America, Darwin was sure of this idea, as he found again layers formed in the sea exposed along the dry shores of the island:

"The successive sheets are either closely united together, or are separated from each other by beds of scoriaceous rock and of laminate tuff, frequently containing well rounded fragments. The interstices of these beds are filled with gypsum and salt; the gypsum also, sometimes occurring in thin layers. From the large quantity of these two substances, from the presence of rounded pebbles in the tuff, and from the abundant amygdaloids, I cannot doubt that these basal volcanic strata flowed beneath the sea."

DARWIN (1844)

At Darwin´s time the origin of volcanoes was still a geological riddle. One model - proposed by the eminent German geologist Leopold von BuchPalma (Canary Islands), published by von Buch in 1814 in his book "Description physique des lles Canaries, suivie dúne indication des principaux volcans du globe". Von Buch assumed that the radial valleys were fissures caused by the uprising "volcanic bubble" - in fact these valleys are formed by fluvial erosion, but von Buch underestimated in the dry climate of the Canary Islands the power of episodic erosion.

However the "crater of elevation" model proposed very fast rates of elevation and Darwin, based on his previous observations, had already adopted the gradual geology as proposed by geologist Charles Lyell.

Darwin used the observations on St Helena to formulate an intermediate hypothesis (published in 1844 in his book "Geological Observations on the volcanic islands and parts of South America visited during the