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Geology of the Provinces of Canterbury and Westland, New Zealand : a report comprising the results of official explorations

Exploration of the Head Waters of the Waimakariri, 1867

Exploration of the Head Waters of the Waimakariri, 1867.

Having visited all the principal rivers, of which the glacier sources are situated on the eastern water-shed of the Southern Alps, with the exception of the Waimakanri, I devoted that year's autumnal journey to that purpose, starting from Christchurch on March 7th. After following the usual road to Porter's Pass, I remained there several days, close to the summit of the Pass, and camped in one of the gullies, during which, I ascended the Mount Torlesse and the opposite ranges for detail geological and botanical examinations. Another day was devoted to an investigation of the interesting cretaceotertiary and younger tertiary beds round Castlehill station, which form an outlier of considerable size amongst older palœozoic rocks, and where the calcareous sandstones have been washed and weathered into most picturesque forms. Passing by the charming Lake Pearson, the present conformation of which may be traced to two gigantic shingle-fans at both ends, which have dammed up the water, whilst in the centre, it is nearly separated by two steep shingle cones, reaching almost the centre of the lake, we arrived at the Cass plains. Lake Grasmere is situated here, and through it the River Cass flows diagonaly. As soon as we left Lake Pearson, we crossed over morainic accumulations belonging to the old Waimakariri glacier, and which at one time had also covered the whole lower country with its vast ice masses. To these morainic accumulations, Lake Pearson, Grasmere and several small lakes, subsequently to be mentioned, owe their existence.

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Before reaching the Waimakariri, we crossed Goldney's saddle, and made rapid progress, the road along the ranges being finished and in good order. The splendid scenery upon which I had gazed with such admiration eighteen months before had lost nothing by being seen again. The broad river-bed, deep below us, with its numerous branches anastomosing and gradually getting narrower before it disappeared amongst the outrunning spurs of the Southern Alps, formed the central portion of the landscape. On both sides stood magnificent ranges, covered for several thousand feet with a fine uniform beech forest. As the eye followed them, the forest line gradually lowered, and before the central range was reached, it had disappeared, to give way to alpine vegetation, of which vivid green patches were visible from here. The background was formed by a high range, with large snow-fields between the rocky buttresses, from which several glaciers descended to lower regions. It is a truly New Zealand alpine landscape, only to be rivalled by one other on the whole West Coast road, and that of a different character, namely, the romantic valley of the Otira, not without justice, so highly praised for its beautiful and diversified scenery.

Arriving on March the 12th at the Bealey, we found this locality, where some 18 months previously a small township existed, now almost deserted, everybody, with the exception of the telegraphist and a sergeant of police in charge of the station, having left. So we had quite a choice of habitations, instead of being obliged to pitch our tents. During my stay at the junction of the Bealey, I once more visited Arthur's Pass, being able, in the almost continuous rock cutting along the banks of the river, to obtain very clear sections nearly up to the summit, whilst after the road had descended into the bed of the Otira, similar cuttings continued to offer reliable information concerning the geological structure of the central chain. The mountains on both sides of the Pass were ascended by us to a considerable height, and large and valuable collections made. The remarkable small rock wren (Xenicus qilviventris), of which I had obtained several specimens previously, was also found to enhabit the large taluses of debris and the morainic accumulations leaning on the sides of the high mountains. Although we were rather late in the year for collecting flowering plants, a very rich flora was found to exist on the summit of the Pass, where, like on all the alpine Passes visited in Canterbury, a considerable area is covered with boggy ground, water-holes, and lagoons, in and around which, a rich harvest of rare alpine plants was made. The geological features proved to be similar to those observed on the page break
Riverbed of Waimakariri with the Southern Alps, from the Westcoast road

Riverbed of Waimakariri with the Southern Alps, from the Westcoast road

page 147slopes of the Southern Alps, at the head of the more southerly rivers. There is the same endless succession of sandstones, slates, shales, and conglomerates of the usual character, and jointed in the same manner, continuing to the junction of the two Otira main branches, to which I followed the beds in question.

On March 15th, we started for the sources of the Waimakariri, and after crossing the river above the junction of the Bealey, where, owing to the remarkable fine autumn weather we were enjoying, it contained very little water, we passed for several miles over a very large shinglefan, here entering the main valley from the west, and which is such a conspicuous object in the landscape, when looking towards the Alps from the West Coast road. From the junction of the Crow river with the Waimakariri, the first true glacier, descending to about 4500 feet, was observed. It is situated at the head of the former tributary, and on the southern flanks of Mount Rolleston. Ten miles above the Bealey the valley begins to narrow considerably, and the spurs of the ranges now generally reach the water's edge. The weather, which hitherto had favoured us so much, now began to alter, and for two days rain poured down almost incessantly, in heavy showers. The high ranges around us, when visible through the clouds, appeared covered with a uniform sheet of snow, which quite altered the whole aspect of the country. However, in the intervals, geological, botanical, and zoological collections were made in the neighbourhood of our camp, and several specimens new to science were obtained.

On the 18th of March the weather cleared, and we started for the main sources of the river, which, owing to the opaque glacial colour of its waters, had previously been named the White river. Near the junction of the northern branch, the White river turns to the south, and its valley for about a mile and a half has still a considerable width; here, at an elevation of 3094 feet, the growth of the Fagus ceases. The view up the valley, narrowing with almost every step, now assumes, every moment, a grander and more alpine aspect. A high peak, with noble outlines, appears at the head of the valley, from which a glacier of considerable porportion descends. The mountains on the left bank also rise high into the sky, they are also covered with perpetual snow, from which small glaciers and torrents issue. Several of the latter form beautiful waterfalls, by which the grand scenery is still more adorned. The mountains on the right bank rise almost perpendicularly for more than 3000 feet above the valley, so that only here and there can snow page 148remain lodged on the lesser declivities. On both sides of the valley, clear signs of enormous glaciation are not wanting, and were also exhibited for many miles down the main valley, by numerous slightly sloping terraces along both banks, often as high as 3000 feet above the river-bed. About a mile above the junction of the northern branch with the White river, a low saddle—Harman's Pass—about 800 feet high, leads from the latter into the northern source-branch of the Taipo river. After two miles, the rocks on both sides now approach close, and for two miles more the river forms a series of rapids and smaller falls, possessing a different character from that of our larger glacier rivers near their sources. At several points old morainic accumulations cross the valley, through which the river has formed a narrow passage. The vegetation became now very rich, many of the alpine shrubs and creeping plants in seed, were visited by the Kea (Nestor notabilis), and an alpine variety of the Kaka (Nestor montanus), which, as we could observe, had also its nest, together with the Kea, amongst the nearly perpendicular rocks on the right bank. The latter (N. montanus) as we had repeatedly an opportunity of observing, can easily be distinguished from the common Kaka living in and near our beech forests, by its more soaring flight and peculiar notes.

Near its termination the valley is again considerably enlarged and has the form of an amphitheatre, into which the main glacier, about two hundred yards wide at its terminal face, descends to 4262 feet above the sea level. About half-a-mile from the head of the valley, at an altitude of about 6000 feet, a magnificent sight is offered to the traveller, by a large glacier broken up in the wildest and strangest forms, actually overhanging a perpendicular rocky wall about a thousand feet high, and only on one spot where a small rill could form, it descends for some distance in the shape of a gigantic icicle. Daring our descent of the valley, we had the rare sight of an enormous ice-fall of a portion of this glacier, pushed over the cliff and precipitated into the valley with a tremendous noise, warning us not to approach too near its channel, where, close by, on alpine meadows, a rich harvest of plants was obtained.

Another day was devoted to the exploration of the northern sources of the river, which, at its Junction, showed by the colourless character and the comparatively small amount of its waters, that it did not come from a glacier source. For more than two miles the valley of the northern branch, as it is called, has quite a park-like appearance, small groves of page 149beech forest growing on its grassy banks, which give it a charming variety. Two miles and a half above the junction the valley divides again, and a considerable stream descends from Mount Armstrong; half-a-mile further on, the so-called Browning's Pass is seen on the western side, (not to be confounded with the Browning's Pass at the head of the Wilberforce), 750 feet above the valley, according to Mr. E. Dobson's calculations, leading into one of the Taipo branches. The line of road to reach the summit of this Pass, begun by Mr. Dobson, and of which the details are given in his report upon the character of the passes through the dividing range of the Canterbury Province, is still discernible. The valley, at an altitude of 3981 feet above the sea level, is closed by a wall of rock, over which the river descends in a series of waterfalls, of which the lowest is about 50 feet, through a deep and inaccessible gorge. We were therefore obliged to ascend the rocks on the right bank in order to reach the sources. After climbing about 1000 feet along these rocky ledges, ice-worn and ice-scratched in a most remarkable manner, the valley opened up again, and amongst alpine meadows, three ponds were situated, the highest at an altitude of 5241 feet. From their outlets the northern branch of the Waimakariri is formed. High rocky walls surrounded us on three sides, with snow-beds, mostly of small extent only, lying in favourable localities, but without forming any glaciers. Some small glaciers of the second order were however seen descending from snow-fields of more considerable extent, reposing on the flanks of Mount Armstrong, and feeding the eastern main branch of the northern Waimakariri.

I remained till March 26th in the upper valley of the Waimakariri, occupied with geological researches, and adding to our botanical and zoological collections, to the completion of which my two companions devoted all their energy. Returning that day by the road to the Cass river which, after leaving the ranges, flows across an old lake-bed, formed after the receding of the huge post-pliocene glacier, we continued our road along roches moutonnées and amongst ancient moraines, over a remarkably glacialised country, to the Waimakariri, reaching the river again about three miles above the junction with the Poulter.

The whole triangular space bounded on one side by the Black and Craigieburn ranges, in which the sources of the Broken and Cass rivers are situated as far as the northern end of the Cass plains; on the second side, by the high ranges on the left banks of the Waimakariri forming the watershed between that river and the Hurunui; page 150and on the east by the Mount Torlesse range and its northern continuation, the Puketeraki range—was once covered by a huge glacier, above which some peaks, as for instance, Purple Hill, Magog, and Mount Binzer, stood as islands, whilst the greater portion of the smaller mountains having a roche moutonneé form, show that the latter were, during a considerable space of time, hidden below the great ice-sheet, and derived their peculiar forms from the astounding work of the great ice plough which had passed over them. When the great glacier retreated, a lake of considerable extent was formed, filling its former bed, and above which the isolated mountains and smaller ranges previously alluded to, stood as so many islands. Gradually this lake was filled with lacustrine deposits in its middle and deeper portion, whilst the mountain streams advanced at the same time with their shingle-fans, forming deltas. In course of time, the shingle deposits of the main river, advancing step by step, filled the whole with their enormous masses, resting upon morainic accumulations and lacustrine deposits. These shingle-beds form a plateau—a continuation of the Canterbury plains—the line being easily traced through the Wainakariri gorge. It is evident that the structure of these newer beds must appear very complex and bewildering, unless the key to the whole has been obtained. Thus in leaving the Cass and passing to the Waimakariri in an easterly direction, we first passed over alluvial beds, which, near Blackwater, a lonely tarn, give place to morainic accumulations; they are succeeded by roches moutonnées, between them the road passes, after which the valley of the Waimakariri is reached, where I observed lacustrine beds overlaid by thick post-pliocene shingle deposits, situated at least 400 feet above the present bed of the river. Instead of following the river-bed to the junction of the Poulter, the road leaves it about a mile above, and ascends to the downs on its right banks, passing over a succession of morainic, lacustrine, and fluviatile deposits. Every moment the view becomes more extensive, the traveller being here surrounded by mountains at least 6000 feet high, whilst deep below him in narrow ravines, the Waimakariri, and Poulter flow. Roches moutonnées rise in every direction amongst the level terraced ground in the foreground, the continuation of which, on the right bank of the Waimakariri, is clearly visible from here. After descending to the Poulter by a well-laid-out road, and crossing the river, a number of terraces, one rising above the other, brought us again on to the plateau. Here the station of Mr. Minchin is situated, where, being most kindly received, I established my head-quarters. On this flat, a page 151number of ice-worn hills rise above the younger deposits, amongst which the small but very pretty Lake Letitia is situated. Several days were devoted to examining the interesting structure of the newer beds and the effects of the enormous glaciation of the country, and of which I shall give some more details in the geological part of this Report. During this stay I followed the Esk—another branch of the Waimakariri—for some distance, where, besides the older palæozoic rocks, several younger outliers of greensand and calcareous sandstones occur, which have been broken through and covered by dolerites, to the hard nature of which they doubtless owe their preservation during the great ice age. Another excursion brought me to Lochnavar; which is reached by following the valley of the Esk for some ten miles, to a number of roches moutonnées, with a flat-bottomed valley between them, which brings the traveller into the broad valley of the Lochnavar. This remarkable valley, to which the small rill of water flowing in it does not stand in the least proportion, has numerous terraces on both sides. Above it ice-worn hills rise conspicuously—the whole having a most glacialised appearance.

Leaving Lochnavar station, and following its continuation towards the northern Poulter, we soon arrived at enormous morainic deposits, about two miles broad and reaching from one side of the mountains to the other, across the whole valley—the apex of the curves, formed by morainic accumulations, being directed towards the centre of the broad Lochnavar valley. Arrived on the banks of the northern Poulter, we looked down about 700 feet into the river-bed, deep below us, into which we had to lead the horses along a very steep slope, having all along a splendid view, in both directions, of the valley and the fine ranges bounding it. Whilst the valley of the river above the moraine was rather broad and well excavated, between the mountains, below it, it assumed the character of a deep rocky gorge, through which we had some difficulty in taking our horses to the junction of the Northern with the main branch of the Poulter. All tended to show that the channel below the moraine did not exist in the Great Glacier period, but that the Northern Poulter glacier, as shown by the size of the moraine, even after the glacier had already considerably retreated, still was nearly two miles broad, its outlet running in the broad valley of the Lochnavar as a large torrent, and joining the Esk in its middle coarse. This newly-formed gorge of the Northern Poulter is very wild and romantic, fine beech forest growing in every suitable spot; and a luxurious vegetation has sprung up amongst the page 152bold rocky walls, wherever the roots can find a hold in the fissures, and through which the effect of the grand scenery is still heightened. As a sign that this gorge is very inaccessible and seldom trodden by the foot of man, I may mention that in two localities we met with a small flock of sheep, covered with long wool, and which evidently had never been handled by man. After four miles travelling, during which we had been obliged to cross the river at least forty times, the valley opened and the junction with the broad valley of the Poulter was reached, in which travelling became comparatively easy. In this valley, the formation of terraces 500 feet above the river, is well exhibited; whilst still 1500 feet higher, or about 2000 feet above the river-bed, glacier shelves, with regular, slight slopes, are very conspicuous. On April 1st I left this interesting district, and, returning by the road to the right bank of the Waimakariri, I examined for several days the corresponding area, which stretches to the western base of Mount Torlesse, and where also a number of ice-worn hills rise above the moramic, lacustrine, and fluviatile beds. Here, also, several small lakes and tarns have been preserved, amongst which Blackwater is the most westerly. They are mostly surrounded by remains of ancient moraines.

On my return journey I devoted a day to an examination of the coal-bearing beds near Lake Pearson, and several days to an investigation of the very interesting series of tertiary beds of different ages, forming the Castlehill series, and where a rich harvest of fossils was made. On April the 6th, I returned to Christchurch having made, with the assistance of my two companions, large geological, zoological, and botanical collections, which were deposited in the Canterbury Museum.