506 



Anniversary Meeting. 



[Nov. 30, 



contiguous coasts. Some explanations were indeed propounded, but 

 were manifestly inadequate to meet all tlie conditions. 



The subject was in this state when Mr. Darwin took it up. Com- 

 bining careful observation upon Coral Beefs and Atolls with reflections 

 upon the range and distribution of Volcanic Islands, he divided the area 

 of the Pacific and Indian Oceans into tracts of elevation and depression. 

 A H the Coral Phenomena of Atolls, Encircling Eeefs, and Barrier Beefs 

 were accounted for upon the supposition of a long-protracted but gra- 

 dual subsidence under the ocean of large areas of land, admitting the 

 Coral Formation to grow up whilst its foundation sunk down ; while 

 Pringing Beefs were explained as appertaining to areas of elevation 

 where the land had risen up or was progressively rising. On this view 

 the apparently discordant facts ranged themselves in perfect harmony. 

 Pringing Beefs were thus converted into Barrier Beefs, and Encircling 

 Beefs into Atolls, " the instant the last particle of land sinks beneath 

 the ocean." Bepresenting on a map the two classes of facts by dif- 

 ferent colours, it was shown that active volcanos are absent in the 

 region of Atolls and Barrier Beefs, while they abound in areas of Coral 

 Pringes and of elevation. 



Mr. Darwin's researches were received by naturalists with lively 

 satisfaction as fixing an era in the history of the investigation, and as 

 contributing one of the most important illustrations which geology had 

 received since it had been shaped into a science. A flood of light was 

 thus thrown upon the ancient calcareous formations which enter so 

 largely into the composition of the superficial crust of the earth ; and 

 something like a definite idea was arrived at respecting areas of depres- 

 sion and elevation. 



In addition to his researches upon coral reefs, Mr. Darwin has 

 made numerous contributions to Geology, both in the descriptive 

 and theoretical divisions of the science. As belonging to the former 

 class may be cited his admirable ' Journal of Besearches,' containing 

 observations on the G-eology of the various countries visited during the 

 voyage of the ' Beagle ' ; notes during a survey of the east and west 

 coasts of South America, with a transverse section of the Cordilleras 

 between Valparaiso and Mendoza ; G-eological observations on South 

 America, published as a separate work in 1846 ; G-eological observa- 

 tions on the Volcanic Islands visited during the voyage of the ' Beagle,' 

 with brief notices of the Geology of Australia, New Zealand, and the 

 Cape of Good Hope, also published as a separate work ; on a remark- 

 able Bar of Sandstone ofi" Pernambuco ; on the Deposits containing 

 extinct Mammalia in the neighbourhood of the Plata ; on the Geology 

 of the Falkland Isles ; on the Distribution of Erratic Blocks in South 

 America. 



In theoretical or speculative geology may be cited his memoir on 

 the connexion of certain Volcanic Phenomena in South America, and 



