Oliveh. — Geologij of ihc KentuuJrc IxhnuU. 527 



to Mr. Speight lor the followuig deseriptiom of a spocinien of lava collected 

 on Napier Islet :— 



" No. 11.— Augite-hyperstheno-andesite. Fornis a large part of Napier 

 Islet, and encloses blocks of coral. 



" Macroscopic : A dark-grey rock with small phenocrysts of feldspar 

 clearly visible throughout. Specific gravity, 2-83. 



" Microscopic : The groundmass consists of basic labradorite micro- 

 lites, grains of augite, and iron-oxides, with a little brownish glass present. 

 Phenocrysts of basic labradorite are very common, and contain numerous 

 glass inclusions. The dominant P\M. mineral is hypersthene in large crystals 

 with characteristic cleavages and pleochroism ; augite grains are common, 

 frequently twinned, and with oblique extinction. There is a little olivine 

 present in the form of small grains stained with ii'on-oxides." 



Day r ell Islet. 



Dayrell Islet consists mainly of beds of submarine origin, dipping to the 

 north at a low angle, about 5°. The lower beds are composed of hard 

 sandy tuffs containing fossils, the upper ones of a white calcite rock. These 

 are covered by andesitic tuffs (No. 20), whilst lava dykes pierce the islet 

 in various directions. The Chanter Islets are similar in structure to Dayrell 

 Islet. (Plate XXIV, fig. 1.) 



On one occasion only I was able to land for abou.t half an hour on Dayrell 

 Islet, when I collected a number of fragments of molluscs and corals. The 

 corals have not yet been examined. Of five species collected, I recognize 

 only one among those found living in the group. The molluscs include the 

 following : Turbo argyrostomus L., Pupura,* Clanculus, Risella, Trochus, 

 Amaltkea, Spondylus ostroides Smith,* Pecten kermade^ensis Watson,* 

 Chama, Chione, Area decussata Sow.* Those species marked with an 

 asterisk (*) also occurred among the recent shells collected on Sunday 

 Island. I am indebted to Mr. C. Hedley, F.L.S., of Sydney, for the 

 identification (though he expresses some doubt) of Turbo argijrostomxis L. 

 Recent examples of this species have never been obtained on Sunday Island, 

 though M ■. R. S. Bell knows the fauna well. 



Structure of Sunday Island. 



Long lines of high cliffs afford splendid opportunities for observing the 

 structure of Sunday Island. Here will be described the arrangement of 

 the various volcanic beds as seen in typical sections in different portions of 

 the island. Further on in this paper an attempt will be made to describe 

 the order in which the material was ejected from the different centres of 

 eruption. 



At the south end of Denham Bay a horizontal stream about 10 m. thick 

 of greyish andesitic basalt (No. 38) is exposed for a considerable distance. 

 Unfortunately, one end is buried under fallen cliff debris, but evidently 

 it must terminate abruptly at the base of Expedition Hill (fig. 2). Above 

 the basalt are beds of tuffs extending to the top of the crater-ridge and 

 Mount Junction. These are arranged in two distinct series. The lower 

 beds, about 60 m. thick, are arranged in perfectly horizontal thin even beds, 

 which, I should say, have undoubtedly been deposited under water. They 

 are composed of small fragments of andesitic rocks in a finer matrix, and 

 include many larger rock -fragments. They contain no pumice, and will be 



