AGASSIZ: THE GREAT BARRIER REEF OF AUSTRALIA. 119 



dead elevated coral reef, which forms the core of the reefs on the dead 

 summit of the reef flats left awash. The slopes of the reef flats are 

 generally very gradual from the edge of the reef left awash at low tide 

 to the clean sand slope found beyond the point at which corals and heads 

 begin to grow. "Where the water is deeper than ten fathoms off the reef 

 flat faces, the slopes are usually somewhat steeper, the coral patches and 

 heads rising more vertically from their first appearance, and thus seeming 

 to grow upon a steeper slope. 



Our next anchorage was south of the Lark Passage (Plate XXXIII.), 

 on the inside of the outer line of breakers in twenty fathoms, about an 

 eighth of a mile from the narrow reef which forms the southern arc of 

 breakers bounding the Lark Passage. As far as the eye could see, the 

 outer reef formed a series of these arcs slightly overlapping, the shape of 

 which was clearly indicated by the line of huge breakers pounding upon 

 the narrow flat belt of dead corals which separated the outer edge of the 

 reef from the interior passage in which we anchored. This part of the 

 exterior edge of the Great Barrier Reef differs in no way from the inner 

 reef flats we have already examined. As we approach it from the west 

 the coral patches and heads make their appearance in from seven to six 

 fathoms. At first widely separated, then in from five to four fathoms 

 they become more closely connected, and finally form a nearly continuous 

 belt incrusting the inner reef slopes. The growth of coral becomes less 

 and less again as we pass into shallower water, and when we reach the 

 reef flats with two to three feet of water upon it, the corals have become 

 reduced to a few small and scattered heads, the greater part of the 

 reef flat being covered with dead corals and fragments of dead corals 

 upon which Alga? and Xullipores flourish. The width of the reef flat, 

 between the inner line of breakers and the inner edge of the reef 

 flat slope, varied from 200 feet to about 800 feet. Unfortunately, 

 the state of the sea on the outside of the reef was such that it was 

 impossible to examine the condition of the corals growing upon the 

 sea face of this outer reef flat. 1 Prom what I have been told by 



1 Kent states thirty fathoms to be the limit at which reef corals grow. He must 

 refer to observations beyond the area of the Great Barrier Reef, as he does not 

 state that he has taken soundings to ascertain their lower limit. As far as my own 

 observations are concerned, they are limited to the bathymetrical range of the reef 

 corals on the slopes of inside reefs, or on the lee of the outer line of reefs, and 

 nowhere have I found them, as stated elsewhere in this paper, to reach the limit 

 assigned to them by Kent. I am unable to understand the assertion so frequently 

 made and repeated by Kent and Kramer that the lee faces of a reef show by far the 

 greatest development of living corals. The growth of the reef corals is so fre- 



