222 CORAL AND ATOLLS 



GloMgerina and Pteropod ooze, these mountains were most 

 probably originally formed by volcanic eruption " (p. 507). 



Sucb, in brief, is the basis which Murray furnished for the 

 building of reefs and islands. Upon this basis the corals form 

 a reef, and at the outer edge of the reef the corals grow 

 best, because here they are enabled to obtain most food. 

 Murray gave up the idea that the corals of the edge of the 

 reef thrived most because of their better supply of oxygen, 

 but he retained the notion that the oceanic currents brought 

 more food to the edge of the reef, and so enabled the corals 

 to grow more freely. The lagoon becomes formed, and con- 

 tinues to grow in size, by the " solution " of the dead coral which 

 forms the central part of the reef — in Murray's own words : 

 " Larger quantities of lime are carried away in solution as a 

 bicarbonate from the lagoon than are secreted by the animals 

 which can still live in it ; the lagoon thus becomes widened 

 and deepened" (p. 511). 



The whole theory of atoll formation on the volcanic 

 mountain base is summed up in this way in the original 

 paper. " That when coral plantations build up from sub- 

 marine banks they assume an atoll form, owing to the more 

 abundant supply of food to the outer margins, and the re- 

 moval of dead coral rock from the interior portions by currents 

 and by the action of the carbonic acid dissolved in sea water" 

 (p. 517). This theory has been further elaborated by Murray, 

 by Murray and Irvine {Nature, June 12, 1896), and by James 

 G. Ross {Nature, March 15, 1880); and it has received new 

 embroideries from the work of Mr. Stanley Gardiner in the 

 Maldives and Laccadives. 



The prevalent shape of the constituent islands of the atoll 

 ring appears to be the subject of no special attention in this 

 theory, and it is not apparent how other coral structures, as 

 fringing reefs and barrier reefs standing far out from shore, 

 are made at all easy of understanding. 



The views of Mr. Stanley Gardiner have been put for- 

 ward in his work on " The Maldives and Laccadives," published 

 in 1902, and more fancifully in an article m. Nature {^. oil , 



