PART 3.] 
Foote: Geological features of the Madura Bislrict, ^'C, 
143 
Tlio gneissic rocks occii 2 :)y tke western part of the area to be described, and 
Tlie gneissic scries. form the highest prominences in it. Amongst them are the 
line of hills stretching from south of Kolatur (Colatoor), 
south'South-wostward to the Pudukotai-Illipur road, near Annavassel; and soyeral 
small granite gneiss hills to the south of the Vellar, at and near Trimiem. 
Between the valley of the Manimut-ar and that of the Vaigaiat Madura, a number 
of hills of small height, but often of very striking outline, occur dotted about at 
no great distance from the eastern boundary of the gneissic area. Between these 
hills the general surface of the gneiss country is gently undulating. 
A considerable part of the surface of the gneissic rocks is occupied by debris 
of the younger overlying rocks, which have been in greatest part destroyed by the 
denuding agency of atmospheric forces. 
The rocks assigned to the Rajmahal section of the Upper Gondwana system 
are very slightly exposed, and their contact with the 
gneiss was not visible, but there is no reason from the 
analogy of other parts of the Coromandel coast to imagine that their base rests 
on anything else than the gneiss. 
The Cuddalore sandstones and grits rest, wherever their base is exposed, on the 
irregular surface of the gneissic rocks, and are them- 
Rajmabal secondary rocks. 
Cuddalore tertiary rocks. 
selves overlaid by lateritic conglomerates, gravels and 
sands, the^relations between the two being extremely obscure fi'om the great 
petrological similarity of two of the princijial members of either group, and 
from the exceedingly limited number and unsatisfactory character of the sections 
in which the two series are exposed in juxtaposition. 
The total absence of organic remains from both series greatly increases the 
difficulty of dealing with them. The unconformity of the two groups is inferred 
fi’om the extensive overlap of the younger of the two. The stratigraphical 
phenomenon of overlap generally involves unconformity between the formations 
affected by it, but no positive physical necessity exists that there should bo 
such unconformity in every case, and I have been often strongly tempted to tliink 
that in this region it is a case of non-jjroven. Only one section was seen in 
which unconformity could be demonstrated, and in several of the host sections 
there is a passing of true mottled grits, which may belong to cither gi’oup, into 
lateritic conglomerates of the most typical character, instances of which will be 
adduced further on. 
The Cuddalore conglomerates, sandstones, &c., appear to be the lower part of 
one formation; the lateritic conglomerates (mostly), gravels and sands the 
upper part of one and the same group of I’ocks ; mottled grits of both ages 
apparently lying in between. 
The conglomeratic beds of both groups occur in the western* parts of the 
areas, and generally close to the boundary, at which they are mostly well displayed. 
The gravelly and sandy members of the lateritic group occupy the eastern 
part of the slope, and sink in most cases very gently 
The latentio roc s. ] 3 elow the delta of the Cauvery, or the coast alluvium. 
^ North of our area the conglomerated forms are hest seen along the iiorthcru houndarv of 
the formation between Vellam and Taujore. 
