Abstract In the northern hemisphere the broad extent of glaciation had been mostly accepted by the start of the twentieth century, but in New Zealand at that time even the general picture of glaciation was uncertain. Julius von Haast had established that in the South Island the glaciers had extended out considerably from the Southern Alps, but the extent of glaciation in the North Island was unknown. Two rival viewpoints were put forward in 1909. James Park thought that there was a widespread ice sheet, which covered the South Island, Cook Strait and much of the North Island; Patrick Marshall thought that the extent of ice was much less, and argued that much of Park's evidence was spurious. The argument was ‘somewhat resolved’ by a young amateur geologist, Leslie Adkin, who showed that glaciation in the North Island was at most modest, and largely confined to the uppermost part of the main axial ranges. Adkin was a farmer and had no university education, but he published nearly 40 articles in scientific journals on topics as varied as Maori archaeology, and glacial and tectonic geomorphology. This article examines the evidence he adduced for the occurrence of a limited Pleistocene glaciation in the Tararua Range in the south of the North Island, and considers the role of the amateur in New Zealand geology.