38 
Records of the Geological Survey of India. 
[VOL, VIII. 
a very hard and thick band of highly quartzose and ferruginous gneiss is met with, in which 
the run of the strata is rather tortuous; while there are indications of a synclinal roll in 
the great wall of rock crowning the ridge above old Dayvallah and in the Needle Rock. 
In the depression north of the Marpanmudi range there is a wide belt of much more varied 
gneisses, which, on the whole, are not so felspathic as the Dayvallah hand, nor so quartzose 
and kornblendic as that of the Ouchterlony valley. This zone is traversable to beyond the 
Cheyrumbadi hill station, when a further curved belt of gneiss with more schistose bands 
comes in as in the Yytheiy Cholady and Sultan’s Battery country. 
Two * cores * of granitic rock. 
In the country just mentioned there are two large hill masses of granitic rock ; namely 
Yeddakulmullay near Sultan’s Battery and Mumramulla or Cul- 
petta hill nearer to Vytkery. These are, as it were, great rocky 
cores around and over which the foliated gneisses were laid down, the great arches or undu¬ 
lations of which are now evidenced by the westerly dip and subsequent synclinal displayed 
in the Chambra, Yellambalari, and Panora peaks and the rest of the Yellaramnlla range, the 
easterly dip of strata on the Sultan’s Battery and Manantoddy side of the country ; and the 
narrow Strip of folded beds in the wall like crests of the Marpanmudi ridge near Dayvalla, 
south of which there is the generally southern dip of the Ouchterlony valley strata. The 
rock of Culpetta hill is a very rough weathering, pale flesh-colored, rather coarsely crystallized 
compound of quartz, felspar, and silvery mica, showing no trace of foliation. It wears away 
into huge rounded masses of still harder rock, giving the hill rather a resemblance to those of 
the Mysore country in which the gneiss is often highly granitoid. Yeddakulmullay is made 
up of a much finer textured rock of quar-tz and felspar, and minute particles of black and 
greenish mica, which when weathered looks very like a coarse buff sandstone. On the 
western flanks of the mass, the roclt is rather laminated or foliated. With both these cores 
of granite there is a decrease in the number and thickness of the quartz veins ; but these 
appear again quite strongly to the northwards crossing the Sultan’s Battery—Culpetta road. 
Otherwise, the country is remarkable for the non-occurrence of any strictly intrusive rocks 
Hardly any intrusive rocks exc ept in a very small way. There is a dyke of hard, compact dark- 
in South-east Wyndd. green diorite seen for a very short distance in the Hamsluck 
estate to the west of Dayvallah. The width of this dyke is about 35 feet; and it is strik¬ 
ing east by north, west by south, nearly vertical. It cuts off the northern end of Hamsluck 
Reef. A few small largely crystallized granite veins occur here and there over the Dayvallah 
hand of felspathic gneiss, as near the dyke just mentioned and around Gudalur. Large 
flakes of mica from these are common on the Nadgani-Gudalur road. 
In connexion with this rare occurrence of granite veins it may be noticed that the 
quartz reefs of Cheyrumbadi are in some cases charged with 
Quartz reefs become granitic. assera p,j a g es 0 f large plates of mica of 2 to 3 inches in diameter; 
and there thus seems to be a tendency in the western veins to become granitic rather than 
simple quartz lodes. Likewise from Cheyrumbadi the quartz of the reefs is becoming 
rather granular and saccharoid. 
Sufficient data have not yet been gathered to he able to write with any confidence as to 
, how the quartz reefs may have been affected by the different belts 
Variation in country rock \ , .. , , , . . , 
does not affect reefs or their of gneiss in which they were deposited. liie ledges certainly 
contents much. Be em to show stronger in tbe Dayvallah belt. They nip out very 
tliin, and even disappear in tbe hard Marpanmudi range; but they come to grass again 
to the north of this. There are perhaps not so many reefs to tbe north of tbe Marpanmudi 
range as to the south of it. The occurrence of gold in the leaders does not seem to have 
been affected one way or other on either side of this ridge, for the old Korumbar works are 
as frequent about Nellialum and Pandalnr as on the Dayvallah side. 
