1918.] N", Anjtaxdale : The Inle Lake. 5 



The age of the rocks is uncertain, but it is sufficient for our purpose to 

 know that they are of marine origin, and very ancient, and that their 

 formation must have long preceded the hollowing out of the Inle basin. 



The superficial deposits of the district have great interest in relation 



to the living fauna in that they prove the former existence of lacustrine 



molluscs at places now devoid of water, particularly 



uper icia eposi s. -^ ^^^ He-Ho plain and in smaller valleys among 



the hills of Yawnghwe. The shells from the deposits will be discussed 

 later in a paper dealing primarily with the living forms. 



The deposits are of four kinds :— (*) Red Soil, (n) Peaty Deposits, 

 [iii) Grey Clay and {iv) Recent Tufa. 



La Touche ^ has shown that the red soil which covers a great part of 

 the Shan Plateau is the insoluble debris of limestone rocks dissolved by 

 water. Soil of this kind covers most of the He-Ho plain and also of the 

 flat ground at the head of the Inle Lake. In a 

 small valley, that of the Hsin-Dawng stream, 

 about three miles east of the town of Yawnghwe and at several 

 hundred feet above the level of the plain, there are two small limestone 

 caves, the floor of which is formed of red soil and contains fossil shells 

 and mammahan remains. The shells are closely related to but distinctly 

 different from those both of the He-Ho and the Inle basins. 



An enormous amount of peaty matter is always being formed round 

 the Inle Lake and in other damp situations on the Shan Plateau. To- 

 gether with the silt brought down by the streams 

 p SI s. \]iqX flow into the lake, it must in the end fill up 



the basin completely. On the He-Ho plain, especially round the margin 

 of the old lake, there are considerable deposits of this origin. They 

 contain numerous shells in a fossil or subfossil condition. These shells 

 belong to the same genera and in many cases to the same species as 

 those now living in the Inle Lake. 



At the western end of the He-Ho plain, between two small limestone 

 spurs, a short distance above the point at which the He-Ho stream begins 

 to descend through its gorge into the Yawnghwe 

 rey ay. valley, there is a deposit of grey clay exactly 



similar to that which is formed when the serni-liquid substance from the 

 bottom of the existing lake is dried. The stream has cut through this 

 deposit to a depth of at least 20 feet. It is full of shells differing in 

 some cases from those found in the«peaty deposits of the same neigh- 

 bourhood but closely allied to them. 



One of the most extraordinary phenomena to be observed in the 

 Shan States is the formation of calcareous tufa 

 Recen Tufa. owing to the deposition of lime from solution in 



water. This phenomenon is thus described by La Touche - : 



" The enormous extent to which the limestone of the plateau is being removed in 

 solution by percolating waters has already been alluded to, and it is not surprising to 



Calcareous Dams ^'"^ that, when the water comes again to the surface in springs 



and rivers, and is either evaporated or loses the carbonic acid 



which keeps the carbonate of lime in solution, the deposits thrown down should reach 



correspondingly huge dimensions. Indeed I doubt whether any other limestone tract 



1 Mem. Geol. Survey Inl., Vol. XXXIX, p. 322. 



2 Mem. Geol. Survey Ind. V^ol. XXXIX, p. 325. 



