140 



DK. E. H. PASCOE OX THE EAKLT HISTOKY [vol. lxXV,. 



Grondwanaland was not conspicuously affected by this conipression r 

 but its northern margin, in an isostatic readjustment, gave way 

 before it. Along this buckling margin, as the pressure continued,, 

 the rocks were thrust and piled to form the preliminary Himalayan 

 chain. The greatest intensity of this impulse was, however, sub- 

 sequent to the Eocene Period. This we know from the great 

 height to which marine Eocene beds have been thrust in parts of 

 Kashmir, for Mr. T. H. D. La Touche found nummulite- bearing 

 strata at 18,500 feet above present sea-level in the Zanskar Kange. 1 

 Considerable movement has taken place since the Pleistocene 

 Period, and it is in fact more than probable that such movement 

 is still proceeding. 



An accompaniment of this intense plication and accumulative 

 mountain-building along the northern fringe of the old continent 

 was the production of a long belt of persistent subsidence between 

 the mountain-range and the more central tract of the continent. 

 The persistence of the subsidence is explained on the theory of 

 isostasy, and was assisted by the weight of the accumulating 

 sediments. 3 This vast trough, in which the Tertiary and Quater- 

 nary deposits were laid down, is bounded on the north by reversed 

 faults, and may be looked upon as a faulted geosyncline, of which 

 the southern slope, according to Mr. R. D. Oldham's convincing 

 analysis of geodetic data, is a very long and gentle one, while the 

 northern is steep and short. 3 It is doubtful whether this trough 

 was appreciable before the Eocene Period, since when it has become 

 increasingly deeper, being filled up simultaneously with accumu- 

 lating sediments, until to-day its calculated depth, deduced from 

 geodetic abnormalities, is between 1-5,000 and 20,000 feet. 1 It 

 stretches from Assam to the Punjab, and in its earlier stage 

 would have formed a natural hydrographic line. There is reason 

 to believe that a similar trough exists along the north-and-south 

 line of the Lower Indus. Speaking of these two great depressions, 

 so far as their alluvial contents are concerned, Mr. Oldham says: — 



' There is no reason to suppose that the two troughs are connected. Apart 

 from the [geodetic] observations, . . . the outcrops of old rocks in the Chiniot, 

 and other, hills which rise from the alluvium, point to the presence of a rock- 

 barrier, stretching under the plains of the Punjab to the Salt Range and 

 separating the two deep troughs.' (Op. jam cit. p. [246].) 



In this great re-entrant between the Himalaya and the Afghan 

 mountains the buckling effect which produced the two troughs 

 seems to have dissipated itself over a much wider area, and gene- 

 rated, not one single connecting trough, but several shallow sub- 

 troughs one after the other, the earlier perhaps nearer the mountains 

 and the later more remote. As will be shown, the hydrographic 

 line has been pushed in stages steadily towards the centre of India. 

 Along the Himalaya, and to a less known extent along the 

 Baluchistan Hills, these stages, we are supposing, were short and 



1 Eec. Geol. Surv. Ind. vol. xxiii (1890) p. 67. 



2 Mem. Geol. Surv. Ind. vol. xlii (1917) p. [270]. 

 4 Ibid. p. "230". 



"' Ibid. p. [243; 



