IN TOUCH WITH NATURE

Hokitika Guardian, 3 July 1928, Page 4

IN TOUCH WITH NATURE

OLD-TIME GLACIERS. (By J. Drummond, F.L.S., F.Z.S. in “Lyttelton Times.”) Visitors to tho Franz Josef Glacier are never disappointed with it. The ice, the snow, the dark vegetation and the blue mountains make pictures that it should be a part of every Now Zealander’s education to -.see. At the same time, there is a fascination in reconstructing tho much greater glaciers that onco ilowed from the highlands to the lowlands on the West Coast of' tho South Island, until they reached the shore-line, and even went into the sea. Many mountain peaks in that district arc so steep and jagged that they do not hold snow. In former times, before valleys and canyons had been so extensively eroded, hugli 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 V.Tiit-eomhe Pass, the Bracken Snowfield, which feeds the Wilkinson Glacier and tho Evans Glacier, gives some idea of the extent of the snowfields tnat fed the old-time glaciers. The Bracken occupies a large area of almost flat or gently sloping country, rooa feet high on the average, with here and there a. rocky peak or a ridge .more than 8000 feet high. Ihe snowfield is at least from 100 feet to 200 feet thick. Creeping over the Alpine divide, it links up with snowfields that feed the Ramsay Glacier, on ihe eastern side of the Soul hern Alps. This g’aeier, 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 Boweu, 0500 feet. Crevasses show that this mass, in places, is 100 feet thick. Quite one-half of the lowlands in some districts is covered by the. accumulation of moraines, piles of stones and gravel left by glaciers ns t.'icv retreated from the land. The moraines reach a height of more than 1000 ft. Near the Wanganui River, the cliffs they form face the Tasman Sea for j many miles. North of the 'Wait-aba. j Be’cl Head is a sheer cliff-face, sonic i 100 feet high, pimpled with enormous boulders. It is the* terminal moraine of the old Waitalia Glacier, which carried tho boulders down from its source in tbe Alps and dropped them at its terminus. There is a little granite amongst tho boulders, but mostly they are a kind of rock known to geologists as grevwacke, with other rocks, all derived from the Alpine chain. Partly washed away by the unceasing barrage of the waves, Bold Head is an ideal section of a great moraine. The Waitalia River, which cuts tho Main South Roatl to the Franz Josef, flows down a valley sculptured by the cild Waitalia Glacier. The river’s source is a very small glacier. W ithin a few hundred yards, two streams, tumbling waterfalls and cascades from cliff-glaciers, swell tho Waitalia, which has further accessions before it enters the immense mountain ditch on whoso floor it spreads itself in times of flood. Two huge piles of debris, known as Bunker Hills and Whnleback Hill, were deposited by a glacier that flowed down the valley cf the Wanganui River and wont round into tho ' sea beyond the present coast-line. West ! and north of lovely Lake lantho, which is almost touched by Lhe main highway, and sparkles unexpectedly into 1 the view of travellers north and south, • there arc masses of moraine debris that - rise to a height of ICKX) feet above the lake, extend to tbe sea-coast, and for : miles form high cliffs that look out . westward on to the ocean. 5 The great ancient glaciers crept down from the snowfields as the Southern 1 Alps were forced higher and higher. - When the mountains reached their greatest elevation, the glaciers flashed t back the rays of a Pliocene sun, at a I time, probably contemporaneous with - the Great Glacial Age in Europe. Def muling forces, reducing the weight of > the mountains and carving deep vali leys, decreased the areas of the snowfields. With reduced supplies, the gla- ' tiers began to retreat. In addition to tliis, tho whole land may have somewhat subsided, and the climate may i have become warmer. In any case, in i their retreat, the glaciers left behind f them the moraines in which geologists 1 read their history. The glaciers advanci ed and retreated again and again. For t a. long time they subdued and occupied 1 a large part of the present lowlands, t Advancing and retreating, they busily 2 carried their loads of rocks and gravel, i to drop them here and there. The s final retreat into the frozen heart of f the mountains was fairly rapid. It is - going on still. A great deal of the material carried by the glaciers was - sorted and distributed by running - water. s New Zealand’s ablest geologists do 1 not believe that the present alpine s chain supplied the bulk of the alluvial f gold won in North Westland, ’the exf tinet glaciers carried large quantities of debris poor in gold. Material known f to miners as Old Man gravels is the e 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 lias stained them brown , or yellow. They were largely derived from coal-measure conglomerates. Much 3 of the alluvial gold in tlio.se parts, prot bably, was freed from its matrix in , early Tertiary times, before the vast , expansion of the glaciers. A great . river believed to have flowed nortli- . west of Ross in the Early Pliocene l broke up and concentrated tbe coal- . measure conglomerates, and the Old , Man gravels have been assorted several . times. Streams that flowed on, in and under the glaciers received what gold the glaciers had. concentrated it with the Old .Man gravels, and left some ' rich deposits. The golden beds to which Ross owes its very existence, j and to which it looks for renewed prosperity, seem to bo largely material deposited by streams that flowed in frontof the old .Mikomii Glacier. In former times, there were many more akes on the Vi est (oast than there are now. Many rock-basins in mountain valleys now filled with rivergravels were lakes, large or small, perhaps immediately after the glaciers retreated. Some large areas on the lowlands formed lakes, partly rock-hound, partly clammed 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, hut they soon were filled by the gravels of rivers that took the glaciers’ _ place as the glaciers retreated into the I mountains. !