Geological and other Reports
Wellington, March 17, 1862
Sir,—I have the honor to report that I left Whanganui on the 24th February, for the purpose of exploring the country in the basin of the Manawatu river. On my way I examined the bed of the Turakina river for some slate rocks which were there said to crop out. These supposed slate rocks I found to consist of some horizontal bands of soft tertiary sandstone; and the general appearance of the rocks, looking up the river, being similar to that of the Whanganui and Rangitikei rivers, gave me no encouragement to proceed farther in their investigation, without having more time at my disposal than I then had.
On arriving at the Manawatu I received every assistance from Captain Robinson, in furthering the objects of the expedition; and on the 28th we proceeded to Puketotara by land, from whence we proposed to ascend the river by canoe.
In consequence of the disinclination of the Maories to be absent from their homes on Sunday, we were detained at Puketotara until Monday the 3rd of March; and as that day was very stormy, we were still further delayed until the following day—bad weather set in, there was a heavy fresh in the river, and our progress was tedious in the extreme.
It was therefore the 8th of the month before we reached a camping place on the west side of the gorge, just above the junction of the Puhangina river with the right bank of the main stream; and at this point, swarming with mosquitoes and sandflies, we were, in accordance with native custom, obliged to remain all Sunday.
On the lower part of the river I had observed what appeared very like the blue clay, showing itself a few feet above the water (particularly on the right bank, about a mile below Puketotara), but at and near the gorge it became unmistakable, appearing in cliffs thirty or forty feet high, capped again by drift gravel averaging abont twenty feet in thickness. At the same time it must be observed that the exposed part of the blue clay was unfossiliferous, the characteristic fossils being doubtless below the river level. Opposite the camping ground I obtained venus and pholadomya, but I am not sure whether they belong to the lower part of the upper sandstone, or to the upper part of the blue clay. These fossils were so soft as to render their removal difficult. At this point, opposite the camping ground, the strata dip to the westward at an angle of 20 deg. to 25 deg.; but I am not satisfied whether this is the true general dip along the side of the grauwacke range, or only a local slip. The general dip over this district is either imperceptible, or slightly to the west.
On the 10th we passed through Te Apiti, or the gorge, which we entered immediately on leaving our camping ground; this pass is entirely through the usual grauwacke rocks, and is certainly a most remarkable feature, inasmuch as one of the principal rivers of the island is enabled by it to traverse the main range, and discharge its waters into the sea on the opposite side of the island from whence they take their rise.
It took us just one hour in the descent of this gorge, and therefore its length cannot exceed six or seven miles, including the windings of the stream. The height of the range above the stream being 700 or 800 feet. With so short a distance and so moderate a height to surmount, there can be no great difficulty in the construction of a road to connect the level land on both sides of the island. The the dip of the stratification of the grauwacke rocks is either highly inclined, or vertical, and their composition is similar to that of the rocks near Wellington.
Passing through the gorge to the 70 mile Bush, we emerged suddenly upon a level forest country, where I immediately again recognised the tertiary rocks resting on the flanks of the grauwacke. Here I found the blue clay and the small “venus” which I had left on the other side of the gorge, and in addition found some of the comminuted shell limestone of Ahuriri.
We proceeded onwards for some miles, when I saw that in a continuation of the journey we page 16 should only be travelling over the tops of the tertiaries, and therefore determined to return, and we accordingly turned the head of the canoe down stream, and reached our old camping ground at Puhangina on the same evening.
On the 11th we reached Puketotara, and on the follwingo day arrived at the township at Te Awahou.
The result of this exploration is to show that the tertiary rocks skirt the Ruahine ranges from the Rangitikei as far as the Manawatu, and point further south in the direction of Otaki. It will be of interest to ascertain if they underlie Otaki; and if they go still farther south and pass through the channel between Kapiti and the front ranges of Tararua.
These rocks lie lower at the Manawatu than in the upper part of the Rangitikei, and only show a small portion of the blue clay above the river level. The upper sandstone is only found in fragmentary patches.
The drift is insignificant in thickness compared with what I supposed it to be. It generally averages however, where present, twenty or thirty feet through.
In none of the drift in any district have I found any boulders of foreign derivation, or that have not been derived from the nearest mountains. The tertiary rocks of the western rivers all point towards Cape Farewell, and there is therefore every appearance of a great tertiary basin, of which the eastern and northern rim lies on the flanks of Tararua and Ruahine, curves from thence round the volcanic zone, and thence to the west coast at some point to me unknown. That the southern rim of this basin will be found in Massacre Bay there is strong reason to suppose, and therefore a comparison of the fossils is desirable. I think it will also soon be shown that the great tertiary basin is in connection with a great tertiary field extending over a great portion of the north, and a large part of the Middle Island.
I feel some disappointment in not having found any coal seams to the eastward of the Whanganui river. At the Manawatu one could not expect them, as the strata are too much drowned; but in the upper part of the Rangitikei, unless I have mistaken what I suppose to be the representative of the coal shales of the Whanganui, one might expect to find the coal seams cropping out. I hope that travellers ascending the western rivers will be on the look out for coal seams. Should they be found where I expect, in the Rangitikei, it may be well to bore at the Manawatu to ascertain if they there underlie the blue clay.
At various points on the Manawatu I observed a carbonaceous seam which, perhaps, might be dignified by the name of lignite. It is probably of the same age as the ancient forest of Whanganui, and apparently of no value.
As I suppose no one will be bold enough to sink through a great thickness of tertiary rocks on the chance of finding gold beneath, the country possible for gold is now pretty nearly reduced to the main range itself, and its few grauwacke outliers. That part of it which I have seen at the gorge of the Manawatu looks neither better nor worse mineralogically than the country round Wellington, except that the whole country is covered by dense bush, and that the gullies which came under my observation were mere acute angles without any level bottom.
Any one wishing to explore the main range from the Manawatu should form a depôt at Raukaua, about five miles below the gorge. This is the residence of Hiriwhanu, the principal chief on the Manawatu, who we found very civil.
At Otaki I examined some specimens which had been brought in lately by an exploring party from the mountains, and they are the most favorable looking for metals that I have seen, although it would be hard to say what metal to expect. There were some good specimens of quartz, some iron pyrites, serpentine, an undeniable slate, and a small piece of rock with very granitic constituents An exploration from Otaki would be desirable, although it is, perhaps, getting too late in the season to go far into the mountains; but where the hills are covered with so dense a forest it will be very difficult to make sure of the ground.
I hardly think that in my former report I have enlarged sufficiently on the Whanganui coal. Although it is probably a tertiary coal, yet it has every appearance of being a valuable product. Mr. Soulby, of Whanganui, has promised to procure enough of the Tangarakau coal for purposes of analysis, and I have written to Topini Te Mamako to send down some kits of the Ohura coal for the same purpose.
I have the honor to be,
Your most obedient servant,
James C. Crawford.
Superintendent of the Pro- [sic]
P. S.—On further consideration of the fossils which I have collected, and the non-appearance of coal strata in the Upper Rangitikei, I am inclined to think that I may have mistaken the relative position of the blue clay, and the rock with linear bands of modules, in the cliffs of that river. It is quite possible that at some point obscured by vegetation, or deceived by a slip, I may have drawn an erroneous conclusion, that the latter rock underlaid the blue clay; I am now inclined to think that this rock is the upper sandstone. In that case the coal seams could not be expected to be exposed page 17 and must be sought for at a lower level in that district, which will be below the level of the bed of that river. It is to be desired that the tertiary rocks should be classified, and their relative ages fixed.