124 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



last gap is still at a considerably lower level than the high beaches on each 

 side of it. These became gradually closed, and finally there came about 

 the conditions existing to-day, with a single gap allowing the sea access 

 to the interior of the lagoon only at certain stages of the tide. 



When the sand blown in, and the material derived from the death and 

 decay of corals and shells, has so shut off the water of the lagoon that its 

 access to the sea is cut off, then the last gap will be closed. We may expect 

 then the lagoon to become a mere brackish sink, growing shallower each 

 year, till nothing is left to indicate the former existence of a lagoon, once 

 in full communication with the sea, except the shallow dishing of the 

 central part of the atoll, more or less marshy, or perhaps consisting of as 

 solid land as any other part of the land rim. In fact, Pinaki may be regarded 

 as a stage antecedent to that of Aki-Aki, of Tike'i, and of Niau. It differs 

 from Niau, however, in not having a sink lagoon, the lagoon of Pinaki being 

 still connected with the sea and constituting what might be called a sound 

 lagoon. 



At Pinaki there is a good-sized water hole, a small sink in which the 

 natives keep turtles, occupying the central part of the land rim where 

 there is but little vegetation, where the land rim is from 400 to 500 yards 

 wide. In the water hole of Aki-Aki turtles are also kept by the natives. 

 At Nukutavake there are also sinks, eight to ten feet long, where water 

 collects. These sinks are the result of the banking of material around 

 depressions. In other islands these depressions are sometimes found in the 

 central part of the islands of an atoll, where water collects in moderate 

 quantities. Their origin is due to the same causes ; they are littoral sinks 

 dating back to a time when the island was probably of very much smaller 

 size. 



The soil of the crest of the land rim of Pinaki is quite fertile, being made 

 up of decomposed leaves and stems and rolled fragments of coral shingle ; 

 while on the steep white sand slope it is quite barren, as well as on the 

 sand beach back of the shingle on the lagoon face. The same conditions are 

 found at Nukutavake and at Aki-Aki, where the humus is a little better. 

 This appears to be the character of the soil of all similar islands wherever 

 we landed in the Paumotus. 



