GNEissic rocks: trap dykes. 57 



The other three occurrences of crystaUine limestones w^re '.-^Firstly ^ 

 a bed of grey crystalline limestone underlying the haematite-schist bed 

 which forms the crest of the ridge south of Bail Hongal in the upper 

 valley of the Malprabha. Secondly, a small out-crop of very silicious 

 grey limestone forming a couple of small iuliers in the Deccan Trap 

 area four miles east of Nelseri traveller's bungalow on the Belgaum 

 Kaladgi road. The third and last of the occurrences of crystalline 

 limestone was observed at Guganhatti six miles north-east by-north 

 of the second locality. A very considerable bed of grey limestone 

 occurs there east of the village, associated with argillaceous and mica- 

 ceous schists. 



Intrusive rocks associated with the Gneiss Series, 



1. Trappean rocks. 



The foreign rocks that are found traversing the ancient gneissic 

 series are of three classes : firstly, trappean rocks ; secondly, granitic rocks ; 

 and thirdly, quartz reefs. Of these the trappean rocks, which occur in every 

 case but one as dykes, are by far the most important, being both numerous 

 and many of them of great size and length, Lithologically they show 

 biit very trijEliug differences ; nearly all consist of basaltic diorite of 

 dark-bluish or greenish-black color and moderately fine grain. A few 

 dykes are porphyritic in their structure, and, from the greater quantity 

 of felspar, they are grey or, more strictly speaking, speckled white 

 and blackish (pepper and salt). Occasionally the felspar is of a green 

 color, mostly of a pale hue. 



Several are remarkable for their great size, such as the Gutt Bichal 



on the noith side of the Tungabhadra opposite Cachapur, from which 



the greater part of the material for the piers the great Cachapur Railway 



bridge was quarried. This dyke is one of the important group which 



H . { 57 ) 



