190 "ALBATEOSS" TEOPICAL PACIFIC EXPEDITION. 



exposure to the prevailing winds ; those which are more protected are 

 covered with a slight vegetation which has prevented their erosion and 

 denudation. Nukualofa, the principal harbor of Tongatabu, is merely a 

 channel left between the innumerable islands which must once have 

 formed a connected flat extending far to the north of the town, a flat 

 which has been changed into a very irregularly shaped lagoon, a lagoon 

 of erosion and denudation, covered with islands and full of mangrove 

 swamps (PI. 215). On landing, it is evident that a great part of the flat on 

 which the town is built consists mainly of JBolian rocks which have been 

 formed by the trades blowing along the sand beaches, derived from the dis- 

 integration of the corfvl reefs and coral reef flats of Nukualofa. In the 

 central parts of the flats, between the islands and islets, corals grow in 

 great abundance, and on the slopes of the reef flat into deeper water they 

 are especially abundant. Numbei'less starfishes belonging to species found 

 on the Australian and Fiji reefs are seen in all directions, and the reef 

 flats are full of fishes which are left at low tide in large pools, where 

 the natives fish for them with hand nets (PI. 115, fig. 3). 



Mount Zion (PL 215), near the shore of Nukualofa, is composed of elevated 

 coralliferous limestone full of fossils ; it and Cook's Hill are probably out- 

 liers of the second or third terraces, showing that the whole of the main 

 island of Tongatabu has been eroded and denuded to its present level, 

 leaving only here and there, as we saw when eiitering the harbor, traces of 

 the greater elevation at wliich the land once stood. This elevation is best 

 seen on the south side of Tongatabu, in the rear of Cook Point, where 

 the terraces rise to a height of more than 270 feet, as well as along the 

 Liku or the windward side of the island ( Pis. 116, fig. 2; 117, fig. 2); 

 from that shore the land slopes gradually to the height of a few feet south 

 of Nukualofa. Near Cook Point lines of blowholes are developed on the 

 outer edge of the reef flat which surpass in size any of the blowholes 

 we have seen in the Pacific (Pis. 117, fig. 1 ; 118). 



On the island of Atata, northwest from the village of Nukualofa, a number 

 of fossils have been found similar to those of Mount Zion, and they in their 

 turn are similar to those we found in Eua, and other islands in the Tonga 

 group. Tongatabu, as seen in the distance, is marked for its flat-topped 



