Masonry : a short text-book on masonry construction, including descriptions of the materials used, their preparation and arrangement in structures

Front matter

I

WORKS OF PROF. M. A. HOWE

PUBLISHED BY

Preface

The following pages have been written to furnish a concise treatment of masonry construction for use as a text in courses of instruction which do not provide sufficient time for the study of a more comprehensive treatise. The matter as presented, however, may serve as a skeleton for an extended course of study by making use of the references at the end of the book which suggest supplementary reading. The references are arranged in the order in which the subject matter is considered in the text.

Modern methods are described and modern tools and machinery are illustrated.

Reinforced concrete masonry has not been considered, as there are numerous books which treat this subject both in an elementary and in a thorough manner.

The specifications in Part III give the best modern methods of selecting materials and their use in structures.

M. A. H.

Janttaby, 1915.

Chapter I Page

Natural Building Stone 1

Geological Classification of Rocks 1

Chemical Classification of Rocks 2

Classification of Rocks According to Their Physical Structure ... 2

Rocks Used for Building Stone 2

Durability of Rocks 2

Artificial Methods of Determining the Durability of Rocks .... 3

The Absorption Test of Building Stones 3

The Crushing Strength of Building Stones 4

Ifreezing Tests of Building Stones 5

Chemical Tests of Building Stones 6

Microscopic Tests of Building Stones 6

Determination of the Specific Gravity of Building Stones 6

Minerals Which Are Injurious 7

Granite 7

Limestone . 8

Granular Limestone 9

Compact Limestone 9

Sandstones 10

Slates 10

Average Physical Properties of Building Stones 11

Fire-Resisting Property of Stone 12

Quarrying 12

Joints in Relation to Quarrying 12

Quarrying by Hand Tools 13

Quarrying by Machinery 14

The Use of Explosives in Quarrying 14

Tools Used in Preparing Building Stones 20

Power Tools for Finishing Stone 24

V

VI CONTENTS

PAGE

Classification of Building Stones According to the Finish of the Surface . 28

Squared Stones 29

Cut Stones 30

CHAPTER II Building Brick 33

Manufacture of Building Brick 33

Drying Brick 34

Burning Brick 36

Modern Methods of Burning Brick 37

Fuel Used in Burning Brick 41

Annealing or Cooling Brick 41

Classification of Brick 41

Essential Requirements for Good Building Brick 43

Ornamental Face Brick 45

Sizes of Brick 45

Sand Lime Brick 45

Cement Bricks 46

Hollow Terra-Cotta 46

Plaster Blocks 48

Fat or Quick Lime 48

Burning Lime 50

Natural Cement 50

Portland Cement 51

Iron-Ore Cement 52

Magnesia Cement 52

Puzzolan Cement 52

Manufacture of Portland Cement 53

Sand 53

Testing Sand 54

Gravel . . . ■ 54

Voids in Sand and Gravel . 56

Mortar 56

Lime Mortar 57

Natural Cement Mortar 57

Portland Cement Mortar 57

Lime Paste Used with Cement Mortar 57

Water-Tight Mortar 58

Colored Cement Mortar 58

Pointing Mortar 58

CONTENTS vii

CHAPTER III Stone Masonrt PAGE

Definitions 59

Classification of Stone Masonry 61

Ashlar Masonry 61

Dressing Joint Surfaces for Ashlar 62

Backing and Filling for Ashlar 63

Bond 64

Relative Dimensions of Stones . 66

Setting Stone 66

Pointing 70

Joint Mortar 71

Pointing Mortar 71

Squared-Stone Masonry 71

Backing and Filling for Squared-Stone Masonry 72

Bond, Mortar, Sizes of Stones, etc., for Squared-Stone Masonry ... 72

Stope-Wall Masonry 73

Stone Paving 73

Specifications for Stone Paving 73

Riprap 73

Strength of Stone Masonry 73

Measurement of Stone Masonry 74

Water-proofing Stone Masonry 75

Cleaning Stone Masonry 75

CHAPTER IV Brick and Hollow-Tile Masonry Brick Masonry 76

Joints for Brick-work 77

Mortar for Brick-work 77

Pointing Joints of Brick-work 77

Bond in Brick-work 78

Crushing Strength of Brick-work 81

Lintels Supporting Brick Masonry 82

Efflorescence 82

Measuring Brick-work 83

VIU CONTENTS

PAGE

Waterproofing Brick Masonry 83

Cleaning Brick Masonry 83

Hollow-Tile Masonry 84

CHAPTER V Concrete 87

Reinforced Concrete 87

Reinforcing Concrete for Shrinkage, etc 87

Constituents of Concrete 88

Proportions of Materials for Concrete 88

Mixing Concrete 89

Machines for Mixing Concrete 90

Concrete Building Blocks 91

Architectural Concrete 93

Surface Finish for Concrete Blocks 95

Monolithic and Mass Concrete 95

Depositing Concrete in Mass Construction 96

Mixing and Depositing Concrete by Compressed Air 98

Mixing and Depositing Grout by Compressed Air 100

Mixing and Depositing Concrete in Freezing Weather . . .... 101

Depositing Concrete Under Water 102

Finishing the Surface of Concrete 104

Bush-Hammer Surface Finish 105

Spaded Finish for Concrete Surfaces 105

Brushed Concrete Surfaces 105

Plaster Coats 106

Sand-Blasted Surfaces ..." 107

Pebble Finish 107

Special Surface Finish for Concrete 107

Cement-Gun Surface Finish 109

Forms for Mass Concrete 110

Wetting and OiUng Forms . Ill

Rubble Concrete 112

Waterproofing Concrete . . .113

Tests of the Absorptive and Permeable Properties of Portland Cement

Mortars and Concretes 114

Waterproofing with Asphalt and Coal Tar 118

Joining Old and New Concrete 119

Effect of Alkali and Sea-water on Concrete 119

Physical Properties of Concrete 120

Fire-Resisting Property of Concrete 120

CONTENTS ix

CHAPTER VI Railroad Masonry, Brick Cement, Etc. PAGE

Classification of Railroad Masonry 121

Definitions 122

Specifications for Stone Masonry 127

Specifications for Plain Concrete I33

Specifications for Building Brick 13g

Specifications for Lime 141

Specifications for Sand I43

Specifications for Cement I44

References

Periodicals 15q

Books 153

Chapter I

Natural Building Stone is obtained from rock which has been formed by natural processes. Its use for a particular purpose depends upon its chemical and physical properties. Rocks may be classified according to their geological position, their chemical composition, or their physical structure.

Geological Classification of Rocks. — The three geological divisions of rocks are igneous, sedimentary, and metamorphic.

Igneous rocks are those which have been formed by ''cooling from fusion," the melted rock having come up through fissures in the earth's rocky crust. When the melted rock has solidified on the surface, it is designated as extrusive or volcanic. Lava is an example. When for some reason the solidification takes place below the surface the rock is designated as intrusive or plutonic. Granite is an example.

Sedimentary or stratified rocks are those which have, in general, been laid down under water by mechanical, organic, or chemical agents. This division also includes those rocks which have been formed through the action of winds. The shales and sandstones (water deposits) are examples of rocks having mechanical origin; gypsum, rock salt, and some limestones are examples of rocks having chemical origin formed from solution; and numerous limestones and coal are examples of organic origin.

Metamorphic rocks have been formed from original igneous or sedimentary rocks chiefly through the action of heat, pressure, and water. CrystaUine limestones are metamorphosed limestones.

Chemical Classification of Rocks. — Chemically, rocks are divided into argillaceous, calcareous, and siHceous.

Argillaceous rocks are those in which alumina gives the characteristic properties, slate being an example.

Calcareous rocks or limestones are those which are principally composed of carbonate of lime.

Siliceous rocks are those in which sihca is the principal constituent. Granite, quartzite (a siliceous sandstone), and buhrstone (a cellular siHceous rock used for millstones) are examples.

Classification of Rocks According to Their Physical Structure.— Rocks are classified according to their physical structure as stratified and unstratified, A large number of the limestones and sandstones are examples of the stratified rocks, and basalt, granite, and lava examples of the unstratified rocks.

Rocks Used for Building Stone.— The principal rocks used for building purposes are granite, limestone, and sandstone. Trap-rock is used but httle, owing to the difficulty with which it is quarried and cut.

The selection of stone for a particular structure depends upon a number of things which differ in different parts of the country. The durabihty of the stone, if exposed to the weather, is of prime importance. For footings of heavy structures it must have the proper strength, and for buildings, etc., the question of color may be an important factor governing the selection. The cost of quarrying, cutting, and transporting will, of course, govern the choice between two kinds of stone which are otherwise satisfactory.

Durability of Rocks.— The durabihty of a rock depends upon the closeness of its texture and the absence of anything in its make-up which is hable to oxidation. Any rock which is sufficiently porous to admit air or water will degrade more or less to the depth of penetration of the air or water. This is due partly to chemical action, and, in cold chmates, to alternate freezing and thawing.

Coarse-grained rocks are injured by alternate heating and cooUng in the daily passage of the sun. Rock which has been protected by a layer of earth, and which shows the marks of glacial action, will disintegrate on the surface when exposed to the air, due to changes of temperature probably.

There is but one way, which is conclusive, to deterniine the durabihty of a building stone in a particular locality, and that is to examine it where it has been used in said locality. It does not follow if a stone is durable in one locality that it will be equally durable in another. This is well illustrated by the almost perfect condition of the obelisks in Egypt, and the disintegration of Cleopatra's Needle after it was transported, in 1880, to New York City.

In general, stones which absorb but Uttle water, and those having smooth surfaces exposed to the weather, are more durable than those which absorb considerable water or have rough surfaces exposed. There are a few exceptions to this statement.

Artificial Methods of Determining the Durability of Rocks.— While not conclusive, artificial methods of determining the durability of rocks are, more or less, in general use. These methods comprise the determination of the amount of water the rock will absorb, the crushing strength, the resistance to the action of frost, the solubihty in acids, a microscopical examination, and the determination of the specific gravity.

The Absorption Test of Building Stones.— To determine the amount of water which a stone will absorb in a given period of time, a small piece is dried for twenty-four hours at a temperature not lower than 212° F. The specimen is then weighed and placed in clean water for at least twenty-four hours; then it is removed from the water, its surface wiped fairly dry, and is again weighed. The difference between the wet and dry weights divided by the dry weight is the percentage of absorption. As this test is comparative, the specimens should be of about the same size and shape, and the time intervals the same for all specimens. As air imprisoned in the stone will prevent the entrance of water, the coefficient of absorption will be materially increased if the dry specimen is placed under the receiver of an air pump, and the air exhausted. Complete saturation of a specimen may be determined by repeated weighings while it is in the water.

The percentage of absorption should not exceed about 3 per cent. There are a few exceptions to this, however, where the percentage of absorption is as high as 6 per cent, and the stones very durable.

The Crushing Strength of Building Stones— This is of prime importance only for very heavy structures, but it is an approximate guide to the durabihty of the stone, the stronger stones being more durable than the weaker stones.

To obtain the crushing strength of a stone, a specimen in the form of a cube is cut from the stone and crushed in a testing machine designed for compressive tests. A record is made when the first crack appears and when the specimen fails. For the best results, the specimens should be sawed approximately to shape and then ground to the proper size. The faces of the specimen should be planes, and the opposite faces should be parallel. Steel plates without any bedding between them and the specimen should be used to transmit the load. These conditions are difficult to obtain, so that it is more or less customary to bed the specimens in plaster of Paris, a piece of oiled paper being placed between the plaster and the specimen.

The use of cubical specimens is quite satisfactory when only comparative strengths are wanted. The strengths obtained from cubical specimens are in excess of the normal strengths as obtained from prisms which are one and one-half the least lateral dimension in height. Stratified stones are usually tested with the stratifications horizontal.

For all ordinary structures, the building stones in common use are very much stronger than necessary to carry the superimposed loads.

Freezing Tests of Building Stones. — Two methods are followed for this test. In one, the stone is saturated with water, frozen and thawed; and in the other, the action of frost is artificially obtained by the action of Glauber's salts. There appears to be no standard course of procedure in either method. For the natural-freezing method, Baushinger used the practical process, "consisting in the exposure of the material twenty-five times to frost in the open air, the (crushing) strength, before and after the test, serving as a guide to the resisting power." (Van Nostrand's Engineering Magazine, Vol. XXXIV, 1886, p. 44.)

For the natural method, the specimens may be two-inch cubes. One set of specimens is thoroughly dried and tested in compression. The other set is thoroughly dried and placed in water for twelve hours, and then frozen. Cold-storage plants are so common now that the specimens can be sufficiently frozen in twelve hours. The soaking and freezing are repeated from ten to twenty-five times, and then the specimens are thoroughly dried and tested in compression. The same soaking and freezing routine is followed if the loss of weight is wanted. Usually, the loss of weight is very small.

The artificial-freezing test, or the sulphate of soda test, is made in several ways. The following method is recommended by Johnson (The Materials of Construction). The solution in which the specimens are immersed is a boiling solution of the sulphate of soda, commonly known as Glauber's salts. "The specimens should be heated before immersion in the boiling liquid, or they should be immersed before the liquid has come to the boiling temperature. The time of immersion need not be over thirty minutes, after which the specimens should be freely suspended in the open air for twenty-four hours. They are then sprayed from a wash-bottle and again immersed and boiled, this process being repeated for any desired number of times, generally from seven to ten. The specimens should be small, about one-inch cubes being a suitable size, as the weighings have to be done with great care on delicate balances to secure reliable results. The specimens must be carefully dried for twenty-four hours, at a temperature above boiling, before the first weighing and after the long soaking in fresh water subsequent to the tests."

The artificial test is much more severe on stone than the natural test. Both tests are comparative and of Httle value. A description of methods with discussion is given in a paper entitled ^'The Relative Effects of Frost, and the Sulphate of Soda Efflorescence Tests on Building Stones," by Lea McI. Luquer, Transactions of the American Society of Civil Engineers, Vol. XXXIII, 1895, p. 235.

Chemical Tests of Building Stones. — These appear to have little value unless made for the determination of constituents which may stain the stone, or in connection with microscopical examinations.

Microscopic Tests of Building Stones. — This test, when made by an expert, is probably the most valuable of any of those mentioned. The structural arrangement, the identification of its constituent parts, and the character of the cementing material of the specimen are determined by this method.

Determination of the Specific Gravity of Building Stones. —

The weight of building stone is of importance in all structures subjected to overturning forces and the pressure of water, the heavier stones being better suited to resist such forces.

A small specimen is thoroughly dried and weighed, then saturated with water, and weighed again in the manner described for the absorption test. The saturated specimen is then weighed in water. Letting W represent the dry weight, Ws the saturated weight, and the weight in water, then the specific gravity, dry, equals Wl (Wg — W^), and the specific gravity, wet, equals Wj{Ws — W^,). The weight per cubic foot is found by multiplying the weight

NATUKAL BUILDING STONES of a cubic foot of water (62.4 pounds, approximately) by the specific gravity.

Minerals Which Are Injurious. — Some minerals are injurious under all conditions, while others are only injurious when distributed in a particular manner.

Chert, or flint, forms the so-called glass seams in limestone. It is very much harder than the surrounding stone and, consequently, interferes with the cutting, and is much more resistant to the weather, forming ridges on weathered stone. A glass seam which extends completely through the stone does not affect its strength, but very often a seam which appears on the surface only extends into the stone a short distance, and beyond this point there may be an open seam. Therefore, for durabihty, all stone with glass seams should be rejected.

Mica occurs in granites, sandstones, and marbles, but usually it is not harmful, especially if uniformly distributed throughout the rock. In stratified rocks, it is harmful if it is segregated along the planes of stratification. It is also harmful in some of the crystalline hmestones where it may occur as scattered grains or in bands. The scattered grains do not do much harm, but bands injure the polish of marbles, and also affect the durabihty of the stone, as the mica bands do not weather well.

Pyrite and other iron sulphides, in small quantities, as specks here and there in stone, do not do much harm. As the quantity increases, the exposure to the weather causes pits, and, in many cases, the stone is stained. Stones which contain iron as ferrous carbonate also stain.

Granite. — As commonly used, the term granite includes all igneous rocks and gneiss (gneiss has mica and other constituents more or less in layers). According to Ries and Watson, granite is an even granular, crystalhne, plutonic, igneous rock composed of quartz and alkalic feldspar (common feldspar), with usually mica, hornblende, or pyroxene.

The quartz (oxygen and silica) is usually grayish white, glassy, and without any appearance of cleavage. The feldspar (silica, alumina, and potash) is whitish or flesh-colored, and is distinguished from the quartz by its cleavage surfaces which reflect hght brilliantly. The mica (sihca, alumina, potash +) is generally in small flat scales, either black, brownish black, or silvery. The combined sihca in the quartz, feldspar, and mica constitutes over fifty per cent of the rock.

The specific gravity of granite ranges from 2.5 to 2.8, which corresponds to weights per cubic foot of 156 to 175 pounds.

The crushing strength of granite is very variable, even for stones from the same region. The range may be taken as 13,000 to 26,000 pounds per square inch, although some granites have considerably less strength, and some a strength as high as 43,000 pounds per square inch.

The modulus of rupture of granite, used as a beam over an opening, for example, is about 1,800 pounds per square inch. This is an average value.

Young's modulus of elasticity varies from 4,500,000 to 9,800,000 pounds per square inch in compression. This is a very uncertain property, as it does not vary directly with the compressive load. The loads corresponding to the above values he between 100 and 1,000 pounds per square inch.

The coeficient of expansion for each degree Fahrenheit ranges from .00000324 to .00000461.

The absorption of water by granite seldom exceeds one per cent.

Granites make very excellent building stones, and can be used for all purposes from the bottom stones in a heavy footing to the carved statuary of a building. The material is one of the hardest to work, but modern methods have done away with many difficulties which formerly existed. The usual color of granite is gray, but pink and red granites are more or less conunon.

Limestone is stratified rock of sedimentary origin, and is the general name for all of the massive varieties of calcite

(lime, carbon-dioxide +) which occur in extensive beds. The principal constituent is carbonate of lime.

Granular Limestone, often called crystalline limestone, is of metamorphic origin, and is composed of crystalUne grains. The coarser-grained stones are used in the construction of marble buildings and the finer-grained stones for statuary.

The colors have a wide range; some of the more common colors are white, gray, black, red, pink, green, and yellow.

Compact Limestone breaks with a smooth, dull surface, and does not show a distinct granular structure. When it can be pohshed, some of it is very beautiful and is used as marble. The famous oolitic limestones of Indiana belong to the compact limestones.

The specific gravity of limestone ranges from 2.52 to 2.69, corresponding to weights of 157 to 168 pounds per cubic foot.

The crushing strength of limestone is very variable. The greatest strength obtains for some stone when tested on edge, and for others when tested on the bed. When specific data are not obtainable, 10,000 pounds per square inch may be considered a fair average value for the crushing strength.

The modulus of rupture varies from 300 to 2,700 pounds per square inch.

Young's modulus of elasticity in compression ranges from 3,600,000 to 13,600,000 pounds per square inch, and, as is the case for all stones, the values are true only for certain compressive stresses.

The coefficient of expansion, for each degree Fahrenheit, varies from .00000058 to .00000634.

The absorption of water may be less than one per cent or over twelve per cent. The hard Hmestones usually absorb less than two per cent of water, but many stones, widely used and of excellent durabihty, have coefficients exceeding four per cent.

Limestone is used for nearly all purposes in construction where stone is suitable. The marbles are used for exterior walls, interior finish, and for decorative purposes.

Sandstones and quartzites are generally composed of grains cf quartz cemented together by some substance. The quartz grains may be coarse or fine, and the cementing material may be clay, calcium carbonate, iron oxide, or sihca. The cementing material affects the strength and color of the stone. The buff and yellow colors are due to limonite (brown hematite), the red and reddish brown colors are due to hematite (specular iron ore), and the bluish gray and black colors are due to clay or carbonaceous matter.

Sandstones always show a bedded structure. The layers are sometimes horizontal, and sometimes tipped.

The specific gravity varies from 2.34 to 2.649, corresponding to weights of 146 to 165 pounds per cubic foot.

The crushing strength, as in the case of hmestones, is very variable, ranging from 4,300 to 19,000 pounds per square inch.

The modulus of rupture has a range of 700 to 2,300 pounds per square inch.

Young's modulus of elasticity for compression varies from 1,100,000 to 7,700,000 pounds per square inch, and, as stated for other stones, the values are only true for certain com- , pressive stresses.

The coefficient of expansion, for each degree Fahrenheit, has a wide range, varying from .00000177 to .00000686.

The absorption coefficients have a range from less than one per cent, for quartzite, to over ten per cent, for the softer stones.

In general, the harder sandstones and quartzite make durable building stones. In all cases, however, the stones should be laid on their natural beds, and not on edge.

Slates are metamorphic rocks formed, usually, from clay or shale, and sometimes from fine-grained igneous rocks. They are used for roofing, stair treads, tubs, sinks, blackboards, etc. Locally, they are used for basement walls in buildings.

The colors are red, green, purple, and black. Some of the slates are unfading, and others are not. The only conclusive way to determine the unfading property is to compare newly quarried slate with that which has been exposed to the weather for several years.

The specific gravity of slate varies from 2.7 to 2.9, corresponding to weights of 169 to 181 pounds per cubic foot.

The crushing strength, when tested normal to the cleavage planes, varies from 19,900 to 29,400 pounds per square inch, and when tested on edge, from 14,200 to 31,600 pounds per square inch, the specimens being cubes in both cases. (Tests of Metals, etc., 1902.)

The modulus of rupture, for the states upon which the above compression values are based, varies from 700 to 10,000 pounds per square inch.

Young's modulus of elasticity in compression, tests made on edge, averages about 14,000,000 pounds per square inch.

The coefficient of expansion is between .0000050 and .0000060, for each degree Fahrenheit.

The absorption of water is less than one-half of one per cent.

Average Physical Properties of Building Stones. — The several properties of stones given above at once show, by their range, that average values may be unsafe for some particular stone about which little is known. Stone from a new quarry should always be tested to the extent of showing that the stone is suitable for the purpose for which it is to be used.

The following table is given by Rudolph P. Miller, in the American Civil Engineer's Pocket Book, Mansfield Merriman, Editor-in-Chief.

AvEKAGE Data for Building Stones of Good Quality

Kind of Stone

Pounds per Cubic Foot

Compressive

Strength, Pounds per Square Inch

Shearing Strength, Pounds per Square Inch

Modulus ofRupture, Pounds per Square Inch

Young's Modulus of Elasticity, Pounds per Square Inch

Coefficient of Expansion per Degree Fahrenheit

Granite

170 150 170 170 175 185

1,500

Sandstone. . .

Limestone. . .

Marble

Slate

Trap

Fire-Resisting Property of Stone. — In general, sandstone is not seriously injured by the heat of a burning building, except it may be stained by smoke.

Limestone is uninjured in strength for temperatures which do not exceed about 900° F. The stone seldom cracks, but reduces to a powder under the application of water.

Granite appears to be a very poor fire-resistant, as it generally cracks.

The rapid change of temperature, due to throwing cold water on the heated stones, generally injures the faces of all building stones.

Quarrying. — All building stones, as a rule, are cut from rough blocks of stone which are separated from large masses of rock by quarrying. The particular method used in obtaining these rough blocks depends upon a number of conditions, such as the kind of rock, the amount required, the capital available, etc. For example, if a relatively small amount of stone is required, it is cheaper to use hand tools instead of power tools in quarrying, while for large quantities of stone the use of power tools is more economical.

The use of explosives is common in some localities, but where the stone is to be used for any purpose other than for rip-rap, broken stone, etc., it is better not to employ explosives.

Joints in Relation to Quarrying. — All rocks which are hard and firm are broken up into masses by joints. These may run in almost any direction, but usually they divide the rock into masses which are more or less regular in shape.

Joints in bedded rocks are generally in two systems running at right angles, and normal to the bedding planes.

In igneous rocks, there are usually two sets of joints, one horizontal and the other vertical, with sometimes an odd set running in a diagonal direction. The horizontal joints in granite are usually parallel to the surface of the rock (see Figs. 1 and 13). Basalt and lava are often divided by joints into vertical prismatic forms of columnar appearance.

The existence of joints greatly facilitates the quarrying of building stones, but they do not improve the quality of the stone, as all joint surfaces are more or less subjected to the action of deteriorating agencies.

Quarrying by Hand Tools. — Hand tools, such as the crow-bar, pick, drill hammer, wedge, and plug and feathers, are used

Fig. 1. — ^"Wood and Water," or Wedging Up. Note Horizontal Joints.

in getting out all kinds of building stone (see Figs. 2, 3, 4, 5, 6, 7, 8, and 9), but such tools are more effective for rock in thin layers and somewhat soft. When the rock is in thin layers, these can be separated by the crow-bar and wedges, the vertical fracture following the jointing. If the pieces are too large, they are divided by driUing shallow holes a few inches apart along the line of proposed division, and then using the plug and feathers in each hole. The plug and feathers exert a tremendous pressure, and when properly used the hardest granite is easily separated. Where granites are in large masses (that is, the joints are widely separated), the bed joints are opened by means of wooden wedges. These are driven dry and then wet with water (Fig. 1). This method was used by the Egyptians, and is now used in some of the largest granite quarries in the United States. Special steel wedges are also used for this work.

Quarrying by Machinery. — Marble is cut out in blocks of almost any desired size by the use of channeling machines (Figs. 10 and 11), which cut a narrow channel, either vertically or horizontally, for the full breadth of the face of the block to be cut out. This method saves a large waste and avoids the forming of incipient cracks which sometimes result from using other methods. In granite quarries of much magnitude and where large blocks are wanted, a series of vertical and horizontal holes are drilled a few inches apart along two faces hj machine drills (Fig. 12), and then the block is separated from the rock mass by a "broach," a chisel used to break the stone between the holes, or plugs and feathers. The depth of the holes depends upon the nature of the rock and the amount of waste which can be permitted. Spires sixty feet long, and from four to five feet square in section, have been quarried by drilhng and broaching (Figs. 13 and 14).