192 CORALS AND CORAL ISLANDS. 
The Great Chagos Bank, This bank lies about ten degrees 
south of the Maldives, and is ninety miles long and seventy in 
its greatest breadth. It is a part of the Chagos Group, in which 
there are some true atolls, some bare atoll-reefs, and others, like 
the Great Chagos Bank, that are quite submerged, or nearly 
so. Its rim is mostly from four to ten fathoms under water. 
Mr. Darwin confirms the opinion of Captain Moresby, that 
this bank has the character of a lagoon reef, resembling one 
of the Maldives; and he states, on the evidence of extensive 
soundings, that, if raised to the surface, it would actually be- 
come a coral island, with a lagoon forty fathoms deep. He 
says that, in the words of Captain Moresby, it is in truth 
“nothing more than a half-drowned atoll.” 
The form of the bank, its margin of shoals, and a line 
of soundings across it, giving the depth of the central or 
lagoon portion, are shown in the map on p. 191, from Darwin, 
and for which, as well as for other information about the 
4to 10 fathoms. 
2POr ms 
Leveh of the Sea. 
EOS HEL 
J \bo 
( 
Poet 
76 miles in length- 
EAST AND WEST SECTION ACROSS THE GREAT CHAGOS BANK. 
bank, he gives credit to Captain Moresby. ‘The cross section 
is still further illustrated in the annexed cut. The whole 
length of the section (or width of the bank in the line of .the 
soundings) is seventy-six miles. From the outer rim of 
the submerged atoll, there is a drop off to a deeper level, which 
is mostly fifteen to eighteen fathoms below the surface ; and 
