INTRUSIVE ROCKS IN THE ARCHAEAN AREA. 173 



disruption of the run by the diorite dyke and the occurrence of the 



malachite in the run. 



As mentioned above, the quartz-runs have, as a general rule, very 



rocky and blocky crests, but an exception to this 

 A smooth ridge. r 



rule occurs in a great run about ij mile north- 

 north-west of Harappanahalli, in which the dirty brownish quartz is so 

 much cut up by excessive jointing on a very small scale that it 

 breaks up into small fragments, and from a little distance presents a 

 strikingly smooth character, such as was noted in no other quartz- 

 run. 



These quartz-runs are, as a rule, far more cut up by shrinkage 



Excessive jointing. J oints than an ? other cr ystalline rock, more so 

 even than the finest grained, almost glassy trap 

 rocks, which are seen occasionally in small veins branching from the 

 great dykes. 



A very unusually pure white run of brecciated quartz is to be 



seen in the hilly tract about i£ mile south-west- 

 Unusually white quartz. 



ward of the south end of the great tank at 

 Harappanahalli. 



The great Harappanahalli run which is longest of all in 



The great Harappa- the district, forms several low hills in the west- 



nahalh run. ern ^^ Q j j ts coursej w hich measures 14 



miles in all, encircles the north side of the town with a great steep 

 u vallum " as it were, across which there are two gaps, and to 

 the east of the more easterly of the two gaps rises into a knot of 

 hills between 300 and 400 feet high, and then gradually sinks down 

 into the plain about 3 miles east of the town. These hills are 

 not rocky except at their crest, but they are so stony on their flanks 

 as to be almost comparable to screes and to be exceedingly rough 

 to climb. In colour they are very pale reddish fawn passing into 

 cream, which may be regarded as the typical colour shown by 

 the great majority of the runs generally, and especially by those of 

 the Harappanahalli Archaean band. 



( '73 ) 



