STRUCTURE OF CORAL ISLANDS. 37 



where it is about twelve feet. To the south-southwest the sub- 

 merged reef extends out nearly a mile, over which the sea breaks. 

 Distinguished no vegetation except the low purslane and some 

 trailing plants. Did not land. 



Swain's.— (Fig. 3, page 23.) Lat. 11° 10' S. Long. 170° 

 52' W. li miles by § ; shape nearly rectangular ; trends east 

 and west. No lagoon, but the centre a little lower than the 

 sides. Surface covered with shrubbery and large trees, among 

 the latter many cocoanuts ; the centre more sparsely wooded. 

 Height fifteen to eighteen feet, excepting on the middle of 

 western side, where the surface is covered with loose fragments 

 of coral of small size : there appears to have been a former en- 

 trance to the lagoon at this place. Shore reef or platform, one 

 hundred yards in average width, and one hundred and fifty yards 

 at the place where we landed. Beach high, ten to twelve feet. 

 At lower part of beach for a height of two to three feet, the coral 

 reef rock was exposed, indicating an elevation of the island. 

 For three or four feet above this, layers of the beach sandrock 

 were often in view, consisting of coral pebbles firmly cemented, 

 and having the usual dip of seven or eight degrees seaward ; in 

 many places it was concealed by the beach sands and pebbles. 

 There was no growing coral on the platform excepting Nullipores. 

 The outer margin of this platform was very uneven, and much 

 intersected by channels, though less so than at Enderby's Island.* 

 Great numbers of Birgi, (large Crustacea,) were burrowing over 

 the island, some of which were six inches in breadth. 



Otuhu, Paumotu Archipelago.— 14° 5' S. 141° 30' W. 1J 

 miles by §, trending north and south. No lagoon. Wooded. 



Margaret, Paumotu Archipelago.— 20° 42' S. 143° 4' W. 

 Diameter one mile, nearly circular. A small shallow lagoon with 

 no entrance. Northeast side alone wooded, and in two patches. 



Teku or Four Croivns, Paumotu Archipelago. — 20° 28' S. 

 143° 18' W. Diameter 1J miles, nearly circular. A small la- 

 goon with no entrance. Southwestern reef bare ; five patches of 

 forest on the other part. 



* The sea was quite heavy -when we attempted to land at low tide upon the edge 

 of the shore platform. As we pulled towards the reef, an anchor was dropped, as 

 usual, some distance out, to hold on and save the boat, from being carried by the 

 surges against the rocks. After some heavy seas had passed, a partial lull seemed 

 to favor, and the boat was pulled in. Taking advantage of the favorable moment, I 

 jumped out, and made rapid speed over the reef to escape the breakers which fol- 

 lowed. Soon turning about, I was surprised to find the boat just behind me, and 

 the crew in the water alongside trying to steady her and save her from destruction. 

 The man who held to the anchor behind had let go his hold, and the next sea, as it 

 came careering on, had borne the boat over the edge of the reef, and far on its sur- 

 face. With even greater risk, after our ramble was completed, we succeeded in 

 launching again and reached the open sea. This was one of many similar dangers 

 experienced in these seas. 



