W. M. Davis— The Great Barrier Reef of Australia. 345 



shore line would not be embayed, and a broad fluviatile plain, 

 composed of the confluent deltas of many rivers, would border 

 the coast ; but as a matter of fact, the shore line is well embayed 

 and the delta plains are relatively small and discontinuous, as 

 at y, fig. 4. Hence the sea floor but not the sea surface 

 probably subsided each time that the highland rose; in other 

 words, the littoral belt was gently and intermittently tilted 

 eastward between a broad highland anticlinorium on the west 

 and a deep sea-bottom synclinorium on the east : in short, the 

 littoral belt occupies a zone of intermittent flexure. 



The line of no change of level or axis of flexure cannot have 

 advanced seaward as the successive flexures took place, as in 

 section E, flg. 1, for in that case as well as in the case of uni- 

 form uplifts, belts of marine sediments would now be found in 

 the coastal lowland. The line of no change cannot have 

 remained flxed, for this would entail a non -embayed coastal 

 lowland bordered by fluviatile deposits ; of less breadth, to be 

 sure, than if no down-flexing had taken place ofl shore, yet 

 much greater breadth than is actually found in the discontinu- 

 ous deltas of today. Hence, as these various possibilities are 

 excluded, the line of change probably shifted w^estward, as in 

 section I). 



This interpretation is adopted in flg. 4, in which nine stages 

 in the physiographic development of the region are represented 

 in successive east-west blocks from background to foreground. 

 The disordered structure of the region demands, as above 

 noted, that it was once mountainous, as in block A. The 

 mountainous mass must have remained long quiescent, for it 

 was reduced in Cretaceous time to an extensive peneplain, FF^ 

 Then as a result of a gentle flexing the seaward area was sub- 

 merged and the interior area was elevated as in block GG^ ; 

 and in this position the seaw^ard slope was reduced to a second 

 but less extensive peneplain, LL^, separated from the uncon- 

 sumed part of the uplifted peneplain, HH^, by a ragged 

 retreating escarpment. This escarpment of differential erosion 

 is analogous to the mountainous escarpment in North and 

 South Carolina known as the Blue Ridge. Similar changes 

 occurred twice again, resulting in the formation of a third 

 peneplain, QQ^, and a fourth peneplain, UU^ But as the 

 present shore line is much embayed, and as many subdued hills 

 rise as islands from the shallow sea bottom, the eastern part of 

 the fourth peneplain, UU^ must have been slightly down- 

 flexed and submerged at a recent date : the interior part of 

 the peneplain, constituting the present coastal lowland, YY^, 

 together with the benched highland, TT^, back of it, w^ere 

 probably upflexed at the same time, for the lowland, where 1 

 saw it, is now trenched by narrow valleys. Hence the latest 



