Introduction

In 1946, one of the writers (F. W. M.) found a single cast of the fossil Monotis richmondiana in the Trent River area, North Westland (Sheet S52). Monotis is widely distributed in New Zealand, particularly in the South Island, and, being an index fossil confined to beds of Noric age, it has considerable importance as a guide to the pre-Tertiary structure. In the South Island, Monotis has been found in three widely separated areas—Nelson, Southland, and Canterbury

(fig. 1). In Nelson and Southland the Monotis-bearing beds are part of a fairly regular and moderately fossiliferous Permian-Triassic sequence, and Monotis has been reported from numerous localities. In Canterbury, Monotis has been found at a few places in the “greywackes” of the Southern Alps and eastern foothills. These “alpine greywackes” continue over the alpine divide into Westland, where with gradually increasing metamorphism they pass westward into the alpine schists. Monotis had not previously been recorded from Westland nor had it been recorded so close to the alpine schist. For these reasons the discovery of Monotis at Trent River has considerable geological importance.