ARCH/EAN AND PLUTONIC ROCKS. 69 



prevail, but it increases to the northward and becomes conspicuous 

 on some of the spurs. 



Signs of the disturbances and strains to which the rocks have 

 Minute faults and dig- been subjected subsequent to their original 

 locations. formation are to be seen occasionally in the 



form of systems of small dislocations and faults. An interesting 

 example of such was pointed out to me by my colleague, Mr. Lake, 

 on the spur east of Isbee (2 J miles north-west of Adoni). 



As extensions of the Adoni group to the north-north-west may be 

 Extensions to the reckoned the detached hills at Yerragiri, Vura- 

 north-west. konda (Oorkoonky), and Halvy (Hallwy), all 



three of which belong to a micaceous band. Vurakonda shows some 

 of the finest masses of granite that I have ever seen. Their size is 

 simply gigantic, and the whole hill, though by no means a large one, 

 is most striking and picturesque. 



Halwy hill, too, is a fine object and very conspicuous, as it towers 

 up at the edge of the Tungabhadra alluvium. 

 The hill is partly gneissic, partly granitoid. 

 In the gneissic beds, which strike N. 5 to 7 W. with a high west- 

 erly dip, black mica (biotite) often abounds, 1 and many examples 

 exist of minute faulting, such as were seen on the Isbee spur near 

 Adoni, and were referred to above. 



The country lying west of the line of extension just mentioned 

 is very flat, the rolls between the different stream valleys being very 

 low, and entirely covered by black soil. Outcrops of rocks are very 

 few and far between and of no special interest. They are mostly of 

 the hornblendic variety. 



The south-easterly extension of the Adoni group shows many 



Extensions to the picturesque hills which belong to the castellated 



south-east. an d pinnacled types rather than to the blocky, 



but they present no features requiring individual notice. Tengul. 



1 As a rule, in the granites and gneisses of this part of the district the ferro- 

 magnesian constituent of the ro cks, whether hornblende or mica, plays a very subor- 

 dinate part. 



( 69 ) 



