1-870.] Notes on the Geology of the Vicinity of Port Blair. 235 



The rocks seen in the vicinity of the road are the same sand- 

 stones and shales as at Koss, &c. There are also some conglome- 

 rates which may be of more recent age. Not far from Homfray's 

 ghat the road crosses what appears to be a dyke of intrusive serpen- 

 tine ; it is, however, not well exposed, the junction with the sand- 

 stones being hidden by soil. I shall speak of this rock, portions of 

 which are very beautiful, again further on. 



The abrupt termination of the rocks at the edge of a mangrove 

 swamp, as above described, seems to point to the former existence 

 of a strait which joined Ports Blair and Mouat and consequently 

 divided the island into two. Such a strait now separates the north 

 and middle Andamans. This would either involve the fact of a 

 general rising of the land having taken place, or be simply the 

 result of silting up of the channel. Mr. Kurz has given evidence 

 of a general sinking ; the question may still be regarded as an open 

 one to be decided on the collection of further data. 



Islands North East of Port Blair. — North-east of Port Blair 

 there is a group of islands of various sizes. The smallest, known 

 by the name of the buttons, being rocky pinnacles covered with close 

 and dense jungle. As seen from a passing vessel, some of the 

 rocks appear excessively white, and it occurred to me as possible, 

 that they may be similar to the clay-stones of Kamorta and Nan- 

 cowry, and therefore distinct from the Port Blair sandstones. I had 

 no opportunity of landing to ascertain the point. 



Narkondam Island. E. Long. 94° I7 y 22", N. Lat. 13° 28'. 



Both when going to and returning from Port Blair I passed with- 

 in a few miles of the remarkable island of Narkondam. From its 

 shape no reasonable doubt can exist as to its being a volcano. Un- 

 like its neighbour on Barren Island,* it has never been seen in action. 

 The central cone which rises to the height of 2150 feet appears to 

 be surrounded, as Mr. Kurz has pointed out, by the remains of an 

 old crater. The cone is furrowed by deep ravines. At one place, 

 I noticed what appeared to be a slip or subsidence of a portion of 

 the crater. I was most anxious to land, and Captain Barrow the 



* Barren Island has frequently been described. See Lieut. Colebrooke, 

 Asiatic Researches, Yol. IV, p. 397 ; Dr. P 1 a y f a i r, Records, Government of 

 India ; Dr. L i e b i g, J. A. S. B. 1860, and Report by a Commission to enquire 

 into the amount of Cattle fodder obtainable on the island, Proc. A. S. B. 1866. 



