HIS THEORY OF CORAL-ISLANDS 249 



laborious life, full of ardour and work to the last, he 

 died at the age of seventy-three, on the 19th of April, 

 1882. 



The story of his life at Down is almost wholly 

 coincident with the history of the development of 

 his views on evolution, and the growth and appear- 

 ance of the successive volumes which he gave to the 

 world. For the first four years his geological tastes 

 continued in the ascendant. During that interval 

 there appeared three remarkable works, his volume 

 on Coral Islands, that on Volcanic Islands, and his 

 Geological Observations on South America. Of these 

 treatises that on coral reefs excited the wonder 

 and admiration of geologists for the simplicity and 

 grandeur of its theoretical explanations. Before it 

 was written, the prevalent view of the origin of these 

 insular masses of coral was that which regarded each 

 of them as built on the summit of a volcano, the 

 circular shape of an atoll or ring of coral being held 

 to mark the outline of the submerged crater on which 

 it rested. But Darwin, in showing the untenableness 

 of this explanation, pointed out how easily the rings 

 of coral might have arisen from the upward growth 

 of the reef-building corals round an island slowly 

 sinking into the sea. He was thus led to look upon 

 the vast regions of ocean dotted with coral islands as 

 areas of gradual subsidence, and he could adduce every 

 stage in the process of growth, from the shore-reef 

 just beginning, as it were, to form round the island, 

 to the completed atoll, where the last vestige of the 

 encircled land had disappeared under the central lagoon. 

 More recent researches by other observers have, in 



