Historians tell us that Polynesian voyagers reached the shores of New Zealand many cen­turies ago. Precisely when is a matter of dispute; some authority’s say they first arrived in the eighth century, others several hundred years later. Yet it is certain that they had been in possession of the land for many generations before the first Euro­peans touched here in 1642, sailing on again to leave the country undisturbed for a further 127 years.  Then followed that troubled period of European contact which ended one hundred years ago with the establishment of British rule and the beginning of organised colonisation.

Thus the historian of peoples, looking back over centuries, generations, and decades, divides the history of New Zealand roughly into periods—first the Maori period: then the period of navi­gators  and   other  casual   visitors   and   settlers: finally the period of settled European occupation. But the history of New Zealand—of the moun­tains and rocks and rivers of this interesting land —goes back infinitely beyond the date when the first voyagers from Hawaiki could have arrived here. Man, indeed, has been in occupation for only a small fraction of time. Through long ages before his coming the land was moulded by rain, running water, and wind; it sank beneath the sea and rose again; it was carved by giant glaciers; it was convulsed by land movements and eruptions; it was clothed by forests long since gone and occupied by strange creatures which have been extinct for millions of years.

This fascinating story is revealed to us by the earth-historian—the geologist—and he, like the historian of men, divides his story into periods which   cover,   not   centuries   and   decades,   but hundreds of thousands and even millions of years. The materials of the historian are the traditions, the legends, the writings, the implements, and so on which men leave behind them during their existence. The geologist builds his story from rocks which he finds exposed on the outer part of the earth’s surface.

The origin of these rocks is extremely varied; were once in a liquid or molten state; others as sandstones are derived from the worn- materials of pre-existing rocks; others again like limestone’s, have been built up from the skeletons of marine creatures. Every rock, if correctly interpreted, tells us something about its history through long geological ages.

But the geologist does not read the book of Nature merely by examining samples of rock. He studies the layers, or strata, of rock exposed in a cliff or in a surface outcrop and from their arrangement construct a longer and more complicated story. The oldest rocks are at the bottom of the cliff, the youngest at the top; in between are the layers of intermediate age. In this simple way a time sequence is determined, and the geological column is built up.

Even more fascinating is the way in which the geologist reconstructs the past from the traces or actual remains of plants and animals long since extinct. Some   550   million years   ago   certain primitive sea-animals, defeated by the intense competition near the surface, were forced towards the shallow sea floor and became bottom dwellers.

The relatively inactive life in these new surroundings caused bodily changes, one of which was the ability to get rid of all the mineral salts taken with food. One way out was to deposit this excess material in the form of a skeleton which kept its shape and solidity after the animal had died. Obviously these hard parts had some degree of permanence and, if buried by sediment, might survive indefinitely to yield their mite of evidence millions of years later.

In the rocks of all ages since the beginning of the Cambrian Period, when this interesting and important change occurred, fossils have been pre­served, sometimes in great abundance and some­times in such exquisite detail that the student of ancient life—the paleontologist, as he is called— can reconstruct the past with great accuracy.