Sect. III. GREAT CHAGOS BANK. J> 3 
are elongated, and so continuous that the northern and 
southern portions of Mahlos Mahdoo may claim to 
he considered as distinct atolls. But the reefs of 
the intermediate portion are less perfect, so that this 
portion hardly yet resembles a distinct atoll. Mahlos 
Mahdoo, therefore, is in every respect in an inter- 
mediate condition, so that it may he considered either 
as a single atoll nearly dissevered into three portions, 
or as three atolls almost perfect and intimately con- 
nected. This is an instance of a very early stage of 
the apparent disseverment of an atoll, and another 
is exhibited at Tilla-dou-Matte. In one part of 
this atoll, the ring-formed reefs stand so far apart 
from each other, that the inhabitants have given 
different names to the northern and southern halves : 
nearly all the rings, moreover, are so perfect, and 
stand so separate, and the space from which they rise 
is so level and unlike a true lagoon, that we can easily 
imagine the conversion of this one great atoll, not into 
two or three portions, but into a whole group of 
miniature atolls. A series such as we have here 
traced, impresses the mind with the idea of actual 
change ; and it will hereafter be seen, that the theory 
of subsidence together with the upward growth of the 
coral-reefs, modified by accidents of probable occur- 
rence, accounts for the occasional disseverment of large 
atolls. 
The great Chagos Bank alone remains to be de- 
scribed . 1 In the Chagos group there are some ordi- 
1 [See Appendix II.] 
