136 OLDHAM: THE STRUCTURE OE THE HIMALAYAS, ETC. 



calculate the amount of contraction which it has undergone, if certain 

 constants are known. These are, the original temperature of solidi- 

 fication, the co-efficient of contraction, the conductivity, and the 

 temperature gradient ; none of these are known exactly, but they 

 are known to lie within certain possible limits, and calculation, 

 based on these, shows that, on this hypothesis, the total decrease 

 in the circumference of the globe, since it became solid, might be 

 as small as a couple of miles and cannot be more than about ninety. 

 In other words the whole of the contraction, which could have 

 taken place throughout geological time, is not greater than the 

 compression of the Himalayas alone, within the limit of the Tertiary 

 epoch. 



The other objection is an even more important one ; it was fore- 

 seen by Prof. Suess, and anticipated by a denial of the existence 

 of compensation. In the case of the Himalayas he must be credit- 

 ed with a greater intuition than many of his successors and followers, 

 for he recognised the fact that an alluvial trough, of the form which 

 had been inferred from geological examination, would account for 

 a large part of the facts on which the concept of the compensa- 

 tion of the range had been based ; from this it was not a long step 

 forward to the suggestion that the whole of the facts might be ac- 

 counted for in this manner, and the absence of any compensation 

 of the range asserted. 1 The position, though difficult, was still 

 tenable at the time when he wrote, but in the light of subsequent 

 observations, and of the investigation of the form and dimensions 

 of the trough in chapter IV, must now be definitely abandoned. 

 There can be no doubt, at the present time, that the Himalayas, 

 as a whole, are compensated, though there are local departures 

 in one direction or the other from exact equilibrium. This being 

 so the only hypothesis of mountain formation which is consistent 

 with a solid, rigid, globe is one of tumefaction, all hypotheses which 

 refer the origin of mountains to compression, due to contraction, 

 being excluded by the impossibility of providing for compensation. 



Another explanation of the origin of the Himalayas and the 

 Gangetic trough, which has attracted some attention of late years, 

 is that offered by Sir S. G. Burrard. 2 Like that of Prof. Suess 



1 Das ArUlitz der Erdc III (2), p. 707, English translation IV, p. 614. 



2 On the Origin of the Himalaya Mountains. Survey of India, Prof. Paper. No. 12, 

 Calcutta, 1912. 



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