CORAL ISLANDS. 



173 



because the current is too sluggish to carry down 

 the sand,* gravel, and mud which it brings down 

 from above. 



The growth of coral is generally supposed to be 

 very slow. In the Pacific, an anchor was discov- 

 ered in seven fathom water, still preserving its ori- 

 ginal form, but entirely incrusted with coral. It is 

 stated, in Captain Beechey's expedition to the Pa- 

 cific, that no positive information could be obtained 

 of any channel having been filled up by coral within 

 a given period ; and that several reefs had remain- 

 ed for more than half a century at about the same 

 depth from the surface. The natives of the Baha- 

 ma Islands point out certain corals now growing 

 in the sea, which, according to tradition, have been 

 living in the same spot for centuries. " It is sup- 

 posed," says Lyell, " that some of them may vie in 

 age with the most ancient trees of Europe." 



Captain Basil Hall thus describes a coral reef 

 near the great island of Loo Choo : 



" When the tide has left the rock for some time 

 dry, it appears to be a compact mass, exceedingly 

 hard and rugged ; but, as the tide rises, and the 

 waves begin to wash over it, the polypi protrude 

 themselves from holes which were before invisible. 

 These animals are of a great variety of shapes and 

 sizes, and in such prodigious numbers that in a 

 short time the whole surface of the rock appears to 

 be alive and in motion. The most common form is 

 that of a star, with arms or tentacula, which are 

 anoved about with a rapid motion in all directions, 

 probably to catch food. Others are so sluggish 

 that they may be mistaken for pieces of the rock, 

 and are generally of a dark colour. When the coral 

 is broken about high-water mark, it is a solid, hard 

 stone ; but if any part of it be detached at a spot 



* The only effectual remedy in such cases is to increase the 

 velocity of the water by narrowing the channel. 



