13 i 
Becords of the Geological Survey of India. 
[vOL. XIII. 
Oopallem well may draw its waters from a source witliin six miles of Pondi- 
clierry. 
The PoNDicniRBY-CcDDALOBM Alluvial Basix. 
The wells are then all in the alluvial deposits; indeed, as will ho seen later on, 
it was not to he expected that any hut very deep borings could reach the older 
rocks, which by their lie might he presumed to hold water with a head; it there¬ 
fore becomes necessary to enquire into the condition of these deposits in this 
region which give this hj'drostatic level to their waters at the sea-board. 
Mr. Poulain is, I think, firmly convinced that the head of water is gained on 
Mr. Poukin’s views on distant western edge of the alluvial plain behind 
tlic source and Lead of Pondicherry from the Pennar and Gingee rivers, his 
water. 
rguments being fully given in his series of papers' 
read 
before the Artesian Wells Commission. The facts relied on are the hydrostatic 
level, much diminished, however, by friction in the distance traversed by the 
water; the immediate growth in it, after discharge, of vegetable matter similar to 
that seen in the riv'er mentioned; and an apparent rise of the hydrostatic level in 
accordance with an observed rise in the riv^ers. The endurance of the flow is 
again very suggestive of a constant and large supply of water, such, indeed, as 
we might think could only be kept up by two rivers of this size and a large basin 
for its receiition and storage. 
The correspondonco between the rise of the rivers and any rise in the jets 
requires more and very careful observation, and Mr. 
Beinaiks on these. Poulain expressed himself to me as not being very sure 
on this point. The vegetable matter is certainly similar to that seen floating 
along the river channels, but the same growth may bo observed on the surface 
of most wells and certainly in the channels leading from them. Little can bo 
made out of the quality of the water, for it must have undergone many changes 
in its passage through the different beds, even if it percolated only along one 
series. I should cei'tainly never take it to be water from the higher levels of the 
Gingee or Pennar, for, outside of the alluvial area these waters have travelled 
over gneiss which is frequently weathered, and over soda soils. To all appear¬ 
ance, it might have come from the great tank some 7 or 8 miles to the west of 
Pondicherry. 
However, there is the hydrostatic level which requires a head, and some 
distance is required for that in a gently sloping plain. Por the constant and large 
supply of water, so far, the difficulty is not groat, the whole amount discharged 
from the three wells in the year being only about 160,065,975 gallons, or say 
737,000 cubic yards. 
The Pondicherry-Cuddalore allurial plain or bay may be said to have its head 
at the village of Allabadi on the Pennar at about 27 miles 
The alluvial basin. -jiii -i 
west of the sea shore. From tins point, the bay widens 
out to the east-north-east and cast-south-east, the one edge going away, without 
much indentation, towards Cuddalore, which town is situated on the southern 
seaward arm or horn of the plain, while the other bends round in two loops up 
‘ Travaux des Commissions Locales, rondicherry, 1877. 
