RECENT : SURFACE CLAYS. 



321 



gravels has none of the appearance of a lacustrine deposit, but is the 

 same that covers both valley and hill slope everywhere in the 

 neighbourhood. 



I have already given an account of the old river terraces in 

 the valley of the Nam-Tu near Hsipaw in 

 Nam-Tu va ley. ^ e p a g es 0 f the Records, 1 and have shown 

 Change in course of h ow they were in all probability responsible 

 nver ' for the peculiar course now taken by the river 



above the town. According to this hypothesis the waters of 

 the river, issuing from the deep gorge above Ta-ti ferry, and carry- 

 ing an immense quantity of debris derived from the old slaty and 

 schistose rocks on its left bank, spread out this material over the 

 broad valley, excavated in the soft red Namyau sandstones and 

 shales, in which the large towns of Hsipaw and Bawgyo are situ- 

 ated. At this time the narrow valley below the junction of the 

 Namhsim with the Nam-Tu was perhaps not cut down to its pre- 

 sent depth ; and the boulder deposits accumulated and blocked up 

 the bed of the river, until it rose to a sufficient height at the point 

 where it debouched from the gorge at Ta-ti to find a way across 

 the spur to the south-east, and so into the Namma, 12 miles above 

 Hsipaw. The remains of old terraces are also to be seen below 

 the mouth of the Namhsim, especially at Htengnoi (F 3), where 

 they reach an elevation of more than 100 feet above the present 

 river level. 



There is no direct evidence indicating the period at which the 

 , } terraces were formed, except that, as they are 

 terraces were formed. now undergoing denudation, they were depos- 

 ited under conditions that no longer exist. I 

 have suggested, in a lecture delivered before the Asiatic Society 

 of Bengal, 2 that in the Himalaya similar terraces may be attributed 

 to the latter part of the Glacial period, when a more rigorous 

 climate deprived the hills of their covering of vegetation, and thus 

 enhanced the action of atmospheric denudation to such an extent 



that the valleys were choked with the debris 

 No evidence of glacial carried into them And , l]tl h t] . 

 action. ° 



no direct evidence of the prevalence of glacial 



conditions among the hills of the Shan States, )'et the high ground 



to the north of the plateau, reaching to altitudes of over 7,0(0 



1 Recent Changes in the Course of the Nam-Tu River, Ihid, Vol. XXXIIT, Pt 1, p. 40. 



2 Relics of the Great Ice Ago in the Plains of India ; Geol. M<tg. Dec. V, Vol. VII, p. 198. 



