1869.] Geological Notes on the Khasl Hills. 7 



thing like glacial action are apparent. Equally puzzling in such 

 valleys are two or three low mounds, all of transported material, that 

 are to he seen at the eastern and upper limits of the Mokasa valley. I 

 may ask, can even these hills have been affected by the glacial period 

 in the Himalayas ? On this supposition, long and deep snow beds 

 extending down the flanks of this ridge, would be quite sufficient 

 to account for the above appearance, without the intervention of 

 true ice streams, but cold sufficient, to cover them deeply in snow, 

 during the winter is by no means an improbable state for them to 

 have passed through ; and we have no reason to suppose, that their 

 mean attitude has altered since the time when Himalayan glaciers 

 extended down to 5,000 feet below their present limits. Such a 

 physical change in a mountain range so close on the north, must have 

 wrought a perceptible one on the highest parts of an outlier like the 

 Khasi Hills. 



Fifteen miles to the west of Maotherichan the higher general level 

 of the hills, some 4,000 feet, comes to a rather sudden termination; 

 and the central main water shed takes a bend to the N. W. Rising 

 again, there in another higher portion called Laobersat 5,400, and 

 Nongkana 3,726 ; overlooking the northern slopes that thence fall 

 very rapidly towards the Assam valley. The watershed is thus 

 brought very close to the northern face of the hills, almost the whole 

 drainage being thrown to the south. The great depression west of 

 Nongkana in the main axis of the range extends quite across them, 

 the highest part the ridge near Nongkulang rises only 2,000 feet on 

 the south, forming there a kind of natural wall, between the main 

 drainage and the plains of India, the Um-Blay cutting through it 

 near Puna Tith. The cause of this sudden fall in the levels of the 

 country, I would suggest, is neither due to subsidence of the meta- 

 morphic rocks, or to their denudation, but that this portion has 

 remained in a more tranquil state, and been less affected by the 

 changes of level, on the west and east, particularly in the latter side, 

 where the intrusion of the trap rocks alone has played so important 

 a part in the present elevation of the whole series. As we shall see, 

 this trap rock entirely disappears on this more western longitude, and 

 in the sections (see pi. III.), I propose to explain, the stratified rocks are 

 seen but little disturbed ; whereas with the proportionate rise in the 



