[vOL. XII. 
aor» Records of Ihe Geological Survey of India. 
Tlie two valleys diverge at a place about ton miles east of the town of Arcot, 
and a small stream (or irrigation channel) still branches fi’om .the Palar here 
and flows down the Kortelliar valley for many miles and eventually joins the 
latter river. To this stream the natives have given the Sanscrit name of 
Vridacharanadi or “ old milk river, ” the Tamil name of the main river “ Palar, ” 
also signifying “ milk river.” The alluvium occupying this valley consists of coarse 
gritty loose silicious sand of gneissic origin. 
The second case is that of the Nagari (Naggery) river, which in former 
Chance of course of times appears to have fallen into the Narnavaram river, 
the Nagari river. just south of the Ramagiri, and close to the village of 
Nagloperam. The present course of the river lies down the old alluvial valley 
for a (little more than throe miles east from the railway bridge. It then turns 
sharply south-east, leaves the alluvium, and flows through a cutting in the 
gneiss about a mile and a half long and falls into the Trittani rivei’, which joins 
the Kortelliar a few miles further east. In consequence of this the broad alluvial 
valley which runs between the Nagaiu mountain and the Alikur hills is now 
di’ained only by small streams and artificial channels. Tlie alluvia deposited by 
the Nagari river both in its old and new valleys consist almost entirely of coarse 
gi’itty sand like that of the Palar. No alluvium appears to be deposited at 
present, but the streams seem to be cutting their bods deeper and deeper every 
season. 
No information was procurable from the natives as to the time w'hen these 
changes took place, but the probability is that, geologically speaking, they are of 
very recent date, as may bo inferred in the case of the Palar from the name 
given to the channel which still falls into the Kortelliar; and in the case of the 
Nagari river, from the fact that the cutting through the gneiss by which the 
river escapes from its old alluvial valley presents every appearance of being of 
artificial origin, and must in that case have been the work of a people boasting 
some considerable civilization. 
The Soils and Sub-aeeial Pormations. 
Of the soils in North Arcot little need be said ; they appear, as a rule, to be the 
product of the weathering of the local rocks, or to have been brought from but tii- 
fling distances by pluvial action. The prevalent soils are red, and of these the 
sandy form is the most common. 
Of the sub-aerial formations the only really interesting and important 
ones are the taluses around the quartzite-capped mountains in the north-eastern 
corner of the district. As already pointed out, the talus accumulations are two¬ 
fold, and consist partly of great collections of well rounded shingle referable to 
the lateritic period, and above them of the angular unrolled debns detached from 
the great scarps by atmospheric agencies, which debris here now shows the deep 
ferruginous stain characteristic of the lateritic shingle beds. On a greatly smaller 
scale, but still of considerable importance, are the talus accumulations on and 
around the newer Rajmahal and lateritic formations in the Sattavedu, Alikur, 
and Pyanur areas. The.se consist in both cases almost entirely of well rolled 
