Art. LXX.—The Glacial Period of New Zealand.

By Thomas Mackay, C.E.

[Read before the Nelson Association, 5th April, 1875.]

To those who in their wanderings throughout New Zealand look with a geological eye at the many evidences they meet with of a glacial period, it is obvious that the moraines and drift formations—many of which form our minor watersheds—have been the result of the same action as that to which similar physical features in tropical climates are due, namely, the breaking up of vast bodies of long accumulated ice, with its stored up forces, in the high altitudes of their great mountain systems. There was doubtless a period in which the region of which this now insular country formed a part experienced greater extremes of temperature, while at the same time the mountain ranges were of a higher elevation than now.

The time, however, of this, or of the changes of eccentricity in the earth's orbit that occasioned the geological revolution, or whatever it may be termed, which supervened, is still to be discovered. By the forces exerted in the latter catastrophe the vast masses of rocks and diluvium were transported to the sites of, and piled up into, the moraines and drifts we now see around us. Assuming, therefore, the present hypothesis to be correct, if ever the periods of alternation of cold and heat in geological times can be measured, an approximate test of the time which has elapsed between geological epochs may be determined, but to do this a reconcilement between cosmical time and geological time must with some certainty first be established. Whenever such a complex problem is solved, a basis of calculation may then be formed by which to measure the distance of time at which our glacial periods happened. For the present, palæontological research is the best key, and when the critical tabulation of the large collections of New Zealand fossils has been completed by Dr. Hector, it will afford a surer criterion than formerly by which to test the several speculations that are current respecting the geological characteristics of New Zealand, and to establish more correct theories regarding them, particularly of recent formations.

While geologists are not yet able to mark the point of union between historical and geological time, nor competent to define when geological epochs terminate and the historical era begins, still, by the aid of palæontological researches and collections, comparisons can be instituted, and indirect inferences formed of the mineral and physical relations of geology proper with the conditions of existence which plants, animals, and the human race bore to each other in prehistoric ages.