2 FLORA OF THE NICOBAR ISLANDS. 
been very fortunate; a large proportion being likewise found on the 
peninsula of India, as well as in Ceylon. But it will be remarked, 
also, that the vegetation is, as it were, aradiation from that in question, 
connecting it with the Flora (the Polynesian Kingdom of Schouw, or 
Reinwardt’s) of the grand groupe of islands extending from Sumatra 
eastwards. This is pointed out by the genera Dissocheta, Orophea, 
Pterisanthes, Arthrophyllum, and Visenia, characteristic of that - 
kingdom. 
If the above view is correct, a tolerable idea of the Nicobar vegeta- 
tion may be formed from what is known of the Indian Flora (the 
continent and islands, as far as the Philippines, with a mean tempe- 
rature of 15°-25° Réaum.) It must be noticed, however, that there 
exists a geognostic difference between the southern islands (Sambelong, 
Little Nicobar, and Catschall*) and the northern, and that hence a 
considerable difference is observable in the distribution and character 
of their plants. The first-named islands seem to be composed of cal- 
careous sandstone and clay-slate. Both of these are easily affected by 
the condition of the atmosphere: the chalk is neutralized by the 
carbonic acid combined with the rain ; and provided the rocky substratum 
be not very inclined, the soil is several feet deep and apparently very 
fertile, consisting of lime, with sand and micaceous clay. We accord- 
ingly find these islands, although the highest of the whole cluster, 
forest-clad to the very top. Quite different is the appearance on the 
northern islands, where plutonian, especially serpentine, rocks pre- 
dominate. Decomposition of these may in time produce a good soil ; 
but the process goes on with far more difficulty than in the southern 
islands, consequently the soil here is much less abundant. Besides, it 
is only on Bompoka, Tillangschong, and Terressa, that the surface is 
naked ; on Nancovry, Trineut, Car-Nicobar, and partly also in 
Terressa, the surface is hidden by a crust of strongly absorbent, 
meerschaum-like clay, containing iron, tale, and sometimes chalk, but 
destitute of alkalies, covered partially by a stratum of soil only a few 
inches deep and unsuited for any sort of cultivation. The undulated 
surface of these islands, contrary to what is seen on the sharp ridges 
of the southern groupe, is covered with grass only, without forest, having 
species of Pandanus and Areca, in small clusters or solitary, scattered 
over it. It is only in valleys, where a somewhat richer soil has accumu- 
* I have invariably adhered to Mr. Didrichsen’s orthography of localities —N. W. 
