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AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 117 
of corals separated by lanes of clean coral sand. Тһе heads are more 
numerous between two and three fathoms, decreasing in size and num- 
ber towards the edge of the reef ; in from one and a half to two fathoms, 
there are found only a few distant patches of corals. As elsewhere, we 
found. among tho coral heads magnificent Асбіпіш, masses of Aleyonari- 
ans and of sponges ; as the coral heads grow in less profusion, they also 
become less abundant; and on the flat of the reef where the coral heads 
are small and widely scattered Aleyonarians disappear.  Actinians are, 
however, still found between the masses of dead corals which cover the 
reef flats; here and there we find a small living coral head. The 
growth on the flat is mainly Algæ and Nullipores. There are fine 
patches of corals in five fathoms off the northwest end of e Reef. 
Negro heads are exposed on one part of the edge, rising perhaps two 
feet above the general level of the flat. They look to me like fragments 
of an elevated reef which has been washed away, leaving only here and 
there an isolated pinnacle, such as we saw so many of on Bramble Reef. 
It is not probable that they are dead masses of coral thrown up from 
the present reefs, as there are huge masses of coral growing up all 
around them. 
Passing on to (Ef) £ Reef (Plate XXXIIT.), we saw at the northeast 
and east face a long line of negro heads, among them a huge rock about 
nine feet high, standing fully 250 yards inside of the edge of the reef. 
It was a mass from a coral head left standing as it grew, but weather 
and water worn, pitted and honeycombed, and full of boring Mollusks 
and Annelids, which had made their abode in this huge Porites mass. 
It was irregular in shape, and black with age, with the general aspect of 
the coral masses we have been accustomed to find as parts of West 
Indian elevated reefs. 
The southeast face of this reef is flanked by a comparatively broad 
belt of fine negro heads. Тһе whole surface of the reef flat, wherever 
we examined it, was covered with larger or smaller fragments of similar 
negro heads, which had become disintegrated by the action of the sea 
and worn to their present size. Оп the parts of the reef flat less exposed 
to the action of the sea, theso fragments were more or less covered with 
sand, cropping out only here and there in patches, and more or less over- 
grown with masses of Alex and Nullipores. On the east face the corals 
were thriving further in, to the very edge of the reef flat, while on the 
lee face they were partially overwhelmed with sand. The coral patches 
on tho east face (windward face) of the reef were growing much more 
luxuriantly than on the other and more sheltered slopes of the reef 
(Plate X XXIII.). 
