Vol. X. 

 igto 



] Barrett, Expedition to Capricorn Group. 185 



ence due to the circumstances under which each arose. Typically, 

 the Central Pacific reefs spring from abyssmal depths, will have, 

 have, or had a deep central lagoon, according to the stage in 

 evolution attained. Their dry land is always greatest on the 

 windward side, and is built close to the reef edge. Mast-Head is 

 a tabular mass set on a platform of about 20 fathoms, common 

 to the archipelago. Its lagoon is almost obliterated, the depth at 

 low water being expressed in inches instead of fathoms. The dry 

 land is massed on the leeward side, and heaped far within the 

 margin of the reef. In the Central Pacific the dry land of the 

 atolls seems to have originated in the spasmodic action of hurri- 

 canes, which tear masses off the reef edge and stack them above 

 high water mark in hurricane beaches. . . . Mast-Head hes 

 beyond the hurricane zone, but is subject to the action of tides 

 of a range of 14 to 15 feet. These tides race over the reef at 

 a rate of two knots an hour, are the chief agents of island building, 

 and operate with more regularity but less violence than the 

 hurricanes." 



Vegetation, 



On all the Capricorn Islands on which members of the expedition 

 landed the vegetation appeared to be of a similar character. The 

 storm beaches — there were three distinct ones on Mast-Head 

 Island — are fringed with graceful casuarina trees, whose pendulous 

 foliage has a most pleasing effect. The boughs at flood- tide almost 

 hang above the lapping water. The trees on the older beach are, 

 of course, much larger than those on the most recent ridge of coral 

 sand, and the mid-beach is crested with trees of medium size. 

 There are the three beaches and the three stages of the casuarina 

 — a most striking object lesson. Behind the casuarinas, which are 

 not so closely ranked but a man may walk among them with ease, 

 come the lusty bushes of Sophora and Tournefortia, the pic- 

 turesque Pandanus, with its spear-shaped leaves, organ-pipe aerial 

 roots, and great fruits. These trees and bushes are rooted 

 in the sand among Wedelia, AbiUilon. Ipomea, and other 

 lesser plants, whose leaves, thickly clustering, form a miniature 

 jungle. The undergrowth does not persist into the forest, 

 but forms a girdle about the inner sand ridges, flowing over 

 crests and filling hollows, creeping down on to the sea-beach, and 

 helping to bind the restless grains of sand together. The Pisonia 

 claims the centre of each island as its domain. Sentinels are sent 

 out, and on Heron Island, for instance, the Pisonia forest runs 

 down to the open beach ; but, generally speaking, the trees over- 

 grow the central portions of the islets. Many specimens noted by 

 our party rose to a height of Oo feet, with spreading branches that 

 cast a generous shadow, so that in the heart of the forest it was 

 cool and twilit, the pale green leafage forming a screen so dense 

 that even the tropic sunbeams were filtered of their fire. Our 

 botanists made complete collections of the plants on Mast-Head, 

 North-West, Heron, and other islands, and were pleased with their 

 beauty and variety. A species of Ficiis, with its tiny olive-red 



