AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 133 



the air and sun. In both instances the exposure was due to the force 

 of the gale at low tide driving the water off the flats upon which the 

 Madrepores were growing. On a later occasion, a similar gale lasting 

 longer completely destroyed this field of Madrepores. 



During a visit which I paid to the Bermudas, the extensive reef 

 patches covered with living corals within the outer lagoons were exposed 

 at an extremely low stage of tide during the time we were steaming out 

 of the Bermudas on our way to New York. It is very evident that in those 

 coral reef regions of the Pacific where there is a great range in the rise 

 and fall of tide, it is not unusual to have great sketches of coral reef ex- 

 posed at low tides, if we may judge from the photographs of a coral reef 

 exposed on the weather side of Levuka (Fiji Islands) which is on exhibi- 

 tion in the coral gallery of the British Museum, from similar photographs 

 from the Hebrides in the coral gallery of the American Museum of Natural 

 History in New York, and from a photograph of a Madrepore reef on the 

 lee side of Apia published by Kramer. 1 



The description which is given by Jukes (Voyage of the "Fly," 

 Vol. I. p. 314) of one of the reef flats of the Great Barrier Reef is a most 

 admirable description of the average reef flat characteristic of the Aus- 

 tralian coral belt. As Kent has not reprinted this account, I here 

 reproduce his description of what I have called a "reef flat or reef 

 patch " : — 



" The size and form of an 'individual coral reef is perfectly indeterminate; 

 it may be circular, oval, or linear ; its surface may vary from a mere point to 

 an area of many square miles. Those, however, which occupy the extreme 

 edge of a mass of reefs (there is a term wanted to express the distinction be- 

 tween an individual reef, unbroken by any deep water channel, and a group of 

 such reefs. For the latter I am almost tempted to use the word ' reefery ' ; 

 for the former I have, in this passage, used the expression 'individual coral 

 reef), or rise on one side from great depths, having on the other comparatively 

 shallow water, have generally a linear form, being three, five, or ten miles 

 long, and varying in breadth from one or two hundred yards to perhaps a mile. 

 This seems to be more especially the case when their direction runs across that 

 of the prevailing wind. The individual coral reefs which rise from an equal 



1 Ueber den Bau der Korallenriffe und die Planktonvertheilung an den Samoa- 

 nischen Kiisten, von Dr. Augustin Kramer, Kiel, 1897, p. 65. On the preceding page 

 Kramer has figured the reef flats to the eastward of the entrance of Apia covered 

 with coral diHjris which resemble the uninteresting reef flats of the Great Barrier 

 Reef, and which I had an opportunity of examining when at Apia. See also 

 A. Agassiz, The Coral Reefs of the Hawaiian Islands, Plates VIII., IX., Bull. 

 M. C. Z., Vol. XVII. No. 3, 1889. 



