454 NATURAL SCIENCE. June. 



colours is a mere convention — as anyone may observe who takes his 

 pleasure in the Row this season. 



Geologists and others will perhaps turn first to the section of 

 the book which deals with the origin of coral reefs. 



A figure which by the kindness of the publishers we have been 

 able to reproduce shows how the reef forms an enormous buttress of 

 rock F pressed against the sloping granite rocks G of the coast. Mr. 

 Jukes, and after him the author, made most careful search for any 

 evidence of upheaval, but failed to find facts against Darwin's sub- 

 sidence hypothesis. At many points along the reef enormous masses 

 of storm-raised coral at first sight simulate the effects of upheaval ; 

 but of exact evidence Mr. Saville Kent could find nothing to oppose 

 seriously the subsidence theory. At many stations along the reef, large 

 expanses of dead coral intervene between the living banks and high- 

 water mark. Such banks are subjected to destructive atmospheric 

 influences at every spring-tide, while living coral is above water only 

 at the lowest spring-tides. Dead bivalve shells of large size such as 

 Tvidacna and Pinna occupy their original positions in close contiguity 

 to the dead corals ; but all these results could have been caused by 

 upheaval of a foot or two, and there is practically no evidence for a 

 prolonged era of upheaval. 



On the other hand, all of the few big breaches in the Barrier's 

 outer rampart are opposite large estuaries. They are at present too 

 remote from the estuaries (from 30 to 60 or 80 miles) for the influence 

 of fresh-water to have retarded coral growth. This condition is 

 by itself strong evidence for subsidence, but Mr. Saville Kent 

 relies most strongly on the evidence from the geographical distribu- 

 tion of animals that Australia had in former times a land-connection 

 with New Guinea. It is not worth while to recapitulate the facts 

 here, as all who are specially interested in the controversy will refer 

 to Mr. Saville Kent's book ; but he concludes that the construction of 

 the Great Barrier of Australia under conditions of subsidence, and in 

 accord with the original hypothesis of Mr. Darwin, is proved. 

 Towards the end of Tertiary times the great Barrier Reef existed 

 as a simple fringing reef, and moderate subsidence, of the occur- 

 rence of which we have abundant geological evidence, has 

 turned it into its present condition. Mr. Saville Kent brings forward 

 a considerable additional quantity of evidence supporting parts of the 

 reef-formation theories of Murray and others. Although the Barrier 

 Reef as a whole has been formed by subsidence, in the details of the 

 process conditions of local growth and decay have played a large 

 part. Thus, much of the actual bulk of a reef is formed of coral 

 debris — debris which comes from the breaking up under the influence 

 of storms of the rapidly-growing, more fragile forms of coral. On a 

 reef at any time only a small area is actually alive, and that small 

 area is turned most usually away from the mud and fresh-water on 

 the landward-side, and turned towards the most abundant and freshest 



