THE NATURE AND 1NTERPRKTATI0N OF GEODETIC EVIDENCE. 33 



tribution of the load of the range, or of the flotation power of its 

 root, over a considerable portion of the crust on either side of the 

 range. This effect may work in one of two ways ; if the growth 

 of the upward protuberance exceeded that of the root there 

 would be a local defect of support, which would be taken up by a 

 depression of the crust on either side till the requisite support was 

 attained. In this case the compensation of the range would be 

 in defect, or in other words the mass of the range would be in excess 

 of the defect of mass below it, while the tract on either side would 

 be over compensated, so that the deep-seated defect of mass would 

 exceed that of the visible elevation. This is a variation from a con- 

 dition of the compensation of the range being complete, in the por- 

 tion of the crust underlying it, which was actually investigated 

 by Mr. Fisher ; but it is also conceivable that the reverse might 

 take place, and the development of the root be in excess of that of 

 the range. In this case the surplus buoyancy would be taken up by 

 a raising of the crust not only under the range but on either side 

 of it, and the range would be over compensated while the tract 

 on either side would show an excess of load over compensation. 



This modification of the hypothesis of support by flotation has 

 not, so far as I know, been investigated as yet, but its possibility 

 cannot be excluded, and, if supported by the geodetic observations, 

 is in some ways an attractive one. It would give a ready explana- 

 tion of some of the features in the geological history of the Hima- 

 layas, such as the simple upward lift, of which there is evidence in 

 the Deosai, north of Kashmir, in the plains of Hundes and else- 

 where ; the peculiarities and origin of the great boundary fault would 

 find an easy explanation, as also the tilting of the surface of the 

 gravel slope along the foot of the Hills, which is noticeable in many 

 parts, and the fact that the range seems still to be rising. 



An alternative group of hypotheses involves no addition to the 

 material under the elevated tract, but regards the elevations of 

 the visible surface as due to an actual swelling up of the matter 

 under them, or, what comes to the same, a greater condensation 

 under the more low-lying tracts of the surface. An hypothesis 

 of this sort may be described as attributing the differences in level 

 of different tracts of the earth's surface to some form of tumefac- 

 tion, and the effect has usually been attributed to differences of 

 temperature. This explanation has the defect of being apparently 

 insufficient, quantitatively, to account for the facts, and even if 



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