Geologically Saint Martin’s Island is a continental island. But many people take this island as a coral island as some corals are found to grow there. It is located about 12 kilometers off in the Bay from the main land of Teknaf. The island is about 5 kilometers in length and 600 meters in breadth at certain places and 100 to 200 meters at some places. There are some small island nearby the island, which are called by the local people as ‘Seradia’ or separate islands. The northern part of the island is wider and known as Zinzira. There are inhabitants. In the south there is no inhabitants but there is mangrove forest. In Zinzira, there is a fresh water lowland.
Coastal Afforestation: To protect the lives and properties from successive cyclone and tidal bore in the open coastal region seedlings of mangrove plants have been planted along the coastal region. As a result an attractive forest has developed. Within a short span of time the soil of the areas has changed its quality and has become cultivable. Plants: In coastal afforestation usually Bain and Keora are planted. Bain is planted in the soil containing comparatively high salinity and Keora in the estuary region where saline water mix with river carried fresh water.