140 OLDHAM: THE STRUCTURE OF THE HIMALAYAS, ETC. 



line of weakness, where the rocks would be compressed, and thickening 

 of the crust take place. If the temperature then sank, the material 

 would not return to its original position, but the contraction be 

 relieved by a general subsidence of the superincumbent rocks and 

 a compressive extension of the lower layers. On an increase of 

 temperature again taking place, relief would -once more be found 

 alon<* the original lines, and the disturbance and thickening of the 

 crust accentuated, till, by a repetition of the process, the largest 

 mountain ranges might be formed. 



There can be no question that this cause is capable of producing 

 much more than the pressure required, and a sufficient range of 

 movement. It is a cause which might quite conceivably act, but, 

 with the masses involved, the process would be slow, so slow in 

 fact that even the vast periods, which have been deduced from the 

 study of radioactive minerals, would seem insufficient for the pro- 

 duction of the effect. 



The explanations which have been passed in review do not by any 

 means complete the list of those which have been proposed, but 

 thev serve as types, and the difficulties which lie in the way of the 

 acceptance of each of them apply equally to the variants of the 

 type. The general result of the examination is that, while the 

 general distribution of the excesses and defects of gravity agrees 

 best with the supposition of a somewhat rigid crust, supported by 

 flotation on a denser yielding layer, we can, neither on this nor any 

 other hypothesis of support, find an explanation of the origin of 

 the Himalayas, which can be regarded as complete and satisfactory ; 

 nor does it seem possible to offer any alternative which can be 

 accepted. In spite of this negative result the investigation has not 

 been in vain ; it was undertaken with no expectation of attaining 

 a solution of the problem of the ultimate cause, to which the 

 elevation of the Himalayas is due, and it has not failed this want of 

 expectation ; but it has yielded a fresh criterion, which must be met 

 before any hypothesis can be regarded as acceptable. The con- 

 clusions, however, must not, at present, be extended to other ranges 

 of a different type of structure, without corroboration of indepen- 

 dent observations, and even in the case of ranges of similar general 

 geological structures, but very different magnitude, such as the Alps, 

 it is not impossible that the difference of scale may seriously vitiate 

 an application of the conclusions, drawn from a study of the greatest 



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