Chapter IV. — The Soils of Tutira—Past and Present
The Soils of Tutira—Past and Present.
Everywhere on Tutira there has been spread at one period a carpet of dark matted humus. Immediately beneath it has lain a streak of clean grey pumice grit three or four inches in depth; beneath that again, dense, slightly greasy beds of packed red sand. On the eastern run there are traces of pale, valueless clay. Such were the primeval soils and subsoils of ancient Tutira.
The relative poverty of the huge district west and north of Napier is usually but wrongly attributed to the presence of the pumiceous band. Really this shallow layer of grit is of trifling import. The bane of the region, of which Tutira forms a part, are its sheets of packed red sand.1
1 The surface soil of humus, dust, and pumice grit is described in the Edinburgh analysis as “poor, light, sandy material, containing only 7.2 per cent of organic matter. It contains no phosphate.” The subsoil of red sand “consisted mainly of silica, the colouring being due to oxide of iron. No phosphates or potash were present.”
These elevated scraps of plateau or “comb” backs—a few acres altogether—still remain samples of what all Tutira was. To this day on them there can be discovered more clearly than elsewhere the original soils in their original order of deposition—the dark musty humus, the grey grit, the bed of packed red sand. On their heights not only has top-dressing by slips been impossible, but they have been less tapped by “under-runners,” less torn up and intermixed by uprooted timber, less slipped away by land avalanches than any other portions of the run.
It will be most convenient to consider the lowermost first, and thus take them in the order of red sand, pumice, grit, and humus. The red sand deposits are of a firm, impervious, slightly greasy texture. The whole run has been plastered with the worthless stuff. It is common to west, central, and eastern Tutira. It shows up red on the naked “wind-blows.” The quadrilateral mosaics of the topmost limestone sea-floors are set in it. It rests in sheets on the conglomerates.
There can be little doubt that these red sand deposits are of volcanic origin. Their substance may prove to be waterlogged pumicestone page 24 fine ground, its greasiness resulting perhaps from some admixture with the scanty pale clays found on the eastern run. Perhaps, too, the coloration of the deposit may be derived from sources similar to those which gave the conglomerate beds their rusty ferruginous hue.
Proceeding still from below towards the top, we come upon the band of pumice grit that lies on the red sand. It is about four inches in depth, the grit perfectly loose and dry, its grain very even, in size resembling the granules of a rough brown sugar. It is remarkably unclogged and free from intermixture of foreign matter. Like other bad things, it has reached Tutira from one or other of the inland volcanoes of the North Island. It is, I think, æolian, wind-carried, and has probably descended on a countryside supporting a vegetation thick enough, stiff enough, and high enough to afford immediate shelter and cover. Its light dry substance, falling like rain from above, would thus either percolate direct through this growth or be at once watered on to the ground by wet weather. It would lie evenly on the ground—as in fact we find it in the undisturbed plateau fragments—and during succeeding centuries became covered with root matter and leaf-mould. The vegetation which thus sheltered and harboured this pumice shower must have been then growing on red sand, for it cannot be doubted that the top spit of humus is merely the accumulated results of decayed vegetation. The pumice deposit appears to have been the result of a single volcanic outbreak. Nowhere, at any rate, do I find the slightest trace of alternate layers of grit and humus. The two substances are clearly distinct. Other showers of pumice may have fallen at other periods on naked surfaces and been blown off, but the result of the one particular eruption incorporated in the soil of the station fell, I believe, on a surface protected from wind. Unless we are to suppose different meteorological conditions, no layer of grit could have endured one hour's nor'-west gale on bare baked sand. Even by the less violent action of rain it would have quickly been washed away.
The alternative to the theory of wind-blown pumice is to suppose the grit to have fallen on water and eventually to have sunk. There are many difficulties, however, to be faced. Falling on open sea the light material would have been soon dispersed; even granted that it may have fallen on landlocked waters, the floating masses would have been heaped together by action of wind and wave, the grit would not have been page 25 evenly distributed on the bottoms. Moreover, even supposing that the grit had become submerged in a level band, upon the rise of the plateau its surface would have dried and the light top-dressing of pumice would have been dispersed by gales. Lastly, there is nothing in the appearance of freshly-exposed red sand beds to suggest that weighted water-clogged grit has rested upon them. Its grains have not become incorporated in any considerable degree with the lower-lying material. It seems to me that whilst there are insuperable objections in the one case, there is nothing hard of belief in the other.
The volcanic mountains Tongariro, Ngaruhoe, Ruapehu, are all within a hundred miles of Tutira. During the Tarawera eruption of '86 the run would have been thickly dusted with fine grit had the wind happened to have blown towards it. On east Tutira flake pumice is rare; there are banks of it on Maungaharuru varying in size from a crown-piece to a man's palm. The Mohaka river, rising in the chief region of volcanic activity in New Zealand, bears in flood-time from its fountain-head quantities of sponge-shaped blocks; in fact, the size and shape of pumice fragments differ according to distance from source of supply.
The dark, dusty, matted humus of the surface requires little description. There can be no doubt that it is the most modern soil of the run, the outcome of rotted fern fronds, forest debris and fine dust, blown from burnt forests and bracken lands.
From the foregoing description of the soils and subsoils of the run, it is apparent how poor the original surface on every part of the run has been. It is apparent, too, that any surface improvement can only have taken place by the superposition of limestone, travertine, marl, and sand, by an admixture of soils due to overblown forests, and by the deepening of vegetable mould. From a sheep-farmer's point of view, the original state of Tutira must have been worthless: indeed for him New Zealand even now has been discovered and Tutira “taken up” many hundreds of thousands of years too soon.
In another chapter the reader has been, I hope, helped to grasp the general configuration of the station by the metaphor of the “comb.” With equal ease he will understand its soils, if another salient fact of another sort be grasped. It is this, that the fertility of the run is in direct proportion to its angle of inclination, that the steepest country is the best, the flattest country—alluvial flats excepted—the worst. From page 26 the former the jacket of pumice and red sand has to some extent been overlaid by washings or stripped by slips. The latter remains as it was centuries ago, even its leaf-mould stolen away by subcutaneous erosion.
Kahikanui swamp, lying beneath the highest marl outcrop on the station, and containing washings almost wholly composed of that substance, is the only first-class piece of soil on the run; in miniature it resembles the far-famed flats of Poverty Bay.
Each of these plains—the one of a few dozen acres, the other of many thousands—has been created by alluvium carried down in flood-water from hills of marl. In each case the rougher, larger particles have been precipitated at the apex of the plain, while the finest, most highly comminuted silt matter has remained in solution until dammed back—in the one case by Tutira lake, in the other by the waters of the Pacific. The result is that although rich throughout, the physical conditions of the soil at apex and base are widely dissimilar, the apex easily worked and friable, the case heavy and hard set. What Herbert Spencer has termed “the multiplication of effects” can further be traced in different weeds, different grasses, a different permanent pasture.
The flats—alluvial is too sumptuous a term—of the pumiceous trough of the run do not exceed some two or three score acres, the largest single patch perhaps not more than five or six acres in extent. As station assets they are of no great value, it is the means by which they have come into being that deserves notice here. That method is not direct deposition from above, but injection from below of water charged with microscopic quantities of rotted vegetation, the soakage from higher slopes. These pumice alluviums in outward semblance differ but little from neighbouring lands. For long, indeed, they were regarded as equally worthless. It was a belief countenanced by the arid grit of the surface and by the appearance of the vegetation supported thereon—groves of pole manuka, their bark tattered and thin, their harsh leaves brown-green and prickly, a foliage yielding neither shelter from winter storms nor shade from summer heats. On the other hand, covering contiguous slopes, flourished luxuriantly green tutu (Coriaria ruscifolia) and koromiko (Veronica salicifolia). It was believed that their foliage was creating leaf-mould on the slopes where it fell; really its manurial value soaked through the humus and sandy grit by a process of filtration to page 27 be explained later, then, unable on the flat to escape further, rose from below in the form of an alluvium of dirty water no stronger than weak tea.1
Sufficient now has been said of the soils of the run and their ancient order of deposition. If the reader has grasped the fact that all steep land is good and that all flat land is bad, he knows everything that need be known.
1 Riding through some such bit of country with a stock and station agent, he remarked of the deep green tutu-covered slopes, wishing presumably to say something pleasant: “That does not look so very bad, but this—!” Without consideration I replied: “You might not think so, but this is really better.” I yet recollect his sour, sick face as he turned in his saddle and looked at me. As I say, he was a stock and station agent inured from childhood to chicanery, yet he was fairly nauseated, not of course at the lie as he necessarily accounted it, but at its ineptitude, inadequacy, futility, the waste and uselessness of such a foolish falsehood.