The mountain backbone of the North Island – generally referred to as the North Island Main Range – extends from Wellington to Cape Runaway, generally marking the divide between the east and the west coast drainage systems. The scenery of the range is that of a series of deeply dissected uplifted blocks, forested to the 4,500 ft level, and grass or scrub covered above this level. There are no permanent snow fields or glaciers, but snow is common down to below the timber line in the winter months, especially in the south.

In Gisborne Land District the Raukumara Range rises to 5,763 ft in Mount Hikurangi, the highest non-volcanic peak in the North Island. West of Waikaremoana the Huiarau Range, rising to 4,602 ft in Manuoha, is the centre of the famed Urewera Country. An offshoot of this range – the Ikawhenua Range – extends north to the Bay of Plenty between the Rangitaiki and Whakatane Rivers. South of the Napier-Taupo highway the lower Ahimanawa Range (4,225 ft) and higher Kaweka Range (5,637 ft) are separated by the Ngamatea depression from the Kaimanawa Mountains, fronting the central volcanic plateau. The highest peak in the Kaimanawa Mountains is Makorako (5,665 ft) at the source of the Rangitikei River.

South of the Napier-Taihape road the mountain system narrows to a single range – the Ruahines – rising to 5,687 ft in Mangaweka. The mountain axis is breached by the Manawatu Gorge east of Palmerston North, a west coast river draining part of southern Hawke's Bay. South of the Manawatu Gorge the Tararua Range and its continuation, the Rimutaka Range, continue to the shores of Cook Strait. The highest peak in this section is Mitre (5,150 ft) in the central Tararua Range.

The North Island main range is composed mainly of the hard-folded sedimentary rocks of late Paleozoic to Mesozoic age, commonly known to geologists as “greywacke and argillite”. The old rocks of the main ranges are flanked by younger sedimentary rocks of the upper Tertiary period – sandstones, mudstones, and limestones – remnants of which are commonly found at high elevations resting on marine-cut surfaces, thus demonstrating the comparative youth of the mountain system. The western outliers of the range in the north are deeply covered with pumice ash and volcanic rocks emanating from the central volcanic region.

by George William Grindley, M.SC., New Zealand Geological Survey, Lower Hutt.