412 PROCEEDINGS OF SECTION C. 



in the east the cay of Green Island and below the gorge of the Barron. 

 While the former disproves elevation and suggests subsidence or qui- 

 escence, the foaming cataracts now carving out the gorge of a youthful 

 and vigorous stream appear to demand great and recent elevation. 

 To harmonise the apparent contradiction we suggest that a capture 

 of the headwaters of the Mitchell by the Barron has lately occurred ; 

 in which transfer the stream would shorten its journey to the sea 

 from 300 miles westerly to 30 miles easterly, and the steepness of its 

 fall would imitate a stream rejuvenated by elevation. The situation 

 reminded one of us (T.) of the Shoalhaven capture lately studied and 

 described in conjunction with Dr. Woolnough {j) 



Such a capture would be assisted if not determined by a down- 

 ward movement east of the Divide. As chronological estimates of 

 the end of the Ice Period have been based on the rate the Niagara 

 excavates its gorge, so the rate at which the Barron digs its valley 

 might provide an estimate of the time of the local subsidence. 



Were the coral crust of the Great Barrier merely a thin veneer, 

 then at its border it should scarcely break the natural curve of the 

 continental shelf. So Professor Agassiz writes {loc cit-, p. 141) — 

 *' There is nothing to show that the slope of the continental plateau 

 has been modified by the growth of the Great Barrier Reef, and that 

 we have a steep pitch (almost a vertical rise, due to the growth of 

 corals) .... on the sea-face of the living Barrier Reef." But 

 the precipitous submarine slope of Raine Island and the adjacent 

 Barrier — a tower beyond a wall — as developed by the Challenger sur- 

 vey (Narrative Chall. Rep. p. 530, inset map 27, opp. p. 464) is com- 

 parable to the submarine cliff of Funafuti, and may be cited as evidence 

 in favor of Darwin. Recent Admiralty surveys abreast of the Hope 

 Islands show the seaward face of the barrier to rise there even more 

 abruptly. At one and a half miles outside the reef the depth is 312 

 iathoms, and at three and a half miles it is 600 fathoms. There is 

 not in all Australia a declivity to match this ; but those who know the 

 mountain towering over Monaco may realise how the Great Barrier 

 would appear if uplifted in the air. Part of this slope is probably talus. 



One of the chief gains to science in the investigation of Funafuti 

 was the generalisation that crystallised dolomite characterised the 

 strata below 638ft., but was unknown above that horizon (Cullis — 

 ■" Atoll of Funafuti," 1904, p. 405). Now large blocks of dolomitic coral 

 were observed to have been ejected by the extinct crater of Mer, Murray 

 Islands, north end of the Great Barrier, by Professor A. C. Haddon 

 (Trans. Roy. Irish Acad, xxx., 1894, p. 433). These blocks have 

 been examined in situ by one of us (H.). This shows that the volcanic 

 pipe burst through an underlying coral reef. It seems a fair deduction 

 to conclude that at this spot sunken reefs exist below the 100-fathom 

 level. 



The last upward vibration of Andrews was not observed by us; 

 possibly it does not extend along the whole coast. A slight elevation 



<;■) Woolnough and Taylor: Proc. Linn. Soc, N.S.W., xxxi., 1906, pp. 546-554. 



