INTRODUCTORY. 7 



calculation of the relative magnitude of the stresses which would 

 be set up, and of the resistance by which they would be opposed, 

 nor does it seem that any such test could be satisfactorily applied, 

 in view of the many unknown factors which would be involved. 

 It will, however, be shown that the hypotheses, of elevation being 

 due to compression or compression the result of elevation, each 

 carry with them certain consequences in the underground distri- 

 bution of matter, which would, in the case of the Himalayas, lead 

 to results of recognisable magnitude. 



(2) No direct measurement of the throw of the main boundary 

 fault can be made, and of the similar faults within the Siwalik area 

 measurement has only been effected in one case. Mr. Middlemiss 

 was able to show that one of the faults, in the Ramganga Valley, 

 must have a vertical throw of 6,380 feet, or 11,880 feet measured 

 along the hade of the fault, 1 and as this is by no means the greatest 

 of the faults we may take it that the throw at the main boundary 

 must be at least as great, but beyond the fact that the throw of 

 this fault must amount to several thousands of feet no more exact 

 estimate is possible. 



(3) Closely bound up with the last, is the depth of the pre- 

 Tertiary floor of the Siwalik deposits within the Siwalik region. 

 It has been generally accepted that the level is higher than in the 

 alluvial area to the south, and that the elevation of the Siwalik 

 hills has carried with it an elevation of the floor on which they 

 rest. This conclusion is illustrated in some of the sections drawn 

 by Mr. Middlemiss and in the generalised and diagrammatic section 

 given in the " Manual " 2 ; it is supported by the mode of occur- 

 rence of the inliers of older rock met with in the Tertiary area 

 beyond the Sutlej, but it is by no means an inevitable conclusion 

 in the region east of the Sutlej, where the main boundary becomes 

 so well-marked a feature. If we consider the cross sections of the 

 Siwalik area, those, for instance, which were reproduced in the 

 " Manual," we find a compression of from 30 to 100 per cent., on 

 comparing the original with the present horizontal extent of the 

 beds. Now a series of deposits 15,000 feet in vertical thickness, 

 if compressed to one-third less than their original extent would 

 be thickened by no less than 7,500 feet. Actually the mean ele- 

 vation of the Siwalik area over the plains to the south is not over 



1 Memoirs, XXIV, p. 87. 



2 Manual of the Geology of India, 2nd edition, p. 473. 



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