GRANITIC AND TRAPPEAN ROCKS. 59 



mass with a triangular base has been separated by the three main joints, 

 but that other less persistent joints, or, preferably variations of the main 

 joints, have given the core of the prism a polygonal and finally a rudely 

 circular base, while the nearly flat joint system with its slight variations 

 assists in the ultimate rounding of the block. 



From the Swarnamukhi northward to B,apur the number of dykes is 

 small, none of them being of importance as to size or length, and they 

 are all of ordinary compact diorite ; but as the latter village is ap- 

 proached, they become frequent and are remarkably persistent up the 

 valley between the Veligondas and the Gelacapad-Kaluvaya hills. At 

 Bodanapali, many wells, 20 to 30 feet deep, are sunk through grey schists, 

 showing numerous small trap dykes, 3 or 4 feet wide, running in all 

 directions and at all angles. They run ' with the bedding, or across it, 

 to the north and to the east, Between Rapur and Gelacapad, all the 

 rocks are very igneous-looking ; a grey pasty porphyritic rock, which I, 

 however, suppose to be the same as that of the grey gneiss series towards 

 the Swarnamukhi valley, fills up the bay between the quartzite ridges 

 and is traversed by strong dykes of aphanite trap in a north-by-west 

 direction with an eastward dip. Further north, and eastward of Ulla- 

 puram, the country is much intersected by trap dykes striking east- north- 

 east, the rock being often a dense black aphanite. The low hill north- 

 east of Pocrapali is a perfect network of dykes, as is also the ridge to 

 the south. 



The cross dykes are also associated with the transition rocks, for the 

 Dykes in the transition most part obscurely, but still at times as undoubted 

 rocks - intrusions. To the south-south-east of Tumoy, 



there is a large dyke at the north end of a low hill of quartzites, and this 

 runs right at and under the ridges in an east-west direction, showing 

 every now and then in the small valleys between, while a small branch 

 of this dyke traverses the beds very clearly. Some of the dykes are very 

 broad and long, that of Tumoy and another parallel one to the north being 

 traceable for 3 to 5 miles with a breadth of 100 feet, while a third 

 runs north-north-west past Panumurti for a length of about 7 miles, 

 with a breadth sometimes of 150 yards. 



( 167 ) 



