Geological and other Reports
Wellington, April 14, 1863
I have the honor to submit the following report of the results of the geological observations made by me in this province during the past and present year.
The characteristic features of this province is the immense area covered by sedimentary tertiary rocks, comprising perhaps eight or nine tenths of the whole.
The older rocks form the mountain chains of Rimutaka, Tararua and Ruahine, the Aorangi range at Cape Palliser, the Kaimanawa range and the islands of Kapiti and Mana, while the sedimentary tertiary rocks occupy all the rest of the Province, with the exception of the igneous tertiary and recent rocks of the volcanic chain of Ruapehu and Tongariro, I must also for the present exclude the limestones and calcareous grits of the East Coast (age still undetermined), although I believe them to be tertiaries also.
I need not again repeat the sequence of the tertiary rocks.
You will bear in mind that there are two lines of dislocation and upheaval traversing the whole length of the Province,
The main ranges of Rimutaka, Tararua and Ruahine, on a line of about N.N.E. true.
A line of fracture and upheaval, nearly parallel to the East Coast and distant about eight or ten miles from it. On a line of about N.N.E. magnetic.
There are also two lines to the Westward but which only advance a short distance into this Province.
These may be said to form the ribs of the Province, while the tertiaries fill in all the rest.
In the tertiary rocks no metals can be expected, although limestones and brown coal may be found in workable quantities.
Although tertiary rocks are deficient in minerals, yet as a general rule I think they may be said to support the densest agricultural populations, and some of the principal cities of the world have been built upon them. I may instance London, Paris, Rome. It is probable that the same rule will hold good here, and that the tertiary rocks of this Province, where comparatively undisturbed will on page 28 both the Eastern and Western sides of the range, but particularly on the latter, give employment to a numerous people. In fact it is only by labour that the resources of these districts can be developed.
Whanganui may be said to be the centre of the tertiary rocks of the West Coast, Napier of those of the Eastern sea board, while the City of Wellington is planted in the midst of the ancient rocks on which these tertiaries abut.
Having determined the great mass of the Province to be of tertiary age and therefore devoid of minerals, the search for these latter was consequently restricted to the ancient rocks of the ranges above named.
In consequence of the favorable opinion formed from an inspection of the rocks of these ranges, of our chances of finding gold, I have lately made an investigation of the various river beds of the Rimutaka and Tararua, and regret to say without finding the “colour” of gold in any of these streams, comprising the valleys near Featherston, the rivers Waiohine and Ruamahunga the Makakahi, the Maungatai noko, the Maungawha, the Uki-uki, the Manawatu and the Otaki.
I have been kindly favoured by the Geological Department at Otago, with a sections of the sinkings at Tuapeka, showing the existence of an old gold drift below some tertiary sandstones and beds of coal. Had we found the colour of gold in any of the streams above named, I should have strongly advised what I have hitherto recommended viz, that trial holes should be sunk at Otaki and in the Wairarapa, in hopes of finding a similar old gold drift below the sedimentary tertiaries.
It may still be deemed advisable to try this plan although the chances of success are small. What I fear, from my experience in the Hutt, is that it may be found impossible to bottom in these places without a steam engine, on account of the quantity of water. No further amount of exploration is likely to give decisive information as to whether an older drift lies below, sinking will be the only proof. At one point only, viz., in Palliser bay, is there any evidence and there it is in the negative. The blue clay with its limestone base is there found resting unconformably on the mudstones and slates of the old rocks and there is no intervening old drift.
Believing, as I have before stated, that the gold line or zone lies far to the Westward, I hesitate to commence a work of deep sinking which might involve considerable outlay unless the Government express a wish that it should be tried, even in that case it might be best to do the work by contract.
I have, as far as practicable, followed Mr. Brough Smyth's suggestions as to a search towards the sources of the streams. Putting the native question entirely on one side and the point whether we should be allowed to examine the sources of the rivers in the direction of the volcanic range, and the centre of the island more minutely than I have already done; the fact is that these rivers run through such thicknesses of tertiary rocks (either volcanic or sedimentary) from their sources to their mouths, that prospecting in that direction would mean deep sinking, with powerful steam engines and immense outlay. I therefore say wait for the knowledge which will be gained by the progress of gold finding on a line from Coromandel southward through the Waikato country.
The sources of the Rangitikei are no doubt in the old rocks of Ruahine, but the rocks of Ruahine appear to be similar in character to those of Tararua and the western flank of Ruahine is remarkably inaccessible, from the great thickness of tertiaries lying against it, cut up by deep chasms and covered by dense bush, which is always an obstacle to geological investigations. The accessible side of Ruahine is from Napier. I believe it has been examined from thence and I fear without finding gold, or we should have heard something of it before now. An examination of the Ruahine range from the western side would be expensive and I fear quite unsatisfactory.
I have obtained in late explorations a good deal of information as to the sequence of the old rocks of Tararua but from the absence of fossils and the broken character of the strata it will be some time before these rocks can be mapped with certainty. A line of veins, of a black mineral supposed to be an iron ore is found in all the valleys on the eastern side of the range. These veins are thin and have not yet been found to come together in a decided lode. They are largely developed in the gorge of the Ruamahunga.
The road party on the Petoni road have laid open a lode from which various minerals have been reported to me. I have sent specimens of these vein stones to Melbourne to be examined but have not yet received the report. A similar quartz to what is there found is observed in various places, including the Waikanae river.page 29
In the Otaki and other rivers what appear to be vein stones of carbonate, of lime in soft slate, are found in great quantities. Their existence on both sides of the range, presenting the same appearance makes me doubt that they are vein stones and suppose that they are stratified rocks. They may furnish a supply of lime at all events. They are pyritous as are many of the other rocks and veins.
In my late examination of the river gorges, although many of the sandstones were found riddled by thin veins of quartz, no decided quartz lode was discovered. It is however possible that veins of auriferous quartz may be found although appearances are not favorable.
Although anxiously on the watch for further evidence as to the existence of coal seams in the Province I have been able to add little to my previous discovery on the shores of Porirua harbour.
Either the plant beds found there have been originally deficient in beds of coal, or they represent the remains of a coal field denuded and nearly destroyed, or the coal beds may be buried and hidden beneath the tertiaries of the West Coast.
Fresh evidence ought however always to be carefully looked for. On the shores of the Porirua harbour the strike of these rocks appears to be North and South, but at the gorge of the Otaki river, the strike of what I take to be the mezozoic sandstone would seem to be East and West. Supposing the latter to be the true strike then it is possible that coal seams may be found along the face of the front ranges, at other points than the river gorges, but as at present these ranges and the flat country at their base are so covered as to render geological enquiry almost impracticable except in the river gorges, my advice almost amounts to this. Settle the country and make roads and then perhaps we may light upon the coal.
Igneous rocks, as described in the report of my last journey, are gradually coming to light. As the igneous rocks are deep seated, seldom shewing themselves, may not minerals be deep seated also?
I trace a line of fracture, or of fault, along both sides of the ranges, generally near where the old rocks and the tertiaries meet (although to the northward, in the Opaki &c., perhaps cutting through the tertiaries only) showing a thrust of the range upwards. This may have taken place during the earthquake of 1855, or it may have been caused by a succession of upheavals. Near Featherston and at the Waiohine, the height of the thrust may be four or five feet, on the Opaki plain, at some distance from the range, it may be thirty feet and I suspect this line will be found to strike the Eastern scarp of the Puketoe range, with a much greater difference of level at that point.
On the western side of the range at the Manawatu, the lift has tilted the tertiaries rather than broken them, inclining them upwards at an angle of about 20°. Thus, during the earthquake of 1855 the main ranges may have been lifted throughout their whole length, without affecting the level of the tertiaries on the coast,
I believe that I have now rapidly passed in review all the main groups of rocks in the Province although the detail remains to a certain extent to be filled up.
In a topographical point of view the result of my explorations is to show that no extent of farm land is likely to be found within the limits of the mountains of the main range, although in all the valleys which I explored there is more or less terrace land which may be occupied by small farmers but these flats are generally at a considerable elevation (in the gorge of the Ruamahunga, for instance, over 1000 feet above the level of the sea) and in all cases the expense of road making would be great. Considering the deterioration of climate which would probably be caused by the destruction of the forest on the steep ranges and that timber is perhaps the most valuable crop that they could grow, I see no reason to encourage settlement within their limits, except in places not remote from the town and in those valleys which are likely to form lines of communication, such as the Akatarewa, the Waikanae and the Otaki. In the central parts of the ranges nature has had quite enough to do to pack an immense mass of material within a limited area, without leaving any level land.
I attach no importance to the bare ridges of Tararua. The edge of the forest appears to reach a height of 3000 feet or more and the open country above is not likely to be profitably occupied by domestic animals, although it might be well adapted, in these days of acclimatization societies, for turning out Himalayan antelopes, chamois, &c.
Colonization must follow the great valleys and plains of the Forty Mile Bush, and the West Coast, and a view from the pass where I crossed the main range, page 30 looking on one side over the Forty Mile Bush and on the other over the Manawatu plain, shows an extent of fertile land, perhaps unsurpassed in New Zealand. The end of Tararua, which here thins out like the point of a wedge, not more than four or five miles broad and 915 feet above the level land, forming the only separation between the fertile plains on both sides.
In fact the gorge of the Manawatu is—the key of the Province—and a few minutes view from the hill above, shews more of the capabilities of the country than days journeys elsewhere.
I have the honor to be,
Your most obedient servant,
James C. Crawford,