44 
ATOLLS. 
Ch. L 
SECTION THIRD. 
Maldiva Archipelago — Ring-formed reefs, marginal and central — 
Great depth in the lagoons of the southern atolls — Reefs in the 
lagoons all reach the surface — Position of islets, and breaches in 
the reefs with respect to the prevalent winds and action of the 
waves— Destruction of islets — Relation in position between dis- 
tinct 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 consi- 
deration. My description is derived from an exami- 
nation of the admirable charts lately published from 
the survey of Captain Moresby and Lieut. 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 posi- 
tion in a double line, may be seen, though imperfectly, 
in the greatly reduced chart (fig. 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 34 hi 
