FIGURE 6.--MALDIVA ARCHIPELAGO, in the Indian Ocean; from the survey by
Captain Moresby and Lieutenant Powell.)


SECTION 1.III.--ATOLLS OF THE MALDIVA ARCHIPELAGO--GREAT CHAGOS BANK.

Maldiva Archipelago.--Ring-formed reefs, marginal and central.--Great
depths in the lagoons of the southern atolls.--Reefs in the lagoons all
rising to the surface.--Position of islets and breaches in the reefs, with
respect to the prevalent winds and action of the waves.--Destruction of
islets.--Connection in the position and submarine foundation of distinct
atolls.--The apparent disseverment of large atolls.--The Great Chagos
Bank.--Its submerged condition and extraordinary structure.

Although occasional references have been made to the Maldiva atolls, and to
the banks in the Chagos group, some points of their structure deserve
further consideration. My description is derived from an examination of
the admirable charts lately published from the survey of Captain Moresby
and Lieutenant Powell, and more especially from information which Captain
Moresby has communicated to me in the kindest manner.

The Maldiva Archipelago is 470 miles in length, with an average breadth of
about 50 miles. The form and dimensions of the atolls, and their singular
position in a double line, may be seen, but not well, in the greatly
reduced chart (Figure 6) in Plate II. The dimensions of the longest atoll
in the group (called by the double name of Milla-dou-Madou and
Tilla-dou-Matte) have already been given; it is 88 miles in a medial and
slightly curved line, and is less than 20 miles in its broadest part.
Suadiva, also, is a noble atoll, being 44 miles across in one direction, and