Physiografhy.Geologij.] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 



739 



by the storms and piled up above the reach of ordinary waves, and this teems with 

 the lower forms of animal-life. No member of the expedition visited the group 

 during the 1907 trip of the " Hinemoa," but Captain Bollons brought back speci- 

 mens of the rocks on tliis and on other occasions. These prove to be granites of a 

 fairly constant type. They are whitish or light brownish on fracture, and show 

 plainly quartz, feldspar, and biotite-mica. The amount of this last mineral varies 

 somewhat in different specimens, and in some it is by no means a prominent con- 

 stituent. Under the microscope it shows the characters of an ordinary biotite-granite. 

 A small amount of plagioclase feldspar (albite) and a very occasional minute flake 

 of muscovite also occurs ; needles of apatite arc also visible. The amount of feldspar 

 present is sometimes much in excess of the quartz, though occasionally the latter 

 mineral approaches the former in importance. The feldspar shows at times the 

 development of sericitic material along the cleavage-planes. This granite shows 

 n nuich closer resemblance to that found in situ at Carnley Harbour than it does to 

 the Snares granite. 



An analysis by R. Morgan, of the Auckland University College, shows that 



nas tne loiio 



wmg cue 



micai con 



iposition 



: — 









Per Cent. 



SiO., 







. • ■ . 





. 73-08 



Alo; 













. 11-98 



Fe,03 













* 



FeO 













2-12 



CaO 













1-93 



MgO 













0-23 



K2O 













6-57 



NaO 













3-58 



P2O5 









- . 





0-01 



Water lost below IOC 



)°C. (H2O-) 







0-23 



„ above 10( 



)°C. (H2O + ) 







0-29 



CI 



, 



. 



, 







. Trace 



100-02 



This analysis presents no remarkable peculiarity, except the low percentage of 

 alumina and the high percentage of alkalies, two properties which are also exhibited 

 by the trachytes of Carnley Harbour. Judging from the petrological character of 

 the rocks of the Bounty Islands, it seems probable that they are part of a great 

 granite mass of which the granites at the Auckland Islands, the Snares, and pos- 

 sibly of Stewart Island and south-west Otago are unsubmerged remnants. Con- 

 clusions as to this being certainly the remains of a wide continental area based on the 

 mere fact that they are plutonic rocks do not seem to be altogether well founded 

 unless supported by collateral evidence ; but this evidence is supplied from other 

 islands in this area. The fact that the sea just east of them rapidly reaches a 

 depth of 2,000 fathoms shows that they are near the edge of the continental 

 shelf, and probably mark approximately the furthest eastward extension of the 

 former continental area. 



* The iron present is all estimated as ferrous iron. 



