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 
^ery 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 
moved 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. 
P3 
