110 BULLETIN: MUSEUM OF COMPARATIVE 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. Unfortunately the surf was too heavy 
for us to land and examine this most characteristic inner roof 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. Тһе depressions near the shore aro filled, accord- 
ing to Captain Thomson, with coral conglomerate, and this is overlaid 
with broken coral and other marine 618.2 
The slopes of Fitzroy Island (Plate XX.), like those of Cape Grafton 
opposite, show the usual marks of great denudation aud erosion, tho 
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 merely aceumulations 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 tue middle of the coral sand 
beach on the northwest side of the island. 
V 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. IL, p. 85.) 
? In order to ascertain the rapidity with which corals 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. Пе 
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 recfs 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. 
