PART 2.] 
136 
King: on the Artesian Wdls at VondicJiemj, 
Surface inclinations. 
tlie Gingee valley before it trends round again with a south-east curve towards 
Pondicherry. In this way the j^lain widens out considerably for a time until it 
has a breadth of some 24 miles, and then it closes in towards the sea-coa.st to a 
breadth of some 12 miles between the low plateau headlands of the Hod Hills of 
Pondicherry on the north and Capper Hill near Cuddalore to the south, after 
which it again widens out to the sea beach by the two arms or horns already 
mentioned, only the northern horn is flanked to the sea by the Eed Hills, which 
drojs down in low cliffs to the holt of sea sands. 
The area of the plain may be roughly stated at 600 square miles, and the bound- 
Its area <tc receptive of waters from the adjacent rising 
ground may be taken as 160 miles long. The drainage 
supply of this basin is, however, tremendously increased by the two large rivers 
flowing into it. 
An estimate of the surface inclinations may be made from a calculation by 
Mr. Carriol, who states that the village of Villapuram 
(23^ miles due west of Pondicherry) is 154'84 feet above 
mean sea-level, which would give a rise of 6| feet in the mile. Allabadi at the 
head of the plain is about 12 miles further west, and at the same rise would be 
232 feet above the sea; but as Villapuram is at the end of a spur of rather 
elevated ground between the two rivers, there can hardly bo such a differeneo 
between it and the bed of the Penndr below the above village. It will bo safer to 
take the level of the river bed as about the same as that of Villapuram: so that 
from its debouchment on the plain to the coast thei’o is a fall of at least 4'3G feet 
in the mile. 
The basin in which the alluvial deposits of the plains are laid down appears 
Form of the hasin and gradually from its western edges, but to deepen 
the lie of its alluvial do- more suddenly on its north and south edges, though it 
again has a shelving edge on the seaward side of the 
Pondicherry Red Hills. The borings themselves do not show very much as to the 
thieknoss of the deposits, though that in the Ville Hoire makes it 642 feet, com¬ 
paratively close (about 1| miles) to the Red Hills. As far, too, as these borings 
go, there appears to bo a tolerably flat lie of the beds, or at any rate a very low 
dip of between 2° and 3° to the eastward. 
The floor of the basin is a wide hollow worn in the gneiss or bottom rock of 
The geology of the floor. country, its northern and southern edges being of the 
overlying cretaceous and tertiary strata which were once 
continuous over what is now the hollow. The latter foiunations are dii^ping at low 
angles to the eastvs'ard, and form a slightly elevated country to the -westward of 
Pondicherry and Cuddalore ; so that a traverse from either of these places passes 
from the alluvium to the rising plateau hills of red tertiary sandstones and 
conglomerates (Cuddalore sandstones) of the Red Hills, across these and down 
to a lowlying belt of cretaceous rocks, and then on to the further rising grounds 
of the crj'stallinc or floor rocks. At the Pondicherry side, this order of outcrop 
is not quite so regular; here the red sandstones have not been so completely 
denuded to the westward, and thus a patch (the well-known fossil wood beds) of 
these still remains at Trivucari lapping over the cretaceous beds on to the gneiss. 
