174 GEOLOGY OF QUEENSLAND COAST, 



extension of the Reef) and the Tweed Heads is also of consider- 

 able width. 



(3) The Barrier Reef rises suddenly from great depths, but in 

 a less marked degree than does the shelf eastwards of Moreton 

 Bay and Sydney Heads.* 



(4) The great shoals of the shelf in the neighbourhood of 

 Stradbroke, Moreton and Frazer Islands are arenaceous and 

 argillaceous in character, and small calcareous patches, as Lady 

 Elliot Isle, have grown on the northern extension of one of these 

 banks, t 



(5) Between the outer Barrier and the mainland the average 

 depth of the water is from 10 to 20 fathoms. A few dejDths 

 exceeeding 30 fathoms have, however, been recorded in the vicinity 

 of Wreck Ba3^l 



(6) The Great Barrier Reef itself is of variable width, and is 

 broken up by long passages arranged parallel and transversely to 

 its length. The depth of the water in these '* lanes " or passages 

 varies from about 20 to 40 fathoms. 



(7) A maze of islands exists on the shelf, occupying a zone of 

 from 10 to 15 miles from the coast, close together inshore and 

 scattered in an easterly direction; 20 miles off shore no trace of 

 continental island occurs above H.W.M. In size these insular 

 areas var}-^ from several acres to rugged mountainous masses, like 

 Hinchinbrook Island 20 miles in length and 3,600 feet in height, 

 or huge masses of sand dunes as Moreton, Stradbroke and Frazer 

 Islands. Frazer Island is 80 miles in length, has a great spit 

 continuing from its northern extremity, with a fairl}^ meridional 

 disposition, and the eastern coast forms a long uninterrujDted 

 curve. Moreton and Stradbroke Islands have lines of sand 

 dunes as much as 800 feet in height, and show masses of conti- 

 nental rocks at their northern extremities. All of these three 

 large sandy islands are associated with large sand shoals, island 



* See also A. Agassiz, Bull. Mus. Comp. Zool. Harv. Coll. xxviii., pp. 129, 



140, 141. 



t Jukes, Voyage of H.M.S. "Fly," Vol. i., p. 318. 

 + Jukes, Ibid., p. 333. 



