372 A. B. WYNNE ON THE PHYSICAL 



Torrents from the mountains, down the valley of the Indus, on 

 reaching the waters in which the post-Tertiary silts &c. were 

 deposited, now supporting (and sometimes partly enclosing) the 

 erratic blocks, would expand, losing their impetus as well as their 

 carrying power, so that the blocks should all be found collected at 

 the exit of the river from the Attock gorge, which is not the case. 



But the river Indus is well known to be subject to violent torren- 

 tial floods at more or less long intervals. I find in the interesting 

 memoranda on the Indus floods by Captains Henderson and Broad- 

 foot, of the Royal Engineers, published by the Government of India, 

 that destructive floods have occurred about the years 1811, 1831, 

 1841, and again in 1856, 1858, 1874, and one was threatening in 

 1875 ; also that these debacles are attributed to the glaciers of the 

 Gilgit and Shyok regions giving way and slipping so as to block up 

 narrow parts of long, but not steeply inclined valleys, at a height 

 of about 9000 feet above sea-level and 8000 feet above Attock. 

 This is supposed to have occurred at from 300 to 600 miles up stream 

 above the last-named place ; and Captain Henderson assumes the 

 mean fall of the Indus and Shyok rivers for this distance at 13^ 

 feet per mile, through a rocky channel as far as Torbeyla, and that 

 of the Indus from Attock to Kalabag at 23 feet per mile*. The 

 velocity of the flood of 1858 he calculates at 15 miles per hour 

 from Attock to Kalabag, and more than this from the upper parts 

 of the river to Torbeyla. 



The flood deposited a fine silt, from description much resembling 

 that of the post-Tertiary beds of the Eawal-Pindi plateau for a foot 

 or more in depth, over the Chutch plains and lower part of the 

 Peshawur valley. 



I have not been able to find it recorded that floating ice has 

 reached even as far as Attock, nor have I any personal knowledge 

 of the large erratic blocks being found along the Indus above that 

 place ; but it can be easily conceived that under different conditions 

 as to climate, when the general elevation of the country may have 

 been greater than it is at present, such floods as these, with a 

 sudden rise in the river of from 55 to 80 feet, might have washed 

 down large fallen fragments of glaciers laden with these crystalline 

 rock masses, the " large rough blocks of granite " which Captain 

 Henderson observed to be important components of the Shyok 

 glaciers. 



It is somewhat remarkable that these large erratics do not occur 

 along that part of the Jhelum valley which is still a torrent east- 

 ward of the Eawal-Pindi plateau. I have seen smaller crystalline 

 (granitic) blocks some hundreds of feet above this river, several 

 miles south of Mozufferabad, and they are of course both larger 

 and more numerous where the river crosses the Palaeozoic schists 

 &c. higher up in the Kashmir territory. Their absence in groups 

 along the lower part of this rapid stream may be due to the circum- 



* There seems to be some error or misprint in this ; the difference of eleva- 

 tion, 288 feet, divided by the distance, 94 miles, gives the fall of the river 

 between these points as 3'06 feet per mile. 



