198 
Records of the Geological Survey of India. 
[voL. XII. 
Divisioxa into two groups. 
jeveram. The most important and the greater number of these patches lie 
around the great Mamdur (Maumdoor) irrigation tank, and hence the group may 
be conveniently called the Mamdur group. Three small outlying patches occur 
twenty miles further to the south-west in the Arni zemindai'i. This group of 
small patches are evidently the remnants of a once extensive spread of the Upper 
G ondwana I’ocks, which, in all probability, was continuous with the beds of the 
same age to the north and north-east, and very likely also extended far enough 
southward to join the Utatur (Ootatoor) “plant beds” in Trichinopoly district. 
Great denudation, especially in the area south of the Palar, beginning pi’obably 
in precretaceous times, separated the Gondwana rocks into the many detached 
outliers now enumerated, while their surface is largely obscured by the overlying 
younger latcritic and alluvial formations. 
As before mentioned, the Upper Gondwana beds of the Madras region have 
been divided into two groups, called after the localities in 
which best developed, the Sattavedu and Sri^jermoiur 
groups ; the division is chiefly based on petrological differences, the actual strati- 
graphical relations being very obscure and somewhat doubtful owing to the in- 
Bufficiency of existing sections. 
The Sattavedu group, which con.sists mainly of coarse, well consolidated con¬ 
glomerates and sand.stones of great thickness, forms the 
The Sattavedu group. Sattavedu and the northern and eastern parts of 
the Alikur hills, while beds of uncompacted conglomerate with intercalated clays 
and shales appear to underlie the hard Sattavedu beds in the western and southern 
parts of the Alikur hills. Unfortunately no section exists (or existed) showing 
the two sets of beds in actual contact, hence their str.atigi’aphical relations are 
still doubtful. 
The soft beds have been refeiTed provisionally to the 'Sripermatur group on 
petrological grounds, the resemblance of the softer rocks 
The Snperinatur group. much stronger to the rocks found in the Sripermatur 
outcrop in Chingleput district, than to the coarse and comjxact conglomerates and 
sandstones of the Sattavedu and eastoi'n Alikur hills. 
The whole of this outcrop is made up of alternate bands of hai'd conglomerates 
and sandstones, m.any hundred feet in aggregate thickness, 
and of more or less red color. The conglomerates are 
made up of large wmll rounded smooth quartzite pebbles, with a small number of 
similar jicbblos of granite gneiss, the whole strongly cemented by a matrix of 
variable character, sometimes argillo-ferruginous, ferrugino-arenaceous, or more 
rarely siliceo-calcareous. The sandstones arc mostly rather gritty in texture, and 
contain here and there a few plant remains, among which Mr. King found a frond 
oi Dictgozaviites 'hidicus, one of the most characteristic Kajmahal plants. The beds 
have a generally eastward dip at moderate angles. The area of the outcrop is 
nearly co-extensive with that of the hill gi-oup, and measures about sixteen miles. 
The Alikui’ area is separated from the foregoing only by the narrow alluvial 
valley of the Narnavaram rivei’, under which the beds arc 
The Alikur area. doubtless continuous. The eastern half of the Alikur hill 
group consists of hard conglomerates and sandstones, apparently continuations of 
The Sattavedu area. 
