196 
Records of the Geological Snrreg of India, 
[voi„ xir. 
5° or so east or west of north. A relatively small number of dj'kes does not 
come under either of these two systems, but they offer no special differences in 
mineral character, or otherwise to reqirire any detailed notice. There is no 
marked difference between the trap rock forming the members of the two systems, 
and they appear to belong to the same geological age. Both agree in being 
older than the Kadapa system of rocks which they nowhere intrude into. The 
relations of the dykes at their crossings, are obscure in all cases in this district, 
but the intersections of other dykes of precisely similar rock and running in 
corresponding directions in more northerly parts of the gneiss area, e.cj., in 
Belhiry district and the Raichur doab, appear to show that the filling up of both 
sets of fissures by the iiTuptive material was simultaneous, no difference or change 
of any kind being observable. Very large and important dykes, such as the 
great dyke at Sholinghur and some in the Maddur (Muddoor) and Trittani hills, 
rise to heights of several hundred feet above the sui-face, and form bold and 
striking ridges and crests. 
Some of the dykes, such as the Sholinghur dyke and the Permalrajapet 
dyke, some eiglit miles to the east, are distinctly and strongly magnetic and affect 
the compass needle greatly. This phenomenon was also noticed in the dyke 
lying to the west-by-south of the village of Poiney, but not elsewhere. 
Excepting a little pale iron pyrites (marcasite) no accessory minerals have 
been noticed in any of the dykes. The pyiites were seen in some of the dykes 
traversing the hill east of Vellore town. 
Well characterized examples of porphyritic greenstones are to be seen to the 
soirth-east of Ranipet cantonment, and in the railway-cutting south of Pudi 
station on the north-west line of the Madras railway. As a rule, with few or no 
exceptions, the greenstone weathers more slowly than the surrounding gneissic 
rock, and consequently the dykes form ridges running over hill and dale, and 
fi'om their dark color contrasting strongly against the gneiss. 
The courses of many of the dykes may be followed for twenty or thirty miles 
or even more, and the lai’ger ones have a width of from 60 to 100 paces. The 
network formed by these multitudinous dykes is one of the most remarkable dis¬ 
plays of trappean injection known in any country. 
The Kadai'A Series. 
The rejiresentatives of the Kadapa series are confined to the north-eastern 
corner of the district, where they form, as already pointed out, the main mass of 
the Nagari group of mountains, the Tripatti hills, and the extreme south end of 
the Vellakonda range. The remarkable and highly picturesque scenery of this 
region is due to the great mural scarps into which the massive quartzite beds have 
been worn. 
The Nagari mountains form several outliers detached from the mni'n area of 
Chief outliers Kadapa rocks, of which the Tripatti hills and the end 
of the Vellakondas form the southernmost extremities. 
The principal outliers are four in number, the Nagari Nose mountain forming the 
most southernly of the number. Noidh of this is the Narnavaram ridge, a long 
