EANGIROA. 45 



rose to .1 somewhat greater height than that of the highest tertiary 

 limestones found in the Paumotus. 



Wherever we examined the bottom of the lagoon we found it generally 

 quite barren of animal life, and covered with a hard Nullipore bottom and 

 coralline Alga3. Fish were quite abundant in the lagoon, and on the flats; in 

 two to three fathoms, corals and other invertebrates flourished. The patches 

 of corals were generally most abundant on the slopes of the ledges and flats 

 in from three to five fathoms. 



The land rim surrounding Rangiroa is quite narrow ; the islands of the 

 land belt are not more than 1000 feet wide, and in many places less than 500, 

 and they are limited to the northern and western sides. The islets of the 

 northern side are wooded. On the southern side (PI. 204) the land belt is 

 reduced to a few wooded islets (Pis. 13, fig. 1; 14), the long reaches between 

 them being composed of a wall of old reef rock from 10 to 14 feet in height. 

 It forms the culminating point of the windward sea face platform of the old 

 ledge, which varies in width from 250 to 500 feet, and of its lagoon ex- 

 tension, which can be traced for a mile to a mile and a half as it slopes 

 gradually into eight to ten fathoms of water ; the lagoon slope is covered 

 with patches of coral. 



The little islet of Paoi, on the way to the south shore, is an elevated old 

 reef ledge with many fossil corals (Pis. 18, fig. 2 ; 19). It is about 12 feet 

 high, and it, as well as Tiarari to the southward, and the few ledges we found 

 scattered through the lagoon, are the remnants of irregular peaks or ridges, 

 or spurs of the land once covering the area of Rangiroa, which have been 

 planed down and eroded at the same time as the higher parts of the belt of 

 land comprising the northern and southern ridges of the atoll. 



On Plate 204 I have given the Ime of soundings run across the lagoon 

 ot Rangiroa by Lieutenant Rodman. It will be noticed that the deepest 

 part of the lagoon is near the northern land rim of the atoll, and that the 

 floor of the lagoon has a very uniform depth ranging from 10 to 16 fathoms, 

 the central part of the lagoon varying from 14 to 16. The slope of the 

 lagoon flat extending north from the southern land rim is much flatter than 

 the lagoon slope off the northern land rim, where it runs rapidly into ten 

 fathoms ; while the lagoon reef flat of the south shore extends more than 



