On the west coast the "plains" are tiny patches interrupted by rocky headlands and backed by high and difficult mountain country as far south as the mouth of the Grey. The peculiar multilevel "plain" of Westland lies south of that river and extends for less than a hundred miles. There may once have been a relatively level or slightly rolling plateau surface at some height above the sea; perhaps the coast has since risen a good deal. The steep slopes of the western mountains and their present heavy precipitation suggest that a great load of detritus would have been available to build such a marginal plain. In this now elevated mass the short, swift, mountain rivers have since cut valleys with the same marked development of terraces which is so generally characteristic of the valleys of the island, leaving terrace remnants which are often more extensive than what is left of the original surface. Progress north or south along the coastal margin is like nothing so much as the alternating ascent and descent of stairs. Even ignoring the tangle of the subtropical rain forest which covers it, this is far from easy country.
Most important of the minor land-form areas is Banks Peninsula. It is essentially a large volcanic island tied in with South Island relatively recently by the advance of the plains. Here, on a basement of rocks like those of the central mountain highland, two volcanoes built up flat cones perhaps as high as contemporary Egmont or Ruapehu on North Island. The results of erosion in the subsequent enlargement of the central craters, the development of radial streams, the drowning of their mouths with the formation of bayhead flats, and the faceting of the inter-valley spurs by wave action.
The configuration of the land surface is an extremely important element of the island's geographic character. South Island has its plains, its downs, and its lower hills, and on these areas the major agricultural and pastoral production has taken place; yet, as a shepherd born in the Scottish highlands told this writer once with pride and fondness in his eyes, "There's nowhere ye can go in the island without there's a friendly mountain looking over ye're shoulder." At many times and to many men, however, the mountains were far from friendly.