"The third principal formation of the Nicobars are coral formations belonging to the most recent or the present period. Coral banks of great thickness are found on Kar Nicobar, Bompoka, Trinkat, and other islands. They consist partly of compact coral limestone, partly of a coral and shell conglomerate upheaved 30 or 40 feet above the present level of the sea. On all the islands the original area is to be observed enlarged by coral land which is only separated by the higher sand-dunes along the shores from the still continuing formation of the coral reefs surrounding all the islands in the character of fringing reefs. Although these raised coral banks are decided evidence of the long-continued upheaval of the islands--that, in connection with the eruption of the serpentines and gabbros--the formation of the flat coral lands elevated a few feet only above the sea, can, on the other hand, be explained by the accumulation of coral fragments, of sand and shells, by the waves and breakers on the shallow surface of the fringing reefs."[112] * * * * * Coal of a brown variety has been found in Little Nicobar, Treis, Milo, and Kondul, but everywhere in isolated masses and single fragments, showing traces of rolling, met with here and there without order, in sandstone and slate, and evidently derived from driftwood. The only traces of minerals discovered have been ores of copper and iron pyrites, finely disseminated through dioritic and serpentine rocks. The possibility of the occurrence of copper ores in the eruptive formation cannot be denied, but no discovery has yet been made which would indicate it. On the other hand, the islands are rich in useful building materials. The sandstone of the southern islands must give excellent working stones; the plastic clays of the north could, doubtless, be worked into bricks or pottery; the natives of Chaura largely employ it in their earthenware manufactures. Although the islands are generally beyond the sphere of cyclonic disturbances, they have more than once experienced the effect of earthquakes. One of the most remarkable of these is said to have occurred from October 31 to December 5, 1847, when fire is reported to have been seen on one of the mountains of Great Nicobar. Part of the northern coast of the latter, especially in the vicinity of Ganges Harbour, sank beneath the sea, and for long the locality was deserted by the aborigines.[113] On December 1881, an earthquake, felt also at the Andamans and throughout the Bengal Sea generally, caused extensive damage in Kar Nicobar to the coconut groves and huts of the natives. Vents were opened in the sandy soil; inland, trees were overthrown; sea-waves broke on the island, and at the village of M[=u]s, water rose into the houses of the Burmese traders, which stood on platforms 2-1/2 feet high.