AGASSIZ: FIJI ISLANDS AND CORAL EEEFS. 57 



enclosing a triangularly shaped lagoon, with a greatest dej^th of 21 

 fathoms. The length of the southern reef flat is a little over ten miles, 

 that of the northern face about nine miles, and that of the western and 

 northwestern faces connecting them is five miles. There are three pas- 

 sages on the western and northwestern faces, and one through the north- 

 ern face. The bottom of the lagoon, between the reef patches and heads, 

 is covered with coralline algee and with coral sand. There ai-e many 

 large heads scattered along the inner edge of the northern reef flat, and 

 on the extension of the western extremity of the island. 



Namuka. 



Plate 23. 



We did not visit Namuka, but steamed near enough to the island to 

 recognize its distinctive features. It is a narrow, undulating ridge, four 

 miles long, rising to a height of 240 feet ; it is composed of elevated 

 limestone. On the southern and western faces there are deep bays, or 

 incipient sounds, which, if extended, would divide the island into a 

 number of islets. The island is surrounded by a fringing reef off the 

 southwestern extremity, and off the eastern point of tlie island. Be- 

 tween these points an outer reef extends off the south coast, forming a 

 narrow and shallow lagoon full of heads, with five fathoms at its deepest 

 point. On the northern face the western part of the lagoon is deeper, 

 having thirteen fathoms. The horns of the outer reef of the northern 

 and westei-n faces are connected by broken patches and heads which 

 form tlie harbor of Namuka. 



About three and a half miles northeast from the entrance to Namuka 

 Harbor lies "Wilkes Reef (Plate 22), a flat a little over half a mile iu 

 length, dry at low water, with outlying rocks and banks within the sur- 

 rounding 100 fathom line. 



*o 



Yangasa. 



Plates 33, 33^, Figs. 8, 9, and Plates 90-93. 



The cluster of Yangasa (Plate 22) consists of four islands and numer- 

 ous rocks and islets, all of which are composed of elevated limestone. 

 The largest island of the group, Yangasa Levu, is nearly two miles in 

 length and about half a mile wide. Its shores are formed of precipitous 

 cliffs, which surround the whole island ; they are deeply undercut at the 

 base, perhaps more than any other island we have seen in Fiji. The 



