THE FORMATION OF THE CANTERBURY PLAINS.

Globe, Volume I, Issue 97, 22 September 1874, Page 4

THE FORMATION OF THE CANTERBURY PLAINS.

Dr Knight, president of the Wellington Philosophical Society, in his annual address, discusses the origin and formation of the Canterbury plains. He refers as follows to the subject : Captain Hutton has come to the conclusion that the formation of the Canterbury plains is due to the action of the sea. His argument is that the plains rise gradually from the seaboard with a gentle slope—that in places they warp round the spurs of the hills at the same level, and that no engineering power could form such level and extensive plains with their beds of water-worn shingle, but the ocean itself. That the singular fact that the Huruuui and Canterbury plains are on the same level is, in his opinion, an irresistible proof of the correctness of his views. I need scarcely add that if this view be correct there has been an elevation of the land of about 2000 ft. Dr Haast, on the other hand, assumes as sufficient for his views that glaciers of enormous size have moved down from the mountain ranges, and ploughed from the mountain sides the drift with which they have covered the more insignificant hills and formed the plains. That when the glacier outlets ceased to flow and deposit any more boulders and gravel, the rivers cut through the deposits until they reached the harder rock on which the deposits reposed. Tie necessities of this explanation require the admission, that a glacial period formerly existed in the Southern hemisphere—such as is generally admitted to have once existed in the Northern hemisphere. The weak points of Haast’s theory is, that it does not account for the distribution of the drift so as to form regular plains. It seems to me impossible to confound the irregular pell-mell deposition of glacial drift with the evident stratification, through the agency of water, which exist in the Canterbury plains. And I observe that Jukes, speaking of the glacial deposits in the low lands of Scotland and Ireland, and in the northern parts of England, even as far south as the northern margin of the Thames Valley, states that he has not the slightest doubt that they were stratified under the sea, notwithstanding the absence of sea shells from the greater part of them. Mr Travers objects to Dr Haast’s assumption of a glacial period, because of its remarkable character, and because we have no evidence whatever that such a change of climate as this supposes ever took place. Mr Travers thinks it more reasonable to conclude that a great elevation of the Middle Island above its present level would give a climate sufficiently cold, An elevation of the Middle Island of about 4000 or 5000 feet would, in Mr Travers' opinion, give a climate quite as cold as that assumed for the glacial epoch. The exigencies of these theories require either a change of climate to something like the cold of Greenland, which would satisfy Dr Haast’s requirements, or a great elevation of the land, Of course, when we use imagination in scientific matters, we have sometimes to draw liberally on Nature for support; and Mr Travers’ theory has an elasticity about it, for, if we object to an elevation of 5000 Teet as insufficient, we might double the elevation without being unreasonable. l he strength of Captain Hutton’s views springs out of the fact that he summons to his aid the great leveller and engineer—the Sea, with its never ceasing waves grinding the rocks into sand, and fashioning the boulders, and assorting the materials brought, to it, either by the glaciers themselves or by the rivers flowing from the mountain ranges, and spreading them out in vast plains Everything seems to show that plains of any extent are the result of the action of the ocean, or of vast inland seas. I do not question the statement that terminal moraines attain great size, and form mounds of rough angular fragments and debris, perhaps some hundreds of feet in height. These are the wastes of the mountains. What I contend for is, that nowhere is this confused debris scattered far and wide and levelled out into strata, forming plains of great extent by the action of glaciers. Captain Hutton admits that the glaciers of the Middle Island have been at some former time of much larger 1 dimensions then they are at present, and that there may have been a glacial epoch in the Southern Hemisphere. But he does not admit that such an epoch bears any relation to, or was contemporaneous with that of Europe. He would refer it, if it ever existed at all, to a period long antecedent. At the same time he guards himself by stating that we have no proof of a change of climate ; and as he considers an elevation of the land of about 3000 feet would be able by itself to account for a great extension of the glacier system, there is no necessity of calling in the aid of any other cause. The existence of a glacial epoch must not be denied here. It is a settled question among geologists that many of the changes on the earth’s surface are due to it. If I am not encroaching too much on your patience I will explain why I do not think we are justified in objecting to Dr Haast’s assumption of a glacial epoch in the Southern Hemisphere on the ground that it is of a very remarkable character, and as being supported by no evidence whatever; at any rate he follows in the wake of great men. We find Professor Agassiz startling the geological world by his strong opinion that a gigantic glacier once filled the entire valley of the Amazon, and he invited the members of the Alpine Club to go out and search for traces of glacial action on the mountains of Geanfi ; and I see by a notice in “ Science Gossip ” that on his South American Expedition he discovered evidences of glacial action on a scale so extensive as to more than suggest that the Southern Hemisphere has undergone a similar general glaciation to that of the Northern. The glaciation has been traced as far as the northern end of Chiloc Island. The Professor believes that during the glacial period the two hemispheres were capped with a sheet of ice of enormous thickness. Ancient moraines abound in South American valleys ; and in the Straits of Magellan one was found damming up ?a valley. But as I said before we must not overstate the action of glaciers. I see that Dr Hector in his address last year states that the mountain ice-cap performs its work of eroding the elevated rock mass into ridges and peaks ; and that after the first rough excavation has been performed, and only the hard cores of crystalline or tough metamorphie rocks have survived.the denudation, and when the valleys have all b; en perfectly moulded to perform their functions of ice gutters, then the process is admitted to be very slow. But to ascribe thus to glacier action the formation

of the very ridges and peaks of mountain tops is, I think, unreasonable. In fact, no larger amount of work can bo assigned to glaciers even of the glacial epoch, as the Duke of Argylo remarks in a quotation made by Mr Travers, than that of deepening the valleys which existed before, That on the one hand when the period began it found the existing system of hills and valleys in the main determined, and on the other that it cannot have left them exactly as it found them. But this is very far from the view which Dr Hector would seem to maintain — that mountain and valley with all their characteristic variety of surface have been cut out of the solid by enormous glaciers. Now, the very opposite is the case. It is the pre-existing configuration of hill and valley and mountain range, which has determined the movement of these glaciers, so that, as the Duke of Argyle says, the effects of glacial denudation become a comparatively narrow question. But whether we ascribe too much or too little to the existence of a glacial epoch, let ua for a moment consider what are the probable causes which might explain the extraordinary changes ef climate which have certainly existed in the earth in very distant epochs of time.