Much of New Zealand is comparatively young geologically in the sense that it has only recently been uplifted. In many places young marine sediments are to be found at high altitudes, as evidenced by the existence in the North Island of Pliocene shell limestones which form prominent escarpments at altitudes of about 3000 ft. in the central part of the Island, and remnants of the same formation found on the summits of the northern Ruahin.e Range at altitudes greater than 4000 ft.