Physiography. Geology.'] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 729 



(5.) The Younger Basic Series. 



The basalts which have built up the greater part of the group were poured out 

 principally from a centre at Carnley Harbour. Other foci no doubt existed to the 

 north, but of that little can be said definitely. On the west coast, nearly opposite 

 Disappointment Island, there is a structure exposed in the cliffs which may be the 

 pipe of a volcano. In any case, the northern limit of the Carnley lavas appears 

 to be just north of an east-and-west line through Norman's Inlet, as there appears 

 to be a change in the dip of the flows to the northward of this line. The northern 

 part of the island was not examined sufficiently to give any definite opinion of the 

 place of origin of the flows. The following descriptions therefore apply to the 

 southern end of the group, although the conditions obtaining in the north appear 

 to have been somewhat similar. 



Carnley Harbour is no doubt an explosion crater, or caldera, which has been 

 subsequently modified by marine and subaerial erosion. The eastern entrance forms 

 the barranco, while the western entrance has been formed by the destruction of the 

 crater-ring, chiefly by marine action. The breadth of the base of the cone at sea- 

 level is now seventeen miles, and no doubt it stretched far out east and west and 

 south in former times, even supposing the land as a whole was not more elevated 

 than at present. There is distinct evidence, however, that it was much higher. 

 The estimate given by Sir James Hector that the volcano was fully 12,000 ft. high 

 is based on a misconception.* He believed that the centre of the volcanic system 

 of the group was at Disappointment Island. This is now known to be incorrect. 

 His estimate of elevation based on the slope of the flows is also in error, for the reason 

 that the dip of the flows on the west coast, especially in the south of the group, is 

 distinctly westerly, at very low angles. The present distance across the Carnley 

 crater-ring is now about seven miles from north to south, but stream-action has 

 considerably modified any regularity of outline if it formerly existed. Even allow- 

 ing for a good deal of denudation, the height of the volcano could never have been 

 much more than at present, unless the islands were raised as a whole. The appear- 

 ance of the harbour is strongly reminiscent of Akaroa. Instead of one pear-shaped 

 peninsula, with its core of syenite, as at Akaroa, there are two similarly shaped 

 peninsulas, with a base, one of gabbro and the other of granite ; nevertheless, the 

 height of the crater-ring, the character of the lavas, and the marine erosion of the 

 outer coasts cause a striking resemblance between the Auckland Island volcano 

 and that of Banks Peninsula. 



The whole system at Carnley has been built up of successive flows of basic lava, 

 with intervening tufl-beds of remarkable regularity. The sequence is best seen on 

 the western cliffs, near the head of the North Arm. Here one cliff, 1,200 ft. in alti- 

 tude, gave exposures of forty -two successive flows ; another, of 800 ft., gave twenty- 

 nine flows. They are distinguished, too, by their remarkable flatness, so that the 

 lava must have been ejected in a very fluid condition. This suggests that the island 

 must have been of very great extent in former times. The flat points stretching 

 far out into the sea on the eastern and north-eastern coast, which suggest by their 

 form a plane of marine denudation, may, perhaps, be the upper almost-level sur- 



* " Note on the Geology of the Outlying Islands of New Zealand," Trans. N.Z. Inst., vol. xxviii ; 

 1896. 



