N.Z. GLACIAL EPOCHS.

Press, Volume LIX, Issue 17939, 6 December 1923, Page 2

N.Z. GLACIAL EPOCHS.

A PAPER BY MR JOHN HARDCASTLE. At last night's meeting of the Canterbury Philosophical Society a paper was submitted by Mr John Hardcastle on New Zealand's Glacial Epochs and Croll's Theory of Ice Ages. Referring to the "Great Glacier Period,',' the vestiges of which are well known in the alpine lakes and moraines, the shingle plains, and the loess clays of Canter- ■ bury and Otago, the author drey.' attention to records of observations which j prove that the commonly accepted explanation of the great glaciers—an uplift of the land —does not fit all the facts. Papers published in the "Transactions" of 1889 and 1890, on the loess clay at Timaru, showed that this formation of wind-borne glacial silt was deposited intermittently, with long periods of pause marked by hot or at any rate arid climate. The variations of climate indicated by these facts required some other explanation of the great glaciers than uplift of the land. The problem was precisely the same as that of .alternate glacial and interglacial periods, which has been discussed in Europe and America —without, as'yet, a satisfactory solution being found. The author claims that Croll's theory is a satis- | factory theory, if amended by the_ incorporation of knowledge, gained since Croll's day, of the character of Antarctic "blizzards." The climates of different regions of the world to-day outside the tropics, are due to interaction between direct sun-heat at different seasons and the stores of cold in the Polar regions, the latter being replenished during winter. The Antarctic regions are colder than the Arctic, all the year round, because the winters in the Southern Hemisphere are seven days longer, and are spent 3J million miles further from the sun, than those of the Northern Hemisphere. Astronomy teaches that from time to time, at long and irregular intervals, these differences are due to the eccentricity (departure from a circle) of the earth's orbit. The eccentricity varies, and from time to time, at long and irregular intervals, it may become so great that those climatic differences may be quadrupled. The effect of high eccentricity on climates was first clearly sketched by Sir John Herschel in 1830. He showed that it might operate to produce in one hemisphere the extreme vicissitudes of a burning summer and a long rigorous winter, while the other hemisphere enjoyed an approach to perpetual spring. These conditions alternated between, the hemispheres every 10,000 years. The astronomical conditions are elaborately worked out by Sir Robert Ball in his book "The Cause of an Tee Age." The abnormal astronomical conditions affect directly the Polar and sub-Polar regions, providing there a great store of cold. Upon this basis Dr. Croll founded a theory of abnormal meteorology to explain glaeiations in temperate latitudes. Croll's theory, strengthened by later knowledge of Antarctic blizzards acquired by recent explorers, is an adequato solution of the problems furnished by vestiges of past glaeiations in the northern hemisphere including the extraordinary localisation of the ice-sheets outside the Arctic Circle; and therefore adequately explains the lesser glaeiations of New Zealand.' These were due to Antarctic blizzards biing the predominant climate-makers during the southern 10,000 years glacial period. In the intervening inter-glacial periods of equal duration, the winters were short and mild, being spent near to the sun, and the summers longer and cooler than at present owing to greater distance from the sun; tlie loess beds however, suggest in their droughtcracked condition, that the summers were dry, and nor'-westers more parching; than they are to-dav. There are good indications that there were five glacial periods with intervening interglacial periods. New Zealand has experienced two post-tertiary glacial epochs the chief vestiges of the earlier being the "older gravels," much oxidised and decomposed and amongst and near the hills more or less tilted. These underlie the gravels of the Great Glacier age in tlio Canterbury plains. Some details of these were referred to, including proofs that the winters were severe enough in the lowlands to cause the rivers to be frozen, so that in spring floods ice lifted and bore away large chunks of the mud or sand or boulders of river or. pool bottoms. To this cold age the author attributes morainic deposits of the Marlborough coast, and near Ruapehu, Tongariro and Egmont, and the so-called Taieri moraine, but the latter is composed of gravels containing much rough rubble transported by river ice. That the interval between the two glacial epochs was a long one is proved by the amount of alteration of the older gravels, and more interestingly by the geographical changes effected during that time. Geological evidences indicate that after the older gravels were laid down the North and South Islands were torn apart at Cook Strait, the Southern Alps were uplifted from quite low ranges, probably .to greater heights than they now have. When the second cold age came on the frosts found easy prey in the newly upraised, shattered and fissured ranges, consequently the first glaciers of the period bore away vast quantities of huge blocks for moraine-making. The miles-wide fields of moraine eastward of the Tasman Valley and south-eastward of the Pukaki were instances of sucli frosts and ice-work. The paper contains a suggestion as to the manner in which New Zealand became glaciated. This reversal of the supposed 'conditions would cause a rapid retreat or even disappearance of the ' great glaciers. (The present glaciers exist under conditions of a minor glacial period in this hemisphere.) The paper concludes with a hope that recognition of the intimate relationship of the glacial vestiges in New Zealand with those of Europe and America will cause them to be looked upon with a new interest.