ON INVESTIGATIONS IN THE INDIAN OCEAN. 208 
ASSUMPTION. 
Assumption was reached on September 6. It, unlike the two pre- 
vious islands, is not an atoll; it is crescent-shaped, about 32 miles long 
and from 1 to 4 mile broad. In composition it is undoubtedly an 
elevated reef, corals in position of growth being easily observed, especi- 
ally on the face of the cliffs and on the sides of pits in the rock, which 
form a marked feature of the island. Much metamorphosis has occurred 
in places in the interior of the island, producing a rock which usually 
includes a considerable proportion of phosphate, derived, as in the other 
islands, from a superficial deposit of guano. The conglomerate men- 
tioned in relation to Astove is common, and confirms the impression 
that it is of the nature of the rock forming on recent reef-flats. Varia- 
tions in level over the island were, owing to the thick bush, difficult to 
estimate, but judging from three tracks cut from east to west across 
the land, there is a slight ridge running north and south near the west 
shore with a maximum height of 20 feet, decreasing on each side to 
the common level (about 12 feet) of the island. In the south-east are 
large dunes (90 feet high) formed entirely of blown sand. The natural 
pits in the rock, before referred to, are most common in the interior of 
the island, but also occur within a few yards of the sea. They seem to 
owe their origin to imperfect consolidation of the reef at the time of 
growth. They vary considerably in size, the largest being 18 yards 
long by 14 yards wide by 3 yards deep, and the deepest 45 feet. Some 
contain salt water, and others are largely filled with guano, though in 
these salt water can be easily reached by digging; in all the water 
seems to fluctuate tidally, though in no case was any connection with 
the sea discovered, except that of free percolation. The sides of the 
pits are always being eroded and weathered, and consequently the 
latter are increasing in size. It was natural to consider whether a 
lagoon could be formed by this means, but the conclusion was in the 
negative, as there seemed no reason why the pits should connect more 
rapidly with each other than with the sea. 
Guano is present in some quantity, especially on a large plain near 
the east coast, while many of the pits contain a large quantity. It 
undoubtedly has had a considerable influence on the rock below. 
The land vegetation is a scrub, dense and thick in places, especially 
in the south-west, and thinning out to an open plain in the east. A 
curious occurrence is that of a growth of mangrove trees in three of the 
pits; as there seems to be no free subterranean connection with the 
sea it is difficult to explain their presence in an island so unsuited to 
them as Assumption. ‘T'wo of the pits contain Brugiera and the other 
Ceriops. A further discovery in these pits was that of the remains 
of giant land tortoises, considerable portions of several specimens being 
obtained. One species appears identical with that of the present 
Aldabra tortoise, but it appears likely that a second species also existed. 
Of the present fauna little need be said except that it resembles that of 
the other two islands. 
The settlement is quite recent and was made to work the guano. 
Green turtles are extremely plentiful, and until killed off will be a source 
of profit to the island. 
