720 



SUBANTARCTIC ISLANDS OF NEW ZEALAND. [Physiografhy, Geology. 



Harbour, and the rock is visible on the shore for nearly a quarter of a mile on either 

 side of that peninsula. It is found also in large boulders in a conglomerate 

 on the opposite shore of Carnley Harbour, near Camp Cove. The rock is very 

 white in colour, but when exposed to the weather it appears brownish at times, 

 owing to a staining of iron-oxides. Large white and pink crystals of feldspar are 

 porphyritically distributed through it, which occasionally reach a length of 5 cm., 

 and sometimes exhibit idiomorphic forms of the Baveno habit. There is very little 

 muscovite present, but a considerable amount of biotite-mica, so it must be classed 

 as a biotite-granite. The amount of quartz varies considerably, and the rock is 

 sometimes quite syenitic in character ; a considerable amount of plagioclase also 

 occurs. It resembles somewhat the granite from the Bounty Islands, but differs 

 altogether from that from the Snares. The following analysis, by Mr. A. M. Wright, 

 F.C.S., chemist to the Christchurch Meat Company, Islington, shows its chemical 

 composition : — 



Per Cent. 



SiO., 

 AI263 



FeO 

 MnO 

 CaO 

 MgO 

 K.,0 

 Na,0 

 P265 

 TiOa 

 CO, 



Water lost below 100° C. (H,,0-) 

 above 100° C. (H.^0 + ) 



73-56 

 11-19 

 1-44 

 3-36 

 0-19 

 1-97 

 2-02 

 2-90 

 3-26 

 Trace 

 0-21 

 0-11 

 0-14 

 0-30 



100-65 



Specific gravity . . . . . . . . . . 2-54 



A partial analysis of the rock by Professor Jarman gave a silica percentage 

 of 73-94. This rock, like the Bounty granite, shows a rather low percentage of 

 alumina, which is also a marked feature of the trachytes occurring later in the Auck- 

 land Islands. It seems highly likely that the granite forms part of a wide great 

 mass of which the Snares and the Bounty Islands are remnants ; and perhaps 

 the granite in Stewart Island and in south-western Otago near Preservation Inlet 

 and Chalky Inlet are but local manifestations of the same widely extended plutonic 

 mass. The occurrence of granite in the Auckland Islands is evidence that these 

 islands once formed part of a continental area. 



Gabbro. 



The gabbro is found in situ at the end of Circular Head, and also at McClure 

 Head, but its actual extent was not determined owing to lack of opportunity to 

 thoroughly examine the localities. Large boulders of gabbro are found plentifully 



