On the Geology of Otago, New Zealand

Abstract

The south-western part of the Province is composed of crystalline rocks, forming lofty and rugged mountains, intersected by deeply cut valleys, which are occupied on the west by arms of the sea, but on the east by the great lakes. The base-rock of this system is a foliated and contorted gneiss, corresponding to Humboldt9s Gneiss-granite of South America. Associated with it are granites, syenites, and diorites. Wrapping round this batch of crystalline strata, and sometimes resting at great altitudes (say 5000 feet) on its surface, are a series of hornblende-slates, soft micaceous and amphibolic gneiss, clay-slates, and quartzites, associated with felstone-dykes, serpentine, and granular limestone. I believe these to be metamorphic rocks of not very ancient date. To the eastward of these two formations the country is traversed by a depression that widens towards the south, and enters the mountain-chain by a pass only 2000 feet in altitude above the sea; this is the “Greenstone Pass” that I discovered last year. Along the line of this depression, and resting on the last-mentioned slates, &c. (unconformably?), are well-bedded sandstones, shales, and porphyritic conglomerates, together with soft greenstone-slates and diabase-rock in patches. This further reminds me of Darwin9s great porphyritic formation in South America, and is probably also all that we have to represent the Lower Mesozoic rocks (No. VI.). In the N.E. and S.E. part of the Province, what I take to be the same formation, or an upper series of it, passes into sandstones and shales, thrown into bold plications