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Page:Popular Science Monthly Volume 32.djvu/257

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A GREAT LESSON.

lutely depend. In the case before us, however, this second objection of Darwin is superfluous. The first was in itself conclusive. If the reef-building corals can not live in a lagoon, or in a protected sea, it is needless to argue further against a theory which credits them with working on a plan to insure not their own life and well-being, but their own destruction.

But next, Darwin had to encounter the theory that atoll-islands were built upon extinct volcanoes, and represented nothing but the walls and craters of these well-known structures. This he encountered not with a sweeping assertion, but with a sweeping survey of the vast Pacific. Had those who believed in this theory ever considered how vast that island-bearing ocean was, and how enormous its supposed craters must have been? It was all very well to apply some known cause to effects comparable in magnitude to its effects elsewhere. The smaller atolls might possibly represent volcanic craters. But what of the larger? And what of the grouping? Could any volcanic region of the terrestrial globe show such and so many craters as could correspond at all to the coral islands? One group of them occupies an irregular square five hundred miles long by two hundred and forty broad. Another group is eight hundred and forty miles in one direction, and four hundred and twenty miles in another. Between these two groups there are other smaller groups, making a linear space of more than four thousand miles of ocean in which not a single island rises above the level of true atolls—that is to say, the level up to which the surf can break and heap up the coral masses, and to which the winds can drift the resulting sands. Some atolls seem to have been again partially submerged—"half-drowned atolls," as they were called by Captain Moresby. One of these is of enormous size—ninety nautical miles along one axis, and seventy miles along another. No such volcanic craters or mountains exist anywhere else in our world. We should have to go to the airless and waterless moon, with its vast vents and cinder-heaps, to meet with anything to be compared either in size or in distribution. And then, the linear barrier-reefs lying off continental coasts and the coasts of the great islands are essentially the same in character as the encircling reefs round the smaller islands. They can not possibly represent the walls of craters, nor can the long and broad sheltered seas inside them represent by any possibility the cup-like hollows of volcanic vents.

These theories being disposed of, the work of synthesis began in Darwin's mind. He sorted and arranged all the facts, such as he knew them to be in some cases, such as he assumed them to be in other cases. Above all, like "stout Cortes and his men," from their peak in Darien, "he stared at the Pacific." The actual seeing of any great natural phenomenon is often fruitful. It may not be true in a literal sense that, as Wordsworth tells us, "Nature never did betray the heart that loved her." But it is true that sometimes she discloses