Distribution of Volcanic Rocks in the North Island.

I have already pointed out that, judging from the relative position of the Maítai and Hokanúi Systems, it is probable that the ge-anti-clinal of New Zealand passes through the centre of the North Island from Wanganúi to the Bay of Plenty. If now we draw a line parallel to this axis from Mt. Egmont, through the Karioi at Raglan, and on to Mercury Bay in the Coromandel peninsula, we find that to the north-west of this line the intermediate rocks have been followed by basic rocks (none of which are known south-east of the line) without any acidic rocks. On the ge-anticlinal itself, from Ruapêhu to the Bay of Plenty, the intermediate rocks are followed by acidic rocks without any traces of basic rocks. To the east of the axis basic rocks occur again on the east coast of page 219 Wellington; but these are thought to be older. I have mentioned that a line of granite- exposures occurs along the ge-anticlinal axis in the South Island, from Paringa to Separation Point in Kelson; and the question naturally suggests itself, Are these rhyolites of the North Island derived from a northerly extension of the granite zone of the South Island? It seems possible that granitic rocks may be nearer the surface here than they are in the northern parts of the province of Auckland, and this may account for the eruption of rhyolites only in the centre of the North Island. They may be merely a réchauffée of Maítai granites of the northern part of the ge-anticlinal.