378 A NATURALIST IN THE PACIFIC chap. 



area of elevation included New Guinea, the islands to the east of 

 it as far as New Caledonia, and as far east as the most distant of 

 the Paumotus, and extended northward of that line to include the 

 Gilbert, Ellice, Marshall, and Caroline Islands." 1 



From the report of Mr. Andrews 2 it is evident that in the 

 Lau Islands of the Fiji Group volcanic outbreaks have taken 

 place since the last upheaval. He describes in the case of Mango 

 and other islands the manner in which cliffs of limestone form 

 inliers in flows of andesitic lava. In the history of these islands 

 he first distinguishes the period of calcareous deposits, when the 

 bedded limestones forming the submarine plateau were laid down. 

 Then followed a period of volcanism during which masses of 

 volcanic materials were erupted along the axis of elevation. Alter- 

 nating epochs of upheaval and stable equilibrium ensued, during 

 the last of which the reefs grew outwards and formed the terraces 

 now so characteristic of the profiles of the islands. After the last 

 upheaval the volcanic forces became again active. There is much 

 of special interest in the account given by Mr. Andrews of the 

 Lau Group. The blocks of limestone included in the volcanic 

 agglomerates distinguish the Lau detrital rocks from those of 

 Vanua Levu. There is no evidence that coral reefs existed 

 during the early stages of the emergence of Vanua Levu to be 

 obtained from the submarine formations found on the higher levels, 

 1,000 to 2,500 feet above the sea. 



The period of emergence for this island may be divided into 

 an earlier and into a later stage, the last corresponding to the age 

 of emergence of the Lau Islands. The earlier stage, which may 

 be termed the " Pre-Lau " stage, is represented by the deposits of 

 the higher slopes of Vanua Levu, that is above 1,000 or 1,200 feet. 

 This is really the critical epoch in the history of this group, and 

 assuming that the movement of emergence has been fairly uni- 

 form over the archipelago we cannot but be astonished at the 

 absence of all traces of ancient reefs in the earlier stage. 



We may infer from the observations of Mr. Lister 3 that the 

 islands of the Tonga Group represent the Lau stage of the 

 emergence. They are similar in height and in general geological 



1 See the paper before quoted on the coral reefs of Fiji. 



2 Bull. Mies. Comp. Zool. Harv. Coll. vol. 38. Geolog. Ser. vol. 5, no. 1, 

 1900. On the Limestones and General Geology of the Fiji Islands, by E. C. 

 Andrews. 



3 Quart. Journ. Geolog. Soc. vol. 47, p. 590, 1891. See also Mr. Harker's 

 paper below quoted. 



