892 Proceedings of the Eoyal Society 
the barrier-reefs of Bougainville Strait and of other localities in the 
group by the action of the waves at the present sea level, can only 
he explained on the assumption of the outward growth of the reefs. 
They are situated on the leeward side of the reef-flat and border the 
lagoon- channel. At their weather margins facing the weather edge 
of the reef, they are but scantily vegetated. Here, on a soil com- 
posed almost entirely of calcareous sand, broken shells, coral debris, 
and pumice pebbles, the Pandanus and Casuarina with such shrubs 
as Scaevola Koenigii alone can flourish. It is at their weather 
margins that these islets are constantly receiving accessions. In 
one place it will be observed that the mangroves push forward their 
lines on the reef-flat whilst it is yet covered by the sea at high 
water. In another place it will be noticed that during the pre- 
valence of strong winds at spring tides the waves have thrown up a 
bank of sand a little above the ordinary high water mark. Under 
cover of this bank, various hardy creeping plants and binding weeds, 
such as Iyomaea yes cayrae and Triumphetta yrocumbens, push 
forward from the edge of the vegetation and invading the newly 
acquired strip prepare the soil for the Casuarina, Pandanus , and the 
different shrubs that rapidly follow in their rear. 
On crossing the islet to its lee side, where it borders the lagoon- 
channel, we find the soil contains a larger proportion of humus. 
Here the vegetation is much denser and of a different character. Such 
trees as Barringtonia syeciosa , Calophyllum inoyliyllum, Thespesia 
yopulnea, &c., form a thick belt, with their branches overspreading 
the water. 
From the foregoing remarks it will be evident that the lee 
side of an islet is its oldest portion, and that its weather side is 
the growing margin. Such islets, therefore, extend themselves 
seaward towards the weather edge of the reef. They would, in the 
course of time, occupy the whole area of the reef-flat, were it not for 
one counteracting circumstance, the more rapid outgrowth of the 
reef. Mr Murray attributes the position of the islets on the inner 
side of the reef-flat to the gradual removal, by solution and other 
agencies, of the lagoon-edge of the reef as it grows outward at its 
seaward edge.* 
The Solution of Dead Coral. — From the manner in which the 
* Proc. Boy. Soc. Edin 1879-80, x. 505. 
