Palms abound; the banian and padouk, that resembles mahogany; marble-wood, of a black, mottled appearance; satin-wood; and the iron tree, which turns the edge of an axe, are all found in the forests, in beautiful confusion with cotton-trees, screw-pines, and arborescent euphorbias, and with large clumps of bamboos, 30 and 40 feet high; while all round the coasts, mangroves, the most satisfactory of firewoods, give shelter to lovely orchids.
A very conspicuous feature of the forests is the distribution (apart from the strictly littoral vegetation) into evergreen forest, very full of large gurjan trees (Dipterocarpeæ), and a leaf-shedding forest, containing a large proportion of padouk (Pterocarpus dalbergioides), or into a mixture of these two types.
The great peculiarity of the Andaman flora is that, with the exception of the Cocos Islands, which are covered with them, and thence indeed derive their name, no coconut palms naturally propagated are found in the Archipelago.[86] This is the more strange when it is remembered that all the shores of the Bengal Sea are the home of this tree, and that it simply teems in all the islands of the Nicobar group to the south. During the past thirty-five years advantage has been taken of trips in the Station steamer (or by other means) to plant coconuts at suitable localities[87] along the coasts of Great Andaman, and in recent years at Little Andaman. Great numbers of the nuts were consumed by the aborigines, or by wild pigs, but at several places fruit has been obtainable, for many years past, from trees which escaped destruction.
The climate of the Andamans is equatorial in its uniformity, and greatly resembles that of Tenasserim and Mergui. It is not generally healthy for Europeans, but improves from a hygienic point of view when the forest is cleared from any locality. During the first two months of the dry season strong winds blow from the north-east, causing sickness, and damage to vegetation.
As the islands are exposed to the full force of the south-west monsoon, only four months of fair weather (January to April) can be counted on. December and January are the coolest months, with a mean temperature of 79° and a mean minimum of 75°, while March and April are the warmest, with means of 82° and 83° respectively, and a mean daily maximum of 92° at Port Blair, where throughout the year the mean is 80°, the highest 96°, and the lowest 66°; so that the absolute range is 30°. The mean diurnal range is as much as 14° to 15° in February, March, and April, while between June and September it is only 8° or 9°. The mean temperature throughout the year is about 80°.
The south-west monsoon sets in, accompanied by heavy rain, in the early part of May, but occasionally in April, and lasts till October. March is the driest month, and January and February somewhat less so; but the rainy season lasts from the middle of May till the middle of October, and what is called the moderate season, from October to January. During the latter the average monthly rainfall is about 8 inches; in the rainy season it is 16 inches, with twenty-four rainy days per month; while, on the average, throughout the dry season rain falls on ten days to an extent of 5 inches. At Port Blair the mean humidity is 83 per cent, and the average annual rainfall is 117 inches; but elsewhere it varies from 100 to 155 inches, and there are about 180 wet days in the year.
At the change of the monsoons stormy weather is common, and the neighbourhood of the Andamans is considered to be the birthplace of many of the violent cyclones that occasionally visit the Indian and Burmese coasts of the Bay of Bengal.
The hurricanes generally both originate either between Ceylon or the N.W. portion of the bay, and take various courses, according to the season; but, although situated near the cradle of these storms, the islands are not often traversed by them. In 1864 one is recorded as having visited the locality, and on the night of November 1st, 1891, a violent cyclone passed over Port Blair, which, after travelling north-westward across the bay, did much further damage at the mouth of the Hugli and on the Orissa coast. The maximum velocity of the wind registered at Port Blair on the latter occasion was 111 miles.
Concerning the geology of the islands, it is curious that in the valley of the Irrawadi hot springs and other evidence of volcanic action occur in the same relative position to the Arakan Hills as the two islands of Narkondam and Barren Island occupy in respect to the Andamans. There seems little doubt that these two islands—now respectively extinct and quiescent—belong to the great line of volcanic disturbance that appears in Lower Burma and extends right through Sumatra and Java and the further islands of the Malay Archipelago. Thus it would seem that the Andamans proper, possessed of no volcanoes themselves, lie just outside the line of activity, and, with the Nicobars, occupy the same position with regard to the volcanic track as do the chain of islands west of Sumatra.
Possibly the land now constituting the Andamans first appeared above the sea as an extension of Cape Negrais in the latter part of the Tertiary epoch, at which time occurred the elevation of the Arakan Yoma Hills, and later became isolated by subsidence due to neighbouring volcanic action. As Mr A. R. Wallace points out,[88] the presence of active volcanoes produces subsidence of the surrounding area by the weight of every fresh deposit of materials ejected either in the sea or on land. "The subsidence such materials produce around them will, in time, make a sea if one does not already exist."