368 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



serving what strata it has disturbed in one district ; for it may have 

 invaded an older formation in one locality, and yet, rising higher, it 

 may have broken in upon a newer formation in another place ; or, 

 applying the principle to the case in hand, the very same amygdaloid 

 which M'Clelland calls secondary trap, because it has been erupted 

 among the oolitic strata of Rajmahal, may be tertiary trap here, if it 

 is, as 1 believe, the identical effusion which has been intercalated 

 between the oolitic and tertiary formations of Nagpur. But for the 

 conclusive determination of this question, the district of Rajmahal 

 with a tertiary formation found in connection with trap in its northern 

 part, and Jurassic strata associated with trap in its southern part, 

 presents the most befitting arena. 



Mode of its Eruption. — Before leaving the volcanic rocks, it is 

 desirable to indicate the lessons which Central India teaches as to 

 the manner in which they were formed. Now the first thing which 

 strikes any observer of the great basaltic field of this country is the 

 comparative absence of all cones or craters throughout. 1 cannot 

 name a spot in all the tract with which I am acquainted, where I 

 could say either the nodular basalt or the amygdaloid came up from 

 below. The nodular basalt seems to have flowed along for immense 

 distances, filling up the tertiary lake, and leaving an arid plain in its 

 rear. Then the amygdaloid inserting itself between the sandstone 

 and the freshwater bed seems to have flowed generally underground 

 on the same scale of grandeur. Sitabaldi Hill, which is almost an 

 outlier of the great basaltic region of Western India, being connected 

 with it by a very narrow neck, would be a favourable place for 

 ascertaining whether the underlying trap, which has there accumu- 

 lated under the tertiary deposit to a considerable thickness, has 

 been forced up vertically through the gneiss and sandstone, which 

 appear around the base of the hill to be inferior to it, or whether it 

 has been horizontally intercalated, as in the generality of places, 

 between the sandstone and the tertiary. I am disposed to take the 

 latter view ; but, if the government quarry were only excavated a few 

 feet lower, as Voysey long ago suggested, it would put an end to all 

 doubt. 



From the statements previously advanced regarding the trappean 

 rocks of Nagpur, taken in connection with the same formation in 

 other parts of the country, it is obvious there is no foundation what- 

 ever for the supposition that the great outpouring of basalt in India 

 took place in the ocean. And, although I believe that the fresh- 

 water in which it really was effused must have stretched over great 

 areas without much interruption, yet the discovery in the tertiary 

 strata of abundance of pulmoniferous molluscs, such as LimncBus and 

 Fhysa, — of plants, such as marsh- or shallow-loving Endogens, buried 

 with their roots and fruits almost entire and therefore not far from 

 the spot where they originally grew, — not to mention the occurrence 

 of an amphibious univalve like Succinea, and of land-shells like 

 Bulimus, together with great quantities of seeds and fruit and timber, 

 the spoils of the neighbouring dry land, — plainly shows that the water 

 in that part of the lake was of no great depth. Indeed it seems 



