120 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



intelligent beche de mer fishermen, they do not think that corals flourish 

 on the outer edge at a greater depth than on the faces of inner reef flats, 

 six to seven fathoms. I have also been assured that the small outer 

 barrier of reef flats which we examined south of the Lark Passage was 

 typical of all the reef flats which form the line of the so called outer 

 linear reefs (Jukes). The surface inside of the breakers of all the outer 

 Barrier Reef flats are covered with dead corals, as those of the interior 

 reef flats are. We may therefore safely conclude that the dead corals 

 which cover the outer reef flats owe their origin to the same cause, — 

 viz. to the disintegration of the former elevated coral reef which once 

 was the outer barrier reef. 



That the outer reef flats all are arcs facing the breakers, and form so 

 uniformly narrow shallow strips between deep inner channels and the 

 outer sea-face, we can only explain by the peculiar action of the sea, 

 which invariably on exposed shores erodes islets into a more or less cir- 

 cular outline, and patches into convex faces turned about at right angles 

 to the general trend of the breakers (Plates XXXII.-XXXIV.) . 



The inner channel of the outside Barrier Reef patches ranges from six- 

 teen to twenty-eight fathoms, the average depth being about twenty 

 fathoms ; from this it shoals somewhat steeply to ten fathoms, and then 

 very gradually to the inner edge of the outer reef flats. Between six 

 and seven fathoms coral masses appear, often forming large detached 

 patches rising quite abruptly on all sides to within one or two feet of the 

 surface at low-water mark. From there in on the slope, in four to five 

 fathoms, the patches become more numerous, often forming long 

 connected stretches of coral heads. The belt between five and three 

 or four fathoms is the one in which the corals seem to thrive best. 

 The masses become more or less disconnected again in from one 



quently determined by local causes that it seems impossible to assign their great 

 development merely to their position on either the lee or seaward face at any 

 locality. Taking the Samoa Islands, the lee face of the islands is the very face on 

 which the coral reefs of that group are developed. At the Sandwich Islands, where 

 we have the northeast trades, while there is a lee face reef, we have an equally 

 well developed sea-face reef. On the Windward Islands, the sea-face reefs are 

 much more developed than those on the lee face of the islands. On Alacran 

 Reef the lee reef is nearly overwhelmed by the sand driven from the islands over 

 that face, while the sea face is a most flourishing mass of corals. While the lee 

 faces of the Bahamas support a most luxuriant growth of corals, it does not com- 

 pare with that growing on the weather side. On Hogsty Reef the corals facing the 

 great swell of the northeast trades are far finer than those on the lee side. The 

 same is the case for the Bermudas. 



