30. Note on the Application of the Principle of Isostatic 



Compensation to the Conditions prevailing* 

 beneath the Indo-Gangetic Alluvium. 



By H. H. Hayden, CLE., D.Sc. 



The appearance last year of a paper by Colonel S. G. Burrard 



on the " Origin of the Himalaya " has drawn a considerable 



amount of attention to a theory put forward by him to the 



effect that the depression in which the Indo-Gangetic alluvium 



lies is of the nature of a deep rift or crack in the surface of the 



earth, and that similar cracks occur beneath the Himalaya. 



The most recent contribution to the question is a note by 



Colonel G. P. Lenox-Conyngham 1 in which he comments 



adversely on certain suggestions made by me in a paper dealing 



with the subject of the postulated rift and designed to show 



that there is at present no valid reason for discarding the 



generally accepted hypothesis that the Indo-Gangetic trough 



is a perfectly normal phenomenon, being merely a wedge-shaped 



depression, having a sloping floor and a depth varying from 



zero at the edge which corresponds with the northern border of 



the Peninsular rock-mass to perhaps 20,000 feet at the moun- 

 tain foot. 



Colonel Lenox-Conyngham's note reached me a few days 

 ago, and, as I am now and shall probably be for several 

 months completely cut off from all literature, I should have 

 preferred to allow the matter to stand over until I was once 

 more within ieach of libraries. This, however, I cannot do, in 

 consequence of the imputation conveyed in the third paragraph 

 of the note, to the effect that in acknowledging my indebtedness 

 to the Trigonometrical Survey, I had given cause for the 

 inference that my results were accepted by that office. I need 

 hardly remark that nothing was further from my intention ; 

 in conformity with the etiquette observed by most writers on 

 scientific matters, I acknowledged to the best of my ability 

 any indebtedness for such help as I had received, and I had no 

 reason to imagine that my readers, who would naturally be 

 expected to be familiar with the ordinary practice, would 

 attribute to my remarks any such designs as that implied, or 

 would mistake them for more than the usual acknowledgment 

 demanded by scientific etiquette. 



The hypothesis usually accepted with regard to the nature 

 of the Indo-Gangetic depression was not discussed by Colonel 



1 Records of the Survey of India, Vol. V. 



