168 Reviews — TJie Origin of the Himalayan Folding. 



There is no doubt that the observed facts cannot be challenged ; 

 they are not limited to a small number of uncorrected observations, 

 and are of the same order of magnitude outside the foot of the 

 Eastern, the Central, and the Western Himalaya. The corrections 

 made for the subterranean partial compensation of the Himalayan 

 protuberance, and even for the assumed disturbing influences of the 

 distant major features of geomorphology leave the relative local 

 variations in gravity still pronounced and unexplained. 



The results quoted by Colonel Eurrard as observed deflections of the 

 plumb-line have been obtained by deducting the geodetic values of 

 latitude and longitude from the astronomical values, the geodetic 

 values being computed by triangulation based on the Clark-Bessel 

 spheroid.^ The deflections that ought to be expected from topo- 

 graphical inequalities are based on the assumption that the superficial 

 crust has an average specific gravity of 2'8, and that inequalities are 

 not compensated by corresponding variations in density below the 

 crust. The deflections mentioned as calculated on the assumption 

 of complete compensation are based on the results published 

 by J. F. Hayford,- who assumes the existence of general com- 

 pensation for surface inequalities uniformly distributed to a depth 

 of 113"7 kilometres. 



A single example will be sufficient to illustrate the results obtained 

 for traverses made from the Himahiya to the plains. Kurseong 

 (26° 52'; 88° 18') ^ in the Darjeeling district at an elevation of 

 4,428 feet, Siliguri (26° 42'; 88° 27') ^ immediately at the foot 

 of the range, standing 401 feet above the sea-level, and Jalpaiguri 

 (26° 31'; 88° 47')^ 13 miles out on the plains at an elevation of only 

 280 feet, are not far from a meridional line. Between Kurseong and 

 Siliguri the deflection of the plumb-line ought to change by 19" 

 if the mountains were not isostatically compensated at all, and the 

 difference should be only 11" if Hayford's hypothesis of perfect 

 compensation were applicable, but the observed difference is as much 

 as 28". Similarly, between Siliguri and Jalpaiguri the ditference 

 should be 7" according to calculations from uncompensated 

 topography, and only 4" according to Hayford's theory, while 

 the observed difference is 17". Thus, for the whole distance of 

 25 miles, between Kurseong in the Outer Himalaya and Jalpaiguri 

 on the plains, the difference in deflection is 45" instead of 26", 

 as it would be without mountain compensation, and 15", as it 

 should be according to Hayford's hypothesis. 



As long as geologists were content to believe in a cooling and 

 shrinking core, we had a satisfactory mental picture of a collapsing 

 and wrinkling skin. But this explanation was found to overreach 

 itself, the folds in the coat being so flagrantly generous that if 

 flattened out the Earth would have a cover several sizes too large for 

 itself. However, the old theory received adventitious aid from the 



' S. G. Burrard, Phil. Trans., A, vol. 205, p. 218, 1905. 



- The figure of the Earth and Isostasy from measurements in the United 

 States, Washington, 1909. 



* As the greatest arc of North latitude in India is less than the smallest arc 

 of East longitude, the values stated in the usual order cannot be confused. 



