The limestones proper are as varied in colour and consistency as they are great in numbers; they comprise every shade and hue, from dark grey and blue to pure white, and every texture and degree of hardness, from stone as hard as basalt to chalks and recent concretions that can be dug with a spade. There is often a difficulty in deciding as to whether certain stones should be called limestones or sandstones; strictly speaking, they should be put in the class to which their predominant ingredient belongs; but, like the purely chemical arrangement referred to at the outset, this brings unlikely relations together; for instance, Caversham stone is more than half lime, though it has all the appearance and attributes of a sandstone. The classification of doubtful specimens is, therefore, made on the general resemblance as to their class rather than on a chemical basis.
Again, commencing with the hardest and most compact, we have a large mass of limestone at the Twelve Mile Creek, on Lake Wakatipu; in colour and texture, it closely resembles ordinary green or bluestone, possibly a little softer, but every bit as tough. The rock seems shattered on the surface, and incapable of yielding anything but materials for rubble work and ordinary ashlar, but it is probable that large blocks will be obtained when the quarry is opened out. The stone has not yet been extensively used for building purposes, but its excellent quality, and the ease with which it can be quarried and shipped, cannot fail to bring it into prominent notice.
A bluish-grey granular limestone is found associated with the marble in the Horse Range; so far as strength, durability, and appearance is concerned, it would make an excellent building material. In all probability it is the best limestone for the purpose yet discovered in the province. It is found on the Shag Valley side of the range, but I have no information as to the accessibility of the rock or the size of the blocks attainable.
There is fine limestone in the Peninsula much darker in colour, but closely resembling in texture the famous Bath stone of England. It has little or no grit, works freely, and seems durable. The colour is a peculiar tint of brown, rather sombre for building in a mass, but suitable for facings and monumental work. The stone is said to exist in large quantities, and to be procurable in moderately sized blocks. I am, therefore, confident it will
become one of our most popular building materials, when means of transit are provided. The deposit is in a very inaccessible situation, near Boat Harbour on the eastern side of the Peninsula, consequently the stone cannot be utilized at present.
A hard shelly white limestone has recently been discovered at Kakaunui, and used in some structures in that locality; it is of a uniform colour and consistency, nearly as hard as Sawyers Bay stone, but much easier worked; it should prove a valuable addition to our stock of building materials. A variety of this stone, from the same place, similar in colour and consistency, but full of large fossil shells, has been quarried for the foundations of the new road bridge; it is admirably adapted for work of that kind, but is altogether too rough for architectural purposes. These stones are both procurable in large blocks, and the supply is unlimited.
A coars grey limestone, of uniform colour and consistency, is found in large quantities on the Totara Station, near the Waireka Creek. With the exception of the foundations of the Waireka road bridge, it has hitherto been little used. Although more friable, the stone is about as hard as the Tasmanian sandstone; it has a beautiful warm tint of an agreeable shade, and seems capable of being dressed in any way, from hammered to polished work.
A valuable addition to the limestones has recently been worked at Waihola Gorge, in the shape of a beautiful grey stone, found on the western side of the main road, about 40 chains from the railway. The stone, when newly quarried, is harder than the Oamaru stone when dry, consequently it must be very much harder after being exposed to the air for some time. It can be dressed in any way is capable of taking a fine polish, and, being easy of access, it cannot fail to become popular as a building material, whenever the Southern Railway is open. A solid face of stone, 20 feet thick, is already exposed in the quarry, consequently the appliances for handling and transporting blocks must alone determine their size.
Both sides of Waihola Gorge contain large quantities of the limestone that is used for lime burning. This is a very hard compact stone, of a beautiful white or light cream colour, without a speck. So far as strength, appearance, and durability are concerned, it makes good building stone, but hitherto it has not been found in blocks of sufficient size. The whole rock is shattered into layers a few inches thick.
The blue and grey limestones of Pleasant Valley come next in order. Several varieties of them exist in large quantities, and they are all remarkable for beauty and uniformity of colour, fineness of texture, and the ease with which they can be dressed and carved. Unfortunately, however, they are too soft and friable for out-door work. This stone has been used in the
Bank of New Zealand, Waikouaiti, Mr. Hepburn's house, Brooklands, and other prominent buildings in that district.
I now proceed to the consideration of the most important building material that hitherto has been used in Otago, viz., the Oamaru Stone.
The use of this material is coeval with the settlement of the district in which it occurs, but it was little known beyond till 1866, when an export trade commenced with Dunedin. The first large building erected of this stone in the city was the University.
The Oamaru stone occupies that large tract of country in the northern parts of the province, extending northward from the Kakaunui to the Waitaki Plain, and outward from the coast to the Kawroo River. The same class of stone is also found from Riverton to the head of the Te Anau Lake in Southland, and at Castle Rock on the Taringtura Downs. Practically speaking, the supply of this material is inexhaustible. There are extensive quarries worked in the Oamaru district, from which a large quantity of stone is produced annually, both for local wants and export to other parts of the colony and Melbourne. The trade with the latter port is of recent birth, but it promises to be ultimately an important one. The principal quarries now at work in the Oamaru district are at Cave Valley and Kakanui. The town of Oamaru is chiefly supplied from Cave Valley, and Dunedin and other southern districts from Kakaunui. The trade to Dunedin alone is sufficient to keep one or two vessels constantly trading to Moeraki.
Much has been said as to the relative merits of the Oamaru stone from different localities, but I do not think that there is any practical difference in similar samples. The constituents of the stone are almost the same throughout the province, so any difference in colour or texture must be due to its proximity to foreign matter or facility of drainage.
The Oamaru stone, correctly speaking, is a white granular limestone. It has a remarkable uniformity of colour and texture; not only can large blocks be got of the same tint and consistency, but whole cities might be built, in which one stone could not be distinguished from another.
According to Mr. Skey, its component parts are—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Carbonate of lime||90.15|
|Oxide of iron||.55|
The ordinary English building stone which most resembles this is the Kelton Oolite, its analysis being—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Carbonate of lime||92.17|
|Iron and alumina||.90|
|Water and loss||2.83|
The weight of Oamaru stone, wet from the quarry, is 105 pounds per cubic foot, and, when perfectly dry, 92 pounds; that of the Kelton Oolite, when dry, 128 pounds. The lightest limestone in England is the Bath Oolite, which weighs 115 pounds per cubic foot. The New Zealand product is, therefore, the lightest by about 23 pounds per cubic foot.
Applying the chemical tests to the Oamaru stone, we place it on a par with the Oolites and common limestones of England and the Caen stone of France. According to Dr. Hector, the resistance it offers to the disintegrating action of Glauber Salts is comparatively feeble. Its inferiority to the above mentioned stones consists chiefly in its excessive porosity. I have made several experiments, with the view of measuring its absorbent powers, the results of which are worth recording; A block of Kakaunui stone, used as a footstool in my office since 1868, and consequently thoroughly dry and hard, furnished the best possible materials for the tests. A piece of this stone, seven inches square and one and a half inches thick, equal to 73.5 cubic inches, weighing, when dry, 56 ozs. 17 dwts. 11 grs. troy, was put in water; within 40 hours it had absorbed 12 ozs. 15 grs., equal to 31 per cent. of its entire bulk, and 21 per cent. of its weight. The specimen was allowed to remain in the water for sixteen days, when the quantity absorbed had increased to 14 ozs. 2 dwts. 19 grs., which gives 36 per cent. of the entire bulk, or 228 gallons of water in a cottage wall ten feet square and one foot thick.
A bar of Oamaru stone, 13 inches long and 1.65 inches square, was next placed vertically in a glass of coloured water; it stood 3.2 inches into the liquid. In six hours the moisture was quite visible to the top of the bar, and in twelve hours the colouring matter had risen 7 ½ inches. As the stone in both these experiments was particularly dry, the maximum results are probably obtained; but, on the other hand, the vertical position of the bar, in the second experiment, was less favourable to the absorption of moisture than that usually occupied by stones in a building, particularly the horizontal parts of mouldings, cornices, copings, and window cills. It should be pointed out that the Oamaru stone absorbs 36 per cent. of its bulk without pressure, while the most porous English stone only absorbs
25 percent., under a pressure of fourteen pounds on the square inch. It is doubtful, however, if an increase of pressure in the former case would give corresponding results, the stone being so excessively porous, gets completely saturated at once. When the dry samples were first put into water, the air rushing from the pores of the stone, caused bubbles to rise to the surface for fully ten minutes. The first experiment shews that the stone is capable of absorbing ten pounds per cubic foot more water than it contains when in the quarry, a result to me quite unexpected, and not easily explained.
One of the most important points, in connection with the use of Oamaru stone, is the degree of induration it attains in drying, and the loss sustained by subsequent exposure to moisture. So far as the hardening is concerned, I am quite satisfied that the largest blocks used in ordinary masonry become equally hard throughout in a few months, and possibly in a few weeks, under the influence of a warm dry atmosphere. The hardness is not confined, as is sometimes supposed, to a thin crust on the surface of the stone, but penetrates to the centre, making the whole a perfectly homogeneous mass. In consequence of the time required, I have not been able to prove by direct experiment that a stone once hardened becomes soft on exposure to wet. I fear, however, that such is the case; the window sills and mouldings on the south side of the University building are now fully softer than when they left the quarry, and the chances are that these stones had acquired a considerable degree of hardness before being placed in the building. The cornice and parapet on Messrs. Dalgety, Nichols, and Co.'s warehouse, although in a much more favourable situation, on the sunny side of the street, is softer still; the stone can be scratched out in handfuls by the finger nails. This is, however, one of the oldest, if not actually the oldest piece of Oamaru stone masonry in Dunedin; it is, therefore, possible the material was bad to begin with.
Against these unfavourable examples, the bridge in Thames Street, Oamaru, built in 1860, and several other buildings of the same age, in that locality, are not decayed, nor unduly charged with moisture. The ultimate durability of our Oamaru stone buildings cannot of course be determined at this early stage of their existence, and any estimate, short of actual trial, is little more than conjecture. Professor Black might, however, give us his opinion as to whether it can long resist the action of the saline breezes from the Ocean Beach, the sulphurous fumes of the Green Island coals, and the other impurities that are now so rapidly accumulating in the atmosphere of Dunedin. I should be loth to prophecy evil, but if the durability of the Oamaru stone is to be measured by its power of resisting moisture, it is to be feared that the handsome spires and facades that now ornament the city
will not transmit the names of their architects to many succeeding generations.
Although the bad qualities of the Oamaru stone are quite apparent, there is, on the other hand, so much to recommend it, that it will always be a popular building, material. I shall, therefore consider the work for which it is well adapted, and the precautions necessary to ensure the best results from its use.
The stone is well suited for any ordinary work in a dry warm climate, like Victoria, and it is unexcelled for internal decorations of all kinds and in all situations. It is suitable for ecclesiastical architecture generally, and forms a beautiful contrast as facings to darker stone.
It should not be used in the southern side of buildings, particularly if they are recessed, and it is altogether unfitted for window-sills, parapets, and the upper side of large mouldings and similar projections. Buildings of this material should be designed to have as few of these as possible, and where unavoidable, the flat tops of the stones might be covered with some preservative; from an æsthetical point of view, this is the only part of a stone building where such should on plea be permitted. Dampness can be prevented, to a certain extent, by an impervious foundation and internal lining, hollow walls, and other expedients of a similar nature. I have made several experiments with Oamaru stone, to test the efficacy of certain appliances occasionally used to prevent damp. A bar of dry stone, after receiving two coats of ordinary oil paint, was deposited in water. In 40 hours it had absorbed 34 per cent. of its bulk, including the weight of the paint, against 31 per cent. absorbed by unprotected stone in the same time. Another sample, coated with soluble glass, the principal indurating ingredient in artificial stone, absorbed 27 per cent., exclusive of the weight of the solution, which was four per cent. more.
Although these experiments give an indication of the results to be derived from the application of the materials referred to, they are altogether too crude to be advanced as conclusive. The oil in the paint was absorbed to such an extent by the stone that the colouring matter, which remained on the, surface, could be washed off by water. It is, therefore, probable that much better results would be obtained by more coats, and the use of a heavier pigment like red lead. With reference to the use of soluble glass as a remedy for damp, I am not sure that this is a property to which it lays special claim. Although porosity is a primary cause of decay, it may be possible to increase the hardness and durability of stone, without removing the lesser evil. Besides, the method of applying the solution adopted by me, may not be exactly correct.
The following is a recapitualation of the results obtained by the various experiments on Oamaru stone.
|Weight, when fresh from quarry||105 per cubic foot.|
|" " quite dry||92 "|
|" after 40 hours' immersion in water||111 "|
|" " 16 days' " "||115 "|
|" painted stone, after 40 hours' immersion in water, including paint||111 "|
|" of stone coated with soluble glass, after 40 hours' immersion, including solution||111 "|
The principal buildings entirely of Oamaru stone in Dunedin are:—The University, First Church and Manse, Union and New South Wales Banks, Fernhill, and the Pier Hotel. In Oamaru, nine-tenths of the buildings are of this material, and several of them, such as the National Bank and the Star and Garter Hotel, are worthy of a place with the architecture of the old world. The private residences in that district can also be classed along with the country houses of England, notably Windsor Park, Elderslie, Moa, and Totara. The stone has also been used in numerous road and railway bridges, many of them of considerable span.
The granular limestone found in Southland resembles closely the Oamaru variety in composition and colour; it is, however, a little coarser in the grain, and, if anything, harder and more compact. Large deposits are known to exist at Aparima Castle Rock, and several adjacent points, but hitherto it has been little utilized.
Sandstones.—The sandstones of Otago are as varied in consistency and more numerous than the limestones, but excel them in diversity of colour. The extremes in the latter are generally connected by gradations of blue and gray; but sandstones merge into all conceivable shades and hues.
As already stated, the Craigleith sandstone, the analysis of which has been given, is the best in Great Britain. It is, however, too hard for many purposes, so the Midland and Scotch stones, that have five or ten per cent. less silica, may be taken as the type of a good and useful building material. A corresponding type, in the colonial product, is found in the Tasmanian freestone, of which the High School, Custom House, and Cargill monument are built; it contains 86 per cent. of silica. Any Otago sandstone that has so much of this base, and has a hard compact texture, may be considered strong, durable, and dry.
The highest class of sandstones, as regards their relation with the hard stones, are grits. These abound throughout the Province, chiefly in the
form of large boulders, or erratic blocks, like the Sarsen or Druid stones of the South of England. Numbers of them exist on the ranges about Kaikorai, Tokomairiro, and Kaitangata. They yield stone of a red or brownish colour that varies in texture from coarse sandstone to conglomerate with large pebbles. The blocks are usually harder than ordinary sandstone; but are sometimes wanting in cementing material, so much so that the stone easily reverts, under pressure, to its original gravel.
The grits furnish good building material for massive coarse work; but are comparatively valueless for architectural purposes. The railway bridges at Chain Hills and Glenore are built of this kind of stone—that in the former work is comparatively fine in the grain, but the others are coarse and full of pebbles. They are both used in large blocks, which, along with the dark colour of the stone, tends to give the structures a massive appearance very appropriate to this clase of work.
Closely allied to the grits, and existing under much the same circumstances in the same localities, we have numerous freshwater sandstones. They are of various colours; but are all extremely hard and compact, apparently highly charged with silica. A very handsome stone of this kind, found in the Hillend district, has been used in the abutments of the Clutha Railway Bridge; it is of a silver-grey colour, and an even hard texture. Other samples found in the same locality, and at Chain Hills, are of a reddish-white colour, equally compact. Both varieties are too hard for dressing with the chisel. There is a good specimen of white sandstone in the Museum, from Murison's Gully, on the Rough Ridge; in all probability it belongs to this class. A connecting link between the grit and sandstone proper is found on the western side of the Waihola Lake, from Mary Hill to the Gorge. It has a tough granular texture, capable of being easily dressed with the pick or chisel, but too hard for smooth work; its colour is a light warm brown, very suitable for architectural purposes. The stone is supposed to exist in large quantities; but has hitherto been little used. Mr. Duff's house is the only building of it that I know.
The sandstones proper, which embrace all sedimentary rocks in situ, are found in immense quantities throughout the Province. Unfortunately the more accessible supplies are of an inferior quality, consequently this stone has hitherto been little used for building purposes.
One of the hardest sandstones in Otago is that at the Falls, Gore Township, and at other places on the Mataura River, it is of a dark green or blueish tint, almost as hard as bluestone and equally unworkable. It is found in large blocks, with natural joints and beds, and so is very suitable for massive coarse work; the two bridges over the Mataura are built of this material.
A sandstone, of much the same quality though scarcely so hard, is
found on the northern slope of the Puketapu; its colour is generally a light blueish grey, like Portland cement, but occasionally merging into yellow. The new road bridge at Palmerston is being built of this stone. Although found in large blocks, the deposit is supposed to be limited.
There is a hard yellow sandstone associated with the limestone at the Twelve-Mile Creek, Lake Wakatipu. The rock is very much shattered, consequently the stone is not procurable in large blocks; but it can be got of a sufficient size for housebuilding. This material has been used to a small extent in Queenstown.
Waikara, as might be expected from the geological character of the district, produces a compact hard sandstone, suitable for building. The only sample in the Museum is rather dark for architectural purposes; but I have no doubt there is an abundant supply of all kinds between the Clutha and Mataura. In 1865, Dr. Hector said of this stone: “It has a disagreeable colour; but its texture and stability is superior to any of the sandstones in the Province which have, as yet, been examined, although others have been seen that will probably prove of quite as good quality.” The Waikara sandstone contains 80 per cent. of silica, which is a near approximation to the Tasmanian stone in its essential constituents. Mount Hamilton, in Southland, produces an excellent sandstone of much the same character as that at Waikara, but firmer in the grain, and of a bluish colour. Altogether this is a first-class building material; but I have no information as to the extent of the deposit, or the facilities presented for working the stone.
The district between Palmerston and Moeraki contains an immense assortment of sandstones, many of them, like a portion of the cliffs in Trotter's Gorge are too soft and friable for building stones; but there are a number of isolated blocks and veins that yield good materials. A fine yellow stone, of much the same texture as the one from Waikara, has recently been worked near Puketuitai, and there is a smooth-grained dark red ferruginous sample from the Upper Horse Range, in the Museum. Both of these would make excellent building stones. The former, having a beautiful colour, should be particularly sought after when the means of transit are provided. These are only quoted as examples of what the district can produce; there are at least five places on the railway line between Pleasant Valley and Trotter's Creek, where good sandstones can be obtained.
Proceeding further up the Waihemo Valley, we find the accommodation house at Coal Creek built of a coarse-grained yellow sandstone, found in the neighbourhood. It is also said that a large deposit of fine white stone exists in the same locality.
A hard brown sandstone has recently been discovered and worked on the north side of the Otepopo Hill. It is being used in lining the tunnel now
in course of construction through that range. Although hard, the stone dresses readily with the axe. It is found in large blocks, with regular vertical cleavages, in both directions, at right angles to each other, which gives the stones two natural faces, as true as can be worked artificially, thereby presenting great facilities for quarrying and dressing. The brown sandstone of Otepopo is too dull in colour for ordinary architectural work in large surfaces; but seems well adapted for basements, facings, and massive masonry.
The class of sandstones that comes next under our notice is the rusty-yellow varieties found at Anderson Bay, Arden Bay, Kaikorai, Saddle Hill, and Greytown. In my opinion these rocks are simply ordinary soft sandstone, like that at Caversham, dried, consolidated, and baked by volcanic fires. In the early days of the settlement, this stone was used to some extent in Dunedin and its vicinity. In the Juror's Reports of the New Zealand Exhibition, analyses are given of several varieties, which show them to have, to a moderate extent, the essentials of a good building material. The reporters, however, say that, in consequence of the excess of impalpable cement contained in the Arden Bay stone, “it will not be durable if much exposed to the weather;” and that the Anderson Bay stone” breaks up rapidly when tested with sulphate of soda, so it will not resist the action of frost.” These two stones happen to have been used in the New Zealand Clothing Factory, built about the year 1861. From its enclosed position, the southern wall of this building never gets the sun, so the stone has been subjected to the severest meteorological test that can be applied in Dunedin. The predictions with reference to the Arden Bay stone have been realized, as the lintels and sills are beginning to decay, but three lintels of the Anderson Bay stone are as fresh as when erected.
The class of sandstone that comes next in order of hardness, I shall call the “Otepopo Free Stone,” as that district furnishes the greatest number and variety of specimens. They, however, occur at other places throughout the province, notably on Mr. Larnach's property, near Broad Bay.
In the Otepopo Valley, the stone is of all shades, from clear white to dark yellows and reds; that at Mr. Larnach's is bluish-grey, like Portland cement. Although it abounds in great quantities, and often in accessible situations, the distances of the deposits from centres of population or a shipping port, has hitherto prevented its use; neither has the stone, to my knowledge, been analyzed. It seems to have most of the attributes of a good building material. The only objectionable feature I can discern is an apparent deficiency of cohesion between the particles of sand. As the cementing ingredient does not appear to be clay or lime, it is possible that this defect does not exist in stone from the bed rock. If the objection just
mentioned is not found to be a serious one, I have no doubt our main supply of freestones for architectural purposes will ultimately be drawn from the Otepopo sandstone.
The lowest grade of freestones, and the last in my list, is the well-known Caversham stone. The deposits of this rock throughout the province are practically illimitable. It can be found anywhere along the coast, and for a considerable distance inland, from Kaitangata to Moeraki. The extent of the deposits in accessible situations increases the regret often felt about the inferiority of the stone, and one is apt to wish that it had exchanged places with the carboniferous sandstones in the neighbourhood of the Dome Pass or Eyre Mountains. This stone has been found below sea level at Green Island and Otago Harbour, and 1000 feet above it, at the Leith Saddle: and the Look-out Point tunnel, 950 yards long, is through a solid rock of the same material. I might almost say a solid stone, for there are only five or six cracks in the entire length. The Caversham stone is generally of a bluish-grey or yellow colour; but these are seldom blended in any way; its texture is also remarkably uniform; in peculiar situations, such as isolated cliffs and near basaltic dykes, the stone occasionally changes, but the solid stratum of rock is perfectly homogeneous.
Although it was extensively used as a building material some years ago, Caversham stone is altogether unsuited for any purpose where strength or durability is required. It does not at first harden on exposure, like the limestones, but begins to decay whenever erected, if exposed to winds, rains, or frost. Some of the Caversham stone, used in old buildings that have been painted, is still sound, but there are a few exposed examples, particularly on southern walls, that are not decayed to a considerable extent.
This completes a description of the principal Otago building stones, on which I have information. You may have noticed that, although they comprise specimens from all quarters of the province, there are a few isolated districts capable of producing good materials, to which no reference has been made, viz., the Upper Waitaki, Tapanui, Switzers, and the Waiau. I know little or nothing of their resources, consequently I am reluctantly compelled to omit them.
The first part of my next paper will be devoted to the consideration of bricks and concrete, after which I shall revert shortly to stones as the building material for which they are substituted, and institute comparisons between the relative merits and cost of the three materials.