534 TroinfaetioiiR. 



The only tuffs from which fragments of hornblende-granite wero actually 

 taken were those ejected by the last, or present, large crater of Sunday 

 Island, and the presence of all the boulders noticed on the sea-shore and 

 elsewhere can be explained by the release of fragments consequent on 

 the removal of the exposed face of sea-cliffs and siirface of the tuffs by 

 marine and subaerial denundation. My observation, therefore, support the 

 opinions expressed by both Mr. Smith (1888, p. 344) and Professor Thomas 

 (1888. p. 315) — namely, the presence of boulders of plutonic rocks on Sun- 

 day Island could be explained by the supposition that they have been 

 brought up from great depths by volcanic agency. 



In the foregoing description of the geological structure of Sunday Island, 

 and attempt to deduce therefrom the history of the island, I have endea- 

 voured to make it clear that (except for the inclusion in some of the lavas 

 and tuffs of coral and hornblende-granite respectively, and some calcite 

 no doubt derived from coral in the Herald Islets) Sunday Island and the 

 adjacent Herald Islets are built up entirely of volcanic materials ejected 

 from five principal points of eruption. The first eruptions were submarine, 

 but shallow-water conditions obtained. Elevation then took place, and 

 jnuch lava flowed above sea-level. The land-surface was afterwards con- 

 siderably denuded, and during a temporary subsidence volcano tuffs were 

 deposited under water. Lava-flows were meantime becoming less frequent, 

 and finally ceased, but the ejection of tuffs above sea-level, the last of which 

 were entirely pumiceous, continued for a long period, so that the main 

 portion of the islands at the present time consists of tuffs which are 

 rapidly disappearing into the ocean. The geological structure of Sunday 

 Island, therefore, shows it to be built up in comparatively recent times 

 on a submerged base, and that it never exceeded its present dimensions 

 more than can be accounted for by marine denudation.* 



The biological evidence which, vnih. apparent exceptions, seems to sup- 

 port the supposition of an oceanic origin for the Kermadec Islands will 

 now briefly be reviewed. 



From a study of the flora, Mr. Cheeseman was convinced that tlu' 

 Kermadec Islands have received their plants by transoceanic migration 

 (Trans. N.Z. Inst., vol. 20, p. 163). My further investigations, as far as 

 I am able to judge, confirm his views. I see no plants in the flora whose 

 presence in the group cannot reasonably be attributed to the agency of 

 ocean-currents (drifting logs), wind, and birds. 



As illustrating classes including land-animals the Gastropoda and Crus- 

 tacea may be mentioned. About eighteen terrestrial species of the former 

 and fewer of the latter were collected. They agree in being all small, and 

 in this respect what ought to be expected of members of these classes 

 capable of crossing wide stretches of ocean, where floating trees have pro- 

 bably been the means cf transport. 



If the presence of migratory birds in numbers at certain seasons of the 

 year is an indication of the spot being on an old shore-line, then the Ker- 

 madec Islands afford little evidence of tliis character for such a connection. 



* The island Eua, in the Tonga Group, has, according to Mr. J. J. Lister, had a hi.s- 

 tory closely ])ai'allel to that of Sunday Island as sketched in this jjaper. (Jabbro occurs 

 as boulders on the shore, while garnet and tourmaline are found in the volcanic tuffs 

 (Lister, Quart. Jour. Geol. Soc, vol. 47, p. 590). Mr. H. L Jensen's views with regard 

 (o Eua, however, are similar to Mr. Speight's concerning Sunday Island quoted above 

 (Jensen, Proc. Linn. Soc. N.S.VV., vol. HI, ]>. (>41). 



