540 



SCIENCE 



[N. S. Vol. XL. No. 103.3 



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. In- 

 trusive rocks of known age are thus often 

 more useful in indicating the age of the 

 fissures through which they have been in- 

 jected, and consequently 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, that is towards the end of the Cre- 

 -taceous period, when the northerly creep 

 lad reached its maximum, just before 

 'Gondwanaland was broken up. If, now, 

 we turn to the geological maps of the north- 

 ern 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.B. 

 trend, and thus parallel to the normal ten- 

 sion 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 geologieal maps of India 

 covering the northern part of the penin- 

 sula, including Ball's maps of the Ram- 

 garh and Bokaro coalfields^^ and of the 

 Hutar coalfield, ^^ Hughes's Rewa G-ond- 

 wana 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 



12 16-id., Vol. VI., Part 2. 



i^Ihid., Vol. XV. 



14 JMd., Vol. XXI., Part 3. 



15 /bid., Vol. XXIV. 



16 /bid., Vol. XXXI., Part 1. 



fissures with a general east-west trend in 

 the northern part of Gondwanaland cul- 

 minated at the end of the Cretaceous 

 period, when they extended down, prob- 

 ably, 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. Throughout this 

 great expanse of lava there are no certain 

 signs of volcanic centers, 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 noth- 

 ing 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 tem- 

 perature not less than about 1,300° 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 mathe- 

 matically by C. Davison, G. H. Darwin, 0. 

 Fisher, and M. P. Rudski, and need not be 

 discussed at present. Professor R. A. Daly 

 has taken advantage of this view concern- 

 ing the distribution of stresses in the crust 

 to explain the facility for the injection of 

 dykes and batholiths from the liquid, or 

 potentially liquid, gabbroid magma below 

 into the shell of tension. ^^ He also shows 



17 ' ' Charaeteristies of Volcanoes, ' ' 1891, p. 200. 



18 E. A. Daly, "Abyssal Igneous Injection as a 

 Causal Condition and as an Effect of Mountain- 

 building," Amer. Jour. Sci,., XXII., September, 

 1906, p. 205. 



