19156. Grey granite, or moorstone as it is called in Cornwall, is got out in blocks by splitting it with a number of wedges applied to notches pooled in the surface of the stone, about four inches apart. The pool holes are sunk with the point of a pick, much in the same way as other hard quarry stones are split. The harder the moorstone the nearer it can be split to the scantling required. Generally speaking, granite has no planes of stratification, and it works or cleaves equally well in every direction; but in the porphyritic varieties there is a rough kind of arrangement of the crystals; and in gneiss there is a species of layer, formed by plates of the mica, which is plainly discernible. When brought to near the size required, it is first scabbled by a hammer with a cutting face 4 inches long by 14 inches wide, weighing 22 lbs.; then brought to a picked face with a pick or pointed hammer weighing 20 lbs., formed by two acute angled triangles, joined base to base by a parallelogram between them thus ; and if to be finely wrought or fine picked, it is further dressed with a similar pointed hammer, reducing the roughness to a minimun. The finer finish or fine axed face is produced by a hammer or axe with a sharp edge on both sides, weighing 9lbs. ; for fine work the "patent axe" is also used, which is a hammer formed of several parallel blades screwed together, capable of being taken to pieces when required to be sharpened. Polishing can then be done by machinery, the granite being rubbed by iron rubbers with fine sand and water, and finished with other materials.

1915c. Aberdeen red granite possesses the property common to all granites, that of a distinct plane of cleavage, which, though not perceptible to the eye, is at once recognisable under the hammer of the workman, and of course can be wrought with much greater precision and effect with the bed, than transversely to it. This bed bears no traceable relation to the natural joints of the rocks, which are indefinite in their directions; and still less so to their stratification. The grey granites are but slightly affected with cleavage, being capable of being blocked with the hammer with about equal facility in every direction. The local varieties of worked granite differ somewhat from those used in England, and are, 1. Hammer-blocked, as in foundations, plinths, &c. II. Scappled blocks, squared with the heavy pick, as in docks and heavy engineering works. III. Picked, a better finish than No. II. IV. Close picked, the bed and arrises made fair, and the outer surfaces made as fine as the pick will make them; used in ashlar work, &c. V. Single axed, a finer finish than No. IV., and used in quoins, rebates, cornices, &c., in house building. And VI. Fine axed, the finest finish before polishing, given to dressed granite by means of the patent are, used in the best work in house building, cemetery memorials, and as a finish to contrast with polished work.

WALLING.

1916. In stone walling the bedding joints are usually horizontal, and this should always, indeed, be so when the top of the wall is terminated horizontally. In building bridges, and in the masonry of fence walls upon inclined surfaces, the bedding joints may follow the general direction of the work.

1916a. Footings of stone walls should be built with stones as large as may be, squared and of equal thicknesses in the same course, and care should be had to place the broadest bed downwards. The vertical joints of an upper course are never to be allowed to fall over those below, that is, they must be made, as it is called, to break joints. If the walls of the superstructure be thin, the stones composing the foundations may be disposed so that their length may reach across each course from one side of the wall to the other. When the walls are thick, and there is difficulty in procuring stones long enough to reach across the foundations, every second stone in the course may be a whole stone in breadth, and each interval may consist of two stones of equal breadth, that is, placing header and stretcher alternately. If those stones cannot conveniently be had, from one side of the wall lay a header and stretcher alternately, and from the other side another series of stones in the same manner, so that the length of each header may be two thirds, and the breadth of each stretcher one third of the breadth of the wall, and so that the back of each header may come in contact with the back of an opposite stretcher, and the side of that header may come in contact with the side of the header adjoining the said stretcher. In foundations of some breadth, for which stones cannot be procured of a length equal to two thirds the breadth of the foundation, the works should be built so that the upright joints of any course may fall on the middle of the length of the stones in the course below, and so that the back of each stone in any course may fall on the solid of a stone or stones in the lower

course.

1917. The foundation should consist of several courses, each decreasing in breadth as they rise by sets off on each side of 3 or 4 inches in ordinary cases. The number of courses is necessarily regulated by the weight of the wall and by the size of the stones whereof these foundations or footings are composed.

1918. Walls are most commonly built with an ashlar facing, and backed with brick or rubble-work. In London, where stone is dear, the backing is generally of brick-work, which does not occur in the north and other parts, where stone is cheap and common. Walls faced with ashlar, and backed with brick or uncoursed rubble, are liable to become

convex on the outside from the greater number of joints, and, consequently, from the greater quantity of mortar placed in each joint, as the shrinking of the mortar will be in proportion to the quantity; and therefore such a wall is inferior to one wherein the facing and backing are of the same kind, and built with equal care, even supposing both sides to be of uncoursed rubble, than which there is no worse description of walling. Where a wall consists of an ashlar facing outside, and the inside is coursed rubble, the courses at the back should be as high as possible, and the beds should contain very little mortar. In Scotland, where there is abundance of stone, and where the ashlar faces are exceedingly well executed, they generally back with uncoursed rubble; in the north of England, where they are not quite so particular with their ashlar facings, they are much more particular in coursing the backings. Coursed rubble and brick backings admit of an easy introduction of bond timber. In good masonry, however, wooden bonds should not be continued in length; and they often weaken the masonry when used in great quantity, making the wall liable to bend where they are inserted. Indeed, it is better to introduce only such small pieces, and with the fibres of the wood perpendicular to the face of the wall, as are required for the fastenings of battens and dressings.

1919. In ashlar facing, the stones usually rise from 28 to 30 inches in length, 12 inches in height, and 8 or 9 inches in thickness. Although the upper and lower beds of an ashlar, as well as the vertical joints, should be at right angles to the face of the stone, and the face and vertical joints at right angles to the beds in an ashlar facing; yet, when the stones run nearly of the same thickness, it is of some advantage, in respect of bond, that the back of the stone be inclined to the face, and that all the backs thus inclined should run in the same direction; because a small degree of lap is thus obtained in the setting of the next course, whereas, if the backs are parallel to the front, no lap can take place when the stones run of an equal depth in the thickness of the wall. It is, moreover, advantageous to select the stones so that a thicker one and a thinner one may follow each other alternately. The disposition of the stones in the next superior course should follow the same order as in the inferior course, and every vertical joint should fall as nearly as possible in the middle of the stone below.

1920. In every course of ashlar facing in which the backing is brick or rubble, bond, or, as they are called in the country, through stones should be introduced, their number being proportioned to the length of the course; every one of which stones, if a superior course, should fall in the middle between every two like stones in the course below. And this disposition should be strictly attended to in all long courses. Some masons, in carrying up their work, to show that they have introduced a sufficient number of bond stones into their work, choose their bond stones of greater length than the thickness of the wall, and knock or cut off their ends afterwards. But this is a bad practice, as the wall is liable to be shaken by the force used in reducing, by chiselling or otherwise cutting away the projecting part, and sometimes with the chance even of splitting the bond stone itself.

1921. In piers, where the jambs are coursed with ashlar in front, every alternate jamb stone should go through the wall, with its bed perfectly level. If the jamb stones are of one entire height, as is often the case when architraves are wrought upon them, and also upon the lintel crowning them, of the stones at the ends of the courses of the pier which are to adjoin the architrave jamb, every alternate stone should be a bond stone; and if the piers be very narrow between the apertures, no other bond stones will be necessary in such short courses. When the piers are wide, the number of bond stones is to be proportioned to the space. Bond stones, too, must be particularly attended to in long courses above and below windows. They should have their sides parallel, and of course perpendicular to each other, and their horizontal dimension in the face of the work should never be less than the vertical one. The vertical joints, after receding about three quarters of an inch from the face of the work with a close joint, should widen gradually to the back, so as to form hollow wedge-like figures for the reception of mortar and packing. The adjoining stones should have their beds and vertical joints filled with oil-putty, from the face to about three-quarters of an inch inwards, and the remaining part of the beds with well-prepared mortar. Putty cement is very durable, and will remain prominent when many stones are in a state of dilapidation, through the action of the atmosphere upon them. The use of the oil-putty is at first disagreeable, from the oil spreading over the surface of the contiguous stones; but after a time this unpleasant look disappears, and the work seems as though of one piece.

1922. All the stones of an ashlar facing ought to be laid on their natural beds. From inattention to this circumstance, the stones often flush at the joints; and, indeed, such a position of the lamina much sooner admits the destructive action of the air to take place. Methods of building in cement and concrete blocks, are noticed in the previous section.

1922a. RUBBLE-WORK. A wall consisting of unhewn stone is called a rubble wall, whether or not mortar is used. This species of work is of two kinds, coursed and uncoursed. In the former, the stones are gauged and dressed by the hammer, and thrown into different heaps, each

containing stones of the same thickness. The masonry is then laid in horizontal courses, but not always confined to the same thickness. The uncoursed rubble wall is formed by laying the stones in the wall as they come to hand, without gauging or sorting, being prepared only by knocking off the sharp angles with the thick end of the scabbling haminer.

19226. Apparently, wherever there was any difficulty in obtaining stone, the mediaval builders employed the worst of all methods of construction in walling, viz., concrete or rubble-work between the two faces of squared stone. In the early period of medieval art, flint or rough rubble, with "short and long work " to the quoins, seems to have been very general; this "short and long work" was also used in faced walls; in both cases the short work consists of stone upon its bed, and alternates with the long work or stone upright: the short work ought to serve as bond throughout the walls. In the 12th century

the use of rubble in conjunction with worked stone became frequent. The chief defect, frequently considered one of the merits, of this system, consists in the omission of sufficient bond both in piers and walls; the occurrence of joints in angles is too frequent; in fact, any expedient seemed better than the trouble of making a back-joint.

1922c. KENTISH RAGSTONE. This material, now so extensively employed for mediæval work in the metropolis and suburbs, is never used internally, as it sweats, that is, the condensed moisture from the atmosphere is not absorbed, and will show itself even through two coats of plastering. Hassock stone, however, which is the sandstone separating the beds of the ragstone, the sand being sufficiently agglutinated to allow of its being raised in blocks, must never be used externally. It is easily worked, and makes a good lining for ragstone walls, as it does not sweat. It should be roughly squared, for if not done, the crumbling nature of the stone would endanger the security of the work, should it be exposed to any unequal pressure: it must not be placed where it would be exposed to very great pressure, as in arches, jambs, &c. Hassock may be procured in London at from 6s. to 7s. per cord (3 feet cube), in roughly squared pieces; while rough rag is about 5s. per ton, and rag headers about 12s. 6d. per ton.

1922d. Sunk and moulded work in so hard a material is to be avoided, and so much wrought surface would cause decay. In using ragstone ashlar, it must be laid upon its natural bed, otherwise rapid decay will almost certainly follow, arising from the thinness of the strata, for blocks of a large size can seldom be entirely freed from hassock; and even what appears to the eye as blue stone, retains for a considerable distance inward the perishing nature of its enveloping crust. A block of ragstone, if the face be worked, will present in damp weather an appearance precisely similar to the heart and sap of timber. In the case of copings, &c., where one bed is exposed, the stone should be skiffled (or knobbled) as much as possible from the upper side, so as to expose only the soundest portion of the stone to the action of the atmosphere. In some situations, as mullions, door and window jambs, an unsightly appearance would be produced by too exact an attention to the beds of the stone, as the ashlar is generally too small to range with more than one course of headers. In these cases the old masons seem to have departed from their usual rule, and to have set the blocks on end, so as to embrace two or three courses; but as the depth of the block required to work an ordinary jamb or mullion is not very great, it is not difficult to get the whole thickness required out of the heart of the stone.

1922e. Stone of the smaller layings are generally worked into headers; it is common to work one side of the stone to a rough face with parallel sides, without paying much attention to the beds and joints, which often recede at an acute angle with the face, so as to bring the stones, when laid, to a closer joint. Such stones, however, must be properly pinned in behind, and carefully bonded with the work at back. Headers are generally knocked out to six, seven, eight, or nine inch gauge for the height; the length and tail being determined by the size of the stone: on the face they do not vary much from the square form. Formerly headers were set on their natural bed, therefore it is not unusual to find stones in an old wall entirely gone from this cause.

1922f. In the Whitelands bridge bed, a very free working stone of a bluish colour can be got 12 feet long with certainty, and the Horsebridge bed yields a good stone to a length of 15 feet. The white rag, the lowest of the beds in the quarry, tumbles to picces on exposure to the air (Whichcord, Kentish Ragstone, 1846).

1922g. In its mechanical properties, ragstone possesses some of the qualities of granite, though in an inferior degree. In respect to resistance to pressure, it stands next to granite in the list of British stones; but when loaded for a transverse strain, the numerous vents to which even the best layings are liable, renders it untrustworthy for lintels, or in a suspended position, without much precaution. In the former case of lintels and architraves, three stones, arch jointed, gives the requisite security.

1922h. WHINSTONE, a material, in one form or another, found almost over all Scotland, makes a very durable arch for bridge work, when well built with good mortar, the stone being in its nature weather proof. In the neighbourhood of Edinburgh, whinstone arches have been erected since about 1770, the greatest span being about 60 feet. The Messrs.

Smith, of Darnick, stated, in the Transactions of the Institute of British Architects, that they had erected bridges with semi-elliptical arches of the spans of 51 feet, and of 62 feet, of whinstone faced with hewn stone. A bridge, almost entirely of whinstone, having an arch 63 feet span, the depth of the masonry being 24 feet on the average, was erected in 1833; while another, 76 feet 4 inches span, at Falshope, was entirely of whinstone, with a rise of about 18 feet. It sunk about seven inches when the centre was struck, but no broken stone was observed. The depth of the arch, requiring three breadths of stone to make it up, was 3 feet; their average thickness was 34 inches; but it varied from 1 to 6 inches. The stones were laid as close as possible, and in crossing the bond the work was made firm, but the stones were not dressed straight upon the beds. Its cost was 3601 exclusive of the digging for the foundations.

1922. The most annoying part in the building of rubble arches, is the slowness of the setting or drying of the mortar, as until the mortar is able to bear considerable resistance the arch is extremely supple, and easily bent out of its proper curve when the centre is struck. This bridge stood five weeks before that measure was considered advisable. Cement would perhaps be best for large rubble arches, and even if expensive, the whole cost would be cheaper than a bridge of hewn stone. With cement, almost any kind of stone, even the refuse of a slate quarry, might be worked into an arch of almost any extent.

1922k. FLINTWORK.-In the chalk districts, the houses of the fifteenth century are frequently faced with flints, cut and trimmed, and arranged with great skill and effect. One of the best examples is a house in St. Andrew's, at Norwich, next the cemetery, a fragment of the decorated period of Gothic architecture, in which the flint work is so delicately finished that a penknife can scarcely be inserted in the interstices.

1922. As flint itself is practically imperishable, and as flintwork becomes, when perfectly set, a mass of concrete, it produces substantial work, if great care be taken in its manipulation. But flint walls frequently fail, by bulging while they are in course of construction, and splitting when they are old. On any sufficient natural cause, as the giving way of the foundation, they are riven into immense masses; hence a flint building gets out of repair less readily than a stone one, but if it suffer at all, it is very apt to become a complete ruin.

1922m. Flint walls intended for durability should not be less than two feet in thickness, built slowly and solidly, flushed up with stiff strong mortar compounded of quick-setting stone lime and coarse sharp sand free from loam. As flint is a non-absorbent, bricks and tiles are often worked into the middle of the walls to assist in the induration of the mortar; but for the sake of economy, lumps of hard chalk, pebbles, and flat-bedded stones are frequently used as the principal components of the core or middle of the wall. work must be kept as dry as possible during its erection, as well as subsequently; frost is found soon to level the work while saturated with water.

The

1922n. Flint walls are strengthened by lacing courses, formed of bricks three or four courses deep, not generally showing outside. At Cambridge, Brandon, and elsewhere, they do show, and are used every two or three feet. The object is not only to get a continuous bond, but to bring the work to a level bed, and again start fair. When round flints are split, and the thicker portion is kept, as usual, at the face of the wall, driving rains are readily conducted by the inclination of the upper bed of each course to the middle of the wall, and by keeping it damp conduce to its decay; but as flints are seldom split at right angles to their axis, they can be so laid in the work as to be flush on the face as well as level, and the lower bed must be firmly pinned up with fragments. It is desirable that cavities for drainage, with exit holes at the plinth level, be formed in the middle of the wall by building in rods of wood or iron vertically, and drawing them up as the work progresses. The face is sometimes finished by inserting in the mortar joints gullets, or the sharp fractured bits of flint, when the work is called galleted or garreted (Dictionary of Architecture).

19220. Amongst examples of a systematic parsimony of labour and material in mediæval art, may be no iced the characteristic tables or courses, where each projection

is taken out of a separate course of stone or out of the smallest stone adjoining to it. The base (fig. 618.) and the capital (fig. 618a.) of a shaft are kept so small as to be got out of single blocks; the astragal belongs to the capital, and not, as in Roman work, to the shaft; the bell is in one stone, the abacus in another (fig. 618d.); each order of an arch is an independent range of stones; the hoodmould is self-existent ; the sills are not dished, and the buttresses are toothed rather than bonded. In two cases, however, the use of large stones prevailed, viz., in shafts of the 13th century (in France, 11601230), which are leng rods of stone 6, 4, or 3 inches in diameter and incapable of bearing any great weight, unless banded or bonded to the nearest wall or

Fig. 618.

Fig. 618a.

pillar, and in the springing stones of vaulting, which are worked with level beds. (See par. 2002f.) The horizontal courses at the bottom of the arch are also seen in the construction of large horse-shoe arches. With the 13th century, also came the decided distinction between decoration and mere construction, which employed stone vertically, not only for shafts of columns, but for mullions and tracery of windows and dwarf walls, such tracery being cut out of slabs and confined by grooves or similar means.

1923. Where walls or insulated pillars of very small dimensions are to be carried up, every stone should be carefully bedded level, and be without concavity in the middle. If the beds should be concave, as soon as the superimposed weight comes to be borne by the pier or pillar, the joints will in all probability begin to flush; and it is, moreover, better, if it be possible, to make every course in the masonry of such a pier or pillar in one

stone.

COLUMNS.

1924. When large columns are obtained in a single block, their effect, from that circumstance alone, is very striking; but as this is not very often to be accomplished, the next point is to have as few and as small joints as possible; and the different stones, moreover, ought to be selected with the view, as much as possible, of concealing the joints, by having the blocks as much of the same colour as possible. It will immediately, of course, occur to the reader that vertical joints in columns are inadmissible, though in many of the great edifices at Paris such do occur, much to their detriment.

1925. The stones for an intended column being procured, and the order in which they are to be placed upon one another having been determined, we must correctly ascertain the exact diameter for the two ends of each of them. To effect this, draw an elevation of the column proposed to its full size, divide it by lines parallel to the base into as many heights as the column is intended to contain stones, taking care that none of the heights exceed the lengths the stones will produce; the working of the stones to the diameters thus obtained then becomes easy. The ends of each stone must first be wrought so as to form exactly true and parallel planes. The two beds of a stone being thus formed, find their centres, and describe a circle on each of them; divide these circles into the same number of equal parts, which may, for example, amount to six or eight; draw lines across each end of the stone, so that they will pass through the centre and through the opposite divisions of the same end. The extremities of these lines are to regulate the progress of the chisel along the surface of the stone; and, therefore, when those of one end have been drawn, those of the other must be made in the same plane or opposite to them respectively. The cylindrical part of the stones must be wrought with the assistance of a straight-edge; but for the swell of a column, a diminishing rule, that is, one made concave to the line of the column, must be employed. This diminishing rule will also serve to plumb the stones in setting them. If it be made the whole length of the column, the heights into which the elevation of the column is divided should be marked upon it, so that it may be applied to give each stone its proper curvature. But as the use of a very long diminishing rule is inconvenient when the stones are in many and short lengths, rules or rods may be employed corresponding in length to the different height.

*385"

A

1925a. The method of setting the blocks or frustra by the ancients, was to dish out the beds to obtain a truly fine joint. In the Parthenon, an outer space of 7 inches in width all round the drum, was left a perfectly level and smooth bed for actual contact. The next space, of 1 foot in width, was very slightly tooled or scratched over. The next, 9 inches in width, was made still lower by being tooled over very roughly. The remaining portion round the centre was left smooth, but was made as low as the surface of the second space. square hole, worked at the quarry, in the centre of the shaft, was filled with a cube of hard wood, in which was a hole to receive the half of a circular pin, also of wood, suggesting the idea that when the marble frustra were set, they were rubbed against each other. The first drum, at the temple of Hercules at Agrigentum, when placed on the stylobate, was turned round until it had been well ground down. (Civil Engineer, &c. vii. p. 241.) The practice of late years, for large columns, has been to place a plate of thin lead between the beds of stone, so as to secure an equal bearing and prevent the edges flushing, any space being filled in with putty or cement. At Paris, in many of the porticoes, the columns have very deep thin rustics (fig. 618b.), which would effectually prevent any broken edges from being observed. The effect is peculiar, especially in strong sunlight. The height of the face of the stone is 385 of a metre; the height of the channel, including the rounded a rises, is 40, and the depth of the channel is 85.

Fig. 6186.

19256. Besides the usual mode of drawing a volute, described in par. 2576, we insert a method recommended by Mr. Gwilt for adoption. A general method of inscribing a spiral in a rectangular quadrilateral, A B C D:-Multiply the given height by the given