13. Since writing the above, I have seen Colonel Sykes’s notes on the formations of Southern India in the Indian Review. The facts there described seem all to support my conclusion, and his map would answer just as well for Central as for Southern India; for the banks of the Nerbudda and Chambal, Son, and Mahanadi, as well as for those of the Bam and the Bima. Colonel Sykes does not, I believe, attempt to account for the stratification of the basalt; he merely describes it. [W. H. S.]
The author’s theory of the subaqueous origin of the greater part of the basalt of Central and Southern India, otherwise known as the ‘Deccan Trap Series’, had been supported by numerous excellent geologists, but W. T. Blanford proved the theory to be untenable, there being ’clear and unmistakable evidence that the traps were in great part of sub-aerial formation’, The intercalation of sedimentary beds with fresh-water fossils is conclusive proof that the lava-flows associated with such beds cannot be submarine. The hypothesis that the lower beds of traps were poured out in a vast, but shallow, freshwater lake extending throughout the area over which the inter-trappean limestone formation extends appears to be extremely improbable. The lava seems to have been poured, during a long succession of ages, over a land surface, uneven and broken in parts, ’with intervals of rest sufficient for lakes, stocked with fresh-water mollusca, to form on the cold surfaces of several of the lava-flows’ (Holland, in I.G. (1907), i. 88). A great tract of the volcanic region appears to have remained almost undisturbed to the present day, affected by sub-aerial erosion alone. The geological horizon of the Deccan trap cannot be precisely defined, but is now vaguely stated as ‘the close of the cretaceous period’. The ‘steps’, or conspicuous terraces, traceable on the hill-sides for great distances, are explained as being ’due to the outcrop of the harder basaltic strata, or of those beds which resist best the disintegrating influences of exposure’.
The general horizontality of the Deccan trap over an area of not less than 200,000 square miles, and the absence of volcanic hills of the usual conical form, are difficulties which have caused much discussion. Some of the ‘old volcanic vents’ appear to have existed near Poona and Mahableshwar. The entire area has been subjected to sub-aerial denudation on a gigantic scale, which explains the occurrence of the basalt as the caps of isolated hills. Much further investigation is required to clear up details (Manual of the Geology of India, ed. 1, Part I, chap. 13)
14. The author took charge of the Jubbulpore District in March 1828.
15. The fossiliferous beds near Jubbulpore, described in the text, seem to belong to the group now classed as the Lameta beds. The bones of a large dinosaurian reptile (Titanosaurus indicus) have been identified (I.G., 1907, vol. i, p. 88).