Littell's Living Age/Volume 129/Issue 1672/Miscellany

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Some New Plants from the Nicobar and Andaman Islands. — Herr S. Kurtz has a very interesting paper on this subject in the Journal of Botany for November, 1875, from which, however, we only abstract some of the physical facts recorded. The most remarkable one is the nature of the clay. Herr Kurtz says that the interest which attaches to the Nicobar vegetation rests chiefly in the peculiar polycistine clay, which looks somewhat like meerschaum, and is also nearly as light and porous. This clay covers large areas on those islands which form the so-called northern group. It contains, according to Dr. Rink’s analysis —

Silica 72'2
Oxide of iron 8'3
Alumina 12'3
Magnesia 2'1
Water 5'6
—— 100'5

Here the total absence of alkalies is very remarkable. In places it becomes red from abundance of oxide of iron, and in this case it is usually literally filled with fossil seaweeds. A microscopical examination of the rock reveals abundance of silica, fragments of polycistines, and diatoms. One would say that on such substrata nothing but wretched scrub and harsh grasses could vegetate; but an examination of the greater part of Kamorta has taught me that luxuriant tropical forests, with an average height of about eighty feet, not only cover the seaside, but the same forests form belts of considerable breadth over the island itself, while the inner hill plateau is covered those peculiar park-like grasslands which Dr. Diedrichsen has called grass-heaths. The next rocks botanically influential are calcareous sea sand, raised coral banks, limestone and calcareous sandstones, which belong to the so-called southern group, in which, however, Katchall (an entirely calcareous island) is enumerated. Then Come the plutonic rocks and their detritus, which, however, were only little developed in those parts which I visited. All islands consisting of the above rocks are characterized by the absence of press-heaths, and are covered with forests from the bottom to the top. The four principal aspects of vegetation in these islands are -— 1, mangrove swamps; 2, beach forests; 3, tropical forests, which fall under three groups, those growing on polycistine clay, those on calcareous or coralline strata, and those growing on plutonic formations; 4, grass-heaths.