What was the title of Darwin's 1842 book on coral reefs?

Darwin's 1842 book on coral reefs was titled The Structure and Distribution of Coral Reefs.

The book was the first part of the geology of the voyage of HMS Beagle and examined how different reef forms develop. Darwin focused especially on fringing reefs, barrier reefs and atolls, arguing that they could represent successive stages as volcanic islands slowly subsided beneath the sea.

His explanation connected observations from the Pacific, Indian Ocean and other regions with geological processes operating over immense periods. In Darwin's model, coral organisms grow upward in shallow, warm water while the land beneath them gradually sinks. This helped explain why a ring-shaped atoll can surround a lagoon even when no central island remains above water.

The title is sometimes confused with The Voyage of the Beagle or Journal of Researches, which describe Darwin's expedition and observations more broadly. On the Origin of Species did not appear until 1859. Darwin revised the coral-reef book for a second edition in 1874.