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THE WORLD. 



growing more vigorously around the outside where exposed to the 

 sea, the outer edges would grow up from the foundation before 

 any other part; thus making a ring or cup-shaped structure; but 

 we are not by this -theory relieved from the difficulty of answer- 

 ing the question, upon what are these massive structures based ? 

 since it is well known that the reef-building corals cannot live at 

 any very considerable depth, though indeed, other species have 

 been found at a depth of GO fathoms. Below we give a view of 

 one of these islands, copied from Capt. Beechy. The circular 

 form is well exhibited in this island, which is called Whitsunday, 

 but it gives a faint idea of the singular appearance of an atoll, 



being one of the smallest size. The immensity of the ocean, the 

 fury of the breakers, contrasted with the lowness of the land, 

 and the smothness of the bright green water within the lagoon 

 can hardly be imagined without having been seen. 



The second great class of reefs are the Barrier-reefs, these are 

 similar in all respects to the atolls except having a high land like 

 a castle rising out of the lagoon. The following sketch from Mr. 

 Darwin, will give an idea of the appearance of one of these 

 wonderful structures, being a part of the island of Bolabola in 

 the Pacific, as seen from one of the central peaks. In this in- 

 stance the whole line of reef has been converted into land, upon 

 which trees are growing; but generally, a snow-white line of 

 breakers, with onlv here nnd there n lowislpt covered with roooa- 



