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Records of the Geological Surrey of India. 
[vor,. m. 
Their general character, as seen at the surface, is that of pure, or nearly pure, silicious 
sands, but beds of black, blue, or grey clay occur largely below the surface in the marine 
alluvium near Madras; these are, however, much less frequent in the fluviatile alluvium 
higher up the river valleys. The greatest depth to which the marine beds have been 
pierced by sinkings is 55 feet, when the gneiss was reached. In the marine and estuarine 
beds along the coast many of the clays are largely filled with shells, all of living species, hut 
in a sub-fossil condition. Such marine beds are known to extend two to three miles inland, 
but I could not ascertain whether they had been penetrated by any sinkings further inland. 
The river alluvia are of more interest than the marine, because they afford evidence of 
some remarkable changes within the human period in the courses of several of the principal 
rivers in the district. Lithologically, the fluviatile alluvia are of no interest, for they consist, 
as a rule, of nothing but coarse, gritty, loose, silicious sand. Gravels or clayey beds are rare, 
and organic remains are hardly ever met with, excepting a few Helices and fresh water 
shells, (all of liviug species), in thin beds of reddish loam. 
The changes in the course of the rivers above referred to are four in number, and concern 
three rivers, the Palar, the Conciliar, and the Naggery river, but I will only notice the two 
most important here. 
The Palar now flows into the sea 42 miles south of Madras, but it, or a large branch 
of it, formerly flowed down what is now the alluvial valley of the Cortelliar, and debouched 
into the sea, somewhere to the north of Madras, probably between Ennore and Pulicat. 
The present Cortelliar valley is very disproportionately large as compared with the river 
which runs through it in a rather deep channel. 
The present valley of the Palar is still more disproportionately small as compared 
with its river; the two alluvial valleys join, or rather diverge, at a place about 10 miles east 
of the town of Areot. A stream is even now connected with the Palar just at the fork 
by which water is still carried down the Cortelliar valley for many miles and eventually falls 
into that river. 
This stream is considered by the natives to be the old Palar and hears a Sanscrit name, 
Yridachara nuddee'or old milk river, the Tamil word Palar also signifying milk river. A 
Similar change, of course, has occurred to the Naggery river, which in former times fell into 
the Narnaveram river, close to the Itamaghiri mountain, atNagloperam. The Naggery river 
was diverted from its old course at a place about t wo miles east by south of the town of 
Naggery, and made, by the cutting of a channel about half a mile in length through 
gneissio rocks, to turn to the south-east instead of flowing due east and east by north and 
to fall into the Trittang river, which joins the Cortelliar a few miles further east. The 
broad alluvial valley which now runs between the Naggery mountain ridge and the Alicoor 
hills is in consequence of this change drained only by small streams and artificial channels. 
I could not obtain any information on this point from the enquiries I made on the spot, 
but from the appearance of the cut through the neck of gneissio rock above described, I think 
the change of the river course was the result of human agency. Like the alluvium of the 
Palar river the alluvia of the Naggery river (both in its old valley and along the newer 
channel as far as its junction with the Cortelliar) and of the Narnaveram river consist almost, 
entirely of coarse gritty sand ; clay beds are rare, but where met with are of black color and 
regur-like texture. All the rivers named appear to be still cutting their channels deeper and 
deeper every season. 
Lateritie formations .—The formations classed under the above heading are of three 
principal kinds, namely, clayey conglomerates, gravels, and sands which occur distributed over 
nearly' the whole of the area under consideration. 
Their occurrence is, however, not so much in continuous spreads as in detached patches, 
many of which are but of small size, though some occupy important areas from one hundred 
to two or nearly three hundred square miles in extent. 
These larger areas occupy, as a rule, the higher grounds lying between the different river 
valleys; the small patches occur at similar levels and are evidently outliers left by partial 
denudatory action by which the once continuous lateritie deposits have been thus broken up. 
The thickness of the laterit ie formations is very small when compared to their super¬ 
ficial extension. They 7 rarely attain a thickness of 12 feet or upwards. 
