INTRODUCTORY. 3 



particular theory, but an attempt to add to the stock of funda- 

 mental facts, on which alone a successful theory can be built. 



In the sequel it will be seen that, so far as the origin of the 

 Himalayas is concerned, the observations help us but little on the 

 way, though they do to some extent diminish our ignorance of the 

 processes which have been at work, but in other directions they 

 have very considerably added to our knowledge of the underground 

 structure of the northern part of India, by converting what were 

 merely conjectural possibilities into well founded probabilities. 

 The investigation has been limited to the region of the Himalayas 

 and the alluvial plain to the south of them, though this does not 

 cover the whole ground of possible cooperation between geodetic 

 and geological observation. The curious band of excess of attrac- 

 tion which crosses the northern part of the peninsula, for instance, 

 may be found to assist in the interpretation of the geology of the 

 country, but the data at present available do not admit of any 

 definite conclusion being drawn, and its discussion has, conse- 

 quently, been omitted, though it is not impossible that, when ob- 

 servations are more numerous and complete, it may be found to 

 help in the elucidation of the origin of the Himalayas. 



The completion of this work has been retarded by the call of 

 other claims on my time, but the delay has enabled the attainment 

 of more complete results. I have to acknowledge with gratitude 

 the receipt of much assistance, in the communication of material, 

 from Sir S. G. Burrard, Surveyor-General, and Dr. H. H. Hayden, 

 Director of the Geological Survey, also to Mr. D. B. Mair, for assist- 

 ance in the mathematical part of the investigation. The actual 

 calculations were done on a machine, in all but the simplest cases, 

 and are sufficiently accurate for the purposes of this investigation, 

 though they do not pretend to the refinement required in geodetic 

 work. 



The first step to be taken in this investigation is a statement 

 of the issues which are or may be affected by the new evidence, 

 and from these all questions of stratigraphy or correlation must 

 be excluded, as well as all those questions of structure which do 

 not involve the distribution of large masses of rock of materially 

 different densities. With this necessary restriction the following 

 seem to be the conclusions which are well enough established to 

 necessitate their acceptance in any discussion of the observations. 



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