BUILDING STONES OF OTAGO.

Otago Daily Times, Issue 784, 18 June 1864, Page 10 (Supplement)

BUILDING STONES OF OTAGO.

(From Dr. Hector's Report.)

_ Preestones, which, m>all; Countries;where they can be procuredj form the' most r desirable bunding material,, on account of the facility with which they are. dressed, occur abundantly throughout the .Eastern .part of the Province, araong^he-Tertiary strata*, and although ;.they;.>a£e.*:-ÜBed^tq/»^cbn» siderable extent as buildingijmateriali thej ; are generally adopted withdisjtrustj-pwing to their apparent want of'durability.; Chemical examination however proves that many of the, varieties -Can be safely re>i commended as quite equal, to freestones | which are in use in England,; provided, proper care be taken in^heir,selection, and. that therefore the distrust is not always; well founded. On the. other hand; Several of the varieties which, have a most promising external appearance/ are found 'to contain a minute per centagejofi: elements that will be certain to cause rapid decay; when exposed ■to the. influenced of the weather. The stones chosen for examina-: tion by chemical analysis have been-there* fore such as present variety of -character* sufficient to; indicate the principle upon: which; their.selection as; building-materials shsuld be made, and it is believed, that all the varieties which may be-examined will fall within the classes into which J the specimens analysed have been divided. ; . < ■ v;t i ;=

divided. , v;■ i In making a scientific examination of a mechanically-formed building,stones we have to regard its chemical and physical properties. • - The formerareof very great-importance ~ a 9 by. a knowledge of the - cotistitaent; minerals of a rock we arrive at .si'fait estlmate of its power of resisting the various destructive chemical influences to which it will be subjected. Chemical analysis in many cases affords the only means by which we can discover that a .stone;of most promising appearance judging by ihe external characters^ contains elements that will lead to discompose speedily, as frequently the stability of the material is seriously affected by the presence of some accidental impurity existing only in very small quantity. ■ Thus experience has clearly shown that it is the presence of minute proportions of alkaline in the stone used for exterior masonry which has caused the disfigura- ■ tion bfjsoine qf the finest edifices in Great i Britain. -^ *,- ■• • "■■■■• <•'' ■'•

.: ;.Itisjtherefore "particularly necessary to ascertain the impurities ~, which are contained iri; freestones, by which means the elements that do. not form an, essential part: of the stone,-but the detection of which is generally : r;bf: more importance than the determin'aijioir jot the principal constituent niihe^alg..,',/ ,rr ;^ In niaking thft various analyses; thereinafter given r > especial ■ attention '<[ has beeti directed to this aubjectj, and in the table appended, the,. presence, nature,- and amount of these impuritieshave been indicated in separate;columns.^ : vii . .. ,Gn the other hand, the durability, and value oi building1 stones depend almost to an; equal degree on'their pnysical. proper^ ties, aa on those above alluded to. Their hardness and tendency to absorb water, their structure whether massive or laminated, the facility with which they »an be

broken into masses of convenient 9ize and shape, or worked with the chisel with plane or curved surfaces, their power of ' resisting'the i effects of froat/theldlyingft *nd baking action of the sun, all these are pointa which can only be imperfectly ascertained in the Laboratory^ and re- ' quire for their determination the opinion of the practical architect, founded on the experience Avhich time alone can furnish.

As a means of increasing the useful &p----plication of the freestones of the Province,; it may be suggested that by the method of '. artificially hardening the surface of stone, which has been patented by RaiVsome of Ipswich, we have a means, of, rendering durable, at a very small expense, even inferior varieties of freestone.!

An experiment was made in the laboratory on a small scale with a cube'of the ordinary yellow Caversham stone, with a very"successful result. Ransome's process consists in first washing the stone withj soluble glass or silicate of potash. After ibis is entered into the grain, of the stone' it is decomposed by a; solution of a'Salt' of lime, which seizes the potash, and,leavea, an insoluable silicate of lime as a cement that binds the particles of stone together* In 'the'experiment that was made it was' found that the stone contained a sufficient quantity of the requisite salt of lime, so that upon''the' application of the " water glass" alone the cementing and hardening processes were found to have penetrated the surface of the stone to the depth of one-sixth of an inch, which would, be, amply sufficient to resist the influence of the weather. :

The following table gives a selection from the various analysis of Freestones which have been made, arranged so as to indicate at a glance the groups under which the principal varieties may be classed, and the relation they bear to one another.

From this table it will be seen that they are naturally divided into three groups, according to the nature of the cement which binds their particles together., A. Silieious sandstone or freestone proper, containing particles of silicious sand cohering by a silicious, ferruginous or argillaceous cement. A perfect stone of this class, that is possessing the reauisite tenacity and freedom from impurities, is the most useful building stone we can have, as it unites great durability with the property of being easily worked into any desirable form.

B. Argillaceous sandstone or claystonea. The gradation from the last class to this is represented in every stage as the silwious matter becomes deficient, and is replaced by clay as a cementing material, The' stones belonging to this group can rarely be depended upon for durability. C". Calcareous sandstones. In this class of freestones, to which most of the varieties used in Dunedin belong, the partfclea or grains of the stone are- still .partly silicious, but the cementing matter consists of carbonate of liraie, derived from marine shells. These stones vary much according to the.proportion of calcareous matter, and the extent to which it has combined the sandy matter, or been dissolved from the fragments of shells, and re-deposited asa true cenient. The great objection to the use of these stonesraris'es from th.c .circumstance, that if uniform in teitureV'tfiey^are soft and destructible, while., \i hard tHeir consolidation has generally been owing; to cbhcretipnary forces that never fail -to. produce I great irregularities in the quality of the stotie

Many calcareous sandstones 'harden , upon! exposure .to the atmosphere, but .■ geneiially "only on the surface, sothat a crust is formed that peels off the first attack of frost; .'■ ''■;'.;■■ ... " -'." . -.- : '•■■",.•. .: The distribution of the Varieties of freestone throughout the Province is by, up .■■ means fairly represented by the " selection. '. ~ which has been made for the purposeof '., analysis. , . . -, ; i , ; .j .:. .^ ; The true silicioiisi freestones arevfound, at the* base of the Tertiary formations, where they are associated with the brown coals. ;, Among the schists there are, however^ ar- ~ ranaceous beds in which the cleavage and ../.., jointing characteristic of metamorphic: strata has been only feebly developed, that might be included among the most valuable. ; ,. building materials of thisi.clajs.; ) Such are to be found In nearly every part of, the

Central distnct of the Province. ~, ; , , -; ;u ,;. . ■ Of the silicious frees^ohes the. jprincipaldevelopment is in the Horse Bjange,; and.l; where those.hills abut on the pQastrat, $hag . Point j there are beds of excellent quality,; ; /exposed, which, apparently, are conjtin'ued '■into; tte interior, underlying "the,'.jgreat . conglomerate formation of which the. broken ground albng^ the east flank of the ' Kakanui Mountains is composed! ."."•■. ; ; ■ To the South of the Molyneus River there -is another great development of this formation, associated with more ancienjt >: strata^ of undeteiroined geological:, age. The Stone mentioned' as from, Waikawa belongs ta those series of rocks and is said , to be!associated with a good quality of brown coal, both being convenient for,. ;sKipment from the little harbor at that.;

'place. '■'" '■ ~ -. '.'■<■■ ~,h ■,i^..;.." ■■ In Preservation and Chalky Inlet on the • S;W. boast, there^i^^a of,-.. \Bilicious.stra't.a\m;an^ shipment," and probably of -jmor'e anclgn^; v .; r > date than those as'socia^wlthihecoal'bji, :the east coast; In this locality and especially on Coal Island, in the first mentionedlnlet, , ,V : many: of the beds'^have^the;.;.c^laracte^ of ,\ "flagstdnes, and might be 'useful as pavmg ~: r, material,' Moreover the strata there rest ( : on clay slates that' present "more perfect ; . clearage than any met with in other parts _ of the iPrbvince, excepting in the valley of the Matakataki and Dart rivers; and. if; , these strata were examined with care for that purpose, it is .very probable that places would be found where_ quarries might be opened for the extraction of valu- t able roofing slate.' ,; . . j. .- .^ The argillaceous and calcareous,sand-.-,., stones are, without exception, confined,to,. ,-..- ---the upper Tertiary Rocks. The variable and concretionary, character has already, been alluded to, but there] undoubtedly exist large deposits which will afford most valuable building, stone. \ The valley of.;. , : the Waiou, the lieighbourhpod. of .Dune- ' ,; din, Waikouaiti, and Oamaru, yield many.. r varieties of the etohe, but n,one. of them... can be expected to present' great .differences in composition from the specimens of which the annexed analyses have been made. .. . .

•; DISTASCE TABLE. Distance from ' s : J „!!? Sydney to Auckland .. : 181»: „ Manukau ..::.... }f^ ;.;. Nelson .... -~.. "80 „ Bluff Harbor,, ... . • • • }"£ Melbourne to Auckland J Iffj „ Manukaii 11 * lit)! , Nelson ..u ... •• ... 1«J ~, ; ., Bluff -1,.;:.;,.. ... .-..1g „ Dunedm ... --■«... ™ Aiicklandtb Napier ...;, r ... iX •• |x 2 „ Port Ch£dnieMdireet) 808 ~ Canterbury- 67U . Napier to WeUington •• .•• •• 2°o Manukau to Raglan ... ■ '" „ Taranaki 1*« Taranaki to Nelson *« „ Wanganui »• «■• »n *w