534 Records of the Indian Mnseiun. [Vol. XXII, 



in the Loktak Lake, in the more open parts of which calcium oc- 

 curs only to the extent of 00148 per cent as compared with 0'022 

 per cent in the Inle Lake, and magnesium to that of o'ooGS to 

 o'oi34 as compared with coajg. On the other hand, the amount 

 of organic matter in the much more congested Loktak Lake is 

 considerably greater than it is in the clear water of the central 

 region of the Inle Lake, while the amount of carbonic acid is more 

 than four times as great in the former as in the latter. The percent- 

 age of silica, further, is much greater in the Loktak I,ake, and 

 this is also so, as might be expected, with SO^. These differences 

 are due doubtless, so far as most of the mineral salts are concerned, 

 mainl}^ to the composition of the surrounding rocks and of those 

 amongst which the water-supply of the lakes flows before entering 

 them. The larger amount of organic matter, of carbonic acid, of 

 SO^ and possibly of silica maj' be accounted for, on the other 

 hand, partly by differences in the vegetation, but these again 

 are correlated with the chemical composition of their environ- 

 ment. 



It is impossible to consider the origin of the Loktak Lake without 

 considering also that of the Manipur vallev 

 Origin of^the^ Loktak in its present condition. Two different views 

 have been held on this point, one, that the 

 whole valley is a comparatively recent lake- bed and that the Loktak 

 once filled it and has shrunk to its present size, perhaps even in his- 

 torical times ; the other, that the valley is of comparativel5' ancient 

 date and has been filled in gradually to its present level by debris 

 brought down from the hills bj' the tributaries of the Imphal 

 River. As I have already said, the valley has never been properly 

 surveyed. From a geological point of view its structure is practi- 

 cally unknown, but the rocks of the surrounding hills api)ear to 

 resemble closely those of the Naga Hills to the north. I have to 

 thank Dr. E. H. Pascoe of the Geological Survey of India for the 

 following note on rock-specimens from islands in the Loktak 

 Lake. 



" The rocks consist for the greater part of hard shale but two 

 of the specimens are of siliceous sandstone. They belong in all 

 probability to the Disang series, about the age of which we know 

 nothing definite bej'ond the fact that it is pre-Tertiary. The 

 Disang series is essentially argillaceous and the rocks thereof would 

 produce somewhat muddy water but not so muddj^ as softer 

 argillaceous deposits. 



"As to any organic connection of Lake Loktak with Assam, 

 there is not sufficient evidence to go upon. An idea which I believe 

 is a very old one and mentioned by La Touche makes the present 

 Chindwin-Irrawadi the former continuation of the Tsang-po or 

 Tibetan-Brahmaputra, the upper waters of this large river being 

 afterwards captured by the Assam-Brahmaputra. Whether Lake 

 Loktak was connected with the Chindwin at the time it was a 

 continuation of the Tsang-po I cannot say, nor do I know whether 

 this would help you in any way." 



