The spread of A&N Islands shows that these islands were once connected with the Arkan Yorua of Burma in the north and with the Indonesian islands in the south. In the Andamans the important rock formations are of sedimentary origin and are known as the Port Blair series and the Archipelago series. The Port Blair series consists of non-calcareous gray sandstones and embedded shells with occasional pockets of poor coal and pale gray limestone’s. The former is older than the later. In Long Island, cream colored porous limestones and calcareous sandstones are found in large quantity. In Interview Island the principal rock formations are limestones. In Little Andaman the predominant rock formations are limestone’s of various types.
The Nicobar Islands form part of the outer non-volcanic islands which extend from Sumatra to Arkan. The rocks of this territory are of recent age and white porous coral and shale limestones cover the greater part of the Car Nicobar Islands. Nancowry, Kamorta and other parts of the Nicobar group contains sandstones. The hills of Katchal are composed of calcareous sandstones and marble slate. In Little Nicobar and Great Nicobar the principle rocks are micaceous and soft micaceous.
Topographically, the Andaman Islands are, generally, hilly and are characterised by low range of hills and narrow valleys, except coastal stretches. The places, in which the hills go down, indicate that the islands are part of the submerged mountains. The land in the Andamans often sheer off the sea, clearly suggesting to their being the visible ridges and summits of sunken ranges. The ranges are form north to south but several spurs and ridges run off the main ranges in all directions indicating a very confused topography.
Generally speaking, the hills on the eastern side of the islands are somewhat higher than those, on the west, the highest point in all the areas being “Saddle Peak” which is in the North Andaman Island. The height of Saddle Peak is 2400 feet (800 mtrs.) above the mean sea level. The slopes are moderate to steep, ragged and liable to suffer from erosion. Flat lands are comparatively scarce and confined to some of the larger valleys as in Betapur and Diglipur. Except for Little Andaman, Interview Islands which are more or less flat, the other islands in the Andaman group have little flat land. The islands in the Nicobar group are largely flat and gently undulating and surrounded by coral reefs and shallow seas of width varying from a few yards to a mile or more. The Nicobar group of islands has narrow but stretches off sandy beaches. Generally, they include more of easy ground. Car Nicobar and Katchal Island of Nicobar group are almost flat and others include hilly terrain. The highest elevation here in Nicobar group is less than 700 meters. In Little Nicobar and Great Nicobar the land surface is very irregular, often broken by steep hill ranges and valleys of varying width with more or less perennial streams flowing therein.
The climate of A&N Islands can be described as tropical and warm. But this is tempered by pleasant sea breeze. As far as the humidity is concerned, it is very high for the most part of the year. The’ Islands have been exposed to both the monsoons and experience north westerly winds from November to December and south easterly gale from May to October, The weather is normally smooth from January to the middle of February and to a less extent in October. From February to May is the hot season and April is the hottest month. From the point of view of comparison, the climate of the Nicobar Islands is different because of the difference between the rainy and the dry season in the Nicobar group. However, there is not much variation in the climatic conditions of the two groups of Islands.
In the Andaman group of Islands, the soils are generally fertile, supporting a varied type of forest vegetation, sandy alluvial soil, resulting from the deposition of fine material from the higher slopes in saline swamps and creeks, support mangrove forests that fringe the islands in the sheltered coasts and Island creeks. The richer gray, brown and red soils, derived from the sandstones and serpentine rocks, support the major crops especially the forest crops. The soils of A&N Islands vary from heavy clay to clay loams, gravely loams and sandy loams, the former being found mostly in the valley areas. Soil depth differs from the slopes and the shallow soils characterise the higher elevations. The soils have low moisture retention capacity. Humus or organic matter is comparatively lacking even in the forest soils, having been washed away by the heavy rainfall assisted by the steep slopes and the loose texture of the soils. In the Nicobar group of Islands, the coralline alluvium on the high beaches is so common, along their coast. This supports rich forest or tree vegetation. The soil set up of Nicobar is eminently suitable for coconut cultivation. In the flat lands and along the river and stream banks, the soil is tresh water alluvium. Where conditions tend to be swampy the soil is very deep but where it is well drained, the soil is rich and fertile and supports excellent forest crops. Soils from calcareous, sand-stones are deep and fertile with luxuriant growth of forests. The hill soil tends to be shallow and rather infertile.