OTAGO INSTITUTE.

Evening Star, Issue 3865, 14 July 1875, Page 2

OTAGO INSTITUTE.

A general meeting of member* of the Otago Institute took place last ererinp, when about sixty gentlemen were present. The President (Mr J. S. Webb) occupied the oh iir. Messrs J. E. Dennistoun, R. A. Lawson, Alex. Armstrong, and Alex, Burt were elected members.

Mr F. Gillies resigned the treasurerahip, and Capt, Hutton consented to act in bis place for the remainder of the year. MR BLAIR'S PAPER. Mr W. N. Blair, 0 E., then read an interest4»g paper on *' The Building Materials of Otago (Part 1., Building Stones), 1 * and furnished specimens of the various Atones treated of. The author said, in introducing this subject, that he did not wish the paper to |be considered exhaustive, or entirely free from errors ; but raiher as an introduction to a thorough investigation of a subject which iB of the utmost importance to the Colony at large. The natural resources of New Zealand generally are equal to those of many old countries that take a prominent position in the affairs of the world, an 1 although Otpgo seemß deficient in some ot the products which ensure permanent prosperity—such as bituminous coal and metals—there is an abundant supply of good building materials of eve y description, and, with the exception of oneor two articles, there are well distributed throughout the Province. In considering.the subject he would do so under the following headß :—First: Stouts, bricks, concrete, and roofing materials. Second : Limes, cements, and their aggregates. Third : Timbers and metals.

Building Btones are usually divided into three classes, determined by their composition—viz.: Silitions, argillaceous, and calcareous. The pi incipal bases of stone are silic, alumina, and Hme, and tho hardest and > most durable stones aro thcße in which the tirßt predominates; many of thtm, such as granite and basalt, being practically indestructibe. The buildiuj, slonesniost subject to decay are sand and limestones. The reddish sandstones generally 'contain iron in considerable quantities : when the iron is naturally in a low state of oxidation, the stone has a tendency to deouy on exposure ; but when the iron is highly oxidised, and the whole a perfect homogeneous aud compact mass, the stone is not aff cted by the changes of the weather, and may therefore be taken as durable. As a general rule, sandstones are hardest and most compact when formed at the lower side of a thick rtratura, or in the vicinity of basaltic dykes, or othei volcanic rockß that may have disturbed them. In building with stones from stratified rocks, it is absolutely necessary that they be laid on their natural bed. A disregard for this rule is the sole cause of decay in a large majority of cases where buildings have failed. 'J he appearance of some of our soft stone buildings fully bears out the above remarks as to the necessity of laying stoneß on their natural bed: some of them are smooth and Bolid after many years' exposure, while othera, from the same quarry, nnd under exactly the same conditions, are in an advanced state of disintegration. Although limestone is generally more compact than sandstone, it absorbs more water; but, on the other hand, the water affects it much less than sandstone. The compactness of limestone seems to keep the water from freezing, ard bo neutralises its most powerful disintegrating property. The ingredients in the atmosphere that have the most deleterious effect on stones are muriatic and sulphuric acid, both of which have an affinity for Jime, and combine readily with it, thus rendeiing the stone Boluble in watsr. All the softer limestones are more or less subject to the pernicious effectß of both these acids, and when magnesia Venters into their composition they are particularly susceptible to the action of sulphuric acid. Tho English Houses of Parliament are built of magnesian limestone from the Bolsover quarries in Derbyshire, its composition being at, follows : Silica, 3.6; Carbonate of Lime, 61.1; Carbonate of Magnesia, 40.2 ; Iron, Alumina, 1.8; Water and loss, 3.3-100.0. It is well-known that this stone has been a decided failure: the buildings were not many years finished when they began to show symptoms of decay, and this result is due entirely to the sulphuric acid with which the smoky atmosphere in London is impregnated; Except in rare cases, such as the arches of a long-spanned bridge and the lower courses in a «pire or chimney, the pressure on stones in a building never approaches their crushing weight; their cohesive properties may there* fore be disregarded in a popular investigation hke the present one. So far as strength and beauty, as well as durability, under ordinary circumstances, are concerned, the roagnesiau limestones are best when the lime and magnesia are in equal proportion. This, however, as already shown, seems the worst proportion for a smoky town. The artificial induration of building store j is a problem that hai occupied the attention of scientific men for years, and numxious processes have been tried with varying degrees of sucaess; but after numerous experiments it is thought that a perfect remedy will ultimately be discovered—a veiy great •lesidcratum when the relative cost of building in hard and soft stone is discovered. I he geography of the Otago building stones comes more properly under the consideration of the Provincial Geologist, and is clearly shown on Captain Hutton's map. It is, however, necessary, for the completeness of this paper, that a general indication of the localities be given. Commencing with the older rocks, we have true granite in mass at I reservation Inlet, aud in numerous veins and isoluted blocks in Stewart's Island, and along the wbolo of the West Coast. Syenite and other granitic rocks are also found in large quantities in tho same localities ; and the Bluff Hill is chiefly composed of the former. Gneiss, mica Kcbists, and other crystalline rooks of a similar character, which compose the Manipori formation, abound from I'reservation Inlet to Martin's Bay and inland to Manipori and the To Anau Lakes. Schists and clay-slates exist in the Wanaka formation, a broad zone extending from the Taieri Plain and Waikouaiti to Lake Wanaka. and which is flanked *n each side by narrower belts of the newer slates, aud possibly limestones of the Kakanui formation. '■ The Kakauui or carboniferous formation extends in a narrow strip parallel to the schists and olay slates, from Balclutha, via Switzers and the Eyre Mountains, to Martin's Bay. There are also large areas between the Big Rivtr and the Monowri Lake - at Orepuki, Stewart's Island, and tie Upper Waitaki • with small patches at tho Bluff, the Takatimos' Akatore, and the Horse Range. The triassic' otherwise Maitai aud Putaki formations, occupy tho whole of the country between the Clutha and Mataura as far iuland as Gore, iheuce extending in nn irregular chain to the Takatiuio Range. The Waipai or cretaceous formation ia represented in this Province by a strip of limited area extending from Shag Point toUtepopo, and a small patch at Mount Hamilton. The Oamaru, Parrora, and Wanganui series corresponding to the Eoceue, Miocene, and Pliocene of geological chronology, oeoupy portions of the coast from the Clutha to the Waitaki, including the Waitaki Plain. The Mamototo Plain, Ida Valley, Manuherikia Valley, and the Tokomairiro Plain all belong to this uroap, and an irregular belt of the same runs from Orepuki to the head of the 1 e Anau Lake. 1 he economic products of tho Pleistocene formation are chiefly clays, gravels, aud sands, which will be considered further on. The volcanic rocks of Otago yield valuable building materials, and are situated chiefly betweeu Saddle Hill and Waikouai'.i; but there are isolated patches at Apaiima, Waihola, Upper Taieri, and between Shag Valley and Oamaru. Granite is the monarch of buildinsr stoneß; although hard and tough, it is not difficult to work with the hammer, pick, or chisel. It can be got in any sized blocks, and takes a polish like marble. Granite has been used for centuries in engineering works and other structures, tlwt were calculated to last for ages but it is only of late years that it has been ex'tensively used for ordinary a ehitectural purposes. According to Captaiu Hutton, Preservation and Chalky Inlets are the ouly localities in the Province where true granite is found in mountain masses, but it exists in large veins and blocks in Stewart's Island and the whole of the Weßt Ceast. Profeßsor Black, in Stewart's Island, and Dr Hector, on the West Coast, report its occurrence at ev<>ry step. In appearance, the Preservation Inlet granite is not unlike that found in the Island of Mull being of a pinkish tinge, with grey Rpots, and rather coarse in the grain. Although it, in all probability, is equal in strength and durability to most of the granites of the old country, and

consequently suitable for kerbing, paving, and engineering purposes, its color will be an obj ctionin architectural works. There isa vein of light grey granite at Seal Island, the color of which is uniform and agreeable; it has a white ground and dark spots, and the grain is very smooth. The chief supply of Byenite now available for industrial purposes is at the Bluff. Practically, the whole of the Bluff Hill consists of this material, and it could therefore scarcely bo in a more accessible situation. In his Blair's) opinion this stone is little, if anything, inferior to the famous Aberdeen granite. lhere_ is a eurious variety of syenite found at Milford Sound, and another vein of syenitic granite exists at Isthmus Sound. Pegmatite, or com- ? act granite, is found at Milford Sound and 'atevson Inlet. Mr Blair concluded bjr spying that he had compared Mr Skey's analysis of the Otago granite with that of the Irish varieties given in "Juke's and Geikie's Geology," and found that, though at opposite sides of the globe, their composition is practically the same. L«ud expressions of thanks were made to Mr Blair for the pleasure afforded by hearing his excellent paper, of which we hav> been able to find space for only a small portion. A Bho: t discussion took place amongst the members, after which the meeting adjourned for a fortnight, Mr Beal being appointed to read the next paper.