110 bulletin: museum of compakative zoology. 



bathymetrical range of the corals of the inner reef banks, but also close 

 to the limit where corals grow on the very inner edge of the outer line 

 of the Barrier Reef. The existence of this telluric mud so close to the 

 outer edge of the reef can only be due to the disintegrated land, islands, 

 islets, and rocks which once existed close to the present outer line 

 of the Great Barrier Reef, — land of which the only indication is the 

 presence of innumerable coral banks which have grown upon its former 

 sites, of islands which have either completely disappeared, or of which 

 only an occasional trace is remaining in an isolated peak, or rocky bank ? 

 or a single rock. 



We examined the western edge of Bramble Reef, lying to the north- 

 east of the Palm Islands. The edge of that reef flat is lined with 

 many clusters of negro heads. 1 Unfortunately the surf was too heavy 

 for us to land and examine this most characteristic inner reef patch. 

 The Family Islands (all within the ten fathom line) are of all shapes, 

 and their aspect, as well as their vegetation of pine and gum scrub, and 

 their geological features, clearly indicate their former connection with 

 the adjoining part of the mainland. The Frankland Islands consist of 

 metamorphic rocks. The depressions near the shore are filled, accord- 

 ing to Captain Thomson, with coral conglomerate, and this is overlaid 

 with broken coral and other marine debris. 2 



The slopes of Fitzroy Island (Plate XX.), like those of Cape Grafton 

 opposite, show the usual marks of great denudation and erosion, the 

 ledges of granitic rocks when exposed being rounded and worn, and 

 broken up into huge boulder-like forms. I could not find on Fitzroy 

 Island any trace of the elevated beaches mentioned by King. What he 

 describes as such appear to me to be mei-ely accumulations of fragments 

 of dead corals thrown up by the sea well above high-water mark. This is 

 specially well seen at the watering place in the middle of the coral sand 

 beach on the northwest side of the island. 



1 The term " negro head " was first applied by Flinders to the large masses of 

 coral flanking the edges of the reef flats. (Terra Australis, Vol. II. p. 83.) 



- In order to ascertain the rapidity with which coraks may grow and become 

 attached to fresh surfaces, I asked Captain Thomson on his way south from Cook- 

 town in the "Croydon" to place large blocks of stone under the Low Isles. He 

 also laid a mark down at the Frankland Islands in a position where it would 

 have the benefit of all the clean water and be free from the influence of the material 

 brought down from the slopes of the islands. Captain Thomson reports walking 

 over the reefs of the Low Isles, which we did not examine on our way north, 

 and finding their surface covered with dead corals and negro heads along the outer 

 edges. 



