152 GEOLOGY OF QUEENSLAND COAST, 



On the northern submarine extension of Breaksea ^Spit, 

 which is composed almost entirely of " siliceous material,' "^ are 

 situated Lady Elliot Island and the Bunker Groups. 



Northwards again the outer edge of the shelf is represented by 

 the Great Barrier Reef itself, occurring at distances varying from 

 15 to 100 miles from the coast. Long lanes of coral sand and 

 wide openings l)reak into the integrity of the ocean front of the 

 Reef. 



Deep gutters of valley form occur in a few instances on the 

 continental shelf, and in the vicinity of the outer barrier, t 



A few miles from the shore line great numbers of precipitous 

 islands exist, rising from shallow water, rarel}' if ever exceeding 

 ten fathoms in depth. These islands are often accompanied by 

 small fringing reefs, and in many cases also by plains, miniatures 

 of the large occurrences on the mainland, and described under 

 "Coastal Plains." In man}'- cases the axes of the mountain 

 ridges composing the islands are parallel to the main coast line, 

 and are separated therefrom by narrow channels {e.g., Hincliin- 

 l:)rook, MoUe, and Albany Passages). 



4. Islands — Stradbroke, Moreton and Frazer Islands are huge 

 sand piles lying to the south of the Great Barrier Reef. They 

 are respectively 35, 20 and SO miles in length, and appear due to 

 the redistribution of tluviatile and other material by marine and 

 ieolian agencies. In the cases of 8tradbroke and Moreton Islands 

 the northern extremities consist of older stratified rocks, and 

 these uncovered masses of continental rocks doubtless belong to 

 a series of small insular patches on which the threefold action of 

 rivers, wind and currents have worked, first to tie the islands 

 together, and afterwards to fashion the large sand}^ masses nito 

 their present appearance. As a result of long-continued residence 

 and observation on those islands, Mr. Hedley is of ojiinion that 



* Jukes, Voya^^e of "FI3'," Vol. i., p. 318. See also A. Agassiz, '• Great 

 Barrier Reef of Australia," pp. 64, 105. 



t Ibid., Yol i., p. 845. 



