The Percy Sladen Trust Expedition to the Indian Ocean. Further Explorations

Abstract

Astove, where we arrived first, is an atoll about 2 miles ong by 1½ miles broad; so far as I could tell it is entirely composed of elevated coral as a basis, with sand distributed in various places. The seaward beach in most parts is formed of sand, but in places coral rock forms small cliffs, showing very evident washing away. There is only one pass. This is narrow, and from the present rate of washing away must be of fairly recent date. On the westward side of the pass are “coral rock” cliffs, while on the east a good deal of piling up of big blocks has occurred. These blocks are all of coral rock, not dead corals. They appeared to have come partly from the present land (washed out) and partly from the reef, which, so far as I could see, was composed of coral rock only, and was not ordinary dead reef such as I saw at Bird Island, to the north of the Seychelles. The coral rock interested me very much. In places one could see regular fields of coral with all the corals in their natural positions, while here and there are small holes, 5 feet to 6 feet deep, with sides all encrusted with corals exactly as they grew. There was absolutely no question of piling up. The whole place is evidently exactly as it was underneath the sea. In parts of the island the corals have been more “metamorphosed” into rock (not retaining their original structure), but I could trace no correlation between the occurrence of this rock and its position on the island. In the north of the island there are some dunes about 50 feet high, purely of wind formation. I dug a hole on. the landward side of one, and found guano underneath with a sort of shingle below. I think the north-west monsoon must have been nuch stronger once, or cyclones more frequent, to have driven this shingle inland.