132 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
struck with the line 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 
débris, 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 indistinetly 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 three hours to the air and the sun will not kill many 
of the coral polyps. . . . I have seen blocks of living Astraa 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 off the coast of Queens- 
land should not have seen 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 
débris. 
In the West Indian district the differences of the tides are 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 Reefs has it been my fortune at the Tortugas 
to see extensive tracts of Madrepores exposed for a while to the action of 
