348 W. M. Davis — The Great Barrier Reef of Australia. 



mature reef plain, Y', formed during the fourth peneplanation 



of the coastal slope, UU^; and the mature reef plain must have 

 been developed from a young, upgrowing barrier reef, Y, that 

 had been initiated by the flexure which tilted the peneplain, 

 QQ', into the coastal slope, RR^, just as the present reef, Z, was 

 initiated by the flexure which tilted the peneplain, UU', into 

 the coastal slope, Y V^ Again, the foundation from which reef 

 Y grew up must, with large probability, have been a down-flexed 

 and submerged mature reef-plain, X^, of an earlier cycle; and 

 so on backwards through the series of flexures. 



Thus, as far as present features can be genetically linked to 

 the chain of antecedent features, the platform, shown in fore- 

 ground section, from which the visible Great Ban-ier reef, Z, 

 has grown up, appears, in its outer part at least, to be in large 

 measure the product of coral-reef agencies that were directly 

 or indirectly in operation through a considerable period of past 

 time; for it must be remembered that reef-forming agencies 

 contribute to the formation of a mature reef-plain not only 

 directly by the constructive growth of tlie reef organisms and 

 by supplying overwashed waste, but also indirectly by serving 

 as a breakwater which encloses a lagoon where a large amount 

 of land waste is locally deposited, instead of being swept off- 

 shore as is the case where unimpeded ocean waves wash and 

 attack the land margin. 



It is believed that this sketch of reef development takes 

 fuller account of the accepted physiographic history of the 

 adjoining coastal highlands than has been taken by other 

 sketches; and that reef-forming agencies are thus shown to 

 have been, with large probability, so long associated with the 

 development of the off-shore structure of this part of the Aus- 

 tralian continent that they cannot be reasonably limited to the 

 brief period needed for the upgrowth of the present barrier 

 reef from a depth of only 30 fathoms; but it is not intended 

 to imply that the above-outlined sketch of the development of 

 the Great Barrier reef embodies unescapable conclusions, for it 

 is easy to suggest alternative possibihties, one of Avhich is men- 

 tioned below. 



It is furthermore believed that, in as much as the devel- 

 opment of an off-shore continental shelf along the cooler coast 

 of New South ^yales is now contemporaneous with the devel- 

 opment of the Great Barrier reef in the warmer waters along the 

 Queensland coast, the contemporaneous development of these 

 two unlike features, one largely by inorganic, the other largely 

 by organic processes, may have been similarly contemporaneous 

 each in its own latitudes, for a long time in the past. It is 

 true that this view traverses the opinions of Guppy,"^ Forbes,f 



*H. B. Guppy, The Origin of Coral Reefs, Proc. Vict. Inst., xxiii, 1890, 

 51-68. 



t H. 0. Forbes, The Great Barrier reef of Australia, Geogr. Jour,, ii, 

 1873, 540-546. 



