20 KING : NELLOUE PORTION OF THE CARNATIC. 



gneiss. This is, however, all that can be safely said at present, for unless 

 the observer is acquainted by very long and careful surveying with the 

 gneiss of both regions, his comparison of their rocks can only be very 

 general. The one great characteristic or feature of the older Scottish and 

 Lewisian gneiss is its persistent transverse strike to that of the super- 

 incumbent gneiss, the most absolute condition of unconformity ; but thjs 

 cannot be cited as existing among the Madras crystalline series ; for, as far 

 as we yet know, there is no marked deviation of strike in any of the 

 gneisses, and the Cuddapah rocks, however unconformable they may be 

 to their subjacent crystallines, have always very much the same strike. 

 Hence in this one particular point the comparison of the Madras gneisses 

 with those of Scotland loses much of its significance. 



In the following more detailed description of the rocks, that of the 

 country north of the Penned* is taken from the progress reports left 

 by Charles iE. Oldham, while that of the country south o£ the 

 river is mainly from my own work, though here also a good part was . 

 surveyed by my colleague. 



The reel massive or granitoid gneiss. — The massive red gneiss, or 

 The massive gneiss of granitoid form, occupies but a small portion of the 

 the Swarnamukhi. south-west corner of the field along the valley of 



the Swarnamukhi and northwards past Venkatagiri, whence it is traceable 

 westward right into the upland of North A root and Cuddapah. Its east- 

 ern edge is ill defined, but it may be considered to run from below Batanaik 

 Konda in a curving north-north-west line, a short distance to the west 

 of Kalahasti and Venkatagiri, after which it passes under, or becomes the 

 floor of, the Transition Series, only showing again very slightly to the 

 north of the Penner. 



This gneiss is generally a close-grained aggregate of quartz and felspar 

 (orthoclase, ? oligoclase and a little albite), hornblende being often scarcely 

 discernible, while mica is even more rare. It is thus very like a binary 

 granite, only it is perhaps more generally smooth and rounded on its 

 weathered surfaces than the granite occasionally traversing it, the latter 

 being very often more distinctly and largely crystallized (felspar easily 

 ( 128 ) 



