20 



Geology of the Country 



[July 



that of the ridge itself, that is nearly N. and S. This of course must be 

 understood of their trunks, because the ramifications had no particular 

 common direction, but shot from their sides at different angles (No. 65). 



This sienite, at the points of contact with the basalt, and for some 

 inches in its vicinity, acquires a greater degree of hardness, the felspar 

 assuming the appearance of the compact variety ; while in the same 

 block, at a distance from the basaltic dyke, the sienite is in a friable de- 

 cayed state ; the same changes in compactness occur in those pieces of 

 rock which are entangled in the trap. In the sienitic porphyry it is 

 not rare to find some veins of chlorite (No. 66). 



On arriving at the foot of the masses below the Pagoda, a bed of an 

 euritic rock is met with, seemingly in tabular masses, jutting through the 

 sienite. It is of the same composition and structure as the blocks 

 placed, mantle-shaped, on the declivity of the ridge further north, 

 where it also appears to form the summit of the hill. 



In appearance, this euritic rock resembles the silicious schist of Se- 

 ringapatam, but I saw no fissures, nor dendritical infiltrations, in this rock. 

 The smaller pieces of this eurite assume a prismatic form, well defined. 



The huge masses at the summit are of a very hard, tough and com- 

 pact sienite, its felspar being of a pale brownish colour, which, toge- 

 ther with the black of the hornblende, gives to the rock a greyish ap- 

 pearance (No. 67). The soil resulting from the decomposition of this 

 sienite is clayey, crumbling when dry, not tenacious, and of a grey 

 colour. 



Tripatoor.— About three miles from, and east of, the Bungalow of 

 Tripatoor, there is a hill in the form of a ridge running N. and S. that 

 is precisely in the same direction as that of Palliconda, which last 

 seems to be a continuation of this of Tripatoor, having probably been 

 erupted by the same convulsion, at the same remote period, and through 

 the same fissure in the crust of our planet. It rises abruptly from the 

 plain, having, in all its length, uniformly the same height, about eight 

 or nine hundred feet above the plain. Its sides are steep, stony, and 

 overgrown with thick bushes and a few trees. The only part I examin- 

 ed was about three miles along the foot of the south side. 



Over the whole plain, before reaching the hill, were scattered loose 

 masses and pieces of a porphyritic rock, which appears to form the 

 entire hill. On arriving at its foot, we see nothing but porphyry, with 

 an occasional block of sienite. 



This porphyry (No. 68) is composed of regularly formed crystals, in 

 general of a pale flesh colour, but, not unfrequently, they are white, 

 imbedded in a paste of compact felspar, of the same colour as the crys- 

 tallized mineral ; so that the rock has an uniform hue. 



These masses of porphyry, which are near the sienite (to be describ- 



