Building Stones, Etc.

Basalts, locally called "bluestones," occur of a quality useful for road-metal, house-blocks, and ordinary rubble masonry. They are page 54 found partly underlying and partly overlying the Tertiary rocks, interstratified with tufaceous clays and local beds of altered volcanic ash. In the North Island these volcanic rocks are largely developed, and include some of very recent date.

True lavas and scorias are of frequent occurrence in the northern part of the Island. The latter have been quarried by the prisoners at Mount Eden, Auckland; their colour is dark-grey, and though absorbent they are very hard and coherent.

In the South Island, on the other hand, the igneous rocks appear to be of much earlier date, and to have been nearly all of submarine origin. They are principally confined to the eastern seaboard, only rarely occurring at a greater distance than forty miles from the coast.

The Halswell quarries, Canterbury, produce an exceedingly hard and close-grained stone of a dull leaden-grey colour; but its excessive hardness will necessarily limit its usefulness.

Diorite.—This stone occurs on the west coast of Otago, at the Great Barrier Island, and in many other localities where it can be quarried.

Aphanite Breccia forms a solid building stone that has been used at Dog Island and elsewhere.

Porphyrites.—These stones are found at Flagstaff Hill, Water of Leith, and in the Malvern Hills.

Syenites occur at Dog Island and the Bluff, and at various localities on the West Coast and in Stewart Island; but the chief supply now available for industrial purposes is at the Bluff, and the Boulder Bank at Nelson, where a beautiful green variety occurs. It is hard, compact, and of a uniformly bluish-grey tint of great beauty; consequently it is suitable for kerbing, paving, and massive masonry, as well as for monumental and architectural work.

Trachytes.—The group of trachytes contains many varieties, both of composition and texture, but they all, together with the granites, are distinguished from the first group by containing a large proportion of silica.

At Port Chalmers a fine grey stone occurs. Another kind, a good freestone, is obtained at Harbour Cove, Otago, and Creightonville, Canterbury.

Granular trachytes are obtained from Governor's Bay, Lyttelton.

Trachyte porphyry is found at Taiaroa Head, Moeraki, and Portobello; and from Port Chalmers a breccia is obtained, with which the graving dock there is entirely built. All the kerbing in Dunedin is from the quarries of this stone.

Sanadine trachyte is found at Portobello, Otago Harbour.

Phonolite or clinkstone of a columnar character occurs at Bell Hill, Dunedin, and a laminated and spheroidal variety at Blanket Bay.

The gaol and some other old buildings of Dunedin are built of a spheroidal clinkstone, which is of a mottled grey colour, and exceedingly hard and compact. The foundations of buildings in that city are frequently constructed with the same stone, which is eminently suited for the purpose. This stone is probably metamorphosed tufaceous sandstone.

Granite.—Granite is only found as mountain masses at Preservation and Chalky Inlets, on the western coast of the South Island, but exists in large veins and blocks in Stewart Island, and along the whole of the West Coast.

At the first-named localities the granite is of a pinkish tinge with grey spots, and rather coarse in the grain.

The veins and blocks supply a fine-grained, beautifully-coloured stone, more suitable for architectural and monumental work than the former.

At Seal Island a fine grey granite vein occurs, having a smooth grain.

Granite rocks occur in detached areas in the Westland District, but not in accessible situations, being very different in that respect from those occurring on the south-west coast, where they admit of being quarried and shipped with great facility. At Astrolabe Island, and Tonga Harbour on the west shore of Blind Bay, is probably the easiest place from which granite could be quarried. It is there of fine quality, and can be quarried out in masses suitable for kerbing and harbour works.

A variety with garnets is found at Metal Mountain, Milford Sound.

Chrystalline Schists.—Gneiss of equally good quality with the granite from the south-west coast is to be found in many other inlets, and on the north shore of Milford Sound there is one point where there is an immense accumulation of blocks of a grey variety mottled with chrystals of garnet, and of all sizes and shapes, lying as if ready for shipment. Other localities are "Connecting Arm" and Anchor Harbour.

Marble.—The purest form of this series is found in many localities in the South Island; statuary marble occurs among the gneiss and hornblende schists of the West Coast. The grain of most samples hitherto found is rather coarse, but coarser-grained kinds exist in Caswell Sound, where a quarry has been opened, and also in the Mount Arthur district of Nelson.

Granular or crystalline and subcrystalline limestones of every shade and colour, texture and hardness, occur plentifully, chiefly in the South Island.

Extensive masses of the harder compact kinds occur in the Upper Palæozoic formations. They are generally speaking of a blue colour and unfossiliferous.

One mass or stratum occurs in the slates of the Kakanui Range; it is several hundred feet thick, with an outcrop of five miles in length, and is probably the best in the District of Otago.

A great variety of excellent limestones suitable for building stones might be obtained from the Horse Range (Shag Valley side); at Twelve-Mile Creek, on Lake Wakatipu; Malvern Hills, Canterbury; and Hokanui Hills, Southland. In the latter district a very fine kind is obtainable, very slightly coloured; it belongs to the Cretaceotertiary series.

A white granular limestone called the Oamaru stone is worked in extensive quarries in the Oamaru district; but it occupies a large tract of the country in the north part of Otago and throughout Canterbury, and has a remarkable uniformity of colour and texture; its weight, wet from the quarry, is 1051b. per cubic foot, and when perfectly dry 921b. A considerable quantity has been exported to Melbourne.

The principal buildings of Dunedin are built of this stone, which shows a very fair amount of durability.

At Waiaroa, Auckland, there is a good hard close-grained stone, of a light, buff colour, mottled with black grains.