52 
ATOLLS. 
Ch. I. 
was found in the channel with 200 fathoms : in the 
wider channel between Horsburgh atoll and the south- 
ern end of Mahlos Mahdoo, no bottom was found with 
250 fathoms. In these cases, the relation consists 
only in the form and position of the atolls. But 
in the channel between the two Nillandoo atolls, 
although three miles and a-quarter wide, soundings 
were struck at the depth of 200 fathoms : the channel 
between Ross and Ari atolls is four miles wide, and only 
150 fathoms deep. Here then we have a submarine 
connection, besides a relation in position and form. The 
fact of soundings having been obtained between two 
separate and perfectly characterised atolls is in itself 
interesting, as it has never, I believe, been effected in 
any of the many other groups of atolls in the Pacific 
and Indian seas. In continuing to trace the con- 
nection of adjoining atolls, if a hasty glance be taken 
at the chart (fig. 4, Plate II.) of Mahlos Mahdoo and 
the line of unfathomable water be followed, no one 
will hesitate to consider it as one atoll. But a second 
look will show that it is divided by a bifurcating 
channel, of which the northern arm is about one mile 
and three-quarters in width, with an average depth 
of 125 fathoms, and the southern one three-quarters 
of a mile wide, and rather less deep. These channels 
resemble in the slope of them sides and general form, 
those which separate atolls in every respect distinct ; 
and the northern arm is wider than that dividing two 
of the Male atolls. The ring-formed reefs on the 
northern and southern sides of this bifurcating channel 
