PAET 2.] 
Kin//: OH the Arle-iuni fFolls at Pondickei'n/. 
137 
ters of tlie latter area, there would not be much probability of success here. 
Its alluvial deposits are, however, not confined to this bay, but are connected, 
to the north-west, Avith the great flat of the Cortelliar and Narnaveram river 
basins, the permeable beds of which may trend down in this dii-ection. 
This western plain is flanked to the north and soutli rcspectivelj^ by the 
Us proper alluvial bay Thomas’ Mount range of high 
small, but still possibly ground, whence it spreads outwards and seaAvards, joining 
able to supply water Cortelliar alluvium on the one side and stretching 
with a head. in . , " 
down the coast to Covelong on the other. It extends to 
the Avestward by a long arm, at the we.stern end of Avhich it is again connected 
Avith the Cortelliar alluviums by a narrow neck across the south-Avcsterly exten- 
sion of the Red Hills plateau ; and it sends another good al'm to the south-we.st 
past the Palaveram hills. Its extreme length to the western neck is about 20 
miles, the breadth between the two low headlands being about 71 miles. Tlie 
receptive edge is not more than 80 miles in length, and the area, including the 
stretch to the coast, is at a rough calculation about 175 square miles. It is only 
fed by the Triplicane (also called the Madras riA'er and the Cooum) and the 
Saidapet (othcrAvisc the Adyar) rivers, Avhich liaA-e, hoAA-ever, only small drainage 
areas. Thei'e is a possibility, hoAA'ever, that a fair supply of Avater may be dravAui 
in at the Avestern neck by the narroAV channel there connecting the Cortelliar 
alluviums with those of the Triplicane riA'er. In fact, unless there i.s a sup])ly 
of this kind at that point, no head of Avater can, I think, be reckoned on until 
Avithin 8 miles of Madras, Avhon AA'aters Avould have a sufficient rccoptiA^e edge 
and length of riA'cr bed for their collection. 
There is CA-ery reason to suppose that the uppermost of the two clay bands at 
Pondicherry may even be found in the Madms plain, the same kind of shelly 
deposit having been met Avith in the few shallow borings which have from time 
to time been made, while the extent of this plain compared with the size of the 
streams floAving into it seems to indicate a wide-spread or westAvard extension 
of estuarine beds. 
I have alreacly expressed my opinion that the water of the Oopallem well is 
from the permeable band under the upper clay seam of the Pondicherry plain, and 
there is just a possibility that this permeable seam may crop up in the Gino-ee 
or Ariancup river a feAV miles west of the town. This is a bare possibility only, 
which, however, does not practically affect the Pondicherry supply; but it is the 
only supposition Avhich gives promise of any rise from small basins like that of 
Madras, and it may be that the head gainable at 6 or 8 miles from the coast 
would be sufficient for a rise. The quantity of Avater is, I belieA^e, attainable in 
the Madras bay, Avithin 8 miles of the toAvn. 
Fortunately, hoAveA’-er, as I think, for Madras, it is situated on the southern 
The proximity of the ^he Cortelliar and Namaveram plains, and in these 
Cortelliar and Nariiaver- there are, to all appearance, all the necessary require- 
am plains. ments as to head of Avater gained by distance on a gentle 
rise, combined with a very large reception edge. The Cortelliar plain is also 
joined in a remarkable way Avith that of the Palar river at a point above where 
the latter has a clear channel through the gneiss, and it is not at all improbable 
