IN TOUCH WITH NATURE

Otago Witness, Issue 3877, 3 July 1928, Page 5

IN TOUCH WITH NATURE

OLD-TIME GLACIERS.

By

J. Drummond,

F.L.S., F.Z.S.

>■ Visitors to the;; Franz Josef Glacier are never disappointed with it. Th e ice, the snow, the dark vegetation and the blue mountains make pictures that it should: be a part ojf every New Zealader’s education to see. At the same time, there is a fascination ■ in reconstructing the much greater glaciers that once flowed from the highlands to the lowlands on the West Coast of the South Island, until they reached the shore line, and even went into' thq|sea. Many mountain peaks in that district are so steep «nd jagged that they do not hold snow. In former times, before valleys and canyons had been so extensively eroded, huge glaciers, now extinct, were -fed by one vast snowfield, which covered almost the whole surface of the alpine chain.

Near the alpine divide, south-west of the Whitcombe Pass, the Bracken Snowfield, which feeds : the Wilkinson Glacier Evans Glacier, gives same idea of the extent of the snowfieldg that fed the old-time glaciers. The Bracken occupies a large area of almost flat or gently sloping«country, 7000 feet high on the average, with here and there a rocky peak or a ridge more than 8000 feet high The; snowfield is at least from 100 feet to 200 feet thick. Creeping over the alpine divide, it links up with sn owfields that feed the Ramsay Glacier, op the eastern side of the Southern Alps. This glacier, an extensive one, is the source of the main branch of the Rakaia River. In the same district as the Bracken Snowfield there is a small snowfield, on a gentle slope that falls from the summit of Mount Bowen. 6500 feet. Crevasses show that this mass in places is 100 feet thick.

Quite on e half of the lowlands in some districts is covered by the accumulations i m ° raines ,. Piles of stones and gravel eft by _ glaciers as they retreated from the land. The moraines reach a height of more than 1000 feet. Near the Wanganui River South Westland, the cliffs they fac e the Tasman Sea for many miles ?h°ee? o°TA e Waitaha Bold Head a sheer cliff face, some 400 feet hi<di led . Wl . fch enormous boulders. It” is mt .™ oraiae of the old Waitaha f 1 ™ •; Whlch Carried the boulders down them 5 •? Ur f e P? the aIDS and dipped at *ts terminus. There is a little g nite amongst the boulders, but mostly SsZ r a kind K Of TOCk kn °- n toZolo 7 gists as greywacke, with other rocks all derived from the alpine chain. Partly washed away by the unceasing barrage of oj'.TS S? w - H “ d “ “ ' dMl oi a gieat moraine

_ _T ke Waitah. River, which cuts tl.» Main South road to the Franz Josef Waitaha W ri a - Valley £r’ ulpture d by the old Waitaha Glacier. The river’- source is a very small glacier. Within a few hund d c yards ’ two streams, tumbling in waterfalls and cascades from cliff-glaciers swell the Waitaha, which has further before it enters the immense “oPntain ditch on whose floor it spreads of / H • T S ° f fl °° d - Two Piles sr°n n aS Bunker Hills aa d haleback Hill, were deposited by a glacier that flowed down the Valleyof the Wanganui River, and went round into th sea beyond the present coastline. West and north of lovely Lake lanthe, which is almost touched by the main highway, and sparkles unexpectedly into i view of travellers north and south, there are masses of morainic aebris that rise to a height of 1000 ft above the lake, extend to the sea coa: t, and for miles form high cliffs that look cut westward on to the ocean.

The great ancient glaciers crept down from tlie snowfields as the Southern Alps were forced higher and higher. ‘When tin mountains -reached their greatest elevation, the glaciers flashed back the rays of a Pliocene sun, at a time, probably contemporaneous with the Great Glacial Age in Europe. Denuding forces, reducing the height of the mountains and carving deep valleys, decreased the areas of. the snowfields. With reduced supplies, the glaciers began to retreat. In addition to this, the whole land may have somewhat subsided, and the climate may have become warmer. In any case, in their retreat, the glaciers left behind them the moraines in which geologists read their history. The glaciers advanced and retreated again and again. For a long time they subdued and occupied a large part of the present lowlands. Advancing and retreating, they busily carried - their loads of rocks and gravel, drop them here and there. The final retreat into the frozen heart of the mountains was fairly rapid. It is going on still.

New Zealand’s ablest geologists do not believe that the present alpine chain supplied the bulk of the alluvial gold won in North Westland. The extinct glaciers carried large quantities of debris poor in gold. Material known to miners as Old Man gravels is the immediate source of the greater part of that alluvial gold. Those gravels are characterised by the very decomposed nature of their pebbles and finer material. Usually they are very clayey. Oxide of iron has stained them brown or yellow. They; were largely, derived from coal-measure conglomerates. Much of the alluvial gold, in those parts, prob--ably, was freed from its matrix in early Tertiary times; -before the vast expan-, sion of the glaciers. A: great river l be-

lieved to have run north-west of Ross in the Early Pliocene broke up and concentrated the coal-measure conglomerates, and the Old Man gravels have been assorted several tinics. Streams that flowed on, in and under the glaciers received what gold- the -glatiers '•had, concentrated it with the Old Mari gravels, and left some rich’deposits. The golden beds to which Ross owes its very existence, and to which it looks for renewed prosperity, seem to. be' largely material deposited ’.by streams ; that flowed in front of the old Mikonui. Glacier.

■ an former times, there were many more lakes on the West Coast than there are now. Many rock-basins in mountain valleys now filled with river gravels were lakes, large or small, perhaps immediately after the glaciers retreated. Some large areas on the lowlands formed lakes, partly rock-bound partly dammed by moraines. Some ■glaciers, advancing from the mountains over the present lowlands, and coalescing, caused huge moraines. These enclosed large basins, which were filled with ice until the retreat of the glaciers. The basins then became lakes, but they soon were filled by the gravels of rivers that took the glaciers’ place as the glaciers retreated into the mountains.

Since Airs N. Whitmore, Wairoa, Hawke’s Bay, wrote inquiring as to the habits of grasshoppers she sees and hears, a record has come to hand of an English naturalist’s observations of members of the same great ancient groups of creatures in the Old Country. New Zealand’s grasshoppers largely are her own, but their methods of life, doubtless, are on the same lines generally as those followed by other grasshoppers. Their story begins with the laying of an egg in the soil or in a dark place. Using a swelling on the neck, the younw grasshopper breaks its prison walls. It is a pale little creature. Its first impulse is to eat roots and moulds it finds at hand. As its skin is flexible and as growth is fairly rapid, the old skin must be removed periodically, to be replaced by a larger one. By fillim' out a tiny bladder on the neck, and humping it up, the skin is rent. The skin not only covers the outward parts of the body, but also forms many internal parts, including the lining of the mouth.- The struggle to get free is so severe that, when it is finished, the fatigued caterpillar lies inert, waiting for his new skin to harden and its muscles to regain their strength. The second coat is brighter than the first. The process is continued as the grasshopper grows. The wings, absent before the first moult, increase in size. Finally, after the last moult, they are sufficiently large and strong for short flights. From infant to grown-up, there is no violent change in structure. Growth is gradual. Unlike some other insects grasshoppers have no metamorphosis. They are strict greenleafers.