94 Correspondence — F. Drew. — F. A. Bedwell. 



coI^:E^ssI^o^5^IDE^^o:B.. 



THE UPPEE INDUS BASIN. 



SiE, — WTienever Colonel Greenwood writes on the subject of rain 

 and river action, we are sure to learn a good deal. I am very glad 

 that he has noticed the facts about the Upper Indus alluviums which 

 I laid before the Geological Society, and has entered into the dis- 

 cussion of their causes. With much that he has written I heartily 

 agree ; and if on one point I still difier, it is with a mind open to be 

 convinced if the causes I proposed to account for the present state 

 of the alluvial deposits should seem after further argument either 

 inadequate or unnecessary. 



I grant the "hard gorge and soft valley" theory of Colonel 

 Greenwood generally ; in some instances where I have observed the 

 alternation, a difference in the rocks can be seen to account for it ; in 

 others the reason is less clear. Still I am ready to believe that 

 further knowledge of the character and position of the rocks would 

 show that this theory is applicable to most cases. 



But I feel greai difficulty in agreeing that the accumulation and 

 subsequent denudation of thick alluvial deposits were due only to 

 the variations in slope of the river-bed. In the first place I cannot 

 see how hundreds of feet of alluvial strata could be formed one 

 upon another in a wide valley ending in a gorge, lohile the bed of the 

 gorge was sinlcing from erosion. 



Secondly, we have the alluvial gravels, to a great thickness, in the 

 gorges as loell. This is evidence that, at the accumulating time, 

 alluvium (of varying degrees of fineness very likely) was deposited 

 all along both valley and gorge ; that the river-bed rose everywhere, 

 though not in all places to the same relative height above its rock 

 bottom, nor probably, with one uniform gradient. 



There are many instances in the narrow parts of the Indus Valley 

 itself of alluvial pebble-beds two and three hundred feet thick, while 

 in the narrow tributary valleys six and seven hundred feet of them 

 are seen. The cases of Khardong and Tainyar are the two most 

 striking ones that come to my mind at this moment. 



This it is that makes me think Colonel Greenwood's theory insuffi- 

 cient. That my own is the right one of course does not follow ; and 

 I will not fill up your space at present in maintaining it, being con- 

 tent to attempt advancing the discussion one stage at a time. 



28, Jermyn Street, Fkedekic DkeW. 



January '2Xst, 1874. 



THANET CHALK. 

 SiK, — I omitted to state in my paper on this subject (Geol. Mag. 

 Jan. 1874) that the average diameter of the Ammonites exhibited 

 in the Isle of Thanet is at least three feet : also that any person 

 visiting the section should go at the first or last quarter of the moon, 

 as " the springs " in the Island bring the high tide on between 

 12 and 1 o'clock in the day, and stop all continuous work between 

 9 in the morning and 5 in the afternoon. F. A. Bedwell. 



23, Old Square, Lincoln's Inn. 

 January nth, 1874. 



