on the 1947 geological map of the South Island (published 1949), its western boundary being the Alpine Fault (see Wellman and Willett, 1942). Neither the age of the rocks that form the schists nor the age of the metamorphism is known.

The general structure of this alpine schist belt is fairly regular. High rank schists close to the Alpine Fault progressively decrease in metamorphism eastward away from it. The schist iso-grads parallel the equally regular strike of the schistosity planes and almost parallel the line of the fault. Metamorphism continues to decrease east beyond the schist belt through a belt of sub-schists and then stays much the same for many miles to the east. The line marking the limit of this progressive decrease in metamorphism lies close to the alpine divide from Mount Cook north to the Spenser Mountains. This paper is concerned with a part of this zone of decreasing metamorphism which has not previously been geologically examined.

McKay (1893) was the first to map and describe the zone in a description of that part of the Alps lying between the Taramakau and Hokitika rivers. In his map the Alpine Fault is represented by the almost straight contact between the granites to the west and the schists to the east. He mentioned the topographic depression along this fault line, but did not map it as a fault. McKay mapped the following divisions in the zone of decreasing metamorphism.

East

Triassic

Carboniferous

Devonian (semi-metamorphic)

Upper Schists

Magnesian rocks or Mineral Belt

Middle and Lower Schists

West

McKay based his ages on metamorphic and lithologic correlation with fossiliferous rocks elsewhere in New Zealand, and not on direct fossil evidence. The northern end of McKay's map adjoins the area described here and his Triassic beds form the southern extension of the Monotis-bearing beds of Trent River. Therefore his age for this group is correct. On McKay's map all the formations west of the Triassic boundary are offset along the line of the Taramakau River. This offset was vertified and measured. It is about five miles near the Alpine Fault, possibly decreasing to the east as indicated by McKay.

Bell and Fraser (1906) mapped and described the zone of decreasing metamorphism from the Taramakau River south for twenty miles to Browning Pass. The next thirty miles of the belt south to Wanganui River was mapped by Morgan (1908). In both these descriptions the rocks within the zone of decreasing rank are mapped as the Arahura Series, with a line dividing the less metamorphosed part from the schists.

In 1927 Henderson and Fyfe mapped the zone of decreasing metamorphism in the Murchison district. The southern end of their area is thirty miles north of the area here described. The maps, but not the Bulletin covering this area, have been published. In their maps they divided the zone into three units: schists, semi-schists, and less metamorphosed rocks. They named the latter “Mt. Robert Series,” and considered it to be Triassic.

In the following table our metamorphic zones are correlated with those of previous workers. Correlation with north-west Otago is based on the hand