Ancient Glacier Deposits.

I have elsewhere^† given my reasons for supposing that the greatest extension uf our ancient glaciers took place during the interval between the Pareora and Wanganui formations, and in the next two sections I shall bring forward the additional evidence bearing on the question that I have collected during my survey of Otago. Of course as glaciers still exist in our mountains, our glacier deposits must range in age from the most ancient period of their greatest extension up to the present time, and in this place I only propose to describe the more ancient deposits.

This, however, is easily done, for, with the exception of the Blue Spur already described, I as yet only know of two morainic deposits in the whole Province that I am inclined to refer to this period. The first of these is the immense accumulation of clay and angular blocks of schist of all sizes that is found on the eastern side of the Taieri Plain, extending from the Taieri River nearly to Otokaia, a distance of about three miles. This deposit is a confused mass of quite angular fragments of schist, some of them of large size and composed of mica schist with quartz laminæ, which must have come either from the neighbourhood of Outram, or down the Waipori River. They could not have come from Brighton, on the sea coast, as many of the blocks are considerably above the highest level of the mica schists there, and there is no conceivable agency by which they could have been brought from there. Consequently, although I could find no trace of striæ upon them, I have very little doubt but that they were placed in their present position by a glacier descending from the Lower Taieri and the Waipori River.

Internally this deposit shows no signs of stratification, and is quite morainic in character, but externally it forms low rounded hills between 400 and 500 feet high that cannot be distinguished in outline from ordinary clay hills. The deposit is situated nearly opposite the place where the Waipori debouches, through a gorge, on the Taieri Plain, and it extends over to the sea coast; but on the seaward side it is covered by water-worn gravels nearly to the top.

The second old morainic deposit is the high terrace-like hill between the Redbank Creek and Black Mount. This hill contains large angular blocks of gneiss, intermingled with water-worn pebbles, and as none of these angular blocks are found below Black Mount, I suppose that this hill represents the terminal moraine of the great Waiau glacier. But the hill has quite lost the shape of a moraine. The top is flat and level, the slopes and minor vallies are quite regular, and the angular blocks are mixed up with numerous rounded pebbles.

The former great extension of the New Zealand glaciers was first pointed out by Dr. von Haast, in 1862,^* and he attributed it to the effect of the glacial epoch, when the land was considerably lower than at present. In November, 1863, Dr. Hector, in his narrative of his geological expedition to the west coast of Otago, said that he thought that an elevation of the land equal to 2000 feet, combined with the greater extent of high land then existing but since removed "by the eroding action of the descending ice," would be almost sufficient to extend the glaciers to their ancient limits.^†

In 1864 Dr. von Haast published his report on the formation of the Canterbury plains, in which he abandoned his former theory, and adopted that of Dr. Hector; but he laid the chief stress on the supposition that when the land emerged from the sea "the physical feature was a high mountain chain, plateau like, but with depressions existing before the tertiary submergence, but now partly obliterated, running generally either on the junction of two formations, on the lines of faults, or on the breaks of bold anticlinal curves."^‡

In 1874, Mr. W. T. L. Travers, in another paper on the subject^† brought forward conclusive proof that New Zealand had never been covered by an ice sheet, as supposed by Messrs. Beal and Thomson, and in May, 1875, I read a paper to the Otago Institute in which I shewed by the distribution of the pleistocene and pliocene fossils that the climate of New Zealand had never been sufficiently reduced to account for the former extension of our glaciers; and that probably it was not in either pliocene or pleistocene times colder than it is now.