W. M. Davis — The Great Barrier Reef of Australia. 349 



Yaiioilian"^ and others, who seem to have thonglit that only in 

 recent times could these two unhke features be developed on a 

 single coast line, and that in earlier times an inorganic conti- 

 nental shelf fronted the whole coast; but no good reason has been 

 shown why a continental shelf and a barrier reef can not have 

 been formerly developed contemporaneously along the cooler 

 and the warmer parts of any continuous continental coast, just 

 as well as they are now contemporaneously developed along the 

 Australian margin, and just as well as they are now developed 

 on many discontinuous coasts; hence I am inclined to regard 

 the present juxtaposition of shelf and reef as a normal and not 

 as an exceptional relation, and therefore as a characteristic of 

 the past as well as of the present. 



As to alternative explanations for the Great Barrier reef: — it 

 is easily conceivable that, until the latest flexure of the coast 

 took place, whereby the coastal lowland was narrowed as in 

 the change from UU^ to NN' ^ fig. 4, no previous shift of the 

 axis of flexure occurred, as in section C, flg. 1; or if such a shift 

 occurred, the axis of no change of level may have advanced not 

 landward as in section D, but seaward as in section E. In this 

 case, reefs may not have been formed, for they do not as a rule 

 occur along coasts that are bordered by recently formed, uncon- 

 solidated sediments. Then, in the absence of off-shore barrier 

 reefs, the unimpeded waves may have formed an inorganic con- 

 tinental shelf along the northern half of the Australian coast, 

 just as they are now and long have been forming a shelf along 

 the southern half of the coast; and Anally after the latest 

 flexure took place, the present barrier reef may have grown up 

 on a continental shelf in the formation of v/hich earlier reefs 

 had taken no part. But in view of the various lines of geo- 

 logical evidence which suggest a large diminution of land areas 

 in the Australasian region during Tertiary time it seems not 

 unreasonable to assume that, on the whole, the earlier flexures 

 of the Queensland coast have, like the latest flexure, involved a 

 westward shift of the axis of flexure and caused an encroach- 

 ment of the sea on the land, as in section D ; and in view 

 of the occurrence of greatly uplifted and elaborately dissected 

 coral reefs on the neighboring islands of Australasia, which 

 imply the presence of corals in this region for a considerable 

 period of past time, it seems unreasonable to assume that reefs 

 have occupied the Queensland coast only for the brief period 

 demanded for the formation of the superficial part of the Great 

 Barrier. 



The Great Barrier reef of today does not in all parts of its 

 extraordinary length rise from the outer margin of its platform, 



* T. W. Vauglian, The Platforms of Barrier Coral Reefs, Bull. Amer. 

 Geogr. Soc, xlvi, 194, 426-429. 



