The inscription on one chunk of greenstone says Sapper Colin Adams, died of wounds, 23 April 1917, aged 22.

A companion piece of pounamu pays tribute to Lance corporal Bernie Fahey, a 26-year-old Irishman, killed in action on 20 April 1917.

Both soldiers belonged to the New Zealand Engineers Tunnelling Company, a First World War unit of tough miners formed to carry out digging work on - or mostly beneath - the Western Front.

Adams and Fahey died, a few days apart, from heavy enemy artillery fire in northwest France, killed while working on a key road for a major advance.

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Their war sacrifice will feature on a memorial wall in Waihi honouring the tunnellers, many of whom came from the Thames-Coromandel region.

The 1.6m high wall will be dedicated, along with a 7.5m T-shaped structure designed by Nicholas Brumder, in January, the start of the centenary year of company's formation.

Sue Baker Wilson, of Waihi Heritage Vision and director of the project, is appealing for tunnellers' descendents to contribute stones for the wall, or plaques which could be attached to rocks.

Besides the tributes to Adams and Fahey, she has a dedication on a piece of quartz to miners from Reefton on the West Coast, from Thames and even the Cook Islands.

Three Cook Islands soldiers served with the unit through the NZ Pioneer Battalion, the contingent of Maori soldiers which undertook dangerous engineering tasks such trench formation, road works and railway construction.

Some 937 men served with the company as part of the main body or in reinforcements.

More still transferred into the unit overseas. Sue Baker Wilson's research has so far identified 52 tunnellers buried in France. She is gathering details of further deaths, both overseas and in New Zealand, and expects a revised casualty list to be higher.

The men were killed in action, died of wounds, perished in accidents and succumbed to illness. A few - like soldiers from all parts of the NZEF - took their own lives.

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Work of the specialist tunnelling group is fondly remembered in the city of Arras, about 200kms north of Paris, where the New Zealand miners left their calling card in the form of placenames painted and carved on the walls of vast chalk caverns and cramped underground tunnels.

There is already a memorial to the New Zealanders in the French city, and authorities there have provided a piece of flintstone for the Waihi wall.

The miners spent two years at Arras, clearing quarries excavated when the town was rebuilt in the 17th century and creating a labyrinthine network of tunnels and galleries that could comfortably house 20,000 soldiers.

The secret underground toil was in readiness for a brazen assault on the German trenches in April 1917.

The work was hard and dangerous. Besides the risk of mine collapse, there was a real prospect that German forces were engaged in nerve-shredding counter-mining, excavating an adjacent cave before packing it with explosives.

Shaped to direct blasts, this underground eruption, called a camouflet, could destroy work crews with explosive force or deadly gas. To detect the enemy, the miners used geophones, listening devices which picked up the sound of the enemy at work.

Sue Baker Wilson said she hoped the tunnellers' motto - Inga Wahi Katoa or 'Everywhere' - would resonate with descendents and encourage them to send named stones for the singular WWI memorial.

Tunnelling Company appeal nzetc.co.nz
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