Ch. V. 
OF CORAL-REEFS. 
143 
latter was originally formed over a reef encircling one 
or more mountainous islands. 
The disseverment of the larger Maldiva atolls . — 
Tlie apparent progressive disseverment of large atolls 
into smaller ones in the Maldiva Archipelago, demands 
an explanation. The graduated series which marks, 
as I believe, this process, can be observed only in the 
northern half of the group, where the atolls have im- 
perfect margins consisting of detached basin-formed 
reefs. The currents of the sea flow across these atolls 
with considerable force, as I am informed by Captain 
Moresby, and drift the sediment from side to side 
during the monsoons, transporting much of it seaward ; 
yet the currents sweep with greater force round their 
flanks. It is historically known that these atolls have 
long existed in their present state ; it is intelligible 
that they might thus remain, even during a slow sub- 
sidence, owing to the continued growth of the corals, 
and to the lagoon being kept at nearly its original depth 
by the accumulation of sediment. But during the 
action of such nicely balanced forces, it would be strange 
if the currents of the sea had never made a direct 
passage across some of these atolls, through the many 
wide breaches in their margins. As soon as this oc- 
curred the channels would he deepened by the removal 
of the finer sediment, and by the check to its further 
accumulation. The sides also of the channels would 
soon be worn into a slope like that on the outer coasts, 
from being exposed to the same force of the currents. 
In fact, a channel like that bifurcating one which 
