N.Z. STONES.

Press, Volume LXIV, Issue 19503, 27 December 1928, Page 4

N.Z. STONES.

USE IN BUILDING. I HUGE QUANTITIES AVAILABLE. In a lecture to the Wellington District Branch of tho New Zealand Institute of Architects recently, Dr. F. Marshall dealt, in a very interesting fashion, with the Dominion's resources in building stones. He uaid: — A geologist is prone to study rocks from a different point of view from that naturally adopted by an architect. A geologist is chiefly concerned with the mineral structure of tho rock; an architect with its practical utility and lasting quality. Since the universal coinposition of rocks is most variable, the accurate study and classification of them has necessitated the use of a great number of names, most of which havo a Latin or Greek origin, and have, therefore, an unfamiliar appearance and sound.

Though a geologist, I shall to-night restrict myself to such a practical classification of rocks as will come within the limits of the terminology of architects and their practical allies—the builders and contractors.

It will, therefore, be most conveni: ent to deal with them under the heads of sandstones, limestones, granites, volcanic rocks, and marbles. I shall have to touch on each of these briefly and omit more than I mention.

Sandstones, taken the world over, arc perhaps more used in construction than any other kind of rock, but they are most variable in quality, both from the lasting and working standpoints. In New Zealand we are in a peculiar position with regard to sandstones—for this is the commonest rock typo in the land —it is tho main constituent of the rock structure of the country, yet one is not able to point to a single locality where satisfactory sandstones can be quarried for .building purposes. Our older sandstones are in inverse quantities, but they are extremely hard, and have no regular bedding of structural planes to facilitate quarrying. Shaping and dressing are associated with great waste and great expense. The most ordinary of these older sandstones is the. greywacke, used so widely for the construction of roads. The younger sandstones are sott, weak, and do not last well. The Dobson sandstone is perhaps the best known. It has been used for basement courses at the G.P.0., Wellington, and Government Offices in Christchurch. Limestones have a wide occurrence m New Zealand, and have been used for. building more widely than any other type of rock. Those used are young geologically, soft, absorptive, and, so far as working goes, are thoroughly free stones. They occur in well defined deposits, lying horizontally, and giving every facility for. quarrying. The best known of these is the Oamaru stone. It is easily worked, of a dead white, or creamv tint throughout, and sufficiently fine grained structure to allow it to be easily moulded into any form. Unfortunately, it is highly absorptive, and reliance cannot be placed upon it to withstand the weathering action of the atmosphere. On exposure to the wea-ther-some stones disintegrate, especially in the higher courses of building. Tot internal use it is hard to surpass this stone, its only slight drawback being a slight coldness. There are hard brae: stonos at Te Kuiti and at Horahora, and other localities near. Whangarci, but these stones break out badly, and there is much loss in shaping and dressing. Although these are admirable building stones, their cost is too high for ordinary construction purposes. Graniteß. , Granites occur largely in New Zealand, especially in Nelson and in the sounds of tho sou'-west and at Stewart Island. These, however, have not been used, with tho exception of stones from Tonga bay and Sandy bay, near Separation Point, Nelson. This happens to be a most friable type of the rock, and is most unsuitable for use in building. It has'been used for tho G.P.0., Wellington, and after 20 years is already in places in an advanced state of de- ■■ cav - . „ Coromandel granite (geologically a tonalite) is an excellent, stone, light to dark grey in colour, takes a good polish, and will last indefinitely. This is wide-

ly used for the lower courses of buildings all over New Zealand. So far it has been obtained from surface blocks of huge size and working and transport have made its cost high. The Bluff granite (geologically hyperite) is a good lasting stone, and takes a good polish, and is available in unlimited quantity. The drawback is that hitherto the colour in the quarry has been found to be most variable, and it has not been possible to produce any quantity of a constant grade of colour. This haß restricted its use greatly. . . Volcanic rocks occur most widely m New Zealand, and have been used to a considerable oxtent in Christchurch and Dunedin. Usually the rocks break out irregularly in, tho quarry, and as they are hard, much expense is incurred in shaping and dressing them. In Auckland a dark baßalt has been used for St. Paul's; in New Plymouth, andesite, for St. Mary's; in Christchurch, andesite and basalt for Canterbury College and Museum, andesite for Canterbury College, basalt for tho Bank of New Zealand; in Dunedin, a trachydolerite for Otago University and Knox Church. The stones that have been used are sombre, and expensive to dress. A volcanic vitric tuff that occurs widely in South Auckland is peculiarly suitable for uso as a building stone. It is most accessible at Hinuera, in the Waikato, and near Ongarue, on the main' trunk lino. The rock occurs in large horizontal be'ds, but is a good free stone. It can be readily sawn, has excellent lasting qualities, can be carved into mouldings, and is easily quarried. Courses have been used in the Catholic Bishop's house at Ponsonby, Auckland, j for 35 years, and the stone is still sound. This stone absorbs water rather more J than the Sydney sandstone, but has a more pleasing colour, a distinct character, and is absolutely immune from atmospheric acids, even strong sulphuric and hydrochloric acids. It is hoped that tho excellent qualities of this stone will now be recognised, and that it will be widely employed in New Zealand buildings. Marblos. Marbles have a wide occurrence in Now Zealand —the kind that has been used for the Parliament Buildings, Wellington is a light grey quarried near Motifcka, Nelson, at Kairuru, m the raigc between Motueka and Takaka. It is somewhat fractured and expensive to quarry, and there is much waste, but the stone is sound, and it has all the lasting qualities of the best marble. Like other light-coloured stone, it becomeß discoloured by the dust and soot of towns in all parts of a building that are not subject to the direct impact' of rain. Some of this stone is well figured and varied in tint. White marble can be obtained from the same quarry in

groat quantity. It is coarsely crystalline, and its surfaces give a sparkling effect in sunlight. A dark groy marble is quarried atTakaka. The lighter stones have been widely used for lining basements in Wellington and for shop fronts. It has a most pleasant appearance. A darker variety is being used for the construction of tho Nelson Cathedral. Ornamental marbles can be obtained in large quantity. At present the rock at Warn, near Whangarei, is on the market. Geologically a limestone, it has all the polishing qualities and colour of marble, and is rightly so named for building purposes.' Soft tints _ from B rey to red are obtainable, with an agreeable mottled effect. It has lately been used for polished slabs for_ lining vestibules in Auckland and Wellington, with 'most satisfactory results. Other beautiful figured and coloured marbles can be obtained near Colling: wood in any quantity. .Stones can be obtained veined with pink or yellow, or brecciated types can be procured in great variety of pattern andjmade. The Quantity and variety of marble of great Etv which can be obtained there is quite unlimited. This stone has not yet Se?n placed on tho market, but its £l™tv and variety must give rise to a for its use before long., Other Slot c ufin Dusky and Doubtful SounS but they have not yet been US Th'is brief resume gives an indication '/*£ weat amount of building stofie Sat i Diablo in New Zealand. Cost a j?ffipulty of quarrying have limit•2 ♦*.Temand, and the soft limestones SI heSprov ded to be deficient in duhavebeenprov rabl ,-.- y ' „? the vitric tuff will soon bo ed, In"that this stone will £ L widely and success ully used as similar types have been m Germany, Italy Japan, and many other countries. During the course of the evening Dr. Marshall handed round for inspection mZ interesting samples of building s on s from New Zealand quarries.