Reviews — The Origin of the Himalayan Folding. 169 



supposition that the crust has received much igneous material from 

 inside, has expanded by hydration, and has otherwise grown. But 

 there still remained, as Dutton pointed out in framing his theory of 

 isostasy, qualitative as well as quantitative difficulties : the superficial 

 overthrusting of folded ranges was still not explained with perfect 

 satisfaction. 



A new suggestion of the kind now made by Colonel Burrard thus 

 deserves more than casual comparison with the data ; for there are, 

 it seems to me, many geological and physical considerations that 

 debatably seem to fall into line with this new theory. Among these 

 reference might be made in this short communication to — 



1. The numerous tension faults, which show a general east to 

 west trend in the northern part of the Indian Peninsula, and have 

 affected in succession the pre-Carboniferous Vindhyan strata and the 

 Permo- Carboniferous Lower Gondwana beds, while newer fissures of 

 the same kind became the channels through which the Deccan Trap 

 was erupted at the end of the Mesozoic era (cf. Mem. Geol. Surv. 

 Ind., vols, vi, pt. ii ; xv ; xxi, pt. iii ; xxiv, pt. i ; and xxxi, pt. i). The 

 general trend of these tension faults is significantly parallel to that 

 of Colonel Burrard's assumed ' rift ' and associated earth-folds. 



2. The welling-up of a great granitic core behind (that is, to the 

 north) of the band of exceptionally low gravity, and on the southern 

 edge of the geosyncline which was slowly fed with marine sediment 

 during much of the Palaeozoic and most of the Mesozoic era. 



3. The possibility that, if there has been at all an appreciable 

 cooling of the earth since the close of Mesozoic times, such cooling 

 would result in the contraction and splitting of what Colonel Burrard 

 calls the sub-crust, while there would be little or no appreciable 

 reduction in the temperature and size of the great central core. 



4. Such loss of heat would be most rapid in the geosynclinal belts 

 on which our great fold-ranges have always risen. This suggestion 

 substantially agrees with that made by Dr. J. Milne from the 

 distribution of earthquakes (Sard Report, Seismological Committee, 

 Brit. Assoc, 1912). 



5. Mr. R. D. Oldham has shown that the megaseisms — earth- 

 shaking quakes — probably originate at great depths, and are but 

 accidentally and rarely connected with the visible superficial faults 

 in the seismic regions (Quart. Journ. Geol. Soc, Ixv, 1-20, 1909). 



6. The symmetrical character of those geanticlines which show 

 overthrusting in opposite directions, does not conveniently illusti'ate 

 even the worn-out textbook idea of a superficial crust collapsing and 

 crumpling on a shrinking core. 



The ' rift' postulated by Colonel Burrard is altogether different in 

 depth and character to the fore-deep of Professor Suess, who regards 

 the peninsula as a stable block against which the Himalayan mass is 

 being rolled ; this would not account for a band of deficient gravity 

 outside and beyond the visible hills. 



Up to last year ideas regarding the production of rifts at great 

 depths were inhibited by the conclusions of C. E. Van Hise and 

 L. M. Hoskins regarding the comparatively shallow depths at 

 which the strongest rocks become plastic under the superincumbent 



