The South Keeling Islands (also known as the South Cocos Islands) are an archipelago in the Indian Ocean that belongs to Australia. In 1836, Charles Darwin landed on board the HMS Beagle in the south of the Keeling Islands and counted the diversity of nature: he discovered 20 species, 19 genera and 16 families among the plants, all descendants of the abandoned seeds that the sea carried here. During his twelve-day stay, Darwin formulated his theory of the formation of atolls through the gradual subsidency of tropical volcanic islands. On April 4, 1836, he notes: "Today the sea was extraordinarily calm, so that I dared to wade across the outer bank of dead rock to the living coral walls on which the swells of the open sea break. Once these corals lined the cone of a volcano and died with it as it sank into the ocean. All that was left of them were calcareous skeletons on which subsequent generations of corals settled. Remnants of the fallen mountain stranded on them; here collected the sand that the wind blew."