LAGOON-ISLANDS, OR ATOLLS. 261 



of the land and the smoothness of the bright green 

 water within the lagoon, can hardly be imagined 

 without having been seen. 



The earlier voyagers fancied that the coral- 

 building animals instinctively built up their great 

 circles to afford themselves protection in the inner 

 parts ; but so far is this from the truth, that those 

 massive kinds, to whose growth on the exposed 

 outer shores the very existence of the reef depends, 

 cannot live within the lagoon, where other deli- 

 cately-branching kinds flourish. Moreover, on this 

 view, many species of distinct genera and families 

 are supposed to combine for one end, and of such 

 a combination not a single instance can be found 

 in the whole of nature. The theory that has been 

 most generally received is, that atolls are based on 

 submarine craters ; but when we consider the form 

 and size of some, the number, proximity, and rel- 

 ative positions of others, this idea loses its plausi- 

 ble character : thus, Suadiva atoll is 44 geograph- 

 ical miles in diameter in one line, by 34 miles in 

 another line; Rimsky is 54 by 20 miles across, 

 and it has a strangely sinuous margin ; Bow atoll 

 is 30 miles long, and, on an average, only six in 

 width ; Menchicoff atoll consists of three atolls 

 united or tied together. This theory, moreover, is 

 totally inapplicable to the northern Maldiva atolls 

 in the Indian Ocean (one of which is 88 miles in 

 length, and between 10 and 20 in breadth), for 

 they are not bounded, like ordinary atolls, by nar- 

 row reefs, but by a vast number of separate little 

 atolls ; other little atolls rising out of the great 

 central lagoon-like spaces. A third and better 

 theoiy was advanced by Chamisso, who thought 

 that, from the corals gi'owing more vigorously 

 whei'e exposed to the open sea, as undoubtedly is 

 the case, the outer edges would gi'ow up from the 



