ECOLOGY OF THE MURRAY ISLAND CORAL REEF. 7 



this appears remarkable and shows that at least one of the chief agents which 

 interfere with the growth of corals is absent from the Murray Islands. If in a 

 hurricane region, the wide floor of the southeast reef-flat would be smooth, 

 hard rock with but little coral upon it, as are the shore-flats of the Paumotos 

 Islands; but at Maer Island the reef-flat is densely covered with one of the 

 most luxuriant coral growths to be found in the Pacific. 



Moreover, there are no "negro-heads"' over these Murray Island reefs, 

 nor indeed over any of the numerous reefs of Torres Straits which the expe- 

 dition visited, from Cape York to New Guinea. It will be recalled that, as 

 a result of his exploration, Alexander Agassiz,- 1898, supposed these limestone 

 masses projecting above high-tide level to be vestigial remnants of elevated 

 reefs, and Semper^ held the same view respecting large stranded coral blocks 

 upon the Pelew Island reefs, but Hedley and Griflith Taylor, 1907,^ and also 

 F. Wood Jones in his "Coral and Atolls," have advanced reasons supporting 

 the contention that they are merely fragments which have been dislodged 

 and then washed inward from the outer edges of the reef in time of hurricanes 

 and finally, in some cases, recemented to the reef-flat by the formation of 

 beach-rock, bryozoa, lithothamnion, nullipores, or growing coral around 

 their bases. In support of Hedley and Griffith Taylor's view we have the 

 fact that the coral reefs of Torres Straits and southeastern New Guinea, 

 which are free from hurricanes, exhibit no "negro-heads," and yet these are 

 found in abundance over those reefs of the Great Barrier from Cooktown 

 southward which are subject to hurricanes. Erratic boulders of living or 

 dead coral are indeed found scattered over the reefs of Torres Straits; but 

 these are all so small that they do not project above the surface excepting at 

 the lowest tides. In short, one finds no geologic evidence of there having 

 been hurricanes at the Murray Islands and there are no native traditions 

 mentioning such phenomena. 



It thus appears that conspicuous "negro-heads" are found only upon 

 those reefs of the Great Barrier region which are subject to hurricanes. 



The rapidity with which an erratic boulder may become cemented into 

 a reef-flat by coquina or beach-rock is remarkable;'" for at the Murray Islands 

 many of the recent moUusks which are imbedded in coquina just above high 

 tide have their nacre wel preserved, and a piece of granite similar to that 

 of Cape York and which had evidently been transported to Maer Island 

 through human agency, probably as ammunition for slings, was found firmly 

 imbedded in hard coquina at high-tide level. 



'Flinders gave the name "negro-heads" to coral boulders which project often above high-tide level and are 

 scattered over the reef-flats of the Great Barrier Reef, especially in the neighborhood of Cairns. 



'Bulletin of the Museum of Comparative Zoology, vol. 28, pp. 114 and 121. 



•Semper, K., 1881, Animal Life, p. 239; International Scientific Series, Appleton. 



'Hedley and Taylor, Coral Reefs of the Great Barrier, Queensland; Australian Association for Advance- 

 ment of Science, Adelaide Meeting, 17 pp., 3 pis., 1907. 



'Cyril Crossland, 191 1, Journal Linnean Society of London, vol. 31, p. 279, describes this process at Khor 

 Dongonab, Red Sea. Here beach-sand draws up sea-water through capillary action; then this sea-water evaporates 

 and finally the rains remove the more soluble, leaving the less soluble constituents of the sea salts as a cement which 

 converts the originally loose sand into stone. 



