STRUCTURE OF CORAL ISLANDS. 



1G9 



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 



HABITABLE 



LENI I'll 



PARTS IN 





BREADTH. 



SO. MILES. i "- ivxo *» 

 ^ SQ. MILES. 



Carlshoff, Paumotus, .... 



27 . 



...13 ... 



200 .. 



.. 10 



Wolchonsky, " .... 



15 . 





3 ... 



40 .. 



.. 3 



Raraka, " .... 



15 . 





10 ... 



90 .. 



.. 8 



Manhii, " 



14 . 





6| ... 



50 .. 



.. 9 



Nairsa or Deans, Paumotus, 



50 . 





19 ... 



1000 . . 



.. 16 



Fakaafo, Union Group, .... 



H ■ 





4i ... 



20 .. 



.. H 



Duke of Clarence, " .... 



8* • 





&i ... 



27 .. 



.. 2 



Tapateuea, Kingsmills, .... 



33 . 





6 ... 



60 .. 



.. 6 



Tarawa, " .... 



20 . 





10 ... 



130 .. 



.. 8 



Nonouti, " .... 



22 . 





9 ... 



125 .. 



.. 7 



Tari-tari, " 



18 . 





11 ... 



110 .. 



.. 4 



The ten islands here enumerated have an aggregate 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 



