AITUTAKI. 169 



Gill, in his " Life in Southern Seas," writes regarding Mituro that it 

 is about fifty feet above the level of the sea. The entire surface of the 

 island, on the way to the lagoon, is sharp coral rock. The lagoon in the 

 interior is about three miles in extent ; the water is very brackish, ahnost 

 black, with no visible outlet. Gill gives a distant view of the island. 



Aitutaki- 



Plates 106. fi.j. 1; 211; 212. fig. 2. 



The volcanic island of Aitutaki is the only one of the Cook group 

 which we examined; it was surveyed by Captain Rooke in 1892. and repre- 

 sents a condition intermediate between Maupiti and Tetiaroa. The summit 

 of Aitutaki is not more than 300 feet (Pis. 106, fig. 1 ; 212, fig. 2). As Atiu 

 is composed of elevated limestone, and Rarotonga is volcanic, I hoped we 

 might find Aitutaki to be in part volcanic and in part composed of elevated 

 coralliferous limestone ; we found it to be volcanic, an island with the 

 structure of Bora Bora on a smaller scale. The principal island is a little 

 over three miles in length and runs north and south. Its northern extrem- 

 ity forms the northern point of the barrier reef flat which surrounds it 

 (Pis. 106, fig. 1 ; 212, fig. 2). This is triangular in shape, the greater part of 

 the reef is awash, the eastern face being about seven miles, the southern six 

 miles, the western the same. On the southwestern point of the reef flat a 

 small sand key has been thrown up, and on the eastern face a series of low 

 wooded islands and islets indicate the position of the barrier reef flat ; the 

 islands are separated by gaps similar to those we observed between the 

 islands on the barrier reef flats of the Society group (PI. 212, fig. 2). 

 Between the islands the sea has free access to the lagoon. Most of 

 these islands run at right angles to the general trend of the outer edge of 

 the barrier reef, and have undoubtedly been formed, as we could judge from 

 the indications of former gaps, exactly in the same way as those on the 

 northern coast of Tahaa, of Bora Bora, and Maupiti. With the exception of 

 Maina Island and the two islets near the southeast horn, there are no 

 islands on the western and southern barrier reef flats ; thej' are comparatively 



