INTRODUCTION. 23 
now reduced by a half also, so as to be only ten miles. 
Where now is the reef? It has not perished; its active 
artificers have been incessantly employed in rearing it up, 
and it is now at the surface of the water; but it is no 
longer a fringing reef, but far out at sea; for though close 
to the shore when the diameter of the island at the water’s 
edge was twenty miles, it is far from the shore now, when the 
diameter of the island at the water’s edge is only ten miles. 
The sea now occupies the intervening space, so that on all 
sides the reef, which is now called a barrier reef, is five 
miles from the island. Let the sinking of the island gra- 
dually go on, and let the little polypes not slacken their 
operations, and in process of time the island will wholly 
disappear, and the reef, which the indefatigable marine 
builders have raised to the surface, will be the only monu- 
ment to show that there ever was an island within the 
enclosing circle, which is no longer a barrier reef, but is 
known by its Indian name—an atoll; and the lagoon of 
placid waters, surrounded by the reef, is now twenty miles 
in diameter, being the diameter of the island when the 
original fringing reef was formed around its shores. 
So long as the island was sinking the polypes wrought 
upwards, but when the sinking ceased and the reef had 
