SECT. iv. ENCIRCLING REEFS. 145 



zling hues. When the shades of evening come on, the 

 lagoon shines like the milky way with myriads of bril- 

 liant sparks. The microscopic medusae and crustaceans 

 invisible by day form the beauty of the night, and the 

 sea- feather, vermilion in daylight, now waves with green 

 phosphorescent light. This gorgeous character of the 

 sea bed is not peculiar to the lagoons of the atolls ; it 

 prevails in shallow water throughout the whole coral- 

 bearing regions of the Pacific and Indian Oceans. 



Encircling reefs differ in no respect from the atoll ring, 

 except in having islands in their lagoons, surrounded 

 also by coral reefs. Barrier reefs are of the same 

 structure as the atoll rings, from which they, only differ 

 in their position with regard to the land. They form 

 extensive lines along the coasts, from which they are 

 separated by a channel of the sea of variable depth and 

 breadth, sometimes large enough for ships to pass. A 

 very long one runs parallel to the west coast of New 

 Caledonia, and stretches for 120 miles beyond the ex- 

 tremities of the island. But a barrier reef off the north- 

 eastern coast of the Australian continent is the grandest 

 coral formation existing. Rising at once from an un- 

 fathomable depth of the ocean, it extends for a thousand 

 miles along the coast with a breadth varying from 200 

 yards to a mile, and at an average distance of from 20 

 to 60 or 70 miles from the coast, the depth of the chan- 

 nel being from 10 to 60 fathoms. The pulse of the 

 ocean, transcendently sublime, beats perpetually in peals 

 of thunder along that stupendous reef, the fabric of 

 almost microscopic beings. 



