AGASSIZ: THE GKEAT BARRIER KEEF OF AUSTRALIA. 129 



no corals grow. 1 The sections plotted off the northeastern coast of 

 Queensland indicate a very moderate slope, with the exception of the 

 sudden drop of from ten to twenty fathoms close to the outer edge of the 

 reef, which marks the limits of greatest depth from which corals can 

 build up. Going farther south, the slope in certain localities increases 

 and varies, but neither more nor less than in adjoining localities south 

 of the Great Barrier Reef where there are no corals. Examine, for in- 

 stance, the sections off Breaksea Spit, off Moreton Island, and then off 

 the coast of Xew South Wales, which are quite as steep as auy of the 

 sections off the Great Barrier Reef, where it is supposed that the great 

 slope is due to the growth of corals during subsidence. (See Plates 

 XXXVII. to XLI.) 



A similar state of things exists off the south coast of Cuba, where the 

 slope in a non-coral reef district is steeper than found elsewhere in the 

 coral reef districts of the West Indian area. 



The older navigators and explorers have naturally given us but little 

 information regarding the Great Barrier Reef. An interesting sketch, 

 giving a condensed history of these earlier discoveries along the north- 

 east coast of Australia, by Captain W. Thomson, will be found in the 

 Proceedings of the Royal Geographical Society of Australia, Vol. II. 

 Part 3, p. 129. 



Flinders is the only one of the early explorers of Australia who not 

 only gave a good description of the Great Barrier Reef, but also specu- 

 lated on the mode of formation of the coral reefs, and it is interesting 

 to read in his " Terra Australis " 2 the ideas which the older navigators 

 had of the formation of coral reefs : — 



" It seems to me that when the animalcules which form the corals at the 

 bottom of the ocean cease to live their structures adhere to each other by virtue 



1 It is interesting to examine what would be the profile of the shore if the pres- 

 ent shore line became the edge of the continental plateau. We should find, as at 

 Mt. Thomas, west of the Hope Islands as far as Cape Bedford, a series of soundings 

 ranging from 2,318 feet, say nearly 400 fathoms, at a distance of less than three 

 quarters of a mile from the shore, to 750 feet, separated by level patches. Or again 

 such a bluff as that north of Cooktown, with summits of from 900 to 1,200 feet or 

 more, often at less than half a mile from the coast. I take these elevations merely as 

 an example of the contrast in depths between points within comparatively short dis- 

 tances, which are in every respect similar to depths off the outer edge of the Great 

 Barrier Reef, — depths which are there assumed to indicate the great thickness of 

 the outer edge of the Barrier Reef, while I look upon them merely as the seaward 

 extension of the continental slope of the Australian continent. • 



2 Vol. I. p. 115. 1814. 



