76 GEOLOGY OF TRICHINOPOLY, &C. [ClIAP. IV. 1. 



the bed^ the current frequently deflected tlie needle till it became parallel 

 with the lamincB of the mass, whatever their direction happened to be. 



(d.) Granitoid Gneiss of South Arcot. — In the central part of the 

 South Arcot district^ a very considerable area is occupied by rocks having- 

 generally a very granitic aspect^ yet showing in many places undoubted 

 stratification^ especially in their mode of occurrence, as great continuous 

 ridges which may be traced for many miles,, and which form apparently 

 anticlinal and synclinal folds. 



These granitoid rocks extend from a little west of Tiagar-Droog 



hill south-eastward to the Trichinopoly and Madras 

 Extent. 



road, which they follow in a north-easterly direction 



to the alluvium of the Guddalum and Punniar rivers. They re-appear 



on the left or north bank of the latter river, and continue their course 



till they pass beyond the limits of our area. The western limit of this 



granitoid gneiss series may be traced from near Tiagar-Droog northward, 



along the eastern side of the road to Manaturpett, on the banks of the 



Punniar river, A line continued thence through the villages of Walliputty 



and Tandri to beyond the limits of the map, would roughly indicate the 



western limit of the pseudo-granitic rocks. The relation of these rocks 



to the other members of the gneissic series is very doubtful and obscure, 



not one single satisfactory case of contact and 

 Relation of position. . . , . , 



juxta-position having been met with around the 



limits of the large area described above, as including these granitoid 



gneiss rocks. 



In the absence of any satisfactory sections, the general position of 



this granitoid area seems to point to the fact of these rocks overlying, 



or being younger than, for example, the iron beds of Paukum and Cur- 



dychittoor to the west, or than the quartzo-felspathic strata forming the 



great curves of Agraram Kotallum Trigouometrical- 

 Metamorphie origin. f^iiii- 



station hill. Should this not be a correct view 



of the position of these curiously granite-like gneiss beds, the only expla- 

 ( 298 ) 



