OF THE TONGA. ISLANDS. 017 



Discussion. 



Mr. HiCKSON said thut Mr. Lister's researches on the coral reef's 

 of the Friendly Islands were of great interest and importance, as 

 they supported the view that atolls and barriers may be formed in 

 regions of elevation, and that the " subsidence theory " is not 

 sufficient to account for all the phenomena that occur in volcanic 

 regions. The Tonga and Kermadec groups of islands are very similar 

 to the chain of islands that stretches from the northern peninsula 

 of Celebes to the southern promontory of Mindanao. Here we 

 find a chain of volcanoes, many of them active at the present day, 

 represented by the Huang, the Siauw, and the Awu, with broad 

 barrier-reefs and ring-shaped atolls in their immediate vicinity. 

 The researches of Sluiter in the Java seas prove that coral islands 

 and reefs are frequently formed on a substratum of soft clay and 

 mud. 



Mr. J. W. Gregory remarked on the great value of Mr. Lister's 

 paper, and the interest attaching to the discovery of a plutonic rock 

 on the islands. Taken in conjunction with the discovery of similar 

 rocks in the Marquesas, and the presence there of genera otherwise 

 restricted to South America and Malaysia, it helped to aiford an 

 explanation of some difficult problems of distribution. Manganese 

 nodules seem characteristic of deep-sea conditions, not only at pre- 

 flent, but in earlier periods ; thus in the Maltese Miocenes they are 

 associated with a fauna of about 1000 fathoms. Their occurrence, 

 therefore, proves considerable elevation, and it is not surprising 

 that the coral limestone occurs as thin crusts ; the Tongas thus 

 fifford only another case of coral formation in shallow or rising 

 areas, for which, as Darwin has so emphatically insisted, his theory 

 was not proposed. 



Mr. GooDCHiLD enquired whether the boulder of gabbro referred 

 to might not have reached its present level as an ejected block ; 

 this view might serve to explain the occurrence of plutonic rocks 

 in an oceanic island. 



