Chap. IV.] nahun and sivalik groups. 113 



Giri and Jumna there is no ridge, its place being occupied by an 

 immense talus of debris. In the Tonse, the Omlao, and the Jumna 

 there is a narrow band of Nahun sandstone well seen, in contact with the 

 slate rocks. Immediately east of the Jumna the low hills again appear. 

 They are very typically developed immediately under Masuri. It is in 

 the eastern portion of the Dehra- dun that the greatest blank occurs in 

 the band of Nahun rocks ; between the Ruspunna and the Ganges I did 

 not find it once exposed ; here, as to the west of the Jumna, a very 

 deep talus of detritus covers the base of the mountains. The Nahun 

 sandstone shows, however, in the Ganges opposite Riki Kase, in the very 

 angle of the sharp bend which there occurs in the boundary, so it 

 is highly probable that it is continuous beneath the bank of detritus 

 to the west. From Riki Kase southwards the section is again 

 covered and obscured ; a trace of the sandstone is seen in the Tal, and 

 there appears to be a narrow remnant of it left between the Sivalik con- 

 glomerates and the slates at the angle north-east of Moondhal, where 

 the boundary turns eastwards. This north and south line from Riki 

 Kase is the termination of the great dun, and it marks a great change in 

 the development of the Nahun band ; from the Ganges eastward, as far 

 as the^rontier of Nepal, this band forms uninterruptedly a much wider 

 and more lofty belt of hills than anything we have as. yet seen to the 

 west. 



It may be noticed that the south boundary of the Nahun group 



_._ lx , , . throughout the duns is mapped coniecturallv, its 

 Difficult boundary m ° x x J J ' 



tk* rtuns - vaguely curved form in this position contrasting 



with its sharply irregular outline in the Nahun region. The uncertainty 

 in mapping this boundary depends upon the difficulty in deciding 

 between superficial and true Sivalik deposits, — a difficulty that may 

 have been anticipated from the Simbuwala section. In the region of 

 continuous hill, about Nahun, the boundary can be traced with consi- 

 derable exactness, and it is seen to be most capriciously irregular ; at 



P 



