STRUCTURE OF CORAL ISLANDS. 19o 



then to the bottom of what was once the lagoon, now for 

 the most part forty to fifty fathoms under water, though hav- 

 ing its shoals that are five to ten fathoms submerged. All 

 points in the map that are shaded, have a depth of less than 

 ten fathoms ; the only emerged parts are three or four spots 

 on the western margin, as indicated on the map above. The 

 bottom over the interior is muddy ; on the flat bordering it, 

 15 to 20 fathoms deep, there is coral sand with "a very little 

 live coral ; the outer rim is coral rock with scarcely any live 

 coral ; " while the shoals or knolls of the interior are " cov- 

 ered with luxuriantly-growing corals." Darwin states also 

 that the rim is steep on both sides, and outward slopes abruptly 

 to unfathomable depths ; at a distance of less than half a mile 

 from one part no bottom was found with 190 fathoms ; and 

 off another point, at a somewhat greater distance, there was 

 none with 210 fathoms. 



Metia and other elevated Coral Islands. — Metia, or Au- 

 rora Island, is one of the western Paumotus. It is a small 

 island about four miles by two and a half in width, and two 

 hundred and fifty feet in height ; and it consists throughout 



METIA, OE AURORA ISLAND. 



of coral limestone. Approached from the northeast, its hio-h 

 vertical cliffs looked as if basaltic, resembling somewhat the 



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