W. M. Davis — The Great Barrier Reef of Axistr alia. 347 



plain, or on the island border, according as the submergence is 

 large and rapid or not. It is interesting to note in passing 

 that Darwin foreshadowed the idea here presented: he noted 

 that, should atolls "remain at their present level, subjected 

 only to the action of the sea and to the growing powers of the 

 coral, .... it cannot .... be doubted that their lagoons and 

 the islets on their reef would present a totally different appear- 

 ance from what they now do. This consideration leads to the 



Fig. 5. 



suspicion that some agency (namely, subsidence) comes into 

 play at intervals, and renovates their original structure" ('42). 



In applying this scheme of reef development to the Queens- 

 land coast, it will be convenient to trace the sequence of events 

 backw^ards from the present into the past. But let it first be 

 noted that the Great Barrier reef is already a mile or more 

 wide in part of its length, and that the coastal embayments are 

 already somewhat encroached upon by deltas; hence the present 

 reef, Z, fig. 4, formed after the fourth flexure of the littoral 

 belt, has passed the stage of earliest youth and is advancing 

 toward maturity; if the coast should stand still for a long time 

 to come, the broad lagoon would be converted into a mature 

 reef plain. 



ISTow as to the origin of the present reef, there can be little 

 doubt that the opportunity for its upgrowth was given by the 

 latest or fourth flexure of the continental border, whereby the 

 formerly wider coastal lowland, UU^, was reduced to the pres- 

 ent narrower lowland, YY^ But the wider coastal lowland 

 must, before flexure and submergence, have been fronted by a 



