124 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 7, 



1 . On the Geology of Otago, New Zealand. 

 Bj J. Hector, M.D., F.G.S., of the Geological Survey of Otago. 



[In a letter to Sir E. I. Murcliison, K.C.B., F.G.S.] 



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 Humboldt's 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 meta- 

 morphic 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, 

 &e. (unconformably?), are well-bedded sandstones, shales, and por- 

 phyritic conglomerates, together with soft greenstone-slates and 

 diabase-rock in patches. This further reminds me of Darwin's 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 and interbedded with diorites. They 

 resemble exactly the formation that is included unconformably in 

 the folds of the Carboniferous Limestones of the Eocky Mountains. 



To the eastward of the depression (see section) we have a great 

 development of the auriferous schistose formations, shaped as a flat- 

 tened boss, rising to 4000 feet, and throwing off h and g to the 

 westward, and only g to the eastward. In the section I have divided 

 the schists into three parts. 



1. Upper (i). — A grey arenaceous, almost slaty rock, containing 

 but little quartz, in the form of veins and laminae. 



2. Middle (i'). — Soft blue slates, often highly micaceous, and 

 intersected with quartz-veins of small size, the quartz often rotten 

 and decomposed. The thickness of this formation is not more than 

 from 100 to 200 feet, and it is probably the same from which most 

 of the gold in the Western or Lake gold-fields has been derived, by 

 the direct erosion of glaciers and mountain-torrents. This blue 

 slate -formation has been removed by denudation from the greater 

 part of the central boss, only remaining in a few localities that are 

 difficult of detection, on account of its soft and perishable nature. 



3. Lower (i"). — Contorted schist. This is a clay-schist, fohated, 

 not with mica nor with felspar, but with quartz. It is often 

 chloritic, and in the upper part the quartz is nearly wanting. The 



