142 -'ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



Beyond that, the barrier reef flat becomes changed into a wide fringing 

 reef flat, which extends ahnost unbroken as far asPaea' (PI. 208, fig. 4). 

 While the reef flat is practically a fringing reef, its outer edge is usually 

 somewhat higher than the adjoining slightly dished flat, so that here and 

 there, between the outer edge and the shore, are short stretches of 

 water from one quarter to half a foot in depth, the beginning of the 

 lagoon which will eventually be formed parallel to the shore line, as it 

 exists in a more or less disconnected channel to the south of Paea (PI. 

 208, fig. 4). From that point the reef flat is separated from the shore by 

 a narrow shallow lagoon opening into Maraa Pass ; the south part of the 

 fringing re6f extending from Paea to Maraa shows traces of an incipient 

 lagoon channel, formed by the cutting back by the tidal currents running 

 parallel to the shore, along the inner edge of the fringing reef; this channel 

 will eventually unite the lagoon at Paea with the Maraa Pass Channel. At 

 the northern end the lagoon is very shallow and narrow, while to the east- 

 ward of Maraa as far as West Ava iti the lagoon becomes quite wide and 

 deep, and is navigable almost to its extremity, which is closed by a regular 

 fringing reef to the east of Apomaoro (PI. 208, fig. 4). This Ingoon con- 

 nects through two somewhat indistinct passes with the sea. At the ex- 

 tremity of the fringing reef to the east of Apomaoro, a small bay, Popote 

 Bay (PI. 208, figs. 3, 4), has been gouged out, forming an insignificant 

 reef harbor; from the inner edge of the adjoining fringing reef flats the tidal 

 currents are cutting back or carrying off in solution the rotten coral on the 

 flats, forming incipient lagoons which will change the fringing reef flats into 

 a barrier reef, separated from a narrow fringing reef by a shallow lagoon, as 

 we noticed it to the north of Maraa Pass. To the west of Popote (PI. 208, 

 fig. 3), the reef flat becomes wider, the lagoon itself is deeper, and we have 

 a condition of things very similar to those which exist to the east and we.st 

 of Papiete, — a series of passes separating wide reef flats bare at low tide, 

 flanked by a deep lagoon, with depths of twelve or fourteen fathoms, studded 

 with islands, islets, and reef patches, which indicate the former extension of 

 the mainland, from which the reef flats have been denuded. The islands of 

 Mapeti and Pururu in the barrier reef of the southern part of Tahiti, indicate 



1 A. Chart 1382. 



