24 
Records of the Geological Survey of India. 
[vol. III. 
water occur in proximity to a large river channel in lower Bengal, it would at once, and 
probably correctly, be referred to a deserted bend or knuckle of the river, and such was my 
impression in the present case before examining the ground. I anticipated finding a con¬ 
siderable ai'ca of newer deposit of river silt marking the former extension of the Daga river, 
but nothing of the sort exists, the permanent banks of the river displaying the ordinary section 
of older clay, and the island occupying the centre of the lake being formed of the older clay 
likewise. No other conclusion therefore remains but to regard it as an annular depression which 
originally existed on the surface of the older alluvium on its first elevation from the sea, 
deepened, enlarged, and wrought to its present shape by atmospheric agency. Besides atmos¬ 
pheric agency, which seems scarcely equal of itself to produce such a piece of water (else would 
they be more common), even when aided by the original contour of the ground, I should 
suspect some peculiarity in the soil constituting the bed of the lake. The older clay of 
the delta is, it is true, remarkably homogeneous as a whole, hut this is not. inconsistent 
with the occurrence in it of thin bands of a different composition. An instance in point occurs 
to me in the Purneah district of Bengal, where a thin band-like portion of the older clay 
usually so tenacious assumes almost the character of a quicksand by mixture with water, 
forming a sludgy compound, easily removable by the action of either springs or a stream. 
Some such band may very possibly occur in the older clay of Pegu, and if it occurred at 
about the mean height of the water on the Daga river, or lower, it would go far to explain, 
by the facility with which it would pulp down and flow away, the annular shap a of the lake, 
which of course, however obscure the cause, is not purely fortuitous. In this view the 
original depression of the ground may have been trifling, sufficient perhaps only to give 
direction to the scouring action subsequently set up.* 
A noteworthy point connected with the physical character of the delta of the Irawadi 
is the more persistent character of the river channels in it. Towards the upper part of the 
delta and above its proper limits, the Irawadi channel is never more than five miles broad 
between its permanent banks as they may be termed, that is the opposite margins of that 
trough scooped by the river in the older alluvium, and of which a considerable portion is 
usually refilled with river deposits. Within the delta proper towards its mouth, the present 
river channels are more permanent, and evince little tendency to deviato from their establish¬ 
ed channel. Even such rivers as the Daga, which wind in the most circuitous fashion in 
a level country, exhibit no such tendency, affording in this respect a striking contrast to 
the habit of rivers in the Gangetic delta. The Kosi for example oscillates from east to west 
(its present direction) over an area of probably not less than 30 miles, and a town which 
stood on the west hank of its main channel at the period of my visiting it first, stood on 
its east bank the following year, through the se-opening and scouring out of a disused 
channel in its westerly course. The station of Kampore Beauleah is in like manner sulFering 
from the encroachment of the river, and so long back as 1855, steamers anchored where 
houses once stood. Nothing too is a commoner process in the Gangetic delta than the 
obliteration of a river channel, and its conversion into a fertile plain, a change not unfre- 
quently effected in the course of a few years. Now, save within the narrowest limits, 
nothing of this sort takes place in the Irawadi delta, and this is I think attributable to the 
different constitution of its delta, and the absence of any extended development of the 
newer group, within which the incessant changes in the Gangetic rivers take place, or in 
other words owing to the greater and more equable resistance to erosion of an homogeneous 
clay like the older deposit, than what is afforded by banks composed of newer silty deposits, 
and such (luviatile accumulations. Local peculiarities may in some spots cause a wasting of 
the older clay, as at the important town of Nioungdon, where a great extent of sand flats 
and shallows have resulted from the excessive denudation suffered by the older clay, giving 
rise to a sprawling channel very different from the deep permanent channel usually seen in 
the delta, but the cause is obviously a loeal one, the clay here resting on an incoherent pebbly 
sand, which melts away and allows the overlying bed to topple into the river, and the process 
which is rather exceptional in Pegu in the older group produces the same result as in Bengal, 
where it is an universal operation in the newer. 
* Mr. O’Riley himself subsequently to the publication of the paper referred to, changed his view of the for¬ 
mation of this “lake”; and believed, as certainly appears the much more rational and simple mode of accounting 
for its formation, that it is simply an unfilled-in bend, or as Mr. Theobald says “ knuckle" of tile river. Every¬ 
thing seems to be in harmony with this view, and Dr. Day, in his recent Fishery enquiries in Btirmah, was also 
satisfied that this was the true explanation of the facts. T. Oldham. 
