36 toote: geological structure of the eastern coast. 



country around and south of Gingi fort, in South Arcot, &c. Only one 

 croup of tors in the Nellore-Kistna country has impressed itself on my 

 memory, and that through its grotesque shape. This group, which when 

 seen from the south by morning light has a most striking resemblance 

 to a huge elephant charging a gigantic tortoise from behind, lies a few 

 score yards off the path leading from Nakri Kallu, on the great trunk 

 road to Gundlapalle, 4 miles to the north-west, and about half-way 

 between the two places. It belongs to the western granitoid band. 



Of the small outliers of granitoid gneiss which, as before mentioned, 



Porphyritic rock at occur here and there within the limits ° f the 

 Yikum. schistose gneiss bands, only one needs special men- 



tion ; it forms a low rocky hill close to Yikuru, 3 miles west-south-west 

 of Narasaraopeth. The rock here is a very typical porphyritic variety 

 of rich purplish-grey colour, which might be quarried and converted into 

 a very handsome building stone. The enclosed crystals are prisms of 

 grey felspar imbedded in a hornblendo-felspathic matrix of darker colour. 

 The dark black variety of hornblendic granite gneiss which I have 

 "Trappoidth" °ranite described as trappoid, occurs mostly in the central 

 g neiss - part of our area, and chiefly in two patches north 



of the Chimakurti mountain, the larger lying to the east of Potha- 

 kamur, in Darisi taluq, the smaller some miles to the north, on 

 the left bank of the Gundlakamma, and running up to and including 

 the Bogala Konda, the reputed centre of the numerous slight earth- 

 quake shocks that are experienced in the Ongole country. 



The typical trappoid rock shows nothing but hornblende and felspar, 

 in a crystalline mass of varying degrees of coarseness. Quartz is very 

 rarely seen in it. The colour ranges from dark blackish-grey to almost 

 absolute black. Weathered surfaces are often absolutely black, and the 

 rock, when seen in detached masses not large enough to show the bed- 

 ding, is not distinguishable from bedded hornblendic trap. 



This is markedly the case at the eastern end of the Pothakamur 



trappoid area above named, especially in the 



At Pothakamur. 



masses of rock seen about a mile to the north o£ 

 ( 36 ) 



