20 ON CORAL REEFS AND ISLANDS. 



These calculations, however, are liable to error from many 

 sources, Very different results might generally be obtained from 

 different sides of the same island ; and the same group often con- 

 tains islands without reefs, and others with reefs one or even sev- 

 eral miles from the shores. Bat since we may show that the 

 absence of a reef or its limited extent may be traced to some 

 causes restricting or modifying its formation, it is obvious that 

 the error would probably be on the side of too low an estimate. 

 Adjacent to the larger islands, such as those of Vanua Levu and 

 New Holland, the error might be of the opposite kind; for the 

 slopes of the land are of a more complex or irregular character 

 than on the smaller islands. In the latter, they may be shown to 

 belong generally to a single elevation of igneous origin, or at the 

 most to two or three combined ; while in the former, they may 

 pertain to different ranges of hills or mountains. For correct re- 

 sults in any instance, the land and its declivities should be care- 

 fully studied beforehand, and the system in its inclinations deter- 

 mined by observation. With regard to Tahiti and Upolu, in- 

 formation bearing upon this point was obtained, and the above 

 conclusions may be received with much confidence. Many of 

 the Peejee reefs, on the same principle, cannot be less than 2000 

 feet in thickness. 



Such accumulations of calcareous rock may appear to be an 

 incredible work for the coral polyp, but only so, because we are not 

 accustomed to contemplate the results which may proceed from 

 the smallest agencies long continued. The operatives in the 

 inorganic world are invisible molecules ; and among living or- 

 ganisms, it is the lowest grade, the minims of existence, that 

 have accomplished the grandest results in the earth's history. 



3. Coral Islands. 



A. Forms and general features of Coral Islands. 



A barrier reef, and a lagoon enclosed by it, are the prominent 

 features of a coral island; yet there are a few of small size in 

 which the lagoon is wanting. In the larger islands, the waters 

 within look like the ocean, and are similarly roughened by the 

 wind, though not to the same extent. Standing on the north 

 shore of the Raraka lagoon, (in the Paumotus,) and looking south- 

 west, nothing is descried but blue waters ; — far in the distance, to 

 the right or left, a few faint dots are distinguished ; and as the eye 

 sweeps around, these gradually enlarge into lines of palms and 

 other verdure, which finally become distinct groves on nearing the 

 observer. At Dean's Island, another of the Paumotus, and at 

 many of the Carolines, the resemblance to the ocean is still more 

 striking. The lagoon is in fact but a fragment of the ocean cut 



