Geological and other Reports
Wellington, February 14th, 1863
Sir,—In forwarding to you a copy of a report which I have received from Mr. Brough Smyth, of Melbourne, on specimens of rocks sent by me for examination, from various parts of this Province, I shall take the opportunity to point out page 14 what my plan of operations has been, and also show wherein I agree with Mr. B. Smyth's very able and valuable suggestions, and where, from causes of which he would necessarily be unacquainted, his views cannot perhaps be carried out.
In proceeding with the Geological Survey of the Province I have thought it advisable, first of all, to obtain a general knowledge of the whole rock formations within its limits; so that when it became necessary to employ men upon the Survey, I might be able to go on with continuous work; otherwise they might have been frequently unemployed, waiting for me to know in what direction to turn.
The kind offer of the Honorable G. S. Evans, Postmaster General in Victoria, to submit specimens of our rocks to the “Savans” in Melbourne for examination, came in aid of my views, and is the more useful, as we have no analytical chemist in this Province, and that, should I attempt to assay minerals myself, it would take up much time, probably the results could not be relied upon, and even the necessary re-agents and laboratory plant cannot be procured without sending to Australia for them.
I therefore collected and sent to Melbourne specimens of rocks from many parts of the Province, but more particularly from these ranges, and awaiting the report, I made such excursions, especially those described in my last letter to you of the 11th instant, as, combined with my explorations last year, enable me to grasp all, or nearly all, the leading Geological features of the Province. By this means I have narrowed the area within which the search for minerals may be expected to be successful, to the main ranges of Rimutaka, Tararua, and Ruahine, with their spurs; the Aorangi range at Cape Palliser, and the Kai Manawa range in the Taupo country. I except coal, of which more hereafter.
You will observe in Mr. Brough Smyth's report, that granite appears among the specimens sent by me from the Upper Hutt. This confirms the opinion of that eminent geologist, the Rev. W. B. Clarke. Doubts, however, having been expressed, I have preferred waiting for confirmatory evidence before announcing the fact.
The theoretical proof which I gave in my letter of December 18th. 1861, of the existence of the “gold constants” in these ranges, is now confirmed by the discovery of granite, combined with the evidence of the ancient character of the bulk of the stratified rocks.
The granite is found in the ridge behind Mr. J. Brown's, in the Upper Hutt, which bounds on that side the Mungaroa swamp; and I have also found it on the Mungaroa Hill. It is very fine grained, and may easily be mistaken for a sandstone. It will doubtless be found nearer Wellington, and may come into use as a building stone. Near it is sandstone with quartz veins, and mudstones of two kinds, but I cannot yet say in what sequence.
With regard to metamorphic rocks, although the semi-crystalline sandstones and other rocks may be said to be of that character, yet as there are neither gneiss nor mica schists within these ranges, it will be advisable to abandon the term as applied to the rocks generally. The fact is, that the more the country is examined, the less metamorphic do the rocks appear.
Thin quartz veins appear to penetrate many of the rocks of these ranges, riddling them in all directions; but the larger quartz lodes are by no means so prominent as in the gold regions of Australis. That powerful lodes of quartz and other vein stones however traverse the rocks, every exploration tends to show; and I can mention one quartz lode fifteen feet wide and many others besides of considerable thickness. I believe the geological hammer now requires the aid of the pickaxe and crowbar, to expose the mineral veins.
Quartz lodes and other mineral veins seem principally exposed in the fractures of the anticlinal axes, which bears out my original impression that minerals will be found to lie deep, and this view will also affect the argument as to the locality of alluvial gold diggings.
If gold lies deep in the rocks while “in situ” the wearing away of these rocks (particularly as here in deep and steep vallies) will deposit it in the lower vallies only, and it may be plentiful there, while entirely absent from the higher ground.
It is suggestive that the rock taken from Mr. Barraud's well should resemble rocks from a district where sulphide of antimony and chrome iron are found, these being two of the minerals reported in the pyritous quartz lodes of the Petoni road. The sandstone with plant impressions, (No. 37,) from Porirua, being decided, on the high authority of Professor McCoy, as of mezozoic age, which page 15 with regard to coal, means oolitic, (the age of at all events the upper beds of the Australian Newcastle coal seams); and the mudstones being declared Palæozoic and probably silurian, it follows that we have sedimentary rocks of two eras in these ranges, folded however together in such a way that I foresee great difficulty in drawing the line of demarcation.
Mr. Brough Smyth's remarks with regard to gold seeking show a masterly grasp of the subject.
A reference to my letter to you of October 21st 1862, will show that I have most faith in gold being found, in the North Island, in the continuation of a line from the Middle Island Gold Fields to Coromandel, and that the present evidence is in favor of micaceous and talcose schists as the best gold bearing rocks of New Zealand; but I have also strong reasons to show, why the search for drift gold in this Province should not be hastily abandoned. I will first of all dispose of Barraud's well. This well is sunk for a few feet only through a sandstone and a felspatho siliceous rock. These rocks were said to be intersected by a vein stone, which was covered with rubbish when I visited the well, and unfortunately on the following day it was bricked up. There is neither drift nor alluvium above the rock and only an inch or two of soil.
That gold dust might have been thrown into the well is possible; but the specimens sent to Melbourne were collected from the rubbish heap afterwards, and therefore not likely to contain any foreign mineral. I shall endeavour to make a further examination, particularly as more grains of gold are said to have been found in the neighbourhood and as I see some appearance of mineral veins close at hand.
I must now make some small corrections as to Mr. Brough Smyth's idea of our mountain chains. His view is, naturally enough, that our main ranges threw off spurs East and West, spreading across the country, whereas the remarkable feature is this, that the mountain ranges of the Rimutaka, Tararua, and Ruahine, including all the mountainous country in this neighbourhood, pass like a wall to the N.N.E. the spurs keeping on the whole the same direction as the main ranges. Of course one does not speak of a wall as built by a stone mason, or rigid line, nor do all the spurs and ridges adhere to a strictly N.N.E. course, but such is the main direction. The main strike of the rocks, being I should say about North (magnetic), with however many exceptions.
Most of the maps give an erroneous impression, by marking a range, curving from the Ruahine N.N.W. towards Taupo, which range does not exist, although the broken tertiary plateau may there reach an elevation of 2,000 feet.*
In its broadest part, from the coast opposite Mana to the Wairarapa, the main range does not appear to exceed twenty three miles wide. At the gorge of the Manawatu, the breadth following the curves of the river, is only about seven miles.
These mountains have assumed their form, less from upheaval than from lateral pressure. The strata are accordingly bent and folded upon each other, and the ranges are separated into a succession of sharp and nearly parallel ridges, culminating in height towards one or more central axes, but high and abrupt also at both sides, where the sea, or the tertiary rocks, meet them in a horizontal, or nearly horizontal line.
One consequence of this conformation is that the rivers, while within the ranges, run in ravines, rarely as in the instance of the Hutt, expanding into vallies.
If we take the valley of the Hutt as an anticlinal axis near the centre of direction of the range, we there find, in the central axis, the granite of the Upper Hutt and Mungaroa; but I have strong doubts whether we shall find it on the surface in the high parts of Tararua, although it may be assumed to form the hidden nucleus of that range. The basalts, like the diorite rocks of the Canterbury Province have not yet been found “in situ,” and are not likely to appear in a prominent way; and the only rock which I can venture to call lava, in this main range, is the red rock of the Rimutaka, (on the authority of the Rev. W. B. Clarke,) but where it is found, and elsewhere in these ranges, there are no signs of volcanic vents.
The stratified rocks, sand stones, mud-stones, slates &c., seem to, and I think will be found to continue to, occupy the main part of the ranges.
The accumulations of drift on the Eastern side of the ranges are fully equal to those on the West, and the tertiary rocks may be said, with some exceptions, to be of the same character and thickness on both sides of the main range. Mr. Brough Smyth, suggests as particularly worthy of immediate attention, the basins of the page 16 Hutt, the Waikanae, the Otaki, the Manawatu, the Rangitikei, and the Whanganui. I would omit the word immediate in reference to the three last named of these rivers and substitute for their names those of the Ruamahunga, and its tributaries on the right bank, the Waipoa, the Wai Ngawa, the Waiohine and the Tauhere Nikau, (perhaps this last cannot be called a tributary.)
Although I should like to see the head waters of the Whanganui prospected, yet, even supposing the natives would consent, the expense of a party would be enormous in proportion to the work done. I only found about two yards of the ancient rocks during a journey of some hundreds of miles in that direction, and then in the bed of the Waipare, a tributary of the Whanganui, with the hills formed I believe of tertiary rocks, rising at an angle of 45° or thereabouts, on both sides, to a height of say 700 feet above the bed of the stream. I consider that the Upper Whanganui, must wait the progress of development of the gold fields from Coromandel through the Waikato country, which may throw sufficient light upon the subject.
The same remarks will apply to the Rangitikei River, and those rivers lying between it and the Whanganui. The heads of these rivers would answer Mr. Brough Smyth's idea of searching towards the sources of the streams, but a prospecting party to explore them must be fitted out and kept supplied at great expense and must be prepared for very deep sinking, and as yet there is no road.
With regard to the Manawatn, although old drifts may lie beneath the tertiaries on its banks, and may eventually be worth sinking for, if we find any reasons to warrant the outlay, the river itself is most unlikely for gold. It presents the curious feature of rising in the tertiaries of the East Coast, bursting through the main range and thence again passing through tertiaries to the sea. The whole course of the river through the ancient rocks does not exceed seven miles and its stream there occupies the whole breadth of the channel.
This brings me to the main point o my argument, which is, if gold exists where is it to be found, as drift and alluvial gold?
I have endeavoured to show the character of the mountain range and from this it will be seen that in general the rivers while confined to the range, run in very narrow and perpendicular channels. After entering the mountains and ascending for a few miles the beds of the streams, the ascent is rapid in the extreme, the drift disappears and the waters rush over a rocky bottom, or over large boulders of the surrounding rocks, and therefore drift gold, if present, could only be worked for a comparatively short distance up the mountain beds of those rivers.
Old drift gravels and clays may certainly be found in various places on the hills, as on the Mungaroa hill to a height of between 700 and 800 feet, but in general the rock is covered by a thin stratum of soil only, and where that is he case of course there are no diggings.
If we then consider the great denudation which has removed the rock from these vallies, say in the glacial epoch, we may ask where has the material gone to? The answer is obvious. It does not lie, or only to a small extent, within the hills, but has been swept into the Wairarapa country on the East, into the basin between Kapiti and the main range, on the West; and into the Hutt Valley on the S.S.W.
If these rocks contained gold, most, if not all it of would follow the same route.
I therefore would suggest that in a search for drift gold attention should be first directed to a careful examination of the Valley of the Hutt; and also, what I have already hinted at, that the question of grappling with deep sinking in the Wairarapa and perhaps also on the West Coast should be considered, combined with an investigation of the river beds previously mentioned as far as practicable.
As Mr. Brough Smyth also suggests that gold may be looked for in unexpected formations. I would not omit the blue clay. Although it is a fossiliferous rock it has a great appearance of being a drift formation, and I submit the following theory of its deposit, say to the Eastward of the Rimntaka and Tararua.
Suppose great degradation going on in the glacial epoch, along the Eastern vallies of these ranges and the materials carried to the Wairarapa,—what would be the natural order of deposition? Why, that the heavier boulders would be left in the vicinity of the range, while the lighter particles of earth, clay and sand would be carried to a greater distance. As a consequence one may expect both deposits to be, in places near the line of demarcation, mixed together; and as the page 17 lighter materials would be soonest exhausted, a deposit of gravel would latterly form over the clay. All this is carried out as far as I can yet speak. I have not as yet been able to find the blue clay to the Westward of the Ruamahunga, and the other conditions are found towards, and to the Eastward of that river. The elevated beds of gravel and blue clay, lying still farther to the Eastward, might not at that time have been upheaved by the force along the axis of elevation of the East Coast. Now, if the denuded rocks were gold bearing, most of the gold would be deposited, with the heavy gravel near the mountains, but lighter particles might accompany the blue clay to a greater distance.
On the other band the gravel and the blue clay may mark different, although consecutive periods.
The gold question will not be set at rest until the Wairarapa and the West coast plains are bottomed at several points.
Now that I have acquired a general knowledge of the rocks of the Province, I quite agree with Mr. Brough Smyth, that my attention should be directed to a minute investigation of some limited district. What I should now propose, with regard to the Geological Survey and apart from a search for gold, would be to make a detailed survey of the rocks of this range from East to West, mapping them and collecting specimens of every stratum taking for the purpose the only lines on which anything like a complete detailed survey can be made, viz, the scarped ends of the ranges from Terawiti to the Wairarapa and the next section further North, from the sea beyond Porirua, up the line of road to this harbour and thence over the Rimutaka to Featherston.
These traverses are absolutely necessary to show the sequence of the rocks and form a basis for further explorations, and as I find fresh mineral veins every time I cross the Rimutaka, we might expect to make some valuable discoveries. But I should like first to know the views of the Government as to the duty of the Government geologist in a search for gold.
Ought I now merely, as above, to point out the proper localities in which to look for that metal, and leave it to private enterprize to complete the research; or would the Government wish me to examine for the above purposes the localities indicated, viz the vallies of the Hutt, &c.
In the latter case I should require a properly appointed party of three or four men, with tents, tools, a Californian pump, and a pack horse, with a good foreman, while if the search for gold should be left to private enterprize, a smaller party would suffice for the detailed survey.
Such an undertaking as the bottoming of the Wairarapa valley would necessarily require special consideration and authorization, for although a small sum might suffice for the work, yet unforeseen difficulties in depth and in the influx of water might arise.
In my letter of December 13th, 1862, I mentioned the discovery of the plant bed series of the Porirua harbor. Since that time I have discovered similar organisms in different directions—at Ohariu, on the banks of the Aka-tarewa, and on the Belmont line, and Mr. Mantell has even found them at the top of the Kai-warra-warra road. As Professor McCoy has decided these rocks to be carboniferous, of the oolitic age, I would fain hope that workable seams of coal will be found, and although appearances are not very encouraging, yet, after having seen the manner in which the Kowhai coal seams at Canterbury were hidden by drift, it will be a long time before I shall despair of success.
The traverse and survey of the rocks which I propose to make from the West coast to the Wairarapa by the line of road, would be a necessary preliminary to the search for coal.
I Lave discovered a black mineral at various points on the Rimutaka, hill, but its character is not yet determined.
For political reasons, it would probably be best that deep sinking should be tried in the Wairarapa, before attempting it on the west coast.
Mr. Brough Smyth will perceive why more attention has been paid to the discovery of quartz veins than of alluvial or drift diggings. The mass of drift having been thrown out of the mountains upon the adjacent plans or basins, rather than deposited within their own area, in a position which often renders it difficult to tell its thickness, or what rocks may lie between it and the undulation of the ancient rocks, I required some support to back my opinion in favour of deep sinking in the plains or basins. You will also observe that the country covered by horizontal tertiary formations can, for all present purposes, be disposed of geologically with great rapidity, while the inclined rocks of the main range require page 18 a most patient and searching investigation.
I have proved the “gold constants,” and I have obtained strong evidence in favour of the probability of finding gold. But should the “gold constants” prove inconstant, and the precious metal elude our search, there is no reason to despair of making discoveries of other valuable metals. I have every reason to think that these ranges are full of mineral veins, and at the present moment I await reports on the character of those already found; but at the same time, I suspect that our mineral wealth lies deep, and will require an expenditure of skill, capital, and patience for its developement.
I have the honour to be
Your most obedient Servant,