1888.] on Structure, Origin, and Distribution of Coral Beefs, &c. 261 



of a sandy cay or slioal at some distance back from the outer edge of 

 the reef — the first stage in the formation of dry Lmd. 



The fragments of pumice thrown up into the ocean during far- 

 distant submarine eruptions, or washed down from volcanic lands, 

 are at all times to be found floating about on the surface of the sea, 

 and these being cast upon the newly formed islet produce by their 

 disintegration the clayey materials for the formation of a soil — the 

 red earth of coral islands. Just within the shore platform these 

 pumice fragments are found in a fresh condition, but as the lagoon 

 is approached they disappear, the soil becomes deeper, and the most 

 luxuriant vegetation and largest trees are found close to the edge of 

 the inner waters. The land is seldom continuous around the atoll ; it 

 occurs usually in patches. The water passes over the shallow spaces 

 between the islets and through the deeper lagoon entrances, these 

 last being kept open by the strong sand-bearing currents which pass 

 at each tide. 



The few species of plants and animals which inhabit these coral 

 islands have been drifted to the new island like the pumice, or 

 carried, many of them may be, by birds ; lastly, savage and civilised 

 man finds there a home. 



There is no essential difference between the reefs forming 

 fringing and barrier reefs, and those which are known as atolls. 

 In the former case the corals have commenced to grow close to the 

 shore, and as they grow outward, a small boat passage, and then a 

 ship channel, is carved out between the reef and the shore by tidal 

 scour and the solvent action of the water on the dead parts of the 

 reef : thus the fringing reef may be converted into a barrier reef. 

 In some instances the corals find a suitable foundation on the banks 

 that surround islands and front continental lands, it may be, at a 

 great distance from the coast, and when they reach the surface they 

 form a distant barrier which proceeds seawards, ultimately on a talus 

 made up of materials torn from its seaward face. 



If the foregoing considerations be just and tenable, then it would 

 aj)pear that all the characteristic features of coral reefs can be pro- 

 duced, alike in stationary areas or in areas of slow elevation and sub- 

 sidence, by processes continually at work in the ocean at the present 

 time. Slow elevation or subsidence would only modify in a minor 

 way a typical coral atoll or barrier reef, but subsidence in past 

 times cannot be regarded as the cause of the leading characteristics 

 of coral reefs. There are abundant evidences of elevation in coral 

 reef regions in recent times, but no direct evidence of subsidence. 

 If it has been shown that atoll and barrier reefs can be formed 

 without subsidence, then it is most unlikely that their presence in 

 any way indicates regions of the earth's surface where there have 

 been wide, general, and slow depressions. 



According to Mr. Darwin's theory, which has been almost uni- 

 versally accepted during the past half century, the corals commence 

 to grow close to the shore of an island or continent : as the land 



