1893.] D. Pram — Flora of Narcondam and Barren Island. 61 



and the various hot-springs in the valley of Assam, like those in the 

 Namba Forest,* are examples of this series, which forms a continuous 

 line parallel on its western side to the tertiary ridge referred to, just as 

 the true volcanoes, to the line of which Barren Island, Naroondam and 

 Popah belong, are parallel to it on the east.f 



Whether they belong to that particular group of volcanoes known 

 as the Sunda Range, or not, there is no doubt that Narcondam and 

 Barren Island belong to the general volcanic system extending from 

 the Kuriles, through Japan and the Philippines, to Malaya — a system 

 of which the Sunda Range itself forms but a portion. Like the other 

 members of this system, these peaks are situated, not on, but just within, 

 the margin of the continental elevation forming Eastern and South- 

 Eastern Asia, wherever this rises abruptly from great ocean-depths; the 

 main difference between them and most of the peaks of the system is 

 that, whereas the space between the edge of the continental area and 

 the line of volcanic activity is in other cases sub-aerial, that space is here 

 for the most part sub-marine. This space forms, in the case of Sumatra, 

 the main body of the island — the volcanic line being much nearer the 

 eastern mar-gin — and the rocks of which it is composed include all those 

 that go to form the islands of the Nicobar Group ; these rocks appear 

 once more, not in the main chain of the Andamans, but in the small 

 islands to the east of South Andaman (north east of Port Blair), known 

 as " The Archipelago."! Neither in, nor opposite, the Nicobars is there 

 any trace of the complementary volcanic ridge; to the east of this "Archi- 

 pelago," however, it is indicated by Flat Rock and Barren Island. 



Not only is the volcanic line of Sumatra absent, from the Nicobars, 

 but no trace has yet been found in that group of the sandstones of the 

 Arracan hills, which are prolonged into the main chain of the Andamans 

 and which re-appear in the Nias. The result, therefore, is that the 

 Arracan- Sumatra chain, in place of constituting a single ridge consists 



* Pram : Proceedings As. Soc. Bengal, 1887, p. 201. 



f The reasons for thinking that the northward prolongation of the Sunda 

 Range has not crossed the Arracan- Andaman ridge are, therefore : — 



1. That the volcanoes on the west side of that ridge, which are supposed to 

 continue the Sunda line, are of a different type from the volcanoes of the Sunda 

 Range. 



2. That these western volcanoes in Ramri belong to a system of vents of the 

 same type as themselves, characterised by a linear distribution parallel to the 

 western base of the Arracan-Andaman tertiary ridge. 



3. That the Sunda Range is continued northward by a series of vents of the 

 same type throughout, the character of linear distribution parallel to the eastern 

 base of the Arracan-Andaman tertiary ridge being maintained unaltered. 



% Oldham : Records of the Geol. Survey of India, xviii., 141. 



