CONTINENTAL SHELF. ^DANNEVIG. 343 



it comes into contact with the submerged shoulder of the 

 continent. \'ery Httle shore deposit is in consequence allowed 

 to settle there, except, perhaps, in crevices and where eddies 

 are formed and all jjrominent points remain exposed. 



From the Admiralty t'harts it will be seen that the fine 60 to 

 80 fathoms deposit is jiractically absent until south from Smoky 

 Cape. In fact it is only southwards from Port Stephens that 

 these beds become prominent and constant. This locality is, 

 however, two hundred to three hundred miles south from 

 the mouth of such voluminous rivers as the Tweed, Richmond 

 and Clarence, each of which conveys enormous quantities of 

 fine silt into the ocean. Examination of the shelf opposite 

 these rivers shows that near land there is a bed of fine sand 

 which no doubt owes its origin to the rivers, but outside of 

 this is a broad stratum of gravelly bottom which cannot be 

 assumed to have traversed across the intermediate fine sand. 

 This bed cannot in consequence be looked upon as in course 

 of formation (buildinsz up), but is maintained by the current 

 in a bare and exposed condition. While the heavy river sand 

 settles within a few miles of the land, the lighter silt 

 is carried southwards at an average rate of about tift}' miles 

 a day. In this light it is easy to understand why practically 

 no silt is met with along the northern portion of the coast 

 as far as Sandy Cape, for the current, which afterwards 

 becomes changed with eroded debris from the rivers and the 

 coast generally, is as j-et " virgin," and bare on its first 

 contact with the continent. The Brisbane River brings down 

 quantities of fine sediment, but this is jDractically all deposited 

 in Moreton Bay, which acts as a huge settling tank to that 

 river. From Port Stephens southwards Ave meet with fine 

 deposits on the outer ledge in increasing quantities until 

 south from Gabo Island, where the final and largest eddy is 

 formed ; the accumulation of silt is proportionately very 

 great and extends for nearly thirty miles from land. 



That the inshore ledge out to approximately 40 fathoms is 

 the direct result of wave and current action appears certain, 

 and the process must be constantly going on. This, however, 

 does not account for the existence of the outer and deeper 

 ledge, where at present no erosion takes place, but building 

 up may even be traced (as settlement of fine deposits — mud, 

 sand, etc.). It is evident also that the whole shelf is mainly 

 moulded on the rocky foimdation. the unevenness of which 

 frequently protrudes, particularly along the outer edge, and 

 may be traced to a depth of seven hundred fathoms. 



The origin of the outer portion of the ledge cannot be 

 directly attribiited to the action of wave or current except 



