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" is difficult to credit that it is the work of nature and not of 

 " art — its utility is great, close within the inner wall there is 

 "a good depth of water, and ships lie moored to old guns 

 "which are fixed in holes upon its summit — a lighthouse 

 "stands on one extremity, and around it the sea breaks 

 " heavily. In entering the harbour a ship passes within thirty 

 " yards of this point, and amidst the foam of the breakers ; 

 " close by, on the other hand, are other breakers, which thus 

 " form a very narrow gateway. It is almost fearful to behold a 

 " ship running as it appears headlong into such dangers. With 

 " respect to the origin of the reef, I believe a bar composed of 

 " sand and pebbles formerly existed beneath the water, (a cir- 

 " cumstance no ways improbable) when the lowland on which 

 " the town now stands was occupied by a large bay, and that 

 " this bar was first consolidated and then elevated. * * * there 

 " is another and slightly different explanation, which possesses 

 "equal probability; namely, that a long spit of sand, like 

 "some that now run parallel to parts of the neighbouring 

 " coast, had its central part consobdated, and then by a slight 

 " change in the set of currents, the loose matter removed, so 

 " that the hard nucleus alone was left. Although the swell of 

 " the open ocean breaks heavily on the outside of this narrow 

 " and insignificant line of reef, yet there is no record of its 

 " decay. * * * this durabibty is much the most curious circum- 

 " stance in its history. Its protection appears due to a layer of 

 " calcareous matter, formed by the successive growth of several 

 "kinds of organic bodies, chiefly serpulse, balani, and nulli- 

 " poree, but no true corals. It is a process strictly analogous 

 " to the formation of peat, and, Hke that substance, its effects 

 "are to preserve from degradation the matter on which it 

 " rests. In true coral reefs, when the upper extremities of the 

 " Hving mass are killed by the rays of the sun, they become 

 " enveloped and protected by a nearly similar process. 



"It is probable that if a breakwater such as that at 

 "Plymouth was built in these tropical seas, it would be 



