igzi.] Mampur Mollnsca. 535 



The most important facts about the specimens from 1113- point 

 of view are that they certainly represent rocks common all round 

 the valley, and that those which represent the rocks most abundant 

 in the neighbourhood are extremely friable and readily crumble to 

 form a fine soil precisely like that in which the cultivated parts of 

 the JManipur valley are deeply buried. Soil of this kind extends on 

 the north and west sides of the lake well down to high water-level and 

 it is only on the east, and probably also on the south side, that 

 large deposits of peat are being formed. The peat in these deposits 

 is less coherent than, and not quite so black as that found round 

 the Inle Lake. There is no sign whatsoever of raised beaches at 

 any point. 



This last fact induced Col. Godwin-Austen, who was the first 

 man with any knowledge of geology to visit Manipur, to doubt 

 whether the lake had ever extended much beyond its present high- 

 wat^r limits. The peaty deposits on its eastern shores are very 

 like those found in other parts of the valley and known to represent 

 swamps that were recently larger than they are now, but even if 

 the whole of these swamps were completely submerged the greater 

 part of the vallej^ would still be above water. 



All of these facts seem to me to support Col. Godwin-Austen's 

 views, to which ilr. R. D. Oldham gave his adherence. The 

 Manipur valley, moreover, although at first sight it closely resembles 

 a lake-bed, with its dead level onl}- broken by small island- 

 like hills rising abruptly from the plain ; nevertheless, on closer 

 examination seems to differ in little but its greater extent from 

 other swampy valleys in the Naga and Khasi hills which have 

 certainh' never been lakes but have been filled in to an almost 

 equal level by the silt brought down in streams that now meander 

 through them with sluggish waters in which flow has been dimi- 

 nished by a gradual filling in of their old beds and consequent 

 diminution in fall. 



No factor is more important in influencing the fauna of any 



bodj' of water than its vegetation, and it 



VegetaUon of jhe Lok- ^^^^^g ^^ ^^ ^ general rule, at any rate in 



warm countries, that over-abundant sub- 

 merged plant-life, especially if it includes a luxuriant growth of 

 small sessile algae, is inimical to many forms of animal life, partly 

 doutbless on account of actual toxins produced by the vital activi- 

 ties of certain species and partly on account of the poisonous nature 

 of the rotting material at the bottom. The latter feature, however, 

 is of a very complex character, evidentlj' depending at least in part 

 on the activities of microscopic organisms. But these again 

 are dependant largely on the physical and chemical characters of 

 the water. As we shall see later, the fauna of the Loktak Lake, and 

 especially the invertebrate fauna, is a rather poor one. I associate 

 this fact with the extreme luxuriance of the vegetation. 



As has alread}' been stated, this luxuriance of the vegetation, 

 both submerged and floating, gives the lake the character of a 

 large swamp. The submerged weeds are of various kinds, but 



