PART 1.] 
Alluvial deposits of the Irawadi, SfC. 
31 
I cannot here enter at length on the relation of either this clay with that (the identity 
of which I presume) of the Jumna valley, which has yielded the as yet undescribed “ Jumna 
fossils” (mammalian) or with the analogous fresh water deposit of the Nerbudda valley, 
so rich in mammalian remains, but will content myself with remarking that the difference of 
level between these two deposits is such, that the deposition of the one in a series of 
morasses fed by a sluggish river (which seems to answer the indications of the Nerbudda 
clay), might have gone on simultaneously with the accumulation in a shallow sea of the 
other of which the Rewah plateau in part formed the southern shore. 
Having dwelt at some length on the older alluvium of Bengal, I will now pass to the 
newer deposits, or Gangetie alluvium properly so called, which will require a much briefer 
notice than the last. The newer or Gangetie alluvium comprises a very varied series of beds, 
directly precipitated from the waters of the Ganges, or its tributaries. It is at once an extensive 
and important group deposited within the trough excavated by the Ganges in the older day, 
or filling up such low lying tracts as receive the flood waters of the Ganges during its annual 
inundations. It comprises some of the most fertile land in Bengal as in Tirhoot, which is 
styled the “ garden of India” where it is largely developed, as also in Purneah, Rajshaie, 
Maldah, and in all the Zillahs which ntervene between them and the sea. Its mineral 
character is very varied from a dark silty brown to a dazzling white sand, and in the sections 
of the deposit exposed in the banks of tie larger rivers we see nothing like the homogeneity 
of the older clay, but a succession of beds of different thickness and various composition, 
as is the normal condition of an unmixed fluviatile deposit. 
It loses something perhaps of its characteristic aspect, within the tideway where the 
presence of tidal waters, and tidal mud, makes itself felt, but with the exception of the belt 
of country within the limits of the present tideway, it is essentially a typical river-deposit. 
About Calcutta however, though its aspect is somewhat altered by the influence of the tides, 
it must still be ranked as a deposit, as it contains several beds of peat clearly a marsh 
accumulation and sufficient to stamp its character and origin. I am aware that at Calcutta, 
and doubtless elsewhere within the tidal zone, oyster shells have been found and other relics 
pointing to marine conditions, as soondrie wood in site of growth, a tree which only flourishes 
on land overflowed by the sea, but we must presume that this deposit during the whole 
period of its growth, of over 60 feet at Calcutta must have been every where traversed by 
deep tidal creeks on the banks of which the soondrie tree flourished and in whose quiet depths 
oysters and other marine organisms lived, and the bore at Fort William leaves small doubt 
that since the epoch when the underlying older clay had been sufficiently elevated to form a 
tract capable of supporting vegetation, a contrary movement of depression has been going 
on at a rate which permits the accession of Cangetic sediment at top adequately to counter¬ 
balance the subsidence simultaneously going on below. 
Let us now compare with the alluvial groups in the Ganges valley as sketched above, the 
similar deposits which occur in the valley of the Irawadi, prefacing the subject with a few 
remarks on the physical character of the country which presents some features peculiar to it, 
resulting from the geological structure of the delta. 
The delta of the Trawadi is embraced between the Myit-ma-kha Choung, on the east, 
which, under the name of the Rangoon river, falls into the sea below that town; and the 
Bassein river on the west, which is given off as a small stream from the main river near the 
village of Thambyadeing, and enters the sea near Negrais Island; Elephant and Poorian 
Points which respectively mark the entrances of these rivers being 137 miles apart as the 
crow Hies. The Bassein river forms naturally the most westerly arm of the Irawadi, though 
at its origin its size is inconsiderable; but the Myit-ma-klia Choung rises near the town of 
Prome, and running parallel with that stream first receives the surplus waters of the Irawadi, 
when flooded by channels which anastomose with it, opposite and below the village of 
Pouktein, 45 miles above the origin of the Bassein river; Menghee, situated between 
these two points, may therefore he fairly taken in our calculations as the head or apex of the 
Irawadi delta; on which supposition, as the distance from Menghee and Elephant and Poorian 
Points is respectively 12'J and 176 miles, the area of the entire delta is about 12,000 square 
miles. By an independent calculation, I estimate the area of alluvial deposits within the 
delta at 11,000 square miles, as some groups older thau alluvial occur within the delta, but 
no exact calculation can be made from the want of any, save an arbitrary boundary, of them 
