AGASSIZ: THE GEEAT BAKEIER REEF OF AUSTRALIA. 117 



of corals separated by lanes of clean coral sand. The 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 the coral heads magnificent Actinia), masses of Alcyonari- 

 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 Alcyonarians 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 Algae 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) f Reef (Plate XXXIII.), 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. The 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. On the parts of the reef flat less exposed 

 to the action of the sea, these 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 Algse 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 the east face (windward face) of the reef were growing much more 

 luxuriantly than on the other and more sheltered slopes of the reef 

 (Plate XXXIII.). 



