First Meeting: 11th May, 1909.
Professor Park, President, in the chair.
The following is a summary of the presidential address by Professor Park, entitled “The Glaciation of Otago”:—
The lecturer stated that, in accordance with instructions received, he made, in three successive years, a geological survey of Central Otago, commencing at the Maniototo Plain and working westward to Wakatipu. He discovered that Central Otago was occupied by a remarkable group of block mountains, which were table-topped, and bounded by powerful dislocations. Practically all the mountains in Central Otago were so distinguished—the Hawkdun, Dunstan, Pisa, Carrick, Garvie, Old Man, and Umbrella Ranges being typical examples.
The origin of these mountains was peculiar, and, in themselves, they belonged to a unique and distinctive type, without a parallel elsewhere in the Southern Hemisphere.
But before considering the origin of these block mountains they might first look at the ordinary type of mountains, with which every one was familiar, as, for example, the Alps of New Zealand or of Europe, or the American Sierra Nevada, or the South American Andes, the summits of which were irregular and deeply serrated, and often so narrow as to form a mere razorback. Examination of their structure showed that the rocks of which they were composed were arranged in folds, often very complex.
Geologists the world over had offered explanations of the peculiar formation of block mountains, but only two of these latter were worth considering. Professor Suess, of Vienna, conceived a great plateau or plain, which he considered had been broken up by great cracks or fissures. Certain sections had, by a subsidence, been left at a much higher level than others, with the result that they now had, with all sharp corners worn off, the table-topped mountains and intervening basins.
Professor Davis, of Harvard, on the other hand, postulated a plain at or about sea-level, cracked by great dislocation, and subjected to unequal uplift.
These were the theories that had been formed regarding the very remarkable mountains of Central Otago, mountains that distinguished New Zealand, and which would in future years attract many scientists to the Dominion. The whole of Central Otago was occupied by these flat-topped mountains, on which a person might, in some cases, conveniently ride for over a hundred miles.
The lecturer next directed attention to the glaciation of New Zealand. During the progress of his geological work he had been fortunate enough to obtain evidence to show that New Zealand at one time had a glacial period similar to that of the Northern Hemisphere. He had been able to prove that Otago and the greater part of the South Island were covered with a continuous ice-sheet—probably an extension of the south polar ice. In the Wakatipu basin the ice in thickness exceeded 7,400 ft., this immense glacier, it would appear, being fed by three streams. It had flowed over the top of Mount Nicholas, which had been cut into the shape of an immense dome, beautifully rounded and smoothed, and flanked by beautiful U-shaped valleys.
Every one had heard of the glacial period of the Northern Hemisphere, often spoken of as the Great Ice Age, that took place in the Pleistocene—the period which preceded that in which we live—the geological yesterday. The north polar ice invaded North Europe, northern North America, and North Asia, and steadily advanced until it reached latitude 50O, carrying with it destruction and desolation.
The forests were overwhelmed and completely obliterated, while the animals and men inhabiting these continental areas retreated southwards before the terrible blighting wall of ice. But animals in the insular areas, being unable to escape, sought refuge in caves and holes in the earth, and there miserably perished. In Western Europe the ice-wall covered Norway and Sweden, the whole of Scotland, and the greater part of England. In Scotland the maximum thickness was 5,000 ft., and in Central Europe 7,000 ft.
In course of time this ice-sheet retreated, and left the features of the land curiously altered. The mountains, ridges, and spurs were ground down and truncated, the valleys
were broadened, and the lakes deepened. Hard rocks were smoothed, polished, and striated by the sheer weight of the moving mass of ice; and everywhere the land-surfaces presented rounded, mammillated, gently undulating contours—all the irregularities and asperities of the country having been worn away by the movements of the enormous mass of ice. Much of the land was covered with a sheet of boulder-clay, mainly composed of transported rocks, and perched blocks, some of them of enormous size, were left here and there on the ice-worn ridges.
The lecturer said he would be able to show them that the evidences of prolonged and intense glaciation were as conspicuous in New Zealand as they were in Europe. He would show them that the slopes of the mountains, up to a height of 6,500 ft., were ice-shorn into what were, without doubt, the most marvellous tiers of ice-steps or benches in existence. As evidence of the presence in the Pleistocene period of that great ice-cap in Central Otago, he could show them ice-cut platforms, glacial lakes, eskars, moraines, perched blocks, erratics, striated and polished rocks and boulders—in fact, all the phenomena of the glaciation of the Northern Hemisphere. That conditions such as these must have attended the presence of this ice-cap had obtained in New Zealand in comparatively recent times was a weird and mysterious thing—something, indeed, almost incredible; yet the evidence that this mass of ice had been all over Central Otago was so fresh that they might easily imagine it had retreated only yesterday.
There had been two phases of the Great Ice Age. The first was that in which there had been a continuous ice-sheet extending from sea to sea, when 7,400 ft. of solid ice stood in the Wakatipu basin. In the second phase the valleys were filled with enormous glaciers.
The extent of these ice-rivers was surprising. There had been one that extended westward from Alexandra a distance of 140 miles—which meant that it was longer than that great glacier traversed by Lieutenant Shackleton in Antarctica, which was believed to be some 130 miles in length. The Wakatipu glacier had split into a number of streams. One passed southward towards Kingston, and another formed the Kawarau glacier, which presently joined with the Shotover glacier. These were joined by the Arrow glacier, which was smaller, and, in consequence, twisted round and jammed up against the Crown Range, the slopes of which were wonderfully and beautifully scored. To the action of the Arrow glacier was due the formation of the Crown Terrace, which was excavated out of the solid rock.
The pictures thrown on the screen showed many photographs of the rocks and mountains of Central Otago. One disclosed a huge boulder of greywacke lying in a country altogether foreign to it—in geological language, a perched erratic. It had been brought on the travelling ice-cap over lake, and mountain, and glen, from the Livingstone Range to its present resting-place.
Another picture, which the lecturer described as the most remarkable of his collection, showed the rocky side of Mount Benmore cut into a series of almost regular rock-terraces. They were the most remarkable terraces or steps he knew of. There was nothing like them in Europe, and no one could doubt their glacial origin.
Close to Arrow there is a perched erratic rock, measuring 24 ft. by 12 ft. by 10 ft., and weighing 240 tons. It is an enormous mass, and yet geology proves that it rode in a glacier all the way from the Livingstone Range. Indications point to its having been nearer the bottom than the top of the ice-river, for a portion of it is deeply striated, as if it had been dragged for many miles over a rocky surface.
Other pictures showed a clay bank at Henley, proving that this was the moraine of a great glacier that had emptied itself into the sea comparatively close to Dunedin; and the Queenstown Domain, also an old moraine, and now covered with striated boulders belonging to far-distant parts of the mountains. Near Cromwell was the old Kawarau moraine, with its foreign and weirdly cut rocks. In fact, right over Central Otago were striated rocks in thousands, and erratic rocks in millions.
Other pictures disclosed the secret of the formation of Moke Lake, near Moonlight. Two glaciers had been forced out of the Wakatipu basin, and had come by separate valleys down towards Moonlight. Truncating the ridge that separate them, they had come together, and their united crushing-power had torn out the “twin” hole now filled by Moke Lake.
It was in a similar way, by lateral branches from the Wakatipu glacier, that Lake Dispute had been formed.
The shape of the hills throughout Otago and Southland indisputably proved glaciation. There were the smooth contours and flowing outlines that necessarily followed the grinding process of a glacier. There were the ice-shorn mountain-tops, and the gentle upward plane torn by the ice as it was pressed upwards, and the place where, having reached the top, and the pressure behind removed, the glacier dropped suddenly down.
The lecturer considered that the Wakatipu Valley existed before the glacial period. The ice had, however, probably broadened and deepened it, at the same time rounding the contours of the overhanging mountains. Three powerful dislocations ran parallel with the arms of the lake. The greatest depth in the lake was 1,240 ft., which was 240 ft. below sea-level. It was, therefore, not possible that the action of water had dug out that enormous hole. The probability was that faults or dislocations had in part formed the lake-basin, for he thought it was not competent that ice could dig to such a depth.
In view of all the circumstances, it was almost impossible to give a dogmatic opinion. Perhaps the simplest solution was to go to the Maoris, who explained the existence of the lake in an interesting way. One legend had it that a Maori wandered among the mountains with a wooden spade in his hand, and wherever he thought a lake should be, there he dug a lake. Another had it that a giant who lived in the mountains came to the coast and abducted a lovely brown maiden, and, taking her to Wakatipu, fastened her to a cabbage-tree. Her father, very wroth, offered the fair one in marriage to the first man brave enough to rescue her from the giant. One young man ventured to Wakatipu, released the maiden, and set fire to the fern, and the sleeping giant was overcome by the fire and smoke, and died. He kicked furiously in his death struggles, and thus tore out of the earth the hole that now holds Lake Wakatipu.