176 On the Granite formation 



the Koondahs ; but the only dykes I have seen are at Deon- 

 hully and at Boredurraputty, two miles south of Coorrumba- 

 putty, on the road between Kistnagherry and Oossoor. This 

 last locality is well worth the notice of a geologist, as also 

 a spot two miles east, further up the little river, where the 

 long veins may be seen. 



These basalt veins and dykes have been considered by 

 most observers in India as having been irrupted into the 

 mass of the granite ; but in this I cannot agree with them. 

 Lieutenant Newbold, (Madras Journal, vol. xi. page 134,) has 

 generally correctly described the dykes at Deonhully, but 

 has omitted some particulars, and some of his remarks are 

 contrary to my observations, and his inferences are alto- 

 gether so. 



In the first place in every case of these dykes no evidences 

 of disruption or violent action has ever been observed, beyond 

 the presence of the dyke itself. Secondly, in every instance 

 there is undeniable proof of the granite having been in as 

 soft a state as the basalt, for the most minute fissures are 

 filled up without the slightest vacuity, and the adherence 

 between the basalt and granite is complete; also the veins 

 fine out, and are separated by fine threads, and at Deon- 

 hully, in Lieutenant Newbold's own words, " short, parallel 

 veins are observed at a little distance from, but having no 

 connection with the main stream" — these fine out at each 

 end, or are lenticular, and one of them ends abruptly ; also 

 lenticular veins run across the lamination of gneiss. Third- 

 ly, the veins in granite shew undeniable evidence of the stone 

 not having been split while solid, for the veins are branched 

 and separated, fining out as they run on; now, converging 

 diminishing fissures may be produced in a solid stone, but 

 I contend that it is impossible to produce in a solid mass 

 diverging diminishing fissures. Fourthly, the structure of 

 the granite is in no way ever altered in the slightest de- 

 gree in the vicinity of the basalt, nor is there any change 



