SUMMARY AND CONCLUSIONS. 129 



anomaly of gravity, traversing the Peninsula, with -its comcomit- 

 ant effect on the plumb-line; and it may be added that the strength 

 of the crust, required to produce these effects, is much the same 

 as .that deduced by Prof. Barrell from the geodetic work in 

 North America. 1 This agreement, between the results of con- 

 clusions drawn from observation and those obtained by deduction, 

 lends considerable support to the hypothesis on which the deduc- 

 tions were based, but it must be confessed that the Himalayas are 

 the only range where anything like this agreement has been found, 

 yet even this may rather strengthen than weaken the support, for 

 it may well result from the magnitude of the range, which is not- 

 attained by any other mountains of the world. It is conceivable 

 that only in the mountain system, of which the Himalayas form 

 the culminating member, do the gravitational stresses set up by 

 the processes of mountain formation reach a magnitude which 

 enable them to dominate all other influences, and to produce a 

 simplicity and magnitude of structure, obscured in other cases by the 

 action of other influences and resistances, which become more promi- 

 nent with the decrease in the magnitude of the gravitational stresses. 2 



We have seen that, the phenomena actually observed, in the 

 region lying in and to the south of the hills, are in agreement with, 

 and are easily explained by, the hypothesis of a solid and some- 

 what rigid crust supported by flotation on a substratum of denser 

 material ; but when we come to consider more especiallv the range 

 itself, difficulties arise in the acceptance of Mr. Fisher's explana- 

 tion of a simple thickening of the crust by compression. In his 

 investigation the crust is supposed to be compressed as a whole 

 and, recognising that the resistance of the lower part would be less 

 than that of the upper, the neutral zone was put at two-fifths of 

 the thickness from the upper surface, so that all above this would 

 be thickened upwards and all below in a downward direction. 

 In these circumstances the downward protuberance would be half 

 as large again as the upward one, which would give an insufficient 



1 Journal of Geology, XXIII, p. 30 (1915). 



2 Too little is known of the Andes, the only other mountain system of comparable 

 magnitude, to admit of comparison with the Himalayas. |Since this was written, some 

 particulars of deflection of the plumb-line in the Andes have been published, indicating 

 that it varies in much the same manner, and to about the same extent, in these two 

 ranges, which are of very much the same magnitude, >n the portions which have a 

 predominating share in the effect on the plumb-line. Geog. Jour. XL Vll* 484-467, & 

 XLVIII, 180-181, (1916) ] 



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