28 



On Coral Reefs and Islands. 



Sivain^s and Jarvis Islands, (figs. 

 3 and 4,) are of still smaller size. 



3. 



4. 



and 



have no lag6on. 



The former 



.•.,j^--'^'-'*- 



•V^VV-c'v'' *v'- 



JARVIS ISLAND, 



is densely covered with foliage, 



while the surface of the latter is swain's isla>-d- 



sandy. Swain's Island is a little depressed about the centre, a 

 fact indicating that there was formerly a lagoon. 



Fakaafi 



(fig- 



5. 



6,) 200 miles north of Sanioa, is 

 the type of a large part of coral 

 islands. The bank of reef has 



emerged 

 from the waves and become ver- 



only here and there 





dant ; in other portions the reef 

 is of the usual height, — that is, 

 near low tide level; — excepting 

 a few spots elevated a little by 

 the accumulation of sand. 



The Paumotu Archipelago, the ^'^^^^_^ 

 crowded cUister of coral islands 

 just northeast of Tahiti, is a 

 most instructive study for the 

 reader; and a map of these 

 islands by the Expedition, in- 

 serted in the Narrative of the 

 Expedition, and also in the Hy- 

 drographical Atlas, will well re- 

 pay close study. Sailing among' 

 these islands — over eighty in number, only four of which are 

 over twelve feet high exclusive of the x^egetation, — 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 surface is 

 water; and the land around the lagoon is but a narrow rim; the 

 reater part of which is usually imder water at high tide. This 

 fact will be rendered more apparent from the following table, con- 

 taining a statement of the sizes and areas of several islands, with 



*he amount of habitable landi The measures are given in geo- 

 graphical miles. 





FAKA 



Greatest breadth. Area in ^qu^re 



niiles. 





Carlshoff'> Paumoiu% 

 Wolchonsky, 



Raraka, 

 iVIanhii, 



Xairsa or Deans," 

 Fakaafo, Union Group, 

 Clareace, " 

 Tupiueeuea, Kingsmills, 

 Tarawa J ^' 



Namoutt, J^ ** * 

 j Tari-lah, , . " 



'ft" 



-V^^ 



% 



13 

 3 



10 



19 



I* 

 10 

 9 



-■f 



20O 

 40 

 90 

 50 



1000 

 BO 



60 

 130 

 125 



no 



Habitable parts in 

 square miles. 



To 



3 



8 



16 

 2i 

 2 

 6 

 8 

 7 

 4 



^ L 



# 



