MEMOIRS 



OF 



THE GEOLOGICAL SURVEY OF INDIA. 



The Structure of the Himalayas, and of the Gan- 

 getic Plain, as elucidated by Geodetic Obser- 

 vations in India. By R. D. Oldham, F.R.S. 



CHAPTER I. 



INTRODUCTORY. 



The annual reports of the Great Trigonometrical Survey have 

 contained occasional reference to certain peculiarities exhibited by 

 geodetic observation near the outer edge of the Himalayas, and 

 to a belt of lesser density as a reasonable explanation of them. 

 These references had attracted little attention on the geological 

 side, for those geologists who could understand them, and were 

 also acquainted with the results of geological examination, knew 

 that just such a belt of rock, of less than average density, did run 

 *long the foot of the hills, and though the form of the trough, in 

 which it lies, differs from that suggested as an explanation of the 

 geodetic peculiarities, it was clear that the effect of the known 

 geological structure would be similar in kind to that revealed bv 

 geodetic observation, and there was no reason to suppose that it 

 might not also be suflicient in amount. 



Matters might have remained in this state but for the publica- 

 tion, in 1912, of a brief paper, by Sir S. G. Burrard, on the Origin 

 of the Himalaya Mountains. 1 The explanation offered would pro- 

 bably have attracted little attention, and in due course have gone 

 to join a respectable company in the limbo of forgotten theories, 



1 Survey of India. Professional Taper No. 12. Calcutta, 1912. 



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