The Southern Alps, Kaikōura ranges and North Island axial ranges are formed mainly from a hard, grey sandstone which in New Zealand is called greywacke (left). When it is deeply buried and heated, greywacke is converted to a flaky rock called schist (right). The western side of the alps has been uplifted more than the east, so the deeper layers that contain schist are revealed there.
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Photograph by Nick Mortimer
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