26 
Records of the Geological Survey of India. 
[vol. in. 
of' elevation present themselves, but as we approach Gwa we find gradually proofs of a some¬ 
what recent rise of the coast, in the shape of coral hanks raise'd above the present limits 
of its growth and in the presence, a few feet below the surface in the plains now removed 
from the shore, of shelly sand and shells of species living on the coast. Above Myanoung this 
dark band is cognizable high above the dry season level of the river, but within the tideway 
it occui s about niidwater mark or lower, and is in many places dug out for pottery, being 
highly plastic and adapted for such purposes. 
Towards the top of the tideway the older alluvium or yellowish clay rests on a pebbly 
sand, which is visible at Nioungdan, where it is rather better than usual. This 
sandy bed is doubtless the homologue of those extensive beds of gravel which towards the 
frontier, underlie the older clay. Opposite the village of Monyo, near Nioungwaing, gold 
washings are carried on in the bed of the river on a shingly bank which belongs to these 
coarse gravels, and these gravels are probably the source of the gold which in many spots 
is occasionally washed for in the Irawadi, though the returns are too poor to attract con¬ 
tinuous labor. This older clay is not confined to the valley of the Irawadi, hilt occurs like¬ 
wise in that- of the Sit-tang—and, which is rather difficult to account for on any other 
hypothesis than that which 1 have adopted, of its estuary origin, in the upper parts of the 
river valleys on the side of the Arakan Coast. In some of these valleys it is seen deeply 
cut through by the river channels, and very often appearing little more than a remnant of 
a once extended deposit. In such positions it is often masked and covered over by an enor¬ 
mous accumulation of rocky detritus swept down over it by rains from the adjoining precipi¬ 
tous hills. This is not a situation favorable to the accumulation of a homogeneous clay, 
through long-continued fltiviatile action, but rather points to a period when its equable 
diffusion took place within the sea. The coarse gravels which underlie the clay towards the 
upper portion of the delta and towards the frontier are clearly of luariue origin, as no other 
agency is adequate to formations of such coarse shingle as that in question. Opposite Prome 
this gravel rises to upwards of 60 feet- above the flood level of the Irawadi and is fully 30 feet 
thick reposing on miocene strata. The older clay is not seen here being apparently denuded, 
but at Thaiotuiio the relation of tlie two beds is well seen. In the neighbourhood of Thaiet- 
mio, this gravel contains numerous well worn and rounded pieces of fossil wood, six inches 
in length and occasionally logs two feet and upwards in length. These logs have, of course, 
not travelled far, and are derived from the miocene sands containing siRcified wood in the 
neighbourhood. Their presence, however, with other hard rocks, in well-rounded lumps is 
clearly indicative of their origin in situ as a marine shingle bank. Equally conclusive is the 
thick deposit of coarse shingle comprising well-rounded boulders, many of six and nine inches 
in length of the hardest schists, exposed in the river bank under "the old Port of Miade 
above Thai etude on the opposite hank, and I can draw no other conclusion from these 
deposits, than that, anterior to the deposition of the older clay, they formed shingle hanks 
in a shallow sea or estuary in which f heir hard silicious ingredients were rolled about and 
polished down as we find them iu the gravel. Having iti a previous notice described the beds 
whence the fossil wood lias been derived I need not here allude to them, hut I think I may 
confidently assume that marine and not atmospheric agency was the force employed in the 
removal (m part at least) of these fossil-wood beds, and in reducing the silicified trunks so 
abundantly contained in them into (lie innumerable smoothed blocks, boulders and pebbles of 
fossil wood so characteristic of the Irawadi gravels. 
I will conclude my remarks on the Irawadi alluvium by pointing out the effect to man, 
and the extent to which his industry is affected by what might seem merely a trivial or 
theoretical difference between the delta of the Irawadi and Ganges. I have already shewn 
that within the Irawadi delta, hut 200 square miles occur of the newer or Irawadi alluvium 
proper, but- without affecting t-o estimate the area occupied by the corresponding Gangetic 
alluvium it may be taken as far more than two hundred times that amount. Now, it is on 
this newer alluvium that the finest indigo is grown, and indigo and may be said 
to be the two main staples of the zillahs in Bengal occupied by the newer deposits. Not 
only this, but the newer alluvium will produce any crop required of it, either rice, sugar, 
opium, oil seeds, &c., and hence from the occurrence of these newer deposits over so large 
au area in Beugal, that province has acquired the name for fertility it possesses. In the 
Irawadi valley, in place of this fertile deposit, we have the older alluvial clay, which. 
