October 16, 1914] 



SCIENCE 



537 



in gravity values near the southern margin 

 of the Himalayan mass can be explained 

 only on the assumption of the existence of 

 a deep and narrow rift in the sub-crust 

 parallel to the general Himalayan axis of 

 folding. A single large rift of the kind 

 and size that Colonel Burrard postulates is 

 a feature for which we have no exact par- 

 allel; but one must be careful not to be 

 misled by the use of a term which, while 

 convejdng a definite mental impression to 

 a mathematician, appears to be incongruous 

 with our geological experience. There may 

 be no such thing as a single large rift filled 

 with light alluvial material, but it is pos- 

 sible that there may still be a series of deep- 

 seated fissures that might afterwards be- 

 come filled with mineral matter. 



"With this conception of a rift or a series 

 of rifts, Colonel Burrard is led to reverse 

 the ordinary mechanical conception of 

 Himalayan folding. Instead now of look- 

 ing upon the folds as due to an overthrust 

 from the north, he regards the corrugations 

 to be the result of an under-ereep of the 

 sub-crust towards the north. Thus, accord- 

 ing to this view, the Himalaya, instead of 

 being pushed over like a gigantic rock-wave 

 breaking on to the Indian Horst is in 

 reality being dragged away from the old 

 peninsula, the depression between being 

 filled up gradually by the Gangetic allu- 

 vium. So far as the purely stratigraphical 

 features are concerned, the effect would be 

 approximately the same whether there is 

 a superficial overthrust of the covering 

 strata or whether there is a deep-seated 

 withdrawal of the basement which is well 

 below the level of observation. 



Since the Tibetan expedition of ten years 

 ago we have been in possession of definite 

 facts which show that to the north of the 

 central crystalline axis of the Himalaya 

 there lies a great basin of marine sediments 

 forming a fairly complete record from 



Paleozoic to Tertiary times, representing 

 the sediments which were laid down in the 

 great central Eurasian ocean to which 

 Suess gave the name Tethys. We have 

 thus so far been regarding the central 

 crystalline axis of the Himalaya as ap- 

 proximately coincident with the old north- 

 ern coastline of Gondwanaland ; but, if 

 Colonel Burrard 's ideas be correct, the 

 coast line must have been very much further 

 to the south before the Himalayan folding 



Representing what the Geological Survey 

 of India regards as the orthodox view, Mr. 

 H. H. Hayden^ has drawn attention to some 

 conclusions which, from our present geo- 

 logical knowledge, appear to be strange and 

 improbable in Colonel Burrard 's conclu- 

 sions, and he also offers alternative ex- 

 planations for the admitted geodetic facts. 

 Mr. Hayden suggests, for instance, that the 

 depth of isostatic compensation may be 

 quite different under the Himalayan belt 

 from that under the r'egions to the south. 

 His assumptions, however, in this respect 

 are, as pointed out by Colonel G. P. Lenox 

 Conyngham," at variance with the whole 

 theory of isostasy. Mr. Hayden then sug- 

 gests that most of the excessive anomalies 

 would disappear if we took into account the 

 low specific gravity of the Sub-Himalayan 

 sands and gravels of Upper Tertiary age as 

 well as of the Pleistocene and recent ac- 

 cumulations of similar material filling the 

 Indo-Gangetic depression. It would not be 

 at all inconsistent with our ideas derived 

 from geology to regard the Gangetic trough 

 as some three or four miles deep near its 

 northern margin, thinning out gradually 

 towards the undisturbed mass of the In- 

 dian peninsula, and Mr. R. D. Oldham,^" 



s Bee. Geol. Surv. Ind., Vol. XLIII., Part 2, p. 

 138, 1913. 



» Becords of the Survey of India, Vol. V., p. 1. 

 10 Proc. Boy. Sac, Series A, Vol. 90, p. 32, 1914. 



