OLDHAM: GEOLOGY OP MANIPUE, AND NAGA HILLS. 15 



rur), which flows to the south of Jakhama, are vertical-sided gorges of 

 aqueous erosion without the least signs of glacial action. 



32. But though I have, as I believe, shown the non-morrainal nature 



of these deposits, it is equally certain that they 

 Cause of origin. 



ware not formed under existing circumstances for 



at present the streams are everywhere cutting into them, nor will any 

 mere alteration of the levels causing a cheek in the gradients of the 

 valleys account for the texture of the older deposits which differs markedly 

 from those at present being formed lower down in the same valleys ; but 

 were the temperature decreased so as to kill off or largely diminish the 

 amount of the forest on the slopes of Japvo, the rock would be disin- 

 tegrated to a much greater extent than at present, and, if at the same 

 time the rainfall increased, the greater rush of water carrying with 

 it large quantities of detritus, would be able to carry with it the 

 largest of the transported blocks now seen some miles from their 

 original position; when this torrent debouched from its gorge into 

 the more open valley below, the velocity being checked deposition would 

 immediately commence, and gradually a long slope of boulders of every 

 size mixed with gravel and sand begin to extend itself down the valley, 

 its ultimate extent depending on the relative slopes of its surface 

 and that of the valley, the former again depending on the relative 

 proportions of water and debris forming the stream ; nor need the fact 

 that the larger blocks as seen near the head of the valley are sub-angular 

 stand in the way of this explanation, for the masses of hard sandstone, 

 originally angular, and which had not been subjected to the weathering 

 that has softened the blocks now found lying on the surface, would 

 need to travel some little distance before they became thoroughly 

 water- worn ; and it is a noticeable fact that as one travels down the 

 slope of these deposits the larger boulders get more and more water- 

 worn and at the same time smaller in size till few are left larger 

 than what may be found at the present day washed down by existing 

 streams. 



33. This increased cold which I postulate, may of course be considered 



( 231 ) 



