PRESIDENTIAL ADDRESS. 357 
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 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 Cretaceous 
period, when the northerly creep had reached its maximum, just before Gond- 
wanaland 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 pre- 
ceding 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 7? and of the Hutar coalfield,*° Hughes’ Rewa 
Gondwana basin,*! Jones’ 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. Throughout 
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 aaa Dana,** with a white heat, that is, at a temperature 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 mathematically by C., 
Davison, G. H. Darwin, O. Fisher, and M. P. Rudski, and need not be discussed 
at present. Professor R. A. Daly has taken advantage of this view concerning 
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 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 geosyncline is a ‘range’ of such batholiths? The idea is not entirely 
new; for O. Fisher made the suggestion more than twenty years ago that the 
abnormal gravity at Kalianpur was due to ‘some peculiar influence (perhaps of 
a volcanic neck of basalt).’ ** 
79 Mem. Geol. Surv. Ind., vol. vi. part 2. 
°° Tbid., vol. xv, 
*t Tbid., vol. xxi. part 3. 
32 Tbid., vol. xxiv. 
°° Tbid., vol. xxxi. part 1. 
** Characteristics of Volcanoes, 1891, p. 200. 
*° R. A. Daly, ‘ Abyssal Igneous Injection as a Causal Condition and as an 
Effect of Mountain-building,’ Amer. Journ. Sci., xxii. Sept. 1906, p. 205. 
86 Physics of the Harth’s Crust, 2nd ed., 1889, p. 216. 
