OB.OGRAPHY. 



7 



west of Herat. For the greater part of its course, however, the Panj- 

 shir-Hari Rud trough would certainly appear to be a truly tectonic 

 feature. We know too little of it to attempt to dogmatise as to its 

 origin,- but one is rather tempted to associate it with an important 

 fault which runs along the northern side of the Koh-i-Baba and probably 

 extends into Ghorband {infra, p. 54). A similar fault was observed 

 by Mr. Griesbach on the northern side of the Doshakh mountains near 

 Herat and is suggestive of a line of structural weakness all along the 

 southern side of the trough. The constant seismic activity of Kabul 

 and Herat also suggests the existence of important faults analogous to 

 those of the Outer Himalaya. 



Whatever be its origin, the Panjshir-Hari Rud trough constitutes 

 a well-marked line of division between the Hindu Kush and the Koh-i- 

 Baba, and it compels us to look for the true western continuation of the 

 former range in the hills along its northern side between Ak Robat and 

 Herat and for the eastern continuation of the latter ran^e in the hills 

 of the Ghorband valley and Pagkman. What the relationship of 

 these two ranges to one another is between Paujshir and Tirich Mir, in 

 the hills of Kohistan and Kafiristan, 1 is hardly even worth conjecturing, 

 so limited is our knowledge of the topography, whilst of the stratigraphy 

 we know absolutely nothing. 2 From the great Tirich Mir massif west- 

 wards we begin to draw away from the stable Indian vorland which is 

 replaced by the depression of the Arabian Sea ; the folds have room to 

 expand, and the high, closely appressed flexures of the Himalayan 

 arc pass into the lower and more open systems of Afghanistan and 

 Baluchistan. The disposition of the trend-lines of the mountains of 

 Afghanistan is therefore the result of the virgation (27, 275) not 

 merely of the Hindu Kush, but of the whole Himalayan system 3 and, 



1 Since the conquest of this country by the late Amir of Afghanistan in 1895 and 

 the conversion of the inhabitants to Islam, it has been re-named Nuristan (from the 

 Arabic word ««r=light). 



2 The U-shaped bend in the water-parting to the east of Panjshir is evidently 

 not a tectonic feature but merely the work of rain and livers. 



3 Since the above was written, a very valuable and suggestive paper, by Mr. F. B. 

 Taylor, dealing in part with the peripheral mountain arcs of Asia, has appeared in the 

 Bulletin of the Geological Society of America (Vol. 21, no. 2, June 1910). 



