i6 



NATURE 



[September 3, 1914 



During the secular subsidence of the northern shore 

 line of Gondwanaland, accompanied by the slow- 

 accumulation of sediment near the shore and the 

 {gradual filing away of the land above sea-level, there 

 must have been a gradual creep of the crust in a 

 northerly direction. Near the west end of the Hima- 

 layan arc this movement would be towards the north- 

 west for a part of the time ; at the east end the creep 

 would be towards the north-north-east and north-east. 

 Thus there would be a tendency from well back in 

 Palaeozoic times up to the end of the Cretaceous period 

 for normal faults — faults of tension — to develop on the 

 land, with a trend varying from W.S.W.-E.N.E. to 

 W.N.W.-E.S.E. across the northern part of Gond- 

 wanaland. We know nothing of the evidence now 

 pigeon-holed below the great mantle of Gangetic allu- 

 vium, while the records of the Himalayan region have 

 been masked or destroyed by later foldings. But in 

 the stratified rocks lying just south of the southern 

 margin of the great alluvial belt we find a common 

 tendency for faults to strike in this way across the 

 present Peninsula of India. These faults have, for 

 instance, marked out the great belt of coalfields 

 stretching for some 200 miles from east to west in the 

 Damuda valley. On this, the east side of India, the 

 fractures of tension have a general trend of W.N.W.- 

 E.S.E. We know that these faults are later than the 

 Permian period, but some of them certainly were not 

 much later. 



If now we go westwards across the Central Prov- 

 inces and Central India into the eastern part of the 

 Bombay Presidency, we find records of this kind still 

 more strikingly preserved ; for where the Gondwana 

 rocks, ranging from Permo-Carboniferous to Liassic 

 in age, rest on the much older Vindhyan series, we 

 find three main series of these faults. One series was 

 developed before Permo-Carboniferous times ; another 

 traverses the lower Gondwanas, which range up to 

 about the end of Permian times ; while the third set 

 affects the younger and Upper Gondwanas of about 

 Rhaetic or Liassic age. Although the present topo- 

 graphy of the country follows closely the outlines of 

 the geological formations, it is clear from the work of 

 the Geological Survey of India that these outlines were 

 determined in Mesozoic times, and that the move- 

 ments which formed the latest series of faults were 

 but continuations of those which manifested them- 

 selves in Palaeozoic times. According to Mr. J. G. 

 Medlicott, the field data showed "that a tendency to 

 yield in general east and west or more clearly north- 

 east and south-west lines existed in this great area 

 from the remote period of the Vindhyan fault." -^ The 

 author of the memoir and map on this area was cer- 

 tainly not suspicious of the ideas of which I am now 

 unburdening my mind ; on the contrary, he attempted, 

 and, with apologies, failed to reconcile his facts to 

 views then being pushed by the weight of "authority " 

 in Europe. This was not the last time that facts 

 established In India were found (to use a field- 

 geologist's term) unconformably to lie on a basement 

 of geological orthodoxy as determined by authority in 

 Europe. It is important to notice that' the series of 

 faults referred to in the central parts of India are not 

 mere local dislocations, but have a general trend for 

 more than 250 miles. 



A fault must be younger, naturally, than the strata 

 which it traverses, but how much younger can seldom 

 be determined. Intrusive rocks of known age are thus 

 often more useful in indicating the age of the fissures 

 through which they have been injected, and conse- 

 quently the dykes which were formed at the time of 

 the eruption of the great Deccan Trap give another 

 clue to the direction of stresses at this critical time, 



^ " Mem. Geol. Surv. Ind.," v.)l. ii., i860, part 2, p. 256. 



NO. 2340, VOL. 94] 



that is, towards the end of the Cretaceous period, 

 when the northerly creep had reached its maximum, 

 just before Gondwanaland was broken up. If, now, 

 we turn to the geological maps of the northern part of 

 Central India, the Central Provinces, and Bengal, we 

 find that the old Vindhyan rocks of the Narbada 

 valley were injected with hundreds of trap-dykes which 

 show a general W.S.W.-E.N.E. trend, and thus 

 parallel to the normal tension faults, which we know 

 were formed during the periods preceding the outburst 

 of the Deccan Trap. This general trend of faults and 

 basic dykes is indicated on many of the published 

 geological maps of India covering the northern part of 

 the peninsula, including Ball's maps of the Ramgarh 

 and Bokaro coalfields^' and of the Hutar coalfield,'" 

 Hughes's Rewa Gondwana basin, *' Jones's southern 

 coalfields of the Satpura basin, '^ and Oldham's general 

 map of the Son valley.^^ 



We see, then, that the development of fissures with 

 a general east-west trend in the northern part of 

 Gondwanaland culminated at the end of the Cretaceous 

 period, when they extended down, probably, to the 

 basic magma lying below the crust either in a molten 

 state, or in a state that would result in fluxion on the 

 relief of pressure. That the molten material came -to 

 the surface in a superheated and liquid condition is 

 shown by the way in which it has spread out in 

 horizontal sheets over such enormous areas. Through- 

 out this great expanse of lava there are no certain 

 signs of volcanic centres no conical slopes around 

 volcanic necks ; and one might travel for more than 

 400 miles from Poona to Nagpur over sheets of lava 

 which are still practically horizontal. There Is nothing 

 exactly like this to be seen elsewhere to-day. The 

 nearest approach to it is among the Hawaiian calderas, 

 where the highly mobile basic lavas also show the 

 characters of superfusion, glowing, according to J. D. 

 Dana,^* with a white heat, that is, at a temperature 

 not less than about 1300° C. 



Mellard Reade has pointed out that the earth's crust 

 is under conditions of stress analogous to those of a 

 bent- beam, with, at a certain depth, a " level of no 

 strain." Above this level there should be a shell of 

 compression, and under it a thicker shell of tension. 

 The idea has been treated mathematicallv bv C. Davi- 

 son, G. H. Darwin, O. Fisher, and M. P". RudskI, and 

 need not be discussed at present. Prof. R. A. Daly 

 has taken advantage of this view concerning the dis- 

 tribution of stresses in the crust to explain the facility 

 for the injection of dykes and batholiths from the 

 liquid, or potentially liquid, g-abbroid magma below 

 into the shell of tension.^' He also shows that the 

 injection of large bodies of basic material into the shell 

 of tension tends on purely mechanical grounds to the 

 formation of a depression, or geosyncline. If this be 

 so, are we justified in assuming that the heavy band 

 following the southern margin of the Gangetic geo- 

 syncline is a "range" of such batholiths? The idea 

 is not entirely new ; for O. Fisher made the sugges- 

 tion more than twenty years ago that the 

 abnormal gravity at Kalianpur was due to 

 "some peculiar influence (perhaps of a volcanic neck 

 of basalt)."'® 



Daly's suggestion, however, taken into account with 

 the history of Gondwanaland, may explain the peculiar 

 alignment of the heavy subterranean band, parallel to 

 the Gangetic depression and parallel to the general 

 trend of the peninsular tension-faults and fissures that 



29 Ibid., vol. vi., part 2. 30 IHJ.^ vol. xv. 



'1 Ibid., vol. xxi., part 3. 32 Ibid., vol. xxiv. 



33 /bid., vol. xrxi., part i. 



3* " Characteristics of Volcanoes," 1891. p. loo. 



35 R. A. r)aly, "Abyssal Igneous Injection as a Causal Condition and as 

 an Effect of Mountain Building," Amer. Journ. Sci., xxii., September, 1906, 

 p. 205. 



'^ " Physics of the Earth's Crust," 2nd ed., 18R9, p. »i6. 



