SUMMARY AND CONCLUSIONS. 



125 



irregularities of deflection superimposed 

 on a general southerly deflection, which 

 remains fairly constant over a wide tract 

 of country ; this condition would be satis- 

 fied if we supposed the belt of greater 

 density to have the form indicated by the 

 dotted lines in fig. 9, that is to say, instead 

 of being narrow and steep-sided, to be 

 broad with a gentle slope downwards on 

 either side. If the excess of gravity along 

 the crest of the range is taken as equi- 

 valent to about 04 dyne, and the zero 

 point at a distance of about 200 miles, the 

 southerly deflection would be about 3"; 

 and if the slope of the Hidden Range were 

 continued into the depression under the 

 Gangetic alluvium, in the manner which 

 will be suggested immediatelv, this deflec- 

 tion would continue in fairly constant 

 amount up to and beyond the boundary 

 of the alluvium. 



So far as I know, the only suggestion, 

 which has yet been mado, to account for 

 the origin of this Hidden Range, is that 

 the excess of density is due to an intrusion. 

 or series of intrusions, of dense basic or 

 ultrabasic rocks. 1 To this the same objec- 

 tion applies as to any ascription of the 

 effect to a comparatively narrow belt of 

 excessive density, and we must look else- 

 where for an explanation of the origin of 

 this feature, which seems marked out, by 

 its courses and position, as in some way 

 connected with the origin of the Hima- 

 layas. One such explanation follows, as a 

 natural consequence from Mr. Fisher's 

 interpretation of the origin of the Gangetic 

 trough. Granted the existence of a floating 



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 1914, p. 358. 



[ 273 ] 



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