206 Notes, chiefly Geological, [No. 171. 



Madras. — Granite and the hypogene schists, have been before stated 

 as the rocks basing the more recent deposits covering the level plain 

 of Madras. In the bed of the river (Adyar) near Marmalong bridge, and 

 on its right bank at the quarries for the old breakwater, in the park of 

 Guindy, around the race course, it usually contains but little mica, being 

 composed of grains of a greyish quartz, with white felspar usually wea- 

 thered and earthy on the exposed bosses and blocks in which the rock 

 makes its appearance. Much of the granite near the Little Mount I found to 

 be pigmatitic, that is, a binary granite of felspar and quartz, without mica. 

 Laterite is seen overlying the granite at the breakwater quarries 

 before mentioned, and I am informed by Capt. Worster, that beds of this 

 rock occur about a mile north of Nabob's Choultry on the Poonamalee 

 road ; — also near Tremungalum, about two miles NE. of Santivellore ; 

 near Vungada, about two miles SE. from Sri Permatoor ; at Cotrum- 

 baucum, half a ' mile north of Raja's Choultry, and about two 

 miles north of Balchitty Choultry ; besides the beds at the Red hills, 

 about eight miles NW. from Madras, so ably described by Mr. Cole, 

 and which occupying an area of about fifty miles, cover an undulating 

 tract, elevated usually forty or fifty feet above the general level of the 

 country. Those near Sri Permatoor tank, I have already noticed (vide 

 notes from Mangalore to Madras.) 



At the bases of St. Thomas' Mount and the Palaveram Hill, granite 

 is seen outcropping, and it also forms some of the smaller hills in the 

 vicinity of Palaveram. 



Both the Palaveram Hill and that of St. Thomas' Mount, are com- 

 posed for the most part of a massive variety of hornblende rock, in 

 which stratification is indistinct. 



This rock, though often entirely composed of black brilliant horn- 

 blende, at Palaveram is usually a dull olive-green colour, translucent at 

 the edges, and appears to be a mixture of hornblende and felspar, 

 with a small proportion of quartz, in an almost homogeneous mixture. 

 This rock occasionally imbeds garnets, crystallized schorl, hornblende, 

 and a little dark mica. A little to the SSE. of the Mount, near the 

 tank, is a lateritic bed. 



The height of the Palaveram Hill, on which the bungalow built by 

 Col. Coombes stands, Lieut. Ludlow informs me, is nearly 345| feet 

 above the plain at its base. 



