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bulletin: museum of comparative zoology. 



struck with the hue of great detached blocks of corals lying a little back 

 from the outer edge of the reef, always quite exposed at low water and 

 not altogether covered even at high tide, and which I consider to be 

 fragments of the elevated coral reef formerly covering the greater part of 

 what are now the reef flats in the district of the Great Barrier Reef. 



Jukes was rather disappointed by the aspect of the coral reefs until 

 one day, on the lee side of one of the outer reefs, when the extreme 

 slope was well exposed and when every coral was in full life and 

 luxuriance. This feeling of disappointment is very natural, for there is 

 no coral district like the Great Barrier Reef, where there are such exten- 

 sive reef flats bare or nearly bare at low water covered with dead coral 

 debris, on the slopes of which or on the deeper flats alone are found live 

 corals extending into seven or more fathoms, the belt nearest the upper 

 edge of the flats not being usually very thriving, or indistinctly visible 

 from the wash of the sea, or not exposed at a particular stage of tide. 



Jukes noticed that corals could remain alive even after having been 

 exposed to the action of the atmosphere for a considerable length of time. 

 He says (page 119) : "I observed to-day that some considerable portions 

 of coral, all alive and colored, were left by the tide six or eight inches 

 above the water, and remained so for nearly an hour. ... I often 

 observed the same fact both before and since, and believe that an ex- 

 posure of two or thi'ee hours to the air and the sun will not kill many 

 of the coral polyps. ... I have seen blocks of living Astraea with the 

 green animals in their cells, the top of which was eighteen inches above 

 the water." 



As Kent has well stated, in a district like that of the Great Barrier 

 Reef, where the tidal extremes are considerable, it is natural that even 

 those who are most familiar with the fisheries oft* the coast of Queens- 

 land should not have Been the coral reefs laid bare at the proper time of 

 tides. Kent's superb photographs leave one no doubts as to the aspect of 

 extensive stretches of live coral reefs when exposed by the tide. But an 

 examination of the photographs accompanying this sketch of the Great 

 Barrier Reef will also leave the reader in little doubt as to the uninter- 

 esting condition of the reef flats covered with dead corals and coral 

 debris. 



In the West Indian district the differences of the tides arc slight, and 

 it is rare when any extensive tract of live corals is laid bare by the 

 receding tides. Only twice during the frequent and prolonged visits I 

 have made to the Florida beefs has it been my fortune at the Tortugas 

 to see extensive tracts of Madrepores exposed for a while to the action of 



