CORAL-REEFS. 57 



Mahlos Mahdoo (see Fig. 4, Plate III.), at the exact point 

 where the two sides of the latter, if prolonged, would meet ; 

 no bottom, however, was found in the channel with 200' 

 fathoms ; in the wider channel between Horsburgh atoll 

 and the southern end of Mahlos Mahdoo, no bottom was 

 found with 250 fathoms. In these and similar 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, besides the relation 

 of form, a submarine connection. 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 connection of adjoining atolls, if a 

 hasty glance be taken at the chart (Fig. 4, Plate III.) 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 bifur- 

 cating 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 their 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 sides of this bifurcating channel are elongated, 

 so that the northern and southern portions of Mahlos 

 Mahdoo may claim, as far as their external outline is 

 concerned, to be considered as distinct and perfect atolls. 



