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 sui-face, 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 



