THE MASCARENES 
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marine formations on the sea coast, forming a fringing-reef 
round the island. 
Darwin, who thoroughly examined the coral reefs of 
Mauritius, remarks that they stretch round the island 
and vary in breadth between half a mile and two or three 
miles ^ the reef is interrupted where the rivers flow into 
the sea, as live coral cannot survive a temporary ex¬ 
posure to fresh water. At Grand Port the reef takes 
the character of a barrier-reef. 
On its external face the reef is formed principally 
of madrepores, star corals and millepores; at greater 
depths the delicate seriatopora is plentiful, and coral 
life seems to cease here at a depth of 20 fathoms. 
Several smaller coral islahds rise above the surface of 
