229 



PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



Geological Society. — April 1. — The Rev. Dr. O. Heer, Professor of 

 Botany in the University of Zurich ; Signor P. Savi, Professor of Geology 

 in the University of Pisa ; Signor G. Ponzi, Professor of Comparative Ana- 

 tomy and Physiology in the University of Rome; Dr. J. Leicly, Professor 

 of Anatomy in the University of Pennsylvania ; II Marehese Pareto, of 

 Genoa ; and Professor A. Daubree, of the Jardin des Plantes, Paris, M ere 

 elected Foreign Correspondents. 



The following communication was read: — "On recent Changes in the 

 Delta of the Ganges." By James Fergusson, Esq., F.R.G.S. 



IV fore describing the local phenomena of the Ganges, the author ex- 

 plained, first, the laws that govern the extent of the oscillations in reaches 

 of rivers, either laterally or in the direction of their course ; secondly, the 

 causes operating to raise the banks of rivers flowing through very flat 

 plains above the level of the country at a little distance from their margins ; 

 and lastly, the immense relative thickness of the early deposits in deltas 

 over those of later periods, when the conditions of the river had come more 

 nearly in (equilibrium. 



Mr. Eergusson then proceeded to point out that in historical times the 

 Brahmapootra and Ganges, on entering the plains of Bengal, — passing 

 Goalparah and Rajmahal respectively, — ran originally to the sea in a nearly 

 due north and south course, parallel to one another. This symmetry was 

 first disturbed by the upheaval of the Modopore jungle, north of Dacca, 

 by which the Brahmapootra was diverted in a south-eastern direction into 

 the depression known as the Sylhet Jheels, which were the result of the 

 upheaval just described, lie then further explained how the river, having 

 filled up these Jheels, had returned to its former bed within the limits of 

 the present century. 



Tne paper then described the effect this change had already produced in 

 reopening the rivers of the western half of the delta, and showed that, if 

 it were maintained, it would have the effect of so raising the eastern half 

 as to restore the course of the two great rivers very nearly to the position 

 they occupied before the disturbance above alluded to. 



The next point adverted to was the gradual retrocession of all the mouths 

 of the tributaries of the Ganges, in consequence of the tilting back of the 

 plain, by the gradual rise of the deltaic plains. 



.Mr. Fergusson then stated that he conceived we had sufficient historical 

 indications to show that within the last 5000 years the plain of Bengal has 

 been nearly in the same condition that the valley at Assam now is, — a 

 jungly swamp, with only a few habitable spots here and there on the banks 

 of the larger rivers. 



The last phenomenon alluded to was the " swatch of low ground " in 

 (be Hay of Bengal. This was ascribed to the action of the tides, which, 

 being accelerated on either shore of the bay. acquired a rotatory motion 

 at the sand-hcads, and, meeting in the centre of the bay, scooped or swept 

 out this depression in the centre, and by tins action prevented the growth 

 of the delta seaward to the extent that would otherwise take place. 



April 22nd. — 1. "On the Gneiss and other Azoic Rocks, and on the 

 superjacent Palaeozoic Formations of Bavaria and Bohemia.*' By Sir R. 1. 

 ]\1 urcnison, K.C.B. 



The recent important discovery by M.Giimbel of a representative, near 

 Ilof, of the primordial zone of the Silurian basin of I'rague, induced the 

 author to obtain some further particulars regarding the older rooks of 

 Bavaria and Bohemia : and a large part of this communication referred to 

 the sketch-map and section supplied to him by that gentleman. 



