THE GLACIAL PERIOD IN NEW ZEALAND.

New Zealand Graphic, Volume V, Issue 46, 15 November 1890, Page 2

THE GLACIAL PERIOD IN NEW ZEALAND.

Since geologists have come to acknowledge the part played by ice in determining the present configuration of the earth’s surface, the glacial period is frequently spoken of, and there are few who have not heard of a past reign of ice ; yet tew outside scientific circles really comprehend what the glacial period means. It does not mean that the whole earth was at any- time under an arctic climate, but that at certain times there was an enormous extension of the polar regions, or, at any rate, of a similar climate, alternately in the north and in the south. While a polar climate extended far into the present temperate regions these were undergoing the rigours of a glacial period. Dr. Croll, who has examined the subject from its astronomical aspect, estimates that the last great glacial period occurred about 240,000 years ago, and endured for 160,000 years. Lesser glacial periods, according to the same authority, occur at intervals of from ten to fifteen thousand years. Whether the north or the south was the last to pass through the experience of a glacial period it is not easy to determine. At any rate, the evidence pointing to ice-action during the glacial period in New Zealand is conclusive. We will assume that the cruel rigours of a polarclimate had given place toalmost tropical warmth in the north temperate regions. While the animals and plants—and probably man—were basking in the glorious sunshine that clothed the earth with verdure and marie food abundant in the favoured north, these southern lands were passing through the life-exterminating influence of the last great glacial period. Where now the noonday sun makes glad the earth with genial warmth, cruel, biting ice-winds swept the plains, bearing down before them almost everything possessed of life, or driving living things northward to where the conditions were less severe. The sunny valleys which are now often seen smiling with golden grain ripening in the summer sunshine, and beautiful with happy homes, and flowers, ami fruit, were filled with rivers of ice. Where noble rivets roll onward to the sea, slow-moving glaciers crept inch by inch downward, crushing and grinding everything in their pathway, till open valleys were gouged out into rugged gorges, and high on the mountain slopes, now clad in vegetation, the thunder of the avalanche made incessant din. The long winters, succeeded by summers of brief duration, made the climatic conditions such that, by alternations of glaciers and turbulent, swollen rivers, the land surface was rent and torn asunder, and the debris borne downward to the sea, or spread out upon the plains. Where the climate was severest the amount of erosion has been very great. The chief centre over which the ice-king reigned during the last great glacial period in New Zealand was over the southern and western I>ortions of the South Island. Then the justly-celebrated West Coast Sounds and the cold lakes were carved out of the solid rock. How great and how long-continued the icesculpture must have been may be imagined by examining the effects to-day over the granitic area in which the Sounds lie. Naked, splintered granite crags rise up around the shores of Milford Sound to heights of over 6,000 feet, while the bottom of the Sound lies fully a hundred fathoms below the water level. The agency that chiselled out these wild West Coast gorges, cutting down through six or seven thousand feet of solid granite, must have been wonderfully potent ; but what could cut out a channel for itself so effectively as a river of ice, whose under surface was armed with shattered fragments of the hardest rock, every square foot being forced down with a pressure of hundreds or even thousands of tons ’ Anyone who has noted the effect of sandpaper on hard surfaces must fully appreciate the effect of a glacier whose under surface was armed with a coating of extremely hard rocky particles. We often find hard pieces of rock that have thus been carried forward grinding and cutting against the rocky channel of some ice-river of the glacial period till the under surface of the piece of rock has been worn flat and smooth ; and often the perpendicular or overhanging wall of some precipice shows a long scar made by a similar piece of hard rock borne forward firm-pressed against the rocky wall. The many gorges cut out towards the sea have since lieen slowly subsiding, or are lieing tilted, owing to the subsidence of the land along the West Coast, till some of them are submerged. This is, in short, the origin of the sombre yet majestic West Coast Sounds. Thegreat depthof water shows the amount of subsidence since these gorges were sculptured

out during the glacial period. Over the lake region the glaciers, as they arrived at a lower level, towards the close of the reign of ice slowly melted and dejiosited their accumulated bundles of gravel, boulders, and rocky masses, filling up the lower end of the gorge, as at Kingston, by means of which the waters of Lake Wakatipu are imprisoned. The sounds and lakes are two of the most striking evidences of the glacial jieriod in this country ; but there are many less striking features which bear testimony to the reign of ice in the past. J. A. Joseph. Dunedin, July 9, IS9':.