156 RAMBLES AND REVERIES. 



rises more than a yard or two above the water, and 

 is richly clothed with vegetation. Here and there 

 rises above the ground a grove of cocoa palms, 

 waving their graceful plumes in the air. The beach 

 is of pearly lustre, and makes a fine contrast against 

 the deep blue of the surrounding water. Before the 

 islet runs a protecting barrier, against which the 

 billows dash themselves and then sink down into 

 the placid lagoon that lies between the barrier and 

 the islet. The lagoon is not completely shut in, but 

 there is a narrow channel between the two ends of 

 the reef and the points of the curved island which 

 they approach. These give entrances to the lagoon 

 for shipping, and also insure a continued supply of 

 fresh water to the haven. That side of the reef 

 which is most exposed to the action of the trade 

 winds attains a greater height than the other or 

 leeward side. This is explained by the fact that on 

 the windward side there is a more abundant food 

 supply for the polypes, and hence their building 

 energy is greater. Some of these reefs are of 

 enormous dimensions. The great reef of Australia is 

 1,250 miles long, and from ten to ninety miles wide. 

 Dana computes that within the coral region of the 

 Pacific there are nearly three hundred islands, in ad- 

 dition to the reefs that surround other islands, which 

 are of coral formation. When we consider that all 

 these vast accretions are the results of the prolonged 

 and united labours of tiny organisms requiring the 

 microscope for their proper observation, and that 

 the entire materials with which the minute architects 

 carry on their work have been derived from the car- 



