8 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



a flat island. He suggested that the lagoons of some atolls had probably 

 been filled by the blowing in of sand over the summit of the encircling 

 beaches, and he noticed the mode of formation of islets and islands on 

 the land rim of many of the atolls he visited. Beechey suggests that 

 openings in the reef are due to their being opposite some stream of 

 fresh water. He quaintly says: "The aversion of the Lithophytes to 

 fresh water is not singular, as, independent of its not being the natural 

 element of these animals, it probably supplies no materials with which 

 they can work." 



He was the first to describe the outer reef platform of an atoll as well 

 as the lagoon platform, and he sounded a number of lagoons. He observed, 

 as is seen from his description of Hao, the mode of formation of sinks par- 

 allel to the lagoon shore. He notes that some of the surveys of Cook do 

 not differ from his, and that where he has instituted carefid comparison he 

 cannot see that any change has taken place in the coral reefs since the 

 days of Cook, for more than sixty years. He further says that when any 

 differences exist they are changes readily accounted for, and generally due 

 to the superficial action of the wind and sea. Beechey speaks of the small 

 number of Islands he examined where no lagoon exists. Of the twenty- 

 nine he visited only Aki-Aki, Nukutavake and Henderson had no lagoon. 



Henderson Island is, according to Captain Beechey, who examined it in 

 1826, a mass of coralliferous limestone rising about 80 feet above the level 

 of the sea. He speaks of it as "compact, having the fracture of sec- 

 ondary limestone.'' It must be in its structure very similar to Nine (PI. 

 212), which we visited ; only the elevation of Nine is somewhat greater, and 

 it is a larger island. Henderson Island is about five miles long, and tw^o and 

 a half miles wide in its greatest width. It is rectangular towards the north, 

 and triangular towards the south.^ Judging from the chart, there must be 

 a well-defined terrace at the height of 50 feet above high-water mark, 

 leading to a second terrace at a height of 80 feet, which forms the sum- 

 mit, the flat surface extending over the greater part of tiie island. 



Beechey observed that in the Paumotus the passages into the lagoons 

 were generally on the lee side of the atolls, and that the direction of the 



1 See A. Chart 1176. 



