RANGIROA. 35 



Island ; to the west of it is a narrow passage not more than a tenth of a 

 mile in width, and with about six fathoms. The slopes of the sides of the 

 pass are steep, and the current rushing through it is often so strong that it 

 is impossible, at certain stages of the tide, to attempt to steam against it. 

 About six miles to the east of Avatoru Pass is another deep passage much 

 narrower and somewhat more shallow (Tiputa Pass, PI. 204, fig. 3). 



The first appearance of such an atoll as Rangiroa was very different from 

 that of any atoll I had thus far visited. The lono-line of narrow low islands 

 covered with cocoanut trees (Pis. 4, fig. 1 ; G) forms the only visible land 

 of the atoll ; extending eastward and westward as far as the eye could reach 

 was presented an aspect very different from that of the atolls of the Fijis, 

 and I was STcarcely prepared for this great difference, in spite of the descrip- 

 tion given of them by Beechey and Dana, though the account given by 

 Lesson of the belt of low sand i.slets thrown up on the barrier reef, and 

 covered with cocoanuts and low shrubs, surrounding the volcanic i.slands of 

 the Society group, had prepared me for what I saw in the Society Islands. 



At a first glance it would seem as if the outer land rim had been formed 

 from tlie disintegration of the material thrown up on the reef platform, 

 forming either a coral shingle or a coral sand beach. Upon the outside 

 shore or in the reaches stretching across the narrow land rim to the lagoon, 

 but few boulders or negro-heads are left to indicate the former position of 

 the old land formed of tertiary coralliferous limestone, the greater part of 

 which has been eroded to below low-water mark or thereabout, when the 

 process of building iip again commenced, — a process which has not been 

 recognized by those who have attributed to subsidence the existing con- 

 ditions in the Paumotu atolls. 



In atolls of such a size as Rangiroa, nearly 45 miles long and from 

 12 to 14 miles wide, the conditions become very different from those 

 which affect smaller atolls. The prevailing southeast trades sweep nearly 

 parallel with tlie longer axis of the atoll, and naturally considerable 

 sea is constantly washing the bars, knolls, and islets found in the large atolls, 

 acting upon them in many instances, according to their position in the 

 atoll, much as if they were exposed to the full force of the seas which break 

 upon the outer sea-shores of the i.slands on the land rim of the lagoon. 



