STRUCTURE OF CORAL ISLANDS. 169 
The Paumotu. Archipelago, the crowded cluster of coral 
islands east and northeast of ‘Tahiti, is a most instructive study 
for the reader; and a map of these islands by the Wilkes Ex- 
ploring Expedition, inserted in the Narrative of the Expedi- 
tion, and also in the Hydrographical Atlas, will well repay 
close examination. Sailing among these islands, over eighty 
in number,—only four of which are over twelve feet high exclu- 
sive of the vegetation,—two or three are almost constantly in 
sight from the mast-head. 
The small amount of habitable land on these reef-islands 
is one of their most peculiar features. Nearly the whole sur- 
face is water; and the land around the lagoon is but a narrow 
rim, the greater part of which is usually under water at high 
tide. This fact will be rendered more apparent from the fol- 
lowing table, containing a statement of the sizes and areas 
of several islands, with the amount of habitable land. The 
measures are given in geographical miles. 
GREATEST AREA IN “ABITABLE 
LENGTH. GreaDra, 99, tus, PARTS IN 
Carlshoff, Paumotus, 25, 13 200 10 
Wolchonsky, ‘“ 15 3 40 3 
Raraka, oe 15 10 90 8 
Manhii, “ 14 64 50 9 
Nairsa or Deans, Paumotus, 50 Me) 1000 16 
Fakaafo, Union Group, + 43 20 24 
Duke of Clarence, “ 84 5s 21 2 
Tapateuea, Kingsmills, 33 6 60 6 
Tarawa, “ 20 10 130 8 
Nonouti, ie 22, 9 125 7 
Tari-tari, e 18 11 110 + 
The ten islands here enumerated have an ageregate area 
of 1,852 square miles, while the amount of actual dry habit- 
able land is but seventy-six miles, or less than one twenty- 
fourth. In the Caroline Archipelago the proportion of land 
is still smaller. Menchikoff atoll covers an area of 500 square 
