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General Considerations.

In treating of the Physical Geography of Canterbury, I have already alluded to the Great Glacier period of New Zealand, as having played such a conspicuous part in the latest history of the two provinces under consideration, that its effects are manifest everywhere as soon as the explorer advances towards the mountains. It would be beyond the scope of this Report to give all the details collected by me during the progress of the Geological Survey, on this interesting formation; the more so, as the principal results have already been laid before the public in several publications. Of these, my Reports on the formation of the Canterbury plains, and on the head waters of the river Rakaia —published by authority of the Provincial Government—are the principal ones, and to them I have to refer the reader who wishes to obtain fuller information on the subject. When, in 1862, I published my first account of the drift formation of Canterbury, I had, with the imperfect data before me, come to the conclusion that the Glacier period in New Zealand had begun during a submergence of the country, and that the country had gradually risen during that period to as high a level as it occupies at present. This conclusion was forced upon me by observing a few miles below the gorge of the Rangitata a series of beds resembling the boulder clays of Europe. Some minute pieces of shells were found by myself amongst them, appearing, from a careful examination, to be portions of a Unio; others, somewhat larger, page 372and of which one fragment had the markings of Venus (Chione) Stuchburyi of our seas, were given to me as having been extracted from the same beds, but a few years later I ascertained that they had been found by my informant at the foot of the cliff. They were doubtless obtained from a kitchen midden of a Maori encampment. A further reason for adopting such a theory was, that I met with apparently horizontal terraces and lines, together with erratic blocks high in the mountain ranges, some of them 5200 feet above the level of the sea, whilst other newer deposits, derived from lateral moraines and descending the valleys, had partly obliterated them. The latter I interpreted correctly, whilst the former (as on the other side of the valley the mountains were often not so high as to suggest the explanation that large inland lakes could have existed), I mistook for old sea beaches. However, when these old lines and beaches were examined by me with the spirit level in hand I found that they had either a slight fall, scarcely noticeable to the naked eye, and thus in that case were the banks of ancient river channels, or, in other instances, where the beaches were really horizontal they proved to be the margin of ancient glacier lakes, the waters of which had been dammed up by enormous ice masses crossing tributary valleys. Fine examples of this latter physical feature I observed in the Upper Ashburton and Rangitata plains, and on the right bank of the Tasman river opposite to the junction of the River Jollie. Moreover, if the country had been submerged for several thousand feet, Banks' Peninsula would, even admitting the possible occurrence of a great unequal ratio of subsidence between east and west, have been at one time entirely, or at least for the greater part, below the level of the sea, and in consequence, would have offered a very favourable locality for the stranding of icebergs, and the deposition of their detritus loads. However, after the most minute examination, I was not able to find the least sign of any boulder or pebble of other than local origin; therefore, the conclusion was forced upon me that the origin of these welldefined beds of the Alps was not of glacial or marine, but of glacier or subaerial origin, and all further observations both on the east and west slopes of the Southern Alps have amply confirmed that view.

In fact the results of my researches proved, that already during the beginning of the Pliocene period the country previously submerged to a considerable depth, had begun to rise gradually, and when emerging again above the sea level, appeared in a plateau-like form, but with some depressions which had existed before the tertiary submergence, now partly obliterated. As soon as the country had risen so high as to reach page 373the line of perpetual snow, the accumulation of névés began, being the more considerable as glaciers and large rivers had not yet begun their task of ridge making, in contradistinction to the action of wares and currents of the sea, on submerged lands, tending to wear off all eminences, and filling the submarine valleys with the debris. Another important cause for still greater accumulation of enormous névés must be assigned to the fact, that when the country had risen to its present level during the Glacier period, the drainage channels were only very imperfectly formed, consequently, a very serious impediment for the flowing off of the glaciers was first to be overcome before the snowfields could get rid of their annual increase. If we admit that only the same amount of atmospheric precipitation fell in the plateau-like ranges, as at the present time—about 115 inches in Hokitika and 100 inches at the Bealey—and that it took, to say the least, only a few centuries before the drainage system was properly developed, and supply and discharge somewhat balanced, it is evident that the snowfields must have assumed such enormous proportions that we canscarcely form a conception of their dimensions. When once the channels were formed, or the proper outlet was reached, the vis a tergo of the ice mass must have been of inconceivable power. That there was a blocking up of the ice masses in many portions of the Southern Alps is clearly shown by the anastomosing of the glaciers, of which the Rakaia, Ashburton, and Rangitata form notable instances.

Returning to the physical features of the country at the beginning of the Great Glacier period, it is evident that the configuration of the area now forming the Canterbury plains would have been a broad arm or channel of the sea running along cliffs of tertiary rocks from Timaru to Double Corner, and surrounding Banks' Peninsula as an island, whilst at the West Coast the ocean would have reached generally to the very foot of the Southern Alps. As before observed, the waters derived from atmospheric sources had only partly begun during the emergence of the land to open an outlet for themselves from the higher regions, cutting at the same time into the tertiary strata, which filled in favourable localities pre-existing valleys, and skirted the foot of the Alps to an altitude of 4000 feet. Under these circumstances the névés—considering the insular and peculiar condition of New Zealand, its principal range or backbone running from S.W. to N.E., therefore lying at right angles to the two principal air-currents the equatorial N.W. and the polar S.E., both bringing moisture with them —soon attained such an enormous extent, even if we do not take the page 374want of efficient drainage channels into account, that the line of perpetual snow descended to a much lower position than it occupies at present, even had the level of the land not been raised to a higher elevation than it now occupies. The natural consequence of such enormous accumulations of snow was the formation of glaciers of gigantic proportions, descending in course of time by the pre-existing or newly formed channels towards the sea, grinding down the rugosities of bottom and sides. The action of the glaciers beginning to lay open the rocks of the higher ranges soon offered sufficient material for morainic accumulations, first on the glaciers themselves, and afterwards at the terminal faces. The scooping action of the ice plough having once begun to eat into the plateau-like ranges, not only in the main course of the glaciers, but also in the lateral valleys, became more extended every day, and furnished more and more material for the formation of huge moraines. In their turn these moraines were destroyed by the great torrents issuing from the glaciers, and ample material was furnished for building up fan-like courses for the former. Boulders, sand, and ooze raised considerably the sea bottom along both coasts of this island, and the low land at the foot of the alpine ranges was more or less enlarged according to the physical features obtaining. It will thus be seen that without invoking the aid of cosmical causes, which might or might not have existed, I attribute the great glaciation of New Zealand to physical causes still now in operation, although on a much smaller scale, and without even assuming that the country had risen to a higher level than it occupies at present.

As I shall show, when treating of the morainic accumulations along the West Coast, it is clear that there at least the land could not have stood at a higher level. We are forced to this conclusion when we examine into the nature of the deposits occurring there. Of course I need scarcely point out that the more plateau-like ranges at the beginning of the Great Glacier period must have been considerably higher than they are at present, without assuming a change of level since then, because the destruction, brought about by the action of the ice masses upon them, must have been enormous. To make my view on the point clearer, I have added an ideal section No. 1 on plate No. 7, delineating the form of these plateau-like ranges, as they must have appeared after their emergence from the sea at the time when they stood nearly at the same level as we find them now. Taking the enormous destruction since then into account, of which this island at every step we take bears ample testimony, I think that, page 375assuming a higher altitude of about 2000 feet for the central range to be not too great an estimate, the mean elevation of the country (an important factor in our calculations) would hare been still greater, and from its form, still more favourable for the accumulation of vast snow-fields, by which the limit of the snow line would have been considerably lowered. I think, therefore, that I have made a very moderate estimate in assuming that the snow line was then 1000 feet lower than it is at present, taking all the combining physical conditions into account. When we consider the enormous amount of detrital matter brought down by the rivers into lower regions, the formation of the Canterbury and Westland plains, the huge morainic accumulations all above the sea level, and the still greater amount deposited in the sea, by which the sea bottom round New Zealand must have been considerably raised, it is clear that an almost inconceivable waste must have been going on for a long period of time to shape our Alpine ranges into their present form. I have introduced into this ideal section the actual section, No. 2 of the general plate, in which the existing perpetual snow-fields have been shaded with a darker tint. Considering their small size compared with those of the Great Grlacier period, and the fact that still glaciers of such considerable extent can be produced by these so greatly diminished snow-fields, it is evident that the prodigious [unclear: néés ], accumulating at that time on the higher plateau-like ranges, must have been able to form glaciers of such gigantic dimensions that we can scarcely form a conception of it. During the geological examination of the two provinces I have become acquainted with the boundaries of the principal glaciers during the period under consideration, and I have thought that their delineation on a map would convey, better than words can do, an idea of the peculiar form and enormous size they once possessed. In the map attached to this Report all the information at my disposal has therefore been given. Many of the glaciers had doubtless still greater dimensions than those marked in the map; but in that case the morainic accumulations near their former terminal face have either been washed away by the sea, or they are now covered with alluvium. The area of the largest glaciers now existing in our Alps has been shown by a darker tint, so that a comparison between both periods can easily be instituted.

Before proceeding to give a short outline of the principal glaciers of the Great Glacier period in New Zealand, it may be useful first, to state my reasons why I consider that the relations of land and page 376sea, as far as the level of the latter is concerned, were nearly the same as they are at present. A great deal has been written to show that the period in question occurred either during a partial submergence of the land, or when the latter stood at a higher elevation than it does at present. It would lead me too far were I to notice here in detail the different theories, but all the principal objections in the principal papers on the subject will be fully answered in the following resumé of the points at issue.

In alluding to the loess beds deposited on Banks' Peninsula I have already pointed out that they have never been disturbed, and we can therefore safely assume that they would have protected marine strata reposing on the volcanic rocks, had they ever been existing. Moreover, the formation of the Canterbury plains in their upper portion by morainic, and in their middle and lower portion by fiuviatile accumutions, is beyond a doubt. Doyne's levels have amply confirmed my views, that the different river systems have formed huge fan-like accumulations. At the same time all the boulders are sub-angular, and all the sand and ooze of fluviatile origin, with the exception of some beds belonging to the loess formation. Where, at the lowest portion of the plains on the northern banks of the Rakaia and near Lake Ellesmere, and in a few other localities to the north of Banks' Peninsula, a small fringe of marine shiugle has been deposited only a few feet above the present sea level, these beds can easily be recognized at a glance. The broad flattened form of the stones distinguishes them at once from the sub-angular fluviatile shingle or boulder deposits near them.

In the anniversary address of'1874, delivered as President of the Philosophical Institute of Canterbury on March 5th, and printed in Vol. VI. of the Transactions of the New Zealand Institute, I have answered the arguments of Captain Hutton, the former chief exponent of the submergence theory, who, in his report on the Geology of Otago seems now to have abandoned it altogether, and adopted the theory of greater elevation. However, in his Report on the North-eastern Districts of the South Island (Geological Survey Report, 1874) he has stated as his own observation, that there exists between Mount Hutt and Fighting Hill, at the narrowest part of the middle Rakaia valley, a shingle bar, according to him, exactly resembling a bar across a sound or harbour of the sea. I may, therefore, be allowed to offer a section of the locality in question on plate No. 7 (No. 3), giving the details, so as not to leave on the reader of that report any wrong page 377impression. In several previous reports I have shown that after the retreat of the great Rakaia glacier a large late was formed behind the rocks and morainic accumulations, through which in time a channel was cut; gradually this lake was filled up by glacier mud (silt), and by shingle and boulders brought down by the rivers emptying themselves into that lake, the latter generally covering the deposits of silt. A careful examination of these shingle or boulder beds—of which some small layers are flattened by wave action of the ancient lake, the greatest portion, however, having the usual subangular form—proves beyond a doubt that all the rocks occurring at the head waters of the Rakaia are represented, but no others. They are, without exception, of sedimentary origin, belonging either to the Waihao or Mount Torlesse formations. Were they brought into their present position by marine action, we should find an assemblage of rocks, such as we meet at present on the shingle accumulations between Lake Ellesmere and the sea; in which,. besides the sedimentary rocks of which the Southern Alps are built up, the quartziferous porphyries and melaphyres of the Rakaia, Ashburton, and Hinds, the felsitic porphyries of the Rangitata, the dolerite of the Timaru plateau would be represented, together with all the peculiar semi-metamorphic rocks found near Mount Cook and the Waihao country brought down by the Waitaki, and taken north by the currents and swell of the ocean, till they find a resting place near the northern slopes of Banks' Peninsula. We also meet near the slopes of Fighting Hill, and on a much larger scale on those of Mount Hutt, with the remnants of ancient moraines, between which several terraced river beds occur.

In proceeding to examine the evidence offered us by the extensive and remarkable morainic accumulations at the West Coast, our task has been much facilitated by the destruction they have undergone from marine action, so that we can study without difficulty their origin and mode of formation. It is easy to trace each of these huge post-pliocene glaciers, its frontal, lateral, and central moraines deposited during the retreat to its present position, to examine the material of' which they were built up, and thus to form a clear conception of the modus operandi of their deposition, and their partial destruction after-wards, by rivers on the one hand, and the sea on the other. It will be observed that in the map in illustration of the Great Glacier period, I have drawn the principal western glaciers as having had a much greater extension than the morainic accumulations that are still preserved, and page 378form such conspicuous cliffs along the West Coast. The reasons for doing so are the existence of enormous erratic blocks standing above the sea in front of the moraines, and the breaking of the surf in many localities far outside the coastline, so as to show that the morainic accumulations continue outwards for a considerable distance below the level of the sea. Examining in that district the intervening spaces between the ancient moraines, we find that they consist generally of level swampy or marshy ground. This at once suggests that when the glaciers advanced far beyond the foot of the ranges they must have extended either upon low level ground, or actually must have entered the sea for a long distance; the latter assumption gains in strength by observing that in front of the swampy ground, between the morainic accumulations, a shingle or sandspit has evidently been thrown across the material having travelled, as it does at the present time in a northward direction.Thus the sea appears to have once entered far between the glaciers and the morainic deposits flanking them being cut off in course of time in the same manner as Lake Ellesmere during its greatest extension was separated from the sea by similar deposits of shingle and sand, both travelling in a north and south direction towards what is now Banks' Peninsula. The lagoons thus formed between the ancient glaciers or their deposits were in course of time filled either by decaying vegetation and silt, or near the slopes of the Alps by the deposits of water-courses descending from the secondary ridges. When standing on some prominent elevation amongst the West Coast moraines, and looking over these low swampy forest covered plains dotted over in many localities with numerous ponds, it is easy to restore the picture as it must have appeared during the Great Glacier period.

Let us now examine if we have at present in the Arctic or even the more temperate regions, any analagous glaciers of the breadth of several miles, advancing 12 to 15 miles into the sea, till their frontal Portion is washed away. I have already alluded to Darwin's researches in South America, showing that in latitudes corresponding to the northern end of Stewart's Island or to the latitude of Central France glaciers of considerable size enter into the sea, their terminal face being ultimately washed away and carried along as huge iceberg and as the mountains where their [unclear: néés ] are situated are not nearly so high as the Southern Alps, similar conditions to those prevailing in New Zealand during the Great Glacier period must still reign in these latitudes.

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Turning towards the Arctic regions, we find that amongst otters the Iceblink Glacier on the shores of Greenland advances into the sea forming a promontory 13 miles in length. A submarine bank formed of morainic accumulations in the shape of a semicircle lies a few hundred yards in front of it; only occasionally blocks of rocks ordebris in larger masses are scattered over the surface of this remarkable glacier. Its thickness is estimated at 5000 feet, and thus the ice grinding upon its bed with prodigious force must form silt in enormous quantities. Judging from the observations made upon the mountains in the Polar regions, also during our Great Glacier period by far the greatest portion of our Southern Alps was doubtless covered with perpetual snow, so that the New Zealand Glacier period, in order that such an immense quantity of morainic matter could be transported must have been of very long duration. Taking all these facts into consideration, there is nothing startling in the, assumption, that in the height of that period in New Zealand, the West Coast glaciers advanced the same distance into the sea as the Iceblink Glacier does at the present time; an assumption forced upon us when we consider the character of the deposits between the morainic accumulations forming the coast line. Thus, whilst the nature of the beds formed during the Great Glacier period along the east base of the Alps, where they are not destroyed or covered by fluviatile deposits, clearly indicates that they could not have been formed during a submergence of the land, the western morainic accumulations and the littoral beds between them go far to prove that no considerable rising of the land could have taken place; in fact, it appears that the same relations of land and sea obtained then, as we find them at present. I may here observe that as far back as 1867, in a paper read before the Geological Society of London, I proposed that the Ice age of New Zealand should be named the Great Glacier epoch; whilst in a former paper read before the same Society on January 15, 1865, I brought forward many reasons to show that the climatic conditions of that period / must have been nearly the same as they are now, a conclusion confirmed by Captain Hutton, who from the examination of a number of pleistocene and pliocene fossil shells, drew the inference that the climate during those times was not colder than it is now. (See Captain Button's Paper "On the Cause of the Former Greater Extension of the Glaciers in New Zealand," Transactions N.Z. Institute, Vol. VIII, page 383 and sequ.) He has also followed my example and adopted the name of Glacier Period for the era during which the New, Zealand glaciers reacted their greatest dimensions.

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In a paper by Count Graston de Saporta, in the Compte rendu of the Seventh Session of the "Congres International d'Anthropologie et d'Archologie Préhistoriques," Stockholm, 1876, Vol. I, some further interesting conclusions on the same subject are offered to us. The learned author in examining a series of fossil plants collected in quarternary tufas at Moret (Seine et Loire), France, of which several —such as the ficus carica—now only grow in the south of France, comes also to the conclusion that during the Glacial period of Europe (or, as he now proposes to call it more correctly, the Glacier Period of Europe) an equable temperate but moist climate was reigning, that this period continued during a long space of time, and that in the valleys, on the slopes of the Alps and of other mountain chains, there was ample room for the existence of a rich animal and vegetable life. Count de Saporta does not assume that the level of the country stood at a higher level than it does at present, but believes that the elevation of the mountain chains from the tertiary seas, together with greater humidity of the temperature, were the principal causes of the extension of the glaciers. He further concludes, that this extension took place before the quarternary period, and that probably already during pliocene times the phenomenon reached its apogee. Consequently the views of this eminent palæontologist are quite in accordance with those advocated by me for nearly fifteen years at the Antipodes, and thus similar simple but effectual causes are assigned on both hemispheres to have produced the remarkable extension of snow-fields and glaciers, of which a delineation has been attempted for Canterbury and Westland in the map attached to this publication. As already pointed out, we find dinornithic remains not only in the silt and loess beds, but they are also met with in the alluvial deposits formed by the large torrents once issuing from the gigantic glaciers, and even in the morainic accumulations themselves. There is thus ample evidence that the moa existed and flourished during the whole of the Great Grlacier period. Now if we examine the map illustrating this chapter, and remember that by far the greatest portion of the Canterbury plains, together with smaller plains of similar origin in other portions of this Island, did not exist, it is difficult to conceive how these large birds could have been flourishing on such comparatively small space of ground—bounded on all sides by vast snow-fields, glaciers, and great torrents. It has been shown by me, and as I think so far conclusively, that there has been neither a great rise or fall of the land during the Great Glacier period, and there remains therefore, if we wish to admit a greater extension of the land in that era, only one page 381other possibility, namely, that from some cosmical or physical causes the level of the sea might have stood at lower level than it stands at present. We have been always accustomed to hear it stated as an axiom that whilst the land sinks or rises, the level of the sea is always the same. It will thus appear heterodox to believe in the level of the sea undergoing, according to changes in the crust of the earth or in the configuration of the land (not to take cosmical agencies into account), more or less considerable oscillations. However, I am convinced that future researches will tend to prove that such changes have repeatedly taken place, and that the character and distribution of plants and animals have been greatly governed by them. Mr. A. R. Wallace, in his valuable work on the Geographical Distribution of animals, when speaking on the same subject quotes the views of Mr. T. Belt,^* and gives afterwards his own views on the subject. I can do no better than quote his own words.

"One of the most recent, and not the least able, of the writers on this question (Mr. Belt) shows strong reasons for adopting the view that the Ice period was simultaneous in both hemispheres; and he calculates that the vast amount of water abstracted from the ocean and locked up in mountains of ice around the two poles, would lower the general level of the ocean about 2000 feet. This would be equivalent to a general elevation of the land to the same amount, and would thus tend to intensify the cold; and this elevation may enable us to understand the recent discoveries of signs of glacial action at moderate elevations in Central America and Brazil, far within the tropics. At the same time, the weight of ice piled up in the north page 382would cause the land surface to sink there, perhaps unequally according to the varying nature of the interior crust of the earth; and since the weight has been removed the land would rise again, still somewhat irregularly; and thus the phenomena of raised beds of arctic shells in temperate latitudes are explained."

"Now it is evident, that the phenomena we have been considering— of the recent changes of the mammalian fauna in Europe, North America, South temperate America, and the highlands of Brazil—are-such as might be explained by the most extreme views as to the extent and vastness of the ice-sheet; and especially as to its simultaneous occurrence in the Northern and Southern Hemispheres, and where two such completely independent sets of facts are found to combine harmoniously, and supplement each other on a particular hypothesis, the evidence in favour of the hypothesis is greatly strengthened. An objection that will occur to zoologists may here be noticed. If the Grlacial epoch extended over so much of the temperate and even parts of the tropical zone, and led to the extinction of so many forms of life even within the tropics, how is it that so much of the purely tropical fauna of South America has maintained itself, and that there are still such a vast number of forms, both of mammalia, birds, reptiles, and insects, that seem organised for an exclusive existence in tropical forests? Now, Mr. Belt's theory of the subsidence of the ocean to the extent of about 2,000 feet supplies an answer to this objection; for we should thus have a tract of lowland of an average width of some hundreds of miles added to the whole east coast of Central and South America. This tract would, no doubt,, become covered with forests as it was slowly formed, would enjoy a perfectly tropical climate, and would thus afford ample area for the continued existence and development of the typical South American fauna, even had glaciers descended in places so low as what is now the level of the sea, which, however, there is no reason to believe they ever did. It is probable, too, that this low tract, which all round the Gulf of Mexico would be of considerable width, offered that passage for intermigration between North and South America, which led to the sudden appearance, in the former country in post-pliocene times, of the huge megatheroids from the latter—a migration which took place in opposite directions, as we shall" presently show."

Without giving altogether my assent to such theory, it nevertheless, will be of some use to apply it to New Zealand, and to see what the effects of the lowering of the sea level for 2000 feet would have been. page 383In the first instance the plateau-like ranges would rise still 2000 feet higher above the sea level than assumed by me, and consequently the size of the snow-fields would not only become of still larger extent, but for this reason would descend to a still lower position. At the foot of these high ranges a plain of considerable extent, sloping gently downwards to the sea, would surround the three islands and unite them into one, Cook's and Foveaux Straits forming both broad valleys. In these plains a luxurious vegetation would spring up, offering ample nourishment for a great number of birds, of which the extinct Dinornitliidæ were forming the most conspicuous part During such physical aspect of the land these large birds would have found an almost unrestricted passage from one part of the united New Zealand to the other. Moreover, peculiar climatological conditions then reigning would soon slightly differentiate the species, to become still more decided when through the rising of the ocean the valley of Cook's Straits would again become an arm of the sea. Such a submergence would, if the theory in question is correct, have occurred at different times, judging from the fact disclosed to us, that the glaciers repeatedly advanced and retreated. Consequently, along the East Coast the glacier torrents would build up their great shingle fans, gradually decrease in velocity and flow at last as broad rivers through rich gently sloping lands for a considerable distance. A different state of things would obtain at the West Coast; here the retreat of the sea would also lay dry a belt of slightly sloping level land along the base of the Southern Alps, and over it the large glaciers would advance fifteen to twenty miles, throwing up their lateral moraines on both sides. The ocean rising again, so as to assume its former level, the waters would of course advance between the morainic accumulations; the same process as already described would then take place. Shingle and sand-bars with lagoons, often of considerable extent, behind them, would be formed. These lagoons would gradually be filled up with decaying vegetation and the accumulations of fluviatile character brought down from the slopes of the mountains forming their eastern boundary. Although, as before observed, I am not as yet in a position to pronounce for or against Mr. Belt's theory, I have nevertheless thought it only right to show that, so far, all the physical conditions of New Zealand during the Great Glacier period, and the abundant animal life then existing, could be explained by it, and I shall leave it to future days to adopt or reject this ingenious theory, when still more facts have been accumulated and more light thrown upon this interesting period of the Earth's history.