STONE FOR HARBOR WORKS.

Taranaki Daily News, 20 July 1921, Page 2

STONE FOR HARBOR WORKS.

A REPORT ON PARITUTU, GOVERNMENT GEOLOGIST’S VIEWS. In the course o£ his report on the use of Paritutu stone for harbor works, and other sources of supply, Mr. P. G. Morgan (Director of Geological Survey) says:— Paritutu is .the most prominent of the wellknown sugar loaves. Unlike the others, it is not an island, but rises almost perpendicularly from the edge of the sea, half a mile west of the base of the Moturoa breakwater, to a height of 505 ft. On the east, south and west sides agglomerate deposits, capped by sand, mask Its base to a height of perhaps 200 ft or more. The hill itself is a plug of igneous rock, which In a bygone age rose in a fluid or semi-fluid condition front a molten mass of rock deep in the bowels of the earth thwjfagh a vent which may be described as the throat of a volcano. Sine that time it has been subjected to the usual geological vicissitudes, but appears to have lost little of its original dimensions, that is to say, its tdp and sides have, not been greatly reduced by erosion. This view differs from that advanced by Mr. R, de C. Clarke in Bull No. 14 (pp. 2125) where Paritutu is regarded as formed of a lava flow or flows.

The Paritutu rock is a hornblends-andesite, similar to that forming the other sugar-loaves. On the whole it is in a fairly fresh condition, but is somewhat affected by weathering, especially near the joint planes. The rock forming the .north-eastern face of the till is highly jointed, and even shattered; elsewhere it is more solid, and joints are much less prominent, but flaws are abundant. The hill is so. situated as tb offer unusual facilities for quarrying. All that is needed to destroy the upper 300 ft is a few hundred feet of drives and say a hundred tons of explosives. The larger masses of rock, although ttey will' nbt be of the highest quality, will be suitable'for the construction of a rubble mole or breakwater. I am of opinion that the proportion of small stone will be large, but, \since- the cost of quarrying will be low, sineb much of the small material can be used for the break-” water construction, and since the remainder' can be easily tipped into the sea, this will 1 not be considered a serious objection from the utilitarian point of view to the proposed destruction of Paritutu.

RESULT OF THE BLAST. A blast has already been fired on tke south side of Paritutu, and is said to have diSt lodged 30,000 tons of rock. Personally 1 would place the amount at somewhat less, but it is certainly well over 20,000 tons. According’ to a newspaper report, (June EL, 1921), Mr. J. Blair consulting engineer to the New Plymouth Harbor. Board, has reported that 20 per cent of the broken rock is in masses of 2 tons to 30 tons'30 per cent, in % ton to 2 ton sizes, 35 per cent, in lumps of % cwt. to % ton -and 15 per cent, in small lumps. All the material, he states, can be used in the breakwater construction. So far as I could judge from an inspection of the broken rock, this estimate is fairly near the mark. Part of Paritutu, however, will yield very little large dimension stone. It may be observed that about 1879 Mr. Rees, then engineer to the New Plymouth .Harbor Board, reported that Paritutu would yield only 10 per cent of stone in large lumps (from % . tons upward was, I think, his statement), and on the strength of this report Sir John Coode advised that a breakwater in the form of a concrete mon®-, lith should be constructed. I think that the upper 300 ft. of Paritutu will yield less than 20 per cent of dimension stone (2 tons and upward), but probably more than 10'per. cent. The lower 200 ft. (down to sea-level) may be somewhat better in this tliair the upper 300 ft. but there is no certainly about this. A -tramline for the removal of the dislodged stone is- under construction, but no further quarrying work was being done at the timt/i of my visit. As requested by the president of the tutu Protection League in his letter of May 31, I examined the quarry at the Fishing' Rocks (Motukuku and Ngataierua) between Paritutu and the breakwater. This quarry tas been worked by the Harbor Board almost to high water level, and must be regarded as exhausted. It was suggested to uno that the quarry could be worked downward, below sea level, but only a comparatively small amount' of stone could be obtained in this way, and; in any case the expense of quarrying under 1 adverse conditions renders the proposal impracticable.

An attempt to quarry stone for harbor works on the little island of Moturoa, which is lessthan , half , a mile north-west of the present breakwater, has lately been made. For the time being the work has been ■ abandoned owing io the somewhat poor quality of the stone (close jointing being prevalent), and to the cost of transport. The island has beendisfigured, and a considerable expenditure incurred, in this unfortunate undertaking..

The small sugar-loaves Pakaraki, Mataora and Motu'-o-Tamatea, south west of Paritutu, are composed of close jointed andesite, and if quarried, would afford only a small aonount of large dimension stone. I am informed that Motumahiinga of Saddleback Island, the sugarloaf farthest to the south-west, is composed of good solid stone, but the Island Is in. an exposed situation add the cost of transporting .tie- stone from it to its final resting place would be great. The volcanic agglomerate which occurs immediately below the soil and subsoil of the district surrounding New Plymouth contains numerous boulders of andesite up to 10ft. in diameter. These have accumulated at the base of sea-cliffs, for instance, between Oakura and the sugar-loaves, and in the stream-beds. They are suitable for breakwater construction, but the cost of collection and transport bo prohibitive. There are some inland quarries, for example, Hawk's Hill, on Frankley Road, which could furnish blocks of stone. In all cases, however, the supply at any one spot Is small, and the cost of transport to the breakwater would be prohibitive. MOUNT EGMONT STONE. Unlimited supplies of large dimension stone, of splendid quality, can be obtained from various parts of Mount Egmont and the Pouakai Range. The only deposit of this nature near a railway line is some distance west from the present terminus of the Mount Egiirymt Branch Railway (Public Works Department), which runs a little south of west from Waipuku Railway Station to the lower slopes of Mount Egmont. At its terminus, 2160 ft. above sea level (barometric observation) is a quarry in volcanic agglomerate. The massive outcrop of andesite said to be two miles to the westward of this point has not been visited by any officer of the Geological Survey, but a report by- Mr. G. W. B. ‘Lowson, engineer to the New Plymouth Har-bor Board, states tl at the stone is In unlimited quantity and obtainable in large blocks. I do not doubt that the stone here is highly suitable for harbor construction. Mr. Lowson states that the stone will be supplied by the Public Works Department on trucks at 5s per ton and that the cost of railage to Mpturoa will be 5s 7d per ton, , making the total cost per ton 10s.

The rock outcrop on the Pouakai Range inspected by me is situated on a high spur between Kiri and Mounona Creeks, tributaries of the Oakura River, within the Mount Egmont Reserve. The rock face actually seen is at an estimated height of 2800 ft. anove sea-level. It consists of massive hornblendeandesite, which is of excellent quality and can be broken in blocks of any size. According to Mr. R. W. Davies, of New Plymouth, who was. my guide to this spot, there is a high cliff on the. Momoma Creek (south) side, from which the stone could be shot down into the creek to a point, accessible by tramline. The distance from this point to Moturoa or to New Plymouth is between eleven and twelve miles as the crow flies, and a railway of say fourteen miles In length would have to be constructed before stone could be delivered to tke harbor works. Owing to the cost of (making such railway, and the time necessarily involved, suggestion that the deposit between Kiri and Momoma creeks can used seems at present impracticable.

Under present conditions the only source'of stone for the New Plymouth harbor works that enters into competition withwi'aritufqj.js the deposit'• two miles - beyond the present terminus of the Mount Egmont .branch railway. The stone 1 , there Is reason to believe, is of better quality than the Paritutu stone, but it will cost much more per ton landed at the harbor works. Moreover, it cannot be supplied at all until the railway (or tramway) is ’tended to the quarry site. It is possible that the railage (5s 7d per ton) can be considerably reduced—if so; the higher quality of the Mount Egmont stone as compared with the Paritutu stone and the fact that its quarrying will not involve the destruction of a monument of great natural and historical interest may well compensate for a somewLitt higher first cost.

In concluding I would Jike to observe that the question of whether Paritutu is to be destroyed or not is only in -small measure a matter for geological report. It happens that the hill is so situated that it appeals to the Harbor Board and its engineers as a probable source of cheap material for harbor works, whilst on the other hand its destruction will cause regret to everyone who has an artistic sense, and is able to realise that there is something more in life than mere utilitarianism. Under the circumstances it appears to be the duty of the Harbor Board and its engineers, before proceeding further with the destruction of Paritutu, to show that this course is absolutely necessary, and that there is no practical alternative. I would therefore recommend that an endeavor to obtain a full report on the proposed harbor works from an absolutely impartial engineer should be made by those concerned that is to say the New Plymouth Harbor Board -and the Paritutu Protection League should agree upon some engineer w!th_Jlafbor Board experience in whom both sides have confidence. A report from such a man would be of great assistance to me if another geological examination should be required.