CONTINENTAL SHELF. DANNEVIO. 339 



VLl.THE CONTINENTAL SHELF OF THE EAST 



COAST. 



FKOM the soundings on the charts of the East Coast it will be 

 seen that a submerged step or shelf of moderate depth is 

 interposed between the mainland and the great ocean abyss 

 of 2,000 to 3,000 fathoms or more, which almost completely 

 surrounds the Continent like an enormous valley of great 

 width and depth. It is generally recognised that this shelf 

 has its origin partly through volcanic faults or breaks, and 

 partly through elevation and depression in relation to sea 

 level. Other and more mechanical agencies are constantly 

 tending to modify the character of this shelf ; erosion from 

 the coast and river deposits is providing fresh building 

 material with a tendency to elevate the shelf, while the currents 

 and waves endeavour to remove all loose and flotsam 

 matter. It is evident therefore that apart from an " original " 

 formation of ancient date, there are constant changes taking 

 place for which the action of waves and ocean currents are 

 mainly responsible. 



Between the southern portion of the Coral Reef and the 

 Queensland Mainland is a comparatively wide area of shallow 

 water. 15 to 30 fathoms being the usual depth. The bottom 

 consists almost uniformly of coral sand and is perfectly smooth 

 and free from obstruction. Coral reefs form the margin 

 towards the ocean deep, and they are the principal producers 

 of the material from which this portion of the continental 

 shelf is constituted. 1 It is at Sandy Cape, however 

 (Lat. 25 S.), that the more typical shelf commences and 

 continues southwards along the coast. For the first three 

 hundred and sixty miles (or south to Smoky Cape in Lat. 

 31 S.) the shelf presents peculiarities which gradually 

 disappear further south. 



These peculiarities are that the shallow portion of the 

 shelf contimies seawards for a considerable distance so that, 

 for instance, at Double Island, the depth is only 50 fathoms. 

 At this depth the shelf may here be said to terminate, as the 

 more or less rocky and always steep edge slopes off very 

 quickly towards great depths. Northwards from Cape 

 Moreton the shallow portion of the ledge is mainly covered 

 with coral sand, which southwards gives way to a somewhat 

 coarse yellow sand, occasionally interspersed with gravelly 

 beds M'here the currents are strong, as off Point Danger. 



1. Medley, C.. ami Taylor, 'I'. (.!. Rep. Aifilr. Astoc. Adv. Sci.. xi., 

 '1907), 1909, pp. 397-413. 



