Wednesday Evenings at 8 o'clock. CANTOR LECTURES. ... [No. 641. VOL. XIII. Forthcoming Publications :-The Applications of Geology to the Arts and Manufactures... ... Correspondence:-Cantor Lectures: Water Supply-The Municipal Organisation of Paris - Volunteer Fire Brigades 266 ... 266 Meetings for the Ensuing Week 267 267 ... 265 268 Proceedings of the Society. CANTOR LECTURES. SECOND COURSE.-FOURTH LECTURE.-MONDAY, FEB. 27. Professor ANSTED commenced by stating that from the consideration of materials obtained from superficial accumulations, not regularly stratified, we pass to stratified and igneous rocks, removed either by quarrying or by The Second Course of Cantor Lectures, the mining, and he proposed to bring under notice the facts subject being "The Applications of Geology to determined concerning stones used for constructive purthe Arts and Manufactures," by Professor D. T.be grouped in many ways. They are required for conposes. So far as their uses extend, these minerals may ANSTED, M.A., F.R.S., is now being delivered on structive purposes (1) as squared or rough stones, fit for Monday evenings, at Eight o'clock, as follows:- building walls of houses, churches, and palaces; (2) for MARCH 6TH.-LECTURE 5.-On Stratified Deposits of paving and roofing; (3) for road-making; (4) for the finer kinds of construction; and (5) for artistic purposes. The Minerals, as Coal and Iron Ore, usually obtained by Mining same kind of stone is often used for two or more of these Operations, and on Mining Methods for such Deposits. MARCH 13TH.-LECTURE 6.-On Metalliferous Veins or Lodes and their Contents, and on the Extraction of In reply to the letter addressed by the Council to the principal City Companies, the following has been received from the Salters' Company:SIE-The application made to the Master and Wardens of the Salters' Company, for aid in forwarding the endeavour of "The Society for the Encouragement of Arts, Manufactures, and Commerce," to improve the artistic taste and skilful manipulation of the art workman, by giving prizes for the best works executed from examples provided by the Society, was laid before the Court of Assistants at their recent meeting. The application was favourably entertained, and I have the pleasure to inform you that the Salters' Company resolved to become annual subscribers of ten guineas in aid of the fund for granting prizes for improving the artistic taste and skilful manufac ture of the art-workman, and I enclose a cheque for the first year's subscription. purposes, but, as a rule, the less perfectly crystalline kinds, being cheaper and more easily worked than the others, are used for commoner purposes; the harder kinds, capable of receiving a high polish, being reserved for more artistic purposes. Commencing with building materials, we may regard them as of three classesgranite, sandstones, and limestones; but there is another division into two classes, namely, those worked by the pick or by wedges, and those worked by the mallet and chisel. The latter are freestones, and include marbles, limestones, and sandstones. The former include granites, quartz rocks, conglomerates, &c. Granites are procured on a large scale from Cornwall and Devonshire, where they are worked with facility and cheapness; others are from Peterhead and Aberdeen. Others, harder than either and of a darker colour, are from Guernsey, Malvern Hills, and Leicestershire. Granite consists of crystals of quartz, felspar and mica in crystalline quartz. The mica is frequently replaced by hornblende, the result being syenite. The felspathic portion of the stone also is sometimes albite, in which the alkaline element is chiefly soda instead of potash. Granite may be coarse or fine grained. Some kinds are brittle and others tough; some break along lines of natural fracture, while others resist regular fracture. Chemically, granite is a silicate of alumina and potash, with a little iron and lime, soda sometimes replacing the potash and magnesia the lime. To a certain extent, granites are mixtures of crystalline minerals in various proportions, and an average variety contains from two to three-fifth parts of crystals of quartz or crystalline quartz, about the same of felspar, and the remainder mica. Granite possesses a mean specific gra- exceeds 50,000 tons. Marbles of inferior quality are vity of 2.66, so that the cubic foot weighs 166 lbs. quarried like limestones. The best black are found in Fourteen cubic feet to the ton is the usual estimate. Its Derbyshire, where they form part of the carboniferous toughness is great, and varies much in different samples. series. Red are rare and valuable. Yellow are chiefly Fresh unweathered granite will bear any direct crushing found in Italy. The mixed colours are more common. weight to which it can be exposed. Granite contains There are numerous varieties found in England, chiefly in about 0.8 per cent of water, that can only be driven off Derbyshire and Devonshire. Ireland also contains many. by continued exposure to heat. In its ordinary state, India is rich in marbles. On the continent of Europe, and containing this quantity of water, it is still Belgium, France, Spain, Portugal, and many parts of capable of absorbing about one-fourth more (or 0-2 per Germany all yield excellent varieties, worked cheaply for cent.), when placed in water for a few hours. Expressed ordinary purposes. Serpentine is used as a kind of in another way, a cubic yard of granite contains some-marble. It is a silicate of magnesia, coloured by metallic thing more than 3 gallons of water, and can absorb oxides, of iron, nickel, and chrome. The Lizard rock nearly a gallon more on being placed in pure water for a contains veins of extreme beauty, remarkable for its short period. To a small extent granite is soluble in pure brilliant colour contrasted by the purest white. The water and hydro-chloric acid. The solubility of granite Italian serpentine (ophite) is different and far less brilliant. in pure water and hydro-chloric acid is among the tests Irish Connemara marble is a variety of serpentine. of its value. A specimen was found to lose 0-25 per cent. Alabaster, of pure white or grey colour, and transparent, of its weight in water, and 5 per cent. in acid. For is a very beautiful material, very easily worked, and invarious public works, as bridges and harbours, and for expensive, but it will not stand exposure. It is obtained some public buildings granite is adapted, but its hardness in large quantities in England, but the largest and best and the cost of working, limit its use to works of practical supply is from Italy and Greece. Ordinary freestones utility where durability is essential. But good varieties are either limestones or sandstones; the former conrequire to be selected, and some granites are not more sisting of two groups-the limestones properly so proof against weather than limestones. Basalt is a material called and the magnesian limestones, or dolomites. used for rough walls and road material. In this rock a large Of sandstones, the Craigleith is one of the best. It is percentage of iron is a prevailing feature, while the per- obtained from the carboniferous rocks in the neighbourcentage of potash and soda is not excessive. The tough hood of Edinburgh. The colour is lightish grey, and na ure of this rock, and the mode in which it weathers, the grain fine. The cement is siliceous. It contains 98 leaving round lumps, separated by powdery rubbish, are per cent. silica. The beds vary in thickness, the thickest due partly to composition and partly to the mode of for- being ten feet. The number of workable beds is very mation of the rock. The columnar form of basalt is due large. A cubic foot of the stone weighs 146lbs., and to the same causes. Greenstones are varieties of basalt, absorbs four pints of water. It resists crushing weights and trap is a name given to rocks of this kind. All are to the extent of 5,800lbs. to the square inch. It darkens useful for road metal. Of other rock not freestones, by exposure to a smoky atmosphere and frost. It is an quartzites and quartz conglomerates, are rarely used for expensive stone. Other coal grits are good, but not equal other than rough walls. Indurated schists are durable, in colour or composition to Craigleith. Stones from the but not ornamental, and very difficult to work into any old red sandstones, on the east coast of Scotland, are darkconvenient form. Indurated sandstones are more valuable coloured and flaky, but hard, and resist atmospheric and are occasionally employed in engineering works. action. Of these Dundee stone is dark-brown, owing to Flag stones are valuable for paving, but not available for the presence of iron oxide. Arbroath is greenish grey; other purposes, except that they are sometimes used for not objectionable. Very large blocks of uniform appearparty walls. These materials are hard, dense, non-absorbent, ance may be obtained, for building and pavements. Yorkand resist atmospheric influences. They are, however, shire sandstones of the millstone-grit series are durable difficult to manipulate, and cannot be recommended both for building and paving. The Stenton quarries, near except for special uses. Paving and road material Durham, have supplied good stone. The Park-spring must be considered among these. In quarrying granite stone, from near Leeds, and others from the neighbourthe nature and position of the system of joints and natural hood of Halifax and Huddersfield, are good. These may fractures that affect the rock are important considerations, be described as fine-grained stones, cemented with argilloand depend on the geological axis of the district and the siliceous cement, coloured by oxide or silicate of iron, the direction of elevation of the rocks. In granites only colour varying from bluish green to pale brown. They certain veins are valuable. These are of small extent weigh about 145lbs. to the cubic foot, and support a crushcompared with the mass of the stone, and are enclosed ing weight about equal to Craigleith; but they absorb on either side by walls of inferior material. Granite is water readily and part with it freely, and are apt to peel irregular in its composition; but the larger the mass the when placed in walls. They are unsafe when in contact less are the irregularities perceived. In England the fine with damp earth, or where there is no circulation of air. and durable qualities occur larger in Cornwall and Scot-Sandstones of the lower new red standstone series, conland than in Guernsey or Charnwood Forest, and the sisting of fine siliceous grains with magneso-calcareous granite for extensive works should be sought for rather cement, are quarried at Mansfield, in Nottinghamshire. in the former than the latter localities. Freestones There are two varieties; one red, weighing 1484lbs. to are stones that may be worked with mallet and chisel, the cube foot, and the other white and heavier. Both and sculptured without difficulty. Of these some are are absorbent, taking up from four to five pints of water crystalline, as the varieties of marble, dolomites, alabaster, to the cubic foot. They wear well, but are not safe in a malachite, spars, serpentine, &c. Of fine marbles only moist, smoky atmosphere. At Liverpool much stone Carrara yields great supplies. Carrara marble is obtained from this rock is used. A sandstone of the lower from a quarry nearly midway between Leghorn and Genoa, secondary period, better than most of the varieties from and close to the bay of Spezzia. The quarries are very contemporaneous beds, is worked near Whitby, in Yorkaccessible. The veins of marble are in the Apennines, shire, and largely exported. Of other sandstones, those and include many varieties. The marble is quarried by of the Wealden period are irregular in their composition first loosening the large masses by blasting, after which and easily acted upon by weather. Some of the sandwedges are applied until the blocks are detached. The stones of the cretaceous series are better. The Godstone finest blocks are removed in the rough, but the others are and Maidstone fire-stones and the Chilmark siliceous shaped into oblong squares. From two to three thousand limestone are very valuable for certain purposes. Chilmen are employed constantly in the quarries now in work, mark is rather a siliceous limestone than a sandstone. which number from thirty to forty for common kinds, and It is heavy and non-absorbent. Sandstones, consisting of ten or twelve for fine marbles. The annual production detached grains of indestructible material, cemented to Only Caen stone resembles Bath in colour, texture, and facility gether by some foreign substance that has been held in water, depend on the nature of the cementing medium for their durability. Where this is calcareous or marly, or even irony, it is affected by weather, but where it is siliceous it is safe. When sandstone is laminated, water enters and ultimately produces disintegration. Many sandstones, ill-adapted for external walls and facings, are valuable as slabs, either for foot-paving, curbs, or other purposes, and also for party-walls. Limestones are better for ordinary constructions than sandstones; they are more easily worked, and therefore cheaper, more varied in quality and appearance; the useful kinds are more thoroughly distributed and the colour is more pleasing. Portland, Bath, Ketton, Barnack, and Caen varieties are the best known limestones in London and its neighbourhood. Their properties are very different. Many other stones are in local use, some from the carboniferous series and even silurian rocks. Even chalk is used occasionally for constructive purposes, in the interior of buildings. Portland stone is the hardest, the least absorbent, the most durable, and the most resembling marble of all English building materials. The upper member of the oolitic series in England, wherever it is developed, contains numerous bands of shelly limestone, partaking of that granular character which has been long known as oolite (eggstone). Some of these bands which are least shelly afford valuable building stone. The upper members of the Portland series pass into the Purbeck series (which contains "Purbeck marble"). Portland stone is heavy, weighing from 135 to 148 lb. to the cube foot. It absorbs about 6 pints of water per cube foot. It is composed of 95 per cent. carbonate of lime, with rather more than 1 per cent. of silica and carbonate of magnesia. It can be obtained in blocks of any size, and can be worked either by the chisel or the plate saw without difficulty. It is, however, expensive. It bears a pressure of 3,279 lb. without crushing. The heavier beds are the most durable for house architecture, but the upper beds, or roach, are preferred for some purposes, especially docks, piers, and other hydraulic works. The roach is less oolitic, and its cementing medium more perfectly crystallized than the other stone, and it resists alterna ions of dryness and moisture; but is less sightly, and could not be trusted in exposed situations in the air. The best quarries of Portland stone are on the eastern side of the island. Bath stones are next in importance to Portland, and their cheap-able, some difficulties arise which do not occur in mining. ness, facility of working, abundance, and pleasing appear In working for stone, it must first be decided whether the ance, have caused them to be adopted throughout the stone is to be reached by drifts or by open cuttings. If south of England, wherever they could be conveyed at there is a thick covering of upper hard beds, open quarrysinall cost. There are numerous quarries, and the quali-ing is impossible, and in that case the work is carried on ties differ a good deal. They occur at intervals in a series whose total thickness is from 60 to 120 feet. The series is as follows: 1. Upper rag stones......... thickness 25 to 50 feet. 2. Fine freestones or building bed by tunnels. Open quarries, however, are common enough, but there is always a large quantity of waste material, whose removal is a matter of consideration before opening a quarry. In getting Bath stone the quarryman cominences operations at the roof, picking it out six or seven feet back. The width of the stalls depends on the nature of the stone. The stone is afterwards cut with a saw, and removed with great care. Besides the limestones used for building purposes, at Bath there are also bands of more compact stone fit for roofing and paving. These flags are inferior to those found in Yorkshire, and to the slates from Cumberland and Wales. Stonesfield slate is one of these. The evenly-splitting flaggy structure is the only important fact. Lithographic stones are worked in large quarries in Bavaria. They are in thick beds, and are remarkable for the extraordinary smoothness and fineness of grain of the surface, and its delicate cream colour. They belong to the upper division of the oolites. Other lithographic stones of inferior excellence are obtained from liassic limestones. Limestones of the tertiary period are not met with in England, but excellent qualities are worked in various parts of the Continent. In and around Paris the limestones of the older tertiaries are opened in extensive quarries, from which the capital is supplied. The stone is of good colour, even texture, and easily and cheaply worked, but does not resist perfectly even the To comparatively pure and dry atmosphere of Paris. Chalk | and in considering the best method of keeping back decay, becomes hard and adapted for building purposes in the the composition and state of aggregation of the rock must south of France, and hard white cretaceous limestones enter into calculation. The causes of decay are partly are found throughout the middle and south of Europe, chemical and partly mechanical, and include (1) the available for construction. Many of these are compact action of rain-water, either by friction or dissolving parts and very durable. Compact carbonates of lime in England of the stone; (2) disintegration of the stone by the action are chiefly members of the carboniferous series, and pass of frost. Rain-water again acts in two ways, decomposing into marbles. Good lias supplies compact material, usually by acids or disintegrating by efflorescence. All deserve argillaceous, but the middle beds or "marlstone" yield a consideration, and depend on the absorbent nature of limestone. All the stones are absorbent, and are rapidly stones. It is by capillary attraction that water is sucked injured by exposure to moist air in changing temperatures, into stones, and there are limits to this attraction. and especially when there is frost. Magnesian limestones gether with the water its contents enter, but are left beoccur in the middle and north-east of England. They con- hind near the surface. When evaporation takes place sist of a variable proportion of carbonate of lime and car- from the surface, it is only the pure water that passes off. bonate of magnesia, and have been used in recent im- The foreign substances are left behind, and produce their portant buildings in London. Their colour is light effect in time. Rain-water contains carbonic acid gas and brown, of warm tint; their density is greater than that ammonia, and, however small the proportion may be, of the oolites; the labour on them is intermediate be- everything that can be affected by these substances will tween gritstones and Portland, and they can be obtained yield in time. Thus, even in granite, the silicates become of any required size. They are four times stronger than decomposed and the felspar destroyed by the constant Portland; certain parts of Derbyshire, Nottingham- action of rain-water, and when the felspar is gone the shire, and Yorkshire, yield this kind of stone. It was rock will become rotten. Such is the case in the islands used for the Houses of Parliament and the Museum of of Alderney and Jersey, in the British Channel. But if Economic Geology in Jermyn-street. The stone in the granite is destroyed. much more so are sandstones with latter building is extremely good. It is well known how calcareous cements and limestones. Owing to the quantity great is the failure in the other building. Whether from of coal burnt, and the impurity of the coal, there is always more trying exposure, or from the quarries ultimately a certain proportion of sulphurous acid in the air in towns, worked not yielding stone like the sample, it is too late and this becomes dissolved in the rain as it falls, and to discuss. The best magnesian limestones are those in rapidly affects the carbonates of lime. This action going which there is at least 40 per cent. of carbonate of on every day, with every change of weather, the surface magnesia and 4 or 5 per cent. of silica. But the compo- of the stone, bruised by the action of the tool, and sition alone is of less importance. Where this is com- deprived of the only protection nature is able to give, very plete the stone resists attack, but it is an unfortunate soon disintegrates. The less homogeneous the stone, the peculiarity of the admixture that it is never the same for more injured is it by this kind of action. The disintegramany yards together, even in the same quarry. It is tion by the action of acid vapours would be slow were it desirable to obtain a test of the relative value of stones not for the alternate expansion and contraction of the to be used for building purposes. An attempt was made moisture contained in it. And this result is obtained in by M. Brard to determine the relative durability of lime- its maximum when the stone is so placed that the stones and sandstones having calcareous cements. This moisture is nearest the surface, which will happen when method consists of boiling small cubes in a saturated the stone is placed at right angles to this natural direction. solution of Glauber's salts (sulphate of soda), and exposing Great care should therefore be taken by the builder to the cubes in the air. The effect of expansion by the place the stones as nearly as possible in their proper efflorescence of the salts, as the water evaporated, tested position. The injuries that take place in absorbent stones by weighing the amount of material removed from the from chemical reactions, are not easily traced, but are not stone in a given time, measures the effect of frost. It inconsiderable. The various substances accidentally present has not been found that the result can be depended on in stones may become changed by the chemical action of for practical purposes on a large scale, and it is now salt contained in the absorbed water, and thus injure the seldom resorted to. Slates belong to argillaceous stone and increase its tendency to decay. Many stones minerals, and are completely metamorphosed so as to suffer efflorescence due to this cause. Loamy clays, places have lost all external marks of mechanical origin. In where sand has been used in mortar, or where salt can in them bedding is replaced by cleavage. They split into any way have been absorbed, and stones in which an unthin plates, in planes parallel to each other, independent usual quantity of organic matter is present, are liable to of original stratification. Those that split into the this cause of mischief. Efflorescence, from whatever cause, thinnest plates are used for roofing purposes, and those is certain to bring away detached fragments of the stone which yield slabs, for paving and walls. Slates of good loosened by weathering. Whatever be the cause of the quality are not very common, and unless accessible destruction of stones, it may generally be traced to the by sea, and there are means of getting rid of the absorption of moisture, and thus any contrivance that will rubbish resulting from the workings, they cannot be check the admission of water will be the most likely to quarried with profit. They are limited to certain veins succeed in preserving the material from decay. Many of comparatively small dimensions, in the midst of a con- such contrivances have been proposed; they all involve siderable mass of schistose rock. Slates are generally some of these principles:-(1) closing the pores of the from rocks of very ancient geological date, but this is not stone by some kind of paint; (2) coating the stone by invariable. The best slates in the London market are some insoluble mineral substance; (3) defending the stone obtained either from North Wales, from the north coast by causing it to absorb a chemical solution, which, on of Cornwall, from the west coast of Scotland, or from the application of another solution, becomes decomposed Valentia, on the coast of Ireland. Very good sorts are and deposits within the stone an insoluble coat. Paint, found in France, in the Ardennes, in Western Germany, by preventing the absorption of water, preserves stone and in the east of Europe. America also yields supplies. so long as it remains undecomposed. In London this Slate hardly weathers when placed horizontally, unless hardly amounts to three years. The injection of oily exposed to foot-wear. In the better qualities of slate and fatty matters acts in the same way and lasts only a there is little or no pyrites, and the veins and joints are so little longer. There have been cases, where the exposure arranged as to assist in the working. The best slates is not severe, and where the treatment has been adopted are obtained from some depth within the quarry, and in before the absorption of moisture, where the result valleys rather than on hills. Exposed and weathered has seemed permanent; but for buildings intended slates seem to have lost much of their fissile properties. to last, such treatment is useless, as it can only stave off All stones are injured by long exposure to the weather; the evil day for a time comparatively very short. About |