Geological and other Reports
Whanganui, February 17, 1862
Sir,—On the 8th of January last I left this place for Rangitikei, accompanied by Mr. Samuel Deighton as interpreter, for the purpose of exploring the country along the course and towards the sources of the Rangitikei river; and as I have now traversed the country from here to Rangitikei, thence by the ascent of that river to the Patea country, thence across the open country to Taupo, and thus, heading the Whanganui river, descended upon its right bank, and from thence passed down stream to the point from whence I started, the journey, although tedious, enables me to dispose geologically of a large extent of country.
It will be seen in this report that I have had to modify several statements which I had previously made; but as geology is essentially a science of observation, one must always be prepared to admit fresh evidence, and to alter one's views accordingly.
In the ascent of the Rangitikei river, the drift, which is largely developed in the settled district, becomes comparatively unimportant, but may generally be seen capping the cliffs; and as it rests throughout on the tertiary rocks, I cannot recommend a search for gold in it; still less can I recommend sinking through a great thickness of sedimentarytertiary rocks on the chance of finding gold beneath; but bearing in mind that the “drift” of the Whanganui district is derived partly, and that of the Rangitikei, and from thence to the southward, principally from the abrasion of silicious slate and crystalline sandstone rocks, there is always a possibility of finding some gold in it. As the drift gravel is accessible in numerous sections of cliffs, this point can easily be settled by driving into them without going to the expense of sinking, by any one curious in the matter; but failing the discovery of gold in this upper drift, no gold can be expected before sinking through the whole thickness of the tertiaries, either sedimentary or volcanic, except possibly near the sources of the rivers.
I think my estimate of 600 feet may in the meantime do for all practical purposes, but the upper sandstone must sometimes alone measure at least 400 or 500 feet. Continuing the ascent of the Rangitikei, the blue clay forms the cliffs for a considerable distance, and higher up is succeeded by a soft rock, striped with frequentbands of sandstone a fewinches thick. This I suppose to be the representative of the coal shales of the Whanganui, although it somewhat differs in mineralogical character. Its characteristic fossil seemed to be “pecten.”
The dip of the rocks in the Rangitikei is generally greater than in the Whanganui and to the south west, from the Ruahine in the direction of Whanganui; but the rise in the bed of the river is rapid and continuous, and consequently the changes of strata intersected page 9 are few. The character of the Rangitikei and its adjoining country is similar to that of the Whanganui; but the river is very inferior for navigation and the district is not equal in beauty of scenery, although in the latter point it is in some respects unique. The deep narrow chasms, through which the river flows in its upper part are singularly beautiful, and the tributary Moawhanga, which we ascended on the 20th presents a cleft, perhaps 150 feet deep and only 18 feet wide, with perpendicular sides, and the trees meeting in an arched overhead, the beauty of which, clothed with ferns and other luxuriant indigenous vegetation, with the rays of light glancing down wards through the trees, can be easily understood. The principal tributaries of the Rangitikei fall into its right bank. The Hautapu and Moawhanga are the largest.
On the 20th we left the canoe, and ascended the cliffs on the banks of the Moawhanga, to Pawerawera, where we found no one at home. On the 21st we proceeded to Popotahi, and here we found very few inhabitants; only two men and some women and children. I had wished to have got fairly into the gorge of the Rangitikei in the Ruahine Range, which appeared to be about fifteen miles distant, where I expected to find the base of the tertiary rocks and ascertain on what they rested, but after some consultation here I found that I was neither supplied for the trip, nor, in consequence of the absence of the inhabitants, could I get the assistance necessary. The actual gorge of the Rangitikei is apparently in a very difficult country, the tertiary rocks, covered with dense forest and no doubt intersected by the chasms which I have described, lying high up on the flanks of the older rocks; and an exploring party ought to go well supplied, making up their minds to work gradually on, if only a few miles a day. Above the junction of the Moawhanga with the Rangitikei, two days poling up the main stream, lies the pa Te Awarua, and from this point the gorge in the mountains would probably be easiest explored. It is likely, however, that the information required might be obtained with little difficulty on the road from Patea to Napier, and had I been able to obtain horses at Patea I should have ridden a day's journey in that direction. It would be desirable to ascertain if the coal seams of the Whanganui extend to the Rangitikei, and this might be found out in the gorges of the mountains. I observed a small seam of semi-lignite at one point on the river, but it seemed to be local and of no importance, and belonged to the upper sandstone. It was a great relief to emerge from the deep clefts and dense forest of the Rangitikei on to the open country at Patea. Ascending a hill near Popotahi I could trace the ter-tiary rocks lying high on the flanks of Ruahine to a height of I should think not less than 2000 feet above the sea; also extending to the North and in direction of Napier, as far as the eye can reach. Some of the hills in the latter direction are capped with a scarped stratum, which I take to be the limestone of Ahuriri.
The question arises, how far do those tertiaries extend to the Southward? and I strongly suspect that they reach the Manawatu, if they do not extend still further.
Having with some difficulty procured a guide, and an old horse to carry our baggage, we proceeded towards Taupo on the 22nd of January, only reaching Pakehiwi on the first day, where we had to stop to change our guide. Our route lay through an open and well grassed country, but also presented a large amount of forest within sight. We crossed the Moawhanga by a bridge over the chasm, and here I found “venus” of a small kind. On the 2rd we passed through a similar but perhaps better country. At Turangerere, on the Hautapu, there is a beautiful waterfall, and here I again found “venus.” In fact, beds of these shells were found until within perhaps ten miles from the base of Ruapehu, when igneous products took possession of the surface. Turangarere was the principal residence of the late worthy chief Te Herekiekie.
We encamped on the 23rd at a place called Poutamurengi, on the banks of the Hautapu. This stream is a tributary of the Rangitikei, tokes its rise in the Ruahine, runs at first considerably to the Westward, but turning about this point falls into the right bank of the Rangitikei in the middle of the forest.
Our ascent from Patea, although not very perceptible to the eye, was evident enough from the change in the vegetation, and on the 24th we found ourselves traversing the bare and blasted volcanic country at the foot of Ruapeha and ascending the stinking bed of the Wangaehu. Here was pointed out the course of the avalanche which had destroyed the Wangaehu bridge. It proceeded from the top of Ruapehu, rushed down through a winding chasm or watercourse on the East side of that mountain, from thence in a broad stream across the plain, or rather inclined plane at the base; clearing off large patches of bushes and other vegetation, and so broadside into the Wangaehu, which here skirts the mountain; thence down that river to the sea; and, let me here observe, that as all the rivers from the Rangitikei to the Whanganui, both inclusive, flow in chasms, which may be blocked up at any time by an avalanche, by an earthquake threwing down the cliff, which actually happened in the Rangitikei in the year 1855, or by other causes, an accumulation of water may be collected which, when it bursts, would page 10 be dangerous to any bridge not constructed with a clear waterway.
It does not follow that the valleys of dislocation, or cracks, through which the rivers flow, have been been caused by plutonic action; probably they may have been, but shrinking of the mass is quite as likely a cause. The tertiary strata are very little disturbed except by local slips.
We next observed the stone on one side of which the Waikato rises clear and bright and flows to the North, while on the other side the Wangaehu with bitter, sulphureous, and nauseous water takes its course to the South. We had not proceeded far, however, before I observed that the Waikato received several affluents of as apparently nasty water as that of the Wangaehu. This is the highest point of the road, and as we gradually descended the vegetation improved, although all along the bases of the Ruapehu and Tongariro the plants are alpine in character. Kahikatea and black birch, full grown, but only a few feet in height are common. The mountain torrents are frequent and often very beautiful, but their height and rapidity during winter, and the depth of snow which is said to lie on these plains, must prove a great obstacle to a permanent road over the high country, which shall be open all the year. On the 24th we encamped on the banks of one of these torrents, called Waihohonu, and I think the prettiest of them all.
On the 25th we passed Roto Aira, and here was the first village we had come to since leaving Turangerere on the Hautapu, at which place we found no one resident. Compared with the population on the Whanganui the country we had passed through is comparatively uninhabited. On the Rangitikei, from the settled districts to Patea, we found only a few families. At Roto Aira the Maories were very civil, and they procured us horses to ride to Tokanu, at the south end of Lake Taupo, where we arrived in the evening. The block of volcanic mountains which we had just passed is of magnificent proportions, and if easily accessible would attract many visitors. Ruapehu is doubtless the most ancient, and is the most elevated land in the North Island, attaining a height of upwards of 9000 feet, forming as it were the chief gem of the volcanic range, placed in a setting of tertiary rocks. Probably its forces have long been extinct. It appears to me to be composed of the harder volcanic products, compact lavas, traps, &c., and puts me in mind of Tapuanuka, the inland Kaikora, in its shape and the apparent character of its products; although it is altogether a much handsomer mountain, with a more lengthened and graceful sweep at its base. Tongariro lies to the north of Ruapehu, and is a mountain of great site but very inferior elevation. It has every appearance of being a broken down crater. No visible signs of volcanic action now appear from the interior of this crater, but the grand active cone is Auruhoe, which is situated on the southern glacis or slope of Tongariro, and is therefore a lateral cone of that mountain. It is a regular cone of a very beautiful shape, and reaches a height above the sea of upwards of 6000 feet. According to the natives its last eruption occurred about twenty-five years ago, when it threw out large quantities of stones; its top fell in, and they say spoilt its appearance. It always sends forth volumes of smoke, and is said frequently to emit ashes, which disagreeably affect the eyes, and to give forth rumbling sounds and discharges as of cannon. It is a remarkable fact, however, that very few natives live in sight of the mountain, and at the same time sufficiently near to be able to give a good account of it. From the village at Roto Aira the cone of Auruhoe is invisible; and the natives at the south end of Lake Taupo are shut out from a view of the mountain by intervening hills; while those at the north end are too remote to observe phenomena correctly,—consequently a great deal may happen which is not observed. On the north west flank of Tongariro, outside the crater, there is a large puia, or hot springs said to be a specific for certain diseases, and which also emits large volumes of smoke and steam.
At Tokanu there is a very large area of hot springs, both in the delta of the rivers, which there flow into the lake, and on the surrounding hills, more particularly where the late chief Te Heu Heu was smothered; and as this was my farthest point I shall omit all mention of the geysers and hot springs, lakes and rivers, to the north eastward of Lake Taupo, which I know of only by hearsay. At Tokanu I found pebbles of grauwacke and quartz, in the middle of the hot springs. There was nothing to show whether they were an old deposit, or had been brought down the rivers from the Kaimanawa and deposited in the delta, which here runs far into Lake Taupo
I have said above that we carried the tertiary rocks to within about ten miles from the base of Ruapehu. When well abreast of that mountain, I observed a range rising parallel to it to the eastward, and forming the other boundary of the valley of the Waikato rivers which is called the Tongariro before it enters Lake Taupo. This range is called Kaimanawa,—is a powerful range, rising to a great elevation, and appears to run about N.N.E. in the direction of the Bay of Plenty; it is not a continuation of Ruahine, but is in a parallel line to it, and is evidently composed of slaty or grauwacke rocks. I was anxious to examine page 11 this range, and was promised horses by the natives for that purpose; but whether they could not really find the horses, or whether they were averse to my visiting the range and would not find them, I do not know; but as I did not care to ford the rivers on foot, I was obliged to leave Taupo without effecting this object. Very little of the range, however, lies in the Province of Wellington; it is principally in the Province of Auckland, although perhaps most accessible, at the southern end, from Napier.
At Tokanu we were detained for a week, partly trying to get the above-mentioned horses, but principally by constant thunder storms and rain. What with the damp and warmth of the atmosphere, and the heat of the hot springs, we found the climate to be most relaxing and debilitating. I was informed by the Rev. Mr. Grace at Pukawa, that pumice stone is excellent for building purposes, being watertight, and an excellent non-conductor. This may be worth knowing in those parts of the Island where other building materials are scarce and pumice is plentiful.
On the 3rd February we left Lake Taupo, proceeding over an open pumice stone country, with very fair grass, on which we observed some of the sheep owned by the Maories, until we were obliged to halt, by a sudden and heavy thunderstorm, at the entrance of the bush, where the path leaves the Rua Mata plains. On the 5th we had a very hard day's walk through the bush, and over a very steep road to the banks of the Whanganui river, which we found we had headed, and consequently struck on the right bank at a place called Terena. During this day we crossed a tributary of the Whanganui called the Waipare. Here I found “in situ” what I suppose to be the base rock of this part of the Island. It is a silicious slate with quartz veins. We waded the Whanganui several times and its tributary the Whakapapa with some difficulty, holding on by poles. The rivers were rapid and cold and the stones very slippery. On the 6th we reached Tapuia Kumera, where we found Topini te Mamako, the principal chief of this part of the river, from whom we received every facility. He informed me that two days' journey up the Whakapapa, which falls into the left bank of the Whanganui, that river runs through slate rocks, with crystals of some metal in them, probably either manganese or iron pyrites. This tends to corroborate my discovery in the valley of the Waipare and goes far to show that a floor or base of slate or other old rock, most likely tilted and folded, lies immediately beneath the tertiary rocks. At the Waipare I could not find a geological section, but it appeared to me that sedimentary tertiary rocks were above the slate, coverd again by pumice and perhaps tufa. I also found here a conglomerate of small pebbles, but not in a position to enable me to draw any conclusions.
The first sedimentary rocks which I observed in the Whanganui I have ventured to call coal shales. They are true fissile shales, striped by bands of a grey sandstone a few inches thick. A little below the Otunui they are seen to pass under the limestone at the base of the blue clay, but they appear again further down, and their upper surface must be near the river level for a long distance. I was unable to discover any fossils in the coal shales, but from the nervous anxiety of the Natives, who supposed every stone I picked up to contain gold, I was obliged to be very chary in my search, to avoid exciting their suspicions. That rock of the Rangitikei, however, which I take to be the representative of the coal shales of Whanganui, yielded a pecten which I suppose to be an undoubted tertiary fossil.
A little above the upper Paparoa rapids I found, among other fossils, a large cucullœa, which I am inclined to think will, on comparison, connect the blue clay of this coast with that of the East Coast and the Upoko Ngaruru, where the fossil cetacean was discovered.
The Upper part of the Whanganui has large deposits of pumice and volcanic ashes, passing into tufa, which sometimes cover the surface to a considerable depth.
I am not prepared to state the relative age of the volcanic and sedimentary tertiary rocks. The deposition of the coal supposes land above the sea at the time, with possibly several elevations and depressions. The eruptions of Ruapehu may have been going on during this period, and while the depression went on during which the higher tertiaries were deposited. The sedimentary tertiary rocks seem to keep at a respctful distance from the volcanic chain, as if the action of heat had prevented organic life within its range. The sedimentary rocks were not observed to be in any place covered by volcanic products, except by pumice, volcanic ashes, and rolled pebbles; all of which might have been carried by water, nor were the sedimentary tertiaries observed to rest upon volcanic rocks. The later volcanic eruptions seem to have thrown out principally pumice and ashes, and to an enormous extent.
The depression must have continued with perhaps some alternations until the deposition of the highest of the tertiaries, when the country must have gradually risen in its present form, the eruptions from some part of the volcanic chain continuing; and the sedimentary tertiary rocks, which would otherwise have presented an even surface, exposed to enormous page 12 denudation, in the present lines of drainage, which has in many places left only sharp ridges behind.
As the deposition of one rock presupposes a corresponding wearing away of another, it is difficult to suppose that the great mass of tertiaries have been formed by the wearing away of the hard slate rocks, assisted perhaps by volcanic ashes and other products, and one would naturally look for the remains of some softer secondary rocks which had supplied the material, but such have not yet been found in this part of the country.
As Topini was finishing his harvest, we found it impossible to press him for a canoe, and were consequently detained for four days at Tapuia Kumera. On the 11th we started from that place, and on the following morning reached Marai Kowhai; at the junction of the Ohura with the right bank of the Whanganui, and where the former river forms a splendid waterfall. Here, a short distance up, is a seam of coal, which unfortunately I did not see, but from which I hope to obtain some coal for inspection. As I had carefully noted the strata, my not having seen the seam is of little present consequence.
At Marai Kowhai we had heavy rain, so that when we started on the morning of the 12th, there was a heavy fresh in the river and many of the rapids were obliterated. Our rate of speed was great, we reached Pipiriki the same evening, carrying the bottom of the blue clay, or the top of the coal shales, about flush with the river past Tangarakau, near which point we met the man who had stopped us on our previous excursion poling up a rapid as we glided rapidly past him to Pipiriki. To give an idea of the scenery of the Whanganni I may state that I counted no less than one hundred and eight waterfalls which we passed in one hour, and that a corresponding number might be counted for two days' journey down stream; of course some of them are not permanent.
At Pipiriki we met the Rev. R. Taylor, who gives the estimate of Ropata Kora (a chief of Utapu) of the thickness of the Tangarakau coal seam at eight feet, and his own estimate of the Ohura coal seem at three feet.
After seeing the river in a fresh my views as to its navigation are considerably altered. I think it possible that steamers constructed for the purpose might navigate the river during the time that it is sufficiently high, which may be for several months in winter, and whenever there is sufficient rain in summer. The vessel would require to have considerable strength to stand bumps, and great power to put on at the rapids. The worst rapids might be cleared out a little and straightened; the numerous eel weirs would perhaps be found a considerable obstruction. The two worst rapids are Ngaporo and Paparoa—the former below the junction of the Maunga Nui te Au; the latter about half-way between the Ngarue and the Ohura.
I should consider the navigation of the river, however, with reference to the opening out of the country rather than as confined only to the working of the coal. Supposing a navigation to be in prospect, there are three points on the river of great importance.
The highest is Taumarunui, two or three miles below Tapuia Kumera, and at the junction af the Ngarue with the Whanganui on the right bank of the latter.
The Ngarue, shortly before, receives the waters of Te Ringa Motu, and from this point an open country is said to extend with only one intervening bush to Ngaruawahia; thus giving communication with the Waikato country, and from here it is likely that a good road can be got to Taupo.
The next point is Marai Kowhai, and the line of the Ohura. This river leads through a fine counry to the Waipa and the Maniopoto country; and here a coal seam crops out.
The next point is the line of the Tangarakau, which leads to Waitara, and two days' journey up this stream coal again crops out. Estimating our rate of speed down stream at six miles an hour, I make the distance of the Ngarue from the township 170 miles;—of Marai Kowhai and the Ohura river, 115 miles;—of Tangarakau river, 86 miles.
I did not think it advisable at this time again to broach the subject of the ascent of the Tangarakau, as it would certainly have ended in a refusal.
With regard to working the coal, supposing it to be shipped at Marai Kowhai, where it could be loaded in the Whanganui river itself, I look upon boats or barges as out of the question; at all events, if constructed of wood, they would soon be knocked to pieces in the rapids, A large canoe might carry two tons,—heavily laden she would probably require and would take on an average four days to descend the river to the settlement, and would require a crew of four men. The return voyage has also to be considered, of not less than eight days, so that no very great result can be anticipated supposing all the canoes, and Maories on the river, to be employed on the traffic. I would therefore strongly recommend a trial bore to be made, near the settlement, to ascertain if the coal strata lie beneath,—choosing a place for sinking as near as possible to the base of the blue clay, but taking care to avoid the actual valley of the river, in which dislocation might have extended through the coal. I would ad-page 13vise the bore to be driven through the whole thickness of the coal shales, to find if there is more than one seam. Should it be wished, however, to prove the coal seam at Tangarakau, it might probably be easily sunk through on the banks of the Whanganui itself. In this case the water carriage would be about eighty-six miles only, and the upper Paparoa rapids would be avoided.
I have stated that no gravel is now brought down from the heads of the Whanganui, but I now find that any amount may be. The river rises in Tongariro, as does its affluent, the Whakapapa; and the commencement of its course is through the volcanic zone. It runs at first in a direction to the northward of west. The Ngarue, which receives the waters of Teringamotu, is at the junction nearly half the size of the Whanganui. Teringamotu rises at the back of Lake Taupo.
I would again call your attention to the immense belt of forest country, thirty or forty miles broad, which extends from the flanks of Ruahine, sweeping round between the settled districts and the open country of Patea, to the Whanganui river, and so on to the westward into the Province of Taranaki. This country is full of rich and sheltered valleys, and is capable of supporting a large population, and of producing most valuable commodities; it is, except on the banks of the Whanganui river, almost without population, and even there it may be said to be in a state of nature. This country is very much broken, but for that reason it enjoys a remarkably warm and sheltered climate, suited, I should think, to the culture of the south of Europe. The lemon-tree of Ohinemutu speaks volumes. I look upon this district as peculiarly suited to the patient industry of German settlers, working in village communities, and giving mutual assistance in road-making and other things, as it is only by steady, unintermitting, and combined labour, that it can be reclaimed. It will be a pity to see this land left unoccupied, and the German settler would understand the culture required.
Of course, as the country rises in height the climate may be expected to be less genial, but up to the head of the Whanganui river we found maize, tobacco, and water-melons thriving.
Not one only, but several roads, should also be opened through the belt of bush, if for nothing else than to allow the driving of stock to Auckland. One line might be improved on the present road from Rangitikei to Patea, and it is said that a very small outlay would open a good road to the Taupo plains, starting from Upoko Ngaro, on the Whanganui, and taking a line between the Maungawhero and the Wangaehu. It would be desirable, if Possible, to avoid the highest part of the plateau below Ruapehu, as the road there could hardly be kept open in winter, from the quantity of snow and the swelling of the streams. The continuation of the eastern road, by the line of Rangitikei to Patea, might possibly intersect the Hawke's Bay road without getting to a great elevation.
The result of this journey may be stated as follows,—
That a broad belt of sedimentary tertiary rocks extends from the flanks of Ruahine, passing under the sea on the coast side, and circling round the volcanic chain in the interior, sweeps round to the Whanganui river, and from thence doubtless to the Western boundary of the Province of Wellington, and indefinitely beyond.
That apart from minor seams these tertiaries may be grouped into three strata, taken at a rough average thickness of 200 feet each, making an average thickness of 600 feet of tertiaries, at any point where all the strata are present.
The above is subject of course to any corrections, that an examination of the intervening country may render necessary.
That taking the height of the upper part of the Whanganu river, (say at the Ngarue), above the sea, ati the same height as Lake Taupo, or 1300 feet, (Hochstetter's estimate); and allowing 300 feet for lift of strata above the line of the river bed, observed between the settlement and the above-named point, and taking the direct distance at seventy miles, the dip of the tertiary strata will be represented by an angle subtended by a perpendicular of 1600 feet, with a base line of seventy miles.
That there is reason to suppose that the tertiary rocks rest unconformably on a base of slate, or other old rocks whose age has not yet been determined, and that these rocks may be found cropping out towards the sources of the rivers, where the volcanic and sedimentary tertiary rocks approach each other, and also in the Ruahine and Kaimanawa ranges.
That in these older rocks only, or in the drift derived from them, is there a chance of finding metals, but that no actual metallic indications have been discovered.
That the cool seam of the Ohura is probably a tertiary coal, and that it may be expected to underlie this settlement.
That the coal seam of Tangarakau is probably of the same age as that of Ohura; out not having been nearer than two days' journey from the outcrop, this point must remain for future investigation. I have, however, a report from Mr. Soulby of this place, who has tried the coal, and reports that it is very inflammable and probably full of gas, but does not yield a strong heat. He will endeavour to get the natives to send down a sufficient sample for inspection and analysis. He also states that it is got in large blocks.
As soon as the native mind is sufficiently tranquil it would be desirable to open up both the seams of the Tangaraukau and of the page 14 Ohura sufficiently to prove them. I have reason to suppose that the tertiary rocks extend at least as far south as the Manawatu, and it is now my object to ascertain that point, and to observe the geology of the gorge of that river, and then to take the Otaki river on my way to Wellington. It is reported to me that there are slate rocks in the bed of the Turakina. This I propose to inquire into, while on my way south. It is quite possible, but I hardly think probable, that they there crop out.
I have a suspicion that we have two drift formations, of different ages, as has I believe been found in Victoria, but am not yet in a position to prove it.
During the journey we found the natives civil and hospitable, without exception.