were higher than any previously observed and the entire 

 area southwest of Samal Id. was filled with water varying from i"Oi45 to 1-0150. 

 At Barkul the specific gravity was still much the same as in February, viz., 

 1-00750. 



The conditions in the main area were very different in September, 1914. In this 

 month, as shown in fig. 2, p. 9, the greater part of the area was filled with fresh or 

 almost fresh water. 



The great volume of silt-laden water brought down into the northern end by 

 the branches of the Mahanaddi system had expelled all that of higher salinity— a 

 phenomenon already noted with reference to the outer channel. It is evident that, in 

 these parts of the lake at any rate, the changes are not due to admixture so much as 

 to the expulsion of one volume by another. 



In September slight traces of a higher specific gravity were met with between 

 Nalbano and Patsahanipur, the water varying from fresh to roo:, and southwards of 

 this line there was a gradual rise in density up to sp. gr. 10065 i n Rambha Bay. The 

 latter reading, the maximum observed in September, is about the same as the mini- 

 mum recorded in the salt-water season. It will be noticed that specific gravities of 

 i*oo6 and over were onlv met with near the shore in the extreme south and that 



