440 LT.-COL. H. H. C40DWIX-AUSTEN ON THE LAND- [Maj' 21, 



and in the ' Journal ' of the same Societ}', 1893, has given an 

 account of his collections principally of the flora of Narcoudam 

 and Barren Island ; although he mentions the presence of land- 

 crabs, spiders, scorpions, and ants on Narcondam, no Mollusca are 

 recorded. 



All the above-mentioned air-breathers, it is quite possible, might 

 reach this island on trees floated off from the Andamans during 

 the monsoon which blows so long from that direction, and they 

 would all have a better chance of survival in sea-water than Land- 

 Mollusca, and might be carried for long distances inside the joints 

 of the bamboos and large grasses. 



Dr. Prain publishes two good maps of the Andaman Group, 

 and the lines of soundings ranging from 100 to 2000 fathoms are 

 shown. These point out very clearly, as he shows, that the xlnda- 

 man Sea, as a physical feature, is distinct from the great oceanic 

 depression outside, which he terms the sea of Bengal, down to 

 about 5° north. 



These contour-lines of soundings also show how the western 

 face of the Andaman-Nicobar line of elevation suddenly descends 

 into the deep vi^ater of about 10,-500 feet in a distance of from 60 

 to 70 miles, and this is proportional nearly to the elevation of the 

 Arakan range above the sea, on latitude 22°, near the head of the 

 Bay of Bengal and to its distance from the present sea. 



The parallel contour-lines of soundings down to the 1000-fathom 

 line extend north up rhe coast of Arakan, and south close to the 

 islands off the coast of Sumatra, Nias, &c., indicating a former 

 extension of land upon this line. 



It is said that the Andamans present evidence of recent sub- 

 sidence^, and these charts of Dr. Praiu's show that an elevation of 

 600 feet in this single group would unite them to Pegu and Arakan, 

 leaving an extremely narrow channel of only 50 fathoms deep 

 south of Preparis. The JN'icobars are more isolated, aud deep wide 

 channels separate them from the Andamans on one side and 

 Sumatra on the other, which accords with the paucity of Land-Shells 

 common to both, and the presence of a few found in Sumatra. 

 That these islands have been cut off for a considerable period from 

 the adjacent continents and islands is shown not only in the 

 specific variation of the moUuscan fauna, but equally in the birds 

 by a great number of distinct and peculiar forms. 



A great deal yet remains to be done : the highest parts of the 

 Nicobars have never been collected on ; here we may yet find 

 species identical with those of the Andamans, for many obtained 

 there come from the higher elevations, while most of those from the 

 Nicobars have been taken near the sea-coast ; and a few hundred 

 feet of elevation would bring in quite a different set of forms. 



^ S. Kurz, ' Eeport on the Vegetation of the Andaman Islands.' 



