188 
Reconla of Ihe Geological Survey of Tinlia. 
[voL. XIr. 
Hydrology. 
The hydrology of the district is very simple, all the drainage falling into the 
Bay of Bengal and chiefly by the Palnr river, which, rising 
on the Mysore jolateau, drains the whole southern half and 
greater pai't of the centre and west of the district. The north-eastern part feeds 
the Koi'teliar and Nagari (Naggory) rivers, and also the hTarnavaram and Suvar- 
namnkhi (Soornamookey). 
The geological formations met with in this district may be conveniently 
classified into six groups, wdiich may bo arranged in their 
true order of suiJerposition as follows :— 
Formations. 
Recent and 
TIAEY. 
Mesozoic 
Azoic 
POST-TEK- 
a; 
Soils and subacrial deposits. 
Alluvial deposits; fluviatllo. 
Lateritic sands, gravels, and conglomerates. 
Upper Gondvvana series, Kajniahal or “plant” beds. 
Kadapa series. 
Gnoissio series, witli intrusive trapipean and granitic rocks. 
Gncissic series. 
The gneissic series, which forms the basement on which rest all the other rocks, 
General distribution of occupies by far the larger part of the whole area of the 
the rocks. district, and it is only in the north-eastern and eastern 
parts that younger rocks occur. The gneissic rocks include all the western part 
of the disti’ict, and form the rugged eastern scarp of the 
Mysore plateau ah’eady referred to (p. 187). Eastward of 
the plateau, are numerous spurs stretching away from it, and eastward of these 
asain are numerous clusters of detached hills, some of considerable size and eleva- 
tion, and remarkable for their bold forms and great ruggodness. These ocenpy 
the gneiss area up to the very convenient geograjihical line formed by the north¬ 
west line of the Madras railway, eastward of which the gneissic rocks soon dis¬ 
appear under neivor formations, to be referred to separately further on. The 
o-ncissic area south of the P41ar shows the northern end of the Javadi mountains 
O 
and the hills east and south-east of Vellore. Further to the south-east the gneiss 
area becomes comparatively flat, and no hills of any importance rise from its 
surface, the two hills of Wandiwash and Chitpat (Chittapett) excejited, which 
have already been named. 
Returning to the north of the Palar, the gneissic rocks are overlaid by great 
masses of quartzite and conglomerate belonging to the 
Kadapa series, which form the greater part of the 
detached mountains collectively known as the Kagari mountains. The south end 
of the Vellakonda and the sacred hills of Tripatti to the north are also formed 
of rocks belonging to the same sub-division of the Kadapa series. 
The tremendous lines of scarp and often vertical cliffs surrounding in many 
parts the Kagari and Trijiatti mountains give a peculiar and grand character to 
the local landscape. 
South-eastward of the Nagari mountains lie the three hill groups before men¬ 
tioned (p. 187), viz., the Sattavedu, Alikur (Allcoor), and 
Upper Gond« ana rocks. Naikenpalem hills, consisting of great beds of hard con¬ 
glomerates and sandstones in the Sattavedu and the eastern half of the Alikur 
hills, and of uncompacted conglomerates, clays and shales in the western half of 
Kadapa series. 
