229 
PEOCEEDINGS OF GEOLOGICAL SOCIETIES. 
Geological Society. — April 1. — Tiie Eer. Dr. O. Heer, Professor of 
Botany in the University of Zurich ; Signor P. Savi, Professor of Geology 
in the University of Pisa ; Sij^nor G. Ponzi, Professor of Comparative Ana- 
tomy and Physioloijy in the University of Pome ; Dr. J. Leidy, Professor 
of Anatomy in the University of Pennsylvania ; II Marchese Pareto, of 
Genoa ; and Professor A. Daubree, of the J ardin des Plantes, Paris, were 
elected Foreign Correspondents. 
The following communication was read : — *' On recent Changes in the 
Delta of the Ganges." By James Fcrgusson, Esq., F.K.G.S. 
Before describing the local phenomena of the Ganges, the author ex- 
plained, first, tbe laws that govern the extent of the oscillations in reaches 
of rivers, either laterally or in the direction of their course ; secondl}-, 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 cequilifjrium. 
Mr. Fergusson then proceeded to point out that in historical times the 
Brahmapootra and Ganges, on entering the plains of Bengal. — passing 
Goalparah and Eajmahal respectively, — ran originally to the sea in a nearly 
due north and so\ith course, parallel to one another. This symmetry was 
, first disturbed by the upheaval of the ]\[odopore jungle, north of Dacca, 
by which tiie 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. He 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 off*eL't this change had already produced in 
reopenmg the rivers of the western half of the delta, and showed that, if 
it were maintained, it would liave 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 Gauges, 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 50(X) 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 
the Bay 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-heads, and, meeting in the centre of the bay, scooped or swept 
out this depression in the centre, and by this 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 Eocks, and on the 
superjacent Palaeozoic Formations of Bavaria and Bohemia." By Sir E. I. 
Murchison, K.C.B. 
The recent important discovery by M. Giimbel of a representative, near 
Hof, of the primordial zone of the Silurian basin of Prague, induced the 
author to obtain some further particulars regarding the older rocks of 
Bavaria and Bohemia ; and a large part of this communication referred to 
the sketch-map and section supplied to him by that gentleman. 
