Ch. III. FRINGING REEFS. 71 



will be described in the ensuing chapter. Between 

 the outer margin and the beach, there is a flat space 

 with a sandy bottom and a few tufts of living coral ; in 

 some parts it is so shallow, that people, by avoiding 

 the deeper holes and gullies, can wade across it at low- 

 water : in other parts it is deeper, seldom, however, 

 exceeding ten or twelve feet, so that it offers a safe 

 coasting channel for boats. On the eastern and 

 windward side of the island which is exposed to a 

 heavy surf, the reef was described to me as having 

 a hard smooth surface, very slightly inclined inwards, 

 just covered at low- water, and traversed by gullies ; 

 it appears to be quite similar in structure to the reefs 

 of the barrier and atoll classes. 



The reef of Mauritius, in front of every river and 

 streamlet, is breached by a straight passage : at Grand 

 Port, however, there is a channel like that within a 

 barrier-reef: it extends parallel to the shore for four 

 miles, and has an average depth of ten or twelve 

 fathoms ; its presence may probably be accounted for 

 by two rivers which enter at each end of the channel, 

 and bend towards each other. The fact of reefs of 

 the fringing class being always breached in front of 

 streams, even of those which are dry during the 

 greater part of the year, will be explained, when the 

 conditions unfavourable to the growth of coral are 

 considered. Low coral-islets, like those on barrier- 

 reefs and atolls, are seldom formed on reefs of this 

 class, apparently owing in some cases to their narrow- 

 ness, and in others to the gentle slope of the reef 



