PROCEEDINGS 
OF THE 
ROYAL SOCIETY OF EDINBURGH. 
vol. x. 1879-80. No. 107. 
Ninety-Seventh Session. 
Monday , 5th April 1880. 
Sir WYYILLE THOMSON, Vice-President, in the Chair. 
The following Communication was read : — 
1. On the Structure and Origin of Coral Eeefs and Islands. 
By J ohn Murray. 
(Abstract.) 
Darwin's Theory . — During the voyage of the “ Beagle” and subse- 
quently, Mr Darwin made a profound study of coral reefs, and has 
given a theory of their mode of formation which has since been 
universally accepted by scientific men. 
Darwin’s theory may he said to rest on two facts — the one 
physiological, and the other physical — the former, that those 
species of corals whose skeletons chiefly make up reefs cannot 
live in depths greater than from 20 to 30 fathoms; the latter, 
that the surface of the earth is continually undergoing slow 
elevation or subsidence. 
The corals commence by growing up from the shallow waters 
surrounding an island, and form a fringing reef which is closely 
attached to the shore. The island slowly sinks, hut the corals con- 
tinually grow upwards, and keep the upper surface of the reef at 
a level with the waves of the ocean. When this has gone on for 
some time a wide navigable water channel is formed between the 
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VOL. X. 
