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The Structure and Distribution of Coral Reefs. By CHARLES DARWIN, M.A., F.R.S. With Three Plates. Second Edition. Revised. Smith, Elder, and Co.

The first edition of this work appeared thirty-two years ago, and Dr. Darwin finds but little to revise. He admits the force of some slight criticisms of Professor Dana, for instance, that in determining the distribution of coral reefs he had not laid sufficient weight on the mean temperature of the sea. Other criticisms of Professor Dana he traverses, and maintains against them the positions taken in his first edition. He does not, for instance, admit the degree in which volcanic action prevents the growth of coral reefs, which Professor Dana asserts, nor that volcanoes in a state of action are found within the areas of subsidence, but only within those of elevation. On the other hand, the late Professor Jukes, in speaking of the great barrier reefs of Australia, fully accepts Dr. Darwin's theory of their formation; while, against Professors Semper and Chamisso, he maintains that atolls or lagoon islands and barrier reefs were formed during a period of subsidence, wherein rocks sunk sufficiently low beneath the level of the ocean to become the foundation of coral structures.

The volume is a beautiful example of facts carefully collected, and of scientific conclusions cautiously reached. After minute descriptions of various coral formations, in which the atoll or lagoon reef, the barrier

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reef, and the fringing reef are discriminated, it is shown that the reef. constructing polypifers cannot live either above the water or at a very great depth beneath its surface; the atoll and barrier reefs, therefore, from which enormous depths have been fathomed as from a perpendicular wall, must have some foundation of rock. The real difficulty is to account for this, the apparent necessity being that the coral formations all rest on mountain summits; which, although rising near the surface of the sea, in no one instance rise above it. Dr. Darwin maintains that there is but one theory possible, namely, the prolonged subsidence of the rocky foundations. On this theory, he thinks every difficulty vanishes. With fringing reefs, or reefs adhering to the land, there is no difficulty, as uprisings and subsidence of parts of the crust of the earth must be admitted. Our only difficulty in accepting Dr. Darwin's theory is the nearly uniform level of the rock foundations, and the wonderful balance of formation and waste that is preserved. He frankly says that direct proofs of subsidence are, from the nature of the case, impossible; as frankly, we admit, that we can urge no scientific objections to his theory. We commend his very charming book to all lovers of science.