At this period we get interesting evidence of his extraordinary insight in the strong protests he makes against the Atlantis hypothesis of Edward Forbes, and the other vast continental extensions which naturalists did not hesitate to make in order to explain the existence of species common to countries separated by wide tracts of the ocean. These lost continents were as generally accepted as they were freely proposed. And yet we find that, even then, one thinker far ahead of his time saw clearly enough--as the _Challenger_ Expedition twenty years later proved beyond all doubt--that the geological evidence is against such extension, and that the means of distribution possessed by animals are such as to render the supposition unnecessary. In June, 1856, he writes to Lyell: “My blood gets hot with passion and turns cold alternately at the geological strides, which many of your disciples are taking”; and after mentioning the extension of continents proposed by many leading naturalists, he says: “If you do not stop this, if there be a lower region for the punishment of geologists, I believe, my great master, you will go there. Why, your disciples in a slow and creeping manner beat all the old Catastrophists who ever lived! You will live to be the great chief of the Catastrophists.” Lyell wrote disagreeing on the subject of continental extension; and hence, on June 25th, 1856, Darwin replied in a long letter, giving in detail his reasons for rejecting the hypothesis. He argued (1) that the supposed extension of continents and fusion of islands would be vast changes, giving the earth a new aspect, but that recent and tertiary molluscs, etc., are distinct on opposite sides of the existing continents; so that, although he did not doubt _great_ changes of level in parts of continents, he concluded that “_fundamentally_ they stood as barriers to the sea where they now stand” ever since the appearance of living species; (2) that if a continent were nearly submerged, the last remaining peaks would by no means always be volcanic, as are, almost without exception, the oceanic islands; (3) that the amount of subsidence which took place in continental areas during the Silurian and Carboniferous periods--viz. during one tolerably uniform set of beings--would not be enough to account for the depth of the ocean over some parts of the site of the supposed submerged continents; (4) that the supposed extensions are not consistent with the _absence_ of many groups of animals--_e.g._ mammals, frogs, etc.--from islands.