48 PEOCEEDINGS OF THE GEOLOaiCAL SOCIETY. 



mountain-region no one would question; and no cause seems so 

 natural as the simple one of gravitation. However puny any 

 mountain-range may be in comparison to the mass which supports 

 it, no grain is without its effect in maintaining the equilibrium. 

 The theory of M. de Beaumont affords a plausible expression* for 

 such a process as I would suggest — a tuberance (bossellement) is pro- 

 duced with a slowness due to the motive source upon which that 

 theory is founded. This upheaval would be scarcely observable, and 

 would produce no structural change, until a limit of resistance was 

 reached, whereupon gravitation, which all along had been the proxi- 

 mate cause of the tuberance, would become partially locahzed as an 

 agent of subsidence, involving contortion. Direct gravitation is sup- 

 posed to be the breaking force, not any rupture analogous to that of 

 the tension produced by the bending of a quasi-rigid mass. Such 

 a process might repeat itself any number of times in the same region. 



In this way one might arrive at the apparent paradox, that the 

 structure of true mountains (those which are in an especial manner 

 regions of disturbance), from core to base, is the immediate result 

 and the record of subsidences.^ And, indeed, that commonest feature 

 of mountain- structure (the convergence of dips to central lines) 

 points directly to such a supposition. Any attempt I have seen to 

 connect such a result directly with an elevatory force has been un- 

 satisfactory to my mind. 



A force such as has here been supposed to produce contortion along 

 the outer zone of a mountain-range might not be simply a lateral force. 

 The partial sinking of the central regions might generate an elevatory 

 motion at the flanks. The mechanical result in this position would 

 be variously apportioned to each of these forces according to the 

 circumstances of resistance. The elevation which brought the 

 Nahun belt under denudation may have been of this kind rather 

 than connected with a general elevation of the whole mountain- 

 region. 



From the foregoing explanations it wiU be evident that I con- 

 sider, first, the present contact of the Sivalik formation with the 

 mountains to be the original one, modified only by pressure without 

 relative vertical displacement ; secondly, that the sinking of the 

 mountain-mass is the proximate cause of the contortions of these 

 Tertiary strata. The annexed diagram section is an attempt to 

 exhibit, with a minimum of contortion, the explanation I would give 

 of the observed features of Subhimalayan disturbance. 



IV. Suggested Paeallelish of the Alpzn^e at^d Sub- 



HliTALATAN" SeCTIOXS. 



Any attempt to apply cii'cumstantially to the Subalpine sections 

 the interpretation I have offered for those of the Subhimalayan 

 region must be left to those who can visit the ground. Adaptations 

 and modifications will be necessary, which can only be made out on 

 the spot. There are manifest differences of orographical conditions 

 in the two regions, that could not but entail corresponding modifi- 

 cations in the results of a process such as I have supposed ; and we 



