Apart from that, everything is clear. Hence the ancient species were made fixed, solid, and unchangeable by God just like the later species that Adam found in Paradise, and that still exist. Without the will of God they could no more have died out than the actual ones; and there were no human beings there to destroy them. But the divine action intervened. At the end of each of these old-world periods a terrible spectacle was witnessed. The heavens poured out their punishing floods; the seas were heated to steam by fiery masses of rock that were summoned by the divine power from the bowels of the earth. In the course of a single day the carboniferous forests were swallowed up; the megatheria disappeared, legs uppermost, like flies in butter, in the sand dunes of the terrible floods. The might of the creative act was equalled by the might of the destruction. The science of these vast new creations and divine revolutions before Adam’s birth was called geology. It lived in peace with Linné’s theory of fixed species. Its parent, Cuvier, was so great a genius that it seemed quite impossible that he had made a mistake. Before twenty years were out he was, in the opinion of a contemporary and equally able geologist, declared to be certainly wrong on one point. Lyell wrote a magnificent work in which he proved, from the point of view of scientific geology, that the whole story of these terrible revolutions was a fiction. There are no such sharp sections in the early history of the earth. Everything goes to show that throughout the whole period of the earth’s development the same natural laws have been at work as we find to-day. It is true that the relative positions of sea and land, hill and valley, forest and desert, have often changed; but very, very slowly, in the course of millions of years. A single drop of water, constantly falling, will hollow out a stone. In these millions of years the water has swept away rocks here, and formed new land by the accumulation of sand there. In these millions of years the sand has been compressed into the gigantic masses that tower above us to-day as sandstone mountains; they are formed of sand that was originally laid like mud, layer by layer, on the floor of the ocean. It was all very plausible; it seemed to picture an eternal flow of things in which there was no room for God. The changes in the earth’s surface were easily brought about without catastrophes, in the course of incalculable ages. God was excluded from geological discussions of the formation of hill and dale. And when it was fully realised, it brought the question of species to the front once more.