Art. XXXV.—Remarks on the Coast Line between Kai Iwi and Waitotara, on the West Coast of the Province of Wellington.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 2, 1869, Unnumbered Page

Art. XXXV.—Remarks on the Coast Line between Kai Iwi and Waitotara, on the West Coast of the Province of Wellington. By R. Pharazyn, F. R. G. S. (With Illustrations.) [Read before the Wellington Philosophical Society, June 19, 1869.] Any One accustomed to the scenery of the East Coast, must be at once struck with the contrast presented to it by that of the West. The former is rugged in the extreme, and, except in a few places, the flats, adjoining the sea beach, appear to have been formed from the slips which take place so frequently from the neighbouring hills, having, as it were, reclaimed the land faster than the waves could wash it away. The scenery on the West Coast is comparatively soft and undulating, this latter character being more marked as we approach Mount Egmont, whose volcanic rocks give a new feature to the landscape. The general impression produced, is, that this country has been formed by the gradual and quiet upheaval of a vast mass of marine deposits, and that there is no such incessant struggle between land and sea going on, on the West Coast, as there is on the East. But such considerations, though sufficient for the purposes of art, either pictorial or descriptive, which deal rather with effects than causes, require to be supplemented by more exact observation to meet the requirements of science. In nature, the forces which are quietest in their operation, are often the most powerful, and in geology, the question is not so much how great is the force, as how long has it operated. I think I shall be able to adduce some facts, which go to prove that the northern portion of the West Coast has been encroached upon by the ocean, to a very considerable extent, and at a rate which is remarkably rapid, geologically speaking. Immediately to the north of Wanganui, the margin of the coast consists of ranges of sand-hills, which are remarkable from the fact, that instead of falling away gradually to the sea beach, they terminate in cliffs which present a bold face to the sea. Between the sand-hills and the tertiary rocks, of which these cliffs consist, are the well-defined remains of an ancient forest. These remains are particularly conspicuous along the line of cliffs between the Kai Iwi and Waitotara rivers. In places they appear on the exact line of junction between the sand and the older rocks, but in general they seem to be about four feet below this level. Probably a careful investigation would show that more than one forest has grown upon the same spot, and that each has been buried at a different epoch, apparently owing to changes of level in the land, as, in places, there appear to be beds of marine shells above the lignite, into which much of the wood has been converted. In addition to this is the curious fact, that the bed of the Waitotara river itself is thickly studded with the stumps of trees, at a level of about 150 feet lower than those above mentioned. We have then the following facts before us. 1. Drift sand extending inland, to a distance of from one to four miles from the edge of the cliffs, and thus lying at an elevation of from 120 to 200 feet above the present sea beach. 2. The remains of one or more forests buried beneath the sand-hills, and

Ideal Sections between Kai-iwi and Waitotara Rivers

in the strata in which these rest, and the remains of the same or other forests as a much lower level, namely, in the bed of the Waitotara river itself. Clearly then, here is evidence either of a very remarkable rise in the land, or of the considerable and rapid action of the waves upon it. On first looking at the sand-hills, in question, it seems as if the whole mass had been lifted bodily upwards from the bed of the ocean. So fresh is the appearance of the sand, that it is difficult to believe that it has not been lately covered by the tide. However, this supposition is a highly improbable one, when the generally horizontal and unbroken nature of the stratification of the underlying rocks is considered, dripping, as they do, at a very small angle towards the sea, and presenting no appearance of having been disturbed since the accumulation of sand upon them. The probability is, then, that the present cliffs have been formed since the great Tertiary system, which underlies all the more recent formations in this province, and in that of Hawke's Bay (being apparently identical, as to fossil contents, on both sides of the island), attained its present elevation. Evidently, then, at one time, the surface of the rocks, in question, sloped gradually to the beach, and became covered with sand-hills (similar, in all respects to those between Paikakariki and Rangitikei), and presented no abrupt termination towards the sea. Rocks at some depth below the surface of the water are protected from the action of the waves, but no sooner do they approach the surface, than they are exposed to the incessant cutting and grinding action of moving water. Hence it is easy to imagine that the ordinary action of the tide, apart from that of ocean currents, (though I believe these have a considerable effect on our coasts), was sufficient to wash away so much of the newly-formed land, as to give rise to the rather singular phenomenon of sand-hills terminating in high cliffs. The present coast line is, in short, a section of that which formerly existed, and apparently at no remote period. That this period was not very remote is, I think, proved by the fact, that, at any rate, some of the trees, of which the stumps, and in some places the trunks, are visible, have not lost the appearance of wood, and though others have become changed into lignite, I have seen none which could be classed as Brown coal. I may mention, incidentally, that the lignite in question is so plentiful that I was informed, when lately in the Waitotara district, that it had been used as fuel at Mr. O'Hanlon's hotel, near the Kai Iwi. It is evident that the trees, I refer to, must have been growing before the sand covered the soil, and the probability is that the sand was drifted by the wind over and amongst the more recent ones. Indeed the remains of an old pa were visible till lately upon a place called Popoia, near the Okehu stream. This, though half a mile from the sea, is now nothing but a vast sand-hill. Hence, it follows, that the sea must have made such inroads upon the part of the coast in question, as not only to have washed away a considerable belt of sand-hills, but to have cut into the fertile land where a forest formerly grew, and it is not improbable, that this formed part of that forest, which middle-aged Maoris say they have heard their fathers speak of, as having covered the present fern and grass lands within their own recollection. For the comfort of land owners, I may mention that the further drifting of the sand has been prevented by the growth of vegetation, and by the formation of a high fern-covered ridge, which forms, as it were, a rampart between the sand-hills and the arable land; though while the sea will still gradually eat into the land, it will do so at a continually decreasing rate, the lower rocks being much harder than the upper, and consisting of an indurated blue clay. The part of the coast which I have attempted to describe is well worthy the attention of a skilled geologist, and a careful examination of it, noting the

dip of the strata, and carefully examining the buried trees, would, I think, put us in possession of some very valuable data for determining the era and the rate of important geological changes. I lay on the table some rough diagrams, in explanation of such parts of my paper as may appear obscure to those who have not seen the part of the country it relates to. (See Pl. IX.)