LOWER TRANSITION ROCKS. 165 



extent to furnish material for inverts and road revetments near its 

 eastern end. It is the very toughest rock I ever tried to break, but 

 the felspar has been weathered to a considerable depth neverthe- 

 less. Two other small patches of similar trap occur about a mile to 

 the north of this dyke. A very small protrusion of similar blotchy 

 trap is to be seen immediately north of Chaganur on the left bank of 

 the Haggari. It looks very much like an extension of the Permade- 

 vanhalli dyke, but if it be so the course of the dyke has made a great 

 trend to the north-west. No other shows of similar trap are known 

 to me anywhere else. 



CHAPTER VI. 

 Intrusive rocks in the Arch^an area. 



As will be seen by a glance at the map, and as has been pointed 

 out in the last chapter, large numbers of intrusive rocks, chiefly in 

 the shape of trap dykes, some of them of great size, occur scattered 

 all over the Archaean or Granito-Gneissic area in such positions with 

 reference to the Dharwar system that their relative ages cannot be 

 determined at present, while a mere macroscopic examination of their 

 texture affords no satisfactory help in this matter. Beside the trap- 

 dykes (A) are a considerable number of runs of Brecciated Quartz 

 (B), many of which attain to great size and form the crests, and in 

 some cases the mass of very considerable hill ridges. Pegmatite 

 veins (C), mostly of small size, are not uncommon, but require but 

 little notice. Epidote- granite veins (D) in which epidote in its pista- 

 citic variety takes the place of mica are also not uncommon, but with 

 a few exceptions to be mentioned further on, they are very small and 

 of little interest. 



A, The Trap-dykes. 



The number of these occurring within the Archaean area is large 



Prevalence of dioritic and manv of tnem are of verv considerable size 

 dvkes - and. length and form marked features in the 



landscape in many places. To the unaided eye they appear to be 



( 165 ) 



