206 REPORTS ON THE STATE OF SCIENCE. 
cliff there is a small belt of bare rock, often worn into hollows contain- 
ing 3 feet or 4 feet of water; then a large area, mainly of broken coral 
fragments covered with Lithothamnia, and edged outside with a small 
boulder zone; and outside this, again, buttresses with a few colonies 
of living corals in the channels. Such are the usual features of the 
fringing reef at Aldabra, the appearance in the Takamaka section being 
quite exceptional. 
After the previous descriptions, it is possible to speak more generally 
of Aldabra. The cliffs, as stated, show their structure wonderfully 
clearly, except in the southern bight, where they are sloping and 
buttressed; they are much overhung, and are crumbling fast. The 
general variations in level across the land are similar; the highest point 
is near the sea, and there is a steady decrease in level to the lagoon. 
As regards the nature of the land, all the northern portion of the 
atoll—Polymnie Island, Malabar Island, and the north-east part of 
Main Island—-consists of Champignon. The south-east portion of 
Main Island is chiefly Platin. In the centre of the south of Main 
Island there is a wide shore zone, and then a belt of Champignon. To 
the east and west of this portion are large mounds (65 feet in height) 
near the shore. They are obviously wind dunes, the seaward slope 
being gradual with little vegetation, the landward very steep and covered 
with bush. Opposite each dune the cliffs have almost entirely 
vanished, a direct slope of sand leading up to the dune. It is noticeable 
that in Aldabra, as in most of the other islands of this part of the ocean, 
dunes are only formed on the coast facing the strong south-east trades. 
The west portion of Main Island is chiefly Champignon. At Couroupa 
there is a dip in the rock which appears to extend from the shore right 
across to the mangrove swamp; it is filled with sand, and attains a 
maximum depth of 8 feet. 
A portion of Picard Island and Esprit Island (in the lagoon) demand 
a fuller description. 
Esprit is largely swamp, but round the south and west there is a 
ridge of rock about 30 feet high, which is obviously not typical coral 
rock. The majority of the ridge is composed of a dark brown hard 
rock; at the lower levels it is very solid and homogeneous, but higher 
up it takes the form of a coarse conglomerate or pudding stone. The 
top of the ridge is capped with a rock which appears extraordinarily like 
flint. On each side are pinnacles of a rock which is evidently com- 
posed very largely of a deposit of mollusc shells, and which has 
suffered excessive denudation. On the outer (lagoon) side of the ridge 
these pinnacles are only a few feet high, but on the inner side, towards 
the centre of the island, they form a series of grotesque up-standing 
pillars and walls, varying up to 15 feet in height; they appear to be 
standing on the brown rock. 
Picard Island, which is mainly of typical coral rock, has in the 
centre (S.W.) a large plain of Platin country, on the east side of which 
is a large basin in the rock, in subterranean connection with the lagoon. 
On the floor of the basin IT found several small pieces of the dark homo- 
geneous rock, and, at one side, much of the brown conglomerate. The 
majority of the rock round the basin appeared purely calcareous, but 
there were some short veins (six inches to a foot wide) and masses 
of highly crystalline rock, some apparently calcite and some also 
