162 
DISTKIBUTION OF COKAL-ltEEFS. Cn. VI 
exist. Secondly, of coasts where the sea is extremely 
shallow ; and the reefs in this case generally lie far 
from the land, and are very irregular, so that they 
cannot always be classed. Thirdly, reefs which appear 
merely to coat submerged banks of rock or of sedi- 
ment ; for such reefs differ in some essential respects 
from those which owe them w’hole thickness to the 
growth of corals. Fourthly, in the Bed Sea, and 
within some parts of the East Indian Archipelago 
(if the imperfect charts of the latter can be trusted), 
there are many scattered reefs of small size, repre- 
sented by mere dots, which rise out of deep water ; 
and these have likewise been left uncoloured. In the 
Bed Sea, however, some such reefs seem once to have 
formed parts of a continuous barrier. There exist, 
also, scattered in the open ocean, some linear and 
irregularly-formed reefs wdiich are probably, as shown 
in the last chapter, remnants of atolls ; hut as they 
cannot safely be placed in this class, they have not 
been coloured ; they are, however, few in number, and 
of insignificant dimensions. Lastly, some reefs have 
been left uncoloured from the want of sufficient in- 
formation ; and some because they are intermediate 
in character between barrier and fringing-reefs. The 
Indian Ocean, has been seen (Naut. Mag. 1838, p. 842) in action. 
Dr. J. Allan, of Forres, informs me in a letter that, when he was at 
Joanna, he saw flames at night, apparently volcanic, issuing from 
the Chief Comoro Island, and that the Arabs assured him that they 
were volcanic, adding that the volcano burnt more during the wet 
season : I have marked this as a volcano, though with some hesita- 
tion, as the flames may have arisen from gaseous sources. 
