194 Beoords of the Geological Survey of India. [voL. xii. 
In a district wliere so large an area is occupied by intensely granitoid gneiss, its 
cbaracteristic features are of course to be seen to great advantage in many 
places, particularly along tlie two lines of railway diverging from Arconum junction. 
Especially characteristic are the hills of Maddur Drug and Trittan on the 
north-west line, and those of Shoirnghur, Nelacontriapetta, and Gudyatam 
(Goriattum) on the south-west line ; all of these show great bare masses of rock 
with tors, and here and there great precipitous cliffs. 
Of the tors the two most remarkable groups are both near Nagari ; the one, 
betw’een the railway and the foot of the Nauari mountain 
Tors. 
close to the northern end of the pass travei’sed by the old 
high road to Kadapa; the other, at Neddiem (Neddum) on the north bank of 
the Hagari river, four miles above the railway bridge. Both groups are of great 
size and height and form conspicuous objects from considerable distances. 
A very common accessory mineral occurring in the granite gneiss is epidote, 
in its pale apple-green variety known as pistacite ; it occurs scattered through the 
general mass of the rocks, or in minute veins, and very commonly as a thin coat¬ 
ing to planes of jointing. 
EOCICS INTRUDED INTO THE GnEISSIC SeEIES. 
The crystalline rocks intruded into the gneissic series are referable to four 
groups—granite veins, felspathic porphyries, quartz veins, and trap dykes. Of the 
four groups, the last is by far the most important, and the first the least so, granite 
veins being very rare and of small size ; the trap dykes, on the contrary, extremely 
numerous, and many of them of large size, and forming important features in the 
landscape in very many parts of the country. 
The granite veins seen in North Arcot are, with one exception, of quite small 
size, and all appear to consist of a binary rock, in which 
VfilllS* 1 ‘iiCt J? 
only quartz and lelspar are recognizable, home oi them 
contain a few scattered crystals of epidote as an accessory mineral. 
Numerous veins of very small size of dark salmon-red color, and highly 
felspathic in character, occur in the gneiss to the south of the railway station at 
Vellore, and a larger but still small vein of the same kind occurs at Vajur 
(Vanjoor), two miles south-west of the railway station. 
The most important granitic protrusion noted is a vein occurring at Tarur 
(Turroor), eight miles east of the great Kaveripak (Covrepauk) tank, and about 
ten miles south-west of the Arkonum railway junction. It forms a bare and 
generally smooth ridge one and a quarter mile long, about 40 feet high at its summit. 
It is a binary quartzo-felspathic granite of coarse grain and full of minute 
cracks. 
The very handsome green and pink syenitoid rock occurring at the western 
base of the Nagari mountain has been referred to before (p. 192) when treat¬ 
ing of the gneissic rocks, but the rock is so extremely crystalline that it might 
easily be taken for a truly intrusive rock, and the more so as the position it 
occupies with reference to the surrounding unquestionably gneissic rocks is rather 
obscure. 
