1864. | The Geological Society. 293 
the bed of the river.” After illustrating these propositions, he next 
discusses the tendency of rivers flowing in alluvial soils to raise their 
banks, and thus to confine themselves in their beds ; and he explains 
the process by means of which this result is brought about somewhat 
differently from Sir Charles Lyell and other writers, as he calls in the 
aid of “backwaters,” or large bodies of still water in the low lands 
beyond the banks of the river, the effect of their existence being that 
the overflowing water of the river is forced to deposit its silt as soon 
as it meets them, which is, in the wet season, soon after it leaves the 
river. In the particular case of the Ganges, Mr. Fergusson is doubt- 
less right ; but it is extremely hazardous to generalize from a solitary 
instance. The secular elevation of deltas, and many other interesting 
subjects, are then treated; and the author also describes in detail the 
principal changes that have taken place, during the historic period, in 
the delta of the Ganges; that is to say, the changes in the courses, 
directions, outlets, &c., of the various rivers, the alteration in the slope 
of their beds, and many other phenomena, all showing the magnitude 
of the results brought about by river-action, and the rapidity of the 
changes, as well as the mutual dependence of the different rivers of 
the same valley. Indeed, we may consider that in the Valley of the 
Ganges there is being played a natural game of chess on a gigantic 
scale ; the valley itself is the chessboard, the rivers are the pieces, 
while the producers of the changes—water and mud—are the players. 
The effect of a move of any particular river in any direction in altering 
the relations of the rest, and the many other ways in which the con- 
nection of the various rivers is shown, together with the laws which 
regulate these changes, and river-action generally, are very curious, 
and deserve more attention from the geologist than they have hitherto 
received, 
The chief object of Dr. Leith Adams’s paper is to prove that the 
Nile has at a comparatively recent period flowed at a much higher 
level than it now does, at any rate north of the second cataract. The 
evidence upon which this conclusion rests consists chiefly of the occur- 
rence of fluviatile shells at high levels. These shells were found in 
beds of alluvium forming terraces on the banks of the river, and they 
belong, according to Mr. 8. P. Woodward, to six species, namely— 
Unio lithophagus, Cyrena fluminalis, Aitheria semilunata (Nile oysters), 
Tridina Nilotica, Paludina bulimoides, and Bulimus pullus. The first 
species is doubtful, the next four all live in the Nile at the present 
day, and the last probably occurs in the neighbourhood. ‘They were 
found at all heights, up to aé least 120 feet above the highest Nile of 
the present time. 
Dr. Adams gives a sketch of the physical structure of the Nile 
Valley, and notices the collateral evidence in support of his conclusions 
to be derived from the position of ancient temples, tombs, and other 
monuments, striving to prove not only that the Nile above the second 
cataract formerly flowed at a much higher level than it now does, but 
also that the primeval river was much larger and more rapid than the 
Nile of the present day. 
This paper is certainly an important contribution to the history of 
VOL. I. x 
