"Coral Reefs" by Charles Darwin is a scientific monograph published in 1842 that presents his groundbreaking theory of how coral reefs and atolls form. Darwin conceived this theory during the Beagle voyage before even seeing a coral island, proposing that vast areas of ocean crust rise and fall over immense time periods. His observations explained how fringing reefs transform into barrier reefs and eventually into atolls as land slowly subsides beneath the sea, solving a major scientific puzzle of his era. (This is an automatically generated summary.)