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Cornell University Library 
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 A practical treatise on coal mining / 
 
 3 1924 032 183 547 
 olin,anx 
 

MINING ENGINEERING. 
 
Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924032183547 
 
PRACTICAL TREATISE 
 
 ON 
 
 COAL MINING. 
 
 BY 
 
 ASSOC. INST. C£.; MINING CIVIL ENGINEER; MEMBER OF THE SOCIETY OF ENGINEERS. 
 
 VOLUME L 
 
 LONDON: 
 
 E. & F. N. SPON, 46, CHARING CROSS. 
 
 NEW YOEK: 
 446, BROOME STEEBT. 
 
 1879. 
 
^xtr-r 
 
 "\. 
 
 CORNELL^ 
 IJNIVERSrrV 
 MBiiARY/ 
 
PEEFACE. 
 
 oX«o 
 
 MiiflNG has at all times held an important position as a branch of Engineering, but at no time 
 has that importance been so great or so manifest as at the present. The dependence of our material 
 prosperity on an abundant supply of fuel, and the enormous and constantly increasing requirements 
 of such prosperity have rendered the labour of the miner as essential to our existence as is that of 
 the agriculturist, and created a demand that has given an amazing impetus to the progress of his 
 calling. Scores of new pits are being sunk in every proved coal field, and new winnings are 
 announced every day ; and in fields yet untried, or only partially known, borings and sinkings 
 are being pushed on with the utmost vigour. This state of things has created a demand for the 
 knowledge of the Mining Engineer which the numbers of his profession are too few to supply ; 
 hence we find many men, whose training and practice have been in other branches of Engineering, 
 abandoning their former duties in favour of those which ofier a greater reward for their services. 
 This is especially the case with young men fresh from their state of pupilage. Yet, notwithstanding 
 this significant fact, and notwithstanding the position which this country holds as the chief producer 
 of coal, the literature of Mining is singularly scant. It cannot be said that a complete treatise on 
 Goal Mining exists in the English Language. There are, indeed, works on the subject, each 
 excellent in its degree, but some are devoted to the description of merely local practice, while others 
 are written in a style that is rather popular than suited to the requirements of the practical man. 
 This is the more surprising, as both in France and in Grermany the same defect has long since been 
 made good. The consequence is, that neither he who turns his attention from other branches of 
 Engineering to that of Mining, nor the pupil of the practising Mining Engineer, can find a work 
 to which he may turn for instruction, and, in the case of the experienced man, to which he may refer 
 in difficult cases for the practice of other districts. Moreover, the Legislature has now laid such 
 responsibility upon the manager, that he, too, finds it necessary to possess a wider knowledge than 
 was formerly found to be sufficient. To this 'class, a trustworthy book of reference, in cases of doubt 
 and difficulty, must be of the greatest value. 
 
 To supply the want, which undoubtedly exists, is the task I have set myself to perform. Of 
 the manner in which I have accomplished this task, it is not needful to speak; this much, 
 however, it may be desirable to say, that nothing but what has been proved by experience, and is 
 now in use, has received consideration; old and generally abandoned methods have been left 
 in undisturbed possession of the realms of oblivion, and novelties introduced in their true 
 character, as schemes whose merits have yet to be proved. Moreover, as the name of the latter is 
 legion, only such have received notice as have already undergone the test of some genuine practice. 
 Thus, practice, present practice, is the subject of this Treatise. And in describing this practice, I 
 have not confined myself to personal experience, which would have rendered the Work a mere 
 
VI 
 
 PEErACE. 
 
 vehicle of personal opinion, nor to the experience of a district, which would have limited its useful- 
 ness. Nor have I hesitated to introduce methods from French, Belgian, and German practice, 
 when they have appeared to be applicable, either in their entirety or in a modified form, to the 
 conditions which exist at home. 
 
 The Work is divided into Fifteen Chapters, as follows : 
 
 Chapter I. Practical Geology. 
 
 „ • II. Coal : its Mode of Occurrence, Com- 
 position, and Varieties. 
 „ III. Searching for Coal. 
 „ IV. Shaft-sinking. 
 
 „ V. Driving of Levels, or Narrow Work. 
 „ VI. Systems of Working. 
 „ VII. Getting the Coal. 
 „ VIII. Haulage. 
 
 Chapter IX. Winding, 
 X. Drainage. 
 XI. VentUation. 
 XII. Incidental Operations. 
 
 XIII. Surface Works. 
 
 XIV. Management and Accounts. 
 XV. Characteristics of the Coal-fields of 
 
 Great Britain and America. 
 
 Each of these Chapters deals fully with the subject to the treatment of which it is devoted ; 
 and the value of the descriptions is materially increased by the addition of numerous drawings of a 
 practical character. 
 
 The importance of geological knowledge to the Mining Engineer is so great and so obvious, 
 that no apology would seem to be needed for prefacing a work on coal mining intended to be 
 eminently practical, with a somewhat extended exposition of geological facts. Yet it may be urged, 
 that the subject might be more conveniently studied in special treatises. My answer to this objection 
 is twofold. First, no suitable treatise exists. Many and excellent works there are, it is true, but 
 they have not been prepared with a special view to the requirements of the Mining Engineer. To 
 obtain that knowledge which is necessary to enable him to discharge efSciently the duties of his 
 profession, he is compelled to search through a mass of information, a large proportion of which, 
 though eminently important and deeply interesting in itself, has only a remote bearing upon the 
 practical operations of mining. I have therefore endeavoured to provide for this want, by supplying 
 only so much of that information as he is in immediate need of. Secondly, the facts of geology are 
 so closely and so inseparably bound up with the principles and practice of mining, that it is 
 impossible to explain the principles and to describe the practice without making continual reference 
 to those facts. Hence, by placing them in the position they now occupy, I have merely disentangled 
 them from the text, thereby removing from the latter a source of interruption, and rendering the 
 former more easy of reference. 
 
 GEO. G. ANDEE. 
 
 16, Ceaven Street, Steand, London, 
 Augvst 1st, 1875. 
 
CONTENTS OF VOLUME I. 
 
 CHAPTEK I. 
 
 PEACTICAL GEOLOGY. 
 
 Origin and Classification of Eocks — Structure, Texture, and Hardness — The Chief Eock-forming Minerals — Determination 
 of Eocks — Igneous Eocks — ■ Aqueous Eocks — Metamorphic Eocks — Formation of Eock-Beds — Inclination of Eock- 
 Beds — Alternation of Eock-Beds — Formation of Eock-Blocks — Cleavage and Foliation — Faults and Dislocations — 
 Unconformity — Chronological Order of Formation — Table of Sedimentary Strata — Characteristic Fossil Eemains 
 of the Silurian, Devonian, Old Eed Sandstone, Carbon, Permian, Triassic, and Liassic Periods — Geological Surveying — 
 Oblique Section Table • Pages 1-55 
 
 CHAPTER 11. 
 
 COAL: ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 
 
 Eocks associated with Coal — Composition of Coal Seams — Distinctive Characters and Identification of Seams — Classi- 
 fication of Coal — Composition of Coal — Analyses of Coal — Calorific Power of Coal — Uses of the Different Qualities 
 of Coal — Produce of Coal Seams — Comparative Value of Large and Small Coal .. .. .. ,. 56-79 
 
 CHAPTER III. 
 
 SEAECHING FOE COAL. 
 
 Preliminary Considerations — Determination of the Existence of Seams of Coal — Determination of the Character of a Seam 
 of Coal — Boring Operations, and Appliances therefor — Special Systems of Boring .. .. .. .. 80-123 
 
 CHAPTER IV. 
 
 SHAFT-SINKING. 
 
 Tools used in Excavating Eock — Classification of Eocks for Purposes of Excavation — Machine Eock-Drills — Borer-Bits 
 — Compressed Air as- a Motor Fluid — Construction of Machines for Compressing Air — Explosive Compounds for 
 Mining Purposes — Means of Firing Explosive Compounds — Eelative Strength of Explosive Compounds — Electrical 
 Blasting Apparatus — The Principles of Blasting — The Operations of Blasting — Designations of Shafts — Number, 
 Form, and Dimensions of Shafts — Position of the Shaft • — The Operations of Sinking .. .. .. 124-276 
 
 CHAPTER V. 
 
 DEIVING OF LEVELS, OE NAEEOW WOEK. 
 Shaft Pillars — The Levels — Form, Dimensions, and Inclination of the Levels .. .. „ „ .. 277 
 
MINING ENGINEEEING. 
 
 CHAPTER L 
 PEACTICAL GEOLOGY. 
 
 " There is no profession that comes so intimately in contact with geological phenomena, or that 
 stands so much in need of a knowledge of geological truths, as that of the mining engineer. It is 
 true that mining was practised, and in many instances successfully, long before geology had shaped 
 itself into a science ; but even the most successful practice was local and limited, and wanted that 
 grasp of general truths which could enable it to pronounce on other districts, and deal successfully 
 with their altered phenomena. The discrimination of the same formation in distant localities, the 
 varying nature of sedimentary deposits, the relations of the eruptive to the stratified rocks, and 
 the laws regulating the direction, character, and effects of faults, dykes, and veins — these, and many 
 kindred problems, can be solved only by a pretty extensive acquaintance with the facts and principles 
 of geology. It is true that much in successful mining depends on mechanical appliances, but the 
 most skilful appliances will not compensate for ignorance of the nature, position, variations, and 
 interruptions of the substances the miner may be in quest of. . . . The practice of mining is no 
 doubt surrounded by numerous diflSculties ; but it is astonishing how many of these may be overcome 
 by an engineer thoroughly acquainted with the geological structure of his field, and ever on the 
 alert to notice the nature, position, and direction of any changes that may occur in the strata 
 through which he is driving." 
 
 The truths thus clearly and forcibly expressed by Dr. Page are so obvious, and so generally 
 acknowledged, that neither explanation nor proof is needed here ; and they are a suflBcient justifi- 
 cation for introducing geological considerations somewhat largely into the present work. Greology 
 must be held to be the foundation upon which the science of mining engineering rests, and as such 
 it claims the first place in a work that pretends to build up the superstructure. 
 
 A rock has been defined as a mass of mineral matter consisting of many particles, either of one 
 species of mineral, or of two or more species of minerals, or of fragments of such particles, which 
 may or may not resemble each other in size, form, or composition. Under the term " rock," the 
 geologist includes all large masses of mineral matter, whether the constituent particles of such masses 
 be agglutinated and strongly coherent or not. Thus, in this sense, loose sand and clay are rocks, 
 and in treating of them from this point of view, they are so denominated. The question of the 
 origin of rocks is not only a very interesting one, but it is of great practical importance, inasmuch 
 as its true determination enables us to solve many other problems that have a direct and immediate 
 bearing upon matters that the mining engineer has constantly to deal vdth. Hence it will be 
 necessary to take a brief view of the agencies and processes by which rocks have been produced. 
 
 B 
 
^ MINING ENGINEEEING. 
 
 The Origist and Classification of Eocks. — It is an obvious fact that in bodies possessing 
 a crystalline structure, the particles of which the crystals are composed must have been free to move 
 and to arrange themselves in the positions due to the nature of crystallization. In other words, they 
 must have been deposited from a fluid state. Such a state can be produced by only two agencies, 
 heat and water, the former of which causes fusion, and the latter solution. To one or the other, 
 therefore, of these agencies, the origin of every kind of rock must be referred, and according as the 
 fluid state was due to the action of fire or of water, the resulting rock is classed as igneous or 
 aqueous. The determination of the agent that has operated to produce a given rock rests upon 
 certain well-known chemical facts. The crystalline particles of which an aqueous rock is composed 
 must consist of minerals which are soluble in water at ordinary temperatures, since otherwise they 
 could not have been deposited from their solutions. If, on the contrary, those particles consist of 
 insoluble minerals, their fluidity must have been caused by fusion. To the latter class belong the 
 silicates, and hence rocks composed of these silicates may fairly be referred to an igneous origin. 
 Silica is, indeed, soluble in water containing carbonic acid gas, and this fact is sufficient to account 
 for the deposition of crystals of quartz. But most of the natural silicates are practically insoluble 
 in water. 
 
 In both these classes of rocks, we find slow gradations of texture, from those in which the 
 component crystalline particles are large and distinct to others in which those particles have become 
 too minute to be discernible, even with the aid of a lens. From this fact we may fairly infer that 
 what is true of the crystalline rocks is also true of the compact rocks of the same mineral com- 
 position, and that therefore compact limestone, for example, has been consolidated from solution, and 
 the compact silicates from a state of fusion. 
 
 The crystalline rocks, whether of igneous or of aqueous origin, have been produced by chemical 
 action, and are therefore frequently described as chemical rocks. But the latter of the two great 
 classes of rocks, namely, the aqueous class, contains another large and very important kind, which 
 owe their origin to other agencies. In examining these rocks, we find the particles distinct, but not 
 crystalline ; or if they exhibit an internal crystalline structure, externally they will not possess the 
 regular form of the crystal, having been subjected to attrition or fracture. These particles sometimes 
 adhere to each other, in consequence of the great pressure brought to bear upon them by the 
 superincumbent mass ; but more often they are cemented together by some other substance, usually 
 of a siliceous nature. The form of the particles, and their worn and rounded edges, show them 
 to have been broken ofi" some parent rock and transported by currents of water to their present sites. 
 This derivative origin is obviously apparent in some rocks which are composed of pebbles and 
 rounded fragments of rocks imbedded and compacted together in sand. But, as from this case of 
 large and distinct constituents, there is every gradation down to that in which the particles have 
 become too small to be discernible with a lens, we are justified in inferring that the compact rocks 
 of this kind have been formed by the same agencies. The rock-forming action of currents of water 
 is, indeed, constantly going on under our eyes. The rain carries away to the streams the particles 
 loosened by the winds and frost ; the streams convey them to the rivers, and the rivers roll them 
 down to the sea, where they are deposited. Thus all the higher portions of the surface of the globe 
 are being continually worn down, and the wasted material carried to a lower level. The particles 
 borne away by the current being held merely in mechanical suspension, as it is termed, to distinguish 
 it from chemical solution, are deposited as soon as the water assumes a state of quiescence. The 
 
PRACTICAL GEOLOGY. 6 
 
 heavier bodies, as gravel, fall first; then follow the finer particles of sand; and finally the light 
 flocculent mud, or clay. By processes such as these, lakes are silted up and become marshes and 
 plains, and estuaries and narrow seas are converted into tracts of alluvial land. As the materials 
 composing these rocks have been mechanically procured and transported, they have been termed 
 mechanical rocks. Moreover, as they have been deposited from suspension, and arranged in regular 
 layers, beds, or strata, they are often called sedimentary and stratified rocks, which terms, however, 
 include the chemical rocks, being appropriately applied to the whole of the aqueous class. 
 
 There is yet another variety of rocks which have an organic origin, that is, they have been 
 formed from living organisms. These organic constituents consist of fragments of animals or plants, 
 which may be only slightly altered from their original condition, or altogether mineralized. In the 
 former case, they are allied to the mechanical ; in the latter, to the chemical rocks. 
 
 Upon consideration and examination, it becomes evident that many rocks, both of the igneous 
 and aqueous classes, have undergone considerable and, in some cases, great changes since the time of 
 their formation. The chemical actions and reactions that may be set up in a mass of rocks by the 
 percolation of various fluids and gases, and by other agencies, and the mechanical forces generated 
 by the pressure of superincumbent masses must have produced change, and such changes exhibit 
 themselves in the nodular, concretionary, crystalline, fibrous, veinous, or other arrangement of the 
 constituent particles. These transformed rocks have been classed by Sir C. Lyell as metamorphic 
 rocks, and they constitute a large and important class, the changes due to the aforementioned 
 agencies having been more general than is commonly acknowledged. 
 
 Thus we have three great classes of rocks — the igneous, the aqueous, and the metamorphic — 
 under one or another of which every variety may be ranged, according to the nature of the agency 
 by which they have been brought into their present state. Geologists acknowledge another class, 
 denominated the aerial rocks, because the chief agent that has operated in their formation is the 
 wind. This class is, however, unimportant for our present purpose. 
 
 Structure, Texture, and Hardness. — Structure is the manner in which the individual 
 particles are built up or aggregated in the rock-mass. Thus the term relates more especially 
 to the external aspect, the larger features of the arrangement of a rock, which can be properly 
 studied only in cliffs, ravines, quarries, or other openings where the strata are exposed. In the 
 aqueous or stratified rocks, the terms stratum or bed are applied to deposits of considerable thick- 
 ness ; layer or band, to a thin deposit holding a subordinate place among the other beds ; and seam, 
 to a rock of peculiar character occurring at intervals among a series of strata. Thus seams of coal 
 occur among strata of clay and sandstone, and a band of ironstone exists in a bed of shale. The 
 structure of an individual stratum may be laminated, flaggy, fissile, or shaly. Rocks, the component 
 particles of which have been deposited from suspension in water, are made up of a number of thin 
 layers, or lamince, obviously the result of successive acts of deposition. Sometimes this lamination is 
 very distinct, and the number of lamina numerous, as many as fifty having been counted in one inch 
 of thickness. The coherence between these laminse varies greatly in different rocks. It would seem 
 that when the depositions occurred in rapid succession, the coherence is greater tlian when long 
 intervals elapsed between them. To this fact is no doubt due the structure termed flaggy, which 
 denotes a greater tendency to separate between some lamina than others, and thus to produce slabs 
 of rock known as fl/igs and flagstones. Any rock that has a tendency to split in any direction, 
 whether in the line of bedding or otherwise, is described as fissile. Clay in its ordinary state is soft 
 
 B 2 
 
4 MINING ENGINEEKING. 
 
 and plastic ; buf when indurated and having a tendency to split in the direction of its bedding, it is 
 described as shale, and its structure as shaly. The term slaty is applied to rocks which, like roofing- 
 slate, split up regularly, in lines generally transverse to those of stratification ; while schistose, from 
 the Grreek schisma, a splitting, is properly applied to fissile rocks having a crystalline texture and 
 irregular lamination, as mica-schist. 
 
 The structure of the igneous rocKs is less varied than that of the aqueous rocks. "When 
 appearing as columns, as in the basalts of the Griant's Causeway, the structure is said to be columnar, 
 or sub-columnar if the columns are not very distinct. In rocks that break up into large square-like 
 blocks, as some granites and greenstones, the structure is described as tabular or cuboidal; but if the 
 blocks have no regular shape, it is massive or amorphous. Some greenstones present a spherical or 
 globular structure, termed also concretionary, from its apparent aggregation round a common centre. 
 The spherical concretions vary from a few inches to several feet in diameter ; on exposure to the 
 weather, they exfoliate, like the coats of an onion. 
 
 Texture is the grain, or manner of arrangement of the component particles of a rock. Thus 
 while structure relates to the external aspect, texture relates to the internal constitution of rocks, 
 and must therefore be studied in their fracture. When made up of distinct grains, like sandstone, 
 the texture is granular ; if the grains have a uniform crystalline aspect, as in many statuary marbles, 
 the texture is described as saccharoid ; oolitic, when composed of round particles, as in oolite ; porous, 
 when open like pumice ; vesicular or cellular, when full of small cavities, like certain kinds of lava ; 
 fibrous, when composed of fibres or filaments, like asbestos ; and acicular, when the fibres are distinct 
 and needle-shaped. The texture is described as compact when close and firm ; crystalline, when 
 composed of sparkhng crystals ; sub-crystalline, when the lustre is dull ; earthy, whea soft to the touch 
 and dull in aspect ; glassy, when possessing the appearance of glass ; porphyritic, when detached 
 crystals are disseminated through a compact base, or large crystals through a fine-grained base ; and 
 amygdaloidal, when the pores or vesicles become filled with a crystalline nucleus or kernel of any 
 mineral, either by subsequent infiltration or during the process of consolidation, so that the dispersed 
 crystalline patches look like almonds stuck into the mass. It must be remarked here that some 
 structural arrangements affect even the most minute particles of a rock, and that therefore structure 
 is occasionally found to pass into what is more commonly described as texture. 
 
 Intimately connected with the texture of a rock, and of great practical importance, is its hard- 
 ness. The hardness of a mineral, and consequently of a rock into the composition of which any 
 given minerals enter, is estimated by a conventional scale of ten degrees, assuming talc to be the 
 lowest and diamond the highest in the scale. 
 
 Talc 
 
 1 
 
 Felspar (Orthoclase) 
 
 6 
 
 Gypsum 
 
 2 
 
 Quartz (Eock-crystal) 
 
 7 
 
 Calc-spar .. 
 
 3 
 
 Topaz 
 
 8 
 
 Fluor-spar .. 
 
 4 
 
 Corundum ., 
 
 9 
 
 Apatite, or phosphate of lime 
 
 6 
 
 Diamond .. .. ,, 
 
 10 
 
 If, for example, a mineral can be scratched by rock-crystal, but which is itself capable of scratch- 
 ing felspar, its degree of hardness evidently lies between 6 and 7 of the scale, and may be repre 
 sented by 6-3 or 6-8, according as it seems to approach felspar on the one hand, or rock-crystal on 
 the other. 
 
 The Chief RocK-FORMiNa Minerals.— The minerals that enter largely into the composition of 
 
PRACTICAL GEOLOGY. 5 
 
 rocks are not numerous. The following are the chief; and the student of geology should early make 
 himself familiar with the distinguishing qualities of each of these rock-constituents. 
 
 Quartz. — The mineral known as quartz is silica or oxide of silicon. The usual crystalline 
 form of quartz is a hexagonal prism, pointed, when complete, at both ends by hexagonal pyramids. 
 It is colourless when pure, and its streak is white. Its lustre is vitreous, sometimes inclining to 
 resinous. It varies from transparent to opaque. The fracture is conchoidal ; the specific gravity 
 from 2 • 5 to 2 • 8. In its transparent crystalline form, the mineral is known as rock-crystal, which, in 
 tbe scale of hardness, occupies the seventh place. One of the most important characteristics of quartz 
 is the total absence of cleavage. It is infusible alone before the blowpipe ; but with soda it fuses 
 readily, with efflorescence, to a transparent glass. 
 
 Calcite or Calc-spar. — Next to quartz, calcite is the most abundant mineral in nature. This 
 crystallized carbonate of lime, the general term for which is calc-spar or calcareous spar, occurs in a 
 great variety of forms and in various degrees of purity. Clear, colourless masses, cleaving readily 
 into rhombohedrons, are found in Iceland, whence the name of Iceland spar given to such cleaved 
 pieces possessing well-marked double refraction. Pure calcite occupies the third place in the scale of 
 hardness; its specific gravity is from 2*69 to 2-75. Lustre, vitreous to earthy, transparent to 
 opaque ; streak, white or greyish ; cross-fracture, conchoidal. Besides the numerous crystalline forms 
 known as calc-spar, calcite occurs saccharoidal as crystalline Hmestone which, when perfectly white, 
 is statuary marble. When occurring in small spherical grains cemented together like the roe of a 
 fish, it is known as oolite. Calcite effervesces strongly on tbe application of mineral acids. It does 
 not fuse before the blowpipe, but shines with an intense light. 
 
 Gypsum. — Calcic sulphate or sulphate of lime occurs hydrated in nature, and is known as 
 gypsum. This mineral, when calcined, forms the well-known plaster of Paris. It is found in all 
 formations, but it is more especially abundant in the carboniferous, permian, and miocene. It is 
 deposited during the evaporation of brine, and is produced by the action of sulphuric acid generated 
 by the oxidation of sulphur or pyrites, or evolved from volcanic fissures. When crystallized, it is 
 known as selenite. It also occurs laminar, fibrous, saccharoidal, and compact, mixed with carbonate 
 of lime, clay, and sulphur of various colours, but usually white. The fine, fibrous variety is known 
 as satin-spar ; alabaster is a term applied to the saccharoidal and compact varieties, consisting of car- 
 bonate of lime and sulphate of lime, the former being distinguished as calcareous, and the latter as 
 gypseous alabaster. G-ypsum does not effervesce with acids. It turns white before the blowpipe, and 
 crumbles ; but is fused only with diflSculty. In hardness it occupies the second place. 
 
 Felspar. — As a rock-constituent, felspar is a very important mineral. It enters largely into the 
 composition of all the igneous rocks, and is variously coloured. Felspars are chiefly composed of 
 silica, alumina, and potash or soda, or sometimes lime. They have been divided into two series, 
 crystallographically, known respectively as orthoclase, straight cleavage, and plagioclase, oblique 
 cleavage. The former are the potash felspars, the latter the soda and lime felspars. The whole of 
 the felspars have been classified into ten series, as follows : — Potash felspars : Adularia, amazonite, 
 pert/lite, loxoclase. Soda felspars : Albite, oligoclase. Lime felspars : Andesin, labradorite, bytownite, 
 anorthite. Orthoclase and albite may be considered as acid felspars, in contradistinction to the anor- 
 thite or basic felspar. All other felspars are mixtures of these three. The specific gravity of ortho- 
 clase is 2 ' 56 ; of albite, 2 • 62 ; and of anorthite, 2 • 76. This mineral occupies the sixth place in the 
 scale of hardness. The cleavage of felspar is highly characteristic, one face of cleavage being perfectly 
 
o MINING ENGINEEEING. 
 
 smooth, and another, nearly at right angles to it, somewhat less perfect. Orthoclase may be recognized 
 from the other varieties by having the two cleavage planes at right angles to each other. Before 
 the blowpipe felspar fuses alone with great difficulty to a blistered, turbid glass; with borax it 
 dissolves slowly, forming a transparent glass. 
 
 Hornblende. — This mineral varies in colour from black to white, through numerous shades of 
 green ; but in its commonest forms it is either black or of a dark green hue. It is usually opaque 
 and translucent. Hornblende is an important constituent of the igneous rocks ; it generally occurs 
 confusedly crystalline, forming with quartz " hornblende rocks " ; with quartz and felspar, " syenite " ; 
 and with felspar alone, the numerous varieties of "greenstones." In hardness it varies between 
 5 and 6 on the scale of Mohs ; it is therefore softer than felspar. Its specific gravity is, however, 
 greater than that of either felspar or quartz, it being between 2*9 and 3 "4. "When breathed upon, 
 hornblende emits a peculiar bitter odour. 
 
 Augite. — The mineral known as augite or pyroxene is, in composition, closely allied to horn- 
 blende. The crystals belong to the monoclinic system, the inclination of the inclined axis being 74°, 
 and the angle ot the type prism 87° 6', parallel to which it cleaves. In colour it varies from white, 
 through various shades of green, to brown and black. The lustre is vitreous, inclining to resinous, 
 and in some cases pearly. The lustre, colour, transparency, and hardness vary with the relative 
 proportion of the metals calcium, magnesium, iron, and manganese which the varieties contain. 
 The hardness lies between 5 and 6, and the specific gravity between 3 • 23 to 3 • 50. Thus the hard- 
 ness is about equal to that of hornblende, but the specific gravity is greater. Chemically the augites 
 may be classified into non-aluminous and aluminous augites. The former consist of meta-silicates of 
 calcium, magnesium, iron, and manganese ; and the latter, of those silicates, with an aluminous 
 silicate. In the augites of both classes the magnesium is sometimes almost wholly replaced by 
 calcium and iron. The common augites are chiefly black, or greenish and brownish black, and very 
 lustrous, whence their name, from auge, lustre. Like hornblende, augites assume a fibrous structure. 
 This mineral enters largely into the composition of the igneous rocks. 
 
 Alica. — The term mica (from mico, to glisten) is applied to several minerals having a different 
 chemical composition, but possessing the quality of being easily cleavable into thin laminae. This 
 laminar structure is hence termed micaceous. Mica is mainly composed of silica, potash, and mag- 
 nesia. Chemically the micas may be divided into non-magnesian and magnesian micas. The former 
 are called potash micas, because they contain a larger proportion of potash than those of the latter 
 class. Common mica, or muscovite, is remarkable for the size of the folia which may be obtained. 
 In thin plates it is always transparent ; but when the plates are thick it is opaque. The colours are 
 white, grey, pale green, dark olive green, brown, and violet yellow. The hardness of mica lies 
 between 2 and 3, and its specific gravity between 2 • 8 and 3 • 1. Mica constitutes the chief ingredient 
 in the slaty rocks called "mica-schist" ; it occurs as scaly crystals in granite, and, in minute scales, 
 in many sandstones, giving them a silvery appearance. The mica of the aqueous rocks is derived 
 from the disintegration of granite. Sandstones containing this mineral have a foliated structure, and 
 are described as " micaceous." 
 
 The DETERMiNATioiir OP Rooks. — Having described the several classes and kinds of rocks, it 
 now becomes necessary to point out the means by which they may be recognized. For the purpo?e 
 of examining and determining in the field any specimen of rock that may come under our notice it 
 is requisite and sufficient to be provided with an ordinary chipping-hammer, a pocket-lens, a knife, 
 and a small bottle of dilute hydrochloric or other mineral acid. 
 
PEACTICAL GEOLOGY, 7 
 
 The first step in the examination is to form, by chipping, two fiissh surfaces as nearly as possible 
 at right angles to each other for the purpose of ascertaining the texture. The subsequent steps will 
 be determined by the results of this preliminary measure. 
 
 If the rock be a compact one, that is, if no crystals or grains are visible with the lens, it must be 
 scratched with the point of the knife ; when, if it scratch easily, it may be inferred that it is either 
 an aqueous rock or a very much decomposed igneous one. A little dilute acid may next be applied 
 to a small portion of the specimen ; and if it effervesce freely, it may be pronounced limestone ; if the 
 effervescence proceed slowly, the rock may be a magnesian limestone ; but if no effervescence is pro- 
 duced, it may be either gypsum or a decomposed rock. If considerable force is required to scratch the 
 rock, it is probably a compact igneous rock ; but if it does not scratch at all, but is merely marked 
 by the steel, it is probably a purely siliceous rock, as flint, chert, or some other kind of quartz, and 
 therefore of aqueous origin. 
 
 If the texture of the specimen to be examined be granular, it will be necessary first to determine 
 whether the grains be innate crystalline particles, or water-worn like grains of sand. If distinctly 
 rounded and water-worn, even ii only one such grain be visible, the rock must be classed as 
 aqueous. But cases will be sometimes met with in which the grains consist of broken crystals bear- 
 ing hardly a trace of attrition, when the rock may be mistaken for one of igneous origin. If, how- 
 ever, these crystals consist of quartz, they are probably aqueous ; and a careful search wiU usually 
 disclose some grain or fragment, the present form of which is evidently due to mechanical attrition. 
 In some igneous rocks there exist small globules of crystalline quartz having the appearance of 
 pebbles ; the observer should be on his guard against being led astray by such deceptive appearances. 
 When the rock is made up of layers differing from each other slightly in form and texture, it may 
 be inferred that the rock is sedimentary, and therefore aqueous ; but such evidence, though strong, is 
 not absolutely conclusive. 
 
 If the texture of the rock be distinctly crystalline, that is, if it be composed of innate crystalline 
 particles, the question to be determined will be whether these particles consist of carbonates or 
 sulphates, or of silicates ; and the determination of this question will decide that of the origin of the 
 rock ; for, if they consist of silicates, the rock has been formed by igneous agencies ; and if of carbo- 
 nates or sulphates, it may with equal certainly be referred to an aqueous origin. To ascertain the ' 
 nature of the crystals, the specimen should be scratched with the point of the knife ; if it scratch 
 easily, they will almost certainly be either carbonates or sulphates. Acid should next be applied to 
 the scratched part : and if immediate and violent effervescence ensue, the rock is some kind of lime- 
 stone. If of magnesian limestone, the effervescence will take place slowly, in which case also the 
 rock will present a pearly appearance, and have a gritty feel. But if no effervescence be produced 
 by the acid, it will probably be gypsum. If the results of the examination prove the crystalline 
 particles to be neither carbonates nor sulphates, they must be silicates ; and it only remains to deter- 
 mine the kind of igneous rock by ascertaining the nature of the minerals present, and the proportions 
 in which they enter into its composition. This may usually be done either with the naked eye, or 
 with the aid of a lens, by recognizing the minerals from their characteristic appearance, or by deter- 
 mining the angles formed by their facets, and thence the form of their crystals. 
 
 When the structure is platy, that is, when the rock has a tendency to split into thin plates, it 
 may be either an aqueous rock, formed by successive depositions in thin layers, or a metamorphic 
 rock. If of the former class, it will be soft or easily broken, and the lines of division will coincide 
 
8 MINING ENGINEEEINQ. 
 
 witli the layers of different colour or texture^ or with the grain of the rock. If of the latter class, it 
 will probably be hard^ and the plates, after separation, will be more or less firm and strong. If the 
 rock be a slate or cleaved rock, the faces of the plates will have a dull and earthy appearance. But 
 if it be a schistose, metamorphic rock, the texture will be crystalline or sub-crystalline, and the faces 
 of the plates will possess a metallic lustre. 
 
 In fine-grained and compact rocks it will happen that the texture and composition cannot be 
 discovered with a lens, and the rough methods described above will, in such a case, be of no avail. 
 For the examination of these rocks, recourse must be had to the microscope. To prepare a rock 
 specimen for microscopical examination, a thin slice is taken and ground smooth on one side, when 
 this smooth surface is securely fastened with Canada balsam to a piece of plate glass, and the other 
 side ground down until the requisite thinness and transparency are obtained. Thus prepared it may 
 be covered with a plate of very thin glass mounted with balsam on the slide, care being taken to 
 exclude all air-bells, and to remove all traces of the emery powder or other substances used in the 
 grinding process. With a rock-section prepared in this way, we may, with the aid of the 
 microscope, ascertain with precision the manner in which the different minerals are built into each 
 other, and throw a flood of light upon the origin of a rock and the subsequent changes it has 
 undergone. Points of structure which could not be discovered in any other way are, by this means, 
 clearly revealed. This method of examination has been recently adopted to distinguish between 
 augite and hornblende, two minerals that are very similar in appearance when occurring as minute 
 crystals. 
 
 The foregoing methods of examination will not always enable us to determine what minerals 
 enter into the composition of a given rock, nor inform us expressly of what elements the minerals 
 themselves are composed. In such cases, recourse must be had to chemical analysis. Such an 
 analysis every mining engineer ought to be capable of making ; for not only does it open up to him 
 fields of research of the highest interest, but it is of daily practical use to him, by enabKng him to 
 determine the relative age of rocks from their mineral composition, and their ability to withstand 
 the disintegrating influence of atmospheric agencies, and hence their suitability to building 
 purposes. The student who wishes to pursue this subject will find it carefully and fully treated in 
 Bischoff's ' Chemical Geology.' The methods of field examination we have been describing may be 
 studied in Jukes and Geikie's ' Manual of Geology,' to which excellent work we have to acknowledge 
 our indebtedness for some of the facts and classifications given in the present chapter. The student is 
 also recommended to examine and make himself familiar with the principal rock-constituents already 
 described, so as to be able to recognize them in any kind of rock that may come under his notice. 
 
 In the determination of rocks, their colour, streak, fracture, and specific gravity afford assistance, 
 and sometimes conclusive evidence, towards arriving at a correct decision. By colour of a mineral 
 is meant the hue which it possesses when first taken out of the earth ; for exposure to the atmosphere 
 may either obscure or totally change its natural colour. A more reliable test than the natural colour 
 of a mineral is the colour of its " streak," produced either by scratching it, or by drawing it across a 
 piece of white unglazed porcelain. Fracture furnishes an important test. There are three kinds of 
 fracture, known as the conchoidal, or shelly, in which the fractured surface presents curved concavities 
 resembling more or less closely those on the inside of a bivalve shell, as in flint and glass ; the even, 
 in which the fractured surface presents no minute elevations and depressions ; and the hackly, in 
 which the elevations are sharp or jagged, as in broken iron. The specific gravity of a mineral is of 
 
PEACTICAL GEOLOGY. 9 
 
 very great importance as a test, and, in some cases, it is almost the only one to -which recourse can 
 be had without injuring the specimen. The determination of the specific gravity is efiected by first 
 weighing a fragment in the usual manner in a delicate balance, reckoning the weight in grains. 
 The fragment is then suspended, by a fine thread from one of the scales, in a tumbler of water, and 
 its weight taken again. Care must be taken to sink the specimen below the surface of the water, 
 and to prevent it from touching the sides of the glass. The second weight is then subtracted from 
 the first, and the latter divided by the difference ; the result is the specific gravity. 
 
 The Igneous Rocks. — The igneous rocks are, as we have previously pointed out, made up of 
 minerals that are silicates. These minerals may be divided into two great classes, namely, silicates 
 of magnesia, and silicates of alumina. The former constitute the hornblendic or augitic minerals, 
 the latter the felspathic. The several varieties are due to an admixture of silicates of potash, soda, 
 lime, iron, manganese, and other substances. There are, indeed, the micaceous minerals, to which 
 may be assigned an intermediate place ; but they must be considered as of minor importance. The 
 felspars are the bases of the igneous rocks, and those kinds in which this mineral greatly 
 predominates are described as felspathic rocks ; while those in which hornblende and augite enter as 
 important constituents are called hornblendic or pyroxenic rocks. 
 
 The igneous rocks have been classed, according to their age, as granitic, trappean, and volcanic. 
 It is true that the relative age of the igneous rocks is not clearly defined like that of the aqueous 
 rocks, since we have neither an unvarying order of superposition nor the presence of organic remains 
 whereby it may be determined. Grranite is sometimes found above the trap, and trap may exist 
 among the older rocks; but generally, granite is the deepest seated, and is associated with the older 
 strata, while trap occurs in those of the secondary epoch, and the volcanic varieties among those of 
 a more recent period. 
 
 Granite.— Granite is the most easily recognized of all rocks. It is a compound of telspar, 
 quartz, and mica; but the proportions of these minerals vary indefinitely. The felspar, however, 
 never -forms less than a third part, and rarely less than half the mass ; generally it exists in a larger 
 proportion. In some cases the quartz, and in others the mica, becomes so minute as to be hardly 
 discernible. The texture of granite is highly crystalline ; none of the crystals are water worn, and 
 no trace is exhibited of deposition or stratification. The texture varies, however, in degree from the 
 compact and fine-grained to the large and coarsely crystalline. The colours of granite are white, 
 grey, and red ; white when the felspar is pure white, and red when the felspar is flesh-coloured. The 
 intermediate grey tints depend chiefly on the abundance and colour of the mica. The felspar of 
 granite is usually orthoclase, and is then either flesh-coloured or white ; but oligoclase often occurs 
 of a. greenish or greyish white- colour. Oligoclase is distinguishable from orthoclase by its fine 
 parallel striations. The mica varies greatly both in colour and in lustre. When silvery-white or 
 golden-yellow, it is usually potash-mica ; the brown and black varieties being magnesia-mica. The 
 quartz is either colourless or white; cases may, however, occur in which the quartz has a dark-grey 
 or brownish hue. 
 
 - In granite the quartz is always visible; indeed, the existence of crystalline particles of quartz 
 among crystalline particles of the other minerals constitutes its most essential character, the quartz 
 being invisible in most of the trap rocks. A remarkable fact is, that though the felspathic and 
 micaceous constituents frequently form perfect crystals in granite, quartz rarely does so ; from which 
 fact it may be inferred that the former were solidified before the latter. 
 
 c 
 
10 MINING ENGINEEEING. 
 
 Though the granite rocks differ considerably in colour, texture, and mineral composition, they 
 possess several features in common which distinguish them from the later igneous rocks. They are 
 more crystalline than any of the other varieties ; they are never vesicular, cellular, or porous, like 
 the traps and volcanic rocks ; they exhibit less structure than the traps, being generally massive or 
 cuboidal, and never columnar, a structure very common in the basalts and greenstones ; and they are 
 never amygdaloidal like traps, conglomerated or brecciated like trap-tuffs, nor scoriaceous like 
 volcanic tufa. They seem to have been formed at greater depths or under greater pressure than 
 either traps or lavas. 
 
 There are several varieties of granite which have been named according to the presence oi 
 accidental minerals. When hornblende takes the place of the mica the rock is known by the name 
 of syenite, and when both mica and hornblende are present, the compound is called syenitic granite. 
 Sometimes, as in the Alpine granite, talc is present. The rock, which then consists of orthoclase, 
 oiigoclase, quartz, mica, and talc, is in this case called protogine. Graphic granite is a variety 
 distinguished by a pecuhar mode in which the quartz is crystallized in the felspar, so as to produce 
 on a cross-fracture of the quartz crystals the appearance of Arabic writing. Hypersthenic granite 
 is a term applied to an admixture of quartz and hypersthene with scattered flakes of mica. 
 Pegmatite is a coarse granite full ot druses, and consisting essentially of orthoclase, which often 
 occurs in very large crystals, quartz, and large plates of silvery-white mica. This variety occurs in 
 veins or layers in other granitic rocks. When, in addition to the crystals composing the general 
 mass of the rock, there are indiscriminately mingled through it larger and independent crystals of 
 felspar, so as to produce a porphyritic texture, the rock is called porphyritic granite. Other varieties 
 exist, but they are of littk importance. 
 
 Trap Rocks. — The term trap or trappean is derived from the Swedish word trappa, stairs or 
 steps, and was originally applied to those igneous rocks which give to many hills of the secondary 
 epoch a terraced or step-like appearance. The term is now applied to all those igneous rocks which 
 are neither strictly granitic on the one hand, nor distinctly volcanic on the other, and which, in point 
 of age, are intermediate between the granitic and the volcanic rocks. The trappean rocks may be 
 conveniently divided into two classes or families according to the minerals that enter into 
 their composition, namely, the felspathic traps, which compose the more siliceous variety, 
 and the hornblendic traps, under which head are ranged those of a more basic character. The 
 felspathic family also includes two groups distinguished by similar qualities, and hence known as the 
 acidic and the basic groups. The former consists of those rocks which contain orthoclase, with an 
 excess of free silica. The rocks of this group are called felstones. The basic group contains those 
 rocks which consist essentially of one or more of the basic felspars.. The rocks of this group are 
 called porphyrites. 
 
 " Felstone " is a designation that has recently been substituted for a variety of terms that had 
 been applied to the same class of rockj such as compact felspar, felsite, eurite, petrosilex, and cornean, 
 which terms are still in use among continental geologists. The rock thus designated is composed of 
 an intimate mixture of orthoclase and quartz, and is compact, smooth, hard, and flinty in appearance. 
 There are two varieties of felstone, distinguished by their colour ; the pale green passing into a 
 greenish white, and the blue or grey varying from pale to dark grey. Both of these varieties 
 weather white. The weathered part, however, frequently exhibits ferruginous stains, sometimes 
 becoming wholly brown, especially in the green variety. Some blocks that appear wholly white 
 
PEACTIUAL GEOLOGY. 11 
 
 have a small blue patch in the centre. The green variety is often very translucent at the edges ; 
 but the grey is commonly opaque. The fracture of felstone is generally smooth and straight ; in 
 some cases it is slightly conchoidal, and in some of the blue or grey varieties it may oftea be rough 
 and splintery. The rock frequently splits into small slabs, and in the green variety into laminae. 
 
 In the most compact varieties, small shining facets of crystals of felspar may be detected with a 
 lens ; these crystals become gradually larger and more numerous, until the rock becomes completely 
 granular and crystalline. Small crystals of quartz are also occasionally present. Mr. Jukes remarks 
 that in some felstones there are small globules of glassy quartz, in appearance like rolled pebbles, 
 leaving round cavities in the rock when they are detached. These he believes to be crystalline blebs 
 of quartz, formed during the consolidation of the rock. 
 
 Felstone in its commonest form is perfectly compact ; when distinct and independent crystals of 
 felspar are disseminated throughout a base of compact felstone, the rock is designated as porphyritic 
 felstone, or felstone porphyry. If it happen, as it not unfrequently does, that the scattered crystals 
 of felspar are of a different colour from the base, the rock is called porphyry, and is used as an orna- 
 mental marble. Usually the base is of a reddish colour, and the scattered crystals whitish or flesh- 
 colour. 
 
 " Pitchstone " is a compact glassy rock, closely allied to the foregoing, and having a pitchy lustre 
 and fracture, whence its name. It varies, however, in colour, from velvet black, through shades of 
 impure green and yellow, to white. Its texture is sometimes porphyritic. This rock is also called 
 Retinite, 
 
 " Minette " is a micaceous felstone, consisting of a felsitic base in which crystals of orthoclase 
 and dark mica are disseminated. 
 
 " Clinkstone," or phonolite, is sometimes classed among the trappean rocks. But the clinkstones 
 so described are probably only platy varieties of felstone, the slate-like fragments of which often emit 
 a ringing metallic sound when struck with the hammer. 
 
 " Porphyrite " consists of a base of oligoclase, with crystals of the same mineral disseminated 
 throughout the base, and a variable admixture of hornblende, mica, augite, and quartz ; the two latter, 
 however, but rarely. The texture of porphyrite is usually very close-grained, and, as its name 
 implies, more or less porphyritic. Frequently the texture is amygdaloidal. In colour, porphyrite 
 varies from white or pale grey, through various shades of red, lilac, and purple, to dark brown. The 
 dark tints are the most frequent. 
 
 " Kersanton " is a form of mica-porphyrite ; this variety contains hexagonal plates of mica dissemi- 
 nated through a greenish or grey base. Kersantite is another variety, containing a little hornblende. 
 
 The Hornblendic traps, frequently designated by their old name of " Greenstones," constitute 
 a numerous- and very important class of trap rocks. They consist essentially of a crystalline 
 mixture of some plaglioclase felspar with hornblende or augite. The felspar is usually oligoclase, 
 but some more basic variety sometimes occurs. In some rocks of this class, augite or hypersthene is 
 substituted for the hornbleude. Compact and dark-coloured greenstone is very similar in external 
 appearance to basalt. But if the weathered part be broken open and tested with acid, greenstone 
 will almost invariably effervesce along the inner edge of the weathered portion. Like felstone, 
 greenstone may become porphyritic in texture in consequence of one or other of its constituents 
 forming distinct crystals in a compact base, or large crystals disseminated through a fine-grained 
 crystalline base. 
 
 c 2 
 
12 MINING EN«INEEEINa. 
 
 " Diorite " is composed of felspar, usually oligoclase, and hornblende. In texture it vafie's from 
 the compact to a coarsely crystalline a:ggregate In colour it is generally of a dull green, varying 
 from light to dark. There exist varieties, however, in which the felspar is very white and in great 
 quantity, and in such cases the rock is white, speckled with dark green spots. It weathers to a dull 
 dark brown. 
 
 " Diallage-rock " is composed of labradorite and diallage. Generally it is of a palish green or 
 grey colour, but sometimes of an olive or greenish brown colour. Its texture varies from fine to 
 coarse-grained, and in some instances it has a granitic, and in others a porphyritic appearance. In 
 Britain it occurs associated with metamorphic rocks. 
 
 " Hypersthene-rock" is a mixture of labradorite and hypersthene. The labradorite is green with 
 glancing shades of blue and red, and the hypersthene is dark brown, inclining to black. In texture 
 it varies from the fine-grained to the excessively coarse-grained. Mr. Jukes mentions the fact of 
 having seen a specimen of this rock in which the two minerals formed crystals as large as the fist. 
 The fine-grained variety resembles diabase or aphanite. 
 
 " Melaphyre" is a term applied to several varieties of dark, compact, heavy rocks of igneous origin. 
 The following description of melaphyre is given by Senft. " An indistinctly mixed rock, of a dirty 
 greenish-brown or reddish-grey, or greenish black-brown, passing to a completely black colour, hard 
 and tough in the fresh state, in which appear crystals of reddish-grey labradorite, with magnetic 
 titaniferous iron, and commonly with some carbonate of lime, carbonate of iron, and ferruginous 
 chlorite, sometimes in crystalline grains, sometimes compact or earthy, sometimes porphyritic or 
 amygdaloidal." 
 
 "Diabase" is a name given by German petrographers to a crystalline-granular mixture of labra- 
 dorite and augite with chlorite, and sometimes with an impregnation of carbonate of lime. This 
 rock occurs in the Silurian, Devonian, and Carboniferous systems of Germany. 
 
 "Aphanite" is a name applied to the compact, close-grained variet'es of greenstone. By some 
 writers it is restricted to the dioretic rocks, by others it is extended also to the compact diabases. 
 
 " Wacke" is a name given by German petrographers to decomposed forms of basic igneous rocks. 
 
 The foregoing descriptions relate to the crystalline traps, which constitute by much the larger 
 portion of existing trap rocks. But there is another kind that owe their origin to mechanical 
 agencies. The detritus in the form of dust and gravel, with large blocks or bombs ejected from 
 volcanoes in past ages, falling into water, was rearranged, and became consolidated into rock. Also 
 large masses of igneous rocks exposed to the action of atmospheric and aqueous agencies became 
 disintegrated, and the detritus, finely comminuted, was deposited in beds to form new rocks. The 
 trappean rocks that owe their origin to such agencies are analogous in character to the conglomerate 
 of the aqueous rocks, and they are distinguished from the crystalline rocks from which they are 
 derived by the name of Fragmental Rocks. 
 
 The fragmental trappean rocks are divided into two groups— Tuff, or trap-tuff, and Trappean 
 Breccia or conglomerate. Under the term " tuff" are included all the fine-grained varieties. These 
 varieties are named according to the nature of the rock from which they have been derived. Thus 
 we have Felstone-tuff, Porphyrite-tuff, and Greenstone-tuff, each of which is distinguished by the 
 qualities characteristic of the parent rock. This remark applies also to the Breccias, which consist of 
 angular fragments embedded in a paste of the same materials. "When the fragn ents are rounded 
 the rock is called trap-conglomerate. 
 
PEACTICAL GEOLOGY. 1 3 
 
 The Volcanic Bocks. — ^The volcanic, like the trap rocks, may be divided into two families, the 
 acidic and the basic ; the former being distinguished as trachytic, and the latter as doleritic. The 
 trachytes, so named because they have a rough prickly feel when handled, are composed principally 
 of a felspar rich in silica, as orthoclase, and are usually light-coloured. The following are the chief 
 varieties. 
 
 " Trachyte" proper is generally of a pale grey colour ; but the tint may vary to a dark grey, and, 
 in consequence of the presence of iron, to a reddish shade. The texture is either compact or fine- 
 grained, and some varieties become highly porphyritic. 
 
 " Pearlstone " consists of a mass of rock, or base, in which are contained a number of globules, 
 varying in size from that of a coarse grain of sand to that of a hazel-nut, easily detachable from the 
 mass, and having a vitreous aspect and a pearly lustre, whence its name. The rock is of various 
 tints of grey, yellow, brown, and red. 
 
 " Phonolite," or " clinkstone," is a compact, greyish rock, weathering white externally. It 
 possesses the quality of splitting into thin plates or slabs, in such a degree that it has frequently 
 been used for roofing-slates. These slabs, when struck with a hammer, emit a clear metallic ring, 
 whence the name of the rock. Sometimes the structure is perfectly columnar, in which case the 
 columns split across into slabs. 
 
 " Andesite," so named from its occurrence in the Andes, is a trachytic rock of various degrees 
 of compactness, and a coarse conchoidal fracture. 
 
 " Obsidian," or volcanic glass, is closely allied to pearlstone, the diiference being due merely to 
 a more rapid cooling from the molten state. Its composition is very variable, depending upon 
 that of the rock from which it has been melted down. In colour, obsidian is generally black, and 
 opaque in mass, but appears grey and translucent at the edges. It is remarkable for its perfectly 
 conchoidal fracture and its sharp cutting edges. 
 
 " Pumice " is a vesicular or porous rock, produced by the solidification of the scum or froth of 
 a molten mass, and closely allied in composition to obsidian. In colour, it is of a pale yellowish-grey, 
 passing into grey, brown, and black. It is very brittle, and its fracture is uneven and conchoidal. 
 Owing to its porous character, pumice floats in water ; but its true specific gravity when pounded 
 is 2-3. 
 
 The doleritic or basic volcanic rocks are of a dark green or black colour, and are composed of 
 a triclinic felspar and augite, with magnetic or titaniferous iron and olivine. They contain a larger 
 proportion of the heavier bases than the trachytes. There are three principal varieties of these 
 rocks, known as dolerite, anamesite, and basalt : varieties that are due rather to differences of texture 
 than of composition. ' 
 
 " Dolerite " is composed of labradorite and augite, with some titaniferous or magnetic iron, and 
 often a little carbonate of iron and carbonate of lime. The labradorite forms white or light grey 
 tabular crystals, and the augite black columnar ones. Both can be distinguished by the naked eye. 
 The magnetic iron exists as small octahedral, scarcely visible grains, which may be removed by 
 the magnet when the rock is pounded. Olivine occurs as minute granules of a yellowish or 
 greenish tint, and constitutes the most characteristic accessory mineral in dolerite. 
 
 "Anamesite" is simply a fine-grained dolerite, in which the component minerals are so intimately 
 blended that they cannot readily be distinguished. It occupies an intermediate place between 
 dolerite and basalt. In colour it is dark green, or greenish or brownish black. 
 
14 
 
 MINING ENGINEEEING. 
 
 " Basalt " is by many writers included among the trap rocks; but in composition and texture 
 it is more allied to the volcanic class. It is a compact and hard rock, frequently columnar in 
 structure, and of a dark or altogether black colour. It is composed of labradorite, augite, and 
 titaniferous iron, usually with an admixture of small spherical crystals of olivine and of carbonate of 
 iron and lime. Besides the ordinary compact texture, basalt may assume porphyritic, amygdaloidal, 
 slaggy, and earthy textures. 
 
 In the South Staffordshire coal-field, dykes of doleritic rocks are intruded among the coal seams, 
 and in these cases the rock is white and of an earthy texture. Such dykes are locally known as 
 " white rock ; " in external appearance they closely resemble sandstones. 
 
 The volcanic rocks have also their fragmentary accompaniments. These are formed in precisely 
 the same manner as the fragmentary trap rocks. The chief varieties are : Scoria, rough cinder-like 
 fragments of lava ; Bombs, which are more or less spherical forms, frequently hollow, that owe 
 their shape to having been thrown into the air while in a liquid state ; Volcanic Agglomerate, an 
 unstratified mass of volcanic stones ; Volcanic Breccia, a stratified mass of angular volcanic stones ; 
 Volcanic Conglomerate, a stratified mass of rounded volcanic stones ; and Volcanic Tuff, named after 
 the variety of rock of which it is composed, as trachyte-tuff, doleritic-tuff, and basalt-tuff. 
 
 The following is a tabular view of the igneous rocks : 
 
 Granitic Eocks. 
 
 Granite, Syenite, Pegmatite, Protogine, Graphic Granite. 
 
 Trappban Eocks. 
 
 Fehpathic. 
 
 Felstone, Pitchstone, 
 Kersanton, Kersantite, ■ 
 
 Clinkstone, Minette, 
 Porphyrite. 
 
 Felstone-tuff and Porphyrite-tuff, with Brec- 
 cias and Conglomerates. 
 
 Hornblendie. 
 
 Diorite, Diallage-rock, Hyphersthene-rock, 
 Melaphyre, Diabase, Aphanite, Wacke. 
 
 Greenstone-tuff, with Breccia and Conglo- 
 merate. 
 
 Volcanic Eocks 
 
 Fehpathic, 
 
 Trachyte, Pearlstone, Audesite, Phonolite or 
 Clinkstone, Obsidian, Pumice. 
 Trachyte-tuffs and Breccias. 
 
 Augitic. 
 
 Dolerite, Anamesite, Basalt. 
 Doleritic-tuffs and Breccias. 
 
 We have already pointed out that the igneous rocks may be classed into two divisions — the 
 acid or siliceous rocks, and the basic rocks. The former contain a larger proportion of silica than 
 the latter, the difference in the proportions being generally 7 to 5. This difference is often of great 
 importance in determining the variety of a rock by chemical analysis, and is therefore worthy of 
 careful note. Durocher, in his ' Essay on Comparative Petrology,' gives a table, which shows at 
 a glance the limits and means of the proportions of the several substances that enter into tha 
 composition of the rocks previously described. This table, which will be found to be of practical use, 
 is given in Haughton's ' Manual of Greology.' 
 
 Mode of Occurrence of the Igneous Rocks. — The igneous rocks differ widely in their mode of 
 occurrence from the aqueous rocks, and this difference is often made the distinguishing feature of the 
 
PRACTICAL GEOLOGY, 15 
 
 class, by describing the latter as stratified and the former as unstratlfied. These two great classes 
 of rocks must, with respect to their mode of occurrence, be viewed as radically different, since the 
 Aqueous rocks have been deposited from above, while the igneous rocks have been erupted from below. 
 The eruptive character of the latter must be constantly borne in mind when considering their relative 
 position and form, both with respect to the other rocks and with respect to each other. Having 
 been upheaved at various periods by internal forces, they may occur in any situation and form 
 possible under such conditions, and in no others. Thus, having determined that a given mass of 
 rock is of igneous origin, we are enabled to predicate concerning it, in some respects with certainty, 
 and in others with a high degree of probability. 
 
 The several modes in which igneous rock may occur have been described as — eruptive, dis- 
 ruptive, intrusive, interbedded, and overlying, according to the effect produced on the aqueous strata, 
 and the consequent positions assumed. These differences in the mode of occurrence are shown on 
 Plate I. When an upheaval ot molten rock takes place beneath a mass of stratified rocks, it is 
 evident that the former may penetrate the latter in either of two ways. It may force its way directly 
 upwards through the strata by disrupting them, or it may force its way upward through some strata, 
 and then intrude itself along the lines of division between other strata. In either case, on reaching 
 the surface, it may spread itself out and form a bed that may subsequently be covered up by new 
 deposits. The nature of the outlet through which the rock escapes, the position of these outlets, 
 and the volume of rock ejected, may be such as to occasion the formation of huge amorphous masses, 
 the boundaries of which at the surface will be more or less indeterminate. Such eruptive masses are 
 shown at A, in Fig. 1. When an upheaval of igneous rock produces a disruption of the overlying 
 strata, the line of disruption may extend to a great distance, and it is clear that this line will be 
 that of least resistance. Frequently we may determine what the lines of least resistance were. 
 They may have been lines of fault or fracture, lines of valley, or of some particular formation. 
 The fissure being filled with the molten mass, a dyke is formed, extending vertically from the 
 fundamental rocks to the surface, and horizontally to a greater or less distance along the line of 
 least resistance. Such a dyke is shown at B, in Fig. 1. These dykes are very numerous, and in 
 some coal-fields constitute a serious obstacle to mining operations. They vary in thickness from 
 6 inches to 70 feet or more. They ascend vertically through the rocks they traverse, or at a 
 very high .angle, like walls, a remarkable feature in them being the singular evenness of their sides. 
 Usually the sides are as parallel as those of a wall of masonry, and much smoother on the face. In 
 most cases, the ends of the strata next the dyke are upturned, and sometimes othervdse distorted ; 
 but instances occur in which they have not been thrown out of position, and if the dyke is intruded 
 along the bottom of a trough, the strata may dip to the dyke on both sides, as shown in the figure. 
 In almost every case, those portions of the strata which are in contact with the dyke will be altered, 
 and the alterations will be such as would be produced by heat. Sandstones are hardened ; sometimes 
 in such a degree as to convert the rock into a quartzite. Shale is likewise hardened, and converted 
 into a kind of porcellanite, or flinty slate. Coal is greatly altered, being converted into soot close 
 to the dyke ; charred cinder, or " clinker," a little farther away ; and " blind coal," or a form of 
 anthracite, at a still greater distance. 
 
 When, as was very frequently the case, the line of least resistance was along the divisional 
 planes of stratification, the igneous rock was intruded along these planes, where they form a sheet 
 or bed, varying in thickness from less than a foot to several hundred feet. Such beds lie regularly 
 
IG MINING ENGINEERING. 
 
 and conformably between the strata, as if they formed an original part of the series. Frequently, 
 however, they do not lie wholly along the same line of bedding, but cut across a stratum at intervals, 
 and continue along the next divisional plane. The same changes in those portions of the strata that 
 are in contact with the intruded rock occur here as in the case of a dyke. Intrusive sheets are 
 shown at C, in Fig. 1. In order to ascertain with certainty whether an intercalated sheet of igneous 
 rock be intrusive, it is necessary to examine the aqueous rock above, which, if the former has been 
 intruded beneath it, will exhibit unmistakable marks of the action of heat. If no such marks exist, 
 the igneous mass must be regarded as interbedded. As coal-seams offer less resistance than the 
 more compact and refractory rocks, where the former exist it will be found that the intrusive rock 
 has been intruded along them. In such cases, besides the change produced in the coal, the intrusive 
 rock itself is altered in a manner that has been already described. 
 
 Frequently on reaching the surface, after disrupting the overlying strata, the igneous mass has 
 spread out as a sheet or bed. Subsequent depositions having taken place, the igneous rock, which 
 may extend over a large surface, appears as interbedded, as shown at D, in Fig. 2. The distinctive 
 indications of an interbedded sheet are, ihe unaltered character of the overlying beds, and the 
 absence of any derangement, of the latter; the slaggy character of the upper and lower surfaces of 
 the sheets, and the association of beds of trap-tuff. In some cases, these beds of igneous rock still 
 lie upon the surface, having either been ejected in recent times, or exposed by the removal of 
 subsequently-deposited sti-ata by denudation. Such beds, an instance of which is shown at E, in 
 Fig. 2, are distinguished as" overlying." 
 
 Besides the foregoing forms of occurrence, igneous rock may appear as veins traversing strata 
 in any direction, and even igneous rocks of an earlier date. These veins are usually connected with 
 a larger mass situate at no great distance. 
 
 The division of the igneous rocks into granitic, trappean, and volcanic series is, as we have 
 already pointed out, more in accordance with their relative positions among the sedimentary strata 
 than with any differences of a lithological character. Thus the granite was consolidated at a great 
 depth beneath the surface, and cooled slowly under great pressure. Hence granite is the most 
 solidly crystalline of all the igneous rocks, and is associated with the older strata. The volcanic 
 rocks, on the contrary, have consolidated at the surface, a circumstance that has associated them with 
 rocks of recent formation, and rendered their texture more or less open and scoriaceous. Between 
 these are the trappean rocks, which have consolidated beneath the surface, but at a less depth than 
 the granite. Hence these are more frequently associated with the secondary strata, and have a 
 texture intermediate between the granitic and the volcanic. From these facts it may be inferred that 
 granite will occur only as eruptive masses, trap as eruptive masses, dykes, intrusive sheets and 
 veins, and overlying beds that have been exposed by denudation ; and rocks of the volcanic series as 
 dykes and overlying beds. And this inference is generally true. 
 
 ' Gi-ranite dykes and veins are sometimes found traversing masses of older granite, in which cases 
 the more recent differs in texture from the older rock. Eruptive masses of trap usually consist of 
 diorite, felstone, or- quartziferous porphyry, and are associated with the Lower Silurian, Old Red Sand- 
 stone, and Carboniferous formations. They are generally compact in texture, but sometimes as in 
 Wales, amygdaloidal. Occasionally they are columnar in structure. Trap dykes traverse all forma- 
 tions. They usually consist of dolerite, melaphyre, or diabase, but sometimes of diorites, and, still 
 more rarely, of some member of the felspathic family. The texture of dykes becomes more coarsely 
 
PRACTICAL GEOLOGY. 17 
 
 crystalline to\yards the interior. In some cases they are minutely amygdaloidal, the kernels heing 
 arranged in lines parallel with the sides of the dyke. These lines of kernels are most marked along 
 the centre of the dyke, and they decrease in number and in the size of the kernels as they approach 
 the outside. In dykes of dolerite, the compactness towards the outside is such, that to a depth vary- 
 ing from that of a mere film to an inch, it passes into a -black glassy substance called tachylite, resem- 
 bling pitchstone in appearance, but distinguished from it by being quite basic in character, pitchstone 
 being highly siliceous. This glassy film is probably due to the rapid cooling of the mass where it 
 came in contact with the surrounding rocks. Generally dykes are traversed by two sets of joints, 
 one crossing the dyke from side to side, the other running parallel with the length. This is 
 especially the case with dolerite, in which the longitudinal series are more strongly marked. A 
 common feature in dykes of dolerite or basalt is the columnar structure. The columns are always at 
 right angles with the cooling surface, and therefore in dykes they will strike inwards from the sides 
 towards the centre. Sometimes the columns do not reach the centre, and when they do, they do not 
 always meet symmetrically. All the varieties of the crystalline trap rocks occur as intrusive sheets. 
 Usually they have an amorphous internal structure, that is, they are divided more or less irregularly 
 by joints. Sometimes, however, they are columnar, and in a few instances of compact felstones, of a 
 rudely fissile character. In texture they are frequently porphyritic, especially those of the felspathic 
 family, and occasionally they are amygdaloidal. As in dykes, the central portion is more coarsely 
 crystalline than the outside. When in contact with highly ferruginous or calcareous rocks, the sheet 
 is frequently veined with hematite, calc-spar, or serpentine, from the infiltration of the iron or lime. 
 And when, as we have previously mentioned, it has been intruded among coal seams, it is converted 
 into a soft white clay to a depth of several inches. Hence, if it be intruded along the parting of a 
 coal seam with a thickness of only a foot or so, it will be changed throughout. Interbedded and 
 overlying igneous rocks, having consolidated at the surface, differ in texture from intruded masses. 
 The latter increase in compactness from the centre outwards, while the former increase in compact- 
 ness from the oiitside towards the centre. The upper and lower surfaces of interbedded sheets are 
 slago"y, the interior being more or less amygdaloidal and crystalline. The vesicles in which the 
 kernels are contained are elongated in the direction of the flow; and this is especially noticeable along 
 the top of the bed where the velocity was greatest. All interbedded sheets possess a jointed structure. 
 The joints are, in some cases, very irregular ; but generally they are well marked in two or more sets 
 crossing one another, and extending perpendicularly to the upper and lower surfaces of the sheet. 
 When developed with great regularity, they give a prismatic structure to the rock, which may become 
 perfectly columnar, as in the dolerite of the Isle of Staffa. 
 
 When thick masses of igneous rocks are interbedded in any formation, and inclined with the 
 other members of that formation, its line of outcrop will constitute a range of rounded or conical 
 hills, often with lines of sharp escarpment, and when a great series of such rocks lie flat, or nearly so, 
 they produce plateaux, the edges of which are lines of precipice or terraced slopes. 
 
 The mode of occurrence of the fragmental igneous rocks has already been described. 
 
 The foregoing description of the igneous rocks are sufiScient to enable the student to identify 
 the principal varieties. Though as a coal-mining engineer he will have much less to do with this 
 class of rocks than with the aqueous, yet it is not only desirable but essential to his success, that he 
 make himself familiar with their characteristic aspects, their mineral and chemical composition, and 
 their modes of occurrence. The igneous rocks are, in the fullest sense of the word, the primitive 
 
 D 
 
18 MINING ENGINEEEING. 
 
 rocks, for from these, directly or indirectly, most of the others have been derived. It is therefore 
 impossible to fully understand the character and the origin of the latter without an intimate 
 acquaintance with the parent rocks. Moreover, as disruptive and intrusive masses, trap occurs with 
 great frequency among the seams of coal, producing those faults which interrupt the continuity of 
 a deposit, and constitute a formidable barrier to further progress. In these cases a knowledge of the 
 character and modes of occurrence of such rocks, as well as of the effect they produce in the 
 strata through which they force their way, is of the highest value to the engineer in enabling him 
 to determine the best means of dealing with the obstruction. To the mining engineer whose 
 labours are directed to the extraction of the metals other than iron, the igneous rocks constitute 
 the most important class, since it is with them that he will have chiefly to do. For these reasons, 
 we have devoted more space to this class of rocks than their importance seems, at first sight, to 
 justify. 
 
 The Aqueous Eocks. — The aqueous rocks are, as we have observed, derivative ; that is, they 
 have been, formed from the debris of the igneous rocks. The agencies that have operated in their 
 formation may have been chemical, mechanical, or organic, and they may be grouped under these 
 three heads. But it seems to conduce more to precision and clearness of arrangement to divide them 
 into three groups according to their chemical composition, and to subdivide these groups according to 
 the agencies that have operated in producing them. Such a grouping will divide the aqueous rocks 
 into Sandstones, Clays, and Limestones. The rocks of these three groups differ from each other, not 
 only in chemical composition but in the conditions under which they were formed. The sandstones 
 are coarse in texture, being composed of grains oi quartz that have been subjected to the action of 
 running water. It may therefore justly be inferred that these rocks have been deposited in water 
 in a state of more or less rapid motion ; and hence they indicate a coast line and shallow water. 
 The clays consist of particles in a state of extreme fineness, such as could only be deposited from 
 still- water. As a matter of fact, the fine particles of mud carried down by a river are borne far 
 out to sea, while the heavier grains of sand are deposited near the beach. Hence we infer that the 
 clays were deposited in deep water. The limestones consist of fine particles like the clays ; but this 
 fact is due to their being the result of chemical action. Limestone is held in solution in water 
 by the presence of carbonic acid in it, and the deposition from the solution may take place in shallow 
 as well as in deep water. Of course, like any other rock it may be worn down by tiie action of 
 mechanical causes, in which case the particles, from their extreme fineness, would be carried far out to 
 sea, and deposited in deep water. Thus we have, according to the conditions of their formation, 
 the sandstone group deposited in shallow water, the clay group deposited in deep water, and the 
 limestone group deposited either in deep or shallow water. 
 
 Sandstones. — Sandstone consists merely of grains of sand compacted together, either by simple 
 pressure long continued or by the presence of some other substance acting as a cement. The grains 
 consist chiefly of quartz, sometimes clear and colourless, sometimes dull white, but oftener yellow, 
 brown, or red. The red colours are due to the covering of each grain with a film of peroxide of 
 iron, which sometimes serves as a cement to bind the particles together. Frequently the iron exists 
 as a siHcate, in which cases the film will be green. In most sandstones the cement is more or less 
 sihceous. The particles are generally distinctly water-worn, and may be seen, even in those of the 
 finest texture by the aid of a lens, to be embedded in the cement. Chemical analysis shows the 
 sandstones to be derived from granite by the mechanical agency of water, which washes away the 
 
PEACTICAL GEOLOGY, 19 
 
 silicates, and leaves only the most Lighly oxidated portion of the granite, the quartz, to form the 
 basis of the new rock. 
 
 The sandstones may be ranged under three divisions : the simple, the compound, and the 
 conglomerates, or breccias. The simple sandstones are those which are composed of pure quartz ; 
 of these we have but few examples. The compound sandstones are composed of quai-tz with one or 
 more of the other minerals found in the primitive granite, as felspar, hornblende, mica, and clay. 
 When composed of quartz and felspar, the rock is termed a felspathic sandstone. The grains of 
 felspar, which sometimes occur abundantly, are distinguishable by their dull white, yellow, or flesh 
 colour, and their peculiar appearance. Mica is rarely altogether absent, and in many sandstones the 
 flakes and spangles occur so abundantly as to cause the surfaces of the rock to glitter, and the rock 
 itself to split into thin plates. These are called micaceous sandstones. Besides these varieties, there 
 are calcareous sandstones, in which the cement consists of carbonate of lime, and argillaceous 
 sandstones, which contain an admixture of clay. The latter appellation is, however, not very 
 appropriate, nor is it often used. When occurring in a very coarse form, compound sandstones are 
 called conglomerates. A conglomerate has been defined to be a sandstone in which there are large 
 particles of quartz, slate, limestone, or any other rock, cemented together by a more or less siliceous 
 cement. The fragments in conglomerate are most commonly quartz, quartz-rock, or some very 
 siliceous substance. This arises partly from the greater abundance of siliceous mineral matters, and 
 partly from the greater durability of quartzose substances and their mode of fracture. The size of 
 the fragments varies from that of a hazel-nut to that of a man's head. The degree of consolidation 
 also varies greatly. In those which have been consolidated by simple pressure, the pebbles may be 
 removed by a slight blow with a hammer, while in others in which a cement occurs the pebbles are 
 very firmly embedded. Conglomerates, though stratified rocks, often show but faint traces of 
 bedding, and it is only when seen on a large scale that their bedded character becomes apparent. 
 The essential idea of a conglomerate is that all the fragments should be rounded, a circumstance 
 which shows that they have been exposed to the action of waves on the sea shore, or of rapid tidal 
 currents in shallow water. When the imbedded fragments are not rounded, but are angular and 
 irregular, the rock is called a breccia. Conglomerate is sometimes called puddingstone, from a 
 fanciful resemblance to the fruit in a plum-pudding. 
 
 " G-rit " and " gritstone " are terms applied somewhat vaguely to sandstone to denote that the 
 particles are hard and angular, in other words "sharper," than in ordinary sandstone. This 
 angularity of the particles is, however, not always a characteristic, since in the sandstone rock known 
 as " millstone-grit " the particles consist of perfectly round grains, sometimes as large as peas, or 
 even larger. The term gritstone is perhaps most applicable to the harder sandstones which consist 
 almost entirely of grains of quartz, most firmly compacted together by the most purely siliceous 
 cement. 
 
 " Freestone " is a term in general use, and it is applied both to sandstones and to limestones. 
 It means a stone that works equally freely in every direction, or has no tendency to split in one 
 direction more than in another. 
 
 " Flagstone " means a stone that splits more readily in one direction than in another, that 
 direction being along the original line of deposition. These stones are usually sandstones, though 
 very argillaceous; but in some cases they are rather indurated clay in thin beds than sandstones. 
 
 Among the materials of a sandstone, a considerable proportion of alumina may occur, thu3 
 
 D 2 
 
20 MINING ENGINEEBING. 
 
 providing the constituents for the formation of clay. Hence it results that the passage from sand- 
 stones to shales and pure clay is an insensible one. The following terms are applied by miners 
 to some varieties of sandstones. 
 
 Calliqrd or galliard is a northern term for a hard, smooth, flinty grit. 
 
 Catsbrain is a calcareous sandstone in which the rock is traversed by little branching veins of 
 carbonate of lime. 
 
 Faikes is a Scotch term for a shaly or fissile sandstone. 
 
 Hazel is a northern term for a hard grit. 
 
 Peldon is a South Staffordshire term for a hard, smooth, flinty grit (the calliard of the north). 
 
 Post is a northern term for a bed of firm, fine-grained sandstone. 
 
 Rock is used generally to denote any hard sandstone. 
 
 Rotche or roche is generally used to denote a softer and more friable sandstone. 
 
 Rubble is rough angular gravel, either loose or compacted into stone. 
 
 Clays, or Schists. — The term " schist " is properly applicable only to indurated clay rocks 
 having a tendency to split up into irregular plates, and to this use it is often restricted. But some 
 writers are in the custom of employing the term to include all the varieties of clay rock, and it is in 
 this extended sense that it is employed here. Perfectly pure clay is a hydrated silicate of alumina, 
 and is known as " kaolin," or " porcelain clay." It is derived from the decomposition of felspar, 
 from which the silicates of potash, soda, and lime have been washed away. It occurs abundantly in 
 some granitic districts, where it is carried down by the streams and dt p )sited in hollows. Hence the 
 clays, like the sandstones, are derived from granite. As pure clay, however, they rarely occur. 
 Usually they contain a considerable proportion of potash and soda, with a variable quantity of 
 minute grains of quartz. Their composition is, indeed, exactly what we might have expected from a 
 consideration of their origin. If a granite rock be finely divided by the action of water, some of 
 its alkaline silicates will be washed away, but the greater part of the constituents will remain in 
 very nearly the same proportion as before. Chemical analysis shows this to have been the case. 
 Hence we must regard the clay group as formed of granite very finely divided, reduced in fact 
 to an impalpable powder, and deposited over the bottom of the sea in deep water. The relation of 
 the clay to the sandstones will now become apparent. Both have been derived from the granite, 
 and deposited from suspension in water. But the heavy particles of quartz were first deposited to 
 form sandstones, while the lighter particles of the other minerals in a finely comminuted state 
 were borne farther out to sea, and slowly deposited in deep water. The particles of quartz, however, 
 would be of various degrees of fineness, and the finest of these would be carried out and deposited 
 with those that were to form the clay, and between the sandstone and the clay it is obvious that 
 the gradation must be such as to render the passage from the one kind of rock to the other an 
 insensible one. 
 
 The clays may be grouped in two divisions ; the simple and the compound. The simple clays 
 are those which are composed of clay only, that is, the clay which is formed by a minute and fine 
 mechanical subdivision of the granite rocks. The compound clays are those which contain a 
 notable addition of some other mineral, of which mica, talc, chlorite, and hornblende are the most 
 important. These compoimd clays or schists are distinguished according to the mineral present, as 
 mica schist, talc or talcose schist, chlorite schist, and hornblende or hornblendic schist. To these com- 
 pounds we shall again refer under the head of metamorphic rocks. It is obvious that there can be no 
 
PEACTICAL GEOLOGY. 21 
 
 conglomerate or breccias among the clay rocks, since the fact of their being deposited in deep water 
 precludes the possibility of such formations. 
 
 " Argillaceous flagstone " is a term applied to an indurated sandy clay or clayey sandstone, 
 which splits into thick slabs or flags. 
 
 " Clay-slate " is a metamorphosed clay having a superinduced tendency to split into thin plates, 
 which may or may not coincide with the original lamination of the rock. 
 
 " Fire-clay " is a term applied to any clay capable of resisting great heat without slagging or 
 vitrifying. This property is due to the absence of any lime or alkalies to act as a flux. It is 
 probable that in good fire-clays the silica and alumina exist in just that definite proportion which, 
 on the application of heat, would combine into a true silicate of alumina. Such clays abound in the 
 coal measures. 
 
 " FuUer's-earth " is a term applied to a soft unctuous clay which, from its absorbent character, is 
 capable of removing grease from woollens ; whence the name. Any clay containing from 20 to 30 
 per cent, of alumina will act as fuUer's-earth. 
 
 " Loam " is a soft and friable mixture of clay and sand, having but little adherence, and being 
 permeable to water. Any mixture of clay and sand, which is neither distinctly sandy nor clayey, is 
 called loam. 
 
 " Marl " is properfy calcareous clay, which, when dry, breaks into small cubical fragments. 
 The proportions of lime in a marl may vary from 10 to 60 or 70 per cent. When the clay 
 predominates the mixture is distinguished as " clay-marl," and when the lime is the more abundant, 
 " marl-clay." 
 
 " Mud " consists of the finely comminuted materials of some form of argillaceous rock, inter- 
 mingled with vegetable and animal matter, borne down by streams and deposited over the bottoms 
 of seas, lakes, and pools. The term is applied to such accumulations only while they are in an 
 incoherent and unconsolidated state. 
 
 *' Mudstone " is a name given to a fine, argillaceous, and more or less sandy rock, void of shaly 
 lamination, and evidently consisting of consolidated mud. 
 
 " Pipe-clay " is a nearly pure clay, white and free from iron. 
 
 " Shale " is regularly laminated, and more or less indurated clay, which splits into thin layers 
 along the planes of deposition. This laminated, or, as it is termed, shaly structure distinguishes it from 
 beds of clay and marl. Clay is massive or plastic ; marl is friable ; shale occurs in leaf-like lamince. 
 
 " Silt " is a geological term for the miscellaneous matter deposited in lakes, estuaries, bays, and 
 other still waters. It may consist of mud, clay, and sand, or of distinct layers of these. 
 
 " Slate " is a term applied to argillaceous rocks, whose lamination, like that of roofing slate, is 
 not produced by lines of bedding, but is due to a metamorphism called cleavage, which often runs 
 at right angles to the planes of deposition. 
 
 As the shales alternate with the sandstones in the coal measures, this class of the clay rocks is 
 the most important that the coal-nainer has to deal with. Hence it is that, as in the case of the 
 sandstones, he has adopted terms to distinguish the several varieties. The following are the most 
 generally used : 
 
 Batt or bass is very fine shale containing a large proportion of carbonaceous matter, called by 
 the geologist carbonaceous or bituminous shale. 
 
 Bind is the colliers' term for ordinary shale. 
 
22 MINING ENGINEERING. 
 
 Blaes is tlie Scotcli term for ordinary shale, such, shale being usually bluish-grej. When lumpy 
 the term is lipey blaes. 
 
 Bluestone is the name applied in Caermarthenshire to common shale. 
 
 Clod is the same as " bind." 
 
 Clunch is the name for a tough, more or less indurated clay, often very sandy, lying beneath the 
 seam of coal. 
 
 Danks is the Scotch term for " batt." 
 
 Kelve, a south of Ireland term for " batt." 
 
 Metal is the same as "bind." 
 
 Pindy, a south of Ireland term, synonymous with " kelve." 
 
 Plate is the same as " bind." 
 
 Pounson is a dense soft clay underlying the seams of coal. 
 
 Shiver is the same as " bind." 
 
 Slig or sliggeen is a term applied in the south of Ireland indiscriminately to shale and slate. 
 
 Warrant is the same as " pounson." 
 
 Limestones. — Limestone is a term for rocks the basis of which is carbonate of lime. As the 
 sandstones and the clays clearly owe their origin to the granite rocks, so it would appear that the 
 limestones have been mainly derived from the later trap rocks. We have already shown that lime 
 and magnesia are much more abundant in the traps than in the granites. Hence, as these became 
 worn down by the action of water and decomposed by chemical agencies, the quantity of lime held in 
 solution in the water would rapidly increase. This would ultimately be deposited as carbonate of 
 limCj carbonic acid being derived from the atmosphere. There can be no doubt that, as a rock, the 
 limestone is subsequent in point of time to the sandstones and the clay. Different varieties occur 
 in the different geological formations ; and hence, though it is difficult, and in many cases impossible, 
 to distinguish between the sandstones or the clays of different epochs from mere lithological charac- 
 ters, an experienced geologist can, from such characters, readily determine the true position in the 
 series of any given specimen of limestone. 
 
 The limestones may, like the sandstones, be divided into the simple, the compound, and the 
 conglomerates, or breccias. The simple limestones are those which are composed either of pure, or 
 nearly pure, carbonate of lime, or of carbonate of lime and magnesia. These may be subdivided, 
 according to their texture, into crystalline, compact, oolitic, and magnesian limestones, though the 
 latter term relates rather to mineral composition than to texture. 
 
 Crystalline Hmestone may vary from fine to coarse grained ; from a fine pure-white rock, resem- 
 bling loaf-sugar in texture, to a rough granular one of various colours. The former variety is known 
 as saccliaroid limestone or statuary marble. The structure of limestones may be either original, in 
 which case it often happens that each crystal is a fragment of a fossil, or superinduced by meta- 
 morphic action on a limestone previously compact. 
 
 Compact limestone is hard, smooth, and fine grained, generally bluish-grey, but sometimes 
 yellow, white, black, red, or mottled. Generally its fracture is conchoidal ; but it may be sharp and 
 splintery, or dull earthy. This variety will frequently take a polish, and it has been used as an 
 ornamental marble. 
 
 Oolitic limestone, or oolite, is so called because its structure resembles that of the roe of a fish, 
 the word oolite meaning roe-stone. In this structure the mineral has assumed the form of little 
 spheroidal concretions, composed of several concentric coats, sometimes enclosing a minute grain of 
 
PEACTICAL GEOLOGY. 23 
 
 some other mineral substance, and sometimes hollow. Oolite is generally of a dull yellow colour, 
 but not unfrequently it is grey. The peculiar structure of this rock gives it the character of a free- 
 stone, that is, one that may be cut with equal freedom in any direction. Hence its value for building 
 purposes. Bath and Portland stone are well-known examples of oolitic limestone. A variety of 
 oolite in which the concretions are as large as peas is called pisolite, or peastone. 
 
 Magnesian limestone or dolomite consists of carbonate of Kme and carbonate of magnesia. Many 
 limestones contain a small percentage of magnesia ; but the term magnesian is not applicable unless 
 the rock contain 20 per cent, and upwards. The occurrence of magnesia in small quantity frequently 
 gives a sandy appearance and gritty feel to an otherwise smooth and compact limestone. The term 
 "dolomite" is used to distinguish the crystalline from the earthy varieties. True dolomite contains 
 nearly equal atoms of carbonate of lime and magnesia ; and though the crystals are sometimes very 
 minute, the crystallization and the pearly lustre are generally very distinct. Its colour is ususally 
 pale yellow, but blue, grey, white, and even black varieties not unfrequently occur. Dolomite is 
 often full of cavities, varying in size from that of a walnut up to that of a man's head. Often it is 
 completely disintegrated, and looks like mere sand ; but when examined with the lens, the apparent 
 grains of sand arc found to be little detached crystals. Magnesian limestone appears to be, in many 
 cases, a product of the gradual metamorphosis of ordinary limestone, carbonate of magnesia replacing 
 carbonate of lime. 
 
 Compound limestones are those which contain a notable admixture of some substance other than 
 carbonate of lime and magnesia; and they are named after the minerals with which they are 
 associated. Thus, as in the case of the schists, we may have micaceous, talcose, chloritic, and horn- 
 blendic limestones. Frequently clay has been deposited with the calcareous matter, producing a 
 variety to which the name of " argillaceous limestone " has been given. The presence of clay may 
 be detected by the peculiar odour emitted when the rock is breathed upon. Some of the argillaceous 
 compounds make a beautiful marble Sometimes the silica which was diffused through the calcareous 
 mass, instead of separating as nodules or layers, has remained so diffused ; in such cases the rock is 
 distinguished as " siliceous limestone." Sand may also be present in considerable proportions, pro- 
 ducing a compound known as " arenaceous limestone." This variety is commonly known as " corn- 
 stone." In like manner, carbonaceous matter, derived from decaying vegetables, or decomposing 
 animals, may produce the black limestones, known as "carbonaceous" or "bituminous limestone." 
 Sometimes the remarkable mineral serpentine may be present as veins and nests ; in this case the 
 rock, which is the verde antique of the ancients, is called serpentine limestone. Many limestones are 
 named from their containing some peculiar variety of fossil, as nummulite, clymenia, orenoidal lime- 
 stone, and shell limestone or muschelhalk. 
 
 Beyond the essential difference that limestone conglomerates and breccias must be composed of 
 a limestone paste, enclosing some limestones, pebbles, or fragments, this division of the limestones is 
 precisely similar to the corresponding division of the sandstones. Grenerally but few limestone 
 pebbles are found in crngloinerates containing sandstone pebbles. This is what might have been 
 expected, since in the grinding process which takes place among the pebbles on a sea-beach, where 
 conglomerate is formed, the harder destroy the softer. Frequently the fragments consist of trap or 
 trap-tuff, and slate. 
 
 " Chalk " is a simple limestone, white and fine grained, sometimes quite earthy and pulverulent, 
 sometimes harder and more compact. This variety is well known. 
 
 *' Fetid limestone," or stinkstone, is a name given to those limestone which emit, when struck or 
 
24 MINING ENGINEEEING. 
 
 rubbed, a fetid odour, like that of sulphuretted hydrogen. The odour from some of the limestone 
 quarries in the carboniferous limestone of Ireland may be perceived at the distance of a hundred 
 yards, and is sufficient to produce nausea in the men at work. 
 
 " Fresh-water " or " lacustrine limestones " have a peculiar aspect, from which their origin may 
 frequently be determined by mere inspection. Usually they are of a very smooth texture, and 
 possess only a slightly conchoidal, and often an earthy, fracture. Their colour is dull white or pale 
 grey. " Shell-marl " is a soft, white, and earthy form of fresh-water limestone, formed of an aggre- 
 gate of shells and a variable quantity of clay. 
 
 " Grypsum " is a sulphate of lime, and often occurs in regular beds. Sometimes, however, it 
 occurs in irregular concretionary masses, or as veins and strings in other rocks. Grypsum has already 
 been described. 
 
 " Rottenstone " is a siliceous and aluminous compound, resulting from the decomposition of 
 impure limestones by the action of the atmosphere. In many cases, where a ferruginous limestone 
 decomposes, the calcareous parts are dissolved and removed, leaving a fine, pulverulent, porous mass 
 of ochre. 
 
 " Stalactite " and " stalagmite " are terms applied, the former to those icicle-like incrustations of 
 lime which form on the roof of caverns and fissures, and the latter to the same incrustations that 
 form on the floor. They are produced by the dropping of water holding these rock materials 
 in solution. 
 
 In the foregoing subdivision of the aqueous rocks into simple and compound, the latter have 
 been named according to the mineral with which they are associated. But it must be borne in mind 
 that in all these cases the mineral exists interstratified by mechanical action. Thus a compound 
 clay consists of a layer of clay, a layer of the mineral with which it is mixed, a layer of clay again, 
 and so on. So also a micaceous sandstone is composed for the most part of quartz divided into sheets 
 or leaves by the interposition of plates of mica. 
 
 The Metamorphic Eocks. — The metamorphic rocks are sedimentary rocks that have under- 
 gone, at a great depth beneath the surface, a process of change called metamorphism, by which their 
 constituent elements have been rearranged, and generally a crystalline texture produced. In some 
 of these rocks the original mineral texture is still recognisable, while in others all trace of it is effaced, 
 and a new texture and mineralogical composition has been developed. The agencies that have pro- 
 duced this change are mainly heat and pressure and chemical action ; but it is probable that other 
 agencies have operated of which we know but little. The metamorphic are the lowest of the aqueous 
 rocks, and are consequently associated with the granite and the primary formations. Many chano-es 
 have, however, been effected in more recent times ; and hence rocks of a metamorphic character may 
 be met with in any of the later formations. Each of the three groups into which the aqueous rocks 
 have been divided has its metamorphic varieties ; but the most important occur among the sand- 
 stones and the schists of which the older rocl^s consist. 
 
 Altered Sandstones. — The most important of the altered sandstones is gneiss. This rock consists 
 of the same mineral ingredients as granite, namely, quartz, felspar, and mica. It differs from 
 granite chiefly in this, that while the crystals of quartz and felspar are distinct and entire in the 
 latter, in gneiss they are broken, indistinct, and confusedly aggregated. Moreover, gneiss never 
 sends out dykes and veins into the contiguous strata, like granite, nor does it ever assume those struc- 
 tures which, being the result of cooling, are possessed by the igneous rocks. It is hard and crystalHne, 
 
PKACTICAL GEOLOGY. 2 a 
 
 and frequently exhibits curved and flexured lines of stratification. These lines of stratification, or 
 the regular arrangement of its component crystalline particles in a certain parallelism, impart some- 
 what of a schistose structure, and in some cases they afibrd the only means of distinguishing the rock 
 from granite, in hard specimens. As might have been expected, the gradations of composition and 
 texture towards granite on the one hand, and towards mica schist on the other, are insensible. It 
 should be remarked that the term "gneiss" is often very vaguely applied to signify any hard 
 quartzose semicrystalline schistose rock for which no other appellation could easily be found. 
 
 " Quartz rock," or " quartzite," is a sandstone that has been altered and hardened by heat. It is 
 compact, fine grained, but distinctly granular, often so divided by joints as to split in all directions 
 into small, angular, but more or less cuboidal fragments. When examined with a lens, it is seen 
 to be composed of rounded grains imbedded in a purely siliceous cement. In colour it is generally of 
 some shade of yellow or white. Occasionally it occurs red, and more rarely green. Quartzite is 
 frequently confounded with vein quartz, from which, however, it may be distinguished by its 
 granular structure. 
 
 " Greywacke " is a name given to certain forms of altered sandstones, consisting of a compact 
 aggregate of grains of quartz, felspar, and mica, cemented by a siliceous, argillaceous, or felspathic 
 base. The compact character of this base, and the way in which the grains often appear to pas^ into 
 it, constitute a distinguishing feature in this rock. In colour it is generally of some shade of giey ; 
 but it may be brown, red, or blue. 
 
 Altered Clays. — The compound schists, which have already been described, are metamorphic. 
 Mica schist occupies, however, so important a position that it deserves special mention under this 
 head. It is composed of alternate layers of mica and quartz, the former consisting of small flakes 
 firmly compacted together. The structure is often minutely corrugated or crumpled. Usually the 
 separation of the layers coincides with the original bedding, but in some cases it may be independent 
 of the bedding. Mica schist passes by insensible gradations into micaceous sandstones. 
 
 " Clay-slate " and " flinty-slate," or " Lydian stone," are also metamorphic rocks, the peculiar 
 cleavage of the former being a superinduced one, and the characteristic flinty feature of the latter 
 being the result of contact with a mass of fused igneous rock. 
 
 Altered Limestones. — The crystalline structure of some limestones is due generally to a meta- 
 morphic cause. That this cause was heat acting in conjunction with pressure has been proved by tbe 
 experiments of Sir James Hall, who by heating chalk under such a pressure as would prevent the 
 escape of the carbonic-acid gas, succeeded in converting it into a hard crystalline marble. The chalk 
 of the north of Ireland is thus changed in many places by the intrusion of trap rocks. Among the 
 altered limestones must be classed saccharoid marble and dolomite, the latter being in most cases, if 
 not in all, the result of carbonate of magnesia replacing carbonate of lime. Serpentine has also a 
 metamorphic character. 
 
 In the foregoing description of rocks, their mineral composition, their structure and texture, 
 their colour, and all other distinguishing features they may possess, have been fully and clearly 
 pointed out for the purpose of enabling the student to recognise any specimen that he may meet with. 
 The importance of this power of distinguishing rocks will be evident when it is borne in mind that 
 such peculiarities of composition, structure, and texture, or the presence of a pebble, fragment, or 
 peculiar mineral, often furnish the only means of identifying strata very widely separated. 
 
 Formation of Eock-Beds. — The aqueous rocks have been formed, as already stated, by the 
 
 E 
 
2tJ MINING ENGINEEEING. 
 
 deposition of mineral matters from suspension or solution in water. This deposition lia,s not been a 
 continuous act, but a succession of acts, between which intervals of varying length have intervened. 
 The non-continuous character of the act of deposition is only what we might have expected from the 
 nature of things. It is only after heavy rains that streams become turbid with suspended matter, 
 and though large rivers bear down to the sea a considerable quantity of matter in the most tranquil 
 seasons, the quantity varies greatly at different periods. Also the velocity of a river varies with the 
 volume of water to be discharged, and hence the turbid waters of a swollen river will be carried 
 farther out to sea than those of a season marked by a more sluggish current. Other causes of 
 turbulence, too, have operated to render the deposition oi sediment fitful and irregular. The con- 
 sequence to the formation of rock-beds of the want of continuity in the act of deposition is that all 
 I'ocks so formed are divided into thin layers or lamince. Each of these layers marks a separate act 
 jf deposition, the materials thrown down on each occasion having in some degree consolidated 
 before the next deposition began. It is not, however, necessary to assume a total suspension of the 
 act of deposition to produce these layers. A raarked retardation of the act for some time, during 
 which time the particles of the deposit would be finer as well as fewer, would still have this effect. 
 But two layers separated by a period of retardation will coalesce more completely, and, therefore, 
 adhere more strongly than two other layers separated by a period of total suspension. Hence it is 
 that sedimentary rocks cleave along the planes of lamination, and more easily along some of these 
 planes than along others. The length of the interval that elapsed between two successive deposits 
 will also influence the degree of cohesion between the layers, that degree being less as the interval 
 was longer. The absolute length of these intervals we have no means of ascertaining. These facts 
 in the deposition of rocks satisfactorily account for the varying thickness of the laminae of which 
 they are made up, and the comparative want of coherence between the component laminae of the 
 shales, which were deposited in deep water, far from land. 
 
 But besides the lamination of rocks, there is their stratification, which may, however, be 
 described as the same thing upon a larger scale. We have shown that a rock-bed is made up of 
 thin laminse laid one upon another by successive acts of deposition, which acts were separated from 
 each other by varying intervals of time. But in no case was the interval a very long one. Long 
 intervals, however, marked by a total suspension of the act of deposition, did sometimes occur. But 
 these caused a complete separation between the last layer deposited and the next subsequent one, and 
 tlius a new bed was begun. These beds, which may vary in thickness from an inch to many feet, are 
 designated as strata, and the divisional planes between strata are distinguished as planes of stratification. 
 \qv\ frequently the physical changes that interrupted the deposit of sediment altered the direction 
 and force of the c"urrents, and, consequently, the matter in suspension having been obtained from 
 other localities, the new bed was formed of quite different materials. Hence we have a bed of sand- 
 stone, for example, resting upon a bed of clay, or a bed of limestone upon a bed of sandstone. As 
 in the case of the laminae, we have no means of determining the length of the interval that elapsed 
 between the deposition of adjacent beds. It seems, however, a just inference to suppose that a longer 
 interval intervened between the deposition of beds composed of different materials than between those 
 of similar composition, since a long period of time must be assumed to produce the physical changes 
 in the earth's surface by which the currents were altered. And when the change is from sandstone 
 or clay to limestone, it becomes necessary to assume a still longer interval, as it was deposited 
 in v/ater in which all currents had ceased, a circumstance that implies great changes ; and if, as 
 
PEACTICAL GEOLOGY. 27 
 
 appears necessary in the case of all marine limestone, we assign an organic origin to the rock, 
 we are compelled to allow a period sufficiently long for the production of the animals from whose 
 secretions it is derived. Sometimes we have evidence that the interval was a long one, in the fact 
 that two beds which are contiguous in one place, in another place are separated by other distinct 
 beds. 
 
 The existence of such interstratified beds, leads to the consideration of the extent and termina*. 
 tion of beds. The nature of the agencies by which rock-beds have been formed would lead us to 
 suppose that they would vary as greatly in extent as in thickness, and such is found to be the case. 
 Some beds cover only a small area ; others extend o\er a wider surface ; while others again are 
 continuous over vast tracts of country. "What is true of a single bed is also true of a group of beds, 
 and hence we find " formations" abundantly developed in some localities, and altogether absent in 
 others. As might have been expected from the nature of the agencies brought into operation in the 
 formation of rock-beds, there exists an intimate relation between their extent and their lithological 
 character. The finer particles of suspended matter were more widely and equally distributed than 
 those of greater specific gravity. And hence we find that ■ beds of clay are of greater extent and 
 more equable in thickness than beds of sandstone, and beds of sandstone than beds of conglomerate. 
 With respect to extent and regularity, the sedimentary rocks may be arranged in the following 
 order : — Limestone, clay, sandstone, conglomerate. The way in which a rock-bed terminates is by 
 thinning out in all directions ; in some cases the thinning out is gradual ; in others, it takes place 
 more abruptly. Thus the form of a bed is that of a cake pared ofi" at the edges. This is the natural 
 form, and it is due to the mode of its formation. But all existing beds do not terminate on all sides 
 in this way. Sometimes one side has been upheaved by subterranean forces, and the action of denu- 
 dation has subsequently removed the thinner portions. In such cases the bed terminates abruptly 
 at the surface. Or denudation without upheaval may produce the same effect on beds that have 
 been deposited in an inclined position. When a bed thins off towards its termination its place is 
 taken by the next adjacent bed, which, in like manner, thins off into it. This adjacent bed, may, 
 and probably will, be of a totally different lithological character. Jukes has employed the diagram 
 given in Plate I., Fig. 3, to illustrate this important matter of the termination of beds. The white 
 beds are supposed to be limestones, which thin out into the adjacent beds of shale, shown in black. 
 These beds of shale, of course, thin out into the limestone in the same way. Thus at the point where 
 the thinning out of the limestones begins, the extremities of the shale-beds will appear, first as a 
 mere parting, perhaps only half an inch in thickness, and then gradually thickening out to the full 
 depth of the bed. In like manner the limestones will dwindle down to a mere parting in the shale. 
 The latter thin out, on the opposite side, into the next adjacent beds, supposed in this case to be sand- 
 stone, and shown in the diagram by the dotted portion. The extent and termination of beds are well 
 ascertained in coal mining, the operations of which consist in following the beds laterally. 
 
 IifCLlisrATiON OF Eock-Beds. — The surface upon which a rock-bed was deposited was not always 
 horizontal. Whenever a deposition has taken place upon an inclined surface the resultant bed is, 
 of course, inclined to the horizon at the same angle as the surface upon which it was deposited. 
 Moreover, as a bed was deposited over a very extensive area, the variations of surface may have 
 been numerous, and hence, in different places, it may be inclined at different angles, and in different 
 directions. But even where beds were originally deposited in the horizontal position, subsequent 
 volcanic convulsions, accompanied with eruption of igneous rock, have frequently upheaved them 
 
 E 2 
 
28 
 
 MINING ENGINEERING. 
 
 into an inclined position. Hence it arises that strata are, in most cases, more or less inclined. 
 This inclination is called the " Dip " when viewed in the direction of the fall, and the " Eise " 
 when viewed in the contrary direction. The " dip " is measured by the angle which it makes with 
 the plane of the horizon. Thus a bed is said to dip at an angle of 14° when it makes that angle 
 with a horizontal plane. It is seldom, however, that miners reckon the dip in degrees. With them 
 it is customary to estimate it by comparing the horizontal distance with the fall, A dip of 14° 
 would in this way be expressed as a dip of one in four, that is, in a distance of four, say, feet, measured 
 along a horizontal line, the " fall," or deviation from that line, is one foot. In the same way an 
 angle of 26° would be expressed as a dip of one in two. The direction of the dip is compared with 
 the meridian. Thus a bed is said to dip n., n.e., n.n.e., &c., at an angle of 18^, or one in three. 
 
 When an inclined stratum comes to the surface, its edge is called the " outcrop," or " basset," 
 Such a stratum is said to crop out to the surface, and the edge exposed is called its basset edge. 
 Among miners these and other terms are used, such as " coming up to grass," " coming out to the 
 day." 
 
 The line at right angles to the dip, that is, the line of outcrop along a level surface, is called 
 the " strike." Like the direction of the dip, it is described by its line of compass bearing. As the 
 strike is at right angles to the dip, when the direction of the latter is known, that of the former will 
 be known also. Thus if a bed dips north or south, its strike will be east and west. But when the 
 direction of the strike only is known, that of the dip does not necessarily follow, since it may incline 
 to either side of the strike. Coal miners generally speak of the strike as the " level bearing," or 
 " water-level " of a bed, because a drift or gallery driven through a bed at right angles to the dip 
 must necessarily be on a true level. 
 
 Fig. 4, Plate II., shows a section through a group of highly inclined beds cropping up to the 
 surface. The section is taken in the direction of the dip, and, consequently, at right angles to 
 the strike. The beds, it will be seen, do not dip at the same angle on both sides of the fault. If we 
 suppose the direction of the dip to be due east, that of the strike will be due north and south, in 
 other words, the basset edges of these tilted beds run north and south. 
 
 It is seldom that the dip and the strike run in straight lines across the country throughout a 
 great distance. On the contrary, both the degree and the direction of the dip are marked by 
 exti'eme irregularity, the result of deposition upon an irregular surface, and the action of local 
 upheaving forces. Hence it follows that the strike, or line of outcrop, may vary continually in 
 direction, sometimes traversing the coimtry in a curved line, or turning short back and continuing 
 in a contrary direction, sometimes running in an iriegular line, frequently breaking off in unexpected 
 directions, and necessitating very careful observation to follow its course accurately. Often the beds 
 dip in a certain direction for some distance and then rise in the contrary direction, forming a trough- 
 like depression, or they may rise, and some of them crop out to the surface, while those beneath are 
 bent over and continued downwards, forming a saddle-like elevation. In such cases, of course, the beds 
 that crop out on one side reappear on the other. Sometimes the beds dip in all directions towards a 
 central point, forming a basin-like depression, or again, though not so frequently, they may rise in like 
 manner to form a conical elevation, Tliese contortions occur on every scale of ma"-nitude, from little 
 crumplings apparent in a ditch to those displacements the radii of whose curves are measured by 
 miles When the rock-beds consist of hard compact materials, such, for example, as crystalline lime- 
 stone, the curves of upheaval or depression are usually regular, having frequently the appearance 
 
PEACTICAL GEOLOGY. 29 
 
 of arches of masonry. But when the composition and texture varies, the beds are crumpled and 
 otherwise distorted, in consequence of the varying nature of the lines of least resistance. An 
 example of this is shown in Fig. 5, Plate II. "When some of the beds consist of comparatively 
 soft material, as shale and coal among sandstones, effects are produced of an important character to 
 the miner. In some parts where the pressure was greatest the softer bed has been squeezed out 
 into other parts where the pressure was less, until equilibrium was restored by the latter parts 
 becoming extended. Hence the softer bed may be reduced in thickness in some places to an inch or 
 less, or it may be pressed out altogether, the harder beds above and below it then coming into contact 
 with each other. But in all such cases, all the material of the softer bed will be found farther on 
 in an increased thickness of that bed. These accumulations are called by miners " pockets," and the 
 squeezing out of the bed is described as the " nip." 
 
 When saddle-like elevations and trough-like depressions assume large proportions, they are 
 spoken of as anticlinal and synclinal curves. Such configurations are shown in Fig. 8, Plate II., 
 in which the beds are thrown into anticlinal curves at A, and into synclinal curves at B. The beds 
 6, 6, 7, 8 at A crop out to the surface on one side of the elevation a-nd reappear on the other side, 
 while the beds 1, 2, 3, and 4 are bent over in the form of an arch. At B, the beds numbered from 
 9 to 13 rest upon the former in the form of a trough. The imaginary line about which the beds 
 may be supposed to be bent is called the axis of the anticlinal or the synclinal. This axis may be 
 either horizontal or inclined. If it be horizontal, sections taken in any part will show the same beds. 
 ]3ut if it be inclined, different sections will cut different beds. An excellent example of this, due 
 to Mr. Jukes, of the Greological Survey, is given in Figs. 6 and 7, Plate II. Fig. 7 is a plan of 
 undulating beds, the axes of the anticlinal and synclinal curves being inclined, in this case, dipping 
 to the north, as shown by the arrows. It is obvious that, unless the surface of the ground slope with 
 the axis, other beds must come in, arching over each other in the case of the anticlinal, resting upon 
 each other in the case of the synclinal. Thus bed No. 4 will sink, or " nose in," as it is termed, under 
 the new bed No. 5, which, in its turn, will " nose in " under No. 6, and so on. In like manner, in 
 the synclinal bed. No. 14 will "^nose out" over No. 13, No. 15 over No. 14, and so on. Hence, if 
 we take a section along the line D in the plan, such a section will appear as in Fig. 8, in which 
 bed No. 4 forms the crest of the anticlinal, and bed No. 13 is the highest in the synclinal. But if 
 another section be taken along the line GrH, this section will appear as in Fig. 6, in which bed 
 No. 7 forms the crest of the anticlinal, and bed No_ 16 is the highest in the synclinal. It is of the 
 utmost importance to observe carefully the inclination of the axes of the curves, especially to the 
 mining engineer, who otherwise may be led to incur fruitlessly enormous expense. Jukes mentions 
 a case that came under his notice in South Wales where a sum of 30,000Z. was wasted in an abortive 
 sinking for coal, the seam having cropped out across the axis of the synclinal a mile or more before 
 reaching the spot where the shaft was sunk for it. A similar instance came under the author's notice 
 in North Wales. 
 
 It has already been pointed out that the flanks of these curves may be more or less flexured 
 according to the nature of the beds that have been subjected to the contorting forces. In some 
 instances these flexures are carried so far as to produce actual inversion of the beds, a circumstance 
 that is not unfrequent in the Belgian coal-fields. Such flexures may bring the same seam twice into 
 a vertical shaft, and in such cases careful observation is requisite to avoid erroneous conclusions. 
 
 Alteknation op Rock-Beds. — Sandstones, clays, and limestones occur either as separate 
 
30 MINING ENGINEERING, 
 
 groups of beds, sometimes of great thickness, or interstratified one witli another. The latter is the 
 more common mode of occurrence. No general rule can be laid down for the association of the 
 different kinds of beds with one another ; but some degree of regularity is observable in the alterna- 
 tion of rocks of different textures. Thus beds of very fine and very coarse materials are rarely found 
 resting upon each other. We should not expect to find shales, for example, resting upon con- 
 glomerate, but rather sandstones. So coarse sandstone is covered by a finer sandstone before the 
 shale appears upon it. Beds of limestone are frequently separated from each other by beds of 
 soft clay, or shale, and in such cases the latter material is commonly of a black or brown colour, and 
 often very calcareous. Sometimes limestone alternates with sandstone, the sandstone in these cases 
 being usually calcareous. But clay-beds more frequently alternate with both. 
 
 FoRMATiON^ OF Rock-Blocks. — Besides the planes of deposition which separate one bed from 
 another, there exist other lines of division running at right angles to these, and forming generally 
 two sets, each of which runs at right angles to the other. These lines of division are called 
 "joints." Sometimes each bed has its own joints, these apparently having been produced before 
 the deposition of the next superincumbent bed. But in most cases the joints run through whole 
 groups of beds. Sometimes, however, in passing from one bed to another, the line is slightly 
 broken, a circumstance that may lead an inattentive observer to believe that the joints are distinct 
 in each. A joint will pass through a pebble, dividing it as cleanly as if cut by a knife. In strati- 
 tied rock, we have thus three planes of division : one horizontal, or parallel with the lamination, and 
 two others perpendicular to the former, and at right angles to each other. Hence the bed will be 
 divided into quadrangular blocks of various dimensions, and more or less imiformity of size according 
 to the greater or less regularity of the joints. In the unstratified rocks the three planes of division 
 are also frequently seen, another set of joints taking the place of the planes of stratification in the 
 stratified rocks. Were it not so, it would be almost impossible to quarry such rocks. Frequently, 
 however, the joints in unstratified rock are such as to produce prismatic instead of cuboidal blocks ; 
 and in such cases the joints traverse the rock with remarkable regularity. 
 
 Master- Joints. — When a set of joints run regularly parallel to each other throughout a consider- 
 able distance, they are called " master-joints " to distinguish them from the lesser joints which may 
 extend for only a short distance. Sometimes such joints have wide intervals between them, and in 
 these cases the resulting blocks are large. Or one set may be at greater intervals apart than the 
 other, in which case the blocks may be of great length. The set of joints that run in the direction of 
 the dip of the bed are distinguished as " dip-joints," and the set at right angles to those are called 
 " strike-joints." The closeness of a joint is generally in proportion to the fineness of the texture of 
 the rock through which it passes. Thus joints are more open in conglomerate than in coarse sand- 
 stones, in sandstone than in shale. In limestones, however, both open and close joints are found, 
 some having been widened by the infiltration of acidulous water. Coal, from its peculiar nature, 
 shows the most perfect system of jointing. Fig. 10, Plate II., from a sketch by Du Noyer, shows 
 the two sets of joints traversing the planes of stratification. And Fig. 11, Plate III., shows a plan, 
 constructed by F. J. Foot, of the Geological Survey, of such joints as they appeared on the surface of 
 a horizontal bed of limestone several feet in thickness and 12 or 13 yards across, in County Clare, 
 Ireland. Many of these joint-planes may be traced for several hundred yards. 
 
 The probable cause of rock-joints is contraction during consolidation. Clay, as is well known 
 cracks while drying ; and molten materials shrink and crack on returning to the solid state. Joints 
 
PEACTICAL GEOLOGY. 31 
 
 of precisely the same character as those occurring in nature may, indeed, be produced artificially. 
 Some years ago an attempt was made in South Staffordshire to utilize blast-furnace slag by casting it 
 in moulds to form blocks of building material. But in consequence of the joints developed in them, 
 these blocks soon crumbled into small cuboidal fragments. 
 
 To the mining engineer and the quarry-master the subject of joints in rock is of the highest 
 importance. 
 
 Slichensides. — The term slickenside is applied in mining to the smooth, striated surface of joints 
 on the opposite walls ot a fissure, apparently produced by convulsive friction, and subsequently coated 
 over with a siliceous or calcareous film or glaze by the passage of water or heated vapours. Slicken- 
 sides occur more abundantly among igneous rocks, and in districts that have been much subjected to 
 disturbing forces. 
 
 Cleavage and Foliation. — Cleavage is the tendency in rocks to split into thin plates in a 
 certain direction. This tendency is especially remarkable in clay-slate, but it exists in other rocks. 
 It is most perfect in the fine-grained kinds, which it divides very regularly into extremely thin plates 
 or leaves. When the texture of the rock is coarse, the cleavage planes become faint, wider apart, 
 and more irregular. These planes, when occurring in conglomerate, pass round the pebbles, leaving 
 them sticking out from the surface, and do not pass through them as joint-planes do. 
 
 The direction of the cleavage planes is wholly independent of those of lamination, which it may, 
 therefore, cross at any angle. In most cases the lamination is obliterated by the cleavage, the laminte 
 having been welded together by the agency that produced the cleavage. There is, however, a 
 greater tendency in the cleavage planes to pass perpendicularly through the coarser than through the 
 finer textures. Hence it happens that in passing from one bed to another the direction varies 
 slightly. A remarkable feature in the direction of the planes of cleavage is that it is constant over 
 large areas, and is unaffected by contortions ; thus it may make any angle with the dip of the beds. 
 But generally this steady direction, which, as it has been observed, may remain constant throughout 
 a large extent of country, is coincident with the main axes of elevation, and hence with the strike of 
 the beds. 
 
 The origin of cleavage is yet a disputed question. There can, however, be little doubt in the 
 mind of one who carefully examines the question that it is due to pressure. It has been observed 
 that fossils have been lengthened in the direction of the lines of cleavage as if they had been drawn 
 out by a movement of the. particles in that direction. This is precisely the effect that would be pro- 
 duced by pressure. Moreover, artificial cleavage may be produced in a substance by subjecting it to 
 pressure under conditions that allow of its expansion in directions at right angles to the pressure. 
 The planes of cleavage are always at right angles to the direction of the pressure that produced it. 
 
 The true dip of the planes of cleavage can be ascertained only at considerable depths, as very 
 frequently superficial agencies have changed the dip for some distance beneath the surface. 
 
 Foliation is a term used to indicate a separation into crystalline layers of different mineral com- 
 position, such as we find occurring in mica schist, for example. Foliation, like cleavage, is a super- 
 induced structure. 
 
 Faults and Dislocations. — One of the most important facts of geology to the coal miner is 
 the existence of " faults." By the term " fault " is understood any interruption of the continuity of a 
 stratum. The interruption may be complete, or only partial, and it may have been produced by 
 one of a multitude of causes. One of these causes has been already described as the " nip." Besides 
 
32 MINING ENGINEERING. 
 
 the term " fault," miners sometimes employ other expressions to signify the same things as " trouble," 
 " check," and others which indicate the nature of the fault ; these will be given as occasion requires. 
 
 Swells, Rolls, or Horses -backs. — Sometimes a ridge of clay, thrown up by currents of water, has 
 existed on the surface upon which deposition has subsequently taken place. Such ridges are some- 
 times from 6 to 8 feet high in the centre, and slope off gently on each side, and are known among 
 miners as " swells," " swellies," " rolls," and " horses'-backs." One of these is shown at a, in Fig. 12, 
 Plate III. It is evident that when a deposition takes place upon this surface, the continuity of the 
 new bed or beds will be wholly or partially broken by the swell. This is shown in the figure where 
 h, b,' b," and b'" are beds of coal. The beds b and b' end evenly against the swell on each side, or, as 
 the miner expresses it, the coal in those beds is completely " cut out " for a distance equal to the 
 thickness of the swell. The continuity of bed b" is only partially broken ; in other words, the coal is 
 cut out through a portion only of its thickness. The evidence of the swell being anterior to the 
 deposition of the higher beds lies in the fact that the latter exhibit no trace of disturbance. The beds 
 cut out end evenly against the swell, and bed b'" in the figure, for example, is uncontorted, 
 
 Erosions, or Troughs. — Another kind of fault is caused by the existence of water-courses on the 
 surface upon which deposition has subsequently taken place. The action of a stream is, by wearing 
 away the soil, to cut out a bed for itself; and the breadth and depth of the excavation will be gene- 
 rally in proportion to the volume and the velocity of the stream, the softness of the strata over which 
 it flows, and the length of time during which it has flowed. Hence the excavations due to erosions 
 of this nature may vary in magnitude to an almost indefinite extent. When of considerable magni- 
 tude^ the effects are classed rather as those of what is called denudation than erosion, the latter term 
 being restricted to the effects of small streams. When the subsequent deposition took place, the 
 hollows or troughs worn out by the stream were filled by the materials formed by the next bed in 
 the manner shown in Figs. 13 and 14. The portion of the upper bed that fills the hollow is by 
 miners frequently called the "horse," and it is spoken of in the same way as the "swell," as "cutting 
 out " the bed beneath. As the softer strata were the most acted upon by the eroding force, coal 
 seams have often suffered greatly. One of these erosions, in a coal seam in the Forest of Dean, has 
 been described as extending over a considerable area, and showing branches in many places, such as 
 would be produced by little tributaries flowing into it. 
 
 Besides the erosions caused by streams, others have been produced by currents of water of a 
 different character. An example of these is shown in Fig. 15, Plate III. Bed No. 2 has become 
 mingled by various currents with materials differing from those of the bed below. Bed No. 3 has 
 been of greater thickness than it is now, and has been worn down in an irregular manner, previous 
 to the deposition of bed No. 4. The latter suffered in the same way before being covered by No, 5. 
 Erosions of this character possess no regularity. 
 
 Dykes. — Dykes of igneous rock are a frequent cause of fault, especially in certain districts. 
 The character and mode of occurrence of dykes and their effects upon the surrounding rocks have 
 been described under the head of Igneous Rocks. 
 
 Fracture and Displacement. — Fracture of the beds, and subsequent displacement of the several 
 portions, constitute the most important and the most common kind of fault. It may easily be 
 conceived that the forces which upheaved and contorted the beds in the manner we have already 
 described, would also crack and break them through. As a matter of fact, such has been the case, 
 and to such an extent that there is, probably, hardly a square mile of country wholly exempt from 
 
PEACTIGAL GEOLOGY. 33 
 
 faults of this character. In some cases, fracture alone was produced; but far more frequently 
 displacements occurred, so that beds which were originally continuous now lie at very different levels 
 on opposue sides of the fault. An example of this is given in Fig. 16, Plate III. Taking the 
 coal seams as the most conspicuous, it will be observed that two beds are shown on the left-hand side 
 of the fracture. On the other side, these beds have sunk down to a much lower level, bringing down 
 nearly to their original level three other beds lying above them. Among miners, such a fault is 
 sometimes called a " slip," or " slide," and the character of the displacement is described as a " down- 
 throw," or " downcast." The expressions " upthrow " and " upcast " are employed — but, in many 
 cases, incorrectly — to describe the position of the beds on the left-hand side of the fracture in the 
 figure when viewed from the other side. 
 
 The amount of displacement, measured in a vertical direction, is called the " throw," and is 
 expressed in feet, yards, or fathoms from the surface, when the latter is horizontal, and from a given 
 horizontal plane, when the surface is irregular or inclined. Suppose, for example, the distance of 
 the bed at a in the Diagram, Fig. 17, Plate lY., from the surface, or an assumed horizontal datum 
 line A B, to be 100 yards, and the distance of the same bed from the same line to be at b 200 yards. 
 The throw in this case would be described as a downthrow of 100 yards, without any reference to 
 the horizontal distance A B, or the inclined distance a b, between the ends of the bed. The horizontal 
 distance A B, which represents the extent of barren ground to be driven through, is, by the miner, 
 frequently called the " width " of the fault. This width will vary with the angle of the fault. 
 Diagram, Fig. 18, Plate TV., shows an inclined bed cut by two faults AB and D, the angle of 
 inclination of the latter being much less than that of the former. In this case, the throw of the 
 fault A B will be measured by the line a b, and that of C D by the line c d. Also the width of 
 the fault A B will be measured by the line A o, and that of D by the line Ajo. Thus the nearer 
 a fault approaches the perpendicular, the better it is for the miner. It is to be observed that, though 
 the amount of throw is much greater in the fault A B than in C D, the position of the two portions 
 of the bed X and Y is the same. Whence it will be seen that in faults inclined at different angles, 
 or in beds lying at different angles, variations in the amount of throw will not be accompanied by 
 a corresponding variation in the position of the beds at a little distance on each side of the fault. 
 
 Faults of dislocation differ from one another in character and in effect. The variations in 
 character are mainly due to differences in the composition and structure of the rocks traversed by 
 the fault. It is, indeed, sufficiently obvious that the alternation of hard with soft beds must influence 
 the consequences of a fracture in no inconsiderable degree. The variations in effect are due to 
 differences in the position of beds, and in the inclinatiou, direction, and number of the lines of 
 fracture. 
 
 When a fault runs through beds of shale alternating with thin beds of sandstone, the fracture 
 may be merely a plane of division. In such cases, the surfaces of the fracture are frequently smooth 
 and polished by the friction to which they have been subjected, and present the appearance known as 
 " slickensides." When the beds traversed by a fault are composed of hard materials, as gritstone or 
 limestone, a fissure of greater or less width will exist. If the line of fracture is an irregular one, 
 which it usually is, the protruding parts on one side may rest against similar parts on the other, and 
 in such a case the fissure will be closed up in some places and open in others. No doubt the 
 irregularities thus produced have been greatly lessened by the wearing down of the protuberances 
 by friction ; but they are still remarkable. By open fissures, it must not be understood that the 
 
 F 
 
34 MINING ENGINEEEING. 
 
 spacewS so formed are now empty. On the contrary, in most cases they have been filled up with the 
 de'bris produced by the friction of protuberance against protuberance, or by materials subsequently 
 brought into them. When hard and soft beds alternate, the fissure is generally closed at those parts 
 where the soft beds occur. 
 
 Sometimes the beds end abruptly against each other without any distortion, as in Fig. 16, 
 Plate III. But more frequently the ends have been bent, as in Fig. 19, Plate lY. In such a 
 case, the beds are said to " dip to the downthrow," or " rise to the upthrow," a result which we 
 should naturally expect a sliding of one bed over another to produce. But instances are by no 
 means rare in which the contrary takes place, the ends of the beds having been crumpled up by the 
 pressure of those on the opposite side of the fracture. No satisfactory explanation can yet be 
 given of the manner in which the forces were brought to bear to produce this contortion. 
 
 As rock beds are rarely horizontal over any considerable area, it is of the utmost importance to 
 understand the effect of faults occurring in inclined beds. If a fault occur in a bed, or set of beds, 
 dipping in a given direction and at a given angle, the vertical throw produces at the surface an 
 apparent shift. Suppose, for example, the bed a, in Fig. 20, Plate IV., to dip to the north at an 
 angle of, say, 25°, as indicated in the figure, which is a plan of the outcrop ; and a fault 66 to have 
 occurred, causing a downthrow to the east. In such a case, the outcrop of the beds will be farther 
 south on the east than on the west side of the fault, as shown. To the mining engineer, this 
 circumstance is obviously of great practical importance. 
 
 To render the effect of apparent shifts more evident. Jukes, in his ' Manual,' which is the most 
 practical treatise on Greology extant, gives a useful diagram, which we have reproduced in Figs. 21 
 and 22, Plate IV. If we suppose this to be a section through the bed a, in Pig. 20, running north 
 and south in the direction of the fault, we may conceive the part b dropped vertically down to c, 
 and the part d, in the former continuation of the bed, down to e. From this position it is clear that 
 a vertical throw of the bed a a on one side of the fault will place it as at a' a' on the other side of 
 the fault, and that the respective outcrops of the two pieces of the same bed will, after being worn 
 down to the same level, at the present surface of the ground, which is everywhere a surface of 
 denudation, be at the points b and e. It is also evident from this diagram that the higher the angle 
 at which the beds dip, the less will be the apparent shift at the surface due to the same amount of 
 throw. In Fig. 22, Plate IV., there is the same amount of throw, that is, the distance 6 c is the 
 same, but the angle having been increased to 60°, the distance 6 e is considerably lessened. Hence 
 it will be seen that when the beds lie at a low angle, a small amount of throw will shift the outcrop 
 to very considerable distances, and that when the beds are vertical, however great that amount may 
 be, it will be almost impossible to detect the fault. 
 
 It is obvious from the relations existing between the dip, the throw, and the shift, or " heave," 
 as it is sometimes called, that when any two of these are known, the value of the third may be easily 
 determined. In the practice of surveying, tables are used in which these relations are conveniently 
 expressed, for ready reference. These tables will be described in a subsequent section. 
 
 The apparent lateral shift at the surface demands careful attention when occurring in anticlinal 
 and synclinal curves, and an examination of its effects on beds so contorted will clearly show that 
 the positions can be accounted for in no other way but that which we have described, since the 
 apparent shift takes place in opposite directions. If we suppose the Diagram, Fig. 23, Plate IV., 
 to be a sectional plan of a bed in a synclinal, or in an anticlinal, a downthrow on the right, B, of 
 
PRACTICAL GEOLOGY. 35 
 
 the fracture in the former case, or a downthrow on the left, A, of the fracture in the latter case, 
 would produce the eifects there shown. The example we have given illustrates a simple case ; the 
 effect may be complicated by changes in the angle or the direction of the dip, or in the amount of 
 the throw. 
 
 The faults we have been considering run at right angles to the strike of the beds. But they 
 may run obliquely to the strike, or even coincide with it. In the latter case, the faults are described 
 as " strike faults." Such faults may entirely conceal some of the beds, and thereby lead to erroneous 
 conclusions as to the succession of the beds. It is possible that strike faults are much more frequent 
 than we suppose, i+ being exceedingly difficult to detect them where the order of succession has not 
 been estabUbLed. A simple diagrammatic section of a strike-fault will show how some of the beds 
 become concealed. It is also clear that when the throw diminishes in one direction, the concealed 
 beds will come out to view in that direction. 
 
 The number and association of faults also demand consideration. When the fault consists of a 
 single fissure, as the beds must remain joined at the extremities of the fissure, it is evident that 
 displacement can take place only by the beds bending downwards, or sagging, like a rope or a 
 flexible rod placed in a horizontal position. In such a case, the deflection or throw will be greatest 
 in the middle. The character of the beds traversed by the fault may modify this result to some 
 extent, by producing undulations in the downthrow portion. The strain due to the deflection which 
 thus takes place frequently causes the fissure to extend itself at one or both extremities in two or 
 more branches. A fault of this character occurs in the South Staffordshire coal-field, where it is 
 known as the Lanesfield fault. 
 
 When the fault consists of two fissures starting from the same point in different directions, 
 tlie greatest amount of throw will occur at the angle or corner of ground included within the 
 intersection of the two fissures. From this point, to the extremities of the faults, the throw will 
 gradually diminish, as in the preceding case; and the beds will be bent along the line joining those 
 extremities. That there may be no bending of the beds, the fault must consist of at least three 
 straight lines running into each other so as to form a triangle, or of two curved lines running 
 into each other, so as to sever the mass from the surrounding beds. Such faults, if they occur at all, 
 
 are rare. 
 
 Step Faults. — Sometimes a long and powerful fault will consist of a number of parallel fissures 
 at small intervals apart. The total amount of throw may then be divided among the several dis- 
 located portions, so as to form a series of steps, as shown in Fig. 24, Plate IV. It need hardly be 
 stated that the division of the throw among those portions is rarely, if ever, an equal one. In 
 some instances two portions are thrown in opposite directions. 
 
 Trough Faults. — Sometimes a junction of faults occurs in such a way as to produce what is called 
 a " trough fault." Such a fault is shown in Fig. 25, Plate Y. The opposite faults, the junction ot 
 which forms the trough, as a c, be may be unequal in throw. In this case, the whole mass of the 
 surrounding rock undergoes displacement, as may be seen in the figure, by tracing the beds through 
 their dislocations. When the opposite faults are equal in throw, as de,fe, only the wedge-shaped 
 mass included between them sufiiers displacement. 
 
 The only satisfactory explanation of the manner in which these faults are formed is that given 
 
 bv Jukes, which is as follows : " Suppose the beds A A, BB, etc., Fig. 26, Plate Y., to have been 
 
 formerly in a state of tension, arising from the bulging tendency of an internal force, and one fissure, 
 
 P 2 
 
3G MINING ENGINEEEING. 
 
 F E, to Lave been formed below, which on its course to the surface splits into two, E D and E 0. If 
 the elevatory force were then continued, the wedge-like piece of rock, "W, between those two fissures 
 being unsupported, as the rocks on each side separated, would settle down into the gap, as shown in 
 Fig. 27, Plate V. If the elevatory action were greater near the fissure than farther from it, the single 
 fissure below would have a tendency to gape upwards, and to swallow down the wedge, so that 
 eventually this might settle down and become fixed at a point much below its previous relative posi- 
 tion. Considerable friction and destruction of the rocks, so as to cut oflf the corners, g h, would 
 probably take place, and thus widen the gap, and allow the wedge-shaped piece, W, to settle down 
 still farther. When the form' of elevation ceased to act, the rocks would have a tendency to sink 
 down again, and resume their original positions. But those newly-included wedge-shaped and other 
 masses would no longer fit into the old spaces, so that great lateral compression might then take 
 place." 
 
 When occurring in nature, the results described above will be more or less complicated by the 
 irregular action of the elevatory forces, and the heterogeneity of the mass through which the fissures 
 pass ; also the lateral pressure alluded to may cause numerous contortions and fractures as the mass 
 settles down. These effects are clearly illustrated by the section. Fig. 28, Plate Y., through the 
 Staffordshire thick coal at the commencement of a trough fault. Here a wedge-shaped piece from the 
 rocks above has come down into the coal, and the beds on each side show much crumpling and dislo- 
 cation as the effects of the consequent lateral pressure. This pressure had reduced the coal on each 
 side of the fault, for a distance of several feet, to a state of powder. Many of the sections of 
 the Geological Survey show similar results in other localities. Fig. 30, Plate VI., shows several 
 examples of faults of dislocation. 
 
 Relation between Inclination of Fault and Direction of tliem. — Though faults are sometimes vertical, 
 as at A B, Fig. 29, Plate V., in the vast majority of cases they are inclined at a greater or less angle. 
 With respect to the direction of the inclination, it has been indisputably established that " no fault 
 traversing any set of beds will make an acute angle with the same bed on both sides of the fault :" 
 that is, a fault such as that represented at E P, in Fig. 29, cannot occur. Hence we have the follow- 
 ing invariable rule, the practical importance of which will be obvious. 
 
 Rule. — The fault inclines, or " hades," as it is sometimes termed, in the direction of the down- 
 throw. 
 
 As a corollary of this rule, it may be stated that whatever the inclination of the fault may be, 
 no portion of any bed will ever be brought vertically under another portion of the same bed. 
 
 Denudation. — We have already described the effects of currents of water in removing portions of 
 beds, as results of erosion. When, however, the same effects are produced upon a large scale, it is 
 customary to speak of them as the result of denudation. As all the aqueous rocks have been formed 
 from the detritus of other rocks, it is evident that denudation must be co-extensive with deposition. 
 A vivid realization of its nature and its effects is of essential importance to the student of Greology ; 
 for apart from the production of sediment, and ultimately of sedimentary rocks, it has acted more 
 than any other cause in fashioning the external contour of the dry land. It is easy to prove that the 
 present surface has been produced by the removal of a great thickness of solid rock. The proof may 
 be found in the geological structure of a district. Take, for example, the frequent case of an escarp- 
 ment and an outUer, such as that shown in Fig. 31, Plate VI. The beds ending in the escarpment X, 
 were evidently once continuous to the outlier Z, and beyond Z. The excavation of the valley Y, 
 
PE ACTIO AL GEOLOGY. 37 
 
 and the formation of the low country beyond Z, thus isolating the hill Z, are the effects of denuda- 
 tion. If the whole of the escarpment X and the outlying hill Z had been removed so as to form a 
 level surface, the character of the agency that produced it would be equally apparent in the fact that 
 the surface was formed by the outcrop of the strata. Such surfaces are numerous, and indicate the 
 removal of an enormous quantity of rock. The actual depth removed cannot be ascertained, but in 
 some instances a minimum depth may be assigned. In the antilinal A, Fig. 8, Plate II., the dotted 
 lines represent the portions of the beds 5, 6, 7, and 8, that have been removed to form the present 
 surface. If the total thickness of those beds at their outcrop be 1000 feet, it is clear that that depth 
 must have originally existed above bed 4, the present surface of the ground. But the total depth 
 removed was even greater than this, because there are beds cropping out beyond No. 8, which must 
 have been covered by them. Another striking indication of the vast effects of denudation is 
 furnished by the fact that, in most cases, the irregularities occasioned by faults have been wholly 
 removed from the surface. When it is borne in mind that faults are by no means rare in which the 
 strata have been elevated or depressed to the extent of 500 or 600 feet^ the magnitude of the powers 
 that have planed down such precipices will be apparent. 
 
 To the mining engineer, the action and the effects of denudation are of the highest importance. 
 In numerous instances, immense sums of money have been expended in sinking shafts for coal in 
 places from which the coal measures have been removed — a circumstance that a little knowledge of 
 geology would have rendered evident. 
 
 Other examples of the effects of denudation are given in Figs. 32 and 33, Plate VI. The 
 former is a diagrammatic section through a portion of the Cleveland districts, surveyed by the writer 
 for ironstone. On the right of the figure, at A, the series consist, in the ascending order^ of the lower 
 and middle lias, a seam of ironstone, I, the upper lias, consisting of the jet and alum shales, and a 
 sandstone capping, representing the lower oolite. At B, the sandstone bed and a portion of the shales 
 have been removed. At 0, the denuded portions reappear ; but beyond this, at D, the whole series 
 down to the lower lias has been carried away. From this example, as well as from Fig. 31, it will 
 be seen how denudation operates to form hills. 
 
 In Fig. 33, Plate YI., we have a section of the county through Trentham Park, in North 
 Staffordshire, as given by Mr. E, Hull, of the Geological Survey. The beds of quartzose conglome- 
 rate which come to the surface at A, have undergone denudation. At A', a downthrow again brings 
 them in ; the upper portions of the anticlinal having been worn away, the beds reappear at A", 
 where an upthrow separates them from their continuation at A"'. 
 
 UiifCOisrFGRMiTY. — The deposition of rock beds takes place^ as we have shown, in parallel layers. 
 This parallelism is not destroyed by any subsequent tilting that may occur. Beds so placed with 
 respect to each other are said to be " conformable," or to lie conformably over each other. When, 
 however, denudation and subsequent deposition take place, it is easy to see that this conformity 
 may not exist. If, for example, the escarpment and outlier, in Fig. 31, Plate VI., were removed, and 
 another set of beds deposited over the surface, these would lie unconformably upon those forming the 
 surface of denudation. Hence it will be seen that unconformity is a consequence of denudation, 
 and is of great practical importance, for it is from it that we derive some of our clearest and most 
 vivid notions of what may be effected in the process of denudation. An example of unconformity 
 is given in Fig. 34, Plate VI., where beds of conglomerate of the new red sandstone rest upon beds 
 of the permian sandstone. 
 
38 MINING ENGINEERING. 
 
 " Overlap " is a term used to express the greater extension or spread of any set of superior strata 
 by which they overlap and conceal the edges of those beneath them. In some instances, an overlap 
 has been mistaken for unconformity, though the two are very different phenomena. 
 
 Chronological Order of Formation.— Hitherto we have been considering rock beds in their 
 lithological and petrological relations. It now remains to view them as members of a chronological 
 series. It is obvious, from the mode of formation of rock beds, that any given bed is of more recent 
 origin than that upon which it rests, and of more remote origin than that which lies immediately 
 above it. This fact furnishes us with the means of ascertaining the relative age of any bed or set of 
 beds. But it is equally obvious, from what we have seen of the effects of disturbing forces and 
 denuding agents, that beds which, in one place, are covered by a vast thickness of other beds, in 
 another place may form the present surface of the ground. Hence it by no means follows that beds 
 which he nearest the surface are of the most recent formation. Extended observation has, however, 
 established these most important facts, namely, that in some places there exist beds which are 
 nowhere overlaid by others ; that the beds lying immediately beneath these are nowhere else over- 
 laid by others ; that the next again in succession are nowhere overlaid by any but one or the other, 
 or by both, of the two former ; and so on down through the whole series of sedimentary rocks. 
 From this we learn that there exists an invariable order of succession. This order is called the Order 
 of Superposition, and by it we are enabled to determine the relative age of any bed or set of beds. 
 The practical importance of being able to correctly assign to any set of beds its chronological posi- 
 tion in the series is very great. To take a simple example : Suppose we find a surface formed of 
 the old red sandstone. It would evidently be futile to sink for coal in that locality, because the car- 
 boniferous beds are of more recent formation than the former, and would, therefore, not exist beneath 
 them. Or, again, if we are sinking through beds which in geological order lie above the coal 
 measures, and come unexpectedly upon the old red sandstone, we know that the coal measures were 
 either never deposited in that place, or that they have been removed by denudation, and that, conse- 
 quently, it would be a sheer waste of money to continue the sinking deeper. 
 
 Having established an order of superposition, it becomes necessary to divide the series of beds 
 in some manner convenient for reference ; and to do this, we very properly look for some natural 
 divisions. We find, for example, a set of rock beds called the " millstone grit," and we speak of the 
 time during which these beds were deposited as the millstone grit age. But the millstone grit 
 occurs among a group of beds remarkable for the carbon which they contain, either as a constituent 
 part, or as interstratified deposits. And in speaking of the time during which this group was 
 deposited, we designate it as the Carbon Period. Again, it has been remarked that the fossil 
 remains indicate a natural division. From the most recent deposits, down to a certain point, the 
 remains are those of species still existing, or of species closely allied to existing species. From this 
 point down to another point, the remains are those of species differing essentially from those now 
 existing ; and from the latter point down to the fundamental granite, the species are again different 
 till they disappear altogether. It must not, however, be supposed that these points are distinctly 
 defined. On the contrary, the species die out gradually. But though somewhat arbitrarily fixed, 
 they are sufficiently well defined for practical purposes. These distinctions divide the whole series of 
 sedimentary rocks into three epochs, called the Primary or Palaeozoic {ancient life), the Secondary or 
 Mesozoic {middle life), and the Tertiary or Cainozoic {recent life). It is necessary, to clearness of 
 understanding, that the distinction here pointed out between the expressions " age," " period," and 
 
PEACTICAL GEOLOGY. 
 
 39 
 
 " epoch," should be constantly observed in all geological considerations. Unfortunately, writers on 
 Geology frequently employ them indiscriminately. 
 
 It must be borne in mind that the names given to a set of beds, as the " chalk," the 
 " Kimmeridge clay," the " old red sandstone," etc., though in themselves indicative of lithological 
 character, locality, or some other attribute of some particular variety of rock, are used solely 
 with reference to time. That is, by the expression the "chalk," we mean not only the chalk 
 itself, but all beds of the chalk age. These may consist of black marble, brown sandstones, or 
 blue slate. In the same way, the old red sandstone may be sandstone in one place, and clay-slate 
 in another ; and Kimmeridge clay may be found at places far remote from the locality whence it 
 takes its name. 
 
 The divisions of geological time are as follows : 
 
 I. — PbIMAKT, or PALiEOZOIO EpOCH. 
 
 1. The Lauren tian Period, 
 
 2. The Cambrian Period. 
 
 3. The Silurian Period. 
 
 4. The Devonian, or Old Eed 
 
 Sandstone Period. 
 
 5. The Carbon Period. 
 
 6. The Permian Period. 
 
 IL — Secondaet, OB Mesozoio Epoch. 
 
 1. The Triassie Period. 
 
 2. The Jurassic, or Oolitic Period. 
 
 3. The Cretaceous Period. 
 
 m. — Teetiaey, oe Cainozoio Epoch. 
 
 1. The Eocene Period. 
 
 2. The Miocene Period. 
 
 3. The Pliocene Period. 
 
 4. The Eecent Period. 
 
 TABLE OP SEDIMENTAEY STRATA. 
 
 n 
 
 o 
 o 
 
 p. 
 
 s 
 
 o 
 o 
 
 < 
 
 m 
 
 Pliocene Period — Crag 
 
 Miocene Period 
 
 O 
 
 
 
 ^ 
 
 O 
 
 Hempstead 
 Bods. 
 
 3 
 
 {Norwich Crag. 
 Suffolk Crag. 
 
 f Leaf Bed of Mull. 
 / Lignite of Antrim. 
 [ Bovey Beds with Lignite. 
 
 Corbula Beds. 
 
 wjjf I Fresh-water and Estuary 
 
 ™« Marls. 
 
 Lower 
 
 Bembridge ( Bembridge Marls, 
 
 Beds. 
 
 Osborne 
 Beds. 
 
 Headon 
 Beds. 
 
 Bagshot 
 Beds. 
 
 1 
 
 Limestone. 
 
 St. Helen's Sands. 
 Nettlestone Grits. 
 
 ( Upper 
 I Middle 
 1 Lower 
 
 Headon Beds. 
 
 Upper Bagshot Sand. 
 
 ( Barton Clay. 
 Middle „ < Bracklcsham 
 
 \ Beds. 
 Lower „ Sand and Pipeclay. 
 
 I London Clay and Bognor Beds. 
 Oldhavcn Beds 
 Woolwich and Heading Beds 
 Thanet Beds 
 
 Plastic 
 Clay. 
 
40 
 
 MINING ENGINEEEING. 
 
 B 
 
 D 
 O 
 
 n 
 
 < 
 
 R 
 
 tn 
 
 o 
 a 
 
 CD 
 
 o 
 •§ 
 
 ai 
 
 o 
 
 6 
 
 
 i 
 
 o 
 
 O 
 
 '73 
 
 O 
 
 o 
 O 
 
 ^1 
 
 Pi 
 
 f3 
 
 Chalk. 
 
 Lower 
 Greensand. 
 
 o 
 
 -a ( 
 
 
 m 
 
 60 
 
 W 
 
 Purbeck. 
 
 Portland. 
 
 Coralline 
 Oolite. 
 
 Oxford 
 Clay. 
 
 Forest 
 Marble. 
 
 Great 
 Oolite. 
 
 Fullers' 
 Earth. 
 
 Inferior 
 Oolite. 
 
 Upper Chalk, with layers of Flint. 
 Lower Chalk, without FHnts. 
 Chalk Marl. 
 Chloritic Marl. 
 
 Upper Greensand, Malm Bock, etc. 
 
 Gault Clay. 
 
 Folkestone Beds. 
 
 Sandgate Beds. 
 
 Hythe Beds. 
 
 Atherfield Clay ; Speeton Clay. 
 
 Weald Clay. 
 
 ' Upper Tunbridge Wells Sand. 
 
 Grinstead Clay. 
 
 Lower Tunbridge Wells Sand. 
 
 Wadhurst Clay. 
 
 Ashdown Sands. 
 . Ashburnham Beds. 
 
 Upper 
 
 Middle 
 
 Lower 
 
 Purbeck Beds. 
 
 f Portland Stone. 
 Portland Sand. 
 ^ Kimmeridge Clay. 
 
 Upper Calcareous Grit. 
 
 Coral Hag. 
 
 Lower Calcareous Grit. 
 
 I Oxford Clay, and 
 \ Kellaways Eock. 
 
 Oornbrash. 
 Forest Marble, and 
 Bradford Clay. 
 
 [■ Great, or Bath, Oolite, 
 / Stonesfield Slate. 
 [ Northampton Sand. 
 
 r Upper Fullers' Earth (Clay). 
 
 / Fullers' Earth Eock (Limestone). 
 
 { Lower Fullers' Earth (Clay). 
 
 Chelten- 
 ham. 
 
 ( ( Eagstone and Olypeous Beds, 
 
 Upper Freestone. 
 Oolite Marl. 
 ( """*• Lower Freestone. 
 Pea Grit. 
 Collyweston Slate, Lincolnshire. 
 Sands. 
 
 Upper Lias. Clay and Shale. 
 Lias. ( Middle Lias. Marlstone. 
 
 { Lower Lias. Clay, Shale, Limestone, and Bone Beds. 
 
PRACTICAL GEOLOGY. 
 
 41 
 
 13 
 
 d 
 
 OS 
 
 o n3 
 
 CO 
 
 
 Keuper. 
 
 Middle ) 
 Triassic. | 
 
 o 
 o 
 
 Ph 
 
 o ,3 
 
 d . 
 
 fSp; 
 
 B 
 
 o 
 ^^ 
 
 o 
 
 
 CD 
 
 d 
 o 
 
 I 
 
 o 
 d 
 o 
 
 -« 
 
 CQ 
 
 i 
 
 CQ 
 
 o § 
 
 a 
 (3 
 
 d 
 
 d 
 o 
 
 > 
 
 n 
 
 o 
 
 O 
 
 (3 
 
 Ph 
 o 
 
 Bunter. 
 
 Bed Variegated Marl, and Upper 
 
 Keuper Sandstone. 
 Lower Keuper Sandstone and Marl. 
 
 (Water Stones.) 
 Muschelkalk, absent in Britain, 
 
 Dolomitic conglomerate. 
 
 Upper Red and Mottled Sandstone. 
 Pebble Beds, Calcareous Conglo- 
 merate, and Bi-eccia. 
 Lower Red and Mottled Sandstone. 
 
 Upper, or ( Red Marl. 
 Magnesian ( Magnesian Limestone. 
 Limestone. I Marl Slate. 
 
 Lower. 
 
 Coal 
 Measures. 
 
 Lower Red Sandstone. 
 
 ( Upper Coal Measures, 
 Middle Coal Measures. 1 
 Pennant Grit. j 
 
 Lower Coal Measures. 
 Gannister Beds. 
 
 Millstone Grit, or Farewell Rock. 
 
 Carboni- f Upper 
 
 C Upper Limestone Shale (Yoredale 
 ferous, or J Rocks). 
 Mountain \ Carboniferous Limestone. 
 Limestone. [ Lower Limestone Shale. 
 
 Devonian 
 Beds. 
 
 
 Ludlow 
 Beds. 
 
 Wenlock 
 Beds. 
 
 ^ Upper Devonian, or Barnstaple and 
 I Marwood Beds, with Petherwin 
 I Limestone in N.E. Cornwall. 
 ' Middle Devonian, or llfracombe Beds, 
 with Fossiliferous Limestones and 
 Comstones. 
 Lower Devonian, or Lynton Beds. 
 
 Tilestones or Passage Beds. 
 
 ( Upper Ludlow Beds (with Bone Bed). 
 ( Aymestry Limestone, 
 I Lower Ludlow Beds, 
 
 I Wenlock Limestone, 
 Wenlock Shale, Sandstone, and Flags. 
 Woolhope Limestone and Shale, and 
 Denbighshire Grits, Shales, Slates, and 
 Flags, 
 
 Llandovery I Upper Llandovery Rocks. 
 Beds, 1 Lower Llandovery Rocks. 
 
 North America, 
 
 (The Carboniferous Beds of the United 
 States, as grouped by Professor Rogers, are 
 as follows : Upper Group. — Alternations of 
 greyish and reddish sandstones, shales, and 
 coalsj thinning out westward. Middle Group. 
 — In Pennsylvania, soft red shales, and argil- 
 laceous red sandstones. In Vii'ginia, blue, 
 olive, and red calcareous shales, with thick 
 red and bro\vn sandstone ; light-blue lime- 
 stones ; and bufl, greenish, and rod shales. In 
 the Western States, grey and yellow sand- 
 st-oncs, and light-blue and yellow sandstones. 
 Lnwer Gionp. — ^ White, grey, and yellow sand- 
 stones, alternating with coarse siliceous con- 
 glomerates, and dark-blue and olive-coloured 
 slates. In some places black carbonaceous 
 slate, and a few beds of coal.) 
 
 Po 
 
 jg oO 
 
 go 
 
 t-i 2 
 
 f^ O P 
 g <HH O ' 
 
 \h1o 
 
 Nova Scotian System. 
 
 Greyish and reddish sandstones 
 and shales, beds of conglomerate, 
 and thin beds of limestone and coal. 
 
 Grey and dark-coloured sand- 
 stones and shales, with red and 
 brown beds of same; coal, iron- 
 stone, and bituminous limestone. 
 
 I Red and grey sandstones and 
 conglomerates, and red and green 
 marls, with thick beds of gypsum 
 and limestone. 
 
 CO 
 
 . ^ 
 Pi p 
 
 o 
 
 7-1 
 
 W 
 a, 
 
 CatskUl Group, or Old Red Sand- 
 stone. 
 
 I Chemimg Group. 
 
 Portage Beds. 
 I Genoese Slate. 
 
 Tully Limestone. 
 
 Hamilton, or Moscow Shale, 
 
 Marcellus Shale. 
 
 Corniferous Limestone, 
 Onondugo Limestone. 
 Scholiarrie Grit. 
 Caudigalli Grit. 
 Oriskajiy Sandstone. 
 
 Lower Helderberg Group. 
 
 Onondago Group. 
 
 Clinton Group. 
 Medina Sandstones. 
 Oneida Conglomerate. 
 
42 
 
 MINING ENGINEEEING. 
 
 P4 
 
 
 £ 
 h5 
 
 ' Caradoc or f ^^^J'^'^"" and Bala Beds. 
 Bala Beds \ Sandstone (often Shelly) with Bala 
 \ Limestone, Shale, and Slate. 
 
 {Upper Llandeilo Flags, and Lime- 
 stone, &c. 
 Tremadoc Slates. 
 
 Bpdk * 1 Singula Flags. 
 
 S O 
 
 Cambrian. 
 
 Laurentian Period. 
 
 ''Harlech Grits, &o. 
 Purple Slates and Grits (St. David's). 
 Llanberis Grits and Slates. 
 Longmynd Eocks. 
 
 Eed Sandstone and Conglomerate 
 (Scotland). 
 
 Fundamental Gneiss of the N.W. Scot- 
 land, &c. 
 
 Hudson Eiver Beds. 
 
 Utica Slate. 
 
 Trenton and Birdseye Limestones. 
 
 Quebec Group (Limestones). 
 Calciferous Sandstones. 
 
 Potsdam Sandstones. 
 St. John's Group. 
 
 Huronian Beds of Canada. 
 
 The Lower and Upper Laurentian Gneiss, of 
 Canada. 
 
 The Laurentian Period. — The rocks of this period consist of ancient sedimentary strata 
 which have become highly crystalline. They are very largely developed along the country drained 
 by the St. Lawrence, in Canada, whence the name has been derived. The rocks of this formation 
 are the most ancient yet known. The only parallel existing in Great Britain is the gneiss of 
 the north-west of Scotland. 
 
 The Cambrian Period. — Next to the Laurentian in ascending order is the Cambrian Period, 
 the rocks of which are largely developed in Wales, whence the name. They consist of schists, 
 grits, and crystalline limestone, and have undergone a less degree of metamorphosis than the 
 Laurentian series. These rocks may be seen largely exposed in the hilly ground between Harlech 
 and Dolgelli, in parts of Caernarvonshire west of Snowdon, and in the Longmynd, a range of 
 hills on the north-west of Church Stretton, in Shropshire, where they show a thickness of 
 23,000 feet. The Penrhyn and Llanberis slate quarries are in a band of slate in the upper part 
 of this series. In Scotland, the rocks which may be assigned to this period are the red and 
 purple sandstones and conglomerates which lie to the south of Cape Wrath, upon the gneiss, where 
 they attain a thickness of 8000 feet. In Ireland, large masses of rock, consisting of dull green, 
 brown, purple, and liver-coloured slates, like those of North Wales, existing in the mountain 
 district of South Wexford, the northern portion of County Wicklow, and in the hill Howth, in 
 County Dublin, have been assigned to this period. 
 
 In Canada, the Laurentian gneiss is covered unconformably by a series of sandstones of great 
 thickness, known as the " Huronian " beds. 
 
 The physical aspects characteristic of Laurentian and Cambrian districts are bold, rugged hills 
 and mountain ranges, abounding in steep precipices and splintery peaks ; deep and narrow gorges, 
 and outlines marked by that irregularity which is always possessed by slaty formations when 
 deeply weathered. 
 
 The Silurian Period. — The term Silurian has been applied to an important series of rocks 
 first surveyed by Sir E. Murchison in the eastern portion of Wales, formerly inhabited by a tribe 
 named the Silures. These rocks consist of dark-coloured laminated shales, frequently with lime- 
 stone concretions, calcareous flagstones, thick-bedded sandstones, and pebbly conglomerates, finely 
 laminated micaceous sandstones, shales, and impure clayey limestones, and limestones of a con- 
 
PEACTICAL GEOLOGY. 43 
 
 cretionary structure. They have been divided into upper and lower groups, a division which 
 holds good wherever silurian rocks have been discovered. 
 
 The Livgula flags lie immediately above the Cambrian rocks, westward of the Longmynd, 
 in Shropshire, and also notably in Caernarvonshire, between the Menai Straits and the crest of 
 the Snowdon range. They consist of masses of dark slate, often ferruginous, with banded 
 arenaceous flags, the surfaces of which are spotted with impressions of lingulcB. The Llandeib 
 flags consist of beds of dark slate and sandy flags, with occasional bands of sandstone. The series 
 is more fully developed in North Wales, but the beds may be well seen near Llandeilo Favor, in 
 South "Wales, whence the name is derived. The Caradoc and Bala beds consist, the former of 
 brown sandstone, with occasional calcareous bands, the latter of grey grits and slates, much 
 invaded by igneous rock. They are most fully developed near the town of Bala, in Merioneth. 
 The Lower Llandovery beds consist of shales, sandstones, and conglomerates. They come in over 
 the Bala beds, near the town of Llandovery, whence they run in a southerly direction. At the 
 same place, the Upper Llandovery beds come in. These are similar to the lower beds in litholo- 
 gical character, but they are distinct from the latter in lying tmconformably upon and overlapping 
 them. This unconformity is everywhere existent between the upper and lower silurian rocks. 
 The upper Llandovery beds usually consist of grey, brown, or yellow sandstones, sometimes 
 passing into a conglomerate. The sandstones are in some places calcareous. The Wenlock beds 
 consist, near Llandovery, on the west of the Malvern Hills, at Great Barr, in Staffordshire, and 
 at May Hill, of grey argillaceous concretionary limestone, interstratified with grey shales. In 
 North Wales they are composed of coarse brown sandstone, with occasional quartzose con- 
 glomerates, and interstratified with black slates, passing up into brown flags. These are known 
 as the DenJnghshire grits, slates, and slabs. The Wenlock limestone consists of an irregularly 
 occurring set of concretionary limestones, which are sometimes thin and flaggy, and sometimes 
 form massive bosses of highly crystalline carbonate of lime. These beds, which are sometimes 
 interstratified with shales, exist between Aymestry and Ludlow, along Wenlock Edge to Bethnal 
 Edge, near Coalbrookdale, at the Castle Hill, and Wren's Nest, near Dudley, near Walsall, and in 
 the neighbourhood of Usk, 
 
 The Lower Ludlow beds are similar in character to the Wenlock shales, consisting of soft 
 dark sandy shales, with spheroidal calcareous concretions. Locally they are known as "mud- 
 stones." The Aymestry limestone is a dark grey limestone, less pure than the Wenlock limestone. 
 The latter is called by the workmen of South Staffordshire " the white limestone," and the former 
 " the black limestone." The Upper Ludlow beds consist of slightly micaceous sandy shale or flag, 
 or soft argillaceous sandstone, closely resembling the lower beds, of a bluish-grey colour, but 
 weathering rusty brown or greenish-grey. They pass upwards by insensible gradations into red 
 sandy flags, locally known as " tilestones." ,, 
 
 Scotland. — The localities in Scotland where silurian rocks occur are the southern uplands, 
 which are formed almost wholly of rocks of the Lower Silurian Period, probably of the Llandeilo 
 age ; and the neighbourhood of Kirkudbright, the Pentland Hills, and the valley of the Grirvan, 
 Ayrshire, where representatives of the upper group exist. 
 
 Ireland.— In Ireland, lower silurian rocks are found in Wicklow, Wexford, and Waterford, 
 and in the island of Lambay, and the promontory of Portraine, in County Dublin. Eepresentatives 
 of the upper group are found in Gralway, near Maam, and at the south-west end of Lough Mask ; 
 
 G 2 
 
44 
 
 MINING ENGINEEEING. 
 
 at Ughool, near Ballaglr^dereen, Lisbellaw, south of Enniskillen, in the Cratloe Hills of Limerick, 
 and in the Dingle Promontory, in County Kerry. 
 
 The Devonian and Old Eed Sandstone Period. — Lying immediately above the silurian 
 rocks is a set of beds to which, on account of their large development in the county of Devon, 
 the name of " Devonian " has been given. These beds, which consist mainly of schists and lime- 
 stones, have been divided into the lower, middle, and upper. The lower, or Lynton beds, consist 
 of red sandstones and conglomerates resting upon the shales and slates. The middle, or Ilfracomhe 
 beds, are formed of grey schists and limestones ; and the upper, or Barnstaple and Marwood beds, 
 are made up of slates, shales, and calcareous bands. Li South Devon these beds produce coarse 
 roofing slates, and in many places consist of red and variegated sandstones and flagstones. The 
 whole have been greatly disturbed and contorted. 
 
 Belonging to the same period, but differing widely in lithological character from the Devonian 
 rocks, there exists, in the district which gave its name to the silurian formation, a set of beds 
 of great thickness. These beds are composed mainly of red sandstones. In some places con- 
 glomerates, limestones, and clays occur, and in others the sandstones may be purple, green, 
 yellow, or even white ; but the prevailing characteristic of the beds is red sandstone. The name 
 of Red Sandstone has, therefore, not inappropriately been applied to this formation ; and to 
 distinguish it from another formation of red sandstone occurring above the coal measures, it is 
 called the Old Red Sandstone. In Shropshire, the old red sandstone beds rest upon the upper 
 Ludlow rocks, and they contain occasional beds of conglomerate, red and green clays, and marls, 
 with bands of impure arenaceous limestones, locally known as " cornstones." The beds dip gently to 
 the south-east, beneath the Clee Hills, whence they spread to the south-west, through Hereford 
 into Monmouth and Brecknock, attaining here a vast thickness, and thence into Caermarthenshire, 
 where they are tilted up into the vertical position. 
 
 Scotland.— The old red sandstone rocks are best developed in Scotland, where they may 
 be divided into three groups : the lower, the middle, and the upper. Besides these divisions, 
 they may be regarded as occurring in two types, one existing on the north, the other on the 
 south, of the Grampian range. The latter is distinguished by an abundance of interbedded 
 volcanic rock, and a poverty of organic remains ; the former by the absence of the igneous 
 rock, and a comparative abundance of fossils. 
 
 In the southern type, the lower group consists of red, chocolate-coloured, and grey sandstones 
 and shales, with great masses of volcanic rock, and occurs largely in the Sidlaw and Ochil Hills, 
 the Pentland Hills, and the country stretching thence into Ayrshire. The middle group is com- 
 posed of reddish, green, and grey sandstones, flagstones, and conglomerates, with an abundance 
 of volcanic rock, and may be seen in the south-west of Ayrshire. The upper group consists of 
 red and yellow sandstones and conglomerates, and is found in Berwickshire, Haddingtonshire, 
 and Fife. Of these three groups, the lower, as developed in Edinburghshire and Lanarkshire, 
 rests conformably upon the upper silurian; the upper lies conformably against the carboniferous 
 formation, and the middle is separated from the other two by an unconformity. In the northern 
 type the unconformity does not exist. The lower group consists of red sandstones and conglo- 
 merates, resting unconformably upon the metamorphic rocks of the Highlands. The middle 
 group consists of grey and dark flagstones, sometimes calcareous or bituminous, and covers a large 
 area in Caithness, and extending thence to the Orkney Islands. The upper group is composed 
 
PRACTICAL GEOLOGY. 45 
 
 of light red and yellow sandstones, and occurs largely at Dunnet Head, and in the Orkney and 
 Shetland Islands. 
 
 Ireland. — In Ireland two groups of old red sandstone exist, separated from each other by an 
 unconformity. The lower group is found in County Kerry, and is known as the Dingle beds. 
 These consist of red and green grits, and purple slates, with bands of purple conglomerate. The 
 upper group, consisting of red sandstones and conglomerates, comes in unconformably over these 
 as the peninsula expands. The old red sandstone beds of Kilkenny, "Waterford, and Cork, com- 
 posed of red sandstones and slates, rest unconformably upon the lower silurian rocks. 
 
 The physical aspects of old red sandstone districts are highly diversified and irregular. 
 The hills are less bold and precipitous than those of older districts, but more lofty and irregular 
 than those of the later secondary formations. 
 
 The Carbon Period. — Immediately above the Devonian and old red sandstone formation 
 occurs a set of beds which, from the large amount of carbon derived from vegetable matter which 
 they contain, have been named the carboniferous series. As it is from these beds that coal is 
 obtained, they constitute the most important of the sedimentary rocks. 
 
 The Lower Limestone Shale consists of dark earthy shales, sometimes interstratified, in its 
 lower portion, with yellowish sandstones, and always terminating upwards in thin flaggy lime- 
 stone, thus graduating downwards into the old red sandstone, and upwards into the carboniferous 
 limestone. In some districts it is very scantily developed ; in others it attains a great thickness. 
 
 The Carboniferous or Mountain Limestone. — The carboniferous limestone constitutes the most 
 distinct and remarkable set of beds of the Carbon, and, indeed, of any Period. So marked are 
 its characteristics, that it becomes a kind of guide-post both to the miner and to the geologist. 
 It occurs as a compact rock, usually of a dark grey, but sometimes of a reddish colour. In some 
 localities it becomes bituminous, forming the statuary "black marble;" in others it forms the 
 " stinkstone " and " rottenstone," already described. In certain localities, as in Derbyshire, for 
 example, the bitumen exists in the joints and fissures in a free state, especially in the neigh- 
 bourhood of trap dykes, constituting petroleum springs. The name of " Mountain Limestone " 
 has. been applied to these beds, because they are very generally found capping the trap hills that 
 intervene between the old red sandstone and the carbon formations. This limestone occurs 
 sometimes in one thick bed several himdred feet thick, separated by a few partings of calcareous 
 shale; sometimes, as near Bristol, interstratified with brown, grey, and red shales in the lower, 
 and with shales and sandstones in the upper portion. It everywhere contains remarkably 
 characteristic fossils. 
 
 The carboniferous limestone is absent from the coal-fields of the midland counties ; the coal 
 measures thpre resting upon Cambrian or silurian rocks. 
 
 The Upper Limestone Shale and Yoredale Bocks. — Above the carboniferous limestone lies a 
 group of shales, with thin, black earthy limestones at the bottom, and thin, fine-grained sandstones 
 at the top, known as the "Upper Limestone Shale." In some districts, but more especially in York- 
 shire, this group becomes confused with the limestone beneath, and the millstone grit above ; the 
 upper portion of the former being split up into beds of shale and thin limestones, and the lower 
 portion of the latter into shales and thin sandstones. To the group thus constituted, the name 
 of " Yoredale Eocks " has been applied ; and the limestone beneath, in the district whence this 
 name was derived, is known as the " Great," or " Scaur Limestone." 
 
46 MINING ENGINEEEING. 
 
 The Millstone Grit, or Farewell Rock. — The Millstone Grrit consists of a series of hard, 
 coarse-grained, quartzose sandstones, usually of a grey, white, or yellow colour, but sometimes 
 reddish, as near Bristol. Locally, and among miners, the mil^^tone grit is known as the " rough 
 rock." It is not a persistent group, but it is largely developed, and consequently occupies an 
 important place in the carbon formation, in some districts, as in the South Wales, Bristol, Lancashire, 
 and Yorkshire coal-fields. Its maximum thickness may reach 1000 feet. It is often interstratified 
 with shales, and occasional thin seams of coal. 
 
 The Gannister Beds. — The beds known as the " Gannister " are composed of hard, micaceous 
 sandstones, interstratified with shales, and in some places thin seams of coal. They are developed 
 in the Derbyshire, Lancashire, and North of England coal-fields. 
 
 The Coal Measures. — The Coal Measures consist of an enormous series of alternations of beds 
 of sandstones, shales, and coal, with occasional bands of ironstone. There does not appear to 
 be any marked order oi succession among these beds; but generally gritty sandstones prevail 
 towards the base, and sandstones and marly shales towards the top of the series. The coal 
 seams vary in thickness from one inch to many feet. In the Bristol coal-fields the measures have 
 a central band of hard sandstones, called the Pennant rock, which divides them into three sub- 
 groups : the lower, the middle or Pennant, and the upper. The sub-divisions here naturally 
 existing have been artificially retained for the sake of convenient reference in other districts. The 
 middle measures generally contain the chief seams of coal, those of the lower and upper being thinner, 
 and of inferior quality. The carboniferous formation is magnificently developed in England, 
 attaining in the Lancashire district the enormous thickness of 18,000 feet. A detailed description of 
 the formation as it exists in the several districts will be found in the last chapter of this work. 
 
 Scotland. — The beds of the Carbon Period are well developed along the great midland valley 
 of Scotland, stretching from the Firth of Clyde to the Firth of Forth. The conditions which 
 gave rise to the Yoredale rocks appear to have operated more strongly as we go northward, so 
 that the massive limestone base has given place to alternating beds of sandstones and shales, 
 interstratified with comparatively few thin limestone bands. The formation, as determined by 
 the Geological Survey, consists of the " calciferous sandstones," the " carboniferous limestones," the 
 "Moor Eock" — the representative of the millstone grit, — and the "coal measures." The calciferous 
 sandstones consist of two groups : the lower and the upper. The former is composed of purple, 
 red, and reddish-grey sandstones, sandy shales, and conglomerates, with occasional bands of corn- 
 stone. These generally rest unconformably upon the old red sandstone and silurian formations. 
 The latter group is composed of white and grey sandstones, blue and black shales, often highly 
 bituminous, limestones, cornstones, and occasional seams of coal. This group is less persistent than 
 the lower, thinning out and disappearing altogether in some places. The Carboniferous Lhnestones 
 consist of sandstones, shales, coals, ironstones, and bands of limestones; the coal-bearino- beds 
 occupying the middle of the series. In the Linlithgowshire and Fife districts, volcanic rock is 
 abundantly intermingled with the carboniferous limestone. The Moor Rock consists of coarse white 
 and grey sandstones and grits, with some thin coal seams. These beds are largely developed 
 in Edinburghshire, Fife, and Lanarkshire, but die away so as to become indistinguishable in 
 Ayrshire. The Coal Measures may be divided into two groups : the lower, consisting of white and 
 grey sandstones, shales, coals and ironstones ; and the upper, made up of red sandstones and clays. 
 
 Ireland.— In Ireland, the lower beds of the Coal Period are very fully developed. In the 
 
PEACTICAL GEOLOGY. 47 
 
 south, a set of beds composed of grey and greenish-grey grits, with interstratified black and grey 
 slates (the coomhola grits), and a succession of black and grey slates intervene between the old 
 red sandstone and the carboniferous limestone. The latter is magnificently developed. In the 
 north a set of shales and sandstones, called the " Calp," exists in its middle portion. Only the lower 
 members of the coal measures are found, the superior beds having been removed by denudation. 
 These members represent a portion of the millstone grit and Yoredale beds of England. They 
 consist of black shales, with occasional bands of thin grit, grey sandy flags, with black shales ; 
 and black shales and grey grits, containing thin seams of coal. 
 
 The physical aspect of carbon districts is generally flat, or gently undulating, and hence the 
 scenery is unpicturesque. And the soil, being derived from the clays, is usually retentive of 
 moisture, and cold. 
 
 The Permian Period. — Immediately above the coal measures occurs a set of beds consisting 
 of red sandstones and marls, similar in general aspect to the old red sandstone, magnesian lime- 
 stones, and red shales. To these beds the name of Permian has been given, from the government 
 of Perm, in Russia, where they are very fully developed. The series has been divided into two 
 portions, known respectively as the "Lower" and the "Upper Permians." 
 
 The Lower Permians consist of the Lower Red Sandstones and Marls. They form an irregular 
 deposit, and are found lying unconformably upon the coal measures, and in hollows eroded in 
 their surface. They contain fossil plants of the same species as the coal measures. The prevailing 
 colour of these beds is a deep red, but in some localities they are purple or yellow. The Marl Slate, 
 the lowest member of the Upper Permians, is a reddish or brown indurated fissile shale, with 
 occasional thin beds of compact limestone. The Magnesian Limestone is an extensive deposit, 
 remarkable for its singular and diversified structure. In some places it occurs compact ; in others, 
 crystalline, brecciated, oolitic, cellular, and earthy. The concretions are often very remarkable ; 
 sometimes appearing like piles of cannon or musket balls, sometimes like bunches of grapes. In 
 hardness the magnesian limestone varies from the very hard to the easily friable. Its prevailing 
 colour is a light yellow or fawn colour ; but occasionally it is red or brown. When of granular and 
 crystalline texture, it is known as " Dolomite." The Red Marl consists of red and mottled marls, 
 gypseous and saliferous, in some places interstratified with thin beds of limestone. The name of 
 marl has been applied to the shale deposits of this period, rather on account of their occurring in 
 a mottled, friable, and non-laminated state, than because they contain any notable quantity of lime. 
 
 The permian beds as described occur in the north-east of England. In the north-west they 
 consist of the lower red sandstone, red marls, with thin beds of magnesian limestones, and the 
 upper, or St. Bees, sandstone. In the midland counties the limestones die away towards the south, 
 and disappear near Nottingham. There is, however, in Warwickshire, Staffordshire, and Shropshire, 
 a set of beds composed of red marls and sandstones, with thick bands of cornstones and trappoid 
 breccia vphich occupy the same relative position as the permian beds. 
 
 Scotland. — There is in Scotland several detached areas of red sandstones that have been 
 referred to this period, notably those of Dumfriesshire and Ayrshire. 
 
 Ireland. — Red sandstones of the Permian Period are found at Rhone Hill, near Dungannon, 
 in Tyrone ; and yellow magnesian limestones occur at Ardtrea, Tyrone. 
 
 The Triassic, or New Red Sandstone Period. — Overlying the permian beds, and consisting 
 mainly of red sandstones and marls of a similar character, occur the beds known as the Tiia^, or 
 
"^8 MINING ENGINEERING, 
 
 New Bed Sandstone. The term "trias" was applied to this formation by G-erman geologists, 
 because on the Continent it consists of three distinct portions : Bunter, or variegated sandstones ; 
 Muschelkalk, or shelly limestones ; and Keuper, or variegated marls. The " Muschelkalk " is 
 wanting in England; but the "Bunter " and " Keuper" series are largely and distinctly developed. 
 In the place of the Muschelkalk, however, some geologists put the Dolomitic conglomerate of Somerset, 
 Grloucester, and South "Wales. 
 
 The Bunter series consist, in the lower portion, of soft red and mottled sandstones ; in the middle 
 portion, of pebble beds, or uncompacted conglomerates ; and in the upper portion, of soft red and 
 mottled sandstones. The Keuper series are composed, in the lower portion, of brown, yellow, and 
 white sandstones, with thin laminated sandstones and marls, called " water stones," and in the upper 
 portion, of red and mottled marls, with rock salt and gypsum. 
 
 A remarkable and very important feature of the new red sandstone, or " Eed Rock," is that it 
 rests unconformably and indiscriminately upon any or all of the formations already described. 
 Previous to the deposition of these beds, the paleozoic rocks had undergone great distortion and 
 enormous denudation. Upon the irregular surface thus produced, the new red sandstone was 
 deposited in a horizontal or nearly horizontal position ; and hence the beds become thick, sometimes 
 suddenly, where former hollows existed ; thin where the older rocks rise to near the present surface of 
 the ground, and end against these older rocks when they rise into hills, around the margins of which 
 they sweep with a flat or gently undulating surface. In this way, the new red sandstone surrounds 
 the Pennine chain of the north of England, from Lancashire, through Cheshire into Shropshire, 
 Staffordshire, Leicestershire, and Nottinghamshire, and runs down the vale of York to the coasts of 
 Durham. In the same way, it bounds the palseozoic rocks of "Wales from the mouth of the Dee to 
 the mouth of the Severn, and continues thence through Somerset and Devon to the mouth of the 
 Exe. Dr. Buckland, in his ' Bridgewater Treatise,' remarks that if we draw a slightly sinuous line 
 from the mouth of the Tees to the mouth of the Exe, we should divide England into two totally 
 dissimilar parts. The part to the north-west of such a line is chiefly palseozoic ground, wild, barren, 
 and mountainous, but full of mineral wealth. The part to the south-east is secondary and tertiary 
 ground, generally soft and gentle in outline, but containing no wealth beneath the soil. 
 
 The practical importance of the irregularity of the new red sandstone beds will be seen in the 
 facts that when the thickness of the beds has been determined at one point, the thickness at another 
 point only a few hundred yards distant, may be enormously increased or diminished, and that when 
 the beds have been pierced, any one of the older formations may be met with. 
 
 Scotland. — No definitely marked representatives of the trias have yet been discovered in 
 Scotland. 
 
 Ireland. — In Ireland, the new red sandstone formation is confined to County Antrim and its 
 immediate borders, where it is largely developed. 
 
 The physical aspect of triassic districts is flat and generally uninteresting. Though coverino- a 
 vast extent of country, it nowhere rises to a greater height than 800 feet. 
 
 The Jurassic or Oolite Period. — Overlying the trias, occurs a set of beds differing in a 
 marked degree from those beneath them. As these beds are largely developed in the Jura Mountains, 
 they have been called Jurassic on the Continent ; but in England they are more commonly known as 
 Oolite, on account of the presence in them of oolitic limestone. The lower portion of this formation is 
 occupied by an important series of beds called the Lias, a corruption of Hers or layers, a name having 
 
PEACTICAL GEOLOGY. 49 
 
 reference to the thin beds of limestone that occur among them. " The pecuhar aspect," says Sir C. 
 Lyell, " which is most characteristic of the lias in England, France, and Germany, is an alternation 
 of thin beds of blue or grey limestone, with a light-brown weathered surface, separated by dark- 
 coloured argillaceous partings, so that the quarries of this rock assume, at a distance, a striped and 
 ribbon-like appearance." The clays, however, generally predominate, the series being essentially a 
 great clay deposit. The clays or shales are mostly bituminous and pyritous, and it is no uncommon 
 thing for the Yorkshire lias clifis to ignite spontaneously, after wet weather, and to burn for several 
 months. 
 
 The Lias. — At the base of the lias, in the south-west of England, occurs a set of beds sometimes 
 included with the lias, but more frequently referred to as the Eh^tic, Penarth, or Passage beds. 
 They consist of white or cream-coloured, and more or less argillaceous Hmestones, largely developed 
 in Somersetshire, and known as " white lias ; " occasional layers of a greenish siliceous limestone, 
 with iron pyrites, and numerous scales, teeth, and bones of fish and saurians, and hence called bone 
 beds ; and alternations of hard and soft grey or greenish marls, passing imperceptibly down into the 
 red marls of the Keuper. 
 
 The Lower Lias consists mainly of alternating bands of bluish grey argillaceous limestones, and 
 laminated clay or shale. In some parts, as in the west of England where the lias has been depo- 
 sited upon the Palaeozoic rocks, the clays and shales are absent, and the Hmestones become more close- 
 grained and harder. The Marlstone constitutes a well-marked division of the lias ; it is more arena- 
 ceous than the rest of the series, and in parts very calcareous and ferruginous. Frequently workable 
 bands of ironstone occur in the marlstone ; the vast iron deposits of the Cleveland district are in this 
 portion of the lias. The Upper Lias is composed of blue clay and shale, graduating up into the 
 inferior oolite above. In some districts, as in North Yorkshire, these shales contain jet and alum. As 
 developed in England, the lias occupies a belt of varying breadth, extending from Lyme Regis, in 
 Dorset, northwards by Bath, Grioucester, Leicester, Newark, and Grainsborough, to the Humber, and 
 thence to the east coast of Yorkshire. 
 
 The Oolite Series. — Resting upon the lias, the oolitic beds occupy in England a broad parallel 
 belt stretching from Dorset to Yorkshire. The series has been divided into lower, middle, and upper 
 groups, the most important beds in which are : In the lower group, the Inferior Oolite, a coarse, 
 often very shelly, limestone, irregularly oolitic, and occasionally interlaminated with sand in the lower 
 portion ; the Great Oolite, a white ooKtic limestone of variable thickness and character, having a 
 series of sandy flags at its base, and shelly beds at the top, largely developed near Bath, where it 
 forms the famous " Bath stone ; " and the Comhrash, a coarse, shelly and somewhat ferruginous 
 limestone, in a very thin and variable, but remarkably persistent bed. In the middle group, the 
 Oxford Clay, a dark blue and greyish clay, having in its lower portion subordinate bands of 
 argillaceous limestones, and local beds of brown sand, and extending from "Weymouth, in Dorset, to 
 Filey Bay, in Yorkshire. And in the upper group, the Kimmeridge Clay, a greyish blue shaly clay, 
 sometimes brownish or yellowish, containing bands of sand, or calcareous grit. In some places it 
 becomes very bituminous, passing into a kind of poor imperfect coal. 
 
 In Scotland, near Brora, beds similar to the inferior oolites and containing impure coal occur ; 
 and patches of lias and Oxford clay are found along the western coast, and in the islands of Mull 
 and Skye. In Ireland, the only beds belonging to this formation are some liassic shales in some 
 parts of Antrim. 
 
 H 
 
£0 MINING ENGINEEEING. 
 
 The Cretaceotts Period. — The beds of the Cretaceous or Chalk Period are : the Wealden Beds 
 of the south of England, consisting of the Hastings sands, fawn-coloured sands and sandstones, m 
 some parts calciferous, in others ferruginous ; and the Wealden clay, a thick blue clay, containing m 
 its upper part septaria of argillaceous ironstone ; the Lower Greensand, a greenish ferruginous 
 sand, containing layers of calcareous grit and sandy limestone ; the Gault, a bluish tenacious clay ; 
 and the Chalk, divided into two groups, the lower and the upper, the latter being softer and whiter, 
 and containing more flints than the former, which becomes reddish to the north of Cambridgeshire. 
 The chalk formation is most abundantly developed in the south of England. 
 
 The Eocene, Miocene, and Pliocene Periods. — These periods include all the deposits of the 
 tertiary epoch, with the exception of a few of more recent origin, to which the names of " pleisto- 
 cene " and " modern " have been applied. These beds are developed chiefly in the south-east part of 
 England, and are therefore of little importance to the miner, 
 
 ORaANic Remains. — "We have already explained and described the order of superposition of 
 beds, and pointed out the means which this order furnishes for determining the relative age of any 
 bed or set of beds. The observations of palaeontologists have disclosed an analogous order of supers 
 position among the fossil remains existing in the beds. Species and genera which formerly existed 
 have given place to newer species and genera, and these again have been supplanted by others of 
 more recent origin. Some are found only during one age, others extend throughout a whole period. 
 The species do not die out suddenly, but pass by insensible gradations into other species. But a 
 sufficiently definite line may be drawn for practical purposes. It follows from this that when the 
 order of succession of the groups of rocks has been established by direct observation in one district, 
 and the characteristic fossils of each group have been determined, these fossils may be used to 
 identify the groups in another district where, perhaps, their order of succession is not open to direct 
 observation. Here, then, we have another and a very reliable means of identifying rock-beds. The 
 mere lithological character of beds is often deceptive ; but the evidence of fossils is conclusive. 
 From what has already been said concerning the manner and place of deposition of the three 
 kinds of rocks — limestones, sandstones, and clays — it might be inferred that each kind would enclose 
 different and characteristic species of fossil organic remains, since the conditions of life would be 
 favourable to some and unfavourable to others. The shallow, troubled waters of the sandstones ; 
 the deep, turbid waters of the clays; and the still, clear waters of the limestones, would be 
 inhabited by only such forms of life as were capable of existing under the physical conditions 
 peculiar to each case ; and as a matter of fact, the inference is found to be generally true. The 
 practical value of this means of identification can hardly be over-estimated. The following remarks by 
 the late Mr. Jukes, of the Geological Survey, on this subject, are worthy of the attention of practical 
 men : " Within my own experience, large sums of money have been absolutely thrown away, 
 which the slightest acquaintance with palasontology would have saved. I have known, even in the 
 rich coal district of South Staffordshire, shafts continued down below the coal measures deep into the 
 Silurian shales, with crowds of fossils brought up in every bucket, and the sinker still expecting to 
 find coal in beds below those silurian fossils. I have known deep and expensive shafts sunk in beds 
 too far above the coal measures for their ever being reached, and similar expensive shafts sunk in 
 black shales and slates in the lower rocks, far below the coal measures, where a pit might be sunk to 
 the centre of the earth without ever meeting with coal. Nor are these fruitless enterprises a thing 
 of the past. They are still going on, in spite of the silent warnings of the fossils in the rocks 
 
PEAOTICAL GEOLOGY. 51 
 
 around, and in spite of the loudly -expressed warnings of the geologists, who understand them, but 
 who are supposed still to be vain theorists, and not to know so much as ' the practical man.' " 
 
 The fossil remains of each geological period include species far too numerous for illustration in 
 a work not devoted to palseontological considerations. To acquaint oneself with the whole of these 
 species in their multitudinous varieties, and in all their suggestive and highly interesting relations, 
 is the labour of a lifetime, and therefore utterly beyond the reach of him whose duties involve the 
 conduct of practical operations. Nor is it desirable that he should possess such knowledge, even if it 
 were obtainable at a less cost of time ; for much of it bears but very remotely, and some not at all, 
 upon the subjects to which his attention is specially directed. It will, however, be evident from the 
 foregoing statements concerning its bearing upon the relative age of rock formations, that the funda- 
 mental principles of palaeontology and the main facts of that science demand his careful study, as 
 constituting an essential part of his practical knowledge. And having acquired this, he should make 
 himself familiar with the commonest and the most characteristic forms of the organic remains of each 
 period, as illustrations which he may every day turn to useful account. Such forms, reduced to the 
 fewest possible number, are included in the following classifications, and will be found delineated 
 upon Plates VII. to XII. inclusive. 
 
 Characteristic Fossil Remahsts of the Silurian Period. 
 
 Radiata {ray or star-like). — Hydrozoa {water animals), Bastrites, Graptolites, Diplograpsus, 
 Didymograpstis. Echinodermata {spiny skin), Echinosphcerites, Caryocystites, Sphceronites. 
 
 Articulata {jointed). — Crustacea {crah class), AsaphuSy Ampyx, Calymene, Trinucleus, Ogygia, 
 Olenus, Agnostus, IHcenus, Hymenocaris. 
 
 MoLLUSCA {soft animals). — Brachiopoda {arm-footed), Lingula, Orthis, Strophom,ena, Leptcena, 
 Pentamerus. Lamellibranchiata {plate-gill), Avicula. Encephala {having a head), Murchisonia, Euom- 
 pJtalus, Bellerophon. Cephalopoda {head-footed), Orthoceras. 
 
 Characteristic Fossil Remains op the Devonian and Old Red Sandstone Period. 
 
 MoLLiTSCA. — Brachiopoda, Spirifera, Calceola, Stringocephalus. Lamellibranchiata, Megalodon. 
 Encephala, Murchisonia. Cephalopoda, Clymenia. 
 
 Yertebrata {hack-boned^. — Pisces {fishes), Dipterus. 
 Plants . — Adiantites. 
 
 Characteristic Fossil Remains op the Carbon Period. 
 
 Radiata. — Hydrozoa, Archimedipora, Ptilopora, Fenestrella. Anthozoa {flower animals), Lithos- 
 trotion, Lithodendron, Amplexus, Syringopora, Woodocrinus. Echinodermata, Pentremites, Pateriocrinus, 
 PaloBchinus, ArchcBOcidaris. 
 
 Articulata. — Crustacea, Beyrichia, Dithyrocaris, Bellinurus. 
 
 MoLLUSCA. — Brachiopoda, Terebratula, Rhynchanella, Spirifera, Athyris, Orthis, Productus. 
 Lamellibranchiata, Atnculopectm, Posidonomya, Posidonia, Anthrocoptera, Anthrocosia, Ence- 
 phala, Conularia, Euomphilus, Bellerophon, Loxonema. Cephalopoda, Nautiloceras, Goniatites, 
 Orthoceras. 
 
 Yertebrata. — Pisces, Pleuracanthus, Cochliodus, Orodus, Psammodtis. 
 
 H 2 
 
52 MINING ENGINEEEING. 
 
 Plants. — Fruit of Calamites, Trigonocarpm, Lepidostrobus, Sigillaria, Lepidodendron, Catamites, 
 Asterophyllites, Spenopteris, Pectopteris, Neuropteris, Cyclopteris, Odontopteris, Otopteris. 
 
 Characteristic Fossil Eemains of the Permian Period. 
 
 Eadiata. — Bryozoa (moss animals), Synocladia, Fenestrella. 
 
 MoLLUSCA. — Brachiopoda, Producta, Strophalosia, Spirifera, Camarophoria. Lamellibranctiata, 
 Schizodus, Mytilus, Pleurophorus, Encephala, Macrocheilus. 
 
 Vertbbrata. — Pisces, Platysomus, Palceoniscus {scales of), Ccelacanthus, Pygopterus, Acrolepis. 
 
 Labyrinthodon Eemains of the Triassic Period. 
 Footprints of Lahyrinthodon ; teeth of the same. 
 
 Characteristic Fossil Remains of the Lias. 
 
 Eadiata. — Echinodermata, Extracrinus, Ophioderma. 
 
 Molltjsca. — Brachiopoda, Spirifera, Terehratula. LamellibrancTiiata, Gryphcea, Amcula, Ostrea, 
 Hippopodium. Encephala, Pleuroto^maria. Cephalopoda, Ammonites, Belemnites. 
 
 Vertebrata. — Pisces, Acrodus, scales of Echinodus, Dapedius. Eeptilia (reptiles), Ichthyosaurus, 
 Plesiosaurus. 
 
 GrEOLOGiCAL SURVEYING. — The making of Greological Surveys constitutes one of the most 
 important duties of the mining engineer. This kind of work does not, indeed, enter largely or 
 definitely into his ordinary occupations as do many of his other duties connected with the active 
 management of a colliery. But he may at any moment be called upon, and frequently is called upon, 
 to inspect and report upon a supposed extension of a known coal-field, or a newly-discovered field iu 
 some new district, in, perhaps, a new country. To do this, he must not only possess the requisite 
 geological knowledge, but he must also know how to apply it so as to enable him to solve the pro- 
 blem in question, and how to present the results of investigations so as to be intelligible to other 
 persons. Moreover, even in the sinking of new pits in well-known districts where he is not closely 
 surrounded by old workings, he will have to estimate from data obtained from a survey the dip of 
 the seam to be won, the depth at v^hich it will be struck, its strike, and other conditions of primary 
 importance to the success of the undertaking. Hence it may be assumed that the following brief 
 directions for the production of geological plans and sections will not be considered as forming an 
 inappropriate close to the present chapter. 
 
 Character of Rock-Beds. — Being provided with the means of determining the nature of rocks, 
 as already described, the first thing to be done is to procure a map of the district to be surveyed, to a 
 scale of six inches to a mile, or thereabout. If no such map exists, one will have to be made. This 
 map should then be cut up into portions of a convenient size for use in the field. In commencino- 
 the survey, the observer should make himself acquainted with the geography of his district by 
 traversing it in various directions, and viewing it from elevated positions, so as to get a thorough ' 
 knowledge of its surface configuration, and in doing this he should note the lithological character 
 of the most prominent I'ock masses. The detailed survey may then be proceeded with by examinino- 
 carefully the whole surface of the ground, and indicating the character of the rocks of which it is 
 composed by conventional signs previously determined upon. This part of the survey is beset with 
 difficulty in consequence of the existence of vegetable soil. Hence the observer will have to seek 
 
PEACTICAL GEOLOGY. 53 
 
 4spots where the rocks are exposed, and these exposed portions he must mark down on his map in the 
 exact space which they occupy. When igneous rock is met with, its character must be observed, and 
 its mode of occurrence noted, that is, whether it be intrusive or otherwise. Obviously the accuracy 
 of the inferences drawn will depend, first, upon the abundance of the data ; in other words, upon the 
 number of places where the rocks are exposed ; and, second, upon the care with which the observa- 
 tions are made. This remark applies equally to the points to be hereafter considered. 
 
 Dip and Strike of Rock-Beds. — While making himself acquainted with the character of the 
 rock-beds, the observer must be careful to ascertain their dip. For this purpose, he will have to seek 
 localities where a " section " can be seen. The best exposures of this character will be found, in ditches, 
 road-sides, pits, quarries, banks of streams, railway cuttings, wells, mining shafts, or any surface 
 openings that may occur. In taking the dip, he must be ever on his guard lest he be misled by 
 oblique lamination, cleavage, or other indications of cross fracture, or by layers displaced by the grow- 
 ing roots of trees. The amount of the dip is measured in degrees by means of a clinometer, and its 
 direction is determined by the aid of a pocket-compass. To ensure accuracy, the dip should be 
 measured and the character of the rock noted wherever a square foot can be found exposed. In 
 examining sections, the observer should endeavour to obtain a view of a group of rock-beds, in order 
 that when he meets with an exposure of any one of them, he may be able to infer the position and 
 thicknesses of the others. The dip is indicated on the map by means of an arrow placed in its proper 
 position with respect to the north point, and marked with the number of degrees. Thus, arrows point- 
 ing in contrary directions will denote an anticlinal curve, while arrows pointing towards each other 
 will indicate the existence of a synclinal curve. Every change in the amount and the direction of the 
 dip demands careful attention. Such changes may be merely local or superficial flexures, instead of 
 belonging to the great and general bendings of the rocks. And it must be borne in mind that when 
 one fold dies out, and another begins at the same time to rise on one side or the other, there will be, 
 as a consequence, transverse strikes over the district between the approximate ends of the two folds. 
 And also that when the dip is slight, the variations in the strike are often great ; and that, therefore, 
 a careful comparison of all the results over a wide range of country, and of the bendings indicated, 
 may be necessary, to ascertain the true direction of the axis ot elevation. As the strike is at right 
 angles to the line of direction of the dip, the latter will, of course, determine the former. 
 
 Boundaries of Rock-Beds. — When the character and the dip of a bed have been determined, its 
 upper and lower boundaries should be laid down on the map. In tracing these boundaries on the 
 ground, the observer should bear in mind that when the surface is uneven, the strike of the bed will 
 not correspond with its line of outcrop. It is obvious that when the angle of the dip is low, a 
 slight undulation of the ground will cause the outcrop to deviate widely from the line of its strike. 
 Also a slight change in the strike or in the amount of the dip will produce a much greater effect than 
 when the beds are inclined at a high angle. The observer must likewise endeavour to keep in his 
 mind the ascertained thickness of the bed he is tracing, and the relation of the changes in the dip 
 and the strike to the different features of the surface. It will be evident from what has been said 
 respecting the thinning out of rock-beds, that the bed which is being traced may, within a short 
 distance, change its character from a sandstone to a shale, or from a shale to a limestone. Also if it 
 retain a uniform composition it may change completely in colour within a few yards, so as to be no 
 longer recognizable by the mere appearance. Such changes are not to be regarded as producing a 
 new bed. 
 
54 MINING ENGINEEEING. 
 
 Faults. — The direction of dykes must be accurately laid down upon the map, as determined by 
 the magnetic needle, and their character indicated. The boundaries should be carefully traced, and 
 their effects upon the contiguous strata noted during the survey. Faults of dislocation demand par- 
 ticular attention ; and here the observer should be cautioned against hastily drawing the conclusion 
 that a fault exists, from certain appearances which at first sight seem to warrant such a conclusion. 
 And this caution is especially necessary when the suspected fault is the first observed in the district. 
 In such a case, absolute proof should be required. When one line of fault has been proved beyond all 
 question to exist, there must be almost necessarily others, either parallel, or at nearly right angles to 
 it. Respecting the existence of these, therefore, a less amount of evidence may be sufficient. But 
 when an appearance may be accounted for on any other grounds than the presence of a fault of dis- 
 location, there is reason for further observations before arriving at a decision. When, however, a 
 dislocation has undoubtedly occurred, the character and the amount of the throw must be ascertained ; 
 and in observing these, the apparent lateral shift, and other effects previously described, must be 
 borne in mind. 
 
 Besides geological plans, " sections " are needed to show the relations of the beds to each other, 
 that is, their lie and relative position. The section shows the direction and amount of their inclina- 
 tion beneath a horizontal plane, and the depth attained by any given bed under any spot at a given 
 distance from its outcrop. In preparing such a section, a horizontal datum line is assumed, and the 
 beds drawn with their proper angle of dip with this line. The undulations of the surface are also 
 drawn in with reference to this datum line. The line of section is generally taken at right angles 
 to the strike, so that the section shows the true dip of the beds. Before, however, a section can be 
 drawn, the thickness of the beds whose boundaries have been previously laid down on the plan must 
 be determined. 
 
 Thickness and Depth. — When the upper and lower boundaries of a bed, in other words, its 
 basset edges, have been determined, and the amount and direction of its dip ascertained, its thickness, 
 its depth, or the vertical distance through it, and the distance from surface at which it will be met 
 with from any given point may be easily calculated. For this purpose it is only necessary to 
 measure the width of the basset edge of the bed, or group of beds, at right angles to the strike. This 
 width must be measured in a horizontal line, and therefore, if the surface of the ground is inclined or 
 undulating, the horizontal distance must be determined by the ordinary methods. For example, 
 suppose we wish to know the thickness of the beds comprised between the points a and d. Fig. 4, 
 Plate II. Let I be the horizontal distance between a and d, and 6 the angle of the dip. Then the 
 thickness of the beds a b, measured at right angles to the dip, will be given by the formula, 
 
 t = I sin. 0. 
 
 So, also, the depth of the beds, that is, the vertical distance from the point a to the point c. will 
 
 be given by the formula, 
 
 d = I tan. 6. 
 
 It is obvious that the thickness and depth of any given bed, and its distance from surface at any 
 given distance from its outcrop, may be readily determined in this way. 
 
 It will also be evident that if a table of natural sines and tangents be constructed to, say, four 
 places of decimals for the whole angles — for the minutes are practically useless, — we may ascertain 
 the thickness and depth by mere inspection ; and, moreover, that such a table may be used for 
 
PRACTICAL GEOLOGY. 
 
 55 
 
 calculating the space between the outcrop of two beds whose angle of dip is known, and the thickness 
 
 between them ; and the distance at which any bed, whose depth and inclination are known, will crop 
 
 out to the surface. Also the probable throw of a fault may be ascertained from the table, when the 
 
 ends of a bed can be fotmd on both sides of a fault, and a mean angle of dip assigned to the whole mass. 
 
 For example, if we have a bed, as a a, in Fig. 20, Plate IV., traversed by a fault h b, and the outcrops 
 
 be foimd in such a position that the distance c b can be measured, the table will give us the depth 
 
 which the downcast portion has attained in the distance cb, which depth will, of course, be the 
 
 amount of throw of the fault. Indeed, such a table is of continual use to the practical geologist. 
 
 Oblique Sections. — In most cases, the line of section is taken at right angles to the strike, and 
 
 such sections will, of course, show the true dip of the beds. But circumstances may exist which render 
 
 an oblique section desirable, that is, one that shall cross the line of the dip at an acute angle ; and, 
 
 indeed, in running a section across a greatly disturbed district, it will almost of necessity cross the 
 
 line of the dip obliquely in some parts. It may even happen that the line of section will run along 
 
 the strike. In the latter case, the beds will appear horizontal in the section, and their apparent will 
 
 not be their true thickness, but will be greater than their true thickness. Also, when the line of 
 
 section crosses the line of dip obliquely, the apparent will not be the true dip, but will be less than 
 
 the true dip. In order to draw such a section correctly, the necessary correction of the true dip must 
 
 be made by means of the following formula, due to Mr. Hopkins, past President of the Geological 
 
 Society : , 
 
 tan. z = — '—, or log. tan. z = log. tan. y — log. sec. x ; 
 
 sec. X 
 
 in which z is the angle of the apparent dip, y that of the true dip,, and x that of the line of section 
 with that of the true dip. The angle x is always to be calculated on that side of the line of section 
 where the angle is less than 90°. And it is evident that the direction of the dip corresponding to a 
 given angle on one side of that line, will be contrary to that corresponding to the same angle on the 
 opposite side. It is important that the correction for the apparent angle should be carefuUy attended 
 to, not only for the purpose of accurately representing it, but also for determining the depth of beds, 
 and for drawing in the true angle of lines of faults, veins, dykes, and cleavage planes. The following 
 table, calculated from the above formula, gives the correction for the most useful angles : 
 
 OBLIQUE SECTION TABLE. 
 
 Angle 
 
 
 
 
 
 
 Angle of the Dip = 
 
 y- 
 
 
 
 
 
 otthe 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Section = x. 
 
 5° 
 
 10° 
 
 15° 
 
 20° 
 
 25° 
 
 30° 
 
 35° 
 
 40° 
 
 45° 
 
 50° 
 
 55° 
 
 60° 
 
 o 
 
 O ' 
 
 o ' 
 
 o / 
 
 O ' 
 
 O ' 
 
 O ' 
 
 o / 
 
 o < 
 
 O ' 
 
 O 1 
 
 O ' 
 
 O ' 
 
 5 
 
 4 59 
 
 9 58 
 
 14 57 
 
 19 56 
 
 24 55 
 
 29 50 
 
 34 54 
 
 39 51 
 
 44 53 
 
 49 54 
 
 54 54 
 
 59 54 
 
 10 
 
 4 55 
 
 9 51 
 
 14 47 
 
 19 43 
 
 24 40 
 
 29 37 
 
 34 35 
 
 39 34 
 
 44 34 
 
 49 34 
 
 54 35 
 
 59 37 
 
 15 
 
 4 50 
 
 9 40 
 
 14 31 
 
 19 22 
 
 24 15 
 
 29 9 
 
 34 4 
 
 39 2 
 
 44 
 
 49 1 
 
 54 4 
 
 59 8 
 
 20 
 
 4 42 
 
 9 25 
 
 14 8 
 
 18 53 
 
 23 40 
 
 28 29 
 
 33 21 
 
 38 15 
 
 43 13 
 
 48 14 
 
 53 18 
 
 58 26 
 
 25 
 
 4 32 
 
 9 5 
 
 13 39 
 
 18 15 
 
 22 54 
 
 27 37 
 
 32 24 
 
 37 15 
 
 42 11 
 
 47 12 
 
 52 19 
 
 57 4 
 
 30 
 
 4 20 
 
 8 41 
 
 13 4 
 
 17 30 
 
 22 
 
 26 34 
 
 31 14 
 
 36 
 
 40 54 
 
 45 54 
 
 51 3 
 
 56 18 
 
 35 
 
 4 6 
 
 8 13 
 
 12 23 
 
 16 36 
 
 20 54 
 
 25 19 
 
 29 50 
 
 34 30 
 
 39 19 
 
 44 56 
 
 50 20 
 
 54 49 
 
 40 
 
 3 50 
 
 7 42 
 
 11 36 
 
 15 35 
 
 19 39 
 
 23 51 
 
 28 16 
 
 32 44 
 
 37 27 
 
 42 25 
 
 47 34 
 
 53 
 
 45 
 
 3 32 
 
 7 6 
 
 10 44 
 
 14 26 
 
 18 15 
 
 22 12 
 
 26 21 
 
 30 41 
 
 35 16 
 
 40 7 
 
 45 17 
 
 50 46 
 
 50 
 
 3 13 
 
 6 28 
 
 9 47 
 
 13 10 
 
 17 28 
 
 20 22 
 
 24 14 
 
 28 20 
 
 32 44 
 
 37 27 
 
 42 33 
 
 48 5 
 
 55 
 
 2 52 
 
 5 46 
 
 8 44 
 
 11 47 
 
 14 58 
 
 18 19 
 
 21 53 
 
 25 42 
 
 29 50 
 
 34 21 
 
 39 19 
 
 44 59 
 
 60 
 
 2 30 
 
 5 2 
 
 7 38 
 
 10 19 
 
 13 7 
 
 16 6 
 
 19 17 
 
 22 45 
 
 26 34 
 
 30 27 
 
 35 32 
 
 40 54 
 
56 MINING ENGINEEEING. 
 
 CHAPTER 11. 
 
 COAL: ITS MODE OF OCCUBKENCE, COMPOSITION, AND VARIETIES. 
 
 EocKS ASSOCIATED WITH CoAL. — Though coal is found, in several parts of the world, among rocks 
 of different periods, practically it may be considered as existing only among those of the Carbon 
 Period, so called on account of the occurrence of abundant coal deposits. For in no other period are 
 the deposits of suflScient extent or of sufficient quality to be commercially valuable. Hence, searching 
 for coal in any other formation is a labour holding out but faint hope of reward, and discoveries of 
 deposits in such situations merit but little attention from a practical point of view. 
 
 The coal measures consist, as we have stated, of an alternation of sandstones and argillaceous 
 rocks, with occasional seams, beds, or bands of coal and ironstone. The sandstones vary in texture from 
 the finest grained rock to the conglomerate. The fine-grained varieties, however, largely predomi- 
 nate. They are frequently micaceous, and of various degrees of hardness. The finer the particles of 
 which a sandstone is composed, the larger is the proportion of quartz present, and, generally, the more 
 strongly agglutinated is the rock. The cement which serves in most cases to agglutinate the particles 
 is silica, and when present in large proportions, the rock requires much labour and time to cut 
 through, and occasions a rapid wear of the tools employed. When a sandstone is micaceous, it 
 becomes brittle, and quickly crumbles on exposure to atmospheric agencies. The ability of a rock to 
 withstand the disintegrating action of these agencies may be known in great measure by its avidity 
 for moisture, the more absorbent being the less durable. The fine-grained sandstones generally form 
 thick and homogeneous beds, extending over large areas; the coarse-grained have been deposited 
 mainly in troughs and basins. The sandstones of the coal measures are white, yellowish grey, or pale 
 blue ; sometimes they are coloured reddish or brownish by a ferruginous cement, and occasionally 
 blackish by the presence of carbon. 
 
 The argillaceous rocks consist sometimes of thick beds of plastic clay, more frequently of 
 thinner beds of indurated schistous clay, called " shale." The foliated structure of these shales is 
 exhibited in numerous thin laminas varying considerably in colour, hardness, and fineness of grain ; in 
 occasional layers of mica ; in vast numbers of vegetable impressions between the laminse, when 
 lying immediately above the coal; and especially in the property which the rock possesses of 
 swelling as it absorbs the moisture of the atmosphere, and finally separating into thin laminae. The 
 surfaces of these laminae are soft and unctuous to the touch, like plastic clay, and adhere to the 
 tongue. If placed in water, shale moulders into powder. The shales are the most distinctly coloured 
 of all the rocks of the carboniferous formation ; generally they are of a bluish or yellowish grey 
 colour, more rarely of a dark blackish or reddish grey, or greyish black, or greenish colour. The 
 black hue is probably due to the presence of bituminous matters, for when exposed to the action of 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 57 
 
 fire this colour disappears. These bituminous or carbonaceous matters are sometimes present in 
 large proportions. They have been derived from vegetable remains deposited with the earthy- 
 materials of which the shale is composed, and, in some cases, from the gases evolved from underlying 
 seams of coal. Such shales are called bituminous, and when rich in characteristic matters, they con- 
 stitute a valuable source of mineral oil. They are less fissile, more compact, and more sonorous than 
 the common shales, which they resemble exactly in external appearance. A pecuKarity which clearly 
 distinguishes them from the common or slightly bituminous shales lies in the fact that when a thin 
 paring is cut along a surface, it curls up before the knife, and leaves a brown, lustrous streak. This 
 peculiarity is very distinctly marked in some of the Scotch shales. Bituminous shale bums with 
 abimdant flame, emitting a dense smoke, and leaving as a residue the pure shale, white, and reduced 
 to thin laminae. 
 
 In most cases, a bed of shale lies immediately beneath and immediately above a seam of coal. 
 That which hes beneath, and which is known as the under clay, forming the floor, thill, or seat of 
 the coal seam, generally consists of a more dense and plastic clay than that which lies above the seam, 
 and forms its top or roof. The under clay formed the soil upon which the plants grew from which 
 the coal is derived, and, as might have been expected, it contains numerous traces of roots. These 
 traces consist of dark, carbonaceous, fibrous-looking streaks, traversing the mass in all directions. 
 Sometimes the rootlets are preserved in a more distinct form. It is remarkable that nothing but 
 roots are found in the under clay. The most common are stigmaria, the roots of the sigillaria. This 
 under clay usually constitutes a fire-clay, and when of the requisite composition and degree of 
 hardness, it becomes of great value for brick making, and other purposes where materials of a 
 refractory nature are required. As the under clay originally formed the soil upon which the coal 
 plants grew, we might expect that it would be everywhere and invariably present, and as a matter of 
 fact it is so generally, the exceptions being of rare occurrence. Whenever the under clay is absent, 
 it may be inferred that the materials of which the coal was formed were drifted into their present 
 situation. The existence of the under clay greatly facilitates the extraction of the coal. The shale 
 of the roof is of a more indurated character than that of the floor, its structure being that of a true 
 shale. It contains remains of plants in wonderful profusion, rivalling in variety the collections of 
 princely conservatories. Erect stumps of sigillaria often exist in the roof shale; sometimes vast 
 numbers are found within a small area. They are pretty uniformly scattered over the seam, and 
 appear to have grown upon the surface of the coal, into which their roots have been incorporated. 
 Grenerally these stumps are but a few feet in height, but they may be as much as six feet in diameter 
 at the base. Being conical in shape, they are liable to drop out suddenly after the coal has been 
 removed from beneath them, and as their weight may be little short of a ton, they constitute very 
 dangerous associates of the shale roof in workings. They are known to the colliers as " pipes," " pot- 
 bottoms," and " bell-mouths," and have to be carefully watched and propped. Their circular outline 
 may be traced in the shale of the roof. The character of the shale constituting the roof is of con- 
 siderable practical importance, a strong, highly tenacious shale being the most favourable to ease and 
 economy of working. The roof shale is more frequently absent than the under clay, and its absence 
 is decidedly detrimental to the quality of the coal. 
 
 Bands of nodular ironstone, of variable thickness and irregular in extent, occur in most of the 
 coal-fields of Great Britain, and constitute one of the chief sources from which our supply is derived. 
 These concretions, which form layers in shale or clay, are sometimes of very small size, and are 
 
 I 
 
58 MINING ENGINEERING. 
 
 locally designated by sucli names as " Pins " or " Pennystones," as, for example, tlie Pin-ironstone 
 seam of Staffordshire. Sometimes they are large spheroidal masses, several inches and even one or 
 two feet in diameter. In some instances a band of clay-ironstone occurs as the roof of a coal seam. 
 There are many districts, notably in North Staffordshire and parts of Scotland, in w^hich seams of 
 ironstone are found containing a large proportion of carbonaceous matter; these are known as 
 " black bands." 
 
 Mode op Occurrence and Origin of Coal. — Coal occurs as beds or seams interstratified with 
 the sandstones and shales of the Carbon Period. It is not the result of a deposition, like the sand- 
 stones and shales, nor had its materials the same origin. The aqueous rocks are formed of the same 
 elements as the igneous rocks, from which they have obviously been derived. But coal is composed 
 of the elements which enter into the composition of vegetable organisms, namely, carbon, hydrogen, 
 and oxygen, though the proportions are different. An examination of its structure reveals evidence 
 of abundant vegetable remains — evidence which is strengthened by the existence of innumerable 
 roots in the under clay. Indeed, there can be no doubt that coal seams are the remains of a former 
 mass of luxuriant vegetation : of submerged pine-forests, jungle growths, and peat-mosses. In most 
 cases these masses were covered up by new deposits on the spots on which they grew ; but some- 
 times they were drifted into other situations previously to the deposition of the overlying beds. 
 The action of chemical agencies, and the enormous pressure of the superincumbent rocks, have 
 produced in these so-called deposits those changes of composition and structure which distinguish 
 the coal seams from the peat-bogs of the present day. Deriving their origin from such a source, 
 coal seams must necessarily vary greatly in thickness, since the vegetation of one age, or of one 
 place, would differ widely in character, luxuriance, and length of existence from that of another 
 age or place ; and as a matter of fact, we find seams varying from one inch to thirty feet and 
 upwards in thickness. 
 
 As coal occurs in beds interstratified with the aqueous rocks, it is subject to all the accidents which 
 the latter are subject to ; that is, to all those various effects which in the preceding chapter have 
 been described as "Faults," and "Results of Denudation." These having been fully described in 
 relation to the soft aqueous rocks, need no further remark here. 
 
 Composition op Coal Seams. — A block of compact coal, though differing essentially in origin 
 and mode of formation from a similar block of shale, is yet, like the latter, made up of thin laminae. 
 These laminae are frequently slightly undulating, and they vary considerably in texture and thick- 
 ness. It is, however, worthy of remark that the thickness is invariably greater in the lustrous than 
 in the non-lustrous varieties. The character of the lamina, too, is very variable, not only in different 
 localities and in different seams, but even in the same block of coal. Some experiments, undertaken 
 by M. Burat, for the purpose of investigating this remarkable phenomenon, showed that in those 
 instances which, on these occasions, came under his observation, there was an alternation of 
 laminae composed of a homogeneous, compact, specular, and very light substance, giving less than 
 2 per cent, of ash, with others of a less pure composition, being largely mixed with earthy matters, 
 and leaving from 20 to 25 per cent, of ash. Other variations occur among the laminae of coal; 
 sometimes in the most bituminous qualities, laminse of an anthracitous character are occasionally 
 present. 
 
 When a seam is of considerable thickness, it rarely constitutes a compact and homogeneous 
 mass, but is formed of two or more beds. These beds are separated from each other, sometimes 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 59 
 
 by a simple plane of division, sometimes, and more frequently, by an interstratified bed of earthy 
 material. Such planes of division are called " partings," the latter kind being distinguished as 
 " dirt partings." Partings constitute a very important feature of coal seams. The more numerous 
 they are in a seam of a given thickness, the smaller will be the blocks of coal extracted. But of 
 greater moment is the impurity which they are liable to occasion when formed of an intercalated 
 bed of carbonaceous shaly matters. Being in most cases of a very tender and friable character, they 
 faR with the coal, and become intermixed with the smaller portions. The labour of picking out the 
 partings when they are numerous or thick adds materially to the cost of getting the coal, and the 
 reduction in the size of the blocks caused by the presence of the partings, and the impurity which, 
 in some degree, they inevitably occasion, lessens the value of coal when got. This is especially the 
 case when the coal is tender and friable. If, however, the partings are few, and only three or four 
 inches in thickness, their presence is greatly advantageous to the miner, inasmuch as it enables him 
 to undercut or hew the coal along these partings. 
 
 The plane of division between the coal and the shale of the roof is often an imperceptible one, 
 the two surfaces so adhering that when the coal is worked away, either a few laminae of the latter 
 remain suspended to the roof, or, if the shale is tender, a few laminae of the roof material may come 
 away with it. Sometimes the plane of division is clear and distinctly determined ; in such cases the 
 coal will come away clean. The same remarks apply to the partings. 
 
 The several beds of coal of which a seam is made up are rarely identical in quality, and, as a 
 general rule, it will be found that the thicker the parting the greater will be the difference in the quality. 
 Thus the same seam may furnish several qualities of coal. This circumstance has always to be taken 
 into consideration in valuing the product of a seam. The difference in quality of the several beds 
 may assume various forms. Thus one may be of a more bituminous character than another, or it 
 may be thinner, and thus furnish smaller blocks ; or it may be more mingled with impurities ; or, 
 again, it may be more tender and friable, in which case the seam will yield simultaneously large 
 and small coal proportionately to the thickness of each bed. All of these circumstances materially 
 influence the value of the seam. 
 
 The constituents of coal we have already stated to be carbon, hydrogen, and oxygen. These 
 constituents, however, never exist pure, but are more or less intermixed with other matters. The 
 impurities may be classed as essential and accidental ; the former being those which entered into 
 the composition of the vegetable substances from which the coal was formed, and the latter those 
 which have been intermixed with these substances. The essential impurities consist of silica, 
 alumina, lime, magnesia, and oxide of iron, to which may be added water. The accidental impurities 
 may consist of any substance other than the three elements mentioned. Some of these have been 
 introduced by the infiltration of water holding the substances in solution. In general, the accidental 
 impurities consist of earthy matters, which were probably deposited from water flowing among the 
 coal vegetation, or blown thither by the winds. The quantity of earthy impurities present in any 
 given sample of coal is estimated by weighing the ash after combustion. When the weight of the 
 ash does not exceed 5 per cent, of that of the coal, the latter is considered very pure. Above that 
 proportion, it begins to lose in quality, and becomes hard and shaly in structure. 
 
 A common impurity is iron pyrites, or bisulphide of iron, a substance known to coal 
 miners as " brasses/' and hence seams containing it are described as " brassy." Pyrites occurs 
 sometimes as a deposit filling the cracks and fissures in the coal; sometimes as thin 
 
 I 2 
 
60 
 
 MINING ENGINEERING. 
 
 intercalated beds. It is not unfrequently met with running with a line of parting ; occasionally 
 it occurs as cubical and octahedral crystals disseminated throughout the mass ; and more often as 
 minute particles imperceptible to the naked eye. The presence of iron pyrites detracts greatly from 
 the value of coal by rendering it unsuitable for many important uses. Coal containing this mineral 
 is totally unfit for metallurgical purposes, and it cannot be burned anywhere in contact with iron 
 without serious injury to the latter. Hence it cannot be employed for the generation of steam, as 
 its corroding action would rapidly destroy the fire-grating and the lower plates of the boiler. 
 Moreover, pyrites is decomposed by moisture and converted into a sulphate, and the expansion 
 which takes place during the process tends to break the coal into very small lumps, and even to 
 a powder. This decomposition is often accompanied with great heat, and spontaneous combustion 
 is not unfrequently occasioned thereby. Heaps of brassy small coal and rubbish, lying as refuse 
 on the pit-bank, often take fire from this cause in wet weather, and, which is of far more 
 disastrous consequence, the exposed coal in the workings will sometimes become ignited. When 
 pyrites occurs as layers, especially when running with a line of parting, it may be picked out 
 without much labour or expense ; but when occurring otherwise, the separation cannot, in practice, 
 be effected. 
 
 Coal seams, even of the same variety of coal, differ from each other considerably in physical 
 condition. Some are very soft and tender. Such seams require but little labour to work, but the. 
 coal is extracted in small blocks, and is therefore of less value in the market. It also gets much 
 broken by the repeated operations of loading, unloading, and conveyance, which, besides lessening 
 the value still further, render it unfit for many uses. Coal of a tender, friable character is described 
 by the miner as "mingey," and "dicey" when it breaks into small cubical fragments like dice. 
 Hard seams furnish strong coal in large blocks, but they require much greater labour to work them. 
 Sometimes seams, even of hard coal, are much broken and traversed by joints. In such cases, the 
 seam will make a large proportion ot small coal, and frequently the quality will be found to have 
 undergone deterioration in other respects. Even the most compact seam may become much broken 
 on approaching a fault. The intrusion of dykes and veins of igneous rock will often injure the 
 contents of a coal seam for considerable distances. Some seams give off large quantities of car- 
 buretted hydrogen gas, and thereby necessitate additional care and expense in the working. All 
 of these " accidents " may be considered general, because every seam is liable to be affected by one 
 or more of them. Others there are of a more local character, but equally requiring to be taken 
 into consideration when estimating the value of a coal seam. 
 
 The Cleat, Slyne, or Face of Coal. — Coal being made up of laminae cleaves most readily along 
 the planes of stratification, like a shale or any other laminated rock. It is also regularly traversed 
 by the joints which run through the rocks associated with the seam. But besides these, it is divided 
 into smaller cubical blocks by two sets of joints running at right angles to each other, and at right 
 angles to the planes of lamination. One of these sets is more persistent than the other, and gives 
 a "more smooth and even face. This set constitutes what is called by miners the " cleat " or " slyne " 
 of the coal, and the even surface produced by it is called the " face," in opposition to the more 
 irregular surface produced by the other set, which is called the " back " or " end." These cleavage 
 planes, which are but slightly analogous to those of cleavage as already defined, are persistent over 
 very large areas ; the direction may, however, be changed by a fault. In some districts both sets are 
 very distinctly developed ; in others, one set becomes confused and faint. Occasionally these planes 
 
COAL : ITS MODE OP OOOUEEENCE, COMPOSITION, AND VAEIETIES, 61 
 
 are oblique to those of lamination, or to each other, and in such cases the coal divides into wedge- 
 shaped or angular blocks. The fresh surfaces formed by these planes of cleavage soil the fingers 
 much less than those corresponding with the planes of lamination. 
 
 The cleat of coal, which may be clearly seen in hand specimens, is a true joint structure, 
 occasioned by the shrinkage consequent on desiccation, its more perfect development in the coal 
 than in the adjacent rocks being due to the greater tenderness of the former. And hence it is that 
 this peculiar structure is more fully developed in the more tender varieties of coal. The cleat is of 
 very great importance in mining, inasmuch as the direction of the workings is determined thereby. 
 
 Distinctive Characters and Identification of Seams. — In consequence of the interruptions 
 occasioned by faults, denudation, and other accidents, it is impossible to identify a seam of coal from 
 its position alone. The upper seam in one portion of a coal-field may not be identical with the 
 upper seam in another portion of the same field, and if we take two separate districts, the upper 
 seam of the one may be the lower seam of the other. It is, however, of the highest practical 
 importance to identify the seam in any new winning, for by this means the whole composition of the 
 field is made at once manifest, and in numerous instances the continuity of the field over an area 
 that was previously thought to be barren, is clearly and indisputably established. In every geological 
 survey, therefore, besides the evidence furnished by the adjacent strata, the characteristic features of 
 a seam of coal as existing in one part require to be carefully noted to enable us to recognize it in 
 another part. Such features are : the number of the layers or beds of coal of which the seam is 
 composed ; their thickness, quality, and physical condition ; the character of the cleat ; the nature of 
 the partings, and of the substances composing them ; the constitution ot the floor and the roof ; tlie 
 fossil remains in the latter ; the character of the adjacent rocks ; and the position of the seam with 
 respect to others previously determined. It must not be expected that when a seam is struck in 
 a new part it will present all the characteristics which it possesses in another ; frequently some will 
 be altogether absent, while others will have undergone modification. But in no case will they be 
 all absent or modified. 
 
 To trace the continuation of a seam of coal throughout a considerable distance when the ground 
 has been much disturbed by faults and contortions, and the characteristic features as determined in 
 another part have undergone frequent and considerable modification, is ofttimes a very diiScult task. 
 In such cases, assistance may be derived from the overlying rocks. , A bed of sandstone, or of shale, 
 may have preserved its distinctive character, when that of the coal has been all but destroyed, and the 
 landmark thus preserved may enable the doubting miner to determine his position with certainty. 
 
 Classification of Coal. — Coal differs widely in chemical composition and in physical con- 
 dition, not only from district to district, but from seam to seam in the same district, and, as we have 
 shown, from bed to bed in the same seam. This variety necessitates a classification, both on scientific 
 and commercial grounds ; and several classifications have been proposed and more or less adopted, in 
 accordance with each of these points of view. None of these, however, are sufficiently comprehensive 
 to be satisfactory even in their own special domain, and hence recent writers have endeavoured to 
 form a new and general classification which should be definite enough to group the most important 
 qualities, and comprehensive enough to include all varieties. 
 
 By tracing the progress of the formation of coal through all its known stages, however, we arrive 
 at certain definite facts upon which a satisfactory classification may be based. Derived originally from 
 vegetable matters, coal has undergone since its submergence changes that have radically altered its 
 
62 MINING ENGmEEEma 
 
 primitive nature. In colour, it has passed from white, through every shade of brown, to black. Its 
 density has been more than doubled. Its constituent oxygen and hydrogen have partially disap- 
 peared. The former especially has been gradually and constantly eliminated, so that the solid 
 combustible subjected to these modifications shows by its excess of carbon and its defect of oxygen 
 the extent of the changes that have been produced. The relative decrease of the hydrogen is also 
 clearly perceptible, though much less well marked than that of the oxygen. Thus we have three 
 important effects of age, by means of which we may characterize any variety ol coal : An increased 
 proportion of carbon ; a consequent augmentation of the specific gravity ; and the ratio of the oxygen 
 
 and nitrogen to the hydrogen — =^—. In proportion as the oxygen diminishes, and consequently 
 
 the proportion of water produced by distillation, the coal tends to become more friable, less sonorous, 
 more dense, and of a blacker colour. Its brightness especially increases with the proportion of 
 hydrogen ; and with the hydrogen also, its caking quality. The readiness with which it ignites, 
 and the abundance of its flame, depend upon the volatile matters which it contains. The varieties 
 which are closely related to the lignites kindle readily, and burn with a long and fuliginous flame. 
 Those which are less rich in volatile matters, and especially in hydrogen, kindle less readily and 
 bum more slowly with less flame. The presence of impurities may greatly modify these qualities, 
 but generally they will be found to exist, and any classification founded upon the conditions which 
 produce them must be in the main satisfactory. Such a classification is the following, which divides 
 coal into four classes, described as the Anthracitous, the Semi-Bituminous, the Bituminous, and the 
 Gaseous. 
 
 Anthracitous Coal. — The seams of anthracite are the lowest in geological order, and they owe 
 their distinctive character to their position. Having been more subjected than those above them to 
 metamorphic agencies, they have undergone a greater amount of change. The volatile matters 
 which originally entered into the composition of the coal have been expelled by heat, and hence the 
 residue which we have in the form of anthracite partakes, in this respect, of the character of coke. 
 Anthracite is the ultimate product of the conversion of vegetable matter into coal. Its structure is 
 perfectly homogeneous, its density greater than the other kinds of coal, and it has a more completely 
 mineralized appearance. Its colour is a jet black, with a somewhat vitreous lustre, often exhibiting 
 a powerful play of colours. It does not soil the fingers when handled, being very hard and firm. 
 Its specific gravity varies between 1'40 and 1'60. In the harder examples, the fracture is distinctly 
 conchoidal, but when of a more tender character, it frequently breaks into small cubical lumps. 
 Anthracite burns with a feeble flame, blue when the supply of oxygen is insufficient, and often 
 decrepitates much in burning. It ignites with difficulty, and is slowly consumed, but when in a 
 state of perfect combustion it evolves an intense heat. The proportion of carbon present is from 
 90 to 95 per cent., and that of the volatile matters never above 9 per cent. The quality of hardness 
 possessed by anthracite enables it to be transported from one place to another without injury, while 
 those of evolving great heat without smoke render it peculiarly suitable for many purposes, as, in 
 certain cases, the generation of steam, and employment in distilleries, breweries, or in lime- or brick- 
 kilns. In the United States of America, it is almost universally adopted for domestic use. 
 
 The coals which are classed with anthracite are those which possess similar physical properties, 
 and contain not more than 12 per cent, of volatile matters. Of these, the anthracitous varieties of 
 South Wales are the best known examples. 
 
COAL : ITS MODE OF OCCUEEENOE, COMPOSITION, AND VAEIETIES. 63 
 
 The elementary composition of this class may be represented as follows : 
 
 Carbon .. ., .. ,, .. .. ,. .. .. .. 90 to 95 
 
 Hydrogen .. .. .. .. ., ,. .. .. ,. „ 4-5 „ 3 
 
 Oxygen and Nitrogen .. .. ., .. .. .. .. .. 5-5 „ 2 
 
 Hence the ratio — ^ — is rather less than greater than 1. The specific gravity varies between 
 
 1-40 and 1-60. 
 
 By distillation we obtain : 
 
 Coke 88 to 92 
 
 Ammoniacal Liquor 
 Bitumen .. 
 Gas ., 
 
 •5 „ Oa 
 3 » 1 1- Volatile matters, 12 to 8 
 8-5 „ 7 J 
 
 The coke obtained from coals of this class is brittle, pulverulent, and useless for commercial 
 purposes. 
 
 Semi-Bituminous Coal. — The term "bituminous," as applied to coal, is somewhat vague and 
 deceptive. Bitumen includes several combustible substances, as asphalt, or mineral pitch, elastic 
 bitumen, or mineral caoutchouc, naphtha, petroleum, and others, all of which are either fluids, or are 
 readily soluble in alcohol, and the application of the term cannot with propriety be extended to 
 substances of a different nature. But coal is not soluble in alcohol, and therefore cannot contain any 
 real bitumen, though it may contain the constituents of it. Hence the term as applied to coal must 
 be understood to mean that the mineralizing process has proceeded to a less extent than in anthracite, 
 and, consequently, a larger proportion of the hydrocarbons remains. 
 
 Coal of the quality described as " semi-bituminous " occurs next above the anthracite in geolo- 
 gical order. Occupying a higher position, it has been less exposed to the action of heat and other 
 metamorphic agencies, and has consequently retained a larger proportion of its volatile matters. 
 Between the anthracitous and the semi-bituminous classes, however, the line of division is purely 
 arbitrary, since from anthracite to cannel there is every gradation of composition. Semi-bituminous 
 coal contains from 12 to 18 per cent, of volatile matters. Its colour is usually a dull black, and its 
 fracture sub-conchoidal. It frequently exhibits a peculiar fibrous structure, passing into a remarkable 
 toothed arrangement of the particles, called " cone-in-cone," or " crystallized coal." It burns with a 
 slightly more abundant flame than coals of the anthracitous class, and evolves more smoke, but not 
 in dense volumes. It possesses the dry character of the latter class, and, from its freedom from 
 a liability to cake together, it is sometimes called free-burning coal, and steam coal. 
 
 The elementary composition of this class may be represented as follows : 
 
 Carbon 89 to 92 
 
 Hydrogen .. .. .. .. ,. .. .. .. .. .. 5 „ 4 
 
 Oxygen and Nitrogen .. .. .. .. .. .. .. .. 6 „ 4 
 
 Hence the ratio — ^5= — is not less than 1. The specific gravity varies between 1 • 35 and 1 ■ 40. 
 
 By distillation we obtain : 
 
 Coke 82 to 88 
 
 Ammoniacal Liquor .. .. .. .. .. 1 „ 1 1 
 
 Bitumen .. .. .. .. .. .. .. 5 „ 3 > Volatile matters, 18 to 12. 
 
 Gras .. •• a. .. .. „ •■ .. 12 „ 8 J 
 
64: MINING ENGINEERING. 
 
 The character of the coke obtained from coals of this class is similar to that obtained from those 
 of the preceding class. 
 
 Bituminous Coal. — The bituminous seams occupy a higher position in the series than those last 
 considered, and hence they contain a still larger proportion of volatile matters. The bituminous 
 class is a very large one, containing numerous varieties of every degree of richness in volatile 
 matters above the limit of the preceding class ; and it therefore becomes necessary to subdivide 
 it into three divisions, according to the proportion of the volatile constituents. These divisions may 
 be described, from the qualities due to their composition, as the clear-burning, the flaming, and the 
 fuliginous. 
 
 The varieties of the Clear-burning division are the poorest in volatile matters, the proportion of 
 the latter being included between the limits 18 and 26 per cent. They are similar in texture to those 
 of the preceding class, but generally of a duller lustre. They are very tender, and break with an even 
 or an irregular fracture, and, in consequence of the very perfect development of the cleat, have 
 always a tendency to break up into small cubical lumps. These coals kindle with difficulty, and 
 burn away slowly with a short, clear, bluish flame, and very little smoke. When reduced to a 
 powder and heated in a close vessel they fuse and agglomerate into a mass of dense and strongly 
 coherent coke, a property which renders them extremely valuable for manufacturing purposes. Both 
 in quality and in quantity the coke obtained from the clear-burning coals is superior to that 
 produced by any of the more bituminous varieties. 
 
 The elementary composition of the clear-burning coals, as given by M. Grrliner, is comprised 
 between the following limits : 
 
 Carbon .. ,. ., .. .. .. ' .. .. .. .. 83 to 91 
 
 Hydrogen .. .. ,. .. .. .. .. .. .. .. 5'5 „ 4"5 
 
 Oxygen and Nitrogen „ .. .. .. .. .. .. .. 6*5 „ 4-5 
 
 Hence the ratio — ^ — varies between 1 and 1 • 2. The specific gravity varies between 1 • 31 and 1 • 35. 
 Distillation gives, according to the same authority : 
 
 Coke 74 to 82 
 
 Ammoniacal Liquor .. .. .. ., .. 1 „ 1 i 
 
 Bitumen .. ,. .. .. .. .. .. 10 „ 5 > Volatile matters, 26 to 18 
 
 Gas 15 „ 12 ] 
 
 The coke obtained from coals of this division of the bituminous class is, as already remarked, 
 of a very superior character. 
 
 The Flaming coals of the bituminous class are richer in volatile matters than the foregoing, a 
 circumstance to which they owe their characteristic flaming quality. Their structure is distinctly 
 laminated, and their colour black and glossy. When reduced to powder, however, their colour is 
 a dark brown. They kindle without difficulty, and burn away somewhat rapidly with a long white 
 flame. Coals of this character become partially fused when strongly heated, and while in a fused 
 state swell into a spongy mass, giving off bubbles of gas, which burns with a bright flame. This 
 property of agglutinating in the fire allows the small coal to be burned which would otherwise be 
 useless, or to be converted into coke, of which it produces an excellent quality. To this property, 
 also, these coals owe the name of caking coal, which has been applied to it in common with some 
 other varieties of the same class. 
 
COAL : ITS MODE OP OCCUKEENCE, COMPOSITION, AND VAEIETIES. 65 
 
 The elementary composition of the flaming coals is comprised between the following limits : 
 
 Carbon 84 to 89 
 
 Hydrogen .. .. „ ., .. .. .. .. .. .. 5 „ 5'5 
 
 Oxygen and Nitrogen .. .. .. .. .. .. .. .. 11 n 5'5 
 
 Hence the ratio — :^ — is between 1 and 2. The specific gravity varies between 1 • 29 and 1 • 31. 
 
 Distillation gives : 
 
 Coke 68 to 74 
 
 Ammoniacal Liquor .. .. .. .. .. 3 „ 1 1 
 
 Bitumen 13 „ 10 > Volatile matters, 32 to 26 
 
 Gas 16 „ 15 J 
 
 The coke obtained from coals of this division of the bituminous class is of excellent quahty. 
 
 The Fuliginous coals of the bituminous class contain a very large proportion of volatile matters. 
 Hence they kindle readily, and burn away rapidly with a long, yellow, fuliginous flame. It is to 
 this latter circumstance that they owe their name. They are somewhat hard and strong, and their 
 fracture is rather shaly than even or conchoidal. Coals of this character fuse in the fire like the 
 flaming varieties, but they do not agglomerate into so compact a mass. The gas obtained from them 
 is abundant and of a high illuminating power. 
 
 The elementary composition of the fuliginous coals is comprised between the following limits : 
 
 Carbon 80 to 85 
 
 Hydrogen .. .. .. .. .. .. .. .. .. .. 5'8 „ 5 
 
 Oxygen and Nitrogen .. .. .. .. .. .. .. .. 14'2 „ 10 
 
 Hence the ratio — z= — is between 2 and 3. The specific gravity varies between 1 • 25 and 1 '29. 
 
 Distillation gives : 
 
 Coke 60 to 68 
 
 Ammoniacal Liquor .. .. .. .. .. 5 „ 3 ^ 
 
 Bitumen 15 „ 12 > Volatile matters, 40 to 32 
 
 Gas 20 „ 17 J 
 
 The coke obtained from coals of this division of the bituminous class is friable and porous, and 
 unfit for many purposes. 
 
 Gaseous Coal. — Coals of the class denominated " gaseous " occupy the highest geological 
 position, some of them occurring in formations more recent than those of the Carbon Period. They 
 are distinguished by the very large proportion of volatile matters which they contain, and to this cir- 
 cumstance it is due that they do not cake when heated. Experience has shown that coal becomes 
 caking when the proportion of carbon reaches 80 per cent., and that of the oxygen descends below 15 
 per cent. On the other hand, when the proportion of hydrogen becomes very small and that of the 
 carbon large, as in the anthracites, the same non-caking qualities result. The gaseous coals are of a 
 brownish black colour, and of a dull lustre. When reduced to powder they are quite brown. They are 
 generally hard, compact, and strong ; their fracture is even to conchoidal. Coals of this class kindle 
 even more readily than the fuliginous varieties of the preceding class, and they burn away very 
 japidly with a long flame. In the matter of burning, indeed, they exhibit all the qualities of the 
 
66 
 
 MINING ENGINEEEING. 
 
 fuliginous coals intensified. Some of the Derbyshire, South Staffordshire, and Scotch coals are of 
 this character. 
 
 The elementary composition of the gaseous class may be represented as follows : 
 
 Carbon .. .. .. .. „ .. ,. .. .. „ 75 to 80 
 
 Hydrogen .. „ ., .. .. .. .. ,. ,. „ 5-5 „ 4*5 
 
 Oxygen and Nitrogen .. .. „ .. .. .. .. .. 19-5 „ 15-5 
 
 Hence the ratio — = — lies between 3 and 4. The specific gravity varies between 1 '22 and 1 * 25. 
 
 Distillation gives : 
 
 Coke 50 to 60 
 
 Ammoniacal Liquor .. .. ,. .. .. 12 „ ,5 V 
 
 Bitumen .. .. .. ,. .. .. .. 18 „ 15 > Volatile matters, 50 to 40 
 
 Gas 20 „ 20 J 
 
 The coke obtained from coals of this class is of a soft and pulverulent character, and useless for 
 commercial purposes. 
 
 There exist certain varieties of coal which, though they da not possess all the qualities mentioned 
 as pertaining to the gaseous coals, yet are of such a character that they must be ranged under that 
 class. These are the important variety known as Cannel ; those of the lignite family denominated 
 Brovm coal ; and the mineral variety described as Boghead cannel, Torbane Hill mineral, and Torhanite. 
 
 " Cannel " is a very hard compact coal, of a black or brownish black colour, sometimes glossy? 
 but more frequently dull in lustre. It does not soil the fingers when handled, and it is capable of 
 taking a high polish. It breaks with a flat conchoidal fracture. Cannel is distinguished from ordinary 
 coal by the absence of a laminated structure. This is a mark of its highest perfection, for when it 
 becomes earthy and otherwise impure, the laminated structure is developed. In this state it is 
 called " hoo-cannel " by the miners. It kindles very readily, and burns away in the hand with 
 a Very abundant white flame. It is from this quality that it derives its name of cannel, i. e. candle 
 coal. It decrepitates much in burning, and from the rattling, chattering sound emitted it has 
 received the name of " rattlers " in Yorkshire, and " parrot coal " in Scotland. Formerly cannel was 
 much used as a source of mineral oil ; but since the discovery of oil in America, it has been employed 
 almost exclusively for gas making, for which purpose it commands a high price in the market. 
 Seams of cannel occur in certain districts with ordinary coal, and often form the upper portion of a 
 seam of bituminous coal, and occasionally of a bed of black-band ironstone. 
 
 "Brown coal," or "Lignite," is a term applied to all coals occurring in formations more recent 
 than those of the Carbon Period. The processes of mineralization having been less completely 
 effected in these later coals, they exhibit their vegetable structure more completely, and as an effect 
 of the same cause, they retain a much larger proportion of volatile matters. In colour, they vary 
 from brown to pitch black ; their lustre is generally dull, but sometimes resinous ; the fracture is 
 various. They contain from 50 to 70 per cent, of carbon, and a much larger proportion of oxygen 
 than the bituminous coals. They burn readily with a dull flame, emitting much smoke, and an 
 unpleasant odour. In consequence of the small proportion of carbon and the large quantity of water 
 which they contain^ the brown coals do not possess great heating power. The deposits are more 
 extensive on the continent of Europe than in England. 
 
 " Torbanite " or " Boghead mineral," is a highly bituminous shale occurring at Torbane Hill, in 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VARIETIES. 
 
 67 
 
 Scotland, and is therefore of merely local importance. It is a brown substance, containing little 
 more than 9 or 10 per cent, of carbon, with a very large proportion of ash. But the volatile matters 
 are so abundant as to constitute from 60 to 70 per cent, of the whole, and hence the great value of 
 this mineral as a source of gas, as much as 15,500 cubic feet having been extracted from a ton. 
 
 Local Names. — Almost every district has its own names to distinguish the numerous varieties of 
 coal of every class. These names have, in most cases, reference to physical conditions. It is not 
 desirable to give a list of them, as they have but httle interest beyond the district in which they are 
 apphed. There are a few, however, more widely employed than the rest, which deserve special 
 mention. " Stone coal," " crow coal," and " Kilkenny coal," are names applied to anthracite : the first 
 having reference to the mineralized character of the coal ; the second, to its iridescent hues, like those 
 of the crow; and the last, which is used in Ireland, to the locality whence it is obtained. " Splint " 
 is a Scotch term, and is applied to a hard variety of coal, capable of being cut in large blocks. It is 
 of a dull lustre, not easily kindled, but when thoroughly lighted it burns brightly and is rather 
 slowly consumed. It is largely used for steam purposes. " Cherry" is a soft and very beautiful 
 variety, of a velvet-black colour, with a slight intermixture of grey. Its lustre is bright resinous ; 
 it is very tender, and its fracture is shaly. It kindles very readily, and burns away leaving but 
 little ash. " Bone coal " and " spiry coal " are terms applied to hard varieties when the hardness is 
 occasioned by the presence of clayey matters disseminated throughout the coal. Bony coal has a 
 dull appearance, and leaves a very large proportion of ash after burning. 
 
 Composition' op Coal. — The vegetable origin of coal is, as previously stated, shown by its 
 chemical composition, as well as by its structure and the remains which it contains. The essential 
 elements of which it is composed are carbon, hydrogen, and oxygen, and the proportion in which 
 these elements enter into the composition of the original wood, and the intermediate substances up to 
 the ultimate product anthracite, show the process of change that has taken place. The formation of 
 coal by the decomposition of woody tissue may be explained by the gradual elimination of hydrogen 
 and carbon as carburetted hydrogen, of oxygen and carbon as carbonic anhydride, and of oxygen 
 and hydrogen as water. The following table exhibits clearly the transformations that have been 
 produced by the slow but continued action of chemical and other agencies, and the relation subsisting 
 among the several classes of coal, and also between these and the vegetation of the present day. 
 
 Name of Substance. 
 
 Specific 
 Gravity. 
 
 C 
 
 H 
 
 + N 
 
 Wood — ^mean of 12 kinds .. 
 
 0-91 
 
 49-00 
 
 6-26 
 
 44-75 
 
 Peat — ^mean of 12 samples 
 
 0-99 
 
 59-30 
 
 6-52 
 
 34-18 
 
 Lignite — mean of 12 samples 
 
 1-25 
 
 72-37 
 
 5-18 
 
 23-45 
 
 Cannel Coal (Wigan) 
 
 Bituminons Coal — mean of the three divisions .. 
 
 1-27 
 
 80-07 
 
 5-53 
 
 13-50 
 
 1-30 
 
 86-17 
 
 5-21 
 
 8-62 
 
 Semi-BituminoTis Coal — mean 
 
 1-37 
 
 91-00 
 
 4-75 
 
 5-25 
 
 Anthracitous Coal — mean .. 
 
 1-50 
 
 92-50 
 
 8-75 
 
 3-75 
 
 It appears from the foregoing table that the proportion of carbon, and, consequently, the specific 
 gravity, increases, as previously stated, with the age of the coal. The large proportions of volatile 
 matters present in the newer coals give them their flaming character, and constitute their value as 
 gas producers. The calorific power of a coal depends mainly upon the excess of carbon which it 
 contains, and hence the older coals possess the greatest value as heat producers. The figures in the 
 
 K 2 
 
68 
 
 MINING ENGINEEEING. 
 
 table give only mean values ; in every class there are insensible gradations between tbe limits which 
 have already been defined, and these variations occur not only from seam to seam, but m the 
 different parts of the same seam. These mean values will, however, constitute a convenient term of 
 comparison. The variations in the composition of coals of the same class are well exhibited m the 
 following table, given in the ' Third Official Report on Coals suited to the Steam Navy.' The 
 percentage of ash and that of the coke yielded by each variety are included in this table : 
 
 COMPOSITION OF VAEIOUS BEITISH COALS. 
 
 Locality or Name of Coal. 
 
 Specific 
 Gravity. 
 
 
 
 H 
 
 N 
 
 S 
 
 
 
 Ash. 
 
 Percentage 
 of Coke left. 
 
 Welsh Coals: 
 
 
 
 
 
 
 
 
 
 Aberamam Merthjrr 
 
 1-305 
 
 90-94 
 
 4-28 
 
 1-21 
 
 1-18 
 
 0-94 
 
 1-45 
 
 85-0 
 
 Ebbw Vale 
 
 1-275 
 
 89-78 
 
 5-15 
 
 2-16 
 
 1-02 
 
 0-39 
 
 1-50 
 
 77-5 
 
 Thomas's Merthyr 
 
 1-30 
 
 90-12 
 
 4-33 
 
 1-00 
 
 0-85 
 
 2-02 
 
 1-68 
 
 86-53 
 
 DuiTryn 
 
 Nixon's Merthyr .. 
 
 1-326 
 
 88-26 
 
 4-66 
 
 1-45 
 
 1-77 
 
 0-60 
 
 3-26 
 
 84-3 
 
 1-31 
 
 90-27 
 
 4-12 
 
 0-63 
 
 1-20 
 
 2-53 
 
 1-21 
 
 79-11 
 
 Binea .. .. -• .» 
 
 1-304 
 
 88-66 
 
 4-63 
 
 1-43 
 
 0-33 
 
 1-03 
 
 3-96 
 
 88-10 
 
 Bedwas 
 
 1-32 
 
 80-61 
 
 6-01 
 
 1-44 
 
 3-50 
 
 1-50 
 
 6-94 
 
 71-7 
 
 HiU's Plymouth Works .. 
 
 1-35 
 
 88-49 
 
 4-00 
 
 0-46 
 
 0-84 
 
 3-82 
 
 2-39 
 
 82-25 
 
 Aberdare Co.'s Merthyr .. 
 
 1-31 
 
 88-28 
 
 4-24 
 
 1-66 
 
 0-91 
 
 1-65 
 
 3-26 
 
 85-83 
 
 Gadly Nine-feet Seam 
 
 1-33 
 
 86-18 
 
 4-31 
 
 1-09 
 
 0-87 
 
 2-21 
 
 5-34 
 
 86-54 
 
 Eesolven .. 
 
 1-32 
 
 79-33 
 
 4-75 
 
 1-38 
 
 5-07 
 
 (included 1 
 \ in ash 
 
 9-47 
 
 83-9 
 
 Newcastle : 
 
 
 
 
 
 
 
 
 
 WiUington 
 
 .. 
 
 86-81 
 
 4-96 
 
 1-05 
 
 0-88 
 
 5-22 
 
 1-08 
 
 72-19 
 
 Andrew's House, Tanfield 
 
 l-'26 
 
 85-58 
 
 5-31 
 
 1-26 
 
 1-32 
 
 4-39 
 
 2-14 
 
 65-13 
 
 Bowden Close 
 
 .. 
 
 84-92 
 
 4-53 
 
 0-96 
 
 0-65 
 
 6-66 
 
 2-28 
 
 69-69 
 
 Haswell Wallsend 
 
 1-286 
 
 83-47 
 
 6-68 
 
 1-42 
 
 0-06 
 
 8-17 
 
 0-20 
 
 62-70 
 
 Newcastle Hartley 
 
 1-29 
 
 81-81 
 
 5-50 
 
 1-28 
 
 1-69 
 
 2-58 
 
 7-14 
 
 64-61 
 
 Hedley's Hartley 
 
 1-31 
 
 80-26 
 
 5-28 
 
 1-16 
 
 1-78 
 
 2-40 
 
 9-12 
 
 72-31 
 
 Bates' West Hartley 
 
 1-25 
 
 80-61 
 
 5-26 
 
 1-52 
 
 1-85 
 
 6 51 
 
 4-25 
 
 
 West Hartley Main 
 
 1-264 
 
 81-85 
 
 5-29 
 
 1-69 
 
 1-13 
 
 7-53 
 
 2-51 
 
 59-20 
 
 Buddie's West Hartley .. 
 
 1-23 
 
 80-75 
 
 5-04 
 
 1-46 
 
 1-04 
 
 7-86 
 
 3-85 
 
 
 Hastings' Hartley 
 
 1-25 
 
 82-24 
 
 5-42 
 
 1-61 
 
 1-35 
 
 6-44 
 
 2-94 
 
 35-60 
 
 DBEBTSHraE : 
 
 
 
 
 
 
 
 
 
 Earl PitzwiUiam's Elsecar 
 
 1-296 
 
 81-93 
 
 4-85 
 
 1-27 
 
 0-91 
 
 8-58 
 
 2-46 
 
 61-6 
 
 Hayland & Co.'s Elsecar .. 
 
 1-317 
 
 80-05 
 
 4-93 
 
 1-24 
 
 1-06 
 
 8-99 
 
 3-73 
 
 62-5 
 
 Earl Eitzwilliam's Park Gate 
 
 1-311 
 
 80-07 
 
 4-92 
 
 2-15 
 
 1-11 
 
 9-95 
 
 1-80 
 
 61-7 
 
 Butterly Co.'s Portland .. 
 
 1-301 
 
 80-41 
 
 4-65 
 
 1-59 
 
 0-86 
 
 11-26 
 
 1-23 
 
 60-9 
 
 Butterly Co.'s Langley .. 
 
 1-264 
 
 77-97 
 
 5-58 
 
 0-80 
 
 1-14 
 
 9-86 
 
 4-65 
 
 54-9 
 
 Stavely 
 
 1-27 
 
 79-85 
 
 4-84 
 
 1-23 
 
 0-72 
 
 10-96 
 
 2-40 
 
 57-86 
 
 Loscoe Soft 
 
 1-285 
 
 77-49 
 
 4-86 
 
 1-64 
 
 1-30 
 
 12-41 
 
 2-30 
 
 52-8 
 
 TiANOASHIKB : 
 
 
 
 
 
 
 
 
 
 Ince Hall Co.'s Arley 
 
 1-272 
 
 82-61 
 
 5-86 
 
 1-76 
 
 0-80 
 
 7-44 
 
 1-53 
 
 64-0 
 
 Haydock Little Delf 
 
 1-257 
 
 79-71 
 
 5-16 
 
 0-54 
 
 0-52 
 
 10-65 
 
 3-42 
 
 58-1 
 
 Balcarres Arley .. 
 
 1-26 
 
 83-54 
 
 5-24 
 
 0-98 
 
 1-05 
 
 5-87 
 
 3-32 
 
 62-89 
 
 Blackley Hurst 
 
 1-26 
 
 82-01 
 
 5-55 
 
 1-68 
 
 1-43 
 
 5-28 
 
 4-05 
 
 57-84 
 
 Ince Hall, Pemberton Yard 
 
 1-348 
 
 80-78 
 
 6-23 
 
 1-30 
 
 1-82 
 
 7-53 
 
 2-34 
 
 60-6 
 
 Haydock Eushy Park 
 
 1-323 
 
 77-65 
 
 5-53 
 
 0-50 
 
 1-73 
 
 10-91 
 
 3-68 
 
 59-4 
 
 Moss Hall, Pemberton Four-feet 
 
 1-258 
 
 75-53 
 
 4-82 
 
 2-05 
 
 3-04 
 
 7-98 
 
 6-58 
 
 55-7 
 
 Scotch : 
 
 
 
 
 
 
 
 
 
 Wallsend Elgin 
 
 1-20 
 
 76-09 
 
 5-22 
 
 1-41 
 
 1-53 
 
 5-05 
 
 10-70 
 
 58-45 
 
 Wellewood 
 
 1-27 
 
 81-36 
 
 6-28 
 
 1-53 
 
 1-57 
 
 6-37 
 
 2-89 
 
 59-15 
 
 Dalkeith Coronation Seam 
 
 1-316 
 
 76-94 
 
 5-20 
 
 trace 
 
 0-38 
 
 14-37 
 
 3-11 
 
 53-5 
 
 Kilmarnock Skerrington ., 
 
 1-241 
 
 79-82 
 
 5-82 
 
 0-94 
 
 0-86 
 
 11-31 
 
 1-25 
 
 49-3 
 
 Fordel Splint 
 
 1-23 
 
 79-58 
 
 5-50 
 
 1-13 
 
 1-46 
 
 8-38 
 
 4-00 
 
 52-03 
 
 Grangemouth 
 
 1-29 
 
 79-85 
 
 5-28 
 
 1-35 
 
 1-42 
 
 8-58 
 
 3-52 
 
 56-6 
 
 Eglington .. 
 
 1-25 
 
 80-08 
 
 6-50 
 
 1-55 
 
 1-38 
 
 8-05 
 
 2-44 
 
 ."54-94 
 
 Dalkeith Jewel Seam 
 
 1-277 
 
 74-55 
 
 5-14 
 
 0-10 
 
 0-33 
 
 15-51 
 
 4-37 
 
 49-8 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 69 
 
 The calorific power of coal is largely influenced by the proportion of water and of inorganic 
 matters which it contains. In the analyses made for the purposes mentioned in the Official Eeport 
 referred to, it was ascertained that the mean proportion of water present in 24 examples experi- 
 mented upon was 3'35 per cent. In some of the softer varieties the proportion is larger. The 
 impurities are contained in the ash : the nature and the origin of these impurities have already been 
 described and stated. When free from iron, the ash is white or light grey. The presence of iron 
 colours the ash brown or red; and when the proportion is large, it causes the other constituents 
 of the ash to fuse, and form clinkers. This quality often constitutes a serious objection to the use 
 of coals containing iron. 
 
 Analyses op Coal. — The foregoing elementary analyses are very interesting and instructive. 
 But proximate analyses are of more practical value, and can be far more easily made. It is a singular 
 and highly suggestive fact that while, in Europe, reliance is almost exclusively placed upon elemen- 
 tary analysis, proximate analysis is as exclusively practised in the United States of America. The 
 latter means enables us to determine readily the proportion of water and of ash present in any given 
 specimen of coal, and the proportion which the volatile matters bear to the carbon. And this is all 
 we require to know to enable us to ascertain the value of coal as a commercial commodity. The 
 mode of conducting such an analysis will be clearly understood from the following descriptions. 
 
 Estimation of the Volatile Matters. — The only articles required in the operations are : a Bunsen 
 gas burner; a blast gas burner, that is, an Argand gas burner with six jets, surmounted by a 
 cylinder; a small covered platinum or porcelain crucible; a triangular support for the same ; a 
 sand-glass running exactly three and half minutes, and a sensitive balance. 
 
 The quantity of coal to be operated upon should be between one and two grammes, as this 
 quantity gives constant results. The coal should not be dried previously to making the analysis, as 
 the practice of some would authorize; for in that case we do not get the results which occur in 
 practice. A small lump of coal might not give true results, because every block contains minute 
 cubical portions differing considerably in quality from the mean of the whole mass. Portions of 
 several lumps should therefore be procured, and reduced to powder in a mortar, and the requisite 
 quantity taken from the mass after being carefully mixed to ensure a fair sample. When the portion 
 to be operated upon has been placed in the crucible and weighed, the latter should be exposed to 
 the constant flame of the Bunsen burner for three and half minutes, to obtain a red heat. At the 
 expiration of this time it should be removed to the blast flame for another three minutes and a half, 
 to obtain a white heat. The crucible with its contents should then be allowed to cool, after which it 
 should be weighed again. The difference of weight represents the quantity of volatile matters 
 removed, and this difference divided by the original weight will give the proportion, from which the 
 percentage may be easily deduced. For example, if the weight of the pulverized coal before treatment 
 was 1*50 grms., and after treatment 1*12 grms., the difference 1*50 — 1*12 = 0"38 grms. = the 
 
 weight of the volatile matters driven off"; and this divided by the original weight = • 25, or 
 
 one quarter, which is 25 per cent. 
 
 Estimation of the Moisture, — For the determination of the proportion of moisture present, there 
 is needed a flat-bottomed iron pan, from 7 to 8 inches in diameter, supported upon an iron tripod. 
 This pan is filled evenly to a depth of half an inch with sand, upon which is placed a thin copper 
 plate. An iron arm, fixed at one end to a leg of the tripod by means of an indiarubber stopper, 
 
70 MINING ENGINEEEING. 
 
 carries at the other end a thermometer, so placed that its bulb is about ^ inch above the copper 
 plate. The coal, having been prepared in the manner and quantity already described, is placed in a 
 watch-glass upon the plate, .and a gas jet (preferably from a Bunsen burner) is applied beneath the 
 iron pan, the thermometer being kept at about 105° 0., or 220° Fahr. At the expiration of one hour 
 the coal is removed, allowed to cool, and then re-weighed. The dijBference of weight represents the 
 quantity of moisture evaporated, and the proportion is ascertained in the same way as that of the 
 volatile matters. 
 
 Estimation of the Ash, — The determination of the quantity of ash yielded by any specimen of 
 coal may be very easily effected. The coal is prepared in the same way and in the same quantity as 
 in the foregoing cases, and burned in a platinum or porcelain crucible over a gas flame until the 
 whole of the combustible matters are consumed. To promote rapid combustion, the crucible should 
 be placed a little on one side, with its lid partially covering its mouth, so as to direct a current of air 
 upon the burning substance. If the coal is of a highly caking quality, it is advantageous not to 
 break the crust of the cake which is first formed, but to allow the mass to be gradually consumed 
 from the outside. "When coke is being operated upon, it is sometimes very difficult to consume the 
 last portions of carbon. In such cases it may be necessary, in order to ensure rapid combustion, to 
 direct a current of oxygen upon the burning mass at a red heat. This is effected by closing the 
 porcelain crucible, when combustion becomes sluggish, with a cover having a hole through its centre, 
 and inserting a suitable tube in communication with a gas-holder, the quantity of gas allowed to pass 
 being regulated by a stop-cock. The residue constituting the ash, after being allowed to cool, is 
 weighed, and the weight thus found, divided by that of the coal, will give the proportion of ash. 
 The colour of the ash will indicate whether or not iron be present in sufficient quantity to have a 
 notable influence upon the combustible. 
 
 Estimation of the Sulphur. — The determination of the quantity of sulphur contained by any 
 specimen of coal presents greater difficulties than that of the volatile matters or the ash, and requires 
 appliances and processes belonging more particularly to the laboratory. As, however, it is very 
 frequently requisite to estimate the quantity of this substance, the following method is given as the 
 most readily applicable : The coal to be operated upon is to be mixed with three times its weight of 
 nitre, and four times its weight of pure carbonate of sodium, and the mass fused in a crucible. After 
 cooling, this mass is to be first dissolved in hot water, and then filtered. Nitric or hydrochloric acid 
 is next to be added to the filtrate to render it acid, which filtrate is then thrown down by barium- 
 chloride. From the weight of the sulphate of barium thus obtained, the percentage amount of 
 sulphur present in the coal may be deduced. 
 
 Determination of the Specific Gravity. — The method of determining the specific gravity has 
 already been described in relation to rocks. The portion to be tested should be taken from the 
 middle of a block of considerable size to ensure correct results. It is also important for practical 
 purposes that the specific gravity found should be that of the coal with all its pores filled with water 
 at a temperature of about 60° Fahr., the condition in which it comes from the pit. Suppose, for ex- 
 ample, a piece of coal which has been exposed for a short time to a dry atmosphere shows a specific 
 gravity of 1*31, and that the same piece after soaking in water shows 1"33. A cubic yard will weigh 
 1685-34 X 1-31 = 2207-80 lb., and 1685-34 x 1-33 = 2241-50 lb. respectively; that is, there would 
 be a difference of 33*7 lb, in the cubic yard. To obtain correct results, therefore, the coal should 
 be previously soaked for twelve hours in water of about 60° temperature. 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 71 
 
 Besides ascertaining the percentage of the constituent elements, it is often desirable, for the pur- 
 pose of forming a proper comparative estimate of the character of the coal, to reduce the composition 
 to a form in which the proportions of the volatile matters and the ash may be compared with that of 
 the carbon represented as a constant quantity. For example, we found in one of the foregoing" 
 analyses that the proportion of volatile matters was 25 per cent. That is, to 75 parts of carbon there 
 were 25 parts of volatile matters. If we wish to represent the carbon as a fixed quantity = 100 ; in 
 other words, if we wish to know how many parts of volatile matters there are to every 100 parts of 
 carbon, we may state the composition as 100 carbon and 33 volatile matters. 
 
 When the burners mentioned in the foregoing paragraph^ are not easily obtainable, the blow- 
 pipe may be used. The cover of the crucible should be left very slightly open, to afford easy escape 
 for the gas, but not sufficient to allow any of the solid matters to fly off. The heat should be increased 
 to redness, and kept up until the escaping gases cease to burn. It may be remarked here that a 
 quick heat will give less coke than a slow heat by several per cent. ; but it will often make a dry coal 
 cake that would not cake at all with a slow heat. In all cases where accuracy is important, experi- 
 ments such as the foregoing should be repeated at least twice, and a mean taken. 
 
 Calorific Power of Coal. — In order to estimate the relative amount of heat evolved in the 
 combustion of the various kinds of fuel, it is necessary to assume some standard of comparison ; and 
 as heat cannot be directly measured, this standard must have reference to the effects which heat 
 produces. Yarious methods of estimating such effects have been devised. One, adopted by the 
 British Admiralty Commissioners, in 1848, was to measure the, quantity of heat by the weight 
 of water at 212° Fahr., that it was capable of converting into steam of the same temperature. This 
 and other methods have been abandoned in favour of what is known as the continental and British 
 units of heat. The former is the quantity of heat required to raise 1 gramme of water from 0° to 
 1° C. ; the latter the quantity required to raise 1 lb. of water from 32° to 33° Fahr. As the former 
 has reference to the only thermometer constructed upon a rational basis, and as, moreover, it is being 
 gradually adopted in England, while being almost universally employed abroad, the following 
 remarks will have reference to it. In this standard of comparison, all that is assumed is, that if a 
 certain quantity of heat produce a given effect upon a given quantity of water, then to produce the 
 same effect upon another similar quantity of water, the same quantity of heat will be required ; that 
 is, in other words, to produce the same effect, twice the quantity of water will require twice the 
 quantity of heat, and so on. 
 
 The calorific power of a fuel, therefore, may be expressed in units of heat ; and the number of 
 such units evolved during the combustion of 1 gramme of the substance is taken to represent its 
 calorific power. Numerous experiments, carefully conducted and reduced to a mean value, have 
 shown that the calorific power of pure carbon, that is, pure as obtained in practice in the form 
 of purified wood-charcoal, is 8080, and that of hydrogen 34,462 ; hence we are able to calculate the 
 calorific power of any fuel when we know its elementary composition. The calorific powers of the 
 foregoing substances corresponding to the British unit of heat, determined for the pound weight, are 
 14,500 and 62,032 respectively. 
 
 To estimate the calorific power of coal^ the following formula was proposed by Dulong : 
 
 P = 8080 C -H 34462 (h - ^ 
 
72 MINING ENGINEEEING. 
 
 in wMcK P represents the calorific power, C the weight of carbon, and ( H — o ) the weight oifree 
 
 hydrogen ; that is, the total quantity of hydrogen less that which would be taken up by the oxygen 
 contained in the coal to form water. This formula has been, and still is, largely employed in deter* 
 mining the relative values of different varieties of coal. But as it does not take sufficient account of 
 the chemical effects of combustion as influenced by molecular constitution and other conditions, it 
 must be considered as giving only roughly approximate results. Carbon develops 2473 units of heat 
 in being converted into carbonic oxide, and the latter gas develops 8080 — 2473 = 5607 units of heat 
 by combining with a new equivalent of oxygen, to form carbonic acid. Hence, apparently, equal 
 quantities of oxygen develop very unequal quantities of heat. But, in the former case, the solid 
 carbon passes into the gaseous state, while, in the latter case, carbon already in the gaseous state is 
 being burned. 
 
 If now we admit that Welther's law holds true so long as the chemical reactions are neither 
 accompanied nor followed by a change of state, we see that the excess of 5607 over 2473, or 3134 
 units of heat must correspond exactly to the heat absorbed by the conversion of the carbon into gas. 
 Consequently, carbon in a gaseous state would develop 8080 + 3134 = 11,214 units of heat, if it gave 
 carbonic acid directly. Eeasoning from these facts, M, Griiner concludes that when applied to the 
 carbon contained in coal, some value nearer 11,214 than 8080 is should be adopted, and suggests 9000 
 as an appropriate value. In like manner he would substitute the calorific power of hydrogen in a solid 
 state for that oi gaseous hydrogen, and gives 30,000 instead of 34,462 as the value required. The 
 
 formula as thus modified would be, P = 9000 C + 30,000 (H — n\, and the results given by it are 
 
 much nearer the truth than when it is in its original form. Even when thus modified, however, the 
 values obtained by it are too low for the anthracitous coals, and too high for those of the richer 
 varieties of the bituminous class. Such a formula can at the best be only approximative ; but when 
 only the elementary composition of a coal is known, it may be useful in determining the relative 
 value, 
 
 A fatal objection, however, to any formula founded upon the elementary composition of coal, 
 lies in the inability of elementary analysis to reveal the actual properties of the coal. Specimens 
 nearly identical in their composition may differ widely in their calorific power, Grriiner gives an 
 example of coals from Le Creuzot and Eonchamp, the composition of the former being C88*48, 
 H 4 • 41, 7 • 11, and that of the latter C 88 • 32, H 4- 78, 6 • 89. Yet the calorific value of the former 
 was 9622, while that of the latter was only 9077; and the former yielded only 19*6 per cent, of 
 volatile matters, while the latter yielded 27 per cent. The Eonchamp coal gives off, when distilled, 
 a larger portion of carbon to the hydrogen and oxygen ; and hence it is evident that in that example 
 the union of the gases with the carbon is more intimate than in that from Le Creuzot, and hence 
 also a larger amount of heat is given off' and lost. The larger the proportion of volatile matters 
 present, the lower is the calorific power of the coal. That the calorific power varies as the proportion 
 of fixed carbon left after distillation is shown, not only by the foregoing example, but by numerous 
 others adduced by MM. Scheurer, Kestner and Meunier, Favre, and Silbermann, and other eminent 
 chemists. It should, however, be remarked, that the proportion of coke decreases somewhat more 
 rapidly than the calorific power. Thus the proximate analysis will reveal not only the proportions 
 of the coke, the volatile matters, the ash, &c,, but also the calorific power, with a much closer 
 
COAL: ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 73 
 
 approximation to the truth, and in a far easier manner, than the elementary analysis aided by 
 doubtful formulae. 
 
 Experiments, carried out under conditions that obtain in practice, have shown the mean 
 evaporative powers of the several classes of coal to be as follows (the evaporative power is the 
 weight of water which 1 lb. of coal is capable of evaporating from 212° Fahr.) : 
 
 Gaseous Class .. .. .. .. .. .. .. .. .. 6*25 lb. 
 
 f Fuliginous Division .. .. .. .. .. .. 8-00 „ 
 
 Bituminous Class < Flaming Division .. .. .. .. ., .. 8-75 „ 
 
 I Clear- burning Division .. .. .. .. ., 9-25 „ 
 
 Semi-Bituminous Class .. .. .. .. .. .. .. .. 9-10 „ 
 
 Antbracitous Class .. .. .. .. .. .. .. .. .. 9' 20 „ 
 
 Uses op the different Qualities of Coal.' — It has been shown that coal varies greatly in 
 quality, both in relation to its composition and its physical properties. Hence it is obvious that some 
 kinds are more suitable for certain uses than others, and that the value of each kind can be taken 
 advantage of only by applying it to that use to which its qualities specially adapt it. This is im- 
 portant to the mining engineer and the colliery proprietor from a commercial point of view, for 
 the selection of a wrong market will certainly entail pecuniary loss. It now remains, therefore, 
 to point out very briefly the qualities of coal that are required in the principal uses to which that 
 mineral is applied. 
 
 Coal for Metallurgical Purposes. — The enormous consumption of coal required in the manu- 
 facture of iron renders this by much the most important metallurgical undertaking, from the coal 
 producer's point of view ; and it is the only one to which the following remarks will have reference. 
 A primary condition which any kind of coal must fulfil to render it fit for employment in iron 
 manufacture, whatever its qualities may be in other respects, is that it shall be free from sulphur. 
 The presence of sulphur in iron is very deleterious to its quality, producing that state of its con- 
 stituted particles which is technically known as " red shortness." Hence the fuel employed in its 
 manufacture must not be capable of communicating this substance to it. It is mainly for this reason 
 that wood charcoal is employed when iron of an unusually tough character is required. All coals 
 contain sulphur : the purest from one half to one per cent. ; the most impure, three and even more 
 per cent. When the proportion exceeds one and a half per cent., the coal becomes unfit in its raw 
 state for metallurgical purposes. Thus the visible presence of iron pyrites wiU at once show the 
 unsuitable character of the coal. 
 
 When a given specimen of coal has been proved to fulfil this primary condition of freedom 
 from sulphur, it remains to test its other qualities which may render it a good metallurgical coal. 
 The calorific power of a coal is, as we have shown, proportional to the amount of carbon it contains. 
 The proportion of ash represents so much loss of heat, besides the inconvenience which the presence 
 of such matters occasions. A greater loss is due to the quantity of water present, for not only does 
 the water occasion a negative loss proportionate to its amount, but a positive loss equal in amount to 
 the quantity of heat abstracted to evaporate the water. Thus a large proportion either of ash or 
 of moisture, or of both, tends to render a coal unsuitable. In metallurgical operations, intense local 
 heat is required, and hence the coal employed must contain a very large proportion of carbon. This 
 condition excludes the flaming and the fuliginous varieties of the bituminous and those of the gaseous 
 classes altogether in their raw state. The anthracitous and the semi-bituminous classes, therefore, 
 
 L 
 
74 MINING ENGINEEEING. 
 
 witli the clear-burning varieties of the bituminous class, can alone be considered applicable to this 
 use. The two former classes also possess two other qualities which are required in the blast and 
 refining furnaces, but which are not found in bituminous coal, namely, strength and freedom from a 
 liability to cake. The great weight of the charge would crush a tender coal to powder, and an 
 agglomeration of the mass would seriously impede the draught. The variety which best fulfils all 
 these conditions is anthracite ; but it possesses defects which go far to render it unsuitable. Though 
 very strong naturally, it may be reduced by decrepitation in the furnace to the state to which the 
 weakest is brought by pressure. It moreover requires, on account of its difiScult combustion, a high- 
 pressure hot blast, and a special construction of the furnace, to avoid a slow descent of the charges, 
 and a consequent loss in the quantity of metal produced. In consequence of these defects, anthracite 
 is not largely employed where more suitable varieties are easily procurable. Such varieties are those 
 of the anthracitous and many of the semi-bituminous classes. 
 
 The defects possessed by coals of the bituminous class may be removed by coking. This process 
 expels the volatile matters and leaves as a residue the carbon and the ash. In this state, that is, 
 when converted into coke, provided the conditions of freedom from sulphur and a large proportion 
 of ash be fulfilled, clear-burning coals of the bituminous class are more suitable for metallurgical 
 purposes than those of the anthracitous and semi-bituminous classes, and they are very largely 
 employed. In coke, the carbon attains its maximum proportions, and the hardness and the strength 
 of the combustible their maximum degree. Another advantage of converting bituminous coal into 
 coke is, that it allows the small coal, which as such is nearly worthless, to be utilized. Coals of this 
 class do not all coke with equal readiness, nor is the coke obtained from them of equal quality. Some 
 varieties require a quick heat to produce the best results, while others will not coke at all after some 
 days' exposure to the atmosphere. These peculiarities demand careful attention. One important 
 gain from the process of coking consists in the removal of a portion of the sulphur present, thereby 
 enabling a coal to be utilized for metallurgical purposes that would otherwise be unfit for that use. 
 Coke, to be suitable for the smelting furnace, besides freedom from sulphur and ash, must possess the 
 qualities of hardness, compactness, and strength to withstand considerable crushing force : that which 
 is brittle or liable to crumble is useless for the purpose. It is also of little value unless it can be 
 obtained in large prismatic pieces. Hence good coke should, on cooling, split into such pieces, 
 somewhat in the manner of columnar basalt. Its colour should be steel grey, almost approaching to 
 a silvery whiteness. An iridescent hue indicates the presence of sulphur. When struck, it should 
 emit a clear and almost metallic ring. Frequently a large proportion of moisture is imparted to 
 coke by the thoughtless way in which the extinction is conducted by the burners. By the applica- 
 tion of large quantities of water, evils are entailed of the first magnitude in the economical working 
 of the smelting furnace. 
 
 In the calcining of iron ores small coal is employed, and the same is sometimes used in the 
 puddling furnace : in such cases the quality of strength is of less importance. 
 
 The coals best suited for forging purposes are the richest of the clear-burning varieties of the 
 bituminous class. Their property of caking is an advantage, by allowing the formation of cavities, 
 or, in the language of the trade, a " hollow fire." The portions of coal cohere into a compact mass 
 on the outside of the fire, so as to form a covering within which the heat is confined. This covering 
 not only intensifies the heat at the point where it is most required, namely, upon the iron to be 
 forged, but it very effectively shields the workmen from it, which, in hot weather especially, is an 
 
COAL : ITS MODE OF OCOUEEENCE, COMPOSITION, AND VARIETIES. 75 
 
 important advantage. Such a fire is, moreover, more economical than an open one. Coals of this 
 quality are usually of a beautiful black colour, with a bright, fatty lustre. They are tender, and 
 break into small cubical fragments. The absence of sulphur is an indispensable condition in forge 
 coal for reasons already stated, and therefore pyritous, or " red-ash," coal is altogether unsuitable. 
 The presence of a large proportion of earthy matters is very objectionable ; for not only is a loss of 
 heat occasioned thereby, but they are apt to stick to the heated iron, and so constitute a source of 
 danger and of irritation to the workmen. 
 
 Coal for Steam Purposes. — ^Next to metallurgical purposes, the generation of steam constitutes 
 the most important use to which coal is applied. The qualities requisite in a steam coal are, in the 
 main, identical with those which render a coal suitable for the smelting furnace, though an intense 
 local heat is not so desirable for the one purpose as for the other. The absence of a large proportion 
 of ash and of water is, of course, an essential condition in a good steam coal, and freedom from 
 sulphur is of primary importance. Yet a slightly larger proportion of the latter substance may be 
 allowed than when the combustible is applied to iron manufacture. The coal should be strong, to 
 withstand rough usage, as otherwise there will be a considerable loss from the small pieces falling 
 through the bars of the grate. Moreover, an accumulation of small coal upon the bars impedes the 
 draught. A similar reason precludes the use of caking coals, except under certain conditions. Their 
 tendency to agglomerate into a fused mass necessitates much intelligent attention, and if this is 
 obtainable, such coals may frequently be used with advantage. But otherwise, they are unsuitable 
 for the purpose, and hence are not largely employed. The free-burning varieties of the anthracitous 
 and semi-bituminous classes unite most of the requirements of a good steam coal adapted to the 
 conditions of practice. Anthracite is objectionable by reason of its difficult combustion, its tendency 
 to decrepitate while burning, and the close attention it requires on the part of the fireman. Also 
 the intense local heat which it develops rapidly destroys the fire-bars. Hence it is but sparingly 
 used as a steam coal wherever other varieties are readily obtainable. Of these numerous varieties 
 each possesses qualities which render it preferable under given conditions. For example, the lively 
 burning coals of the semi-bituminous class, and the poorer varieties of the clear-burning coals of the 
 bituminous class, are peculiarly suitable for the quick generation of steam. Much may often be 
 gained by a judicious admixture of two varieties, or of two classes, the compound in such a case 
 possessing qualities which neither of the constituents have separately. Bituminous coal may often, 
 without skilled attention, be advantageously employed in this way. 
 
 A very large proportion of the steam coal raised is burned at sea, under conditions somewhat 
 different from those prevailing on land. The same qualities of coal are needed ; but some of these 
 qualities must exist in a higher degree. The rough usage which coal must necessarily be subjected 
 to before it reaches the fire-grates requires great strength ; and the limited space available for 
 storage demands a high specific gravity combined with a high evaporative power. The following 
 conditions were laid down as necessary in coal for use at sea by the Commissioners appointed 
 by the Admiralty to inquire into the merits of the several kinds of steam coal in use in the 
 Eoyal Navy : 
 
 " 1. The coal should burn so that steam may be raised in a short period, if this is desired; in 
 other words, it should be able to produce a quick action. 
 
 "2. It should possess high evaporative power, that is, be capable of converting much water into 
 steam, with a small consumption of coal. 
 
 L 2 
 
76 
 
 MINING ENGINEERING. 
 
 "3. It should not be bituminous, lest so much smoke be generated as to betray the position of 
 ships of war when it is desirable that this should be concealed. 
 
 " 4. It should possess considerable cohesion of its particles, so that it may not be broken into 
 too small fragments by the constant attrition which it may experience in the vessel. 
 
 "5. It should combine a considerable density with such mechanical structure that it may easily 
 be stowed away in small space ; a condition which, in coals of equal evaporative values, often 
 involves a difference of more than 20 per cent. 
 
 "6. It should be free from any considerable quantity of sulphur, and should not progressively 
 decay, both of which circumstances render it liable to spontaneous combustion. 
 
 " It never happens," they say, " that all these conditions are united in one coal. To take an 
 instance : anthracite has very high evaporative power, but not being easily ignited, is not suited for 
 quick action ; it has great cohesion in its particles, and is not easily broken up by attrition, but it is 
 not a caking coal, and therefore would not cohere in the furnace when the ship rolled in a gale of 
 wind ; it emits no smoke, but from the intensity of its combustion causes the iron of the bars and 
 boilers to oxidate or waste away rapidly. Thus, then, with some pre-eminent advantages, it has 
 disadvantages which, under ordinary circumstances, preclude its use. The conditions above alluded 
 to may, however, often be united in fuels artificially prepared from coals possessing these various 
 qualities." 
 
 Coal for Gas Purposes. — The manufacture of gas for lighting purposes constitutes one of the 
 chief uses to which coal is applied. And as the qualities demanded are different from those required 
 for other purposes, this application of coal is of peculiar importance to the producer. The first 
 essential condition which a coal must satisfy to render it suitable for gas making is, that it shall 
 possess a large proportion of hydrogen ; and hence, other things being equal, the value of a gas coal 
 will be proportionate to the quantity of that constituent. This condition is most fully satisfied by the 
 flaming and fuliginous varieties of the bituminous and gaseous classes ; and of the latter, torbanite 
 and cannel possess the requisite qualities in the highest degree. The former will yield from 14,000 
 to 15,000 cubic feet of gas a ton, of an illuminating power equal to thirty-four sperm candles. But 
 as this mineral is found developed only in one locality, and that locality is now nearly exhausted, 
 commercially it is of small importance. The yield of cannel is from 9000 to 10,000 cubic feet of gas 
 a ton, of about twenty-four candle illuminating power. On account of the quality of the gas yielded, 
 this variety is much sought after by the manufacturers, who employ it to increase the illuminating 
 power of the gas produced from coals of an inferior class, and hence it commands a high price in the 
 market. But though the production of gas is the primary object of the gas-maker, another verv 
 important consideration presents itself to his notice, namely, the utilization of the residual products. 
 The chief of these is coke, which is the residue of the coal after the volatile matters have been 
 abstracted. As fuel is required in the process of gas making, a portion of this residue may be em- 
 ployed for that purpose, and the remainder sold for uses in which coke of the highest quality is not 
 needed. Thus a good coking coal may be equal in value to another of superior gas-producing, but 
 inferior coking qualities. And, if we except cannel, it may be laid down as a necessary condition 
 that a good gas coal must also be a fairly good coking coal. Cannel yields coke of a very inferior 
 quality ; but the extraordinary quality of its gas more than compensates this defect. With this 
 exception, the requirements of a gas coal are best fulfilled by the richer varieties of the bituminous 
 class. These yield from 8000 to 10,000 cubic feet of gas a ton, of an illuminating power varying 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 77 
 
 from ten to twelve sperm candles. Generally, the greater the quantity of gas obtained, the higher 
 will be the illuminating power. A fortunate circumstance to the coal producer is that strength is 
 not an essential condition in a coal to be used for the manufacture of gas, as it is in those employed 
 for metallurgical and steam purposes ; and hence the tender varieties may be applied to this use, and 
 a market is obtained for the smaller portions which otherwise might not be saleable. It should be 
 remarked that freedom from sulphur is requisite in this as in the other uses which have been de- 
 scribed. Indeed, it may be said that the presence of this substance, in any but very small proportions, 
 unfits a coal for every purpose. 
 
 Coal for Domestic Use. — A large proportion of the coal raised is consumed in heating the 
 atmosphere of dwellings, and other domestic purposes ; and as this use affects, in a greater or less 
 degree, every member of the community, it constitutes from more than one point of view one of the 
 most important to which coal is applied. The qualities required in a good house-coal are numerous, 
 and such as are rarely found united and fully developed in one variety. An essential condition is 
 that it shall be clean in itself, and clean in burning. The former quality necessitates a considerable 
 degree of strength to prevent crumbling, and the consequent production of dust ; and the latter 
 requires comparative freedom from earthy impurities. A coal that leaves a large amount of ash is 
 highly objectionable. There is in some parts, especially in London, a prejudice against coals leaving 
 a white ash, even when the proportion is small, due probably to the conspicuous character of the ash. 
 On the other hand, the red-ash coals are liable, when the proportion of ash is large, to fuse and form 
 clinkers on the bars. Coals that are to be consumed in domestic fireplaces of the ordinary , construc- 
 tion, must be capable of burning with a light draught, and with a bright, lively flame, the cheerful 
 character of the fire, so much desired, depending mainly upon the latter quality. The coals in which 
 most of these qualities are found united are the fiaming varieties of the bituminous class ; and these 
 are exclusively employed wherever they can be readily obtained. In the United States of America, 
 where until very recently bituminous coal was not easily procurable, anthracite, as before stated^ 
 is generally employed. This coal is, however, very far from fulfilling the conditions, considered 
 essential in England, of burning with a light draught and with a cheerful flame. The caking quality 
 of bituminous coal is an advantage in ordinary fireplaces, by occasioning the formation of a cake or 
 " mat " at the top of the fire, whereby the upward flow of the heated gases is impeded, and the heat 
 caused to radiate more into the room. This " mat," however, requires to be broken occasionally, or 
 the impediment to the draught will become so great as to prevent combustion. This tendency to 
 mat, which is an advantage in a sitting-room with an open fire, renders caking coals unsuitable for 
 the kitchen, where the heat is needed for cooking purposes, and where frequent stirring is undesirable ; 
 and for use in stoves to which constant attention cannot be given. For these purposes, coals of the 
 semi-bituminous class are used, either alone, or mixed with the small of the bituminous class. 
 
 Besides the foregoing uses to which coal is applied, it may be desirable to mention its employ- 
 ments in kilns of various kinds, for which purpose the anthracitous varieties are generally the most 
 suitable. 
 
 Produce of Coal Seams. — When the thickness of a seam of coal is known, its yield per acre 
 may be readily calculated. In determining the thickness of a seam, care must be taken to deduct that 
 of dirt partings or of any inferior layers of coal that may exist, as a calculation of the produce 
 founded upon the total thickness, irrespective of the quality, might prove utterly delusive. Also, 
 in some cases, it is necessary to leave a portion of the coal to form the roof, when, of course, such 
 
78 
 
 MINING ENGINEEEING. 
 
 portions will have to be deducted. By the thickness of a seam, as determined for purposes of calcula- 
 tion, is understood the total available thickness of marketable coal. When this thickness has been 
 ascertained, the produce of a seam may be estimated in the following manner. Taking the average 
 specific gravity of gaseous coal as 1*24, a cubic foot will weigh 1-24 x 62-4 = 77-37 lb. ; hence a 
 square yard one foot thick will weigh 77-37 x 9 = 696-33 lb. ; and an acre of the same thickness, 
 696-33 X 4840 = 3,370,092 lb. = 1505 tons. Thus for every foot in thickness, a seam of coal of 
 this character contains 1505 tons an acre. When a seam is inclined at a considerable angle, an acre 
 of surface, assumed to be horizontal, will cover more than an acre of the seam, and in such a case 
 the necessary correction for inclined measure must be made. In the same way it may be shown that 
 bituminous coal, having a mean specific gravity of 1-30, will yield 1577 tons; semi-bituminous coal, 
 with a specific gravity of 1-37, 1662 tons; and anthracitous coal, with a specific gravity of 1-50, 
 1820 tons an acre. As an example, suppose a seam of bituminous coal, 5 feet thick, of which 
 3 feet 9 inches = 3-75 feet is of marketable value; the total yield of such a seam will be 
 1577 X 3-75 = 5914 tons an acre. But as there will always be a certain proportion of coal lost, 
 either in pillars or in other situations, this proportion must be deducted from the total to obtain the 
 actual yield. What this proportion will be will depend upon the system of working and the par- 
 ticular conditions of the case, and can therefore be determined only by experience. Also, when it is 
 known what proportions of large and small coal a seam makes under given conditions of working? 
 the actual yield may be divided according to those proportions, and its value accurately estimated. 
 
 Coal, like rock, when removed from its natural position in the bed and broken up, increases 
 greatly in bulk. This increase is an important element in the question of production with reference 
 to labour and time ; in other words, the daily output. For it will determine the duration of a given 
 portion of the seam relatively to the number of tub loads extracted daily, and the number of loads 
 which a given working face will yield for every three feet in depth, that is, at every " holing." The 
 actual amount of the increase in bulk varies with the character of the coal, so that only an approxi- 
 mate value can be assigned to it. But the approximation will be sufficiently close if we take the 
 mean value as 60 per cent.; that is, a cubic yard of coal will, when broken up, occupy a space equal 
 to 1-60 cubic yards, or 43-2 cubic feet. Hence if the tubs used be 3 feet 6 inches in length, 2 feet 
 9 inches in depth, and 2 feet 6 inches in mean width, which dimensions will give a capacity of 
 3-50 X 2-75 X 2-50 = 24 cubic feet, one cubic yard of coal will require for its transport to bank 
 
 43-2 
 
 -X— =1-8 tubs, or 5 yards will require 9 tubs. 
 
 Comparative Yaltje of large an"d small Coal. — Coal is greatly deteriorated in value by being 
 broken up into small fragments. Hence this matter of the condition of coal is one that will enter 
 largely into the economy of mining, and constitutes, therefore, an important element in the success 
 of every undertaking. And it is for this reason that the practical ability of an underground 
 manager is, as we shall subsequently show, judged, to a very great extent, by the proportion of large 
 coal that he is able to send to surface. The question of profit is mainly dependent upon three 
 circumstances : first, the character of the coal ; second, the cost of production ; and third the 
 condition in which the coal is delivered. It has already been shown that the first of these circum- 
 stances determines the suitability of a coal for any given use, and therefore its market. The 
 character of the coal, which will largely influence the price obtained, is, however, beyond the control 
 of the engineer. The other circumstances, namely, the cost of production and the condition of the 
 
COAL : ITS MODE OF OCCUEEENCE, COMPOSITION, AND VAEIETIES. 
 
 79 
 
 coal, he may modify to a considerable extent. But it must be borne in mind that however the cost 
 of production may be modified, it will remain the same for all conditions of the coal ; that is, a ton 
 of the worst quality will have cost as much by the time it is delivered at surface as a ton of the best 
 quality. Thus it is obvious that the circumstance of the condition of the produce demands special 
 attention, as, if unfavourable, it may nullify the advantages obtained from the others. 
 
 The relative values of the several sizes into which the coal is broken during the process of 
 extraction may be shown in a convenient tabular form as follows : 
 
 Best Coal 
 
 Seconds 
 
 Thirds 
 
 Slack 
 
 Smudge 
 
 The lest consists of all large. pieces; the seconds consists of smaller pieces, but with the slack 
 taken out ; the thirds is the coal as it comes from the pit, with the large and small mingled, the small 
 in this case being assumed to form an average proportion of the whole; the slack is the portion 
 which has passed through a screen having a mesh of IJ inch; and the smudge that which has passed 
 through a screen the meshes of which are ^ inch only. 
 
 A glance at the foregoing table will show the value of the physical condition of strength in the 
 coal, and the necessity for careful attention in laying out and directing the workings. 
 
 1-000 
 
 
 = Bay 11. 
 
 0-900 
 
 
 = „ 18s. 
 
 0-825 
 
 
 = „ 16«. 6d. 
 
 0-450 
 
 ■ ■ a 
 
 = „ 9s. 
 
 0-240 
 
 
 = „ 4«. 2d. 
 
^^ MINING ENGINEEEINQ. 
 
 CHAPTER III. 
 
 SEAECHING FOE COAL. 
 
 Prelimijtart Considerations. — Before commencing an active search for seams of coal in a district 
 where their presence is suspected, certain questions of paramount importance which present 
 themselves for immediate consideration must be indisputably and favourably solved. An essential 
 condition of existence in every undertaking of a commercial character is, that it shall " pay." Profit 
 is the object and end of every kind of industry, and if this end be not attained, the industry must 
 cease. All readily enough acknowledge this fact, and yet, strange though it may seem, great 
 undertakings, and especially great mining undertakings, are frequently entered upon without having 
 first clearly determined the satisfactory fulfilment of this necessary condition. It is evident that the 
 question cannot be finally decided in the affirmative until all the important circumstances of the case 
 are known ; and these can be ascertained only by careful and extensive explorations judiciously 
 devised and skilfully executed, aided by patient inquiry, and guided by an unbiassed judgment. But 
 if certain clearly apparent circumstances exist which are suflScient of themselves to show that the 
 undertaking cannot be commercially successful, even if all the other circumstances should prove 
 favourable, it is plain to ordinary common sense that it would be sheer folly to prosecute a search 
 which must necessarily be an expensive one, and which must as necessarily end in disappointment. 
 Enormous sums of money have been expended in this way to the great and manifest injury of all 
 legitimate enterprise. The preliminary questions which present themselves for solution may be 
 glassed under two heads, as general engineering questions, and general commercial questions, the 
 latter being greatly dependent on the former. 
 
 General Engineering Questions. — A primary question which the engineer will have to take into 
 consideration is that of labour. Is hand-labour abundantly available, or is it otherwise ? The value 
 of labour, like that of every other merchantable commodity, is determined by the demand and the 
 supply, and therefore varies inversely as the abundance of the supply. A scarcity of labour may 
 arise from several causes : one cause is the sparseness of the population. In such a case, the engineer 
 will have either to restrict his output to the capabilities of the available resident population, or to 
 import labour from other localities. If he is compelled to adopt the latter alternative, the cost of the 
 labour must necessarily be high. For though he may obtain his workmen from localities where, 
 in consequence of the supply being greatly in excess of the demand, the rate of wages is low, he will 
 have to ofi"er a considerable premium to induce them to migrate ; and this premium must be large in 
 proportion to the distance and the unattractive character of the new settlement. Moreover, the 
 same rate of payment will in a short time be demanded by the natives, so that the maximum rate 
 will have to be taken as the basis of calculation. In some localities the population may be numerous, 
 
SEARCHING FOR COAL. 81 
 
 but there may exist on the part of the inhabitants a strong dislike for the work of the miner. This 
 is not unfrequently the case where the natives gain a comparatively easy livelihood by agricultural 
 pursuits. In such cases, not only is it necessary to combat the prejudice by the offer of a high 
 premium, but a large proportion of the labour required will, at least in the first instance, have to be 
 imported. Similar conditions exist where, in perhaps a densely populated district, other large 
 industries are carried on. Here, again, the workmen will have to be tempted by the offer of higher 
 wages to relinquish their former occupation for that of mining. When estimating this cost of 
 labour, the engineer must bear constantly in mind that the creation of a new and important 
 industry, like that of mining, must necessarily tend to constantly raise the value of labour in that 
 district, by the increased demand occasioned by the extension of that industry. 
 
 Next to the cost of labour, the cost of materials must be estimated. In a country where timber 
 is plentiful, the cost may remain low for many years, notwithstanding the increased demand for it. 
 But even in this case the value must tend gradually to rise. When, however, it becomes necessary 
 to import timber from a great distance, its cost will constitute an important item in that of pro- 
 duction. The other materials required will vary in cost according to the facility with which they 
 may be obtained. 
 
 Another matter claiming serious consideration is the means afforded by the locality for the 
 conveyance of the produce to points where it may be disposed of. A mountainous district may 
 offer insuperable obstacles. In some localities, practicable means of conveyance may be devised ; 
 but the labour of constructing roads or short lines of railway may entail enormous expense. 
 Frequently, where lines of railway are needed, it will be prudent to wait till other parties are found 
 to take up the question of conveyance, before commencing the opening out of a new field. But 
 whether the difiSculties presented be great, or small, this question of transport is an exceedingly 
 important one, influencing in no inconsiderable degree, not only the present, but the future success 
 of the undertaking, and demanding, on the part of the engineer, knowledge, skill, and prudence. 
 
 General Commercial Questions. — Founded mainly upon the foregoing, there exist certain other 
 questions of an entirely commercial character, demanding careful consideration. The first is, the 
 cost of production at the pit's mouth. In estimating this, the conditions of working may be assumed 
 to be of an average character, and a comparison made with the district from which the present 
 supply is obtained. Suppose, for example, that the cost of production at the pit's mouth in this 
 district is 5s. a ton. If it can be shown that labour, after the premium for its attraction, previously 
 described, has been allowed for, can be obtained for 20 per cent, less cost in the new district, as this 
 constitutes by much the most important item in the total cost of production, we should not be far 
 wrong in assuming that cost to be 20 per cent, less, or 4s. Qd. per ton. In like manner, if the cost 
 of labour were 20 per cent, more, the cost of production in the new district would be 5s. 6rf. a ton. 
 Whenever a great difference exists in the cost of materials, this difference must, of course, also be 
 taken into consideration. By these means, the value of the coal when raised to surface may be 
 approximatively determined; but this value is of itself not sufficient to indicate the price at which 
 the produce of a colliery may be sold to obtain a given profit. This question may be involved in the 
 jaext which we have to consider, namely, the market for the produce. 
 
 By the term " market " is understood the geographical area over which the produce may be 
 profitably distributed. The extent of this area will evidently depend upon several conditions. The 
 natural market of any given district is included within a radius from the centre of production of 
 
 M 
 
82 MINING ENGINEEEING. 
 
 Buch a length that the produce may be delivered at its extremity at the same price as that demanded 
 by the competing districts. To make this clear, suppose a district, 0, supplied with coal from two 
 other districts, A and B, situate on opposite sides of C, and at equal distances from the centre of the 
 latter. If A is placed in more favourable conditions of working than B, its produce will be raised 
 at a cheaper rate ; and if, in addition to this, it is more favourably situate with respect to in the 
 matter of conveyance than B is, it is plain that A's market will extend beyond the centre of 0, 
 because it can deliver its produce at that point at a lower price than B can. And the boundary 
 of the two markets may be shown on the map by a line drawn through those points at which the 
 two districts deliver their produce at the lowest possible price consistent with a reasonably remunera- 
 tive profit. If the facilities for transport were equal in all directions, such boundary lines would 
 be circles tangent at the point at which they cut a straight line joining their centres. But as this 
 equality never exists, the boundary will be an irregular, and frequently a very irregular, line. 
 Suppose, again, that coal is discovered in the centre of the C district ; the question is. What will be 
 the boundary of C's market ? Evidently the whole of this market will be taken from A and B ; but 
 in what proportions ? Assuming the cost of production in C to be the same as in A, it is clear that 
 the latter's boundary will be driven farther back than B's, because of the greater facilities of 
 transport that exist between A and than between B and C ; and also that the boundary line of 
 the latter in the direction of A will be midway between the centres of production of and A. In 
 the opposite direction towards B, C's boundary line will extend beyond the midway point by a 
 distance which will be proportionate to the difference in the cost of production in C and B. In all 
 of these considerations it is assumed that the quality of the produce is the same" in all the districts. 
 Variations of quality, however, except in special circumstances, may be considered as variations in 
 cost, a deterioration in quality being equivalent to a proportionate increase of the cost of 
 production. 
 
 It will be evident on reflection that the consumption of the produce within the area comprising 
 a market will be much greater in some points than in others. G-reat industries, populous towns, or 
 important seaports, may exist, which may occasion a very large demand within a limited area. 
 Whence it follows that a very small market, geographically, may be of far greater importance than 
 one of much wider extent. But it is equally evident that the larger the market is geographically, 
 the greater is the chance of its increasing in importance by the growth of new industries, and the 
 development of the districts included within it. 
 
 It follows from the foregoing considerations, that the conditions which determine the extent of 
 the market are, first, the cost of production ; and, second, the facilities which exist or may be 
 created for transport. In general, the latter condition will be the more important ; and in taking it 
 into account, future contingencies must be kept clearly in view. A district which, for example, is 
 imperfectly served by a railway now, may by its development attract fresh capital towards the 
 extension of the system, or the construction of new and competing lines. And the same remark 
 is applicable, with a change of terms, to a service of shipping from a seaport, or other means 
 of transport. 
 
 Thus, in considering the commercial questions afi"ecting a new district, it may be ascertained 
 that the market for the produce would be too limited in extent to justify the employment of a large 
 capital in an undertaking of a somewhat hazardous nature. Or it may be, that in consequence of the 
 absence of any means of transport, and the existence of insuperable natural obstacles to the creation 
 
SEAECHING FOR COAL. 83 
 
 of any such means, there can be no market at all. Or, again, a wide market may exist ; but in con- 
 sequence of the absence of large industries, a numerous population, or seaports, or the possession of 
 an abundant supply of wood, it is at present valueless. If any one of these circumstances should be 
 proved to exist, it would be folly to undertake an expensive search for coal, and prudence will 
 dictate the abandonment of the scheme at this stage, or at least its postponement until the progress 
 of events shall have changed the existing condition of things. But if, on the other hand, it be 
 indubitably proved that no one of these circumstances can occur, then we have ample justification for 
 entering upon the search, and prosecuting it with vigour. And here we may venture the remark, 
 that when once the preliminary considerations have been determined favourably, neither time nor 
 expense should be spared in bringing the search to a satisfactory issue. If it is folly to begin before 
 having carefully considered the commercial aspects of the question, it is still greater folly to 
 prosecute the search in such a way that the problem cannot be finally solved thereby, or to cease 
 before that end has been attained. 
 
 Determination op the Existence of Seams op Coal. — The determination of the existence 
 of coal seams in any given locality, whether that locality be a wholly new and unknown one, 
 or bordering upon another in which seams are known to exist, is a labour of a purely geological 
 character. And the knowledge to be applied in such investigations must be wide and general. 
 That which is obtained by experience in the mine, and which may be described as local and 
 particular, is totally insufficient for the purpose. An acquaintance with the broad facts of geology, 
 as well as a familiarity with local phenomena, are absolutely indispensable. And these must be 
 supplemented by accurate mineralogical knowledge, upon which the truth of geological inferences 
 often greatly depend. Possessed of such knowledge, the explorer is able to prosecute the search for 
 coal in a rational and systematic manner, that must infallibly lead to certain results. The mode of 
 conducting the search in a wholly new locality will vary somewhat in detail from that observed in a 
 partially known district. 
 
 Searching in a New Locality. — ^A search for coal in a new locality should consist of two stages, 
 which may be described as the " general," and the " particular." The first, or general stage of the 
 search, will be devoted to the making of a geological survey of the district, in the manner described 
 in the first chapter of this work. As the object of this survey is rather to determine the character of 
 the rock-beds than to define their extent, the latter may be laid down on the map approximatively, 
 leaving its accurate definition for the second stage of the survey. Every care must, however, be 
 taken to determine rightly the relative age of the beds, for on this the result almost wholly depends. 
 The means by which this determination is effected have been described in the chapter previously 
 referred to. 
 
 The nature of the evidence obtained from the geological constitution of a district may be either 
 negative or positive. If the results of the preliminary survey show indubitably that the rock-beds 
 of the Carbon Period are absent, it may be justly inferred that coal does not exist in that locality. 
 And if the same results are obtained throughout the district, further search would be useless ; but if, 
 on the other hand, the coal measures are met with, though not absolutely conclusive of the existence 
 of seams of coal, such evidence is positively and strongly in favour of their existence. It is, indeed, 
 only where the measures are found in insignificant fragments that coal is absent. The determination 
 of the carboniferous formations is, however, often a matter of great difficulty, and one that requires 
 long and patient observation. The explorer should be warned against drawing hasty conclusions, 
 
 M 2 
 
84 
 
 MINmG ENGINEEEING. 
 
 especially concerning the absence of the carboniferous rocks. He will find it necessary in sucb 
 circumstances to suspend bis judgment until be has obtained complete evidence, and, as previously 
 remarked, tbe obtaining of sucb evidence will require much time and labour. The configuration and 
 general aspect of the surface, which, in the older formations, never deceive the eye of an experienced 
 geologist, are, in this case, of but little assistance, on account of the readiness with which the 
 carboniferous rocks yield to atmospheric influences. The only indication of this character of any 
 value is that the general aspect of the surface is flat, or varied by low and gently sloping hills. This 
 circumstance renders it difficult to find " sections " of the strata, or bold outcrops from which their 
 character, dip, and thickness can be ascertained. In numerous cases, too, the outcrops are covered 
 by more recent deposits. These circumstances — complicated, perhaps, by the presence of faults — may 
 render it necessary to have recourse to boring, in order to accurately determine the geological 
 constitution of a given tract of country. 
 
 When the existence of the coal measures has been placed beyond doubt, or even when a strong 
 probability of their existence has been made out, the second or particular stage of the search will be 
 entered upon. This consists of special observations and investigations, having for their object the 
 discovery of the outcrop of the coal seams, and of exact surveys for the purpose of laying down on 
 the map, in plan and in section, the true extent and positions of the rock-beds among which the 
 seams occur. As the outcrop will in most cases be hidden beneath vegetable soil, a vigilant eye will 
 be needed to detect the traces of it on the surface, and the observer will find it necessary to make use 
 of every possible source of information. He should carefully examine every exposed surface, and 
 especially every " section," such as may be found in roadsides, escarpments, quarries, wells, and the 
 banks of streams. The latter are particularly deserving of attention, for besides showing a section 
 of the strata through which they have cut their way, they afford valuable information of another 
 character. The bed of a stream contains a collection of mineralogical specimens obtained from all the 
 country above the point at which they are found. By ascending the bed of streams, therefore, and 
 examining minutely the pebbles and sands which have been brought down, and noting the height at 
 which fragments whose special character have attracted attention cease, a clue may be obtained to 
 the spot whence they came. Whether this spot be near or remote, may be judged from the more or 
 less worn state of their edges, considered in relation to their hardness. Among the substances indi- 
 cative of the presence of coal seams, nodules of carbonate of iron merit special mention. Pieces of 
 shale should be examined with particular minuteness for vegetable impressions and organic remains. 
 The latter may often be found in the beds of streams washed clear of earthy matters ; these afford 
 evidence of a most important character in determining the existence or otherwise of the object 
 sought. If they be true coal fossils, every care should be taken to trace them to their origin up the 
 country. Small grains of coal may also be found in hollows of the bed, for wherever a seam of coal 
 crops out, it is pretty sure to be crossed in some part by one of the streams in the locality. But 
 even where this is not the case, particles will be carried down to the streams by heavy rains. 
 
 When, from all the indications observed, the locality of the outcrop of a coal seam has been 
 determined as nearly as the nature of those indications permit, the surface of the ground must be 
 attentively examined. The observer will bear in mind that the coal measures consist, as described 
 in the chapter on geology, of an alternation of beds of coal, shale, and sandstone, and that each of 
 these resist the disintegrating action of atmospheric agencies in different degrees. Thus, the sand- 
 stone is the most enduring, the shale being very destructively acted upon, and the coal still more so 
 
SEAECHING FOE COAL. 85 
 
 than the shale. Hence the outcrop of the coal seam may be expected to occur in a depression or 
 hollow of the surface, and, therefore, depressions should be looked for, and carefully examined. If a 
 depression is found following everywhere the direction of a ridge formed of protuberant sandstones, 
 it will probably be the outcrop of the seam sought. It must not be expected, however, that the line 
 of depression will be a continuous one ; many causes may operate to prevent this. On the contrary, 
 in most cases it will be formed by a succession of hollows, irregular in their intervals and their 
 degree of depression. The action which thus tends to render the position of the outcrop conspicuous, 
 also tends to conceal the seam itself, by bringing down upon it and overlaying it with the detritus 
 of the higher and more durable rocks, especially the contiguous shales. Hence small superficial 
 indications must be looked for. A darker colour of the soil generally throughout a certain breadth 
 of country, such as may frequently be observed in a freshly ploughed field ; darker patches of soil 
 here and there ; protruding bands of dark shale in certain spots, and minute particles of black 
 carbonaceous matter left as a sediment from water in cattle tracks, or other holes in the surface — any 
 one of these circumstances may be taken as indicative ot the presence of the outcrop. It now only 
 remains to prove the truth of the inferences drawn. This is done by digging small pits, at intervals 
 of a few yards, in a direction, as nearly as can be judged, at right angles to the strike of the beds. 
 These pits must be carried sufficiently deep to pierce the overlying drift. If the outcrop is discovered 
 by these pits, the sinking of others will be proceeded with until the outcrop has been passed in 
 opposite directions, that is, until the line of the trial pits extend beyond the upper and lower 
 boundaries of the seam. The two outer pits on each side of the central one should then be joined by 
 a trench of the same depth as the pits, in order to discover clearly the upper and lower boundaries of 
 the seam, and to ascertain approximatively its dip. It must be remarked here that coal seams often 
 diminish singularly in thickness at their outcrop, so that a seam two or three yards thick may appear 
 at the surface as a mere line of black shale. This fact is probably due to the disintegration and 
 decomposition of the coal by atmospheric agencies, and the consequent spreading of the beds that lie 
 immediately above and below the seam. Hence, if the outcrop is not struck by one of the trial pits, 
 it will be well to join them all by a trench before abandoning the search. T\Tien the existence of a 
 seam of coal has been proved in this manner, the bearing of its strike should be determined, and at 
 least two other trials of the outcrop made at about equal distances on each side of the proved point. 
 By means such as these the object of the search is attained, and it only remains to record the 
 information accurately on the map. In prosecuting the search, local traditions should not be 
 neglected ; often a hint obtained from such a source will put the observer at once upon the right 
 track, and so save him much time and labour. 
 
 Searching in a partially known Locality. — In order to fully understand the character of the search 
 which we have here to consider, it is necessary to possess a clear and definite notion of the nature of 
 the boundaries of a coal-field. A seam ot coal may terminate, actually or practically, (1) by cropping 
 out to the surface; (2) by thinning out and being replaced by a bed of another nature; (3) by 
 dipping beneath more recent deposits to a depth too great to allow of its being worked ; and (4) by 
 being thrown by a fault of dislocation, either out altogether, or down to an impracticable depth. It 
 will be plain, on reflection, that we shall have to consider only those boundaries which are due to the 
 occurrences described in (3) and (4), since the seam in the former cases (1) and (2) actually and 
 finally terminate. There may be an exception in the case of (1), which will be explained liereafter. 
 
 When a seam of coal is lost by plunging beneath a set of beds of more recent formation than 
 
86 
 
 MINING ENGINEEEING. 
 
 those of the Carbon Period — as, for example, when the coal measures disappear beneath permian or new 
 red sandstone rocks — there is no question of the existence of coal in the area covered by the latter beds. 
 The continuance of the seams which have been worked up to the boundary of the district may fairly 
 be assumed. The only question is, Can the seam be reached at any point within a practicable distance 
 of the surface? It is obvious that this question must be answered in the negative if all the 
 conditions remain the same, since the seam, which was abandoned at the boundary of the district in 
 consequence of its great depth, must continue to sink deeper as it passes through the new locality in 
 which it is to be sought. Hence, in this case, the object of the search is not to discover the existence 
 of the seam, as in the preceding case, but to ascertain whether any of the conditions have changed 
 since the seam known to exist disappeared beneath the newer formations. The possible changes are 
 of three kinds, any two or all of which may occur at the same time. The overlying beds may, at no 
 great distance from the point at which they come in over the coal measures, have been subjected to 
 great denudation. This occurrence, provided the seam dipped at a low angle, might so reduce the 
 depth as to render working again practicable. Or the seam may by a synclinal curve be brought up 
 towards the surface. It has been shown, in Chapter i., that the palaeozoic rocks were greatly contorted 
 before the deposition of the new red sandstone, which accordingly lies unconformably upon them. 
 Whence it is evident that this second case is by no means remotely probable. Or, again, a fault of 
 dislocation may have occurred to throw the seam nearer the surface. The frequency of such faults 
 renders this case one of peculiar importance. 
 
 The first and last of these possible cases may be determined by a careful and detailed geological 
 survey. The principles upon which such a survey is conducted, and the means employed in its 
 execution, having been already fully described, the reader is referred, for information on this subject, 
 to the sections in which the descriptions are given. We here do no more than point out the circum- 
 stances and conditions towards which the attention of the observer should be specially directed. 
 The determination of the second case, when the paleozoic rocks do not come up to the surface, 
 necessitates a recourse to boring. Reference has been made to the fact that the outcrop of a coal 
 seam is not necessarily its actual limit in that direction. When the outcrop occurs on an anticlinal, 
 its continuation may be expected on the other side of the curve ; and a fault of dislocation may, by 
 a downthrow, bring the seam in again for a distance proportional to the, angle of inclination 
 and the amount of the throw. These are questions to be determined by a survey. 
 
 The question of the depth at which the extraction of coal ceases to be practicable, is one the 
 conditions of which are constantly changing with the improvements effected in mechanical appli- 
 ances. The determination ot the question is almost entirely dependent upon the means possessed of 
 raising the coal to surface, and of providing sufficient ventilation ; and as these means are improved, 
 pits are sunk deeper and deeper, so that depths formerly considered altogether impracticable are 
 now of common occurrence, and in some instances are greatly exceeded. The deepest coal workings 
 in England are those of the Rosebridge Colliery, near Wigan, which are situate at 2400 feet from 
 surface. But in Belgium there is a colliery now being worked, the depth of which exceeds 3400 
 feet. As, however, it seems hardly possible to raise coal through a greater height than 2500 feet 
 in one lift, we must consider this the present limit, though, with better appliances and other arrange- 
 ments, it is probable that coal seams may be successfully worked at much greater depths. This limit 
 is that which is imposed by the conditions of winding and ventilating, and may be termed the 
 mechanical limit, inasmuch as it is dependent on mechanical appliances. But the thickness and 
 
SEAECHING FOE COAL. 87 
 
 quality of the seams may be such as to render this depth far too great to allow of profitable working. 
 Thus we have another limit which, being dependent on commercial circumstances, may be called the 
 commercial limit. The latter must be determined for each individual case from the data possessed. 
 
 Determination op the Character op a Seam op Coal. — With the determination of the 
 existence of a seam of coal, the labour of the mere geologist ends, and that of the mining engineer 
 proper begins. It would be an exceedingly hazardous venture to undertake the opening out of 
 a colliery, and the erection of costly plant for its development, in reliance upon the evidence obtained 
 from the survey alone. Before commencing the extraction of the discovered mineral, and, indeed, 
 before making any preparation for its extraction, prudence will dictate further researches, involving 
 a large expenditure both of time and money certainly, but indispensable to safety from ultimate 
 failure. Every seam of coal is not profitably workable. The necessary, though not sufficient, 
 conditions which a seam must fulfil to be considered ot a workable character are, that it shall be 
 sufficiently thick, of considerable extent, and of suitable quality. Besides these essential conditions, 
 there are others of grave importance, such as the character of the roof, the inclination and regularity 
 of the seam, and the nature of the strata which will have to be sunk through, claiming careful and 
 early attention. To determine accurately and clearly these conditions is the object of the researches 
 which it is incumbent upon the engineer to make in continuation oi the labours of the geologist. 
 The methods of prosecuting these researches are (1) by headings, (2) by trial pits, and (3) by borings. 
 
 When the outcrop of a seam of coal has been discovered and tested in the manner previously 
 described, its character may be partially determined by driving headings or drifts into it to a 
 sufficient depth. Such headings may be driven in the seam following the direction and inclination 
 of the strata, or horizontally to cut the seam in a given point. Generally the former plan will be 
 preferred when the angle of the dip is low, and the latter when the beds are highly inclined. In 
 choosing the spot for a trial heading, care should be taken to avoid such as are liable to be flooded 
 by surface water during heavy rains. If the excavation is to be an inclined one, this precaution is 
 especially necessary. Supposing the heading to be of this character, and a suitable spot determined 
 upon, the excavation will be commenced in the outcrop of the seam. The dimensions will be the 
 least possible consistent with convenience of working. The minimum imposed by this condition is 
 3 feet wide by 4i feet high ; but in general it is better to allow more space than this, 4 feet by 
 5 feet 6 inches being more suitable dimensions. In any case, however, excepting, perhaps, seams of 
 extraordinary thickness, a sufficient height must be given to the heading to remove the whole of 
 the seam, so as to discover the character of the roof and the floor. It has already been remarked 
 that coal seams often diminish greatly in thickness at the outcrop. Whatever the character of the 
 roof may be, some timbering will be required, for the strongest rocks become tender and broken up 
 by fissures near the surface of the ground. The methods of timbering and the means employed in 
 making the excavation being precisely the same as those applied in driving the levels for the deep 
 workings, the description of them will be reserved for a subsequent chapter. 
 
 The explorer will not be discouraged by the inferior quality of the coal met with at the com- 
 mencement. The action of atmospheric agencies will necessarily have greatly deteriorated the 
 quality near the outcrop ; and its physical condition will have suffered no less than its composition. 
 At first it will be extremely friable, and will exhibit hardly a trace of stratification or cleat, being in 
 a completely disintegrated state. It will also be largely mixed with earthy matters introduced by 
 intiltering water holding them in suspension. But these qualities gradually disappear as the heading 
 
88 • MINING ENGINEEEING. 
 
 progresses, and the latter should be continued until it has got beyond the reach of atmospheric, 
 influences, when the true character of the coal will appear. It must not, however, be supposed that 
 the actual quality of the coal will ever be seen in a heading. This is found only at a considerable 
 distance from the surface ; but sufficient indications will be obtained of what will be met with at 
 greater depths. When the heading has been carried far enough to attain the object sought, branches 
 or side drifts should be thrown out at right angles to the heading, so as to expose a larger face of 
 coal, for the purpose of forming a more accurate estimate of its character. During the progress 
 of these excavations every care should be taken to determine exactly the dip of the seam and the 
 character of the adjacent rocks. 
 
 When the strata are inclined at a considerable angle, or when the infiltration of water into the 
 excavation is feared, a horizontal heading will be preferred. Such a heading, however, like the 
 so-called " levels " of the deep workings, is not strictly horizontal, but is slightly inclined outwards; 
 from the face, for the purpose of discharging any water that may enter, and to facilitate the extrac- 
 tion of the broken rock. When, from the preliminary observations, the dip of the beds has been 
 approximatively determined, a suitable spot beneath the outcrop of the seam is selected for the opening 
 of the excavation. The distance of this spot below the line of the outcrop is made such that the 
 heading will strike the seam at a point sufficiently remote from the outcrop to afford the required 
 information. The heading is driven through, the seam, and side drifts put out in it at right angles 
 to the heading, as in the preceding case, and for the same purpose. The horizontal heading, besides 
 the advantages afforded for extracting the rubbish and keeping the workings free from water, 
 furnishes a better neans of discovering the character of the adjacent rocks. 
 
 Instead of headings, vertical pits are sometimes resorted to for the purpose of ascertaining the. 
 character of a seam. The pit is located above the outcrop, and at such a distance from it that the 
 evidence obtained when the seam is struck shall be sufficiently indicative of its character. This 
 method is usually more expensive than the preceding ; but a better knowledge of the superjacei t 
 rocks is obtained by it. The same knowledge would, however, be afforded by the horizontal heading 
 if the latter were continued sufficiently far beyond the seam. Grenerally, headings should be preferred 
 to trial pits, except when the strata are nearly vertical, in which case pits can alone be employed. 
 
 Boring affords the only means of determining whether the seam be continuous or not over a 
 given area. The operation consists in excavating a hole of only a few inches in diameter, by means 
 of suitable tools fixed to the end of a line of rods worked from the surface, which line is lengthened 
 as the hole progresses in depth. The rubbish formed at the bottom of the hole by the cutting action 
 of the tools is extracted from time to time by means of other tools specially designed for the purpose. 
 By making alternate use of these two sets of tools, the hole is gradually deepened, and the nature of 
 the bed which is being passed through is ascertained from the rubbish brought up from the bottom 
 of the hole. By means such as these, a hole may be bored to a depth of 2500 feet, the limit of 
 workable depth previously described. A number of such bore-holes judiciously distributed over the 
 area under examination will determine in the most decisive manner the character and thickness of a 
 seam of coal ; its dip and continuity ; the number, direction, and amount of throw of the faults of 
 dislocation, if any exist; and many other questions of the gravest importance to future mining 
 operations, such as the nature of the superjacent rocks, and the existence of water-bearing strata. 
 
 In determining the position of the bore-holes, it will be borne in mind that no bed cropping out 
 on the dip side of the boring will be passed through, and that the depth at which the seam will be 
 
SEAECHING FOE COAL. 89 
 
 struck by a second boring farther to the dip, may be accurately calculated from the horizontal 
 distance between the two borings, as explained in Chapter i. If the seam is not met with at that 
 depth, it may be inferred that some interruption exists, the character and extent of which must be 
 made the objects of further search. 
 
 We have already alluded to the use of boring in searching for seams of coal under conditions 
 in which no other means are available. Besides this use, it may be appHed to the discovery of 
 parallel seams existing above or below the one upon which attention has been directed. 
 
 Boring constitutes, indeed, the most valuable means which the mining engineer has at his 
 disposal, not only for revealing the existence of seams of coal, but also for ascertaining their actual 
 character at any given point, and the conditions that will be encountered in sinking the shafts 
 to it. To these circumstances it is due that the use of this means has of late been rapidly extending, 
 and it is destined no doubt, with improved appliances, to take a more important position than it 
 now occupies among engineering resources. 
 
 Boring Operations, and Appliances therefor. — The tools used in boring penetrate rocks 
 by percussive action, that is, by having their cutting edges forcibly and repeatedly applied to them in 
 a manner to constitute a rapid succession of more or less heavy blows. Each blow chips off small 
 fragments of the rock, and in this way, by the continued action of the tool, the rock is gradually worn 
 away. But if the blows were continually delivered upon the same point, this chipping action could 
 not take place, and the tool would merely pound the rock to a powder at that point without making 
 much onward progress. Moreover, in such a hole as would be produced by that means, the tool 
 would soon become fixed, and farther advance would be rendered impossible thereby. Hence, in 
 addition to the reciprocating motion required to produce the percussive effect, it is necessary to 
 impart a rotary motion to the tool, the two motions being so proportioned to each other that the 
 edge of the tool may not fall twice in the same place. As the motions have to be transmitted from 
 the surface to the tools at the bottom of the bore-hole, the apparatus required for the purpose will 
 evidently consist essentially of three distinct portions : the tools by means of which the excavation is 
 effected ; the medium through which the motion is transmitted ; and the appliances by which the 
 motion is produced. The first consists of cutting, clearing, verifying, and regulating tools; the 
 second, of iron or wooden rods ; and the third, of shear-legs, pulleys, windlasses, levers, and other 
 implements forming the surface apparatus or head-gear. It will conduce to a clear imderstanding of 
 the subject to describe these portions separately. 
 
 Cutting Tools. — The term " cutting " tool apphed to an instrument for penetrating rock is not a 
 strictly correct one. The student who has examined the mineral composition of rocks will have 
 recognized the impossibility of cutting them, in the ordinary acceptation of that term, inasmuch as 
 the rock constituents are frequently harder than the tools which are used to penetrate them. This 
 fact has, as we shall see later, very important practical bearings. When a rock cannot be cut, the 
 only way of removing portions of it is by fracturing it by a blow delivered through the medium of a 
 suitable instrument. Hence it is that the percussive action is adopted in all rock-boring operations, 
 as already explained, the end to be attained being the removal of the rock by a constant process of 
 chipping. To effect this chipping, the instrument used must present only a small surface to the rock 
 BO as to concentrate the force, and that surface must be bounded by inclined planes or wedge-shaped 
 surfaces so as to produce a lateral pressure upon the particles of rock in contact with them. In other 
 words, the instrument must be provided with an edge similar to that possessed by an ordinary cutting 
 
90 MINING ENGINEEEING, 
 
 tool. The conditions under which the instrument is worked are obviously such that this edge will be 
 rapidly worn down by the friction against the harder rock materials, and by fractures. To withstand 
 this destructive action, two qualities are requisite in the material of which the instrument is 
 composed, namely, hardness and toughness. Thus there are three important conditions determining 
 the suitability of a cutting tool to be used for rock boring : the necessity for a cutting edge ; the 
 necessity for a frequent renewal of the edge ; and the necessity for the qualities of hardness and 
 toughness in the material of the tool. The difficulty of satisfying these conditions has led to 
 extreme simplicity in the form of the tools. The question of the most suitable form for penetrating 
 hard rock has received much attention, and numerous modifications have been proposed ; but nearly 
 all have failed in practice, and consequently have been abandoned because of their unsuitable 
 character in relation to the second condition. When it is borne in mind that a boring tool cannot be 
 used in hard rock for longer than a few hours at the best without resharpening, the importance of 
 this condition will be recognized. The form of the tool may be admirably adapted for penetrating 
 the rock, but if it be a difficult one to work upon in the smithy, where the tool must necessarily be 
 perhaps several times in a day, it is obvious that more time may be lost upon the forge than is 
 2;ained in the bore-hole. Hence, as the result of experience in this direction, all complicated forms, 
 except for certain special purposes, have been generally abandoned, those at present in use being the 
 simplest forms first employed, or those forms very slightly modified. It will be apparent from the 
 circumstances referred to in the foregoing statements, that the smithy holds a very important 
 relation to the boring apparatus. As a matter of fact the success of the undertaking depends in a 
 notable degree upon the care and skill with which the smith's work is performed. But as we shall 
 have occasion in the next following chapter to treat of the hand-boring tools that are of daily use in 
 every mine from the time when the shaft is begun to the time when the last load of mineral is drawn, 
 we shall defer our remarks on this subject, as well as on that of the quality of the metal, till that 
 opportunity. It should, however, be remarked here, as appropriate to the subject in question, that 
 the smith must be recommended to exercise especial care not to alter the dimensions of a tool he is 
 required to work upon ; and as a precautionary measure, it will be prudent, whenever a tool has been 
 returned from the smithy, to pass it through a ring of the requisite diameter before lowering it into 
 the bore-hole. If this precaution be neglected, grave injury may result to the sides of the hole, or 
 irregularities may be produced that may occasion insuperable difficulty should it subsequently become 
 necessary to tube the hole. 
 
 The simplest form of tool is shown in Figs. 161 and 162, Plate XIII., and is known as the "flat 
 chisel " or " straight bit." It is formed of the toughest wrought iron, and steeled at its cutting edge 
 with the best material. The length is usually 18 inches ; at the upper end it is provided with a thread 
 by means of which it is screwed to the rods. The breadth of the cutting edge is, in this example, 
 3 inches ; and it may be remarked here that the whole of the tools and appliances illustrated in this 
 chapter are for a bore-hole of 3 inches diameter. This form of tool is of very common use, being 
 applicable to all but the softest and hardest strata. The ease with which it may be resharpened is a 
 quality that commends it to the choice of the practical man. 
 
 The form shown in Fig. 163 is designed for penetrating hard rock, and is variously known as 
 the diamond-point drill or V-chisel. This tool differs from the preceding only in the form of its 
 cutting edge, which is very suitable for rock of a highly resisting character, and which offers but 
 little more difficulty in the smithy than the straight edge of the flat chisel. 
 
SEARCHING FOE COAL. 91 
 
 Figs. 164 and 165 represent another form of chisel, intended for piercing very hard rock. This 
 form is commonly employed on the continent of Europe ; but though it effects very satisfactorily the 
 object for which it was designed, the difficulty of resharpening and repairing it has prevented its 
 general adoption in this country. Like the preceding, it differs from the first only in the form of its 
 cutting edge. 
 
 For boring through gravel, the form of cutting tool shown in Fig. 166 is used. It consists of 
 two cutting edges at right angles to each other, one of them being curved towards the extremities. 
 This form, which in other respects is identical with the foregoing, is known as the T-chisel. 
 
 For boring through soft clay or loose sand, the auger. Fig. 167, is employed. This tool is very 
 similar to that used for boring in wood. The bottom is partially closed by the lips, which are turned 
 down to a greater angle than in the case of wood angers. The clay auger is made of greater length 
 than the chisel bits, but it terminates upwards in the same form as the latter. Usually it is half 
 cylindrical, as in the figure ; but sometimes it is made wholly cylindrical, with the exception of about 
 six inches at the bottom, where it is left open to allow of the admission of the material being bored 
 through. When used in clay, this tool, on being raised to surface, carries the core with it. 
 
 The angle of the edges of cutting tools is determined by the character of the rocks to be pene- 
 trated, the obtuseness increasing with the hardness of the rock. Too small a degree of obtuseness is 
 to be especially avoided, since the fracture of the edge not only diminishes the efficiency of the tool 
 and necessitates repairs on being drawn to surface, but, by leaving fragments of hardened steel at the 
 bottom of the bore-hole, is liable to cause the same injury to the tools subsequently lowered. It is a 
 good plan to test every fresh tool before fixing it to the rods, by dropping it from a considerable 
 height, edge downwards, upon a hard stone. 
 
 Clearing Tools. — "When the action of the cutting tools has been continued sufficiently long to 
 produce a mass of debris at the bottom of the hole, it is necessary to remove that mass ; for it is 
 evident that the presence of those materials will tend to diminish the action of the tools upon the 
 rock by forming a protective covering. Hence an accompanying set of tools is needed for the 
 extraction of the rubbish. As in the case of the cutting tools, many forms have been designed 
 for this purpose ; but though the same conditions do not hold, only the simplest remain in common 
 use. These tools may be divided into two clases : those which act by rotary motion, and those 
 which act by percussion. The former are attached to the rods in the same way as the cutting tools, 
 and are worked by simply turning the rods ; the latter are not used with the rods, but are jerked 
 up and down in the bore-hole on the end of a rope. The following are the clearing tools in 
 common use : 
 
 The most generally employed tool of the revolving class is that represented in Fig. 169, and 
 known as the " auger-nose shell," or " wimble." It is of the same form and dimensions as the 
 cylindrical clay auger, with the exception of the diameter of the cylindrical portion, which, as in all 
 clearing tools, is slightly less than that of the cutting tools. To prevent the escape of the loose 
 material, it is furnished on the inside with a valve. It has already been remarked that the clay 
 auger removes the material from the hole, and therefore does not necessitate the use of a clearing tool. 
 Another form of tool, known as the " flat-nose shell," is shown in Fig. 170. This tool differs from 
 the preceding only in the form of its lower extremity, which is flat, and not open at the side : it is 
 provided with a valve for the retention of the material, as shown in the figure. 
 
 For use in harder ground, a modification of the preceding form has been adopted, known as the 
 
 N 2 
 
92 
 
 MINING ENGINEEEING. 
 
 " shoe-nose shell." The point of this tool, shown in Fig, 171, enables it to sink into the debris more 
 readily, and also to gather it into the part above the valve. 
 
 Occasionally a pebble, a flint, or a hard piece of rock will get into the bottom of the bore-hole, 
 from which it cannot be readily extracted by the ordinary valved clearing tools. In such cases 
 recourse must be had to the special tool, represented in Fig. 168. This tool, which is called a 
 " wad-hook," consists of two steel spiral blades, arranged as shown in the figure. A few turns of the 
 rods are generally sufficient to make the blades clasp the obstruction, which may then be withdrawn 
 without difficulty. The wad-hook may also be used for extracting a broken tool, as will be 
 explained later. 
 
 The foregoing revolving tools clear the bore-hole very effectively, and this is a merit which can 
 hardly be exaggerated, since the presence of debris, as before remarked, tends greatly to retard the 
 progress of the operation. But they have one serious defect, namely, that of requiring much time 
 and labour in lowering and raising, connecting and disconnecting the rods. The tools of the second 
 class are not open to this objection, inasmuch as they are lowered rapidly by a rope. This class of 
 clearing tools are called sludgers, from their being employed to remove the debris, as sludge or mud, 
 from the bore-hole. Numerous forms have been given to sludgers also, but the only one that has 
 continued in general use is the simple ball-valve sludger, represented in Fig. 172. 
 
 This instrument consists of a wrought-iron cylinder of the same dimensions as the shells already 
 described, and similar to the latter in external appearance, with the straight portion of the shank 
 removed. The lower extremity is furnished internally with a ball- valve ; this valve is either of 
 wood or of metal, preferably the latter, and its weight is proportioned to the degree of fluidity of 
 the matters to be extracted. It rests, as shown in the figure, upon a conical seating formed by an 
 annular piece riveted to the cylinder. As previously stated, the sludger is worked by jerking it up 
 and down in the bore-hole. During the descent of the tool, the valve is raised by the water in the 
 hole ; for it must be borne in mind that the presence of water is essential to all boring operations, 
 and that, therefore, when water does not enter through the strata, it must be supplied from above. 
 The' weight of the sludger causes it to sink into the debris which is thus forced above the valve. As 
 the sludger ascends, the material which has entered acts with the water to close the valve. By this 
 means, the escape of the sludge is prevented, though a large portion of the water passes out through 
 the accidental interstices occasioned by small pieces of stone upon the valve seating. The action of 
 the sludger is very effective, as much as a cubic yard having been removed at one time by a large 
 tool. When the operation of " pumping " the sludger has been continued sufficiently long to clear 
 the hole, it is raised, and its contents removed by turning it upside down. On account of the facility 
 with which this clearing tool may be used, it is very generally adopted. It may be said, indeed, to 
 occupy among clearing tools the position occupied among cutting tools by the flat chisel. 
 
 It has been proposed, for the purpose chiefly of saving time, to remove the debris from the bore- 
 hole during the operation of cutting by means of a jet of water. This proposal has in many instances 
 been adopted with success, by the employment of hollow rods, through which the water is forced by 
 means of a pump connected with the rods by flexible tubing. The advantages of the system when 
 used with the ordinary boring tools have, however, been overestimated. The work of cutting has 
 to be frequently suspended to raise the rods for the purpose of renewing the tool, so that the only 
 time that can be saved is that during which the sludger is being used. But as this tool can be very 
 rapidly lowered and raised by means of the rope, it is not long in the bore-hole. Thus the advantage 
 
, SEAECHING FOE COAL, 93 
 
 gained in time, is compensated by the necessity of employing hollow rods, which, for small borings, 
 must be of larger diameter than the solid bars, and more expensive. 
 
 Verifying Tools. — The materials brought up by the clearing tools show the nature of the stratum 
 that is being passed through. But as these materials are in a divided state, being reduced to small 
 fragments by the action of the chisels, they indicate but little of the physical condition of the rock- 
 bed, and nothing whatever of its dip. Moreover, their indications concerning the nature of the bed 
 are hardly trustworthy, inasmuch as particles of the higher beds are continually falling from the 
 sides of the bore-hole. As it is highly desirable that full information on all points should be obtained 
 when boring in search of coal, and especially on the dip of the beds, their physical character, and 
 their geological age as evinced by contained fossils, it becomes necessary to have recourse to 
 special tools for that purpose. The use of such tools is to bring up a solid core of the rock, and to 
 bring it up in such a condition that the lines of stratification will show the dip of the bed. To obtain 
 this result, the core must be marked relatively to the north point before it is broken from the rock. 
 This is effected by means of a chisel with an eccentric cutting edge. Having previously cleared out 
 the hole, this chisel is lowered, care being taken, by suitable marks on the rods and a fixed plumb- 
 line, that it be not turned in the least degree during the operation. When it has reached the bottom 
 of the hole, two or three light blows are struck without turning the rods, and it is again raised. A 
 special tool. Fig. 173, Plate XIII., composed of a number of chisels set in a ring, is then lowered, and 
 worked with light blows in the same manner as the common chisel. By this means an annular space 
 is cut round the marked core. "When this space has been cut nearly to the depth of the chisels, the 
 tool is raised^ and another special extracting instrument. Pig. 174, let down. This instrument drops 
 over the core, and by means of a wedge thrust in by the weight of the rods, exerts a sufficient 
 lateral pressure to break it off. The core is held between the wedge and a spring fixed on the inside 
 of the instrument for that purpose, and in this way it is raised to the surface. The inclination of 
 the lines of stratification may then be observed relatively to the mark upon the upper end, and 
 the direetion and amount of the dip determined. By repeating this series of operations, a complete 
 section of the strata may be obtained. 
 
 Regulating Tools. — Besides the foregoing cutting, clearing, and verifying tools, others are 
 occasionally required for the purpose of regulating the diameter of the bore-hole, or of restoring it to 
 its original dimensions when the hole has partially closed in by the swelling of the clay beds. One 
 of these is shown in Pig. 175; it is worked by combining the vertical and, rotary motions, and may be 
 used at any height in the bore-hole. The tool shown in Pigs. 176 and 177, and formed of a helical 
 blade steeled at the edges, may be used in the same manner and for the same purpose, or for boring 
 through feebly coherent sand-rock. 
 
 Rods. — The rods by means of which the excavating tools are worked from the surface constitute 
 a very important part of the boring apparatus. They consist usually of bars of iron one inch 
 square, for borings of ordinary dimensions. Other sections have been employed, notably the 
 circular and the octagonal ; but the greater simplicity of the square section, and the advantage which 
 it possesses of allowing the application of keys and spanners to any portion of its length, have caused 
 it to be preferred to the more complex forms. As fracture of the rods is likely to be attended with 
 disastrbus consequences, and as moreover they are subjected to constant shocks, it is very important 
 that only the best material should be employed in their construction. Swedish iron of the toughest 
 quality should be chosen for this purpose. In judging of the quality by the appearance, only such 
 
^4 MmiNG ENGINEEEING. 
 
 samples are to be relied upon whicli are of a soft and fibrous character, and possess a clear, smooth 
 skin free from cracks, and full sharp edges. To test the sample by fracture, one side of the bar 
 is slightly nicked with the chisel, and the bar bent slowly to and fro until it breaks. If the iron is 
 of good quality, the fractured surface will exhibit fine, bright, silky-looking fibres of some shade of 
 dark-grey colour. A bar of such iron of one-inch section will break with a tensional strain of about 
 28 tons, while a bar of the same dimensions, but of average quality, will yield with a strain of 20 
 to 23 tons. 
 
 The rods are generally made up of 10 or 15 feet lengths. It is evident that the fewer the 
 number of joints in a rod, the better it is in many respects, and hence attempts have been made to 
 reduce the number by employing lengths as great as 25 feet. But, for reasons which will hereafter 
 appear, such lengths are inconvenient in use, and they have consequently been abandoned in favour 
 of those mentioned above, the greater length being the one which satisfies most fully the conditions 
 imposed. A few shorter lengths, forming a convenient fraction of the main lengths, are required 
 for the purpose of keeping. the "head," or upper extremity of the rods, within a certain distance of 
 the surface of the ground as the sinking progresses. 
 
 The several lengths of rod are connected by a screw-joint. Other modes of connection have 
 been employed, but all have failed in practice, some for one reason and some for another, leaving the 
 screw-joint in universal use. One end of each length of rod is provided with a male, and the other 
 end with a female screw, as shown in Fig. 178, Plate XIY. The thread is of the simple triangular 
 form, and makes not fewer than six revolutions. The section of the cylindrical portion upon which 
 the thread winds should be equal to that of the rod, namely, one inch ; hence the section of the rod 
 must be increased at each end to allow for the thread of the male and the sides of the female screw. 
 This will make the diameter of the rods at the joints about twice that of the solid section. The 
 female socket should be bored a little deeper than the length of the male plug, in order to bring the 
 sides of the former in close contact with the shoulder of the latter. This joint may yield either by 
 the force of the shock slipping the thread, a liability that is greatly lessened by bringing the sides 
 and shoulder firmly together ; or, which is a far more common case, splitting the sides of the socket. 
 The only means of obviating the latter contingency is to give the sides a sufficient section, and to 
 reduce as much as possible the shock of the falling rods. All the joints should be identical in every 
 respect, so that any two lengths may be connected together ; and in making up the rod, care should 
 be taken always to have the socket on the lower end of each length, to prevent rubbish from being 
 jammed into it. The enlarged portion at the joint serves as a point of support to suspend the rods 
 from during the operations of raising and lowering. 
 
 A grave objection to the employment of iron rods for deep borings is their great weight. A 
 rod of one-inch section, such as we have been describing, weighs, exclusive of the increased quantity 
 of metal at the joints, 10 lb. a yard, and as the specific gravity of iron of that quality is about 7* 78, 
 a yard immersed in water will weigh 8*7 lb. Hence the rods in a bore-hole 300 yards deep will 
 weigh 8*7 X 300 = 2610 lb., or upwards of 1 ton 2 cwt., and a depth of 600 yards will give a 
 weight of 2j tons. It is obvious that in practice serious difficulties must result from this circum- 
 stance. So great a weight distributed throughout a long length of rods cannot be suddenly arrested 
 by a shock applied to its lower extremity without throwing a dangerous strain upon the rods near 
 the bottom, and causing them to vibrate violently against the sides of the bore-hole — consequences 
 that would be extremely perilous to the success of the undertaking. Two methods have been pro- 
 
SEAECHING FOE COAL. 95 
 
 posed of overcoming this difficulty : the first is the substitution of wooden rods for the iron ones when 
 the depth is great. Such rods, with their iron connections, lose the greater part of their weight in 
 water, and thus are not exposed to the danger mentioned. They have been successfully employed in 
 many instances. These rods are made of sound, straight-grained pine, ia lengths of 25 and 35 feet, 
 have a square section of not less than 2^ inches side, with the angles slightly planed off. They are 
 connected by iron screw-joints in the same manner as the iron rods, each end being provided with an 
 iron joint-piece forming a socket into which the rod is bolted, as shown in Fig. 179. A fatal objection 
 to wooden rods for small borings is the necessity for a large section. Less than 2 inches side could 
 not be used, and for great depths 3 inches and 4 inches would be required. But when the bore-hole 
 is of sufficient diameter, they may be employed with advantage in some cases, and as a matter of fact, 
 they are frequently adopted for deep borings on the continent of Europe. 
 
 The second method proposed possesses greater advantages, inasmuch as it removes the difficulty 
 without abolishing the iron rods. It consists in forming the rods of two distinct portions : a short 
 and massive part at the bottom, to which the cutting tool is attached, and on which alone the force of 
 the shock is expended ; and the rod proper, which is used solely to raise the former part, and which, 
 not being attached to it in an invariable manner, is not exposed to the shocks occasioned by the 
 percussive action of the former. As this method allows all the advantages attending the use of iron 
 rods to be retained, it is by much the more important of the two, and has, consequently, been very 
 generally adopted. 
 
 The forms of construction by which the latter method has been carried out have undergone 
 numerous modifications since its first introduction. But, as in the case of the tools, the lessons of 
 experience have led to the abandonment of all or most of the recent devices in favour of the 
 extremely simple form which was first proposed, and which is due to the inventive genius of 
 QBynhausen. This joint is known as the " sliding joint," and is the only one that can be relied upon 
 for borings of an ordinary character ; for it must be evident that complicated devices are totally 
 unsuitable for use at the bottom of a deep bore-hole where they are far removed from reach and 
 sight. The construction of the sliding joint will be clearly seen in the three views given in 
 Figs. 180, 181, and 182. The lower part to which the cutting tool is affixed terminates upwards in 
 a head moving in a slot in the lower extremity of the upper portion constituting the rods proper. 
 When the rods are raised, the tool is lifted by this head, which then rests upon the bottom of the slot. 
 On dropping the rods to produce the percussive action of the tool, the latter falls with the former till 
 it comes in contact with the rock at the bottom of the hole, when it is abruptly arrested and thereby 
 subjected to a violent shock. But the rods continue the descent by allowing the head of the arrested 
 portion to slide up in the slot, and by that means the shock is confined to the part carrying the tool. 
 As soon as the head of this part begins to move up the slot, the end of the lever at surface to which 
 the rods are attached comes in contact with an elastic stop which is capable of bringing the rods to 
 rest within the space allowed by the play of the slot. In this way the descent of the rods is 
 gradually arrested, and injurious shocks avoided, without diminishing in any degree the action of 
 the cutting tool. Another advantage of no small importance that has been gained by the use of the 
 sliding joint is the possibility of considerably reducing the section of the rods, which are required 
 only to raise the part to which the tool is affixed. 
 
 Guides.— Sometimes in borings of moderate depth, when the sliding joint is not used, guides 
 are employed to prevent dangerous vibration of the rods. These may consist of a kind of cage 
 
96 MINING ENGINEEEING. 
 
 constructed of small iron rods of circular section, as shown in Fig. 185, and offering but little 
 resistance to the passage of water; or of a wooden or an iron cylinder encircling the rods and 
 provided with water passages. But a more efficient means of avoiding resistance from the water is 
 to allow' the cylinder to play between two stops on the rods, placed at a distance apart somewhat 
 greater than that passed through by the rods at each stroke. 
 
 Stirrups. — For the purpose of suspending the rods from the oscillating lever or the pulley, the 
 top length of the jods terminates above the surface of the ground in a stirrup, the construction of 
 which allows the rods to be turned round during the operation of boring and to be lowered as the 
 boring progresses. Several forms of stirrup are in use, but the most convenient is that represented 
 in Figs. 183 and 184. This stirrup keeps the upper end of the rod always at the same height above 
 the ground, a necessary condition for the perfect working of the lever, and it enables the borer to see 
 exactly the progress that is being made at the bottom of the hole. The construction of the stirrup 
 will be clearly seen in the figure.< Sometimes the rods are suspended from the lever by means of a 
 chain fixed at one end by a ring to a hook on the upper side of the lever, and having at the other 
 end a hook which is passed through the eye of- a swivel head on the upper length of the rods, and 
 inserted in one of the links. The swivel head allows the rods to be turned without twisting the 
 chain, and the lowering of the rods may be effected during the progress of the boring by removing 
 the hook to the next lower link. The use of the stirrup is, however, in all cases to be recommended. 
 
 Head-Gear. — The head-gear consists of shear-legs or a boring frame, with the accessory parts 
 and appliances for raising, lowering, and turning the rods. The use of the shear-legs is to furnish 
 an elevated point of support from which the rods may be conveniently suspended. In construction, 
 they may vary, according to the importance of the boring, from a simple tripod formed of scaffold- 
 poles lashed together at the top with rope, to a complete framed structure similar to the permanent 
 head-gear erected over a drawing shaft. But as the erection is in every case only a temporary 
 one, and as it may be required in another locality when the bore-hole over which it is erected 
 is finished, whatever the importance of the work rnay be, it must be very simple in construction, 
 and so designed that it may be readily erected and taken to pieces without the assistance of skilled 
 workmen. 
 
 The height of the boring frame is mainly determined by the depth of the boring. It has 
 already been remarked that the rods have to be very frequently raised for the purpose of changing 
 the cutting tool ; it will be evident that the time re'quired for this operation will depend in a great 
 measure upon the height of the boring fi:ame. If the height of this structure were equal to the 
 depth of the bore-hole, the rods might be withdrawn at one lift. If it were equal to half the depth, 
 one half the length of the rods might be withdrawn at one lift ; but this half would then have to be 
 disconnected from that remaining in the bore-hole by unscrewing the joints, and the latter half 
 subsequently raised by a second lift. So if the height of the frame were one-fourth the depth of the 
 hole, the rods would have to be raised in four lifts, and three joints would have to be unscrewed. 
 Thus it will be seen that a high boring frame saves much labour and time, by increasing the length 
 of the " offtake," as it is called ; and that for deep borings a high frame is practically indispensable. 
 The height found most convenient in practice is between 30 and 45 feet ; in some instances, 60 and 
 even 80 feet structures have been employed, but such structures must necessarily be of a complicated 
 character. Whatever the height may be that is adopted, it is essential that it be a multiple of the 
 lengths of which the rods are made up, so as to bring the joint to be unscrewed a convenient distance 
 
SEAECHING FOE COAL. 
 
 97 
 
 above the top of the bore-liole. Thus, if 15-feet lengths are employed, the boring frame must be 30 
 or 45 feet high ; whilst if the lengths are only 10 feet, the height must be either 30 or 40 feet. 
 
 Besides a considerable height, great strength is essential to a boring frame. Perfect rigidity 
 in the support is necessary to the efficient working of the apparatus, and this rigidity can be 
 obtained only by means of ample dimensions. It must be borne in mind when designing a boring 
 frame, that the strain thrown upon it while raising the rods by means of a pulley and windlass is 
 equal to the tension of the rope increased by the weight of the rods and their accessory parts, or, 
 more generally, equal to the tension of the rope increased by the resistance of the rods, which will 
 be greater than their weight in cases when they have by some accident become jammed in the hole. 
 
 The support furnished by the top of the boring frame is provided with a pulley, usually of cast 
 iron, and grooved to receive a rope. This rope is attached at one end to the rods, and at the other 
 to a windlass, by means of which the rope is drawn in and the rods raised. This windlass forms an 
 essential part of every boring frame. It is in most cases fixed upon the frame at a convenient 
 height above the ground, and is worked either with an intermittent motion by levers and ratchet- 
 wheel and paul, or with a continuous motion by crank handles, as in the case of a common 
 drawing well. The former method is unsuitable for any but small depths, and even in such cases is 
 inferior to the latter. Sometimes the windlass is arranged with a vertical axis, and worked with 
 horizontal bars, like a capstan. When the depth and, consequently, the weight of the rods, become 
 great, the windlass is worked by intermediate gearing, which may be so contrived as to increase the 
 speed when a large portion of the weight has been taken ofi". In very deep borings, a steam-engine 
 may be used to work the windlass. In all cases a brake is attached to regulate the descent of 
 the rods. 
 
 The sludger is the clearing tool generally employed, and being used independently of the rods, 
 :t is usually provided with a special pulley and windlass of smaller dimensions. This windlass is, 
 like the larger one, fixed to the boring frame, but, for convenience, upon the opposite side, and 
 furnished with a sufficient quantity of rope. The pulley is so contrived that it may be run out exactly 
 over the bore-hole when about to be used, and back again out of the way of the rods when done with. 
 The sludger being swung over the hole, is lowered rapidly by its own weight, its descent being 
 checked by a brake upon the windlass. To raise it, the windlass is turned by crank-handles, and 
 these are also made use of to produce the reciprocating or " pumping " motion required to fill the 
 sludger. But sometimes this motion is derived from the oscillating lever by winding the rope two 
 or three turns round the head. 
 
 The simplest form of shear-legs, which maybe employed for shallow borings, consists of three fir 
 spars set in a triangular frame at the bottom, and connected at the top in the manner shown in Figs. 
 186 and 187, Plate XIV. The spars should be of perfectly sound and straight Norway fir, and not less 
 than 8 inches in diameter at the bottom. They should be loosely mortised, and firmly wedged into the 
 bottom framing, or fixed to it by iron straps and bolts. This bottom framing can never be dispensed 
 with. The spars are fixed at the top by placing the head of the middle one between the heads of tlie 
 two others, and passing a bolt 1 inch in diameter through them. This bolt also passes through the 
 eyes of a wrought-iron sling, which carries the pulley, as shown in the figure. The windlass may be 
 fixed upon the two outside legs at a vertical height of about 3 feet 9 inches from the ground. One 
 of the legs should be provided with staves fixed to its outer side, to enable a workman to ascend to 
 the pulley. h- 
 
 
 
98 MINING ENGINEEEING. 
 
 A modification of this construction of shear-legs, more suitable for deeper borings, where the 
 strain due to the weight of the rods becomes greater, is shown in Figs. 192 and 193, Plate XV. In 
 this example, the two legs upon which the windlass is fixed are stayed by cross-bars or ties mortised 
 into the legs and keyed on the outside. The lower ends of the shear-legs are fixed into a triangular 
 wooden frame, and connected at the top in the same manner as in the preceding example. The 
 pulley may also be slung in the same way, or fixed as shown in the figures. Figs. 188, 189, 190, and 
 191 show several modes of connecting shear-legs and fixing the pulleys. 
 
 The simplest form of boring frame is shown in Figs. 194 and 195. It consists of two pairs of 
 shear-legs inclined towards each other, and held in their positions and stayed by ties or cross-bars 
 mortised into the legs and keyed with wooden keys. The lower ends of the legs may either be set 
 in the projecting extremities of the side pieces of a rectangular frame, or, if the bottom tie be placed 
 within a foot from the ground, the ends may be supported upon brick foundations about 18 inches 
 square, and capped with wood or flagstone to distribute the pressure, the top of the foundation being 
 level with the surface of the ground. When the latter plan is adopted, ties will be required between 
 each pair of shear-legs ; but with the bottom frame, these, as well as the bottom tie of each pair, may 
 be omitted. The pairs are connected at the top by two cross-pieces notched and bolted to the inside 
 of the legs. As these pieces form the support for the pulley, they require to be firmly fixed and to 
 possess ample dimensions. In the example referred to, the section is 8 inches x 3 inches, and the 
 diameter of the bolts f inch. The shear-legs are 6 inches x 4 inches at the bottom, tapering to 
 6 inches x 3 inches at the top. The ties are 3| inches x 2 inches, 3 inches x If inch, and 
 2i inches x 1^ inch, reckoning from the lowest upwards. The pulley is of cast iron, 16 inches in 
 diameter. The windlass is fixed upon one pair of the shear-legs, and consists of a wooden barrel 
 10 inches in diameter, turned by an iron crank-handle. This frame is suitable for borings of an 
 inconsiderable depth only. 
 
 For deeper borings a frame similar in construction to that shown in Figs. 196 and 197 will be 
 required. This frame is composed, as in the preceding case, of two pairs of shear-legs, the timbers of 
 each pair being inclined towards each other, and stayed at intervals by ties. But in the present 
 example, on account of the increased height and the greater strains contemplated, the staying is 
 I'epeated between the two pairs of legs. The bottom tie on each side is, however, omitted for the 
 convenience of the men at work. The legs are 6 inches X 6 inches, and of the same scantling 
 throughout the whole length ; they are set in the projecting ends of the side pieces of a rectangular 
 wooden frame, 12 inches x 8 inches, and connected at the top, the timbers of each pair by being 
 mortised into a cross-piece of the same dimensions, and the two pairs by cross-pieces also of the 
 same dimensions, notched into the former pieces, and nailed down to them. Upon these latter pieces, 
 at right angles to them and parallel with each other, two other pieces are fixed over the centre of 
 the frame to support the pulley, as shown in the drawing. The tie-bars are mortised into the shear- 
 legs and keyed as in the preceding example; they are all equal in section, 4 inches x 2^ inches. 
 The pulley is of cast iron, and 16 inches in diameter. The windlass — the barrel of which is of 
 wood 15 inches in diameter, and provided with horns — is fixed upon one pair of the shear-legs. 
 Sometimes a roof is thrown over the pulley, as a protection from the weather. 
 
 For deep borings by hand power, the frame shown in Figs. 198, 199, and 200 is, perhaps, the most 
 suitable that could be devised. This boring frame consists of two pairs of shear-legs, of 12 inches 
 X 9 inches scantling, set into the projecting ends of the side pieces of a strong rectangular wooden 
 
SEAECHING FOR COAL. 99 
 
 framing, constructed of balks, 12 inches X 9 inches for the side pieces, and 9 inches x 9 inches for 
 the end pieces. The timbers of each pair of legs have a slight inclination towards each other, being 
 3 feet 8 inches apart at the bottom, and 14 inches at the top in a vertical height of 30 feet. These 
 timbers are stayed at intervals of 3 feet by horizontal wooden ties, each 9 inches x 6 inches, mortised 
 into them, and keyed on the outside with wooden keys. The two pairs of legs are connected at the 
 top by two cross-pieces into which they are mortised : these pieces carry the pulleys. One pair of 
 the shear-legs is provided with stout diagonal timbers fixed between them and the bottom framing, 
 for the purpose of carrying the windlass, which is moved by spur gearing, and furnished with a 
 ratchet stop. The barrel of this windlass is 18 inches in diameter, and the proportion of the driving 
 to the driven gear is 1 to 3. The two top cross-bars carry a horizontal wrought-iron axle upon 
 which two independent cast-iron guide-pulleys run loosely. The use of the two pulleys is to save 
 time in raising and lowering the rods. To effect this object, the ends of two ropes are led over 
 the pulleys and coiled in contrary directions upon the barrel of the windlass. By this arrangement 
 one of the ropes is always down in readiness to be attached to the rods the moment the offtake has 
 been removed, without the labour of uncoiling it from the windlass. The importance of saving time 
 in all boring operations renders the adoption of the double-pulley arrangement desirable in all cases 
 of deep borings. 
 
 For the purpose of raising and lowering the sludger, a pair of traverses, 9 inches x 6 inches, 
 is fixed across from one pair of shear-legs to the other, at a distance of about 8 feet below the top 
 traverses supporting the pulleys. These pieces, which are mortised and keyed into the shear-legs, 
 are intended to carry another and a smaller pulley, mounted on a cast-iron frame capable of motion 
 between horizontal wooden slides provided for the purpose and fixed upon the traverses. The 
 slides are made to project beyond the shear-legs, and are furnished with a roller, as shown in the 
 figures, for the purpose of carrying the rope out clear of the frame. The end of the rope, after 
 being led over the pulley and roller, is brought down and wOund upon a smaller windlass fixed upon 
 the shear-legs opposite those carrying the larger windlass. The sludging windlass is provided with 
 a brake, to regulate the descent of the tool, as before described ; and it may be remarked here that 
 such brakes should be self-acting, the power being obtained preferably by means of a weight. The 
 rope used for the sludger will be f inch or 1 inch in diameter, according to the dimensions of the 
 tool. Hempen rope is usually employed, but aloe fibre, allowing of smaller dimensions, has often 
 been used with advantage. 
 
 Sometimes, especially when the boring is expected to occupy a long time, the boring frame is 
 made to cover a larger surface of ground, and is boarded in, with the exception of the necessary 
 openings, for the purpose of protecting the workmen from the weather. 
 
 Next to the boring frame, the most important part of the head-gear is the oscillating or 
 " rocking " lever. It is by means of this lever that the requisite motion is communicated to the 
 rods when working the cutting tools. It consists of a piece of straight-grained ash,, provided with 
 an iron axle, upon which it turns as a fulcrum. This axle is supported upon a wooden framing, 
 composed of four upright pieces, fixed at the bottom in two cross timbers, inserted for that p" rpose in 
 the framing of the shear-legs, and connected in pairs at the top by two cross-pieces, into which they 
 are mortised. The two inner upright pieces are connected in the same way, to afford a support for 
 the lever axle. Sometimes, however, this axle is supported in the middle of the framing, as shown 
 in Fig. 198; but that arrangement is not to be recommended. The height of the support thus 
 
 o 2 
 
100 
 
 MINING ENGINEEKING. 
 
 obtained is about 5 feet 6 inches. The dimensions of the lever will be determined by the weight of 
 the rods, and will therefore vary with the depth of the bore-hole. The same conditions will determine 
 the proportions of the iron axle and its attachments. This axle is fixed upon the lower side of the 
 lever by means of straps and bolts, in the manner shown in Figs. 202 and 203, Plate XVIL, an iron 
 carriage being bolted down to the framing to carry the axle. As these parts will be subjected to 
 severe strains, the materials should be of good quality and the dimensions ample. The proportion of 
 the shorter to the longer arm of the lever will be determined by the weight of the rods and the 
 length of the stroke. One to four and one to five are the usual proportions ; but in some instances 
 as much as one to nine has been adopted. The total length of the lever will depend somewhat upon 
 the proportion of the arms, but in most cases from 10 to 12 feet will be found to be a convenient 
 length. And with a proportion of one to four, or one to five, and a bore-hole of considerable depth, 
 say from 500 to 700 feet, a scantling of 9 inches x 7 inches will be sufficient. The diameter of the 
 axle in such a case should be 2^ inches. 
 
 The length of the stroke should, as far as is prarticable, be proportioned to the hardness of the 
 rock which is being bored through. For moderately soft clay, 6 inches may be sufficient; but 
 compact limestone may require 24 inches or even more. 
 
 To allow several men to work at the end of the longer arm of the lever, a cross-bar of suitable 
 dimensions is affixed to it. This cross-bar should be of tough ash, of circular section, and of such a 
 diameter as to be conveniently grasped by the hand ; it should be fixed, by means of iron straps, 
 upon the upper or upon the lower side of the lever, and never passed through it or notched into it. 
 Instead of the cross-bar, straps of iron provided with a hook at each end may be fixed across the 
 upper side of the lever, leaving the hook projecting over the edge. Short pieces of rope with a ring 
 on one end, and a piece of wood, of circular section and about 8 inches in length, on the other end, 
 may then be used instead of the cross-bar, by placing the ring over the hook and grasping the piece 
 of wood to pull by. In this way four men can work with two hooks on each side, or six men with 
 three hooks. One advantage gained by this method of working the lever is the directness of the 
 strain. With the cross-bar, a preponderance of force on one side — aud such a preponderance must 
 always exist, since the men will never be exactly equal in strength — produces a torsional strain great 
 in proportion to the amount of the preponderating force and the leverage of the cross-bar. To 
 steady the lever, the longer arm is sometimes made to move between guides. 
 
 The head of the lever should be formed of a sector of a circle, the centre of which is the point 
 of support. This is needed to raise and lower the rods in a straight line. Usually this sector-head 
 is of cast iron, as shown in Fig. 198, Plate XVI. Above the head a stout hook is firmly fixed by means 
 of bolts. To this hook the rods are hung by one of the devices already described, a short piece of 
 chain, or preferably of flat hempen rope, furnished with a ring at one end, and a swivel-head and 
 hook at the other, being required when the lengthening stirrup is used. As the head of the lever 
 partly overhangs the bore-hole, the axle must be so set in its bearings that the lever may be with- 
 drawn when it becomes necessary to use the sludger. The usual manner of providing for this 
 requirement is shown in Fig. 202^ where the construction of the carriage allows the lever to be 
 readily hfted off its bearings. 
 
 The weight of the rods is constantly increasing as the boring progresses in depth, and 
 consequently, the force required to work the lever must be constantly augmented in a like proportion. 
 This entails an increased expenditure of labour and money without any compensating gain, for when 
 
SEARCHING FOE COAL, 101 
 
 a sufficient weight of rods is obtained to give a certain force to the blow, nothing is gained by- 
 increasing that force, while great risk of fracture is incurred. When the sliding joint is employed, 
 it is obvious that no increase of weight in the rods can influence the power of the blow in any degree. 
 For these reasons, when the weight of the rods has become sufficient, a counterweight is suspended 
 from a hook at the extremity of the longer arm of the lever, which counterweight is gradually 
 added to as the length of the rods increases. By this means, the force requisite to work the lever is 
 within certain limits kept constant. 
 
 It has already been remarked that when the sliding joint is used an elastic stop is provided at 
 surface, to arrest the descent of the rods within the limits allowed by the extent of the slide. Such a 
 stop may be constructed in various ways. The spring pole is perhaps the most suitable, as it is 
 certainly the most simple. The pole should be fixed upon the ground parallel with the surface, and 
 care should be taken so to determine its dimensions that it may not be strained up to near the limits 
 of its resistance, for fracture of the pole would probably occasion fracture of the rods. For the same 
 reason, the rope or chain by which the lever is attached to the pole should be of ample strength. 
 Another matter demanding attention is the extent of the motion allowed by the elasticity of the pole. 
 This extent must be somewhat less than that allowed by the sliding joint in the lower end of the 
 rods, and sufficient precaution should be taken that the limit be not exceeded by the stretching of the 
 rope or the loosening of the pole. Instead of the pole, a very good spring may be made of fir boards 
 f inch thick and about 9 inches broad, placed one upon another in such a manner that the bottom 
 one shall extend beyond or overlap the second by 8 inches; the second overlap the third by the 
 same distance, and so on. These boards must be firmly fixed to the ground, and the end of the lever 
 attached by a chain or rope to the end of the bottom board, which must be provided for that purpose 
 with a stout iron hook, securely fixed to the under side with iron straps. 
 
 For the purpose of enabling the master borer to ascertain the number of blows made with the 
 cutting tool during a shift or in any given time, a stroke counter is sometimes placed upon the axle 
 of the lever. Such an instrument would be a highly desirable one if it could be constructed in such 
 a way as not to impede the ready withdrawal of the lever from its bearing carriage. 
 
 Steam power may sometimes be advantageously substituted for hand labour to work the rocking 
 lever. In such a case, the most simple method of depressing the longer arm of the lever — which may 
 then be to the shorter in the proportion of 2 to 1, or 1| to 1, or the two may be equal — is by means 
 of cams fixed upon a horizontal axle, supported on a strong frame similar to that for the lever, and 
 turned by a spur-wheel of 5 or 6 feet diameter, driven by a pinion. The engine should be of the 
 portable class, and it should be made to work the windlasses when the lever is not in action. 
 
 An essential part of the surface apparatus is the bore-hole guide-tube, shown in Fig. 198, Plate 
 XYI., and Fig. 201, Plate XVII., the latter being a plan of the former to a larger scale. This tube is 
 of wood, and for bore-holes of ordinary dimensions is about 12 inches in diameter and 6 feet in length. 
 The diameter of the bore of this tube is the same as that of the bore-hole, so that the thickness of 
 the wood is about 4| inches for a 3-inch hole. It is to be inserted in the bore-hole, in a manner to 
 be described hereafter, to a depth that will leave about 10 inches of its length above the surface of the 
 ground, and firmly held in its position by four pieces of timber 9 inches x 6 inches in section. 
 These pieces are laid upon the ground in pairs, one piece on each side of the tube, the pairs being at 
 right angles to each other. The ends of the pieces forming each pair are then pressed partially 
 together, to make them tightly clasp the tube, and are held in a state of tension by iron straps across 
 
102 MINING ENGINEERING. 
 
 the ends, and these ends are firmly fixed to the ground. Sometimes they are fixed to the framing in 
 which the shear-legs are set ; but this practice is not to be recommended, as the vibration of the 
 framing tends to produce injurious effects. When a staple is sunk, they are, of course, set at the 
 bottom of the staple. Yarious means of fixing these timbers may be employed, the only necessary 
 condition being that there shall be no liability of their becoming loose during the progress of the 
 work. The upper surfaces of these timbers are an inch below the top of the tube. The aperture 
 of the tube is provided with a pair of iron shutters, opening and closing horizontally, as shown in 
 Fig. 201. The form of these shutters and the mode of fixing them will be clearly seen from the 
 figure. Each shutter is notched to form a square aperture of 1-| inch side through which the rods 
 may freely move from joint to joint when the shutters are closed. The use of these shutters is to 
 prevent anything from falling down the bore-hole. Instead of this kind, flap shutters may be used. 
 These consist of two semicircular iron discs hinged upon the tube, and opening vertically like a 
 clock-valve, a notch in each forming the aperture for the rods, as in the preceding kind. 
 
 The top length of the rods terminates, as previously described, in a swivel-head, by which it is 
 suspended from the rocking lever. For the purpose of adjusting the height of the head to the 
 requirements of the lever, several short lengths are needed, varying from one foot to three feet, which 
 are screwed on as the boring progresses, the shorter lengths being removed and a longer one substi- 
 tuted at each change. These lengthening pieces, one of which is represented in Fig. 204, are all 
 provided with a screwed socket. Sometimes they are furnished with an eye through the shank just 
 below the head, through which a piece of wood is passed to form a lever, by means of which the rods 
 are turned round during the operation of boring. This arrangement, shown in Fig. 205, is common 
 in Belgium, but in England it is more usual to employ the brace-head or tiller for this purpose. 
 
 The tiller may be of wood or of iron. When of wood, it consists of a piece of ash, 4 inches in 
 diameter, square in section in the middle, and rounded off and rediiced in size towards the end, as 
 shown in Fig. 206. The middle portion is provided with a notch one inch square to receive the rod, 
 one side of the notch being formed by an iron plate turning on a bolt at one end and fixed at the 
 other by a screw. On withdrawing this screw, the plate drops and leaves the notch open. Another 
 screw through the centre of the plate is provided for the purpose of fixing the tiller upon the rods. 
 When the tiller is of iron, it is constructed in the manner shown in Figs. 207 and 208. It consists of 
 two portions, each 18 inches or 2 feet in length, joined by two screws. To apply the tiller to the 
 rods, the two portions are separated by withdrawing the screws, and the portions are applied one on 
 each side of the rod, and fixed in that position by reinserting and tightening the screws. Or, when 
 the rods are not suspended from the lever, this tiller may be applied by passing it over the head of 
 the upper length. The ends of the tiller are turned up, as shown in the figure, to afford a convenient 
 hold for the workmen. 
 
 For the purpose of raising and lowering the rods, " Hfting dogs " are required. These consist 
 of a claw-hook, through the shank of which a ring is passed, by means of which it is attached 
 to the rope. When in use, the claw is placed under the head or the shoulder of the top length of 
 rod, and the latter hauled up or lowered by means of the windlass. The lifting dog is represented 
 in Figs. 209 and 210. 
 
 Another instrument required for raising or lowering is the " nipping fork," or " tiger." When 
 the rods have been hauled up as far as the height of the shear-legs will allow, they must be sup- 
 ported in that position while being unscrewed. For this purpose, the nipping fork, represented in 
 
SEARCHING FOE COAL. 103 
 
 Fig. 211, is placed upon the top of the guide-tube beneath the joint in the rod, and the latter 
 lowered till the joint rests upon the fork. In like manner, in lowering, the rods are let down till the 
 lifting dog rests upon the fork ; the next offtake is then screwed on, and the lifting dog hanging 
 from the other pulley placed under the shoulder of the top length, and the rods slightly lifted, 
 thereby to allow the lower dog to be removed. When only one lifting dog is used, after the first 
 offtake has been removed, a short swivel-head lengthening piece must be screwed on to each sub- 
 sequent offtake, to afford a hold for the dog. Provided the. shutters of the guide-tube be made 
 sufficiently strong, they may be made to fulfil the purpose of the nipping fork. 
 
 For the purpose of screwing up and disconnecting the rods, a kind of wrench, called a " hand- 
 dog," is required. This instrument is shown in Fig. 212, from which its construction will be under- 
 stood without description. 
 
 Extracting Tools. — The shocks to which the rods are necessarily subjected occasion a change 
 among the constituent molecules of the iron, the fibrous structure being gradually converted into a 
 crystalline one. This change renders the iron brittle, and as the weight of the rods increases as the 
 boring progresses, the danger of fracture becomes rapidly greater as the work proceeds. The screw- 
 joints also become loose from the same cause, and liable to yield. Moreover, the vibrations become 
 greater as the length and weight of the rods increase, and these vibrations tend not only to knock 
 down the sides of the bore-hole, but to cause a rupture of the rods. To these inevitable sources of 
 danger must be added another and a much more prolific one, namely, the negligence of the workmen. 
 Yery frequently the nipping fork is carelessly placed under the joint, or is as carelessly forced out of 
 its place during the unscrewing of the joint, and, as a consequence, the rods fall back into the bore-hole. 
 Or the same result may follow the negligent placing of the lifting dog beneath the rod-head. Accidents 
 from these causes are lamentably frequent, and they are attended with the worst consequences. 
 When the rods are in this way let fall in the bore-hole, the shock to which they are subjected is 
 nioet violent, and its effects most destructive. The rods may be fractured in one part and bent in 
 another, and the fragments may be jammed into the sides of the bore-hole. The cutting tool may be 
 fractured, or if nearly through a hard rock resting upon a soft one, it may be driven through and 
 tightly held in the cleft. The concussion may also bring down stones from the sides of the bore-hole, 
 to complicate the consequences and increase the difficulty. Thus it is evident that not only is it 
 necessary to take due precautions to prevent the occurrence of such accidents, but that means must 
 be at all times held in readiness to remedy the evil should the accidents happen. These means consist 
 of tools designed to remove the fragments of the rods or the cutting tool from the bore-hole, and are 
 designated as " extracting tools." 
 
 When a portion of the rods has been dropped into the bore-hole, the first thing to be done is to 
 ascertain the form and position of the broken portion. For this purpose a ball of clay is well 
 kneaded with oil and hemp fibres to render it phistic and coherent, and let down on the end of the 
 sludger rope. On being raised to surface, the impression on the soft clay indicates the circumstances 
 which it is required to know, and the borer selects his tool accordingly. When a rupture has 
 occurred accidentally, an inspection of the end of the suspended portion of the rods will show 
 whether they have parted above or below a joint. If the fracture has occurred either in or 
 immediately above a joint, the rod may be seized by an instrument called a " crow's-foot " or 
 "crow," represented in Fig. 213. This instrument, the form of which will be understood without 
 description, is lowered at the end of the rods into the bore-hole, and turned round till it has grasped 
 
104 
 
 MINING ENGINEEKING. 
 
 the broken rod beneath the joint, when the whole may be raised without difficulty. The first 
 attempt with this instrument is usually successful. 
 
 When the fracture has occurred immediately below a joint, or near the middle of a length, the 
 crow's-foot cannot be used, because the long portion above the joint would catch in the side of the 
 bore-hole. In such a case, a tool called a " bell " is employed. There are two kinds of bells used, 
 known respectively as the " screw-bell " and the " box-bell." The former, which is represented in 
 Fig. 214, consists of a frustrum of a hollow cone, provided on the inside with a steeled screw-thread. 
 The lower portion is larger in diameter, and the upper portion smaller in diameter, than the 
 diagonal of the rods. Upon its lower edge, a piece of thin plate iron is fixed, to form a kind of 
 funnel-shaped continuation, the use of which is to guide the end of the rod into the bell. When the 
 bell has been dropped over the rod, the former, which should be well greased on the inside before 
 being let down, is turned slowly round until the thread has sufiiciently bitten the rod to allow it to 
 be lifted. It is hardly necessary to remark that the bell must be turned in the direction that will 
 not disconnect the joints. 
 
 The box-bell. Fig. 215, is similar in form to the preceding; but, instead of the screw-thread, it 
 is provided on its upper side with two iron catches opening upwards. The aperture through the 
 bell is, in this case, greater than the diagonal of the rods, and the distance between the ends of the 
 catches when down is slightly less than the length of the side. The bell being dropped over the 
 end of the rod, the latter passes through by raising the catches ; but when the bell is raised, these 
 catches grip the rod, and by this means it is brought to surface with the bell. 
 
 Instead of the bell, the wad-hook, or spiral worm, shown in Fig. 216, Plate XYIII., is frequently 
 employed. This hook is attached to the end of the rods, and lowered as far as the broken portion, 
 when it is turned round till it has taken a firm hold of the rod. This tool is a very efiective one. 
 The form shown in Fig. 168, Plate XIII., may also be employed for the same purpose. These tools 
 may be used to extract a broken chisel, or anything that may have been accidentally dropped into 
 the bore-hole. Numerous forms of extracting tools have been proposed; but the foregoing are 
 sufficient for every case that is likely to occur, and they possess the merit of simplicity. 
 
 Tubing. — When a bed of soft clay or loose sand is passed through, a difficulty arises from 
 the s-welling of the bed. The pressure of the superincumbent rocks forces the soft material out into 
 the vacant space made by the boring, and so tends to stop up the bore-hole. The swelling of the 
 bed is indicated by the friction of the cutting tool against the sides on raising and lowering it ; and 
 when this friction is remarked, no time should be lost in remedying the evil which, having begun, 
 tends to increase rapidly. The means employed to combat this evil consist in lining the bore-hole 
 with iron tubes. These tubes are provided with screwed plug and socket for joining in the same 
 manner as the rods, and they are usually in 10-feet lengths. Other forms of joint are used, but the 
 screw joint, though somewhat more expensive, is always to be preferred. An example of a lining 
 tube is shown in Fig. 217, Plate XYIII. 
 
 A regulating tool having been put down to enlarge the bore-hole at the part which has begun 
 to close in, a length of pipe of the same outside diameter as the bore-hole, and having its lower edge 
 steeled and sharpened, is inserted in the hole and driven down till its socket is nearly level with 
 the top guide-tube. Another length is then screwed on, by means of the pipe-clamp, represented 
 in Fig. 220, and driven down in a like manner. This is continued till the clay or sand-beds are 
 passed, when the boring may be again resumed. As, however, the cutting tools will have to pass 
 
SEAECHING FOE COAL. 105 
 
 through the pipes, it is obvious that the hole must be continued of a smaller diameter. Should other 
 soft beds be subsequently met with, additional lengths of tubing will be screwed on, and driven 
 down to the swelling rock. But a limit to this proceeding is soon reached. The friction of the 
 running material against the tubes is sufficient in most cases to prevent a much greater length than 
 100 feet from being driven. When this limit has been reached, another set of tubes, having an 
 outside diameter equal to the inside diameter of the first, is driven down within the first lining, and 
 the same thing must be repeated for greater depths. Inserted in this way, the lining of a bore-hole 
 appears like the several slides of a telescope when drawn out. An example is shown in Fig. 218. 
 
 As the diameter of the bore-hole is considerably reduced by each set of lining tubes inserted in 
 this manner, it should be sufficiently large at the commencement to allow of these successive reduc- 
 tions without diminishing the bore-hole, at the depth to which it is proposed to carry it, to 
 impracticable or undesirable dimensions. In undertaking a boring, the necessity for lining the hole 
 should always be anticipated, for though in many cases the whole of the beds passed through will 
 be of a sufficiently resistant character to stand, the possibility of meeting with unstable rocks always 
 exists. When the soft bed occurs within a moderate distance from the surface, it will be prudent, 
 unless the character of the strata beneath is well known, to enlarge the bore-hole from surface before 
 putting in the lining tubes. When the hole has been enlarged in this manner, or when only the 
 contracted portion has been rebored to its original dimensions, no time should be lost in getting the 
 tubes down ; for when a bed once begins to run, the motion, however slow it may be, is continuous. 
 So in boring through a soft bed, the operations should be pushed on with all possible speed, and the 
 tubing driven down before the swelling begins. This is one of the questions to which the master 
 borer will be required to direct particular attention. 
 
 Appliances for Driving Tubes. — The operation of forcing the tubes down the bore-hole is one 
 demanding great care. Proper provision must be made for keeping the tubes perfectly vertical 
 during the driving, to avoid the danger of fracture arising from transverse strains and indirect 
 shocks. The driving is effected either by blows or by pressure. When the former method is 
 adopted, a block of wood bound with an iron hoop to prevent crushing, and having a hole through 
 the centre sufficiently large to allow the free passage of the rods, is placed upon the socket of the 
 upper length of tubing to receive tlie blow ; the object being to prevent fracture of the tube by 
 interposing an elastic medium between it and the instrument with which the blow is given. The 
 latter consists of another block of wood bored and bound in the same manner as the first, and 
 constituting a kind of " monkey," to be used as in pile-driving. This monkey is fixed by pressure- 
 screws upon an upper length of rod, as shown in Fig. 219. Several lengths of rod are then 
 screwed on to give weight, and passed through the hole in the lower block, and allowed to hang 
 down the tube and bore-hole. A rope is then attached to the head of the rod, carried over the pulley 
 at the top of the shear-legs, the ordinary rope having been lifted off for the occasion, and wound 
 with one turn upon the windlass. Frequently it will be found convenient to use the sludger pulleys 
 and windlass for this purpose. To work the monkey, two men turn the windlass, a third man 
 holding the end sufficiently taut to enable the former, by means of the friction, to raise the rods with 
 the monkey attached. The drop is occasioned by releasing the end of the rope. The descent of 
 the tubes may be assisted by giving them a partial turn after each blow by means of the clamp-lever, 
 represented in Fig. 220. 
 
 Sometimes, when the depth has become great, and the blows, by reason of the vibrations, insuf- 
 
 p 
 
106 MINING ENGINEERING. 
 
 ficiently eflfective or dangerous, recourse is had to pressure. A very simple and efficient appliance 
 of the character required in such a case is represented in Fig. 221. Two stout balks of timber, 
 designed to furnish the points of support, are firmly fixed to the ground by being passed beneath 
 the framing of the shear-legs, and otherwise held down if additional resistance is necessary. Into 
 these balks are fixed vertical iron or steel rods, upon which a screw-thread is cut nearly throughout 
 their length. The upper ends of these rods pass through a stout wooden block provided with a central 
 aperture sufficiently large to allow free passage to the tube, and are each furnished with a broad 
 washer and a nut. Into the block two other vertical rods are fixed ; these terminate upward in an 
 iron collar resting upon and encircling the socket of the tube. The latter rods are of the same 
 length as the former, and all are jointed in the manner shown in the figure. The nuts above the 
 block and upon the lower rods being turned by keys aifording a sufficient leverage, the tube is 
 pressed down into the bore-hole. Care must be taken to give each nut the same amount of turn, to 
 keep the strains direct and equal. 
 
 Tools for Extracting Tubes. — When the bore-hole has been completed, and the end for which it 
 was undertaken attained, it becomes desirable to recover the tubes used to line the hole. Also when 
 more sets of tubes are required than anticipated, and the diameter of the bore-hole has consequently 
 been so reduced that farther progress is impracticable, it becomes necessary to withdraw the lining 
 and to enlarge the hole from surface. The operation of withdrawing the tubes is always a difficult 
 one, and when the hole is deep is seldom altogether successful. But in most cases a large pro- 
 portion of the tubing may be recovered if suitable means are employed. These means consist of 
 tools for disconnecting and lifting the several lengths of tubing, or for lifting them altogether. 
 
 Of the former kind, the simplest and most effective is the screw-plug. This instrument consists 
 of a conical plug having its lower end slightly less in diameter than the bore of the tube, and its 
 upper end slightly greater, and provided with a left-handed steeled screw-thread. This plug 
 terminates upward in a shank and screw-socket for the purpose of fixing it to the rods. The latter, 
 which are constructed specially for this purpose, are of large section, and are connected by left- 
 handed screw-joints. The screw-plug is lowered at the end of these rods into the end of the tube, 
 and turned slowly round till the thread has bitten. When the plug has obtained a firm hold of the 
 tube, the latter will be unscrewed by the continued left-handed motion of the former, and may be 
 lifted by it. The same operation is repeated for each length of tubing. 
 
 Of the tools designed to lift the whole length of tubing, the best is that known as " Kind's 
 plug," from its having been first employed by Kind. It consists of a block of oak of an ovoid 
 form fixed upon the end of an iron rod. This rod passes through the centre of the plug, which it 
 holds by means of a nut, and terminates upwards in a screw-plug for the purpose of attaching 
 it to the ordinary boring rods, as shown in Fig. 222. The diameter of this wooden plug at its 
 largest part is slightly less than that of the tube, so that a little amount of play is allowed between 
 it and the sides of the tube. When it is required to raise the tubes, the plug is lowered to the 
 desired depth, and one or two shovelfuls of coarse, gravelly sand, washed and sifted, are thrown down 
 upon it. This sand fills the space between the sides of the tubing and the plug, and the latter is 
 thereby firmly wedged in. The rods being then hauled up, the tubing is raised with them. If it be 
 desired to make the plug leave go its hold on the tube, it is only necessary to lower it below the 
 lining, when the sand will run out. 
 
 When the tubing is too firmly held by the friction against the sides of the bore-hole to allow of 
 
SEAECHING FOE COAL. 107 
 
 it being raised altogether, and it is deemed undesirable to have recourse to the special rods required 
 for the screw-plug, Kind's plug may be used in conjunction with another kind of tool to raise the 
 tubing in portions. The use of the latter tool is to cut through the lining so as to divide it into 
 portions capable of being raised at once. Numerous forms of tools have been invented for this 
 purpose. One of the simplest of these, and the most certain in its effects, is that represented in 
 Fig. 223. By suspending this tool at a requisite and fixed height in the bore-hole, on the end of 
 the boring rods, and turning it round, the cutting edge, which is pressed by a spring against the 
 sides of the hole, cuts through the lining, the severed portions of which may then be raised by Kind's 
 plug in the manner described above. The cutter is so constructed that it may be readily withdrawn 
 from the cut and raised to surface. 
 
 The Operations of Boring. — The foregoing descriptions and illustrations are intended to give a 
 clear and full understanding of the nature, form, and use of the various tools and other appliances 
 required in boring. It now remains to take a connected view of the operations, from the preliminary 
 arrangements to the completion of the undertaking. 
 
 The first duty of the engineer is to choose a suitable site for the boring, and in this choice he 
 will be guided mainly by considerations of convenience. The locality will, indeed, be determined by 
 the indications furnished by the geological survey ; but the particular spot in that locality will be 
 selected in accordance with other conditions of a wholly practical character. The consideration of 
 these conditions will demand knowledge, forethought, and a sound judgment. A primary object is 
 to reach the seam with the least possible expenditure of labour and material. The engineer will, 
 therefore, seize any opportunity that may offer itself of abridging the depth of the bore-hole. To 
 this end, he will prefer a hollow to an eminence as a site on which to commence the boring. By 
 this means several yards may often be'saved in depth ; and it must be borne in mind that the cost 
 saved thereby is that of an equal length at the bottom of the bore-hole, the importance of which 
 saving will be understood when the mode of calculating the cost of boring is considered. But though 
 the lowest surface is the most advantageous in this respect, a grave error might be committed ' in 
 selecting it without reference to other circumstances. Such a surface may be composed to a con- 
 siderable depth of alluvial soil, incapable of standing without support, and full of water. Or it may 
 be subject to inundation in times of heavy rains. Any one of these circumstances would entail 
 greater expense than that saved by. the reduction of depth, besides occasioning a risk of total 
 i'ailure. In addition to these considerations, and others which will occur peculiar to each locality, 
 that of facility of access will require the bore-hole to be located near a road. Of course, in a question 
 of mere convenience like this one, much liberty exists ; but as all the materials will have to be 
 carried to the spot, and as easy means of access must be provided for the workmen, who will require 
 to make daily use of the approach during several months at the least, the desirability of choosing a 
 spot in the neighbourhood of a highway will be apparent. 
 
 When a suitable spot for the boring has been selected, and a passable road provided to it from 
 the highway, the operations are begun by sinking a pit five or six feet in diameter, called a staple, 
 down to the solid rock. The staple has two important uses ; the first of which is to remove the 
 surface soil and loose rock so as to allow the boring to be started in the solid rock ; and the second, 
 to increase the length of the offtake by augmenting the height of the lift. The cost of sinking the 
 staple is fully compensated by the consequent reduction of the depth of the boring, which reduction, 
 as before remarked, must be valued according to the cost of the last ten yards of the boring. 
 
 p 2 
 
108 MINING ENGINEEEING. 
 
 Sometimes the staple Is omitted, and the boring commenced from the surface ; but the advantages 
 afforded by it are sufficient to render its adoption desirable in all cases. When sunk to the required 
 depth, the staple is lined, either with poling boards and curbs, or with bricks set dry. 
 
 From the bottom of the staple a hole is dug to a depth that will leave the guide-tube projecting 
 about ten inches or a foot when placed vertically in it. This tube is carefully plumbed, and fixed 
 in its position by filling in and firmly ramming the earth around it. It is of the utmost importance 
 that the tube should stand exactly vertical, as it is to act as a guide to the direction of the bore-hole, 
 and too much care therefore cannot be expended in fixing this tube. The cross-timbers for holding 
 and guarding the top of the tube are next placed in the manner already described. 
 
 When the guide-tube has been fixed in its position and provided with its shutters, a floor of 
 planking must ^be constructed for the workmen who guide the boring. This floor is sometimes 
 supported upon the timbers holding the guide-tube ; but as such an arrangement tends to loosen 
 the tube by the constant jarring of the floor, it is better to introduce other and independent 
 
 supports. 
 
 While the foregoing operations are in progress, the erection of the shear-legs, or boring frame, 
 should be proceeded with. The form and dimensions of this apparatus will be mainly determined 
 by the depth of the boring. In every case, however, unless the boring be one of small- importance, 
 provision should be made for two pulleys for raising and lowering the rods, and other pulleys for 
 the sludger-rope. In fixing these pulleys, it is of the highest importance to bring the periphery 
 of the wheel into such a situation over the guide-tube that the centre of the rope shall coincide 
 with the centre of the bore-hole when hanging vertically. If these simple matters are neglected, 
 the consequences are often very prejudicial to the success of the undertaking, and as a matter of fact, 
 they are frequently neglected on account of their simplicity, attention being directed to things of 
 apparently greater importance. These remarks apply with still greater force to the erection of the 
 rocking lever, from which the rods are suspended when in use. 
 
 Besides the boring frame, certain surface erections will be required for all important borings. 
 These are a small smithy, a shed for the protection of the workmen, and a hut for the man in charge 
 of the boring. Of course, these erections will be of a slight and altogether temporary character. 
 
 When the whole of the apparatus and materials have been provided and placed in their 
 respective positions, the number of workmen required must be determined and the duties of each 
 assigned to him. Probably in no part of the undertaking will the sagacity of the engineer, or 
 whosoever else acts as chief, be called into action so much as in this. Whenever a number of 
 workmen are brought together, there is one whose constitution both of mind and body renders him 
 better capable of performing certain duties than the rest. To recognize these characteristic qualities 
 in each of the men assembled under him, and to assign to each the work which he is best able to 
 perform, are thus duties of the engineer, the importance of which can hardly be over-estimated when 
 it is borne in mind that the success of a boring depends very much upon the several operations 
 being performed in an intelligent and a careful manner. A sufficient number of men should always 
 be provided, since delays are above all things to be avoided; for not only are some of the men 
 kept idle by delays, but, which is of graver consequence, the bore-hole may be exposed to danger 
 from the swelling of the strata. On the other hand, too great a number of men cause delay by 
 getting into each other's way. 
 
 When everything has been prepared, the boring will be commenced by screwing a short 
 
SEARCHING FOR COAL. 109 
 
 length of rod witli swivel-head upon the cutting tool, and lowering it into the guard-tube. The 
 rod will then be suspended to the lever by means of the stirrup, or whatever other connection has 
 been provided, the tiller affixed to the rod, and the shutters of the tube closed to guard the bore-hole. 
 In commencing operations, the weight of the cutting tool and rod will be insufficient to perform the 
 work required, and therefore a weight will have to be hung upon the shorter end of the lever. As 
 the rock at starting will probably be soft, only light blows will be needed till some degree of depth 
 has been attained, when the constantly increasing length of the rods will furnish the requisite 
 weight. The cutting tool must, of course, be chosen according to the nature of the stratum to be 
 pierced. Thus at the commencement, when the rock is soft, the shell-auger will probably be the 
 most suitable tool ; and the same, or the clay-auger, will be required whenever a soft stratum is met 
 with. When a hard rock is reached, the chisel will be substituted for these tools. The length of the 
 stroke will also be determined by the hardness of the rock. This matter should be left entirely to 
 the master borer, who will direct the length of stroke in accordance with the indications which he is 
 observing. Under no pretence whatever should the men who work the lever be allowed to alter the 
 stroke at their discretion. The limits within which the stroke may be varied may be stated 
 generally as 6 inches and 26 inches. 
 
 To work the lever, the men chosen for that duty seize the cross-bar on the end of the lever, or 
 the ropes used instead of the cross-bar, as previously described, and pull it down with an even 
 motion : a jerky motion being very objectionable. They then suddenly release their hold, thereby 
 allowing the rods to fall back into the bore-hole. The number of strokes made is generally about 
 18 or 20 a minute. While the rods are being raised, a man upon the floor or platform at the 
 bottom of the staple turns them partially round by means of the tiller, to prevent the cutting 
 tool from falling a second time into the same place. The amount of turn given at each stroke is 
 about one-eighth of a revolution ; this amount should, however, be varied slightly. The man 
 appointed to this important duty should possess intelligence and a sense of the responsibility resting 
 upon him. Frequently the master borer undertakes this duty himself An experienced man can 
 judge very accurately of the nature of the stratum which is being passed through, by the character 
 of the shock transmitted through the rods. And thus at every change he is able to direct the 
 length of the stroke in accordance with it, or to order a change of tool, if that be necessary. 
 
 The time during which these operations are continued, as well as the depth by which the 
 bore-hole is advanced by them, will depend upon the character of the rock. When the rock is only 
 moderately hard, the chisel may penetrate six inches or even more before it will need resharpening ; 
 when the rock is very hard, two inches, or even less, will be sufficient to blunt the edge. As soon as 
 the bore-master deems it necessary to raise the tool for the purpose of replacing it by another, he 
 orders the men at the lever to cease. These then place themselves at the windlass, and the man at 
 the bottom of the staple, being provided with a key, detaches the rods from the lever connection, and 
 places the lifting dog beneath the head. This operation, simple as it is, requires very great care, for 
 if the rods are allowed to fall, immense and perhaps irreparable damage may be caused. The men 
 at the windlass having raised the rods to the height of the shear-legs, the man in the staple places 
 tlie other lifting dog under the lower joint in the rods, which joint will then be a little above the 
 guide-tube, and calls out to the former to lower. The rods are then let gently back till the second 
 lifting dog rests upon the guide-tube shutters, and the man with his key then unscrews the joint, 
 'li'he offtake, that is, the portion of the rods removed, is then hung up, a kind of rack being provided 
 
110 
 
 MINING ENGINEEEINa. 
 
 upon the shear-legs for that purpose. Sometimes the offtakes are stood up, or laid down ; but it is 
 far better to suspend them, for by that means the joints are kept free from dirt, and the rods ai e 
 protected from transverse strains. As soon as the offtake is detached, the men at the windlass a^ain 
 wind up the rods to the top of the shear-legs, and the same operations are repeated. This is con- 
 tinued till the whole of the rods have been raised. 
 
 As the greater part ^ of the time occupied in sinking a bore-hole is taken up by raising and 
 lowering the rods, every arrangement should be made to facilitate and expedite these operations. 
 And not only is this desirable for the purpose of economizing labour, but in boring through a soft 
 stratum, such as plastic clay, for example, success is often to be gained only by rapidity of execution ; 
 for it is essential that the retaining tubes should be got into their place before the stratum begins 
 to swell. 
 
 When the cutting tool has been removed from the bore-hole, the sludger is immediately put int(> 
 operation. For this purpose the lower pulley is run out over the bore-hole, and the sludger let down 
 v/ith all possible speed. Its descent is checked, as previously described, by means of a brake. In 
 the case of a hole 1000 feet deep, the time required for the descent of the sludger is about 3| minutes, 
 The operation of " pumping " the sludger is then begun and contimied for about 4 or 5 minutes ; 
 after which the instrument with its contents is raised by means of the windlass provided for that 
 purpose. The time occupied in raising the sludger will be, for the afore-mentioned depth, from 12 to 
 15 minutes. 
 
 While the operations of sludging have been going on, the worn cutting tool has been removed 
 from the rods, and a fresh one, after undergoing the proper tests, substituted for it. As soon as 
 the sludger has been withdrawn, the upper lifting dog hanging from the pulley is placed under the 
 upper joint of the offtake, to which the cutting tool is attached, and lowered by means of the 
 windlass till the dog rests upon the closed shutters of the guide-tube. Another offtake is then 
 screwed on, the other lifting dog placed under the upper joint or socket, the rods are slightly lifted 
 by it to free the lower dog, and then lowered till the other dog rests upon the shutters. These 
 operations are repeated till the whole of the rods have been lowered. 
 
 It will be remarked that by using the guide-shutters instead of a nippingfork, in the manner 
 described, the necessity for screwing on a short length of rod, or topit, at each lift is removed and 
 much time saved. When intended for this use, the shutters are made sufBciently strong to take the 
 weight of the rods, and the aperture through them of such form and dimensions that when closed 
 they shall grip the rods like a key. To keep them securely closed while the joint is beino- 
 unscrewed, a hook fixed upon one shutter is dropped into the outer eye on the other. During the 
 operations of boring, this hook is set into the inner eye for the purpose of holding the shutters 
 partially open to allow of the rods being turned. 
 
 When, in the course of the boring, a weak clay stratum is met with that will evidently not 
 stand long unsupported, the operations should be pressed forward with all possible speed, and 
 continued by night as well as by day without intermission till the stratum has been passed. As 
 soon as strong ground has been reached, the boring operations should be suspended and every 
 exertion directed to get the retaining tubes down before the stratum begins to swell. These tubes 
 with the appliances for driving them, should be always in readiness ; for though they may never 
 be required, if the necessity for them does occur, and they are not at hand, the consequences of 
 waiting till they can be procured may be Very serious. In this matter, delays are especially 
 
SEAECHING FOE COAL. Ill 
 
 dangerous. When the tubes have been got down beyond the dangerous portion, the boring may 
 be resumed. 
 
 A stratum of running sand will often occasion considerable difficulty. The progress made by 
 the ordinary means is in such cases extremely slow, and the final result seldom satisfactory. 
 Frequently, indeed, it is impossible to pass through such a stratum, especially when it contains 
 much water, with the common boring tools, and it therefore becomes necessary to have recourse to 
 other and more appropriate means. Generally the most effective of these extraordinary appliances 
 is a jet of water. The simplest and most satisfactory method of sinking by means of the water-jet 
 is as follows : A lining of tubes is put down the bore-hole till the sand stratum is reached. A tube 
 — which may be of metal with screw joints, or of flexible material — provided with a pointed metal 
 nozzle, pierced laterally with several holes, is then let down inside the lining till the nozzle rests 
 upon the sand, and the other end at surface is placed in communication with a force-pump. An 
 ordinary fire-engine is very suitable for this purpose. Water being forced down the tube, the sand 
 is stirred up at the bottom of the bore-hole, and raised to surface in the annular space between the 
 tube and the lining. During the operation pressure is kept upon the latter to sink it as the sand is 
 removed. The nozzle of the water tube must, of course, be lowered as the sinking progresses. In 
 this way the sand may be passed very quickly. On firm ground being reached, the lining should be 
 driven hard down into it to prevent the running sand from escaping beneath the tubes, after which 
 the boring may be resumed by the ordinary means. It may be remarked here respecting the 
 operation of lowering lining tubes, that each length of tube should be numbered, and marked 
 with its exact length in feet and inches ; and that, as each fresh length is screwed on, its number 
 and dimensions should be plainly entered in a memorandum-book by the master borer. If these 
 matters be neglected, there will soon be uncertainty as to the exact depth to which the lining 
 has been driven. 
 
 Accidents, which in spite of every precaution will in general be frequent, will call forth the 
 ingenuity of the engineer, and test his resources to the utmost. He will, however, do better in 
 displaying his skill and forethought in devising means for preventing the occurrence of accidents, 
 than for remedying the mischief after they have happened. In directing the operations of boring, 
 he cannot take too many precautions or show himself too careful, for he should remember that his 
 example will influence the men under his orders. One of the worst accidents that can happen, and 
 one that unhappily is not of rare occurrence, is the falling back of the rods into the bore-hole while 
 they are being raised or lowered. Such an accident may be prevented by proper care in placing 
 the lifting dog and the guide-shutters or nipping fork. Another bad accident is the closing in of the 
 bore-hole upon the cutting tool. The precautions to be taken in this case consist in boring through 
 a dangerous stratum as rapidly as possible, and in lining the hole immediately the stratum has been 
 passed. The means for extracting broken rods have already been described. Sometimes a tool will 
 become jammed in a cleft of the rock at the bottom of the bore-hole. In such a case, force should be 
 applied to the rods gently rather than in a violent and jerking manner, for such a manner would be 
 likely to fracture the joints. If the tool is very firmly held, a succession of light blows will loosen 
 it when violent wrenching fails. To lessen the risk of the rods being fractured and becoming 
 jammed in the bore-hole when accidentally dropped, a device called a " parachute " is sometimes 
 employed. This consists of a thick leather washer affixed to the rods towards the lower extremity. 
 This washer has a diameter equal to about two-thirds of that of the bore-hole, and is allowed to 
 
112 MINING ENGINEEEING. 
 
 move up and down npon the rod between two stops set at a distance apart somewhat greater than 
 that required by the longest stroke. When in use, the rod passes freely through the washer, the 
 motion of which is impeded by the water in the bore-hole. Should the rods fall, the upper stop 
 catches the washer, and the resistance of the water, which is forced to escape between the edges of 
 the washer and the sides of the bore-hole, then causes the rods to fall gently to the bottom. The 
 washer offers but little resistance to the raising and lowering of the rods, the motion of the windlass 
 being comparatively slow. Accidents are frequently caused by iron bolts and nuts being dropped 
 into the bore-hole. To prevent this the guard-shutters should be kept constantly. closed. Sometimes 
 these obstructions, and others of a like character, as fragments of a tool or a pebble, cannot be 
 seized by the common extracting tools. In such a case they may often be raised by a simple 
 expedient. A lump of clay moistened with oil to make it soft, and mixed with hemp fibre to give it 
 cohesion, is fixed into the bottom of the sludger below the valve. The sludger is then lowered to the 
 bottom of the bore-hole, upon which it is struck lightly two or three times. The obstruction is 
 pressed into the clay, to which it adheres with sufficient firmness to allow of its being raised with 
 the sludger. Numerous other minor accidents will frequently occur which could not be foreseen ; 
 the remedy for these must be left to the ingenuity of the engineer in charge. 
 
 We have already described the difficulties presented by a stratum of running sand, and shown 
 the necessity of lining such portions of the bore-hole. Oases may, however, occur in which this 
 necessity can be obviated. In prospecting for minerals, when the bore-hole is not required to stand 
 after the boring has been completed, if the sand stratum is a thin one, and free from water under 
 pressure, it may be retained in the following manner : As soon as the stratum has been passed, tlie 
 cutting tool is withdrawn, and a sufficient quantity of plastic clay thrown down to fill the bore-hole 
 to a height a little above the stratum. This clay is then rammed firmly down by means of a sjiitable 
 instrument at the end of the sludger rope, for the purpose of rendering it compact and forcing it 
 into the hollow sides of the bore-hole formed by the escape of the sand during the boring. The clay 
 is then bored through by means of the clay-auger, leaving a lining of that material to support the 
 sand. Whenever practicable, this simple expedient should be adopted, for it not only saves the cost 
 of tubing from surface, but it allows the bore-hole to be continued of the same diameter. 
 
 Occasionally, when the strata are highly inclined, and composed of alternating hard and soft 
 beds, the bore-hole will deviate from the vertical. In such a case, the defect has been remedied by 
 filling up the hole, to the point at which the deviation commenced, with flint pebbles, and after 
 having rammed them firm, resuming the boring through the hard mass. When, however, proper 
 care is taken, deviation from the vertical is of very rare occurrence. 
 
 The de'bris brought up from the bottom of the bore-hole by the sludger must be treated with 
 careful attention, for it must be borne in mind that in prospecting for minerals it is to obtain this 
 de'bris that the boring is undertaken. Being composed of the rock through which the cutting tool 
 is passings it is evidence of the nature of that rock, and the only evidence of that character that the 
 boring can afford. It is an unfortunate circumstance doubtless that by the ordinary methods of 
 boring the debris is reduced to almost a powder, so finely comminuted, indeed, that it is often 
 designated as bore-meal. It is true that a solid core may be obtained by the special tools already 
 described, and such cores should be extracted from every bed passed through ; but throughout the 
 greater length of the bore-hole the rock is necessarily broken up into meal. In this state its 
 indications are more or less of a doubtful character, and it therefore becomes necessary to exercise 
 
SEAECHING FOE COAL. 113 
 
 care and caution to eliminate tlie sources of error. The debris at the bottom of tbe bore-hole 
 becomes mixed with the materials from the higher beds, which fall from the sides of the hole during 
 the process of boring. For this reason, that portion which comes from the bottom of the hole, and 
 which, consequently, is situate in the lower end of the sludger, is deserving of more attention than 
 that which is first taken up. Argillaceous materials should be dried; fragments of shale and sandstone 
 should be well washed to remove the mud from them ; and when the materials are found to be mixed, 
 that which constitutes the major portion must be taken to represent the rock which is being passed 
 through. A sample of the rock should be preserved whenever a change occurs, and for this purpose 
 a box divided into suitable compartments will be required. The sample, when placed in the com- 
 partment, should be numbered, and the number should be entered in a journal. In this journal the 
 character of the rock should be accurately described. The usual descriptions in sections of strata are 
 wholly insufiScient and unworthy of the knowledge of the present day. Such expressions as stiff 
 blue clay, hard rock, soft rock, and metal, convey no notion of the actual character of the rock, and 
 can be of no other use than to cloak ignorance. On the other hand, the composition of the rock may 
 be clearly shown by such compound terms as " arenaceous," " calcareous," or " ferruginous clay," 
 " calcareous shale," " bitumino-calcareous shale," " silicious sandstone," argillaceous sandstone," 
 " argillo-calcareous sandstone," and " argillaceous limestone." The contents of the sludger should 
 also be carefully examined for organic remains, and special search for these should be made in the 
 solid cores raised. Such remains are, as previously pointed out, of the highest importance in deter- 
 mining the formations through which the boring is progressing. 
 
 General Considerations concerning a Boring. — Enough has already been said to show that boring 
 to great depths is an undertaking demanding great care, skill, and experience. To ensure success, 
 difficulties must be anticipated : it is not sufficient to provide for them when they occur, or even 
 when indications of their approach appear. An immediate remedy may often be efficacious ; a tardy 
 remedy is rarely so. To have ready at hand whatever is wanted is to prevent dangers the existence 
 of which may never be suspected. This foresight is everywhere necessary, in the apparently trivial 
 as well as in the visibly important matters, and from the preliminary arrangements till the com- 
 pletion of the undertaking. 
 
 In commencing a boring, the initial diameter of the bore-hole demands careful consideration 
 The important point is to begin with a sufficiently large diameter to allow of subsequent reductions 
 by tubing. If anything is known of the strata to be passed through, the diameter will be determined 
 according to the difficulties anticipated. But if the strata be wholly unknown, it will be prudent to 
 assume difficulties, especially if the boring is to be carried to a great depth, and to proportion 
 the initial diameter so as to allow of several reductions. In easy ground, when the boring is 
 expected to attain a great depth, the hole should be commenced with a diameter not less than 
 8 inches, and this diameter should be increased to 12 inches in difficult ground. The minimum 
 practicable diameter at the bottom of the bore-hole may be taken as 3 inches. 
 
 The shear-legs or boring frame should be as high as possible within the limit previously stated, 
 and the height of the lower side of the pulley above the top of the guide-tube should, as before 
 i-emarked, be a multiple of the lengths of which the rods are made up. Two pulleys should in every 
 case be provided for raising and lowering the rods, and other pulleys for the sludger rope, for 
 by means of such arrangements much time is saved ; and it has already been shown that rapidity ol 
 execution is often essential to success. Iron rods are preferable to wooden ones in bore-holes 
 
 Q 
 
114 
 
 MINING ENGINEEEING. 
 
 of ordinary dimensions, and the screw-joint should always be employed. When the depth has 
 become considerable, the use of the sliding joint for the cutting tool should be deemed indispensable. 
 Only the simplest tools, such as we have described, will be required ; complex forms will rather 
 retard than hasten the progress of the work. Eetaining tubes of the diameter of the bore-hole 
 in that portion in which the cutters are at work should be always at hand, together with the means 
 of forcing them down. For depths exceeding 300 yards, it will generally be advantageous to 
 employ steam power to work the lever, and also to raise and lower the rods and the sludger. 
 Besides being in such a case more economical than hand labour, it contributes greatly to the success 
 of the undertaking by hastening the progress of the boring, and by reducing the number of men 
 required to a few experienced and skilled hands. To diminish the risk of accident, the connection 
 between the engine and the machinery should be made by means of a belt. 
 
 Journal of the Boring. — Besides the master borer's memorandum-book, in which he will record 
 everything of the slightest importance that occurs, with the time and other details of its occurrence, 
 and the ordinary books in which the hours of labour, the time expended on every operation, and the 
 materials employed are entered ; another book, called the ' Journal of the Boring,' should be kept by 
 the engineer in charge. If a boring, which must of necessity be a long and costly operation, be 
 undertaken solely for the purpose of ascertaining the nature of the strata, it is obvious that the 
 journal in which the information so obtained is recorded will demand the most careful attention, 
 and that its value will be proportionate to the attention bestowed upon it, and the fulness with 
 which the information is given. The loose manner in which the journal is frequently kept renders 
 it of little value for the immediate purpose for which it was undertaken, and utterly worthless for 
 the more extended use of determining the geological constitution of the district. Thus full advantage 
 is not taken of the information obtained by a boring upon which much time and money have been 
 imgrudgingly expended. To render it adequate to the requirements demanded of it, the journal should 
 give a full and accurate description of the strata passed through ; it should indicate the thickness of 
 each stratum, and its depth from surface ; it should show the angle of its dip, and its water-bearing 
 character ; it should exhibit to the inquirer the nature and species of the organic remains contained 
 therein ; and it should describe the cutting tool employed to penetrate it, and tell the time occupied 
 in passing through it. Other information may profitably be added ; but the above mentioned should 
 be considered as indispensable. The following arrangement of the page may be taken as a guide in 
 preparing the journal : 
 
 JOUENAL. 
 
 Boring executed at in the County of 
 
 Begun May 1, 1874:. 
 
 On the Estate of 
 
 Completed Nov. 10, 1874. 
 
 Date. 
 
 ■Description 
 
 of 
 
 Strata. 
 
 No. of 
 Specimen 
 in Case. 
 
 Thickness. 
 
 Depth 
 
 from 
 
 Surface. 
 
 Angle of 
 Dip. 
 
 Diameter 
 
 of 
 Bore-hole. 
 
 Description 
 
 of Tool 
 employed. 
 
 Time actually 
 
 occupied in 
 
 passing through, 
 
 Quantity of 
 
 Mater 
 
 met with. 
 
 Organic ! 
 Remains. I 
 
 Eemarks. 
 
 The entry under each of these heads should be full and clear, so that it may be easily intelligible 
 
SEAECHING FOE COAL. 
 
 115 
 
 to everyone who has occasion to refer to it. The descriptions of the strata should be made in the 
 manner suggested on a foregoing page. 
 
 Rate of Progress and Cost of Boring. — There are probably no engineering operations in which 
 the rate of progress is so variable as it is in that of boring. That such must necessarily be the case 
 will be obvious when we bear in mind that the strata composing the earth's crust consist of very 
 different materials ; that these materials are mingled in very different proportions, and that they 
 have in different parts been subjected to the action of very different agencies operating with very 
 different degrees of intensity. Hence it arises not only that some kinds of rocks require a much 
 longer time to bore through than others, but also that the length of time may vary in rocks of the 
 same character, and that the character may change within a short horizontal distance. Thus it is 
 utterly impossible to predicate concerning the length of time which a boring in an unknown district 
 may occupy, and only a rough approximation can be arrived at in the case of localities whose 
 geological constitution has bee a generally determined. Such an approximation may, however, be 
 attained to, and it is useful in estimating the probable cost ; and to attain the same end, for unknown 
 localities, an average may be taken of the time required in districts of a similar geological character. 
 The following, which are given for this purpose, are the averages of a great number of borings 
 executed under various conditions by the ordinary methods. The progress indicated represents that 
 made in one day of eleven hours. 
 
 1. Tertiary and Cretaceous Strata 
 
 2. Cretaceous Strata, without flints 
 
 3. Cretaceous Strata, with flints .. 
 
 4. New Eed Sandstone 
 
 5. New Eed Sandstone 
 
 6. Permian Strata .. 
 
 7. Coal Measures .. 
 
 8. Coal Measures .. 
 
 General Average 
 
 ft. in. 
 
 To a depth of 100 yards. Average progress, 1 8 
 
 » » 250 „ „ „ 
 
 » » 250 n n » 
 
 n n ^"0 „ „ „ 
 
 S3 » OUU „ ,, „ 
 
 3» S) ^^^ 99 99 99 
 
 99 99 ^uU „ „ „ 
 
 99 99 iUU „ „ „ 
 
 99 99 AID ,, ,, ,, 
 
 2 
 
 1 
 
 1 
 
 4 
 
 1 
 
 10 
 
 1 
 
 5 
 
 2 
 
 
 
 2 
 
 3 
 
 1 
 
 8 
 
 1 
 
 9 
 
 When the cost of materials and labour is known, that of the boring may be approximately 
 estimated from the above averages. Should hard limestone or igneous rock be met with, the rate of 
 progress may be less than half the above general average. Below 100 yards, not only does the rate 
 of progress rapidly increase, but the material required diminishes in like proportion, so that for super- 
 ficial borings, such as are frequently undei'taken for the discovery of hematite iron ore, no surface 
 erections are needed, and the cost sinks to two or three shillings a yard. 
 
 Arrangements with Contractors. — Borings are usually executed by contract ; but the terms of the 
 contract are very variable. As the work is of such an uncertain character, no contract could be 
 made that would render the contractor liable to unlimited loss in the event of unforeseen difficulties 
 occurring. Hence the condition is always accepted that the cost of such difficulties shall, with certain 
 limitations, be borne by the parties for whom the boring is to be made. The difficulties included in 
 this saving clause are : meeting with hard limestone, igneous rock, or quicksand, and any great 
 and unusual obstacle arising from any cause. When such difficulties occur, the work proceeds as day 
 labour, to be paid for weekly by the employer, at a rate previously agreed upon, till the difficulty 
 
 Q 2 
 
116 
 
 MINING ENGINEEEING. 
 
 has been surmounted, wten the terms of the contract again come into force. A clause in favour of 
 the employer enables him to abandon the boring whenever the contract becomes so suspended. 
 
 The uncertainty of the work, even under these conditions, renders it necessary for the contractor 
 to allow a wide margin for contingencies, and hence these terms of contract are the most expensi\e 
 to the employer. Probably the cheapest arrangement that could be made would be to agree with the 
 contractor to furnish the necessary materials, to provide the requisite labour, and to conduct the 
 operations for a fixed sum per week, the employer paying the cost of carriage. Such an arrange- 
 ment is not, however, an altogether equal one, inasmuch as no provision is made in favour of the 
 employer for delays on the part of the contractor. The most equitable terms of contract seem to be 
 the foregoing, with the addition of some such clauses as the following. That if the boring be com- 
 pleted before a given time, the contractor shall receive a premium of a certain sum per week for 
 every week unexpired, which sum may be the amount paid for the last week's work, or a certain pro- 
 portion of that amount. That if the boring be not finished within the time specified, the operations 
 shall be carried on from that time, with the same men and appliances, at a reduction of 25 per cent, 
 on the weekly cost previously agreed upon. And that should any delay or neglect on the part of the 
 contractor be proved to the satisfaction of an arbitrator mutually accepted, the employer may, if he 
 think fit, cause the contractor to abandon the work, and to remove the material at his own cost. On 
 the continent of Europe such terms as these are frequently made. 
 
 When the contractor undertakes to execute the work for a fixed sum^ exclusively of the special 
 difficulties already described, he does not include in that sum the cost of conveying the materials to 
 and from the spot, or that of erecting sheds, or making a road if one be required. These expenses 
 are borne by the employer. The sum demanded by the contractor is calculated in the following 
 manner. It is assumed, allowing a sufficient margin for contingencies, that the mean cost of the first 
 10 yards will be 3s. 6d. a yard; that of the second 10 yards, 7s. a yard; that of the third 10 yards, 
 10s. Cd. a yard, and so on in arithmetical progression, increasing by 3s. 6d. at each 10 yards. Thus 
 by multiplying the mean cost a yard for the total depth, as determined in this way, by that depth, 
 the total cost is readily found. The following formula will give this cost in pounds sterling, with the 
 least possible labour of calculation : 
 
 S = 0-5(^(0-175-|-0-0175(Z) 
 
 S being the sum sought, and d the depth of the boring in yards. 
 Example. — Required the cost of a boring 200 yards deep. 
 
 Here 100 {0- 175 + (0- 0175 x 200)} =£367-5. 
 
 In some cases, the engineer will find it advantageous to purchase a set of boring tools and 
 apparatus, and to execute the work himself rather than entrust it to a contractor. Under such an 
 arrangement, he will purchase the material with the intention of selling it again when the borings 
 are completed, the difference between the buying and the selling price being considerably less than 
 the amount allowed by the contractor for contingencies, depreciation, and profit. It is hardly- 
 possible to give an exact estimate of the cost of the apparatus for a given depth until all the 
 conditions of the case are known; moreover, the variations in the price of raw material must 
 necessarily affect the cost in no inconsiderable degree. But an approximate mean value may be 
 found which may serve as a basis of calculation. The following values are of this character the 
 
SEAECHING FOE COAL. 117 
 
 estimates being founded upon the assumption that the tools and appliances employed are such as we 
 have previously described. 
 
 £ 
 
 1. Hand-boring apparatus for a depth of 6 or 7 yards .. ., ,. „ .. „ about 4 
 
 2. Tools and other appliances for a depth of 15 yards, including shear-legs and one diameter of tools .. 12 
 
 3. Tools and other appliances, as in No. 2, but including two diameters of tools, and tubes ., .. 18 
 
 4. Tools and other appliances for a depth of 25 yards, including shear-legs complete, two diameters of 
 
 tools, and tubes ., .. .. .. .. .. .. .. .. ., .. .. 40 
 
 5. Tools and other appliances for a de^th of 50 yards, including shear-legs complete, three diameters of 
 
 tools, and two diameters of tubes .. .. .. .. .. .. .. .. .. 90 
 
 6. Tools and other appliances for a depth of 100 yards, including shear-legs complete, three diameters of 
 
 tools, and two diameters of tubes .. .. .. .. .. .. .. .. .. 240 
 
 7. Tools and appliances for a depth of 200 yards, including shear-legs complete, four diameters of tools, 
 
 and three diameters of tubes .. .. .. .. .. .. .. .. .. .. 400 
 
 8. Tools and appliances for a depth of 300 yards, including boring frame complete, four diameters of tools, 
 
 and three diameters of tubes .. .. .. .. .. .. „ „ ., .. 1000 
 
 The diameters of the tools in the foregoing sets are 3 inches ; 4 inches and 3 inches ; 5 inches, 
 4 inches, and 3 inches ; and 6 inches, 5 inches, 4 inches, and 3 inches respectively. 
 
 Special Systems of BoRma. — Improvements effected in the mechanical appliances used in 
 boring have led to the introduction and establishment of special systems by which rapidity ot 
 execution is gained. Another advantage which these systems aim at securing is the possibility 
 of extracting the rock in the form of a solid core without having recourse to extraordinary and 
 slow means. The advantages accruing from rapidity of execution and the extraction of solid cores 
 are very great, and hence the system which renders such advantages obtainable is of very great 
 importance and value. As an offset against these merits, however, there exists in every case the 
 defect of complexity of parts. The appliances required by the ordinary methods of boriog are few 
 and extremely simple. They are such as anyone may obtain for himself, and use without much 
 special knowledge. But the systems in question involve complicated erections, the employment of 
 steam power, and the attendance of trained and experienced workmen. Hence such a system can 
 be applied only by a firm or a company who make it their special business to execute borings with 
 it, and it therefore becomes necessary to contract with these if it be desired to obtain the advan- 
 tages which the system offers. For this reason it seems undesirable to describe the details of such 
 systems of boring with the minuteness observed in respect to the ordinary methods. The following 
 descriptions will, therefore, deal only with their main and distinctive features. 
 
 The systems of the special character in question, which have proved their merits and come into 
 common use, are two in number, and are known respectively as " Mather and Piatt's system," and 
 the " Diamond system." The former of these is less special in the character of its appliances than 
 the latter, and demands, therefore, fuller description and illustration. The essential principle of 
 Mather and Piatt's system consists in the substitution of a flat hempen or wire rope for the iron rods 
 employed in the ordinary methods. By this means a great saving of time is effected in raising and 
 lowering the cutting tools, the operations being performed as rapidly as those of raising and lowering 
 the sludger. The appliances introduced, and the methods of working adopted to render such a 
 substitution possible, as well as other and minor advantages claimed for the system, will be best 
 understood from the following description, given by Mr. Mather in a paper read before the Institutic n 
 of Mechanical Engineers : 
 
 Mather aiid Piatt's System of Boring. — '* The distinctive peculiarities of this method of boring 
 
118 MINING ENGINEEEING. 
 
 consist in the means adopted for giving the percussive and rotary actions to the boring tool; and 
 also in the construction of the tool or boring head, and of the shell pump for clearing out the hole 
 after the action of the boring head. Instead of these implements being attached to rods, they are 
 suspended by a flat hemp rope, about | inch thick and 4| inches broad, such as is commonly used at 
 collieries ; and the boring tool and shell pump are raised and lovs^ered in the bore-hole as quickly as 
 the buckets and cages in a colliery shaft. The following is a description of the construction and the 
 methods of working this machine : The flat rope A, Fig. 224, from which the boring head B is 
 suspended, is wound upon a large drum C, which is driven by a steam-engine B, having a reversing 
 motion, so that one man can regulate the operation with the greatest ease. This winding drum is 
 10 feet in diameter in the large machine, and is capable of holding 3000 feet length of rope 4^ 
 inches broad and ^ inch thick. Ail the working parts are fitted into a wood and iron framing E, 
 thus rendering the whole a compact and complete machine. On leaving the drum the rope passey 
 imder a guide pulley F, and then over a large pulley Gr carried in a fork at the top of the piston-rod 
 of a vertical single-acting steam cylinder H ; this cylinder, by which the percussive action of the 
 boring head is produced, is shown to a larger scale in the vertical sections. Figs. 226 and 227. In the 
 larger size of machine here shown, the cylinder is fitted with a piston of 15 inches diameter, having 
 a heavy cast-iron rod 7 inches square, which is made with a fork at the top carrying the flanged 
 pulley Gr of about 3 feet diameter, and of sufficient breadth for the flat rope A to pass over it. The 
 boring head having been lowered by the winding drum to the bottom of the bore-hole, the rope is 
 fixed secure at that length by the clamp J ; steam is then admitted underneath the piston in the 
 cylinder 11 by the steam valve Iv, and the boring tool is lifted by tbe ascent of the piston-rod and 
 pulley Gr ; and on arriving at the top of the strolvc the exhaust valve L is opened for the steam to 
 escape, allowing the piston-rod and carrying pulley to fall freely with the boring tool, which falls 
 with its full weight to the bottom of the bore-hole. The exhaust port being 6 inches above tie 
 bottom of the cylinder, wliilc the steam port is situated at the bott(jm, there is always an elastic 
 ciishion of steam retained in the cylinder for the piston to fall upon, thus preventing the piston from 
 striking the bottom of the cylinder. The steam and exhaust valves are worked with a self-acting 
 motion by the tappets M M, which are actuated by the movement of the piston-rod ; and a rapid 
 succession of blows is thus given by the boring tool on the bottom of the bore-hole. As it is neces- 
 sary that motion should be given to the piston before the valves can be acted upon, a small jet of 
 steam N is allowed to be constantly blowing into the bottom of the cylinder; this causes the piston 
 to move slowly at first, so as to take up the slack of the rope and allow it to receive the weight of 
 the boring head gradually and without a jerk. An arm attached to the piston-rod then comes in 
 contact with a tappet, which opens the steam valve K, and the piston rises quickly to the top of the 
 stroke; another tappet worked by the same arm then shuts off the steam, at the same time the 
 exhaust valve L is opened by a corresponding arrangement on the opposite side of the piston-rod. 
 By shifting these tappets the length of stroke of the piston can be varied from 1 to 3 feet, according 
 to the material to be bored through ; the height of fall of the boring head at the bottom of the bore- 
 hole being double the length of the piston stroke. The fall of the boring head and piston can also 
 be regulated by a weighted valve on the exhaust pipe, checking the escape of the steam, so as to 
 cause the descent to take place slowly or quickly as may be desired. 
 
 " The boring head B, Fig. 224, is shown to a larger scale in Figs. 228 to 231, and consists of a 
 wrought- iron bar about 4 inches diameter and 8 feet long, to the bottom of which a cast-iron cylindrical 
 
SEARCHING FOE COAL. 
 
 119 
 
 block a is secured. This block has numerous square holes through it, into which the chisels or 
 cutters h, of which two diiFerent arrangements are shown, are inserted with tapered shanks, so as to be 
 very firm when working, but at the same time easily taken out for repairing and sharpening. A little 
 above the block a another cylindrical casting c is fixed upon the bar B, which acts simply as a guide 
 to keep the bar perpendicular. Higher still is fixed a second g-uide d ; but on the circumference of 
 this are secured cast-iron plates made with ribs of a saw-tooth or ratchet shape, catching only in one 
 direction. These ribs are placed at an inclination like segments of a screw-thread of very long pitch, 
 so that, as they bear against the rough sides of the bore-hole when the bar is raised or lowered, they 
 assist in turning it, causing the cutters to strike in a fresh place at each stroke. Each alternate 
 plate has the projecting ribs inclined in the opposite direction, so that one half of the ribs are acting 
 to turn the bar round in rising, and the other half to turn it in the same direction in falling. These 
 projecting spiral ribs simply assist in turning the bar, and immediately above the upper guide d is 
 the arrangement by which the. definite rotation is secured. To effect this object two cast-iron collars, 
 e and/, are cottered fast to the top of the bar B, and placed about 12 inches apart. The upper face 
 of the lower collar e is formed with deep ratchet-teeth of about 2 inches pitch, and the under face of 
 the top collar/ is formed with similar ratchet-teeth, set exactly in line with those on the lower collar. 
 Between these collars, and sliding freely on the neck of the boring bar B, is a deep bush g, which is 
 also formed with corresponding ratchet-teeth on both its upper and lower faces ; but the teeth on the 
 upper face are set half a tooth in advance of those on the lower face, so that the perpendicular side of 
 each tooth on the upper face of the bush is directly above the centre of the inclined side of a tooth on 
 the lower face. To this bush is attached the wrought-iron bow h, by which the whole boring bar is 
 suspended with a hook and shackle 0, Fig. 224, from the end of the flat rope A. The rotary motion 
 of the bar is obtained as follows : When the boring tool falls and strikes the bow, the lifting bush g, 
 which during the lifting has been engaged with the ratchet-teeth of the top collar /, falls upon those 
 of the bottom collar e, and thereby receives a twist backwards through the space of half a tooth ; and 
 on commencing to lift again, the bush rising up against the ratchet-teeth of the top collar / receives 
 a further twist backwards through half a tooth. The flat rope is thus twisted backwards to the 
 extent of one tooth of the ratchet, and during the lifting of the tool it untwists itself again, thereby 
 rotating the boring tool forwards through that extent of twist between each successive blow of the 
 tool. The amount of this rotation may be varied by making the ratchet-teeth of coarser or finer pitch. 
 The motion is entirely self-acting, and the rotary movement of the boring tool is ensured with 
 mechanical accuracy. This simple and most effective action taking place at every blow of the tool 
 produces a constant change in the position of the cutters, thus increasing their effect in breaking the 
 rock. 
 
 " The shell pump, for raising the material broken up by the boring head, is shown in Figs. 232 
 and 233, and consists of a cylindrical shell or barrel P of cast iron, about 8 feet long and a little 
 smaller in diameter than the size of the bore-hole. At the bottom is a clack a opening upwards, 
 somewhat similar to that in ordinary pumps ; but its seating, instead of being fastened to the cylinder 
 P, is in an annular frame c, which is held up against the bottom of the cylinder by a rod d passing 
 up to a wrought-iron bridge e at the top, where it is secured by a cotter/. Inside the cylinder works 
 a bucket h similar to that of a common lift-pump, having an indiarubber disc valve on the top side ; 
 and the rod d of the bottom clack passes freely through the bucket. The rod g of the bucket itself is 
 formed like the long link in a chain, and by this link the pump is suspended from the shackle 0, at 
 
120 MINING ENGINEEEING. 
 
 the end of the flat rope, the bridge e preventing the bucket from being drawn out of the cylinder. 
 The bottom clack a is made with an indiarubber disc, which opens sufficiently to allow the water and 
 small particles of stone to enter the cylinder ; and in order to enable the pieces of broken rock to be 
 brought up as large as possible, the entire clack is free to rise bodily about 6 inches from the annular 
 frame c, thereby affording ample space for large pieces of rock to enter the cylinder when drawn in 
 by the up stroke of the bucket. 
 
 " The general working of this boring machine is as follows : When the boring head B is hooked on 
 the shackle 0, at the end of the rope A, its weight pulls round the drum and winding engine, and by 
 means of a brake it is lowered steadily to the bottom of the bore-hole ; the rope is then secured at 
 that length by screwing up tight the clamp J. The small steam jet N is next turned on, for starting 
 the working of the percussion cylinder H ; and the boring head is then kept continuously at work 
 until it has broken up a sufficient quantity of material at the bottom of the bore-hole. The clamp J 
 which grips the rope is made with a slide and screw I, whereby more rope can be gradually given 
 out as the boring head penetrates deeper in the hole. In order to increase the lift of the boring head, 
 or to compensate for the elastic stretching of the rope, which is found to amount to 1 inch in each 
 100 feet length, it is simply necessary to raise the top pair of tappets on the tappet rods whilst the 
 percussive motion is in operation. When the boring head has been kept at work long enough, the 
 steam is shut off from the percussion cylinder, the rope undamped, the winding engine put in motion, 
 and the boring head wound up to the surface, where it is then slung from an overhead suspension 
 bar Q, by means of a hook mounted on a roller for running the boring head away to one side, clear of 
 the bore-hole. 
 
 " The shell pump is next lowered down the bore-hole by the rope, and the debris pumped into it 
 by lowering and raising the bucket about three times at the bottom of the hole, which is readily 
 effected by means of the reversing motion of the winding engine. The pump is then brought up 
 to the surface, and emptied by the following very simple arrangement : It is slung by a traversing 
 hook from the overhead suspension bar Q, and is brought perpendicularly over a small table R in the 
 waste tank T ; and the table is raised by the screw S until it receives the weight of the pump. The 
 cotter /, which holds up the clack seating c at the bottom of the pump, is then knocked out, and the 
 table being lowered by the screw, the whole clack seating c descends with it, as shown in Fig. 233, 
 and the contents of the pump are washed out by the rush of water contained in the pump cylinder. 
 The table is then raised again by the screw, replacing the clack seating in its proper position, in 
 which it is secured by driving the cotter/ into the slot at the top, and the pump is again ready to be 
 lowered down the bore-hole as before. It is generally necessary for the pump to be emptied and 
 lowered three or four times in order to remove all the material that has been broken up by the 
 boring head at one operation. 
 
 " The rapidity with which these operations may be carried on is found in the experience of the 
 working of the machine to be as follows : The boring head is lowered at the rate of 500 feet a 
 minute. The percussive motion gives twenty-four blows a minute. This rate of working continued 
 for about ten minutes in red sandstone and similar strata is sufficient for enabling the cutters to 
 penetrate about six inches in depth, when the boring head is wound up again at the rate of 300 feet 
 a minute. The shell pump is lowered and raised at the same speeds, but only remains down about 
 two minutes, and the emptying of the pump, when drawn up, occupies from two to three minutes. 
 " In the construction of this machine it will be seen that the great desideratum of all earth boring 
 
BhAfiCHING FOR COAL. 121 
 
 has been well kept in view, namely, to bore boles of large diameter to great depths with rapidity 
 and fiafety. The object is to keep either the boring head or the shell pump constantly at work at the 
 bottnin of the bore-bole, where the actual work has to be done ; to lose as little time as possible in 
 raising, lowering, and changing the tools ; to expedite all the operations at the surface ; and to 
 economize manual labour in every particular. With this machine, one man standing on a platform 
 at the side of the percussion cylinder performs all the operations of raising and lowering by the 
 winding engine, changing the boring head and shell pump, regulating the percussive action, and 
 clamping or unclamping the rope : all the handles for the various steam valves are close to his hand, 
 and the brake for lowering is worked by his foot. Two labourers attend to changing the cutters 
 and clearing the pump. Duplicate boring heads and pumps are slung to the overhead suspension 
 bar Q ready for use, thus avoiding all delay when any change is requisite. 
 
 " Solid cores, showing perfectly the nature and quality of the rock, with its angle of inclination 
 and other particulars, may be obtained by operating the boring head in the following manner : 
 Ha^'ing removed all the inside cutters, leaving only the outside circle of cutters and the few cross 
 chisels alternating with them round the circumference of the block, by continued working a slightly 
 conical core will be formed, which may be made longer or shorter according to the length and 
 inclination of the cutters ; this core becomes finally jammed fast between the cutters and broken off 
 at the root, and is then brought up to the surface by the boring head. Beautiful specimens of coal 
 have by this means been brought up, large enough to show the quality and dip of the seam." 
 
 The Diamond System of Boring. — The diamond system differs essentially in principle from 
 every other method of rock boring. We have already shown that the percussive action invariably 
 attributed to the common boring tools was rendered necessary by the difference of hardness between 
 the cutting tool and the rock being in favour of the latter. The inventor of the diamond drill 
 sought to reverse this condition by employing for the cutting tool the hardest known substance, 
 namely, the diamond, and thereby to remove the necessity for the percussive action. The costly 
 character of the material would, however, have precluded the practicability of the idea had it existed 
 only in the form in which it is used as a gem. But fortunately it is found in comparative abundance 
 in an imperfectly crystallized form known as " caibonate." This carbonate, which until recently had 
 but little commercial value, is of a dull black colour, and is characterized by little or no cleavage. This 
 latter quality is a very valuable one, as it removes the liability to split, to which the more perfect 
 variety is exposed. But although the carbonate is much harder than the rock to be pierced, it could 
 not be made to cut the latter by means of a cutting edge after the manner of steel instruments, and 
 therefore another mode of applying it had to be discovered. It it is a well-known fact, that when 
 two substances of unequal hardness are rubbed together, the softer is worn away by the friction ; this 
 action of abrasion was chosen as that through which the diamond could be made to act most effectively 
 in piercing rock. Thus, in the diamond system of boring, the rock is worn down by abrasion ; and 
 though such a process may appear at first sight a slow one, experience has shown that when effected 
 with suitable appliances, it is, on the contrary, far more rapid than the ordinary process of fracture 
 by blows from a falling tool. 
 
 In applying the diamond to rock drilling, a number of the stones are set in the edge of a steel 
 cylinder or crown to which the rods are attached. To fasten the stones in securely, holes are made in 
 the metal just sufficiently large to receive them, and the metal is hammered over so as to bury them, 
 leaving (lach itone only the amount of projection necessary to enable it to rest upon the rock, and to 
 
 K 
 
122 
 
 MINING ENGINEEEING. 
 
 allow the ddbris and water to pass beneath the crown. The setting of the stones needs to be done 
 with care, for the greatest danger to the drill arises from the liability of the stones to come out. The 
 wear of the stones even in hard rock is trifling ; but the loosening of one of them, besides occasioning 
 trouble and loss, is a source of danger to the others. As the stones are set in a ring, the minimum 
 amount of work is performed ; for the work of abrasion by the stones is required only to form an 
 annular space, and not to remove the rock within the circumference of the bore-hole, as in other 
 systems. When this annular space has been cut, the solid core may be extracted, and the advantage 
 gained thereby is not merely an economy of labour, but the obtaining of clear and certain evidence 
 concerning the character of the strata passed through. Indeed, the chief merit of the diamond system, 
 great as that of expeditious execution may be, consists in its bringing out the core of the bore-hole 
 solid instead of in the powdered state to which it is reduced by other systems. 
 
 The crown in which the diamonds are set is screwed on to the end of steel tubes, which serve as 
 rods for transmitting the motion from the surface. These tubes or hollow rods terminate at their 
 upper extremity in a universal clutcn, whicti allows them to turn, and which is connected with a 
 cross-head sliding between two vertical uprights. To keep the bore-hole truly vertical, these need to 
 be very carefully set and fixed. A rotary motion is communicated to the rods from a steam-engine 
 by means of suitable gearing. The speed of rotation is usually about 250 revolutions a minute. The 
 weight upon the crown is made to vary, according to the hardness of the rock and the rate of pro- 
 gress required, from 400 lb. to 800 lb., which weight is furnished by the rods, increased by a weight, 
 or diminished by a counterweight, according to the depth attained. During the progress of the 
 boring, water is forced down the hollow rods to remove the de'bris from the annular space in which 
 the diamonds are working, and to keep the latter cool. The core, when formed, passes into a core- 
 tube, in which it is held, on the rods being withdrawn, by sliding wedges or clips. Suitable gearing 
 of an ordinary character is provided for raising and lowering the rods ; and for remedying accidents 
 the common appliances are made use of. 
 
 The diamond drill will cut through the hardest rock ; even emery having been pierced at the 
 rate of 2 inches a minute. The ordinary rate of progress during actual boring is stated to be from 
 2 inches to 3 inches a minute in granite and the hardest limestones ; 1 inch a minute in quartz ; and 
 4 inches a minute in sandstone. These are the speeds attained in ordinary practice. In soft strata, 
 such as clay and sand, the diamond cutter is of no use whatever. When these strata are met with, 
 the ordinary tools are employed until hard rock is reached. 
 
 The following statement, showing vosults obtained in some of the bore-holes executed by the 
 Diamond Eock-Boring Company, is due to Major Beaumont, R.E., chairman of the Company : 
 
 Locality. 
 
 Girrick 
 
 Moorsholme 
 
 Fishburne .. 
 
 Beeston 
 
 Chewton 
 
 Loftus 
 
 Ballymena .. 
 
 Including the Time occupied in getting the Machinery 
 on the Ground. 
 
 Commenced. 
 
 October 1, 1872 .. 
 June 1, 1872 
 November 9, 1872 
 February 22, 1873 
 December 31, 1873 
 March 16, 1873 .. 
 April 7, 1873 .. 
 
 Ended. 
 
 November 30, 1872 
 July 27, 1872 .. 
 February 1, 1873 
 July 22, 1873 .. 
 July 13, 1873 .. 
 June 7, 1873 
 May 24, 1873 .. 
 
 Actual 
 
 
 Working 
 
 Depth. 
 
 Days. 
 
 
 
 ft. 
 
 54 
 
 902 
 
 48 
 
 641 
 
 54 
 
 434 
 
 146 
 
 1008 
 
 168 
 
 802 
 
 60 
 
 H\) 
 
 42 
 
 558 
 
SEAECHING FOR COAL. 123 
 
 At present, the Diamond Eock-Boring Company, who own the patents for the invention, do not 
 sell machines, nor allow them to be used on payment of a royalty. But they undertake to execute 
 borings upon terms similar to those already described, though at higher rates. The cost of the 
 transport of the material to and from the site of operations is borne by the employer when the depth 
 does not exceed 500 feet ; above that depth and below 1000 feet the employer pays only the cost of 
 transport to the site of the boring; and above a depth of 1000 feet, the whole cost of transport is 
 borne by the Company. The employer finds engine power and water, or pays the Company 25Z. 
 a month for providing the same. The engine required is an ordinary portable engine, with a 
 cylinder of about 11 inches diameter. The cost of a covering for the machinery and of a shed for the 
 protection of the workmen from the weather is also charged to the employer. 
 
 Upon the foregoing conditions, and the usual one relating to difficult strata, the Company under- 
 take to bore up to 1500 feet in depth, at the following rates of charges, exclusive of the cost of 
 lining, namely, 8s. a foot for the first hundred feet; 16s. a foot for the second hundred feet; \l. 4s. a 
 foot for the third hundred, and so on in arithmetical progression, increasing 8s. at each hundred feet. 
 Above 1500 feet in depth, special rates are charged. Upon this basis, the cost of a bore-hole may be 
 readily calculated by the following formula : 
 
 S = 0-5rf(0-4 + 0-004 (Z). 
 
 S being the sum sought, and d the depth of the bore-hole in feet ; the amount is given in pounds 
 sterling. 
 
 Example. — Required the cost of a bore-hole 600 feet in depth. 
 
 Here 300 {0-4 + (0-004 x 600)} = 840?. 
 
 R 2 
 
124 
 
 MINING ENGINEEEINQ. 
 
 CHAPTEK IV. 
 
 SHAFT-SINKINa. 
 
 SECTION I. 
 
 Tools used in Excavating Eook. — The tools used in coal-mining are few in kind and simple in 
 construction ; but though their simplicity of form and generally well-known character are such as to 
 lead writers on subjects of mining engineering frequently to omit them altogether from their 
 descriptions, they nevertheless constitute a subject of no small importance, and one that is deserving 
 of close attention. In the adapting of means to an end, the design and quality of tools should form 
 a primary consideration. In mining especially, where the efEciency of the tools employed depends 
 so much upon their being suitably designed for and applied to the work required of them, the subject 
 claims careful attention. It is impossible to obtain the highest degree of productiveness in the 
 labour of the miner without a full and accurate knowledge of the mineral composition and the 
 structure of the rocks among which he works, and of the particular capabilities of the several means 
 which he employs in attacking them. Also the character of mining operations is such as to occasion 
 a rapid wear of the tools, and a consequent necessity for their frequent repair and renewal. In a mine 
 employing several hundred men, these are matters involving a considerable cost, both of time and of 
 money. Moreover, in countries and localities that are far removed from the centres of manufacture, 
 it becomes necessary not only to repair, but to make all, or nearly all, the tools required in the 
 mine ; and in such a case a knowledge of the methods of manufacture, as well as of the principles 
 upon which their construction and use are founded, becomes absolutely indispensable. A want of 
 such knowledge has often occasioned the failure of important enterprises that might otherwise have 
 proved eminently successful. We shall, therefore, describe somewhat in detail the tools and 
 appliances used in excavating rock, and the labour of keeping them in a proper condition, before 
 entering upon the subject of opening out a colliery. 
 
 Shovels. — The shovel is a well-known and very serviceable tool, the use of which is to collect 
 and remove into corves, tubs, barrows, or carts, the rock that has been loosened by other means. 
 It consists essentially of a " plate" for passing under and retaining the loosened material, and a 
 wooden handle to which the plate is fixed. To give lightness and stiffness to the plate, and at the 
 same time to enable it to pass readily beneath the rock and to retain its load, it has received 
 several forms according to the use to which the tool is to be applied ; and to allow it to be used in 
 more or less confined spaces, the handle has been made of various lengths. The plate is always 
 of iron, and the front edges are steeled. Stiffness and carrying capacity are obtained by making the 
 plate slightly concave. The upper portion, or " shoulder" of the plate, is provided with " straps " 
 or " ears" to receive the handle; and at the part where it joins the straps it is buckled upwards to 
 
SHAFT-SINKING. 125 
 
 give strength. This part is called the " crease." The handle or helve is alvpays of ashwood, and is 
 circular in section. It terminates in a crutch-handle or hilt, a form which is preferred by miners to 
 the common D or " eyed" handle. To lessen the necessary degree of stooping, the handle is set at 
 an angle with the plate. The sizes of shovels are distinguished by the width of the plate, measured 
 in its widest part ; they vary from 10 inches for heavy work, to 16 inches for light work, such as 
 shovelling coal or loose earth. The strain upon the shovel when in use is mainly thrown upon the 
 crease and the top strap, and it is at this part that they yield by the parting of the strap. 
 Strength in the strap and the crease is therefore a requirement in a shovel. 
 
 The form of shovel used for gravel is that shown in Fig. 234, Plate XXI. The plate is 10 inches 
 wide, and the " mouth" or entering part is pointed so as to form two edges. This form renders it 
 very suitable for entering closely compressed or heavy ground. The handle is 30 inches long, and 
 is set at an angle of about 150° with the surface of the plate. 
 
 Fig. 235 represents a " frying-pan" filling shovel, as used in the north of England and in some 
 other districts. The plate is nearly circular, with a short point, and the edges are turned up to 
 give it concavity; the breadth is 14 inches, and the length 16 inches; the handle is 24 inches 
 long, and is set at an angle of 142° with the plate. The weight of this tool is 7 lb. 14 oz. ; it is very 
 well adapted for loading coal into tubs, and it is very extensively employed at collieries. 
 
 Fig. 236 represents a " round-mouthed" filling shovel, which is very generally employed for 
 shovelling loose stuff not too heavy. The plate is 16 inches wide, and 15 inches long ; the handle is 
 23 inches in length, and is set at an angle of 147° with the plate. The weight of this tool is also 
 7 lb. 14 oz. Fig. 238 represents a sinking shovel, 11^ in. x 14 in., the handle of which is 23 inches 
 in length. 
 
 For use in clay ground, liie " clay-spade," shown in Fig. 237, is used. The plate of the spade is 
 long and narrow, and has a square mouth. Sometimes the plate is curved so as to form a portion of 
 a cylinder, as shown in the figure. "When of this form it is often called a " grafting spade." The 
 clay-spade is used by forcing it into the ground with the foot placed upon the shoulder, and to form 
 a convenient tread a piece of iron is riveted upon the shoulder. This tool is much used in soft or 
 clay ground. 
 
 The shovel is the only tool which is never made at the mine : it is always purchased ready 
 made, and when broken it is seldom capable of being repaired. The cost of gravel shovels, 10 in., 
 11 in., and 12 in. wide, is from 25s. to 35s. a dozen; all steel, from 60s. to 70s. Frying-pan and 
 I'ound-mouthed filling shovels cost, according to size, from 35s. to 48s. a dozen ; aU -steel, round 
 mouths, from 45s. to 60s. ; and clay-spades, 12 in. x 6| in., about 35s. a dozen. 
 
 Picks. — The pick, maundril, or hack, as it is variously named, is the most important tool of the 
 miner. Its use is to loosen masses of rock, or to chip away small fragments. It consists of an iron 
 head formed of two arms, and a wooden handle or helve fitted into an eye in the middle of the head 
 or stem. The arms are steeled at the tips, and are either pointed or chisel-edged, according to the 
 work required of the tool. When pointed, the point is formed by a square taper. Such wedge-shaped 
 extremities enable the arm to penetrate the joints of fissured rocks, or between the laminai of shaly 
 rocks. When the tip of one arm of the pick has been forced into the rock, it is used as a lever to 
 fracture the mass by pressing or prising upon the helve. Thus the action of the pick combines that 
 of the hammer, the wedge, and the crow-bar or lever. It acts as a hammer in delivering a blow ; as 
 a wedge, in penetrating and disrupting the rock ; and as a lever, in forcing out large masses. These 
 
126 MINING ENGINEEEING. 
 
 several actions must be borne in mind when considering the form and construction of a pick. With 
 the chisel edge it is very frequently used to chip off fragments of rock, as in dressing the sides of 
 an excavation. In this case it combines the action of the chisel and the hammer. 
 
 In using the pick as a lever the strain is thrown on the helve in the eye, and the helve yields 
 in that part by " wincing," that is, by a crushing of the fibres. To provide against this wincing, the 
 bearing surface at each end of the eye should be made as long and as wide as possible. It is obvious 
 that the sharper the edges of the feather, that is, the widened portion of the helve that fits into the 
 eye, the greater will be the tendency to wince. "Wedging the helve very tightly into the eye, so as to 
 make it press against the cheeks, also lessens the liability of the fibres to yield. Many devices 
 against wincing have been adopted; the most effective of which, however, consist in lengthening 
 the eye in the direction of the helve, in flattening the edges of the feather, and in providing the 
 helve at that part with an iron strap or ring. 
 
 The pick-head is usually made of wrought iron. It consists of a central part called the "eye," 
 made to receive the helve, and two shanks or stems. The sides of the eye are spread out to form 
 cheeks, against which the sides of the helve may be firmly wedged. Grenerally the shanks are 
 square in section, and their side varies in dimension from | inch in light picks, to 1| inch in heavy 
 picks near the eye, diminishing gradually towards the point. Sometimes the section of the shank 
 is I5 inch x 1 inch, or Ij inch x ^ inch, the longer side being in the direction of the helve, to 
 give greater strength for prising. Frequently, when the section is square, the edges are chamfered 
 down, and in some cases the chamfering is carried so far that the section approaches the octagonal 
 form. The ends of the shank are steeled, and brought, as before remarked, either to a point or a 
 cutting ed;. e. The weight of the head varies from 2 lb. to 7 lb., according to the nature of the work 
 to which the tool is to be applied ; the difference of weight being caused by the larger section and 
 the greater length of the shanks required for certain purposes. The helve is of ashwood, and consists 
 of two portions, the haft and the feather ; the latter portion is inserted into the eye, and fixed by 
 wedging. The length of the helve also varies according to the nature of the work to be performed, 
 from 24 inches to 34 inches. 
 
 Pick-heads are made straight, curved, or anchored. Straight-headed picks assist the reach, and 
 are more suitable for getting into corner work than the curved or the anchored forms. They are 
 always preferred for long-reaching or overhand work. When curved, the head is said to " sweep," 
 and such a form is preferred for underhand work, the sweep causing the tool to fall into its 
 work better than it would do if the head were straight. The degree of curvature is always slight. 
 Sometimes, instead of curving the shanks, they are made straight and converging to the eye. This 
 form is described as the anchored, and is very common in the north of England. 
 
 The tips of the shanks are sharpened on an anvil, and tempered to the requisite degree of hard- 
 ness. The form of the cutting edge will be determined by the nature of the work to be performed. 
 For hard ground the four-sided pyramid point is generally the most suitable. The rate of taper in 
 such a case will also be determined by the character of the work. A quick taper or "bluff" point 
 is stronger than a slow taper or " slim " point ; but if the point is very bluff it will not penetrate the 
 rock readily. When the tool is required to work in a narrow slit, it is obvious that the point must 
 be slim, even if the nature of the rock is such as to require a bluff point, since the pick-head cannot 
 be turned sufficiently to enable the bluff point to catch the side of the cut ; and such a circumstance 
 would soon cause the sides to come together, or " cut out," as it is termed. As the bluffness of the 
 
SHAFT-SINKING. 127 
 
 point under sucla conditions is mainly dependent upon tlie length of the head, the latter is usually 
 shortened to increase the bluffness. This relation between the rate of taper of the point and the 
 length of the head is evident, for the shorter the head, the more obliquely it may be turned in 
 a narrow cut. The pyramid point is very generally used for holing the coal ; that is, for cutting 
 a narrow slit in the seam ; but the conditions existing in this case seem rather to require a chisel 
 edge. The operation of holing consists in chipping, and for such a use the point is not suitable. It 
 is somewhat remarkable that this form of cutting edge should still be used by hewers. With the ex- 
 ception of this case, whenever the pick is to be used for chipping the rock the chisel edge is adopted. 
 The chisel edge is also suitable for penetrating the joints of rocks, or between their laminee, as before 
 remarked, so as to disrupt them by acting as a wedge, or to dislodge them by acting as a lever. 
 
 Picks may be divided, according to the nature of the work to which they are applied, into three 
 classes, and described as "stone picks," " holing picks," and "cutting picks." The first of these are 
 used in rock only ; and to render them suitable for such heavy work they are made very strong and 
 heavy. Holing picks are used for undercutting the coal, and are used either in the coal or in the 
 underelay. In using them they are swung horizontally. Cutting picks arie swung vertically for 
 downward cutting, and are used for cutting or shearing off the coal at the sides of the stall or face, so 
 as to divide the seam on each side after it has been "holed," for the purpose of causing it to fall. To 
 avoid wasting the coal these side cuts are made as narrow as possible. Cutting picks have a slim 
 point, and are sometimes made slightly heavier than the holing picks. Various forms are given to 
 picks by continental nations, but those which we have described, and which will be found illustrated 
 on Plate XXI., are almost exclusively employed in Great Britain and America. 
 
 Fig. 239 represents a holing pick in common use in South Wales. The head is straight, and 
 18 inches in length from tip to tip. The helve is 33| inches long, and the weight of the whole tool, 
 fitted as shown, is 3 lb. 8 oz. The points of this pick are somewhat bluff. 
 
 Pig. 240 is a cutting pick used with the former. The head is straight, as in the holing pick. 
 The length, however, is somewhat less, being 17 inches instead of 18 inches, and the helve is only 
 20| inches in length. The weight of this tool complete is 2 lb. 14 oz. The shanks of the pick 
 in this case taper directly from the centre to the points, which it will be observed are slim. 
 
 The stone picks used in the same districts have curved heads, and are of considerably larger 
 dimensions. Fig. 241 represents a "bottom pick," that is, a pick used for cutting the floor or 
 thill of the coal seam. The head is 21:j inches in length, and the helve 30| inches. The weight 
 of this tool is 7 lb. 3 oz. The shanks in this case are provided with a chisel head 1 inch wide, one 
 edge being horizontal and the other vertical. 
 
 Fig. 242 represents a stone pick, the head of which is 24 inches in length, and the helve 
 30- inches. The shanks are octagonal in section, and terminate, one in a wedge point, and the other 
 in a chisel edge. The weight of this tool is 9 lb. 5 oz. 
 
 Fig. 243 represents a holing pick as used in North Wales. The head is 18 inches in length, and 
 the upper side has a strong curvature or sweep. The cheeks are Y-shaped, and the shanks terminate 
 in chisel edges. The length of the helve is 28 inches, and the weight of the whole tool 2 lb, 10 oz. 
 Tlie cutting pick used with this holing tool is of a similar form, but has less sweep. It is also slightly 
 heavier, and has slim points. 
 
 Fig. 244 is a heading pick used in the same locality. The head is 16| inches in length, and has 
 a top sweep only. The cheeks are Y-shaped, and the shanks taper regularly from the eye. The 
 
128 
 
 MINING ENGINEEEING. 
 
 helve is 27| inclies in length, and the weight of the tool is 3 lb. A somewhat heavier form of this 
 pick is used for dead work, and is called a "driving" or "metal driving" pick. It has a head 
 17^ inches in length, a helve 27^ inches long, and weighs 3 lb. 10 oz. 
 
 Fig. 245 represents the form of coal picks common in the north of England. The head is 
 17| inches in length; the lower side is straight, but the upper side forms two inclined planes. In 
 plan the head is a regular lozenge-shaped figure, diminishing gradually from the eye to the points. 
 The cheeks are semicircular and very small. The length of the helve is 32 inches, and the weight 
 of the tool is 4 lb. 5 oz. 
 
 Fig. 246 is similar to the preceding, except that the head is anchored, a form much in favour in 
 the northern coal-fields. The shanks in this case meet at an angle of 155°. The length of the head 
 is 18 inches, that of the helve 32 inches, and the weight of the whole is 4 lb. 5 oz. 
 
 Fig. 247 represents a stone pick of the same district. The head is slightly anchored, and is 
 provided with tapered V-shaped cheek pieces. The angles are deeply chamfered or bevelled, so as to 
 give an octagonal section. Sometimes, however, the section is square. The shanks terminate in four- 
 sided pyramidal points. The length of the head is 19f inches, that of the helve 30 inches, and the 
 total weight of the tool 7 lb. Frequently these stone picks are madt stronger, the length of the head 
 being increased to 23 inches, and the weight to 8 lb. 
 
 An improved form of pick is shown in Figs. 248 and 249. This pick, which is made of cast 
 steel throughout, is manufactured by Burys and Co., of Sheffield, and is known as the " interchangeable " 
 pick. The merits claimed for this pick are, that being of solid cast steel, it will never require to be 
 re-steeled, and will last longer than the ordinary pick ; that as the helve is very endurable, and 
 capable of being readily affixed to and removed from the head, one helve is sufficient for a number of 
 tools ; and that being thus interchangeable, when the pick requires to be resharpened, the helve need 
 not be sent with the head to the fire, where it is liable to become shrunken from exposure to the heat. 
 By sending only the head, not only does the helve escape damage, but the labour of carrying it is 
 saved, and as one helve is sufficient for several picks, the labour of carrying helves is, under all 
 circumstances, greatly lessened. To strengthen the helve, as well as to facilitate its easy application 
 to the eye of the head, the feather is reduced, and a ferrule or hoop is affixed, as shown in the figure. 
 By this means the liability to wince is removed, or at least very materially diminished. The 
 cost of these helves is Is. 9d. each, and that of the picks, 9d, per lb. for the lighter, and 8d. per lb. 
 for the heavier kinds. 
 
 The re-sharpening of picks forms a very large and important part of the smith's work at a 
 colliery. Even when used in coal, the point or edge of a pick will not stand long ; but an hour's 
 work, or less, is often sufficient to blunt the edge of a stone pick. Hence it will be evident that in a 
 colliery employing several hundred men the repair of picks must necessitate a considerable amount of 
 labour. It has been already remarked that picks are sharpened on the anvil. When much blunted, 
 as stone picks frequently are, the tips will have to be drawn out a little by the striker's sledge. 
 Heavy blows should in all cases be avoided, as they are liable to injure the quality of the steel, and 
 the heat should not be allowed to exceed cherry redness. Care should also be taken to employ coal 
 of a suitable quality. The tempering requires particiilar attention, and the smith will do well 
 to regulate the degree of hardness by the character of the blunted edge. For example, if the edge 
 be battered, a little higher degree of hardening may be desirable ; if fractured, it may be well to 
 temper to a lower degree. As we shall consider the subject of hardening and tempering when 
 
SHAFT-SINKING. 129 
 
 ■treating of borers or drills, to avoid repetition we shall merely remark, witK respect to picks, that the 
 tips are tempered iu the same manner by retaining the heat behind the tip, and quenching at a straw, 
 or a very light blue colour. 
 
 A smith can, with the assistance of a boy, sharpen from eighty to one hundred tips an hour of 
 coal picks, which are usually only slightly blunted when sent to the smithy. Some smiths will get 
 through a larger number than this, but one hundred an hour is very good work. In the case of 
 stone picks, however, the points and edges of which are usually sent up much battered, a smaller 
 number of tips will be sharpened in the hour. It should be considered satisfactory work if a smith, 
 with the assistance of a striker, can draw out, sharpen, and temper fifty tips in that time. 
 
 The spare time of the smith is usually occupied in making picks. There are two methods of 
 making picks, which we shall briefly describe, and as an illustration we will assume that the tool is 
 to be of medium size. A length.of about 14 inches is first cut off an inch bar of iron square in section. 
 I^he middle of this piece is then heated and " upset " by striking it on the ends until a " swell " is 
 formed in that part about 1| inch diameter. Next a cut is made through the middle of the swell by 
 means of a "clift," as shown in Fig. 250, and a "drift" of the required form and shape driven in to 
 form the eye. The sides of the eye are subsequently hammered out to form cheeks of any desired 
 shape. The next process is to steel the tips. This is effected by splitting the ends of the bar, inserting 
 a tongue of steel, as shown in Fig. 251, and welding the whole together. Plenty of sand should be 
 used in this operation to preserve the quality of the steel. It is a good plan to heat the iron to a 
 welding heat, and then to insert the steel tongue, heated only to a cherry redness. Hard striking of 
 the steel, as before remarked, should also be avoided. When the welding is complete, the shanks are 
 reheated and drawn out to the required taper, and the sweep is given to the head if such be desired. 
 It then only remains to sharpen and temper the tips. 
 
 Instead of forging the pick from a single bar of square section, a common practice is to take two 
 flat bars, half the thickness of the single bar, and to curve them slightly in the middle to form the 
 eye. The two bars are then welded together from the eye to the tips, a tongue of steel, as in the 
 former case, being welded in between the ends, as shown in Fig. 252. To strengthen the eye, and to 
 form a good bearing surface for the helve, a piece of iron may be welded iu at each end of the eye. 
 When this method of making picks is adopted, it is essential to make perfect welds, as otherwibe the 
 parts are liable to separate when in use. 
 
 A smith, with the assistance of a striker, will make about twelve pick-heads of medium weight 
 in a day. Of the lighter kinds, he will make about fifteen ; and of the heavier stone picks, only ten. 
 Picks may be bought in England ready made at a price that is about equal to the cost of making 
 them. But as they are made when the smith has nothing else to do, there will always be a gain in 
 making them at the mine. 
 
 When the shanks of a pick have become worn down too short to be of any further use, it is a 
 common practice to "line" them. The process of lining consists in cutting off the old tips, and 
 welding on new pieces of iron, which are steeled in the same manner as the original tips. The 
 labour of cutting, welding, steeling, and drawing down to the requisite taper is nearly as great as 
 that of making a new pick. But an advantage lies in having an eye that has been proved capable 
 of standing well. A smith and a striker will line from fourteen to sixteen picks a day, according 
 to their weight. 
 
 The material employed in making picks should be of good quality. The nature of the work to 
 
130 
 
 MINING ENGINEERING. 
 
 which a pick is applied is such as to subject it to severe strains ; and to enable it to withstand 
 these strains it should be made of the toughest iron. The steel used in the tips should also be 
 of the best quality. If inferior steel be sent into a mine, its speedy return in a battered and 
 fractured state will show that a saving of cost in that direction is not conducive to economy. Picks 
 of cast steel throughout have lately been introduced; the only objection to their use is, their 
 brittleness. 
 
 Wedges. — The wedge constitutes an important instrument in the hands of the miner. Large 
 numbers of them are employed in every colliery, as many as a dozen being sometimes required by 
 one miner. They are used to break down large masses of hard coal, to force out blocks of rock by 
 driving them into the joints, and to dislodge masses of rock that have been loosened by blasting. In 
 jointed or vughy rock they often do great service. Wedges are made of iron, and are steeled at the 
 edge. In length they vary from 6 inches to 18 inches; but a common size is 12 inches. Their 
 thickness is generally about 1 inch, and their breadth If inch. These dimensions, however, are 
 frequently varied slightly. 
 
 Fig. 253 represents a coal wedge used in South Wales. The penetrating side forms a slender 
 rectangular pyramid ; the striking side is of an irregular eight-sided section, tapered from the base of 
 the wedge. In side elevation the breadth diminishes uniformly from the striking face to the point. 
 The length is 13j inches; in central section the breadth 1| inch, and the thickness I inch. On the 
 striking face the breadth is Ij inch, and the thickness 1 inch. The weight of this wedge is 
 3 lb. 14 oz. 
 
 Fig^ 254 is a coal wedge used in North Wales. The tapering sides of this wedge are bounded by 
 curved lines, instead of straight ones, as in the preceding example. The length is 11| inches, and 
 in the greatest section the breadth is If inch and the thickness | inch. The weight of this wedge 
 is 3 lb. 9 oz. 
 
 Fig. 255 represents a wedge used in the north of England. The sides are straight, like those of 
 South Wales. The length is 12 inches, and the greatest section, or base of the wedge, 6 inches 
 distant from the point; is a rectangle, 2^ inches broad by | inch thick. The striking face is an 
 irregular octagon, 1 inch broad by | inch thick. The point is cut off to a rectangle | inch in the 
 side. The weight of the wedge is 4 lb. 
 
 Fig. 256 is a stone wedge, from the same locality. The length is 6| inches; the wedge end is 
 3| inches long, and is drawn in from a rectangular section 1^ inch wide and 1\ inch thick. 
 The opposite end is drawn in by a tapering eight-sided section to a striking face j inch in diametei'. 
 The weight of this wedge is 2 lb. 1 oz. 
 
 Sledges and Hammers. — Sledges and hammers are important tools in the hands of the miner. 
 The distinction between a sledge and a hammer is founded on dimensions only ; the hammer being 
 intended for use in one hand, is made comparatively light, and is furnished with a short handle ; while 
 the sledge being intended for use in both hands, is furnished with a much longer handle, and is made 
 heavier. Sledges are used' for striking the drill in boring blasting holes, for driving wedges in rock 
 and in coal, and for breaking up large masses of the latter. The blasting sledge and the wedge- 
 driving sledge being employed under different conditions, require different forms and dimensions. 
 The striking face of the -blasting sledge should be flat, to enable the striker to deliver a direct blow 
 with certainty upon the head of the drill ; and to facilitate the directing of the blow, as well as to 
 increase its effect, the mass of metal composing the head should be concentrated within a short length. 
 
SHAFT-SINKING. 131 
 
 To cause tlie sledge to fly off from the head of the drill in the case of a false blow being struck, and 
 thereby to prevent it from striking the hand of the man who holds the drill, the edges of the striking 
 face are chamfered or bevelled down till the diameter is reduced by nearly one-half. This require- 
 ment is, however, but seldom provided for. When used for wedge driving, the head of the sledge is 
 very frequently required to follow the wedge into the cleft, and to enable it to do this, the head must 
 be made long and of small diameter ; that is, the mass of metal composing the head must be 
 distributed throughout a greater length. The striking face should be rather convex than flat, to 
 avoid a sharp edge, which would soon be battered off by coming in contact with the edges of the 
 rocks in the cleft. A longer handle or helve is also needed for the wedge-driving than for the 
 blasting sledge. 
 
 The head of a sledge is of iron ; it consists of a pierced central portion called the eye, and two 
 shanks or " stumps," the steeled ends of which form the striking faces or " panes." The form of the 
 head varies in different localities, but whatever the variation may be, the form may be classed under 
 one of four types or " patterns." A very common form is that shown in Fig. 257, and known as the 
 "Bully" pattern. By varying the width, as shown in Fig. 258, we obtain the "broad bully," the 
 former being called for the sake of distinction the " narrow " bully. Another common form is the 
 " Pointing " pattern, represented in Fig. 259. The form shown in Fig. 260 is designated as the "Bloat" 
 pattern; and that given in Fig. 261 the "Plug" pattern. Each of these forms possesses peculiar 
 merits which render it more suitable for certain uses than the others. The same forms are used for 
 hammers. The eye is generally made oval in shape, but sometimes, especially with the bloat pattern, 
 it is made circular, as shown in Fig. 260. The weight of a sledge head may vary from 5 lb. to 
 10 lb., but a common and convenient weight is 7 lb. The length of- the helve varies from 
 20 inches to 30 inches ; a common length is 24 inches for blasting, and 28 inches for wedge-driving 
 sledges. The average weight of hammer heads is about 3 lb., and the average length of the helve 
 10 inches. 
 
 All the forms of sledge heads may be used for wedge -driving purposes, but that which is 
 generally employed, especially for coal wedging, is the pointing pattern. The modification made in 
 the form illustrated is merely in the length of the bead. A common length of a coal-wedging sledge 
 is 12 inches, with a diameter of about 2j inches in the thickest part. The stumps are tapered down 
 to about 1^ inch at the panes, and the angles of the stumps are taken off by a chamfer beginning 
 near the eye and gradually increasing to form an octagonal section at the panes. 
 
 Fig. 262 represents a blasting sledge used in South Wales. The stumps are octagonal in section, 
 and spring from a square block in the centre. The panes or striking faces, however, are circular and 
 flat. The length of the head is 8f inches, that of the helve 27 inches, and the weight of the tool 
 complete 7 lb. 
 
 Fig. 263 shows a coal sledge from the same district. The stumps in this, as in the preceding 
 case, are octagonal in section, and are reduced by a uniform taper from a square central section. The 
 panes are octagonal and slightly conical. The length of the head is 11 inches, that of the helve 
 28 inches, and the weight of the tool complete 8 lb. This sledge is also used as a stone sledge. 
 
 Fig. 264 represents a blasting sledge used in North Wales. The central block is an irregular 
 octagon in section, formed by slightly chamfering the angles of a square section, and the stumps are 
 chamfered down to form a regular octagon at the panes, which are flat. The length of the head is 
 7| inches, that of the helve 22 inches, and the weight of the tool complete 6 lb. 7 oz. 
 
^32 MINING ENGINEEEING. 
 
 The coal sledge used in this district is similar in form to that used in South Wales. The length 
 of the head is 11^ inches, that of the helve 27 inches, and the total weight of the tool 7 lb. 
 
 The sledges used in the north of England have shorter heads, and are lighter than the fore- 
 going. Fig. 265 represents one of these blasting sledges. The head is nearly square in section at the 
 centre, and the panes are flat. The length of the head is 5 inches, that of the helve 24| inches, and 
 the weight of the sledge complete 4 lb. 14 oz. 
 
 Fig. 266 is a coal sledge from the same district. The length of the head is 10 inches, that of the 
 helve 30 inches, and the total weight 6^ lb. 
 
 Sledges and hammers are usually made at the mine. The mode of manufacture may be briefly 
 described as follows. Supposing it to be required to make a bully-head sledge of the ordinary 
 weight, a length of about 12 inches is cut off a 2-inch bar of iron of square section. The angles 
 of one end are then chamfered down, the chamfering being begun at one quarter of the length 
 and continued to form an irregular, or, if desired, a regular octagon at the end, as shown in 
 Fig. 267. The eye is then punched, and a drift of the requisite form and size is worked in, and 
 left to keep the eye in shape during the operations of forging. The other end of the bar is treated in 
 the same way, and the bar then divided in the middle by a clii't. The angles of the newly formed 
 ends having been chamfered down in the same way as the others, it only remains to steel the 
 striking faces. This operation is effected in the following manner : A flat bar of steel, about 
 two inches wide and half an inch thick, is heated to dull redness, and a piece of the bar equal in 
 length to the width is nearly cut off by a cliffc, as shown in Fig. 268. The object of leaving 
 the piece slightly attached is to enable it to be handled conveniently. The four corners of the 
 piece are then hammered down to give it the form and dimensions of the sledge pane. This 
 may be easily effected by bending the nearly severed piece first on one side, and hammering 
 down two of the corners, and then bending it back on the opposite side, and hammering down 
 the other two. This piece is then again heated to a cherry redness, and one stump of the 
 sledge having been heated to a welding heat and placed with that end uppermost upon the 
 anvil, the steel pane is laid upon it. A few blows upon the steel weld it firmly to the iron. 
 The steel may then be broken from the bar by a few twists ot the latter. When the other 
 end has been steeled in the same manner, and the chamfered angles properly dressed down, the 
 faces are hardened by heating them both to dull redness, and plunging the head into cold water. 
 
 Sledges made in the manner described will stand their work well, and when worn out, they 
 may be easily resleeled. A smith, with the assistance of a striker, will make about seven 7 lb. 
 sledges in a day, and resteel twelve. Ready-made sledges can be bought at a priie equal to 
 about the cost of making. But, like the picks, they occupy the smith's spare time. Ready-made 
 iron sledges, however, seldom stand so long as the home-made ones. Instead of the iron 
 sledges, solid cast-steel heads are very frequently employed in England. These are very durable. 
 They cost from 9d. to Is, per lb., according to size. 
 
 Pick and Sledge Handles or Helves. — The supply of pick and sledge handles, " helves," " shafts " 
 or " sticks," as they are variously termed in different districts, constitutes a feature of some impor- 
 tance in the economy of a mine. The cost does not indeed iorm a large item in the accounts but a 
 prompt supply conduces to a full utilization of the time of the miner by preventing delay. More- 
 over, though handles may be purchased as cheaply as they can be made, there are times when the 
 carpenters of a mine are unemployed, and the utilization of this leisure in making handles then 
 
SHAFT-SINKING. 133 
 
 becomes a source of economy. The duration of a pick helve, of course, varies greatly with the quality 
 of the wood and the character of the work to which it is subjected. Assuming a uniformity of 
 quality in the material — for none but the most suitable should be employed — tue life of a helve 
 will depend mainly upon the hardness of the rock to be excavated. Thus a pick helve will last 
 longer in soft coal than in hard coal, in hard coal than in moderately hard rock, and in moderately 
 hard rock than in very hard rock. The extremes of duration may be taken as one month and 
 twelve months ; the latter is, however, seldom reached, and the mean will have to be taken much 
 nearer the lower than the higher limit. Probably three months may be taken as a fair average. 
 Thus every hundred hewers will require 400 helves a year, or about three do^-en a month. In the 
 hard coal seams of South Wales, the average life of a holing-pick helve is found to be only six weeks ; 
 in such a case, the supply required is about six dozen a month for every hundred hewers. In the 
 hands of a stone miner, that is, one who works in rock as distinguished from coal, a pick helve will 
 rarely last longer than a month. Thus every dozen of such men will require a dozen helves a month. 
 
 The qualities requisite in the material of a helve are, toughness combined with a moderate 
 degree of hardness, elasticity, and lightness. The only wood readily procurable in this country 
 which possesses these qualities in a suflScient degree is ash, and this wood should alone be employed. 
 Besides the qualities of the material, the other requirements of a helve are, that its dimensions shall 
 be such that it may be completely grasped by the hand, and held without cramping the fingers, a 
 consequence of the diameter being too small, and that its section shall be such as will facilitate the 
 use of the tool. To fulfil the latter condition, the handle oi a shovel which has to be frequently 
 turned in the hand is made circular in section ; and the handle of the pick, which has to be held 
 firmly in one position, and truly directed to a given point, is made oval. For similar reasons, the 
 same section is given to sledge and axe handles. The shovel handle is made to terminate in a 
 crutch or eye, both to afford a large and convenient pressing surface to one hand, and to give control 
 over the plate so as to turn it, or prevent it from turning, as occasion requires. Shovel handles are 
 rarely made at the colliery : they are furnished with the tool, and when broken the tool is generally 
 rendered useless. 
 
 To make pick and sledge helves, a piece of ash of straight grain is selected, and cut up in the 
 round into the length of the helves required. The diameter of the logs should be a little more than 
 twice, or a little more than four times, the widest part of the feather, that is, the widened portion of the 
 helve which fits into the eye. The cost of such logs varies in different localities, but generally they 
 may be purchased in the rough state for Is. 4d. or Is. 6d a cubic foot. "When larger logs are used, 
 some judgment is required to avoid waste of material. As wood increases in porosity from the centre 
 of the tree outwards, the outer portion shrinks more in drying than the inner, and this circumstance, 
 unless provided against, would cause the helves to warp. To remedy this tendency to warp, which, if 
 not counteracted, would render the helve utterly useless, the log is so divided that the major or long 
 axis of the ellipse formed by the cross section of the helve shall radiate from the centre of the log. 
 To effect this, the log is first cleaved into halves, and then quartered by means of iron wedges, after 
 which each quarter is cleaved in the most advantageous manner, as shown in Figs. 269 and 270. 
 The portions nearest the centre make the best helves. When there is much difference in the size 
 of the logs, or when helves of different sizes are required — for it is not always practicable to obtain 
 timber of the exact size desired — the logs may be cleaved into unequal portions ; and if the cleaver 
 possess skill, there will never be much waste. A log 7 inches in diameter will cleave into nine 
 
134 MINING ENGINEEEING. 
 
 pick helves, and a log 13 inches in diameter will cleave into about three dozen pick helves, the 
 width at the largest part of the feather being 3 inches, and the thickness from 1| inch to l;j inch. 
 The necessity for the feather occasions a waste of material, a portion having to be cut away. As the 
 feather is not required in sledge handles, the same log would furnish nearly twice as many of the 
 latter as of the pick helves. It is well to cleave and rough-hew the helves while the timber is green, 
 l)oth because the operation is then more easily effected, and because any warping during the setting 
 may be easily corrected in the dressing. The dressing, or shaping and smoothing, is performed by 
 means of draw-knives and spokeshaves. 
 
 Two men can saw, cleave, and rough-hew about twelve dozen pick helves. Fig. 271, or nearly 
 twice as many sledge helves. Fig. 272, a day. And of these rough-hewn helves, a man will dress 
 about five dozen of pick, Fig. 273, or ten dozen of sledge helves, Fig. 274, in the same time. If 
 only one man be employed after the logs are sawn, one and a half dozen of pick helves or three 
 dozen of sledge helves may be considered a fair day's work. 
 
 The fitting of a helve requires some care. As it must be firmly fixed into the eye, it should be 
 made to fit exactly. To ensure a perfect fit, it may be driven partly in and then withdrawn, when 
 tlie too prominent parts will be indicated by the marks of the pressure to which they have been 
 subjected. These parts having been reduced, the helve may be again inserted and driven into its 
 place. But before wedging it in permanently, it will be necessary to ascertain that the stem is square 
 with the helve. To do this the end of the helve should be placed against the toe of the left foot, to 
 keep it in a fixed position, and an arc struck with the point upon the ground. The pick should then 
 be turned, and with the helve in the same position against the foot, the other point should be applied 
 to the ground, when, if it move in the same arc, the stem is shown to be properly set. The wedge 
 ysed for fixing the helve should be of hard oak, and equal in breadth to the length of the eye. An 
 entrance for the wedge is made in the middle of the feather by means of a chisel. Sledge and axe 
 helves are set and fixed in a similar manner. 
 
 The proper fixing of helves is a matter of some importance, for, as we have already remarked, a 
 perfect condition of the tools employed is greatly conducive to their efficiency, and hence to the 
 jiroductiveuess of the labour of the miner. At many collieries the carpenter fits the helves to the 
 picks, and for the helves so fitted the men pay from 5d. to Qd. each for picks, and M. each for sledges. 
 The price of a pick helve, unfitted, is usually Ad. When bought by the dozen of helve makers, pick 
 helves cost from 4s. 6d. to 6s. Qd. a dozen, according to length. Ordinary axe handles cost from 4rf. 
 to 6c?. each when straight, and from Qd. to 8c/. when bent. 
 
 Drills or Borers. — When the rock to be removed is too hard and tenacious to yield readily to 
 the pick and wedge, recourse is had to the action of explosives. This mode of dislodging rock masses 
 is described as " blasting." The operations of blasting consist in boring holes of suitable dimensions 
 and in favourable positions in the rock, in inserting the charge of the explosive compound in the 
 lower portion of the hole, in filling up with suitable material the remaining portion of the hole, and 
 in exploding the charge. The principles upon which these several operations are conducted will be 
 explained, and the details of their performance described, in a subsequent section. At present we 
 have to deal only with the tools employed, and of these the drill or borer constitutes, for blastino- 
 purposes, the chief. The use of the drill is to bore the hole which is to receive the explosive charge. 
 When describing the operations of prospective boring in search of coal, we called attention to the 
 fact of rock being superior in Ivirduess to steel, and to the consequent necessity of devising tools to 
 
SI£ AFT-SINKING. 135 
 
 penetrate rook by fracturing it. In deep boring this end was attained by means of a sharp blow 
 delivered through the medium of suitable tools, the chief of which was the chisel bit. The blow in 
 this case was obtained by dropping the tool with the rods attached from a suitable height. In boring 
 shallow holes for blasting purposes, the same conditions of hardness in rock and steel of course exist, 
 and therefore the SEtme modes of penetration, modified only to suit the altered circumstance of 
 dimension, must necessarily be adopted. Thus, in rock drilling, as the operation of boring blasting- 
 holes is called, to distinguish it from deep or prospective boring, the chisel bit is employed, and in 
 some cases the impact of the falling tool is relied upon to produce the necessary fracture or chipping of 
 the rock. Such a tool is shown in Fig. 275, Plate XXIL, and is called the "jumper." It consists of 
 an iron or a steel rod, provided at each end with a chisel edge, and having a swell, technically known 
 as the " bead," between the extremities, to give it greater weight. The bead divides the jumper into 
 two unequal portions, each of which forms a chisel or cutting bit, with its shank or " stock." The 
 shorter stock is used while the hole is shallow, and the longer one to continue it to a greater depth. 
 The mode oi using the jumper is to lift it by both hands to a height of about one foot, and then to 
 let it drop, assisting it by a little force when necessary. After each blow the tool must be turned 
 partially round, for reasons that have already been fully explained. Thus both in form and in action 
 the jumper is similar to the chisel used in deep boring. But in rock drilling the conditions of 
 position and direction are frequently changed. So long as the boring is vertically downwards, the 
 jumper is a very effective tool ; and in open quarries, where such borings are constantly needed, it is 
 commonly employed. But in mining operations, drill-holes are more often required to be bored in 
 some other direction, or, as it is termed, at an angle. The direction may be inclined downwards, 
 horizontal, inchned upwards, or even, in some cases, vertically upwards. It is plainly obvious that 
 in any one of these directions the jumper is utterly useless. To meet the requirements of these cases 
 recourse is had to the hammer Avherewith to deliver the blow, and the cutting tool or " drill " is 
 constructed to be used with the hammer. To render the form of the jumper suitable for use in this 
 way it is only necessary to cut out the bead, and to leave the ends flat for a striking face, and the 
 form of the two chisels thus produced is that adopted for the ordinary rock drill. 
 
 It will be understood from the foregoing descriptions that a rock drill consists of the hit or chisel 
 edge, the stock, and the titr iking face. Formerly drills were made of wrought iron, and steeled at each 
 end to form the bit and the striking face. Now, however, it is usual to make them entirely, of cast 
 steel, which is sent to the mine in octagonal bars of the reqiiisite diameter. The advantages of using 
 steel stocks are numerous. The superior solidity of texture of steel renders it capable of transmitting 
 the force of a blow more effectively than iron. Being stronger than the latter material, a smaller 
 diameter of stock, and, consequently, a less weight are sufficient. This circumstance also tends to 
 increase the effect of the blow by diminishing the mass through which it is transmitted, and to lessen 
 tlie labour of transport. On the other hand, a steel stock is more likely to break than an iron one. 
 
 The cutting edge of a drill demands careful consideration. The remarks already made relatively 
 to deep-boring tools apply equally to a drill, and therefore, to avoid repetition, the reader is referred 
 to them. It may, however, be observed here, that though it will be necessary to adapt the angle of 
 the edge to the hardness of the rock to be penetrated, that angle may be much less obtuse than in 
 1,he case of deep boring, where the force of the blow is very great. To enable the tool to free itself 
 well in the b(n-e-hole, and to avoid introducing unnecessary weight into the stocks, the bit is made 
 wider than the latter ; this difference in width may reach as much as an inch. It is evident that in 
 
136 
 
 MINING ENGINEEEING. 
 
 hard rock the liability of the edge to fracture increases as the difference of width. The edge of the 
 drill may be straight, as in the flat chisel for deep boring, or slightly curved. The straight edge cuts 
 its way somewhat more freely than the curved, but it is weaker at the corners than the curved, a 
 circumstance which renders it less suitable for very hard rock. It is also slightly more difficult to 
 forge. Figs. 276, 277, and 278 show the straight and curved bits, and the angles of the cutting 
 edges for use in rock. The width of the bit varies, according to the size of the hole required, from 
 1 inch to 2i inches. 
 
 The stock is octagonal in section, and is made in lengths varying from 20 inches to 42 inches. 
 The shorter the stock, the more effectively does it transmit the blow, and therefore it is made 
 as short as possible; for this reason several lengths are employed in boring a blast-hole, the 
 shortest being used at the commencement of the hole, a longer one to continue the depth, and a still 
 longer one, sometimes, to complete it. To ensure the longer drills working freely in the hole, the 
 width of the bit should be very slightly reduced in each length. It has already been remarked that 
 the diameter of the stock is less than the width of the bit ; this difference may be greater in coal 
 drills than in rock or "stone" drills; a common difference in the latter is f of an inch for the 
 smaller sizes, and from ^ inch to | inch for the longer. The following proportions may be taken as 
 the average adopted : 
 
 Width of 
 
 
 
 Biaraoter of 
 
 the Bit. 
 
 
 
 the Stock. 
 
 1 inch 
 
 ,, 
 
 •• 
 
 f inch 
 
 H ,. 
 
 .. 
 
 •• 
 
 .. f „ 
 
 H ,. 
 
 •• 
 
 •• 
 
 7 
 
 -g n 
 
 n „ 
 
 •• 
 
 p ,1 
 
 : 1 „ 
 
 T '11 1 11 
 
 Width of 
 
 
 Diameter of 
 
 the Bit. 
 
 
 the Stock. 
 
 If inch 
 
 •• 
 
 1| inch 
 
 2 inches .. 
 
 ,, 
 
 .. If ,, 
 
 n ,, .. 
 
 .. 
 
 1 1 
 
 H „ .. 
 
 .. 
 
 1 5 
 
 The striking face of the drill should be flat. The diameter of the face is less than that of the 
 stock in all but the smallest sizes, the difference being made by drawing in the striking end. The 
 amount of reduction is greater for the larger diameters ; that of the striking face being rarely more 
 than J of an inch. 
 
 The making and resharpening of rock drills constitute an extremely important part of the 
 labour of the colliery smith. The frequent use of the drill and its rapid wear necessitate a daily 
 amount of work of no trifling proportions, and the judgment and skill required in proper tempering 
 render a high degree of intelligence in the workman indispensable ; indeed, so much depends upon 
 the smith whose duty it is to repair the miners' tools, that no pains should be spared to obtain a man 
 capable of fulfilling that duty in the most efficient manner possible. Tools sent into the mine in an 
 unfit condition are a source of delay as well as of irritation to the miners ; and it must always be borne 
 in mind, that the best tools may be spoiled in the smithy. The engineer or manager will do well to 
 frequently direct his attention to this important adjunct to a colliery ; and besides insisting on the 
 work being carefully and properly performed, he should take care that coals and steel of suitable 
 quality be supplied ; for with bad materials it is impossible for the smith to turn out good work. 
 Coals unfit for forge purposes will greatly injure the steel or the iron exposed to their influence, and 
 inferior metal can never be wrought into good tools, 
 
 "When the borer steel bars are supplied to the smith, he cuts them up as required into the desired 
 lengths. To form the bit, the end of the bar is heated and flattened out by hammering to a width a 
 little greater than the diameter of the hole to be bored. The cutting edge is then hammered up with 
 
SHAFT-SINKING. 137 
 
 a light hammer to the requisite angle, and the corners beaten in to give the exact diameter of the 
 bore-hole intended. As the drills are made in sets, the longer stocks will have a bit slightly 
 narrower than the shorter ones, for reasons already given. The edge is subsequently touched up 
 with a file. In performing these operations heavy hammering should be avoided as well as high 
 heats, and care should be taken in making the heat that the steel be well covered with coal, and far 
 enough removed from the tuj'ere to be protected from the "raw" air. Overheated or "burned" steel 
 is liable to fly, and drills so injured are useless until the burned portion has been cut away. 
 
 Both in making and in resharpening drills, great care is required to form the cutting edge evenly, 
 and of the full form and dimensions. If the corners get hammered in, as shown in Pig. 279, they are 
 said to be " nipped," and the tool will not free itself in cutting. When a depression of the straight 
 or curved line forming the edge occurs, as shown in Figs. 280 and 281, the bit is said to be " backward ;" 
 and when one of the corners is too far back, it is spoken of as " odd-cornered." When either of these 
 defects exists — and they are unfortunately common — not only does the bit work less effectively 
 on the rock, but the force of the blow is thrown upon a portion only of the edge, which, being thereby 
 overstrained, is liable to fracture. 
 
 The hardening and tempering of steel is a matter requiring careful study and observation. It 
 is a well-known fact, that a sudden and great reduction of temperature causes a notable increase of 
 hardness in the metal. The reason of this phenomenon is not understood, but it is certain that it is 
 in some way dependent upon the presence of carbon. The degree of hardness imparted to steel , by 
 this means depends upon the amount of the reduction of the temperature, and the proportion of carbon 
 present in the metal, highly carburetted steel being capable of hardening to a higher degree, under 
 the same conditions, than steel containing less carbon. Thus for steel of the same quality, the longer 
 the range of temperature, the higher is the degree of hardness. But here we encounter another 
 condition which limits the degree of hardness practically attainable. The change which takes place 
 among the molecules of the metal in consequence of the change of temperature causes internal 
 strains, and thereby puts portions in a state of unequal tension. This state renders the strained parts 
 liable to yield when an additional strain is thrown upon them while the tool is in use; in other 
 words, the brittleness of the steel increases with its hardness. Here again the proportion of carbon 
 present comes into play, and it must be borne in mind, that for equal degrees of hardness, the steel 
 which contains the least carbon will be the most brittle. In hardening borer-steel, which has to 
 combine as far as possible the qualities of hardness and toughness, this matter is one deserving 
 careful attention. It is a remarkable fact, and one of considerable practical value, that when oil is 
 employed as the cooling medium instead of water, the toughness of steel is enormously increased. 
 
 The tempering of steel, which is a phenomenon of a similar character to that of hardening, also 
 claims careful consideration. When a bright surface of steel is subjected to heat, a series of colours 
 is produced, which follow each other in a regular order as the temperature increases. This order is 
 as follows : Pale yellow, straw yellow, golden yellow, brown, brown and purple mingled, purple, 
 light blue, full clear blue, and dark blue. Experience has shown that some one of these colours is 
 more suitable than the rest for certain kinds of tools and certain conditions of working. The selection 
 of the proper colour constitutes a subject for the exercise of judgment and skill on the part of the 
 smith. For rock drills and picks, straw colour is generally the most suitable when the work is in 
 very hard rock, and light blue when the rock is only of moderate hardness. 
 
 The processes of hardening and tempering drills are as follows : When the edge of the bit has 
 
 T 
 
138 
 
 MINING ENGINEEEING. 
 
 been formed in the manner already described, from three to four inches of the end is heated to cherry 
 redness, and dipped in cold water to a depth of about an inch to harden it. While in the water the 
 bit should be moved slightly up and down, for were this neglected, the hardness would terminate 
 abruptly, and the bit would be very liable to fracture along the line corresponding with the surface 
 of the water. In cold weather the water should be slightly warmed by immersing a piece of hot iron 
 in it before dipping the steel. When a sufficient degree of hardness has been attained, the remainder 
 of the hot portion is immersed until the heat is reduced sufficiently for tempering. At this stage it is 
 withdrawn, and the colours carefully watched for. The heat which is left in the stock will pass down 
 to the edge of the bit, and as the temperature increases in that part, the colours will appear in 
 regular succession upon the filed surface of the edge. When the proper hue appears, the whole drill 
 is plunged into the water and left there till cold, when the tempering is complete. When the edge 
 is much curved or " bowed," the colours will reach the corners sooner than the middle of the bit. 
 This tendency must be checked by dipping the corners in the water, for otherwise the edge will not 
 be of equal hardness throughout. As the colours can be best observed in the dark, it is a good 
 plan to darken that portion of the smithy in which tempering is being carried on. 
 
 The degree of temper required depends upon the quality of the steel and the nature of the work 
 to be performed. The larger the proportion of carbon present in the metal, the lower must be the 
 temper. Also the state of the blunted edges, whether battered or fractured, will show what degree of 
 hardness it is desirable to produce. From inattention to these matters good steel is not un- 
 frequently condemned as unsuitable. 
 
 To form the striking face, the end of the stock is heated to a dull red, and drawn out by the 
 hammer to form a conical head. The extremity. is then flattened to form a face from } inch to 1 inch 
 in diameter. This head is then annealed to a degree that will combine considerable toughness with 
 hardness. The constant blows to which the head is subjected tend to wear it down very rapidly. 
 There is great difference in the lasting qualities of steel in this respect ; some drills will wear away 
 more quickly at the striking than at the bit end. 
 
 A smith will, with the assistance of a striker, sharpen and temper about thirty single-hand 
 drills of medium size in an hour, or twenty double-hand drills of medium size in the same time. Of 
 course, much will depend on the degree of bluntness in the cutting edge ; but assuming the drills to 
 be sent up only moderately blunted, the foregoing may be taken as a lair average of the work of 
 two men. 
 
 The cost of octagonal cast-steel bars for rock drills is about 55s, a cwt. Eeady-made cast-steL-l 
 drills may be purchased at about 65s. a cwt. Cast-steel hammers may also be purchased at a cost of 
 about 9d. a lb. Such hammers deal a more effective blow than those made of iron, steeled on the 
 panes, which are commonly used. They are also far more durable. 
 
 It will be evident from the foregoing remarks, that to enable a drill to stand properly it must 
 be made of good material, be skilfully tempered in the smithy, and provided with a cutting edo-e 
 having an angle and a shape suited to the character of the rock in which it is used. To these 
 conditions may be added another, namely, proper handling ; for if the drill be carelessly turned in 
 the hole so as to bring all the work upon a portion only of the cutting edge, or unskilfully struck by 
 the sledge, fracture or blunting will speedily result. Improper handling often destroys the edge in 
 the first five minutes of using. 
 
 Drills, as before remarked, are used in sets of different lengths. The sets may be intended for 
 
SHAFT-SINKING. 139 
 
 use by one man or by two. In the former case, the sets are described as single-hand sets, and they 
 contain a hammer for striking the drills ; in the latter case, the sets are spoken of as double-handed, 
 and they contain a sledge instead of a hammer for striking. It may appear at first sight that there 
 is a waste of power in employing two men, or, as it is termed, the double set, for that two men 
 cannot bore twice as fast as one. This rate of speed can, however, be attained, and it is due less to 
 the greater effectiveness of the stroke than to the fact that two men can, by repeatedly changing places 
 with each other, keep up almost without intermission a succession of blows for an indefinite length of 
 time ; whereas, with the single set, the man is continually obliged to cease for rest. 
 
 On Plate XXII. will be found three sets of blasting gear : a set of coal-blasting gear; a set of single- 
 hand stone-blasting gear ; and a set of double-hand stone-blasting gear. In the first set, the drill 
 shown in Fig. 283 is 22 inches in length ; the cutting edge is straight and 1^ inch wide, and the 
 weight is 2^ lb. The other drill. Fig. 284, is 42 inches in length; it has a straight cutting edge 1^ inch 
 wide, and weighs 4 lb. 10 oz. The hammer used with this set, and shown in Fig. 282, weighs 
 2 lb. 14 oz. ; the length of the head is 4} inches, and that of the handle 7f inches. In the second, or 
 single-hand stone set, the shorter drill. Fig. 288, is 22 inches in length ; the cutting edge is strongly 
 curved and is 1} inch in width, and the weight is 3 lb. 10 oz. The longer drill. Fig. 289, is 
 36 inches in length; the width of the cutting edge, which is curved as in the shorter drill, is 
 1^ inch, and the weight is 6 lb. 5 oz. The hammer used with this set, and represented in Fig. 287, 
 weighs 3 lb. 6 oz. ; the length of the head is 5 inches, and that of the handle 10 inches. In the 
 third, or double-hand stone set, the first or shortest drill. Fig. 294, is 18 inches in length. If inch 
 wide on the cutting edge, and weighs 4j lb. The second drill. Fig 295, is 27 inches in length, 
 1-j^ wide on the cutting edge, and weighs 6 lb The third, or longest drill. Fig. 296, is 40 inches in 
 length, 1| inch wide on the cutting edge, and weighs 9^ lb. The cutting edges of all these drills 
 are strongly curved^ as in the preceding set. The sledge used with this set, and represented in 
 Fig. 293, weighs about 5 lb. 
 
 Auxiliary Tools used in Boring. — Besides the drill and the hammer, other tools are needed in 
 preparing the hole for the blasting charge. If the bore-hole is inclined downwards, the debris or 
 bore-meal made by the drill remains at the bottom of the hole, where it is converted into mud or 
 " sludge" by the water there present. This sludge, as in the case of deep boring, has to be removed 
 as the work progresses, to keep the rock exposed to the action of the drill. The removal of the 
 sludge is effected by a simple tool called a " scraper." It consists of a rod of iron from \ in. to ^ in. 
 in diameter, and of sufficient length to reach the bottom of the bore-hole. One end of the rod is 
 flattened out on the anvil and made circular in form, and then turned up at right angles to the stem. 
 The disc thus formed must be less in diameter than the bore-hole, to allow it to pass rettdily down. 
 When inserted in the hole, the scraper is turned round while it is being pressed to the bottom ; on 
 withdrawing the instrument the sludge is brought up upon the disc. This operation, two or three 
 times repeated, is sufficient to clear the bore-hole. The other end of the scraper is sometimes made' to 
 terminate in a ring for convenience in handling, as shown in Fig. 285, Plate XXII. Instead of the 
 ring, however, at one end, a disc may be made at each end, as shown in Fig. 290, the discs in this case 
 being of different diameter, to render the scraper suitable for different size bore-holes. Sometimes 
 the scraper is made to terminate in a spiral hook or " drag twist," as represented in Fig. 297. The 
 use of the drag is to thoroughly cleanse the hole before inserting the charge. A wisp of hay is pushed 
 do"v\Ti the hole, and the drag end of the scraper introduced after it, and turned round till it has 
 
 T 2 
 
140 
 
 MINING ENGINEEEING. 
 
 become firmly entangled. The withdrawal of the hay by the drag wipes the bore-hole clean. Instead 
 of the twist drag, the ''loop" drag is frequently employed. This consists of a loop or eye, through 
 which &, piece of rag or tow is passed. The rag or tow is used for the same purpose as the 
 hay, namely, to thoroughly cleanse and dry the bore-hole previous to the introduction of the 
 charge. 
 
 Very frequently the "swab-stick" is used instead of the scraper to clear out the bore-hole. This 
 is simply a deal rod bruised at one end by blows with a hammer until the fibres separate to form a 
 kind of stumpy brush or " swab." When this is pushed down the hole, the sludge passes up around and 
 between the fibres, which are then spread out by being pressed against the bottom of the hole. On 
 withdrawing the swab the sludge is brought out with it. This operation, two or three times repeated, 
 is sufficient to clear the bore-hole. 
 
 When the charge has been placed in the bore-hole, and the fuse laid to it, the hole needs to be 
 tamped, that is, the portion above the charge has to be filled up with, some suitable substance. For 
 this purpose, a rammer, stemmer, or tamping iron, as the instrument is variously called, is required. 
 This instrument is illustrated in Fig. 286. It consists of a metal bar, the tamping end of which is 
 grooved to receive the fuse lying against the side of the bore-hole. The other end is flat, to afford a 
 pressing surface for the hand, or a striking face for the hammer when the latter is needed. To 
 prevent the danger of accidental ignition from sparks caused by the friction of the metal against 
 silicious substances, the employment of iron stemmers has been prohibited by law. They are usually 
 made of copper, or phosphor-bronze, the latter substance being more resisting than the former. 
 
 Sometimes in wet ground it becomes necessary to shut back the water from the bore-hole before 
 introducing the charge of gunpowder. This happens very frequently in shaft-sinking. The method 
 employed in such cases is to force clay into the interstices through which the water enters. The 
 instrument used for this purpose is the " claying-iron" or " bull," represented in Fig. 292. It consists 
 of a round bar of iron, called the stock or shaft, a little smaller in diameter than the bore-hole, and a 
 thicker portion, called the head or poll, terminating in a striking face. The lower end of the shaft 
 is pointed, to enable it to penetrate the clay, and the head is pierced by a hole about an inch in 
 diameter to receive a lever. 
 
 Clay in a plastic state having been put into the bore-hole, the bull is inserted and driven down 
 by blows with the sledge. As the shaft forces its way down, the clay is driven into the joints and 
 crevices of the rock on all sides. To withdraw the bull, a bar of iron is placed in the eye, and used 
 as a lever to turn it round to loosen it ; the rod is then taken by both hands, and the bull lifted out. 
 To allow the bull to be withdrawn more readily, the shaft should be made with a slight taper, and 
 kept perfectly smooth. As the bull is subjected to a good deal of heavy hammering on the head, the 
 latter part should be made stout. This tool, which should be considered as an extra instrument rather 
 than as an essential part of a blasting set, is a very serviceable one, and should always be at hand in 
 wet ground when gunpowder is employed. 
 
 Another instrument of this auxiliary character is the beche. Fig. 300, used for extracting a 
 broken drill. It consists of an iron rod of nearly the diameter of the bore-hole, and hollow at the 
 lower end. The form of the aperture is slightly conical, so that the lower end may easily pass over 
 the broken stock of the drill, and being pressed down with some force, may grasp the stock in the 
 higher portion of the aperture with sufficient firmness to allow of the two being raised too-ethei'. 
 Wlien only a portion of the bit remains in the hole, it may often be extracted by means of the dra<'-- 
 
SHAFT-SINKING. 141 
 
 twist end of the scraper, or the swab-stick may be driven down upon the broken portion, and the 
 latter withdrawn with the swab. 
 
 Cartridges. — Cartridges are merely cases made to contain the charge of the explosive compound 
 employed. It was formerly the custom, when blasting in wet situations, to enclose the gunpowder 
 in a canvas bag, well greased to keep out the water. The end of the fuse was inserted into the 
 mouth of this bag, which was then firmly tied with string and dropped into the bore-hole. This bag 
 constituted a cartridge, but of unsuitable form and material. Now paper cartridges are made of a 
 size and shape that will fit the bore-hole, and the fuse is inserted into these through a hole in the 
 upper end left for that purpose. When intended for use in wet situations, the cartridge is covered 
 with linen and overlaid with various compounds to render it waterproof. In such a case, the hole 
 through which the fuse is introduced is countersunk, and the sunken portion is, after the introduction 
 of the fuse, filled up with grease. Cartridges are made of various diameters to suit bore-holes of all 
 sizes, and of various lengths, according to the weight of the charge required. The use of cartridges 
 greatly lessens the risk of accidental explosion ; and a recent Act of Parliament prohibits the employ- 
 ment of gunpowder in coal mines in any other form. The cost of the cases is fully compensated by the 
 prevention of occasions for waste. 
 
 Fuse. — The means by which the charge of explosive matter placed in the bore-hole is fired 
 constitutes a very important part of the set of appliances used in blasting. The conditions which 
 any such means must fulfil are : (1) that it shall fire the charge with certainty ; (2) that it shall 
 allow the person whose duty it is to explode the charge to be at a safe distance away when the 
 explosion takes place ; (3) that it shall be practically suitable, and applicable to all situations ; and 
 (4) that it shall be obtainable at a low cost. To fulfil the second and most essential of these 
 conditions, the means must be either slow in operation, or capable of being acted upon at a distance. 
 The only known means possessing the latter quality is electricity. The application of electricity to 
 this purpose is of recent date, and though rapidly extending, it is yet confined within narrow limits. 
 The means in common use are thus those which are slow in operation, and which allow thereby 
 sufficient time between their ignition and the explosion of the charge for a person to retire to a sate 
 distance. These means consist generally of a train of gunpowder so placed that the ignition of the 
 particles must necessarily be gradual and slow. Formerly, the mode of constructing this train was 
 as follows : An iron rod of small diameter and terminating in a point, called a "pricker," was inserted 
 into the charge and left in the bore-hole while the tamping was being rammed down. When this 
 operation was completed, the pricker was withdrawn, leaving a hole through the tamping down to 
 the charge. Into this hole a straw, rush, quill, or some other like hollow substance filled with 
 gunpowder was inserted and pushed down to the charge. A piece of touch-paper was then attached 
 to the upper end of this train, and lighted. When the train became ignited, the powder being 
 confined in the straw, except at the upper end, burned slowly down and fired the charge, the time 
 allowed by the touch-paper and the train together being sufficient to enable the man who applied the 
 match to retire to a place of safety. This method of forming the train did not, however, satisfy all 
 the conditions mentioned above. It was neither practically suitable, nor readily applicable to all 
 situations. The use of the iron pricker was a source of danger. The friction of this instrument 
 against silicious substances in the sides of the bore-hole or in the tamping frequently occasioned 
 accidental explosions. This danger was, however, very greatly lessened by the employment of 
 copper or phosphor-bronze instead of iron for the prickers. But the method was very defective iii 
 
142 MINING ENGINEEEING. 
 
 other respects. With many kinds of tamping tliere was a difficulty in keeping the hole open after 
 the pricker was withdrawn till the straw could he got down. When the holes were inclined upwards, 
 besides this difficulty, another was occasioned by the liability of the powder constituting the train to 
 run out on being ignited. And in wet situations, special provision had to be made to protect the 
 trains. Moreover, the manufacture of these trains by the workmen was always a source of danger. 
 Nor was the system satisfactory under the most favourable conditions, for the aperture through the 
 tamping was so large relatively to the size of the bore-hole that the effective work of the explosive 
 was materially reduced thereby. 
 
 All of the defects pertaining to the foregoing system were removed by the introduction of the 
 fuse invented by Bickford, and known as Bickford's safety fuse. The merits of this fuse are indeed 
 such as to render it the most perfect of the slow-action means that could be devised. The train of 
 gunpowder is retained in this fuse, but the details of its arrangement are changed so as to fully satisfy 
 all the conditions previously laid down as necessary. It consists of a flexible cord covered with 
 waterproof materials, having a central core of fine gunpowder, surrounded by hempen yarns twisted 
 up into a tube, and called the countering. The outer casing is made of different materials according 
 to the circumstances under which it is intended to be used. A central touch thread passes through the 
 core of gunpowder. This fuse, which in external appearance resembles a piece of plain cord, is very 
 certain in its action : it may be used with equal facility in holes bored in any direction ; it is capable 
 of resisting considerable pressure without injury ; it may be used without special means of protection 
 in wet ground ; and it may be transported from place to place without risk of damage. 
 
 The combustion of the train of powder in a fuse takes place gradually, and the rapidity of the 
 process greatly depends upon the dimensions and nature of the envelope or covering. In consequence 
 of the compression, the gases liberated by the combustion of the first grains of powder cannot extend 
 themselves in a backward direction, and hence the grains below become ignited only in consequence 
 of the conductability of the several elements of the fuse as their temperature is brought up to the 
 requisite degree. In the safety fuse, the conditions of slow burning are well provided for, and 
 certainty is ensured by the touch thread through the centre of the core. As the covering of the core 
 is indestructible, and as, moreover, the combustion of the core leaves in the small space occupied by it 
 a carbonaceous residue, there is no passage whatever left through the tamping by which the gases 
 of the exploding charge may escape, as in the case of the straw trains. Hence results an economy of 
 force. Another advantage offered by the safety fuse is, that it may be made to carry the fire into the 
 centre of the bursting charge if it be desired to produce rapid combustion. This fuse can also be very 
 conveniently used for firing charges of compounds other than gunpowder, by fixing a detonating 
 charge at the end of it, and dropping the latter into the charge of the compound. This means is 
 usually adopted in firing the nitro-glycerine compounds, the detonating charge in such cases being 
 generally contained within a metallic cap. 
 
 In using this fuse, a sufficient length is cut off to reach from the charge to a distance of about an 
 inch, or farther if necessary, beyond the mouth of the hole. One end is then untwisted to a height 
 of about a quarter of an inch, and placed to that depth in the charge. The fuse being placed against 
 the side of the bore-hole with the other end projecting beyond it, the tamping is put in, and the 
 projecting end of the fuse slightly untwisted. The match may then be applied directly to this part. 
 The rate of burning is about two feet a minute. 
 
 Safety fuse is sold in coils of 24 feet length. The price varies according to the quality, and the 
 
SHAFT-SINKING. 143 
 
 degree of protection afforded to the train to render it suitable for use in diflScult situations. The 
 lollowing are the most useful qualities and prices : 
 
 ^ ^ Per Coil of 
 
 24 feet. 
 
 No. 2. Common fuse, for use in dry ground .. .. „ ., ,. ,. .. ,. Ad. 
 
 „ 3. White fuse, for use in dry and close places .. .. ,, ,. .. .. .. 4d. 
 
 „ 4. Red fuse, for use in very damp and close places ., .. .. .. .. .. .. iid. 
 
 „ 6. Thread sump fuse, for use in wet ground . .. .. .. ,. .. ,, ,, 5d. 
 
 „ 8. Tape sump fuse, for use in wet ground ... ., ,, .. .. ., ., .. &id, 
 
 „ 10. Treble-countered fuse, for use in very wet ground where it is liable to be subjected to rough 
 
 treatment .. .. .. .. .. .. .. .. .. .. .. .. 7id. 
 
 „ 12. Small guttapercha fuse, for use in very wet ground, or in water .. .. .. .. lOd. 
 
 „ 22. Treble-wove fuse, of superior q^uality, and suitable for almost every mining requirement .. 6d. 
 
 Fuses similar in character and in quality to the foregoing are manufactured by several firms, 
 and sold at about the same prices. 
 
 Classtfication of Eocks for Pukposes op Excavation. — From the time of the commencement 
 of the shaft in a new winning, to the final closing of the mine when the last load of mineral has been 
 drawn, the whole labour of the miner proper consists in cutting and removing rock. All other 
 operations are subsidiary to this. Hence it will be obvious on reflection that a knowledge of the 
 mineral composition, the structure and texture, and the distinctive characters of rocks, is essential to 
 the miner to enable him to apply his strength and his skill to the best advantage. An intimate 
 acquaintance with the nature of the materials upon which he has to work, as well as of the tools by 
 means of which the various operations are performed, is absolutely necessary to the production of a 
 superior workman. Undoubtedly he may, by observation and reflection, acquire such knowledge in 
 the course of his daily practice. But, unfortunately, the miner, as a rule, neither observes nor reflects 
 beyond what is necessary to enable him to imitate his companions. Not having been taught how to 
 look or what to look for, he performs his work like a machine, without troubling himself about the 
 whys and the wherefores, or endeavouring to conform his action to the peculiar conditions of the case 
 in which he finds himself. Moreover, when the circumstances are favourable, the lessons of indi- 
 vidi al experience are long and costly, while the collective experience of whole generations of former 
 workmen and students is ready at hand, and may be had for the seeking. The miner, therefore; who 
 wishes to excel in his arduous but useful calling, will do well to acquaint himself with the recorded 
 observations of others, and to study diligently the principles upon which the operations that he is 
 continually performing are conducted. He should also observe carefully for himself the nature of 
 the rocks upon which he is working, and consider attentively the forms of the tools employed, and 
 the modes of using them which long experience has taught to be the best. He will find a sound 
 reason for every peculiarity of form and of method, and will come to discern the relations existiiig 
 between these and the character of the rock. The possession of such knowledge will give him at 
 least the satisfaction of feeling that he is working in an intelligent manner. But if the observant 
 and thoughtful miner be compared with his unthinking comrade, it will be seen that this knowledge 
 leads to something more than mere sentiments. The labour of such a man is rendered thereby far 
 more productive, and his influence over his fellow-workmen becomes more marked in proportion as 
 his knowledge is superior to theirs. The fact must have been remarked by every mine manager, and 
 there will bo none who will not desire to see such eminently practical knowledge more common 
 among his men. It is, perhaps, too much to hope that the ordinary coal miner will, for some time 
 to come, exert himself to labour thus intelligently. But the progress which is observable in the 
 
l-i^ MINING ENGINEEEING. 
 
 improvements in mechanical appliances every day brought under his notice must tend to bring 
 about such a result ultimately. Till then it is the duty of those who are set over him to direct his 
 operations even in those minute details to which reference has been made. 
 
 In the first chapter of this work the composition and mode of formation of rocks were treated 
 of somewhat in detail, and it is very necessary that these subjects should be fully understood, It was 
 therein shown that rocks are composed mainly of a few mineral constituents differing from each other 
 widely in appearance, and especially in hardness. It was also shown from the manner in which the 
 rocks were built up, how these constituents were compacted together, and in many instances cemented 
 into a strongly coherent mass. From these facts it is evident that great variation must necessarily 
 exist in the hardness and coherence of rock, and that the more or less perfect development of the 
 system of joints during the process of consolidation and desiccation must influence in a high degree 
 its resisting powers. Thus rock composed mainly of quartz, as some of the silicious sandstones, will 
 require much more labour to cut than some compounds of lime, as chalk or gypsum. And a rock that is 
 abundantly jointed may be excavated with much greater facility than one in which the joints are but 
 sparsely developed. Also itisevident that a stratified rock will yield more readily than one of the igneous 
 class, in which no lamination exists. Thus it will be evident that the classification of rocks according 
 to their power of resistance to excavation, and the adaptation of tools and other means to the require- 
 ments of each class, constitute a matter of great importance in the economy of mining. The employ- 
 ment of unsuitable means, or of suitable means improperly applied, occasions a wasteful expenditure 
 of force, time, and money. Unfortunately, however, no complete classification is possible, nor can 
 exact instruction be given respecting the manner of applying the means of extraction. The hardness 
 and coherence of rocks varies by insensible degrees, and is not wholly dependent on their mineral 
 composition. Hence, a general classification only can be adopted. And as the conditions of hardness, 
 coherence, lamination, jointing, and cleavage are constantly varying, the instruction to be given 
 respecting the most effective application of tools must partake of the same general character. Such a 
 classification and such instruction are, however, valuable, inasmuch as they indicate the points upon 
 which attention should be directed ; and the educated engineer will find that he has gained much when he 
 has explained the one and imparted the other to the uneducated wielder of the pick. In insisting 
 thus strongly upon the necessity of the working miner being thoroughly acquainted with the 
 character of the rock in which he is occupied, we have, besides the productiveness of his labour, 
 another care in mind, namely, the security of his hfe and limbs. It can hardly be doubted that the 
 lamentably large number of deaths that are annually caused by falls of rock are in a very great 
 measure due to ignorance in this respect. 
 
 For the purposes of excavation, rocks may be classified into (1) Loose Rock; (2) Soft Rock ; 
 (3) Tender Rock ; (4) Compact Rock ; and (5) Hard Rock. The first of these classes, or loose rock 
 includes uncompacted sand, vegetable earth, and disintegrated rock of any kind that has little or no 
 coherence among its particles. Soft rock comprises plastic clay, loam, and marl. Tender rock 
 includes all rocks of an indurated character that have but little coherence between their laminse as 
 shale, or that are much broken up by joints. Compact rock includes rocks of a moderately fine 
 texture that have been firmly compacted and cemented, as sandstones, and some limestones. And 
 hard rock comprises the igneous rocks, the hardest limestones, and the conglomerates. 
 
 Loose and soft rocks may be easily cut by the shovel and spade, and these tools will, therefore, 
 be chiefly employed in excavating them. The pick will be required as an auxiliary instrument to 
 
SHAFT-SINKIxXG. 145 
 
 loosen tlie rock in some cases. In excavating tender rock, the pick will constitute the chief tool, the 
 shovel being used merely to clear away the dislodged rock. In applying this tool, it must be borne 
 in mind that rocks of a shaly structure cleave readily along the planes of lamination, but are often 
 very resisting in the direction of right angles to these planes. When the rock is jointed, there will 
 always be one direction in which any given block will yield more readily than in another. By taking 
 account of the planes of lamination, cleavage, and jointing, means will be perceived by which the 
 block may be dislodged with the least expenditure of force. Also the most suitable form and angle 
 ol cutting edge and degree of temper may be determined by a consideration of the mineral composition 
 and structure of the rock. These and other circumstances peculiar to the case to be dealt with will 
 afford abundant opportunity for the exercise of the judgment. When tender rock of a jointed 
 character occurs in the roof of underground workings, it is of the highest importance to note its 
 features attentively. Hardness and strength are qualities by no means identical. A rock-bed 
 composed of silicious materials strongly cemented together may be so fissured by jointing as to fall 
 readily when undermined. To ascertain the strength of a rock roof, the miner strikes it with some 
 iron instrument, as a hammer, sledge, or pick; a dull sound indicates the existence of joints; and a 
 sharp sound, free from ring or echo, continuity and strength. In placing the prop timber, it is 
 obviously necessary to consider the character of the jointing, in order to obtain a maximum degree 
 of security with a minimum expenditure of material. The excavation of compact rock is effected by 
 means of the pick, the wedge, and explosive compounds. In proportion as compact rock approaches 
 in character tender rock on the one hand, and hard rock on the other, the use of the manual tools or 
 of the explosives will predominate. It must be remarked, however, that the use of explosives is 
 rapidly extending even to rocks of the tender class. The dislodgment of hard rock can be effected 
 only by means of explosives. The pick and the wedge are required as auxiliary tools to complete 
 the dislodgment of blocks which has been only partially eifected by the action of the explosive. The 
 effective placing of the blasting holes requires a full appreciation of the character of the rock rela- 
 tively to its mineral composition, its structure, texture, and system of jointing. In rock drilling by 
 machinery, the structure and texture are particularly important ; for while the mineral composition 
 of the rock will determine the proper temper of the drill and the angles of its cutting edges, the 
 structure and texture will determine its most suitable form. A cellular or " vughy " rock, for 
 example, may be best penetrated by a form of drill which would prove less effective in a rock of 
 compact texture. These questions will be more fully discussed in a subsequent section. 
 
 Machine Eock-Drills. — It will be understood from the foregoing descriptions and statements 
 that the use of explosive compounds constitutes a large and an important part of the work of the 
 miner. The application of these substances necessitates a very great expenditure of labour in drill- 
 ing holes by means of which a favourable position for the charge may be obtained, and involves the 
 occupation oi long periods of time. The labour thus applied is becoming day by day greater in 
 amount, not only in consequence of the more extensive use of explosive compounds for purposes of 
 rock excavation, but also by reason of the rapidly increasing demand for mineral produce. The 
 desire to keep pace with the general material progress, and to meet the requirements of an increasing 
 consumption by lessening the manual labour of drilling and shortening the time occupied by the 
 operation, has led to numerous attempts being made to substitute machine power for hand-labour. 
 There also existed a weighty reason of a different character for making this substitution, a reason 
 which is becoming every day more important, namely, the growing inclination of the miner to toil 
 
 u 
 
1-4:6 MINING ENGINEEEING. 
 
 less arduously tlian formerly, and to shorten tbe hours of work. Such a disposition on the part of 
 the mining population has produced its natural effect in an augmentation of wages, and a consequent 
 and proportionate increase in the cost of the produce. The restriction placed upon the output, and the 
 frequent strikes by means of which this disposition has been carried into effect, have also rendered 
 hand-labour uncertain, and this fact furnished an additional reason for making dependence upon 
 it less absolute. Had these potent influences not been at work, it may be doubted whether 
 sufficient inducement would have existed to persevere in the attempt after the first disheartening 
 failures consequent on want of experience. But the circumstances of the times were such as hardly 
 to admit of defeat, and hence, as the lessons of experience were multiplied, success was gradually 
 achieved. The improved machines, actuated by steam in some situations, and by compressed air in 
 others, showed themselves, after long and severe trials under the actual conditions that obtain in 
 practice, capable of performing the work for which they were designed. This success, which has 
 been attained in spite of the opposition of much prejudice and ignorance, has at length brought them 
 into an established position, as a common mechanical appliance for mining purposes, and their use 
 thus adopted and securely founded must rapidly and widely extend. Hence the subject of machine 
 rock-drills has become one of great and pecuHar importance, and as such it claims a prominent 
 place and particular consideration in a work devoted to the principles and the practice of mining 
 engineering. 
 
 If the substitution of machine for hand drilling be considered only from an economical point of 
 view, it will appear less a saving of money than a saving of time. The merit of the machine lies m 
 its ability to concentrate the work of a number of men upon one point, or, which amounts to the 
 same thing, to increase the amount of work executed in a given time by a given number of men. 
 By bringing the power of a more potent motor in aid of the miner, more rapid progress in exca- 
 vating is made ; but the cost, in most cases, remains undiminished. No doubt as improvements are 
 effected in the machinery, and as the rate of wages increases, a marked diminution of the cost will 
 make itself conspicuous among the advantages derived from machine work. But at present the gain 
 is, in the main, limited to rapidity of execution. This gain will, of course, in numerous instances — 
 perhaps in all in a greater or a less degree — involve indirectly a gain of money ; but it will be by 
 means of the saving in time. The saving of time is, however, a highly important advantage. In 
 the cases of the Mont Cenis, the St. Grothard, and the Hoosac tunnels, it rendered practicable that 
 which would otherwise have been impracticable. And in the case of ordinary mining operations, the 
 ability to sink a shaft or drive a level or heading rapidly may ensure the success of an undertaking, 
 and save indirectly the expenditure of large sums of money. It would, indeed, seem to be almost 
 impossible to overestimate the magnitude of the numerous advantages accruing from the increased 
 rate of progress due to the substitution of machine power for hand-labour. Hence the importance of 
 the question remains paramount, even if no direct economy result from the substitution. 
 
 In comparing the rate ot progress made with the machine drill with that obtained by hand- 
 labour, the advancement of the excavation must be considered rather than the time occupied in 
 boring the blasting holes. When a machine is once set in motion, the speed with which the boring 
 progresses very greatly exceeds that which is reached when, under the most favourable circum- 
 stances, the operation is performed by hand. But the placing of the machine in the desired position • 
 the fixing of it at the necessary angle, and the attention demanded by its other requirements ; its 
 lemoval from one situation to another as it becomes necessary to bore each succeedino- hole • its 
 
SHAFT-SINKING. 147 
 
 Withdrawal for the blast, to take place, and the inconvenience arising from its more or less 
 bulky presence — all these matters, which together often occupy more time than the actual 
 boring, tend to greatly reduce the rate of progress due to the more rapid action of the tool. 
 Also the chances of accident to the machine, its inevitable wear and tear, and the time conse- 
 quently spent in effecting repairs, must be taken into account. Hence the only comparison that 
 can be of any value whatever is that which is founded upon the rate of progress of the ex- 
 cavation during a period oi time sufficiently long to include the contingency of breakage, and 
 the necessity for repairs. The longer the time of observation, the more trustworthy, of course, the 
 information gained will be ; thus the average daily advance of a heading during a period of six 
 months v?ill constitute a surer basis of comparison than the average daily advance which has 
 been ascertained for only half that length of time. A justification of these remarks may be found in 
 the fact that competitive trials extending over a few hours at the most are not unfrequently 
 made the foundation for wild statements concerning the superiority of machine drilling. As this 
 superiority actually exists, nothing is to be gained by attempts to enforce it by arguments which, to 
 the experienced man, are of an obviously fallacious character. 
 
 The conditions under which a rock drill is required to work are of an altogether exceptional 
 character. To suppose that the qualities which recommend a machine in ordinary situations must be 
 equally desirable in a drill is to misunderstand the exigencies of the case. Under ordinary circum- 
 stances, the situation is chosen and the extent of space determined to suit the requirements of the 
 machine, and all other conditions are made conducive to its efficient action. In the case of a rock 
 drill, on the contrary, the conditions are determined by other considerations, and they are. generally 
 unfavourable in character. The machine is required to work in confined and difficult situations, and 
 in positions that do not tend to promote its perfect action. It has to be quickly brought into and 
 fixed in the place where it is needed, and as quickly removed when it has done its work. It is 
 necessarily subjected to sudden and severe strains, and to rough handling, and it is exposed for long 
 periods of time to the influence of moisture. And last, but not least, it is entrusted to the direction and 
 care of ignorant men. This latter circumstance exercises an obstructive influence of which the inex- 
 perienced in these matters have but little conception. Hence it is evident that however effectively a 
 machine drill may operate on the rock, it will be unfit for the purpose intended if its construction be 
 not such as will render it conformable to these conditions. 
 
 One consequence of the peculiar conditions to which a machine drill is subjected is the exclusion 
 of steam as a motor. The confined character of the situations in which the work has to be executed, 
 and the difficulty of providing an adequate ventilation, render it undesirable to raise the temperature of 
 the atmosphere, or to vitiate it by the abstraction of oxygen. Thus it has become necessary to have 
 recourse to compressed air, which, besides being free from the qualities objectionable in steam, 
 possesses others that render its employment conducive to coolness and purity in the atmosphere into 
 which it is discharged. The compression is effected at surface, or outside the heading, and conveyed 
 through pipes of suitable dimensions and materials to the points at which it is required. The neces- 
 sity which exists for employing special machines to compress the air constitutes the chief objection to 
 the use of the latter, which objection is doubtless of a somewhat serious character. 
 
 Machine drills of the common form penetrate rock in the same way as the ordinary hand drills 
 already described, namely, by means of a percussive action. The cutting tool is, in most cases, 
 attached directly tp the piston-rod, with which it consequently reciprocates. Thus the piston with 
 
 u 2 
 
148 MINING ENGINEEEING. 
 
 its rod is made to constitute a portion of the cutting tool, and the blow is then given by the direct 
 action of the steam or air upon the tool. As no work is done upon the rock by the back stroke of the 
 piston, the area of the forward side is reduced to the dimensions necessary only to lift the piston, and 
 to overcome any slight resistance due to the friction of the tool in the bore-hole. The piston is made 
 to admit steam or air into the cylinder, and to cut off the supply and to open the exhaust as required, 
 by means of tappet valves, or other suitable devices ; and provision is made to allow, within certain 
 limits, a variation in the length of the stroke. During a portion of the stroke, means are brought 
 into action to cause the piston to rotate to some extent, for purposes that have been already explained. 
 To keep the cutting edge of the tool up to its work, the whole machine is moved forward as the rock 
 is cut away. This forward or " feed" motion is usually given by hand; but in some cases it is com- 
 municated automatically. The machine is supported upon a stand or framing which varies m form 
 according to the situation in which it is to be used. This support is in all cases constructed to allow 
 of the feed motion taking place, and also of the cutting tool being directed at any angle. 
 
 In another class of machine drills the diamond cutters are employed. As the construction and 
 application of these drills are, with the exception of certain modifications of detail to suit the altered 
 circumstances, precisely the same as those of the large machine for prospective boring, which has 
 been already described, the reader is referred to the section in which that description is given for 
 information on those points. 
 
 The foregoing is a general description of the construction and mode of action of percussive rock- 
 drills. The numerous varieties now in use differ from each other rather in details of construction than 
 in principles of action, and the importance of the difference is, of course, dependent upon that of the 
 details. Before proceeding to describe and to illustrate these varieties, there are certain conditions 
 to be laid down which every rock drill must fulfil in order to render it in all respects sufficient for 
 the exigencies of practice. These conditions, which have been determined by experience, are the 
 following : 
 
 1. A machine rock-drill shall be simple in construction, and strong in every part. 
 
 2. It shall consist of few parts, and especially of few moving parts. 
 
 3. It shall be as light in weight as it can be made, consistent with the first condition. 
 
 4. It shall occupy but little space. 
 
 5. The striking part shall be of relatively great weight, and it shall strike the rock directly. 
 
 6. No part other than the piston shall be exposed to violent shocks. 
 
 7. The piston shall be capable of working with a variable length of stroke. 
 
 8. The sudden removal of the resistance shall not be liable to cause injury to any part. 
 
 9. The rotary motion of the drill shall take place automatically. 
 
 10. The feed, if automatic, shall be regulated by the advance of the piston at each stroke. 
 
 11. The machine shall be capable of working with a moderate degree of pressure. 
 
 12. It shall be capable of being readily taken to pieces. 
 
 The support for a rock drill constitutes an indispensable and a very important adjunct to the 
 machine. Upon the suitability of its form, material, and construction, the efficiency of the machine 
 will largely depend. The material and the construction may be made to differ, and the form to vary 
 widely ; but whatever they may be, it is necessary to the effectiveness of the support that in its 
 design the following conditions be fulfilled : 
 
 1. A machine-drill support shall allow the machine to be readily adjusted to any angle. 
 
SHAFT-SINKING. 149 
 
 2. It shall be adjustable to uneven ground, and capable of being easily and quickly fixed in 
 any position. 
 
 3. It shall be simple in construction, and of sufficiently light weight to allow of its being easily 
 portable. 
 
 The first of the conditions laid down respecting the design of machine drills will be acknowledged 
 as self-evident, when the circumstances under which they have to work are borne in mind. The 
 character of these circumstances has already been described. It is important that the necessary 
 simplicity should extend to every part of the machine, and not be confined to the mechanism proper. 
 In every case it must be assumed, as an inevitable condition, that the machine will be entrusted 
 altogether to unskilled hands, and therefore its construction and action must be such as to require 
 no special knowledge to understand or to direct. The use ot every part should be obviously 
 apparent, and its position in the machine and its form should be such as to occasion no difficulty in 
 removing and replacing it, or in repairing it when out of order. Small levers and all kinds of jointed 
 gear are objectionable, by reason of the rapid motion communicated to them, and their consequent 
 liability to fracture and speedy wear, which liability is largely increased by the splashing with gritty 
 water and other inevitable occasions of dirt to which a machine is constantly subjected in a mine. 
 For the same reasons, external gear is especially to be avoided. It is open to question whether 
 the increased simplicity obtained by hand-feeding gear does not outweigh in advantages the 
 comparative complexity due to an automatic feed. There is much to be said in favour of both 
 arrangements, and experience has not yet decided which of the two possesses the superior merits. It 
 is urged against automatic feeding, that it introduces unnecessary complexity, for that if the action 
 were perfect it could not give better results than those obtained by careful hand feeding ; and that a 
 perfect automatic action cannot be obtained by reason of the continual variation in the character of 
 tlje rock. Against hand feeding it is urged, that it requires the constant attention of the man in 
 charge, a fact which necessitates the employment of a man for every machine when several are fixed 
 upon the same support : that it is impossible, when every care is taken, to feed at the same rate as 
 the piston advances, and that, consequently, there must necessarily be a loss of efficiency in the 
 blow due to this cause : that therefore it becomes necessary to employ an experienced and skilful 
 attendant ; and that, as a matter of fact, even with such an attendant, the work is often carelessly 
 performed; the inevitable consequences of such negligence being in all cases a diminution of the 
 efficiency of the machine, and in numerous cases a jamming or fracture of the tool. On the other 
 hand, it is urged in favour of hand feeding, that there must always be a man in attendance upon a 
 machine, and that he may as well be employed in actuating the feed-gear as in watching the action 
 of the machine. That the system possesses the great advantage of enabling the attendant to vary 
 the length of the stroke from less than an inch to several inches, according as light blows are needed 
 to commence a hole, or full blows when the hole is fairly started. Also, this power of varying the 
 force of the blow may be turned to useful account in sparing the cutting edge of the tool when 
 excessively hard rock is met with, an advantage that tends to promote the regular progress of the 
 work. On the part of the automatic feed, it is contended that the advantage of light blows when com- 
 mencing the hole may be obtained by only partially opening the passage through which the steam or 
 compressed air is admitted ; and that it is possible, without introducing much complication of parts, to 
 render the action of the feed perfect by making it dependent upon the advance of the piston at each 
 stroke. These disputed points must, as before remarked, be decided by the results of experience. 
 
150 
 
 MINING ENGINEEEING. 
 
 The same circumstances which necessitate simph city in a machine rock-drill also require strength 
 in its several parts. It is evident that the rough work performed by a drill operating upon hard 
 rock by percussive action, and the often rougher treatment to which the machine is subjected at the 
 hands of those in charge of it, will speedily result in loose joints, and wear and fracture of the moving 
 parts, unless each part possesses a degree of strength proportionate to the work required of it. In the 
 endeavour to reduce the weight of the machine, this necessity is sometimes not borne sufficiently- 
 in mind. 
 
 The second condition, which requires a machine rock-drill to possess only few parts, and 
 especially few moving parts, is to a great extent included in the first. Yet the parts themselves may 
 be extremely simple in form, while, in consequence of their being multiplied, the machine possesses 
 a considerable degree ot complexity. The possession of numerous parts constitutes a serious defect, 
 and when the multiplication oi parts extends to those in motion, the defect assumes still graver 
 proportions. As the larger portion of the wear and tear must come upon the moving parts of any 
 machine, it is obvious that the greater the number of such parts, the more will the wear and tear be, 
 and the greater the risk of breakage. Moreover, a large number of parts renders the design and the 
 action of a machine difficult to be understood and directed by the persons in whose charge rock drills 
 are usually placed, and to whose ignorance of mechanical principles we have already alluded. 
 
 The third condition, of light weight in a machine drill, is one the importance of which is 
 generally acknowledged, but the bearing of which is not fully understood. In transporting the 
 machine to the spot where it is required to work, in fixing it in the necessary position and at the 
 desired angle, and in removing it when its work is completed, manual power has to be largely 
 employed. Hence it is highly desirable that the weight of a machine should be such as to render it 
 portable. In spacious headings for railway tunnels, where wheeled carriages running upon tramways 
 may be used as the support, the necessity for portability in the drill liardly exists ; but for all mining 
 and quarrying purposes, that quality must be considered as an essential one. As before remarked, the 
 necessity for reducing the weight in such case to the lowest practicable limit is generally acknow- 
 ledged, and the efforts of inventors and maniifacturers have been directed to effect this object. But 
 in the prosecution of these attempts at improvement, the necessity of strength has not been kept 
 always in view, and hence the first condition has been encroached upon. Light weight constitutes a 
 very desirable quality in a machine drill for reasons already given ; but for other reasons, strength is 
 still more desirable. Lightness and fragility are related and inseparable ; and it is certainly preferable 
 to have a machine that can keep itself out of the repair shop, even if it necessitate a greater cost of 
 labour to place it in position, than another of a more easily portable character that is subject to 
 frequent derangement. Hence, in designing a rock drill, the necessity for strength and the 
 necessity for light weight should be fully observed ; but the exigencies of the case will require that 
 the latter be made subordinate to the former. 
 
 The fourth condition is also one of considerable importance, especially when the machine is to be 
 used in mining operations. In all underground workings, the free space is extremely limited, and 
 everything which obstructs that space constitutes an impediment and a source of delay to the 
 operations which are there being performed. The degree of obstruction, and consequently the 
 importance ot the hindrance, is dependent upon the extent of the space and the dimension of 
 the obstructing body. When this space is a circular shaft, it is rarely more than 15 feet in diameter ; 
 and when a heading, its dimensions are usually much more restricted. Hence it is obvious that a 
 
SHAFT-SINKING. 151 
 
 macMne drill in such a situation must necessarily occupy a large proportion of the space in which 
 the workmen are engaged, and that if this proportion he such as to greatly impede operations, the 
 gain in rapidity of execution, due to the employment of the machine, will be nulHfied by delays in 
 other directions. Thus the importance of compactness in the machine will on reflection be apparent, 
 A due fulfilment of the condition of light weight will, to a great extent, satisfy that of compactness, 
 since, other things being equal, the weight will depend upon the dimensions. Sometimes, in view 
 of the great length of the space in a heading comparatively to its breadth, the dimensions of the 
 machine have been accumulated in one direction, that is, it has been made of small diameter and of 
 great length. This expedient is, however, objectionable on two grounds : first, because the great 
 length renders the machine cumbrous to handle ; and, second, because it prevents holes from being 
 bored at any but slight angles. The latter consequence must be regarded as constituting a serious 
 defect. 
 
 The fifth condition is one of great mechanical importance, and this importance does not appear 
 to be generally recognized. In comparing the relative merits of rock drills, the number of strokes a 
 minute which anyone is capable of making is often insisted upon as the basis of a comparison 
 of efficiency, that one being considered the most efficient which is capable of making the greatest 
 number of strokes. This notion is an altogether erroneous and a pernicious one, inasmuch as it 
 tends to perpetuate and increase a somewhat serious defect. A high piston speed is undesirable in a 
 rock drill mainly for two reasons. First, the resistance to be overcome is great. The operation of 
 boring consists, as we have already shown, in fracturing the rock by a succession of heavy blows, and 
 it is evident that the heavier the blow, within the limits of the endurance of the tool, the greater will 
 be the effect. To obtain a heavy blow there must be a large moving mass. But an augmentation 
 of the mass is, other things being equal, incompatible with an increase of the velocity. Hence it 
 becomes desirable, as far as the third condition will allow, to renounce velocity in favour of mass ; 
 that is, as much as practicable of the weight of the machine should be concentrated in the piston and 
 piston-rod. With such a disposition of the parts, the work of a drill must necessarily be more 
 effective. Second, when the moving mass is light and the velocity high, not only is the great 
 resultant vibration absorbent of force, but very destructive to the joints and conducive to fracture in 
 the moving parts. And, moreover, the inevitable wear and tear are thereby immensely increased : 
 so that the tendency to derangement is greatly augmented by the adoption of high velocities. 
 
 That part of the condition which requires the striking mass to impinge directly upon the rock is 
 also worthy of careful attention, since the efficiency of the machine depends upon it in no inconsider- 
 able degree. As several machines have been constructed in which this principle has been violated, 
 it becomes desirable to determine clearly what the effect of interposing a body between the striking 
 part and the rock is. Let M denote the mass of the striking part, M' that of the body interposed, 
 that is of the tool struck, V the velocity of the striking mass, and Vi the common velocity of the two 
 bodies after impact. Then we have 
 
 MV = (M' + M) Y, ; whence V^ = ^r^^ V. 
 Hence the effect of the blow will be proportional to 
 
 (M' + M) V,^ = j^^ X MV^ 
 
152 
 
 MINING ENGINEEEING. 
 
 The work developed by the motor is | MY^, and thus it is evident that the effective work done 
 
 upon the rock will be proportional to the fraction tit r-, ; that is, it increases as M increases, or as 
 
 ^ ^ M' + M' 
 
 M' diminishes. To take an example : Suppose a machine the piston and piston-rod of which weigh 
 
 24 lb., to which a tool is fixed weighing 8 lb., the velocity of the piston being 5 feet a second. 
 
 32 
 In this case M = 2272' ^' = ^' ^^^ V = 5, and the work developed will consequently be 
 
 /'32 X 5^\ 
 H 32-2 / — ^^'^ ^^^^ of work. Suppose now the tool to be detached, and the piston to strike 
 
 94- 8 
 
 the head of the tool. In such a case M = — -^, M' = ^^, and Y = 5, as before. The work 
 
 32 ■ Ji 32 ' 2 
 
 done upon the rock will be 
 
 K 
 
 24 
 
 24 X 5== 32-2 ^ „ ., r 1 
 1F2- X ^+-24^ = 7 units of work. 
 
 32-2 
 
 Suppose, again, the weight of the tool to be added to the piston in order to have the same 
 dng mass as in th( 
 upon the rock will be 
 
 32 8 
 
 striking mass as in the first case. Then M = , M' = qTTo » ^^^ Y = 5 ; and the work done 
 
 32 
 
 , (^ 2 X 5" 32-2 \ .. .^ 
 
 32-2 
 
 Thus the loss of efficiency due to the interposition of the tool, or, in other words, its separation from 
 the piston, is about 1&\ per cent. 
 
 The sixth condition, which provides that no part of the machine shall be subjected to violent 
 shocks, is one that is common to all kinds of machines. But in a rock drill there is greater difficulty 
 in complying with the condition than there is in the case of machinery of an ordinary character. 
 The impossibility which exists of connecting the piston with the means of admitting the moti\e 
 fluid in an invariable manner is naturally the source of an irregularity in the action that is conducive 
 to the occurrence of sudden and violent strains in various parts. In this respect, a rock drill is 
 somewhat similar to a steam hammer ; but the higher speed at which the former is driven, and the 
 different conditions under which it has to work, intensify the effects in a very considerable degree. 
 Hence it becomes necessary to direct special attention to the design and construction of those parts 
 which are necessarily subjected to some degree of shock, or upon which a sudden and violent strain 
 may be thrown. In the majority of cases, the valve gear is actuated by means of tappets, which are 
 struck by the piston as it travels in the cylinder. It is evident that in such a case the whole of the 
 parts which compose the valve gear are constantly subjected to shocks the violence of which increases 
 with the speed of the piston. This must tend to cause a rapid wear and tear of these parts, which 
 are necessarily of feeble dimensions. And as a matter of fact, these are the parts of a drill that are 
 continually subject to derangement. What is needed, therefore, is a design and form of construction 
 which shall reduce the inevitable shock to its lowest possible degree of intensity. A source of 
 
SHAFT-SINKING. 153 
 
 accidental shock of an extremely violent and destructive character lies in the necessity for a variable 
 piston stroke. The provision for this variation of stroke allows the piston, under certain circum- 
 stances, to come into contact with the cylinder cover. When, as is sometimes the case, the valve 
 gear acts independently of the piston, the liability to this accident is greatly increased, and becomes 
 a very serious defect. In the design and construction of every machine drill, this tendency of the 
 piston to exceed the proper limits of its stroke should be constantly borne in mind, and means should 
 be employed both to check that tendency and to lessen its effects. 
 
 A rock drill operates upon the rock, as we have seen, by striking a blow, and it is essential to 
 the success of the operation that the blow should be struck with the full force of the stroke. When 
 the rock is very hard, several blows may be struck in succession without either penetrating the rock 
 or breaking away any part of it. A subsequent blow acting on the parts weakened by those already 
 received, causes fracture, and the fractured portion instantly becoming detached, the hole is suddenly 
 deepened. The piston will therefore have to advance farther at the next following stroke. More- 
 over, rocks vary suddenly and greatly in hardness, and often contain cavities, besides which they are 
 always more or less traversed by joints. If all these circumstances are borne in mind, a little reflec- 
 tion will suffice to show that, even assuming perfect feeding to be possible, a rock drill could not 
 operate with an invariable piston stroke, and that the piston must, in the matter of length of stroke, 
 accommodate itself to the requirements of the moment. But as no automatic feed motion could be 
 devised sufficiently accurate in its action to satisfy the demands of practice, and as hand feeding is by 
 its nature more imperfect still, the necessity becomes obvious, not merely for a possible variation 
 in the length of the stroke, but for a variation between somewhat wide limits. This condition 
 renders it impossible to connect the piston in an invariable manner with the valve gear. Hence 
 recourse has been had to tappet movements to actuate the valve, and in some instances the valve 
 motion has been made wholly independent of the piston. 
 
 The eighth condition, which requires that the sudden removal of the resistance shall not be liable 
 to cause injury to any part, is really comprised within the sixth, which lays it down that no part, other 
 than the piston, shall be subjected to violent shocks. But it has been placed out in a separate form to 
 give special prominence to a source of accidents to which machine rock-drills are especially ex- 
 posed. As previously pointed out, rocks frequently contain vughs or cavities, and these cavities are 
 not uncommonly of considerable dimensions. When a bore-hole enters one of these cavities, the 
 resistance to the tool is suddenly removed. The removal of the resistance causes the piston to give 
 its extreme length of stroke, and, in consequence of a tendency to exceed the limit, it often strikes 
 against the cylinder cover. The destructive character of this accident has been already alluded to. 
 A provision against its occurrence consists in allowing ample clearance space at the lower end of the 
 cylinder. 
 
 The necessity for an automatic rotary motion in the drill or borer-bit is sometimes questioned, 
 and recently a machine has been introduced in which this condition has not been complied with. 
 But it ought to be evident on reflection that the non-fulfilment of the condition must occasion grave 
 inconveniences. Besides the reciprocating motion communicated by the piston, the borer has two 
 other motions, one of rotation, and one of progression. These motions must be both automatic, both 
 communicated by hand ; or one must be automatic, and one communicated by hand. In the first of 
 these cases, of course, the condition will be fulfilled ; in the second, it will not ; and in the third, it may 
 not be. If both motions are to be communicated by hand, it is evident that, to perform the operation 
 
 X 
 
154 MINING ENGINEEEING. 
 
 satisfactorily, two men will be needed to work the machine, for the attention required to give the 
 progressive or feed motion is such as to preclude the practicability of one man attending to the 
 other motion at the same time. This necessity would constitute a very grave objection to the use of 
 a machine drill. If one motion is to be automatic and the other to be communicated by hand, it 
 ought to be equally evident that self-regulation should be applied preferably to that motion which 
 is the more simple in character, or which has to take place under the more simple conditions. 
 When, therefore, we take into account the conditions under which the forward or feed motion 
 must take place, which conditions have been already described, it will be obviously apparent that 
 the automatic action should be given to the mechanism of rotation, and the more delicate motion 
 of progression reserved for hand guidance. 
 
 The tenth condition, which requires an automatic feed to be regulated solely by the advance of 
 the piston at each stroke, is one of essential importance. Indeed, it may fairly be stated that without 
 an observance of this condition an automatic feed is practically impossible. It is true that mechanical 
 contrivances that are not founded upon such a principle have been adopted, and are still in use ; but 
 their action is so unsatisfactory that it may reasonably be doubted whether a feed motion so produced 
 is not inferior to that which may be communicated by hand ; and when the superior simplicity of 
 the latter is borne in mind, it will be plainly evident that such imperfect devices must sooner or later 
 be abandoned. It has been shown by what means and in what manner the edge of the tool 
 penetrates the rock, and a little consideration of those means and that manner will show also that 
 any mechanism by which a regular progressive motion is communicated to the tool must necessarily 
 be unsatisfactory in its action. With such a motion, no account is taken of the irregular manner of 
 producing fracture in the rock, of variations in hardness, of the occurrence of joints and cavities, or 
 of the comparative sharpness or bluntness of the cutting edge of the tool. A certain velocity of 
 progression having been assumed, the inevitable consequence is, either that the tool is not kept 
 properly up to its work, or it is pressed forward too rapidly. In both cases the result is a serious loss 
 of effective work, often accompanied with no less serious delays. With these facts in view, the 
 practical mind will at once comprehend the importance of observing this condition in the design of 
 means for producing an automatic feed motion for a rock drill. 
 
 The eleventh condition, which requires that the machine shall be capable of working with a 
 moderate degree of pressure, is one that must tend greatly to promote the successful employment of 
 rock drills actuated by compressed air. The notable loss of work occasioned by a high degree of com- 
 pression of air by means of steam, the heat generated by tlie process, the increased difficulty of storiu<>- 
 and conveying the air, and the intense cold produced by its expansion when exhausted from the 
 machine, all these consequences of high compression, with others of a less important character, tend 
 to render the employment of high pressures objectionable ; and, as a matter of fact, they are being 
 abandoned. The use of a pressure exceeding four atmospheres is now rare ; three atmospheres and 
 under are the common pressures, and it may be predicted that the machine drill which will be 
 generally adopted for mining operations will be capable of working effectively with a pressure of 
 two atmospheres. 
 
 With respect to the twelfth condition, requiring a machine drill to be capable of being readilv 
 taken to pieces, little need be said. It will be sufficiently obvious from what has been stated alread\' 
 that under the most favourable circumstances rapid wear and tear must necessarily occur, and that 
 iiacture and derangement are not altogether preventable. Hence it becomes necessary so to construct 
 
SHAFT-SINKING. 155 
 
 the machine that it may be readily taken to pieces, and as readily reconstructed, by men who possess 
 little knowledge of the nature of machinery. 
 
 A machine rock-drill may satisfy all the foregoing conditions, and yet by reason of the 
 defective character of the support to which it is attached, it may be unsuitable to the work required 
 of it. Hence it becomes desirable to carefully study the design and construction of a drill support, 
 and to consider the requirements which it is needful to fulfil. Assuming the necessity for a high 
 degree of strength and rigidity in the support, a primary condition is that it shall allow the machine 
 to be readily adjusted to any angle, so that the- holes may be bored in the direction and with tlie 
 inclination required. "When this requirement is not fulfi.lled, the machine is placed, in this respect, 
 at a great disadvantage with hand-labour. If a machine drill is not capable of boring in any 
 position and in any direction, hand-labour will have to be employed in conjunction with it, and such 
 incompleteness in the work of a machine constitutes a serious objection to its adoption. 
 
 Besides allowing of the desired adjustment of the machine, the support must be itself adjustable 
 to uneven ground. The bottom of a shaft which is being sunk, or the sides, roof, and floor of a 
 heading which is being driven, present great irregularities of surface, and as the support must of 
 necessity, in most cases, be fixed to these, it is obvious that its design and construction must be such 
 as will allow of its ready adjustment to these irregularities. The means by which the adjustment is 
 effected should be few and simple, for simplicity of parts is important in the support as well as in 
 the machine, and for the same reasons. A large proportion of the time during which a machine 
 drill is in use is occupied in shifting it from one position or one situation to another. This time 
 reduces in a proportionate degree the superiority of machine over hand labour in respect of rapidity 
 of execution, and it is therefore evidently desirable that it should be shortened as far as possible. 
 Hence the necessity for the employment of means of adjustment which shall be few in number, rapid 
 in action, and of easy management. 
 
 For reasons similar to the foregoing, the drill support must be of small dimensions, and suffi- 
 ciently light to allow of its being easily portable. The limited space in which rock drills are used 
 renders this condition, as we have shown in the case of the machine itself, an important one. 
 It must be borne in mind that after every blast, the dislodged rock has to be removed, and rapidity 
 of execution requires that the operations of removal should be carried on without hindrance. A 
 drill support that occupies a large proportion of the free space in a shaft or a heading is thus a 
 cause of inconvenience and a source of serious delay. Moreover, as it has to be continually 
 removed from one situation to another, it should be of sufficiently light weight to allow of its being 
 lifted and carried without difficulty. In underground workings, manual power is generally the 
 only power available, and therefore it is desirable that both the machine and its support should be 
 of such weight that each may be lifted by one man. Of course, when any endeavour is made to- 
 reduce the weight of the support, the necessity for great strength and rigidity must be kept in 
 view. 
 
 In spacious headings, such as are driven in railway tunnel work, supports of a special kind may 
 be used. In these situations the conditions of work are different from those which exist in mines. Tlie 
 space is less limited, the heading is commenced at surface, and the floor laid with a tramway and 
 sidings. In such a case the support may consist of a massive structure mounted upon wheels to run 
 upon the rails. This support will carry several machines, and to remove it out of the way wheti 
 occasion requires, it will be run back on to a siding. But foi' ordinary mining purposes, such a support 
 
 X 2 
 
156 MINING ENGINEEEING. 
 
 is unsuitable. That which is now commonly used, and which appears best to satisfy the require- 
 ments, consists simply of a stretcher bar, which is fixed against the sides of a shaft or heading, or 
 against the roof and floor of the latter, by merely lengthening it when in position. The machine is 
 fixed to this bar by means of a clamp, which, when loosened, allows it to be directed at the desired 
 angle. Another kind of support, often furnished with a drill, consists of a tripod, the legs of which 
 are capable of being increased in length, and extended laterally to meet the inequalities of the 
 ground. This support, however, has not sufficient stability, and — if the case of open quarry work 
 requiring vertical or nearly vertical holes in situations where the stretcher bar cannot be applied be 
 excepted — ought, therefore, never to be used. 
 
 An account of the gradual development of rock-drilling machines from their origin in America, 
 through all the successive stages, down to the latest degree of perfection, would be intensely inter- 
 esting and highly instructive; but it would be beyond the scope of the present work. We shall, 
 therefore, merely remark that the first really practical solution of the problem is due to M, Som- 
 meiller, whose machine was employed in excavating the Mont Cenis tunnel, and proceed at once to 
 describe, illustrate, and compare the various machine drills that are now in successful operation. It 
 is necessary to premise, however, that for the purpose of comparison, the following machines are 
 selected of a size to bore a hole 1| inch in diameter. 
 
 The Dubois- Franqois Rock-Drill. — The design, mode of action, and construction of the Dubois- 
 Fran9ois rock-drill are founded upon those of Sommeiller's machine ; but the improvements effected 
 are of such a character as to render the former greatly superior to the latter. In consequence of this 
 sriperiority it has superseded its prototype, and firmly established itself in favour upon the Continent, 
 but especially in Belgium and in France. Its general employment in these two countries, the 
 importance of the work to which it has been applied, and the protracted character of the, tests 
 to which it has been subjected, are sufficient evidence of its merits. The design and construction of 
 this machine are shown in Figs. 301 to 304, Plate XXIII., and its mode of action will be understood 
 from the following description, and the illustration afforded by the drawings. 
 
 The percussion piston B reciprocates in a cylinder 0. The rod A of this piston is of compara- 
 tively large dimensions, and is provided at its lower extremity with an enlarged section pierced to 
 receive the cutting tool. The valve gear is altogether of a special character. An ordinary slide- 
 valve Gr is connected to two pistons H and H', each moving in a cylinder provided for it. The 
 piston H', it must be observed, has a larger surface area that the piston H. When the compressed 
 air enters the valve-chest, it exerts a pressure upon both pistons, which pressure tends to force them 
 in contrary directions. But as the area of H' is greater than that of H, the pistons, being connected 
 by their rods and the valve, move forward. This motion opens the port x, air is admitted above the 
 piston B, and the drill-bit is driven against the rock. The piston H', however, is pierced by a small 
 passage i i, which allows the compressed air to pass to the other side of it in J, by which means 
 equilibrium is restored upon the two surfaces. When this equilibrium is established, the action of 
 this piston is destroyed, and, consequently, the pressure acting upon the other piston H, forces the 
 pistons in the contrary direction. This motion opens the port z, air enters below the piston B, and 
 the drill-bit is withdrawn from the rock. To cause this action of the pistons to be repeated, an 
 annular projection C, upon the rod A, comes in contact during the back stroke with a lever D, which 
 being raised, opens the valve B. The air in the space J escapes, and the equilibrium of the piston 
 H' is thereby destroy ed. 
 
SHAFT-SINKING. 157 
 
 It will be seen that the action of this valve gear throws the motive force suddenly upon the 
 percussion piston for the forward or working stroke, while it effects the return stroke in a less violent 
 manner. The size of the air passage through the valve-pistou H' is a matter of importance. 
 To determine the most suitable proportions, many experuuents were needed. If this passage were 
 too large, equilibrium would be established too soon, and a consequent jerky motion would be 
 produced in the percussion piston ; if it were too small, the motion of the latter would be too 
 slow and irregular. The results of experiments have shown that to obtain a perfectly satisfactory 
 action in a machine of the dimensions given in the drawing, the passage should be O'l inch in 
 diameter. 
 
 The rotation of the drill-bit is obtained by the alternate action of two small pistons P and P', 
 Fig. 303. These pistons, which are single acting, receive compressed air through the opening 
 m, n upon the ports of the percussion piston. The alternating action thus obtained is transmitted by 
 a rigid rod Z to a ratchet-wheel V, Fig. 304, fixed upon the rod A, in the fore part of the machine. 
 By this means the rotation of the bit is accomplished in a satisfactory manner at a cost of only a 
 small quantity of air. The feed motion is communicated by hand by means of a screw, as shown in 
 the drawings. 
 
 The principal dimensions of the machine are as follows : Total length, 7 feet 2 inches ; weight, 
 484 lb. ; diameter of the cylinder, 2\ inches ; diameter of the piston-rod, l\ inch; maximum stroke, 
 7f inches ; weight of the striking mass, including 8-lb. borer-bit, 68 lb. ; length of feed, 31| inches. 
 
 If this machine drill be examined relatively to the conditions previously laid down, it will be 
 found that it only partially satisfies the first. Though extremely simple in some of its parts, an un- 
 necessary degree of complexity is occasioned by the presence of no less than five pistons. Those 
 which actuate the rotating gear also appear to be too much exposed to injury from dirt and gritty 
 water. The ratchet gear being exposed, is liable to injury from blows and strains otherwise caused, 
 and to be impeded in its action by grit. The second, third, and fourth conditions are not 
 complied with. The fifth condition is fully satisfied. The sixth is only partially satisfied, in- 
 asmuch as the percussion piston is liable to strike against the cylinder covers. The valve gear 
 being totally independent of the motion of the piston, there is no means of preventing this accident, 
 and as a matter of fact it continually occurs at the back stroke of the piston. To lessen the destruc- 
 tiveness of the blow upon the cylinder cover, the latter is usually protected by an elastic cushion of 
 indiarubber or guttapercha. In consequence of the independent action of the valve gear, the 
 seventh condition is perfectly satisfied, the length of stroke being capable of variation from the 
 maximum down to f of an inch. This constitutes a great advantage at the commencement of a boi-e- 
 hole. The eighth condition, like the sixth, is not satisfied ; the ninth is complied with ; and the 
 eleventh and twelfth are fulfilled in a fairly satisfactory degree. 
 
 It appears, therefore, that this machine is more suitable for employment in headings at surface, 
 8ur;h as are driven in excavating railway tunnels, than in ordinary underground mining operations, 
 in which the unfulfilled conditions are of paramount importance. 
 
 The Sachs Roch-DrilL — The machine rock-drill known by the name of its inventor, Carl Sachs, 
 is widely employed in Germany, where it has executed very important work. The ingenuity and 
 refinement evinced in the design and construction of this machine claim careful attention. 
 
 The Sachs drill is shown in section and in end elevation, in Figs. 305 to 308, Plate XXIII. As 
 the details of construction are therein clearly shown, a general description of the action will be suffi- 
 
-L^o MINING ENGINEERING. 
 
 cient to make It fully understood. The slide-valve, it will be observed, is of the ordinary character, 
 and the mode of admitting, cutting off, and exhausting the motor fluid precisely the same as in an 
 ordinary steam-engine. Tbe valve is worked by a bell-crank lever connected with the piston-rod in 
 the manner shown in the drawing. Thus the motion of the valve is wholly dependent upon that of 
 the piston. It will be observed that ample clearance space is provided at each end of the cylinder. 
 To give the requisite rotary motion to the tool, another arm of the rocking lever communicates 
 a reciprocating motion to a rod, shown partly in Pigs, 305 and 306, but more fully in Fig. 307. 
 Upon this rod are fixed two ratchet-pawls held up against the teeth of a ratchet-wheel upon a 
 cylindrical piece, through which the rod passes at the upper end of the percussion cylinder. This 
 cylindrical piece is provided on the inside with a groove in which a rib upon the rod slides. The 
 action of the pawls in causing the wheel to revolve will be apparent from the drawrng. 
 The feed motion is communicated by hand in the usual manner by means of a screw and crank 
 handle, or wheel, as described in Dubois-Fran9ois machine. This is the mode of feeding 
 adopted in wliat is known as the " low-pressure " machine. In the " high-pressure " machine, 
 which is made of smaller cylinder dimensions, the feed is made automatic by connecting the 
 mechanism with the rotating gear. 
 
 The following are the principal dimensions of the machine : Total length, 23 inches ; weight, 
 100 lb. ; diameter of cylinder, 2^ inches; diameter of back piston-rod, 1 inch ; diameter of forward 
 piston-rod, 1^ inch; maximum length of stroke, 4 inches; weight of the striking mass, including 8-lb. 
 borer-bit, 24 lb.; length of feed, ISj inches. 
 
 If this machine be considered in relation to the afore-given conditions, it will be found that it 
 fails to satisfy the first and the second. There is a considerable degree of complexity in 
 the design, and many of the parts are exposed. Hence we should expect that when subjected to 
 the ordinary conditions of work, it would be liable to frequent derangement ; and as a matter of 
 fact the inference is true. No machine could work more satisfactorily than the Sachs so long as the 
 circumstances are favourable, and the various parts remain in perfect order ; but the rough usage of 
 actual practice speedily occasions a necessity for repairs. The third, fourth, fifth and sixth con- 
 ditions are fully satisfied. The complete dependence of the motion of the slide-valve upon that 
 of the piston, and the ample clearance allowed at each end of the cylinder, effectually remove 
 any tendency that might exist for the piston to strike the cylinder covers. A. large amount 
 of clearance is usually condemned as wasteful of the motor fluid. Such an opinion is, however, an 
 erroneous one. It is true that the quantity of fluid represented by the cubic capacity of the 
 clearance space is not utilized upon the rock, but it is utilized in a very effective manner upon the 
 machine. A rock drill cannot be compared with an ordinary engine. The circumstances under 
 which it has to work are such as tend to cause its rapid destruction ; and if this tendency can be con- 
 siderably lessened by the expenditure of a small additional quantity of fluid at each stroke, such an 
 expenditure ought to be regarded as a true economy. It costs less to generate a little more steam or 
 to compress a little more air per hour, than to have a machine constantly in the repairing shop, a store 
 of spare machines at hand as a provision against breakage, and, which is still more important, con- 
 tinual delays at the working face. 
 
 The seventh condition is not fulfilled by the Sachs drill. The connection between the slide-valve 
 and the piston is such that the latter must always make its full stroke. The eighth and ninth condi- 
 tions are fulfilled, but the tenth is not satisfied. The automatic feed takes place in a regular manner, 
 
SHAFT-SINKING. 159 
 
 the forward motion proceeding by a certain definite quantity at each stroke of the piston. The 
 eleventh condition is not satisfied in the high-pressure machine, and the twelfth neither in that nor 
 in the low-pressure machine. 
 
 The Burleigh Rock-Drill. — The Burleigh machine-drill, which is of American origin, claims 
 attention by reason of its having been employed in the important work of excavatii.g the Hoosac 
 tunnel. Since that time it has been somewhat largely applied to mining operations, and with a 
 considerable degree of success. This machine, which is shown in the sections, Figs. 309 and 312, 
 consists essentially of a cylinder A, a piston B, with its rods, and a valve gear a, h. Both the back 
 and forward piston-rods pass through stuffing boxes in the cylinder ; to the forward rod the borer-bit 
 is fixed by the means shown in Figs. 309 and 310 ; the back rod, which is made smaller in diameter 
 than the forward rod, to give a larger piston area on that side, terminates in an annular protuberance. 
 This protuberance on the piston-rod is intended to strike alternately during its reciprocating motion 
 the back and forward arms of the tappet lever a, to which the rod of the slide-valve is attached. It 
 will be evident that the rocking motion of the lever thus produced will communicate the requisite 
 reciprocating motion to the valve, and by this means the desired action of the piston is ensured. To 
 effect the rotary motion of the latter, the back piston-rod is provided with a spiral feather, which 
 works in a corresponding groove in a cylindrical piece fitting into the back portion of the cylinder. 
 This cylindrical piece is provided on the outside with teeth, thereby forming a kind of ratchet-wheel, 
 as shown in Fig. 312. A detent held up by a spring prevents the piece from turning in one 
 direction, but allows it to revolve freely in the contrary direction. By this means the piston is made 
 to turn partially round during the back stroke ; but during the forward stroke the piston turns the 
 cylindrical piece before described, the motion of which in that direction is unrestrained by the detent. 
 The forward motion of the cylinder, or feed motion, is effected automatically by means of the screw 
 F, actuated by suitable mechanism. This feed-screw passes through a gallows-frame M, affixed to the 
 back end of the bed-plate, and again through a feed-nut into the cylinder. The end of the piston is 
 drilled out, in order that the feed-screw may not be struck by the former during its oscillations; The 
 feed-nut is secured between two collars in a manner to allow of easy revolution, and its outer edge is 
 cut into a ratchet, into which works a pawl actuated by the piston. The turning of the nut by this 
 means upon the fixed screw moves the cylinder forward. The mechanism by which this is accom- 
 plished is shown in Figs. 311 and 312. When the tool has penetrated the rock, and the piston 
 consequently advanced nearer the front cylinder cover, the protuberance upon the back piston-rod 
 strikes against the catch d, and thereby releases the lever e. The latter is then forced inwards by a 
 spring, so as to be struck by the head of the piston at the return stroke, by which means it is again 
 restored to its original position. The other end of the lever being connected to the pawl before 
 mentioned, the feed-nut is turned by the extent of one tooth. This action is repeated as the penetra- 
 tion of the tool progresses. Frequently the automatic feed gear is omitted from the construction, 
 and the necessary motion communicated by hand. 
 
 The principal dimensions of this machine are the following: Total length, 51 inches; weight, 
 166 lb. ; diameter of cylinder, 2f inches ; diameter of back piston-rod. If inch ; diameter of forward 
 piston-rod, 2\ inches ; maximum length of stroke, 4| inches ; weight of the striking mass, including 
 8-lb. borer-bit, 34 lb. ; length of feed, 22 inches. 
 
 An examination of the Burleigh machine relatively to the conditions previously enunciated will 
 show that it does not satisfactorily fulfil the first and the second of those conditions. There exists 
 
160 MINING ENGINEERING. 
 
 considerable complication of parts, and many of the parts are of a fragile character. The strildng 
 gear by which the valve is actuated would appear to be liable to very rapid wear and frequent 
 derangement. Also its exposed situation on the outside of the machine must tend to favour the 
 occurrence of such results. The mechanism for producing the automatic feed is of a delicate and 
 somewhat complicated character. The third and the fourth conditions are fairly, and the fifth 
 perfectly satisfied. The sixth condition is not fulfilled, inasmuch as the tappet gear is exposed to 
 violent shocks. The seventh condition is not satisfied. The eighth condition is fairly complied with ; 
 the ninth and tenth are fully satisfied. The eleventh condition is not fulfilled, and the twelfth is 
 fulfilled in only a fairly satisfactory manner. 
 
 The Kainotomon Rock-Drill. — The Kainotomon machine-drill was introduced as an improvement 
 upon the Burleigh, and a glance at its parts will show that the design- and construction of that 
 machine have been greatly simplified. The Kainotomon has been extensively em]')loyed in mining 
 and quarrying operations. The variety of the work to which it has been applied has furnished a 
 severe test of its suitability for the purpose for which it is designed, and it would appear from report 
 that it has undergone this test in a satisfactory manner. The quality which above all others is recom- 
 mendatory of a machine rock-drill is durability, and durability is mainly dependent upon simplicity. 
 Judged from this point of view, the Kainotomon should be greatly superior to the Burleigh. The 
 machine will be found illustrated on Plate XXIY. Fig. 314 is a front elevation of the cylinder ; 
 Fig. 313 is a longitudinal section through the machine ; Fig. 315 is a cross section showing the valve 
 in position; Fig. 316, an elevation showing the valve face with cover removed; and Figs. 317 and 
 318 represent different views of the valve. 
 
 The Kainotomon rock-drill consists essentially of a cylinder A, a piston and piston-rod B 0, and 
 the valve gear at F. The valve F, shown in Figs. 313 and 315, is pivoted at H ; it has an arm Gr, 
 the projection / on which is struck by the two pistons alternately during the reciprocating motion 
 of the latter ; by this means the requisite motion is communicated to the valve. The motor fluid is 
 admitted through k and the ports g g, Figs. 313 and 316, and exhausted through the port h. The 
 rotation of the tool is effected by the same means in the Kainotomon as in the Burleigh machine, the 
 position only of the parts being changed. The piston-rod passes through a cylindrical piece D, called 
 the rotation tube, placed in the neck of the cylinder, and held in position by the washer D'. This 
 tube is provided with a spiral slot a, in which works a projection or feather h in the piston-rod. On 
 the upper end of the tube D are ratchet-teeth c, into which is forced the pawl d by means of a spring 
 e, the pawl and spring being held in position by the gun-metal cap d'. The teeth and pawl are 
 arranged so as to compel the piston-rod to rotate during the backward stroke, and to allow it to turn 
 freely during the forward stroke. In the forward end of the cyhnder is an elastic packing-rino- E', 
 which is held in position by a steel washer E ; this packing ring serves as a buffer to mitigate tlie 
 destructive effects of the blow should the piston strike against the forward end of the cylinder. The 
 feed motion is commxmicated by hand, by means of the feed-screw L, which runs parallel with the 
 cylinder, and is held by the lugs M M cast upon the cylinder. The machine slides in the jacket T. 
 The universal clamp U deserves special attention, as it allows the machine to be turned in any direction 
 and to be fixed upon the cylindrical bar Y, by simply tightening the set-screw W, which acts upon 
 the gripping plates i and k, and the washer to. 
 
 The following are the principal dimensions of the machine : Total length, 36 inches ; weight, 
 205 lb.; diameter of cylinder, Z\ inches; diameter of piston-rod, 2 inches; maximum length of 
 
SHAFT-SINKING. 161 
 
 stroke, 4| inches ; weight of the striking mass, including 8-lb. borer-bit, 53 lb. ; length of feed, 
 18 inches. 
 
 Considered relatively to the conditions necessary of fulfilment, the Kainotomon will be found to 
 satisfy the requirements of the first and the second in a manner that leaves but little to be desired. 
 The construction is extremely simple ; there is no outside gear to be exposed to injury, and the 
 moving parts consist only of the piston and the valve. The third condition is not fulfilled. The 
 fourth and the fifth conditions are fully satisfied ; but the sixth is not wholly complied with, as 
 the valve is subjected to violent shocks from the blows of the pistons. This defect prevents the 
 attainment of a high piston velocity, and not unfrequently results in the valve being knocked off 
 the face. The seventh condition is fulfilled in a fairly satisfactory manner. The eighth condition is 
 not satisfied, inasmuch as the forward piston is liable, under the circumstances indicated, to strike 
 against the forward end of the cylinder. There is no clearance space allowed at this end of the 
 cylinder ; but there is, as already described, an elastic packing-ring, which tends greatly to mitigate the 
 destructive effects of the blows struck. The remaining conditions, with the exception of the tenth, 
 which does not apply in this case, as the feed motion is comnmnicated by hand, are completely fulfilled. 
 
 The McKean Rock- Drill. — The characteristic peculiarities of the McKean machine drill are 
 shown on Plate XXV., Figs. 315 to 318. Besides the anterior piston-rod to which the tool is attached, 
 there is a posterior rod which passes through the back end of the cylinder, and is prolonged through 
 the valve and feed-gear chamber situate behind the cylinder. Upon this prolongation of the rod is 
 an enlargement or a swelling of an ovoid form, as shown in Fig. 315. During the reciprocating 
 motion of the piston, this enlarged portion strikes alternately the arms I and V which hang upon the 
 opposite sides of the piston-rod. By this means an oscillating motion is produced in the rod upon 
 which the arms are fixed, which motion is communicated to the valve ; the form and action of which 
 will be understood from the drawings. To give the requisite rotary motion to the tool, the enlarged 
 portion of the piston-rod is provided with spiral teeth which gear into corresponding spiral teeth on a 
 rotary cam-spindle o. This cam-spindle is provided with a ratchet-wheel which is held by a pawl, so 
 that the cam may turn only in one direction, namely, during the backward stroke of the piston. To 
 produce the feed motion, a ratchet-wheel q is placed loosely upon the feed-screw n. This wheel is 
 connected by means of the arm q' with the arm or lever V upon the valve-rod, as shown in Fig. 315, 
 and by this means the oscillating motion of the latter is communicated to the wheel. This motion 
 is transmitted to a crown ratchet-wheel p, which is held up to the wheel 5- by a spring, and by 
 means of which the cylinder is moved forward upon the feed-screw n. Such are the general and 
 distinctive features of the McKean drill as applied in the St. Gothard tunnel. A lighter form of 
 this machine is made ; but as the proprietor has thought it desirable to withhold information con- 
 cerning the details of its construction, we are unable to consider it here, or to enter more minutely 
 into the design of the form we have illustrated. This action is the more to be regretted, as it points 
 to inferences of an unfavourable character. 
 
 The following are the principal dimensions of the McKean drill: Total length, 38 inches; 
 weight, 150 lb. ; diameter of cylinder, 3 inches ; diameter of anterior piston-rod, 2 inches ; diameter 
 of posterior piston-rod, 1-j inch; maximum length of stroke, 4 inches; weight of the striking 
 mass, including 8-lb. borer-bit, 32 lb. ; length of feed, 12 inches. 
 
 An inspection of the figures on Plate XXV., illustrative of the McKean drill, will show that it 
 fulfils the first four conditions in a fairly satisfactory manner. The fifth condition is fully satisfied ; 
 
 T 
 
162 MINING ENaiNEEEING. 
 
 the sixth fairly. The seventh condition does not appear to be fulfilled. The remaining conditions, 
 except the tenth, are satisfactorily complied with. The tenth is clearly violated, as the feed motion, 
 being communicated by the lever which actuates the valve, is continuous. Sometimes the McKean 
 drill is constructed to be fed forward by hand ; and in this case the rotary motion of the tool is taken 
 from the feed motion : thus the tenth condition is violated in this construction also. 
 
 The Tngersoll Hock-Drill. — The Ingersoll machine-drill is of recent introduction, and as an 
 improvement upon many pre-existing machines of a like character, it possesses numerous claims to 
 notice. The designers of this drill have evidently kept in view the conditions under which rock- 
 perforating machinery has to work, and they have succeeded in fulfilling the requirements in an 
 eminently satisfactory degree. The peculiarities of the Ingersoll drill will be rendered apparent by 
 the following description of its design and construction, and the illustrations upon Plate XXY. 
 
 In Figs. 319 to 321, E is the cylinder, M the piston, and L the piston-rod. The valve gear is 
 actuated by the piston through the medium of tappets, and consists of a slide-valve M', two valve 
 rods or spindles B, and two tappet levers H, The action of this valve gear and of the piston needs 
 no description. The rotary motion of the tool is obtained by means of the spirally grooved bar S 
 recessed into the back end of the piston. A cap screwed into the piston is provided with studs or 
 feathers to run in the grooves of the bar. On the end of the latter is a ratchet-wheel, into the teeth 
 of which a pawl is held by a spring. This pawl, as in the case of some of the machines already 
 described, forces the piston to turn during the back stroke, but allows the spiral bar to rotate during 
 the forward stroke. The forward motion of the cylinder, or feed motion, is produced automatically 
 in the following manner. As the tool penetrates the rock, the piston approaches the forward end of 
 the cylinder, and strikes against a tappet lever H', which partially rotates the rod R in the manner 
 shown in Fig. 319. This rod turns, by means of pawls and ratchet-teeth, a nut upon the back end 
 of the cylinder, through which nut passes the feed-screw P, as shown at V. The rotation of this 
 nut upon the fixed feed-screw causes the cylinder to advance. 
 
 The following are the principal dimensions of this machine: Total length, 30 inches; weight 
 155 lb. ; diameter of cylinder, 2f inches ; diameter of piston-rod, 2 inches ; maximum length of 
 stroke, 4 inches ; weight of the striking mass, including 8 lb. borer-bit, 26 lb. ; length of feed, 19 inches. 
 
 If the Ingersoll drill be considered relatively to the conditions laid down on a foregoing page 
 as necessary of fulfilment, it will be found to satisfy the whole of them, with the exception of the 
 sixth, in a more or less complete degree. The design and the construction are simple and strong, and 
 the moving parts are few in number. By the use of two tappet levers rocking through a small arc, 
 the violence of the shock produced by the blow delivered at each stroke of the piston is much lessened 
 and the durability of the parts proportionately increased. Another contrivance for ensurino- dura- 
 bility in the valve-gear consists in making the spindles B separate from the valve and from the 
 tappet levers. This expedient has been found in practice to act very satisfactorily. An ample 
 clearance space is provided at the forward end of the cylinder, but there is none at the back end. 
 Hence there is no hability of the piston striking the front cylinder cover, but this liability exists 
 for the back cover. To lessen the destructive effects of the blow, however, an elastic cushion is 
 provided. Thus it will be seen that the sixth condition is not satisfied. Judged by this standard 
 the Ingersoll appears to be an excellent machine ; and there can be no doubt that, hj its numerous 
 and great merits, it is destined to occupy a foremost place among rock drills. 
 
 The Darlington Bock- Drill.— The Darlington rock-drill is remarkable as the attainment of the 
 
SHAFT-SINKING. 163 
 
 highest degree of simplicity of parts possible in a machine. The valve gear of a machine drill is 
 especially liable to derangement. It mnst necessarily consist of several parts, and these parts must 
 as necessarily be of a somewhat fragile character. Besides this, when actuated by the piston 
 through the intervention of tappets, the violence of the blow delivered at each stroke is such as to 
 rapidly destroy the parts. In some of the machines already described, the force of these blows and 
 their destructive tendency have been reduced to a minimum ; but when every means of remedying 
 the evil has been employed, there remains a large amount of inevitable wear and tear, and a 
 liability to failure from fracture or displacement exists in a greater or less degree. Moreover, as 
 these effects are greatly intensified by increasing the velocity of the piston, it becomes at least unde- 
 sirable to use a high piston speed. To remedy these defects, which are inherent in the system, 
 J. Darlington proposed to remove altogether the necessity for a valve gear by radically changing 
 the mode of admitting the motor fluid to the cylinder. This proposal he has realized in the machine 
 which we have now to consider, and which will be found illustrated on Plate XXVI. 
 
 The Darlington rock-drill consists essentially of only two parts: the cylinder A, Fig. 322, with 
 its cover; and the piston B, with its rod. The cover, when bolted on, forms a part of the cylinder; 
 the piston-rod is cast solid with the piston, and is made sufficiently large at its outer end to receive 
 the tool. These two parts constitute an engine, and with less than one fixed and one moving 
 part, it is obviously impossible to develop power in a machine by the action of an elastic fluid. 
 The piston itself is made to do the work of a valve in the following manner : The annular space 
 affording the area for pressure on the fore part of the piston gives a much smaller extent of surface 
 than that afforded by the diameter of the cylinder, as shown in Fig. 322 ; and it is obvious that, by 
 increasing or diminishing the diameter of the piston-rod, the area for pressure on the one side of the 
 piston may be made to bear any desired proportion to that on the other side. The inlet aperture 
 or port C being in constant communication with the interior of the cylinder, the pressure of the fluid 
 is always acting upon the front of the piston ; consequently, when there is no pressure upon the 
 other side, the piston will be forced backward in the cylinder. During this backward motion the 
 piston first covers the exhaust port D, and then uncovers the equilibrium port E, by means of which 
 communication is established between the front and back ends of the cylinder, and consequently the 
 fluid made to act upon both sides of the piston. The area of the back face of the piston being greater 
 than that of the front face by the extent occupied by the piston-rod, the pressure upon the formei- 
 first acts to arrest the backward motion of the piston, which by its considerable weight and higli 
 velocity has acquired a large momentum, and then to produce a forward motion, the propelling 
 force being dependent for its amount upon the difference of area on the two sides of the piston. As 
 the piston passes down, it cuts off the steam from the back part of the cylinder and opens the 
 exhaust. The length or thickness of the piston is such that the exhaust port D is never open to its 
 front side; but in the forward stroke it is open almost immediately after the equilibrium port is 
 closed, and nearly at the time of striking the blow. It will be observed that the quantity of fluid 
 expended is only that which passes over to the back face of the piston, since that which is used to 
 effect the return stroke is not discharged. 
 
 The means employed to give a rotary motion to the tool are deserving of special attention, as 
 being simple in design, effective in action, and well situate within the cylinder. These means 
 consist of a spiral or rifled bar H, having three grooves, and being fitted at its head with a ratchet- 
 wheel Gr, recessed into the cover of the cylinder. Two detents J J, Fig. 324, also recessed into the 
 
 Y 2 
 
164 MINING ENGINEERING. 
 
 cover, are made to fall into the teeth of the ratchet-wheel by spiral springs. These springs may, in 
 case of breakage, be immediately renewed without removing the cover. It will be observed that 
 this arrangement of the wheel and the detents allows the spiral bar H to turn freely in one direc- 
 tion, while it prevents it from turning in the contrary direction. The spiral bar drops into a long 
 recess in the piston, which is fitted with a steel nut, made to accurately fit the grooves of the spiral. 
 Hence the piston during its instroke is forced to turn upon the bar ; but during its outstroke it 
 turns the bar, the latter being free to move in the direction in which the straight outstroke of the 
 piston tends to rotate it. Thus the piston, and with it the tool, assumes a new position after each 
 stroke. 
 
 The following are the principal dimensions of the Darlington drill : Total length, 36 inches ; 
 weight, 100 lb. ; diameter of cylinder, 3| inches; diameter of piston-rod, 2^ inches; maximum 
 length of stroke, 4 inches; weight of the striking mass, including 8-lb. borer-bit, 35 lb.; length of 
 feed, 24 inches. 
 
 The mode of fixing the cutting tool to the piston-rod is a matter deserving some attention. As 
 the tool has to be changed often more than once during the progress of a bore-hole, it is important 
 that the change should be accomplished in as short a time as possible ; and as the vibration of the 
 machine a ad the strain upon the tool are necessarily great, it is equally important that the tool be 
 firmly held. It is also desirable that the mode of fixing the tool shall not require a shoulder upon 
 the latter, a slot in it, or any peculiarity of form difficult to be made in the smithy. If the foregoing 
 machines be compared in this respect, it will be found that the Darlington fulfils the requirements of 
 expedition in fixing, firmness of retention, and simplicity of form most satisfactorily. The means 
 and the method are the following : The outer end of the rod or holder is first flattened to afford a 
 seat for the nut, as shown in Figs. 322 and 327. The slot is then cut and fitted tightly with a piece 
 of steel K, forged of the required shape for the clamp, and the holder is afterwards bored to receive 
 the tool while the clamp is in place. This clamp K is then taken out, its fitting eased a little, and 
 its end screwed and fitted with a nut. When returned to its place in the holder, the clamp, in 
 consequence of the easing, can be easily drawn tight against the tool, by which means it is firmly 
 held in position. The shank of the tool is turned to fit the hole easily, and the end of it is made 
 hemispherical to fit the bottom of the hole, upon which the force of the reaction of the blow is 
 received. 
 
 If the Darlington drill be considered relatively to the conditions laid down as necessary to be 
 fulfilled, it will be found not only that it satisfies the whole of them, but that it satisfies them in 
 the most complete manner. It would seem impossible to attain a higher degree of simplicity of form, 
 or to construct a machine with fewer parts. The absence of a valve or striking gear of any kind 
 ensures the utmost attainable degree of durability, and allows a high piston speed to be adopted 
 without risk of injury. As the piston controls its own motion, there is no liability to strike against 
 the cylinder cover. The stroke may be varied in length from half an inch to 4 inches, and as the 
 machine will work effectively with a pressure of 10 lb. to the inch, holes may be started with the 
 greatest ease. With a pressure of 40 lb., the machine makes 1000 blows a minute, a speed that may 
 be attained without causing undue strains or vibration. This alone constitutes a very great advan- 
 tage. It must, indeed, be conceded that a careful consideration of the merits of this drill shows it 
 to be admirably adapted to the work required of it, and leads inevitably to the conclusion that it ia 
 the most perfect machine for rock boring that has yet been produced. 
 
SHAFT-SINKING. Ifio 
 
 The Wavsop Roch-Drill. — The Warsop machine-drill claims special attention on account of 
 certain peculiarities of design of a strongly characteristic nature. The designers of this drill have re- 
 introduced, under greatly improved conditions, a principle long since abandoned. Schwarzkopf was 
 the first to construct a rock-perforating machine in which the cutting tool was detached from the 
 piston-rod, and in which it was struck by the latter after the manner of a steam hammer. The 
 principle thus adopted is, as we have already shown, false, and as the general design of 
 Schwarzkopf s machine was defective, it failed to establish itself in favour. This is the principle 
 that Messrs. Warsop and Hill have reintroduced; but they have so modified and improved the 
 general design and construction of the machine as to make it superior to many of its predecessors in 
 which the tool is made to reciprocate with the piston. This fact does not, however, render a false 
 principle true ; and it should be acknowledged that from this point of view the design of the Warsop 
 machine is defective. But it is claimed by the inventors, and it must also be acknowledged that 
 their statements in this respect are in some degree true, that the adoption of the principle of the 
 hammer involves the introduction of advantages which compensate any loss due to that princijjle. 
 The nature of these advantages will be described when we come to consider the machine relatively 
 to the conditions previously laid down as necessary of fulfilment. 
 
 The design and construction of the Warsop machine will be found illustrated upon Plate XXYI. 
 Fig. 328 being a longitudinal section of the drill ; and Fig. 329 a front elevation of the same. 
 
 In Fig. 328 C is the cylinder or main body and frame of the machine, cast in one piece. An 
 inner cylinder or casing D fits accurately into the cylinder C at its upper part, and is free to par- 
 tially rotate in cylinder 0. In the top of casing D is firmly fixed a twisted bar E of a flat section. 
 This bar passes through a disc of steel F firmly fixed in the piston Gr, down the centre of which a 
 hole is bored to receive the full length of the twisted bar. At the opposite end of the piston-rod A 
 is firmly cottered a head H having two wings h^ h^, fitting grooves cast in the frame C, and capable 
 of sliding freely up and down them. The head H is made to strike at each blow an anvil I, having a 
 recess at its lower part made to receive a drill or chisel. The end of the anvil is formed with a rim 
 round it, against which the end of the main body rests : this rim of anvil I has teeth cut round its 
 periphery, into which gears a smaller toothed wheel J, formed in one piece with the rod K and handle 
 L, in such a manner that by turning the handle L the drill inserted in I will be rotated. 
 
 The reciprocating action of the piston Gr is as follows : In the casing D four narrow longitudinal 
 portways are cut, shown in Fig. 328. These slots correspond, one at the top and one at the bottom 
 at opposite sides of the casing, with corresponding portways in the cylinder C, and in such a manner 
 that when the casing is partially turned round, one port at the top and one at the opposite side at the 
 bottom are closed, and the other two are open. Steam or air is admitted to the cylinder through 
 opening B, passes alternately through port 2 or 1 into the casing D, forces the piston Gr up and down ; 
 the steam or air exhausting alternately through ports 3 and 4, and out at the passage A. The 
 partial rotation of the casing D in the cylinder, and consequent regulation of the steam or air and 
 exhaustion from the interior, is efiected by the reciprocating motion of the piston G, which is pre- 
 vented from turning round by the wings K-, h^, causing the bar E to turn partially backwards and 
 forwards at each stroke in the disc F. By this means the piston Gr and anvil H are made to give 
 a succession of rapid blows on the anvil I, and consequently to the drill point, which is constantly 
 being turned round by the handle L, the machine itself being prevented from turning round 
 by a sleeve in which it slides, carried by the support upon which it rests. 
 
1-66 MINING ENGINEEEING. 
 
 In order to obtain increased simplicit}' of construction, the feed is made automatic. When 
 boring downwards, it is obvious that the machine will follow the tool as the latter penetrates the 
 rock. The same result is obtained when boring in an upward direction by means of a counterweight 
 suspended over a pulley fixed upon the support upon which the machine rests. 
 
 The following are the principal dimensions of the machine: Total length, 24 inches; weight, 
 80 lb. ; diameter of cylinder, 4 inches ; diameter of piston-rod, 3 inches ; maximum length of stroke, 
 4 inches ; weight of the striking mass, 40 lb. 
 
 Considered relatively to the conditions which every rock drill is required to fulfil, the "Warsop 
 machine will be found to satisfy the first four in a very complete manner. Of the fifth, the 
 first part, which requires the striking mass to be relatively of great weight, is satisfactorily fulfilled ; 
 but the second part, which requires this striking mass to strike the rock directly, is violated. 
 It has already been demonstrated that the loss of vis viva, due to the separation of the tool 
 from the piston, increases as the weight of the tool increases, and as the weight of the striking 
 mass decreases. In the Warsop drill, the weight of the anvil upon which the hammer-headed piston- 
 rod strikes must be added to that of the tool attached to it, and hence calculation will show that the 
 loss of work due to this cause must be very considerable. We are therefore compelled to view the 
 principle adopted as constituting a grave defect ; and we are also impelled, by the unquestionable 
 merits of the machine, to express our opinion that by the removal of this defect the machine 
 would be rendered a very efficient one. It is, hov^ever, claimed by the designers that when the 
 ordinary method of reciprocation is adopted, the friction of the tool against the rubbish in the 
 hole, or against the sides of the hole when the machine support has been shaken a little out of 
 2DOsition, is very great, often amounting, indeed, to more than the work of actual boring, and that 
 by the adoption of the principle of the Warsop drill this loss is not incurred. This estimate of the 
 value of the friction, which is doubtless considerable, is certainly excessive ; and though it may 
 perhaps be proved that in certain cases the loss by friction occasioned in this way is equal to that 
 due to the principle adopted in the design of the machine, it is diificult to see what is really gained. 
 
 The remaining conditions, with the exception of the ninth, are satisfactorily fulfilled. The non- 
 fulfilment of the ninth constitutes another defect. It has been proved upon a preceding page that 
 the rotation of the drill shall, rather than the feed, take place automatically. In the Warsop 
 machine, the rotary motion is communicated by hand, while the feed is made automatic. Moreover, 
 the nature of this feed motion is objectionable. The coimterweight, by constituting a heavy load to 
 remove from place to place, and occupying considerable space when suspended in position, tends 
 to destroy the advantages of fight weight and small dimensions in the machine itself. Also the use 
 of this counterweight would seem to militate against the att linment of perfect freedom of posi- 
 tion in the support, and of expedition in removing the machine from one situation or position to 
 a;nother. 
 
 The Diamond Eock-Drill. — The diamond drill, the principle and the construction of which were 
 explained and described when treating of deep borings, has been successfully applied to boring for 
 ordinary blasting purposes. As this machine cannot under existing arrangements be used by any 
 other than the Diamond Rock-Drill Company, who undertake to perform the work by contract it 
 does not seem desirable to illustrate its construction. Such illustration, moreover, appears the less 
 necessary, as the principle of the diamond drill, unequalled as it is for deep prospective borings, is 
 less suitable for the ordinary purposes of shaft-sinking and heading driving than that upon which 
 
SHAFT-SINKING. 167 
 
 the machines described in the foregoing pages act. For such work, the diamond will probably fail 
 to hold its ground against the percussive machines. 
 
 It will appear that, when judged by the standard which we have adopted, the foregoing 
 machine drills differ widely in point of merit. Some are constructed upon principles and in a 
 manner that are at variance with the conditions of work to which they must necessarily be subjected ; 
 while others, embodying the teachings of experience, fulfil every requirement in a manner that 
 leaves little to be desired. There can be no reasonable doubt that the latter are destined not only to 
 occupy alone the field at present shared by the inferior machines, but to do important service in 
 expediting mining operations, and in thereby promoting, in no insignificant degree, the prosperity of 
 mining enterprise. Arranged according to their fulfilment of the conditions necessary in a rock drill, 
 the machines previously described appear in the following order, which order will be observed in the 
 subsequent table of dimensions : The Darlington, the Ingersoll, the Kainotomon, the Warsop, the 
 McKean, the Sachs, the Burleigh, and the Dubois-Frangois. 
 
 Borer-Bits. — ^The form and the dimensions of the cutting tools, variously described as " drills," 
 " borers," and " bits," used in machine rock-perforators, are matters of great practical importance, 
 and therefore deserving of careful attention. The dimensions are determined mainly by two 
 conditions, namely, the necessity for sufficient strength in the shank of the tool, and the necessity for 
 sufficient space between the shank and the sides of the hole to allow the debris to escape. Experience 
 has shown that these two conditions are best fulfilled when the distance between the sides of the hole 
 and the shank of the tool is from -^ inch to \ inch. The form of the cutting edge is affected by 
 several conditions. The form first adopted was very naturally that possessed by hand drills, namely, 
 the chisel edge, which was sometimes made straight, and sometimes bowed. It was then attempted 
 to increase the useful effect of the machines, and especially the rapidity of the boring, by enlarging 
 the surface of the cutting edge. This was first effected by forming the bit of two chisel edges 
 crossing each other at right angles, and called therefrom the " cross " bit. The tool thus constructed 
 was found to effect the object desired in a very satisfactory manner at the commencement of the 
 boring, when there was a free surface to strike upon ; but as the boring progressed in depth its 
 action became less and less effective, owing to its form preventing the ready escape of the de'bris. 
 To remedy this defect, the cutting edges were made to cross each other obliquely, so as to form the 
 letter X, and called therefrom the X bit. By this means the two chisel edges were retained, while 
 the breadth of the bit was considerably reduced. This form cleared the hole much more effectively 
 than the cross, but yet not in a sufficiently satisfactory manner to warrant its general adoption. 
 Another modification of the form was therefore made, and this time that of the Z was adopted, the 
 upper and lower portions of which were arcs of circles struck from the centre of the bit in tlie 
 direction contrary to that of the rotation. With this form of tool, the hole cleared itself readily of 
 the debris. But besides this advantage, which was the only one sought, others of an important 
 character were involved. With the forms thitherto adopted, the corners of the bit were rapidly 
 worn off by friction against the sides of the hole. With the Z form this wearing no longer occurred, 
 by reason of the comparatively large surface exposed to the friction. Another advantage possessed by 
 the Z form of bit lies in its tendency to bore the hole truly circular. It is evident that the single chisel- 
 edge bit may rotate in a hole, not only when it is circular in section, and of a diameter equal to the 
 width of the edge, but also when the section is a curvilinear triangle, constructed upon an equilatei-al 
 triangle, the side of whicK is equal to the width of the edge, and each summit of which is the centre 
 
168 MINING ENGINEEKING. 
 
 of a circular arc of 60° passing through the other two. Again, and more geueral^^ the section 
 might be a polygon composed of an odd number of curvilinear sides, each of which was an arc of a 
 circle described from the opposite summit, as a centre, with a radius equal to the width of the cutting 
 edge. This tendency to deviate from the circular form of section in the bore-hole was found to be 
 completely corrected by the adoption ot the Z bit ; and hence it has come to pass that this form of 
 cutting edge is now generally employed. It must not, however, be inferred from this statement that 
 the other forms have been altogether abandoned ; on the contrary, they are constantly employed 
 under those conditions to which they have been proved suitable. Thus, the cross-bit is well adapted 
 for the pui'pose of starting a hole, and for boring in fissured rock, and the single chisel-bit may be used 
 with advantage in rock of a very hard nature. Also, generally, each of the various structuies and 
 textures of rocks will be found to yield more readily to one form of cutting edge than another, and 
 these circumstances afford occasion for the application of knowledge and the exercise of judgment. 
 
 The sharpening of bits of a form other than that of the single chisel is effected by means of 
 " swages." The tempering is performed in the way already described in reference to hand drills. 
 As in the latter case, both the degree of temper and the angle of the cutting edge should be 
 determined according to the hardness of the rock to be penetrated. The percussive action of the tool 
 in machine drills appears to be admirably suited to its nature, since it has been found by experience 
 to lead to this remarkable result, namely, that for a given length of boring, executed far more 
 rapidly than by hand, the wear of the cutting edge is five or six times less. The saving of steel due 
 to this cause constitutes one source of economy in machine boring. The quality of the steel used for 
 borer-bits should be the best procurable, since it will be found conducive both to rapidity of boring 
 and to economy of cost to employ the most suitable material. Sometimes the shank is of wrought 
 iron ; but more often the tool consists wholly of steel, the bars from which it is cut being usually 
 octagonal in form. The cost of these bars has been given in another place. As in the case of hand- 
 boring, each successive length of tool must diminish slightly in the width of its cutting edge, for 
 reasons that have been already explained. The diminution need not be great ; about ^ of an inch 
 may be considered sufficient. Care must, however, be taken to ensure the proper dimensions being 
 given to the edge, and it will be advantageous to possess an accurate gauge through which the tool 
 may be passed previously to its being fixed in the machine. It is also important that the tool should 
 be truly centered, that is, the centres of the edge of the bit, of the shank, and of the piston-rod, 
 should be perfectly coincident. It may be observed here that it will be found conducive to rapid 
 progress to have an abundant supply of bits always ready at hand. 
 
 The Stretcher Bar. — The stretcher bar has been already alluded to as fulfilling most completely 
 the requirements of a machine-drill support. Such a bar is represented on Plate XXVII., Fig. 330. 
 In this bar, which is that used with the Darlington drill, rigidity and lightness are combined in the 
 highest possible degree by adopting the hollow section. The stretcher bars used with the other 
 machines are similarly constructed. 
 
 Economy of Machine Drilling. — It was stated on a former page that the substitution of machine 
 for hand drilling led rather to a saving of time than of money. This remark had reference solely to 
 the machines that have been for some time in use. With those of recent introduction, in which the 
 numerous imperfections of the early perforators do not exist, the saving of cost may be made fully 
 equal to the saving of time. Increased simplicity of construction must notably reduce the annual 
 outlay in repairs, which, together with the cost occasioned by the consequent delays, has hitherto 
 
SHAFT-SINKING. 
 
 169 
 
 formed so large a proportion of the working expenses ; and increased facilities for boring in any 
 desired situation or position must lead to a diminished consumption of explosive compounds. Hence 
 we may reasonably expect that as improved methods are adopted, and greater skill, the result of 
 more extensive knowledge, is applied, the proportionate cost of excavating by machinery will be 
 lessened in a marked degree. 
 
 EOCK-BOEING MACHINES— COMPAEATIVE TABLE OE DIMENSIONS. 
 
 Total length of the macliiiie, borer-bit not 
 included 
 
 Weight of the machine complete, without 
 the borer-bit 
 
 Internal length of the cylinder 
 
 Diameter of the cylinder 
 
 Length of the piston .. 
 
 Effective posterior area of the piston 
 
 „ anterior » » •• 
 
 Maximum stroke of the piston 
 
 Weight of the striking mass — piston, 
 
 piston-rod, and 8-lb. bit 
 
 Volume of air expended in the forward 
 
 stroke 
 
 Volume of air expended in the back stroke 
 Volume of air lost on account of clearance 
 
 space 
 
 Volume of air expended for each blow 
 
 Force of propulsion with pressure of 30 lb. 
 Force of repulsion with pressure of 30 lb. 
 Nature of the feed motion 
 
 Length of feed 
 
 Darlington. 
 
 In. 
 
 86 
 
 lb. 
 
 100 
 
 tn. 
 11 
 
 Si 
 
 9-62 
 4-71 
 
 4: 
 
 lb. 
 
 35 
 
 in. 
 
 38-4:8 
 0-0 
 
 14-43 
 52-91 
 
 lb. 
 
 182-3 
 
 106-3 
 
 hand 
 
 in. 
 
 24 
 
 2 
 
 IiigersoU. 
 
 80 
 lb. 
 
 155 
 
 In. 
 11 
 
 6 
 5-94 
 2-80 
 
 4 
 
 lb. 
 
 28 
 
 In. 
 
 23-76 
 11-20 
 
 2-80 
 87-76 
 
 lb. 
 
 206-2 
 
 66-0 
 
 automatic 
 
 in. 
 
 19 
 
 Kaiiioto- 
 mon. 
 
 in. 
 
 36 
 
 lb. 
 
 205 
 
 in. 
 15 
 
 8 
 9-62 
 
 6-48 
 
 lb. 
 
 53 
 
 In. 
 
 45-69 
 30-77 
 
 20-86 
 97-32 
 
 lb. 
 
 341-6 
 141-4 
 hand 
 
 in. . 
 
 18 
 
 4 
 
 Warsop. 
 
 6 
 
 McKean. 
 
 In. 
 24 
 
 lb. 
 
 80 
 
 in. 
 
 8 
 4 
 
 2^ 
 
 12-56 
 5-49 
 4 
 
 lb. 
 
 40 
 
 in. 
 
 50-24 
 21-96 
 
 15-30 
 87-50 
 
 lb. 
 
 416-8 
 
 124-7 
 
 automatic 
 
 In. 
 
 38 
 
 lb. 
 
 150 
 
 In. 
 7 
 
 8 
 
 2 
 5-85 
 3-93 
 
 4 
 
 lb. 
 
 32 
 
 in. 
 
 23-40 
 15-72 
 
 4-99 
 44-11 
 
 lb. 
 
 207-5 
 85-9 
 
 6 
 
 Sachs, 
 
 7 
 
 Burleigh. 
 
 23 
 
 lb. 
 
 100 
 
 * in. 
 
 8 
 
 2f 
 4-13 
 3 15 
 
 4 
 
 lb. 
 
 24 
 
 in. 
 
 16-52 
 12-60 
 
 5-04 
 34-16 
 
 lb. 
 
 171-3 
 
 70-5 
 
 in. 
 
 51 
 
 lb. 
 
 166 
 
 in. 
 
 2f 
 
 n 
 
 3-54 
 1-97 
 
 4.1 
 lb. 
 
 34 
 
 15-93 
 8-86 
 
 1-86 
 26-65 
 
 lb. 
 
 140-2 
 25-1 
 
 8 
 
 Duhois- 
 Fran(}ois. 
 
 in. 
 86 
 lb. 
 
 480 
 
 In. 
 
 H 
 H 
 
 4-91 
 3-14 
 
 n 
 
 lb. 
 
 68 
 
 48-05 
 24-33 
 
 5-16 
 
 77-55 
 
 lb. 
 
 215-3 
 26-2 
 
 automatic automatic automatic hand 
 
 12 
 
 18 
 
 22 
 
 32 
 
 Compressed Air as a Motor Fluid. — The employment of compressed air as a means of trans- 
 mitting force may be regarded as one of the most remarkable mechanical achievements of the present 
 times. No doubt as a means of utilizing distant and yet unavailable sources of force, the importance 
 of this medium can hardly be over-estimated, for it is abundantly clear that it possesses qualities 
 which may render it productive of immense benefits in that direction. But it is in its application to 
 mining purposes, which afford the most favourable opportunities for its employment, that it is 
 destined to undergo its complete development and to attain its highest degree of usefulness. To the 
 altogether exceptional nature of the situations in which mining operations are carried on, the 
 peculiar character of these operations themselves, and the otherwise difficult conditions under which 
 they have to be performed, the qualities of compressed air render it particularly suitable. Its easy 
 conveyance to any point of the underground workings, and its ready application at any point ; the 
 improvement which it produces in the ventilative currents ; the complete absence of heat in the 
 reservoir and conducting pipes, a condition which tends greatly to their preservation ; these and 
 numerous other advantages, when contrasted with the defects of steam under like conditions, give to 
 compressed air a value which the mining engineer will fully appreciate. In applying a motor fluid 
 
 z 
 
IVO MINING ENGINEERING. 
 
 ■underground, it is rather a question of distributing eniall forces over a large number of points, than 
 of concentrating a large force at one or two points. This is particularly the case when it becomes 
 necessary to employ hauling engines, coal-cutting machines, and portable rock-drills, the posi- 
 tions of which are daily changing. To satisfy conditions such as these, compressed air is alone 
 admissible. 
 
 Great, however, as the merits of compressed air as a medium for transmitting force are, it 
 possesses defects of an important character. These defects, which have been strangely overlooked, lie 
 chiefly in its inherent and essential qualities as a gas, whereby a loss of the force to be transmitted is 
 occasioned. The amount of the loss due to this source is necessarily considerable ; but when due 
 precautions are not taken to keep it near its minimum limits, it may assume very grave proportions. 
 There can be no reasonable doubt that the best machines and appliances now in use for the compres- 
 sion of air are excessively wasteful of the motive force. This excessive loss must be attributed to 
 two causes : first, to a mistaken notion respecting the position held by air-compressing engines among 
 machinery ; and second, to a general want of attention to the mechanical properties of air. 
 
 It would seem to be assumed that air-compressing machines are mere temporary expedients, to 
 be erected for a time at a given place, and then removed to another. Hence small dimensions, 
 portability, and, above all, cheapness, have been the objects chiefly aimed at, to the sacrifice of 
 efficiency and the obstruction of improvement. It will be vain to look for a realization of the highest 
 attainable degree of perfection in the machinery designed for the production of compressed air, until 
 such machinery is viewed as constituting a portion of the permanent plant of a mine, to be protected 
 by suitable buildings, entrusted to competent hands, and in every way as attentively cared for as the 
 winding engines themselves. When compressing machines are regarded in this light, air will begin 
 to assume its proper development as a medium for the transmission of force. The second cause 
 alluded to, namely, the marked want of attention to the mechanical properties of air, may, perhaps, 
 be considered the natural concomitant of the first. Hence we may expect that when the one has 
 been removed, the other will speedily follow. Indirectly dependent upon the former cause, the 
 latter is, however, directly due to a general ignorance of the principles of thermo-dynamics. Thus 
 it becomes desirable to expound briefly these principles in so far as they affect the application of 
 compressed air to practical purposes. It would be beyond the scope of the present work to enter 
 into these questions abstractedly and in detail, or to discuss the means of determining with absolute 
 precision the values of given quantities under all conditions : such considerations find their place in 
 special treatises. But it will be found useful to place clearly before the mind of the engineering 
 student the fundamental principles of the subject, and to furnish him with the means of ascertaining, 
 with a degree of approximation sufficiently near for practical purposes, the value of the phenomena 
 which occur in an air-compressing machine. 
 
 The Tliermo-Mechanical Properties of Air. — In considering the properties of permanent gases, 
 that is, gases which, as far as our present knowledge extends, cannot be liquefied by the application 
 of cold and pressure, there are three variable quantities to be taken into account, namely, the volume 
 of the gas in question ; the elastic force exerted by it, or what amounts to the same thing, ih^ pressxire 
 necessary to retain it in that volume, and its temperature. These quantities, as it will hereafter 
 appear, are to a great extent dependent upon one another. 
 
 Volume.— By volume is understood the space, measured in cubic feet occupied by a unit, as 1 lb. 
 of air, at auy given moment. 
 
SHAFT-SINKING. 171 
 
 Pressure. — By pressure is understood the weight in pounds avoirdupois required upon every 
 square foot of surface to retain the air in a given volume. This pressure, it must be borne in mind, 
 includes the weight of the atmosphere, which is assumed to be in ail cases 14 • 70 lb. upon the square 
 inch, the actual weight when the mercurial barometer stands at 29*92 inches. 
 
 Temperature. — By temperature is understood the number of degrees measured by Fahrenheit's 
 scale on a perfect gas-thermometer, from a zero 461°* 2 below the zero of Fahrenheit's scale, that is, 
 49 3° • 2 below the freezing-point of water. This zero-point is that at which the elastic force of air 
 would completely disappear. 
 
 To illustrate the application of the foregoing terms, suppose a pound of air, a mean atmospheric 
 
 ■ J)ressure of 14 "7 lb. to the square inch, and a temperature of 60° Fahr. Under such conditions, 
 
 1 lb. of air will occupy a space of 13 "09 cubic feet; and if we represent the volume by v, the 
 
 pressure hj p, and the temperature by t, we shall have,j) = 18'09, jp = 14" 7 x 144 = 2116*8, and 
 
 ^=461*2 + 60 = 521*2. 
 
 Conditions of Equilibrium. — It is known that for a unit of weight of air, or any perfect gas, 
 the product of the pressure and the volume, divided by the temperature^ remains unaltered through 
 
 all conditions of change. That is, ^ = c, or pv = ct, c being a constant, which for air has the 
 
 value, 53* 15. 
 
 It now remains to show the relation existing between any two of the variable quantities when 
 the third is made constant. And here we confront three important and well-established laws, which 
 are the following : 
 
 I. If the volume be made constant, the pressure will vary directly as the temperature. 
 Symbolically expressed, \i pt represent the initial pressure and temperature, and pi ti the same 
 
 99 t 
 
 quantities changed in degree, then ^ = j . 
 
 II. If the pressure be made constant, the volume will vary directly as the temperature. That is, 
 
 V t 
 a vt and Vx t^ represent the volumes and temperatures, — = -; . 
 
 III. If the temperature be made constant, the volume will vary inversely as the pressure. Or, 
 
 expressed symbolically as before, \i pv and p^ v^ represent the pressures and volumes, — = t- . 
 
 V pi 
 
 As illustrations to these laws, suppose the following examples : First, if a pound of air at 
 atmospheric pressure and 60° Fahr. be retained in a closed vessel and heat applied to the latter, the 
 pressure of the enclosed air will be doubled when the temperature has been doubled. That is, the 
 initial temperature being 461*2 -f 60 = 521*2, the pressure will be doubled when the temperature 
 has been increased to 521*2 x 2 = 1042*4, or when the Fahrenheit thermometer marks 
 1042*4-461*2 = 581*2 degrees. 
 
 Second, if the air be retained in a cylinder in which is a piston free to move as the air expands, 
 and heat be applied, the volume of the enclosed air will be doubled when the temperature has been 
 doubled. That is, the initial temperature being 521*2 degrees absolute as before, to double the 
 volume the temperature must be increased to 521*2 x 2 = 1042*4, or to 1042*4 — 461*2 = 581*2 
 degrees Fahr. 
 
 And third, if it be required to reduce the volume of the air in the cylinder to one-half that 
 
 z 2 
 
1~2 MINING ENGINEEEING. 
 
 which, it possesses at any given, say atmospheric, pressure, when means are adopted to keep the 
 temperature constant, the pressure must be doubled. That is, if the air in the cylinder occupy a 
 space of one cubic foot, to compress it into a space of half a cubic foot, a pressure of 2116'8 X 2 
 = 423S'6 lb. to the square foot must be exerted. 
 
 Specific Heat. — It is -known that if a certain quantity of heat will raise the temperature of 
 a body one degree, twice that quantity will raise its temperature two degrees, three times the 
 quantity, three degrees, and so on. Thus we may obtain a measure of heat by which to determine 
 either the temperature to which a given quantity of heat is capable of raising a given body, or the 
 quantity of heat which is contained in a given body at a given temperature. The quantity of heat 
 requisite to produce a change of one degree in temperature is different for different bodies, but is 
 practically constant for the same body, and this quantity is called the specific heat of the body. The 
 standard which has been adopted whereby to measure the specific heat of bodies is that of water, the 
 unit being the quantity of heat required to raise the temperature of 1 lb. of water at its greatest 
 density 1° Fahr., that is, from 39° to 40°. The quantity of heat required to produce this change 
 of temperature in 1 lb. of water is called the "unit of heat," or the "thermal unit;" and as heat 
 and work are mutually convertible, it is evident that work may be expressed in thermal units, 
 or, if so desired, heat may be expressed in foot-pounds. The mode of measurement by thermal 
 units possesses the advantage of leading to the employment of smaller numbers than the other ; but 
 the foot-pound is, on the whole, the more convenient unit. The value of the thermal unit has been 
 indisputably proved by Joule to be equivalent to 772 foot-pounds. In other words, a weight of 
 772 lb. falling through a height of 1 foot generates sufficient heat to raise the temperature of 1 lb. 
 of water 1° Fahr., assuming that the whole of the heat so generated could be collected and applied to 
 that purpose. Or, conversely, the heat given out by 1 lb. of water in cooling 1° is sufficient to raise 
 772 lb. through a height of 1 foot, assuming that the whole of the heat so given out could be 
 collected and employed in doing work. 
 
 Having determined the specific heat of water, that of air may in like manner be ascertained and 
 expressed either in terms of the former or in foot-pounds. It has been proved by exhaustive 
 experiments, that if air be heated at constant pressure through 1° Fahr. measured on the air- 
 thermometer, the quantity of heat absorbed is 0*2375 thermal units, or 772 x 0*2375 = 183*35 
 foot-pounds, whatever the pressure or the temperature of the air may be. Thus the specific heat of 
 air at constant pressure is, measured in foot-pounds, 183*35. Similarly, it has been shown that 
 the specific heat of air at constant volume is, in thermal units, 0*1687 nearly, or in foot-pounds, 
 772 X 0*1687 = 130*20. Hence the ratio of the specific heat of air at constant pressure to that at 
 
 183 "35 
 constant volume is TgQToQ = 1'408, or, for practical purposes, say 1*41. We now observe that the 
 
 difference of the two specific heats of air is 53*15 ; that is, it is equal to c in +he foregoing equation 
 of equilibrium. Thus, if K^ represent the specific heat of air at constant pressure, and K„ the 
 specific heat at constant volume, both expressed in foot-pounds, we have the relation K — K = c. 
 
 Conversion of Heat into Work. — We now come to the important consideration of the conversion 
 of heat into work. As a convenient illustration, frequently employed, of what takes place in such a 
 case, suppose a cylinder of 1 square foot sectional area, and of indefinite length, fitted with a 
 balanced air-tight piston; and assume that the piston stands at a height of 13*09 feet from the 
 bottom of the cylinder; then, if the temperature be 60° Fahr., the cylinder will contain 1 lb. of a^r 
 and the pressure upon the piston will be that of the atmosphere only, that is, 2116*8 lb. 
 
SHAFT-SINKING. 173 
 
 First, let the piston be fixed, and let heat be applied to the cylinder until the temperature of the 
 contained air has been doubled, that is, until it has been raised from 60 + 461-2 to 2 (60 + 461-2) 
 degrees absolute. The volume being in this case constant, the pressure will by Law I. be doubled ; 
 that is, the pressure exerted against the piston and tending to force it upwards will be 2116 '8 lb. 
 in excess of that of the atmosphere tending to force it downwards. Also the quantity of heat 
 expended to produce this change will be 130 "2 x 521*2 = 67,860 foot-pounds; and in cooling 
 down to the original temperature this quantity of heat will be given out. In this case no work is 
 done, the whole of the heat expended has been employed in raising the temperature of the air. 
 
 Second, let the piston be free to move, and let 67,860 foot-pounds of heat be applied to the 
 
 pound of air contained in the cylinder. In this case, the pressure being constant, the air will expand 
 
 and force up the piston through a height equal to 1 9 ■ 3 feet, where it will stand at a height of 
 
 22*38 feet above the bottom of the cylinder, the experiment thus showing that the volume of the air 
 
 13 * 09 
 has increased in the ratio of = 1*71. Also, in accordance with Law II., the temperature will 
 
 y * t> 
 
 have increased in the same proportion, and therefore will be 521*2 x 1*71 = 891*2, the increase of 
 
 temperature being 891*2 — 521*2 = 370 degrees. The quantity of heat absorbed in producing this 
 
 change of temperature is 130*2 x 370 = 48,174 foot-pounds, leaving 67,860 - 48,174 = 19,686 
 
 foot-pounds to be accounted for. The air in expanding has forced up the piston through a height 
 
 of 9*3 feet against an atmospheric pressure of 2116*8 lb., and thus has done work equal to 
 
 2116*8 X 9*3 = 19,686 foot-pounds, the exact equivalent of the heat which has disappeared. Hence 
 
 it is evident that of the 67,860 units of work applied in the form of heat, 19,686 have manifested 
 
 themselves as external work, and 48,174 have been absorbed in raising the temperature of the air 
 
 to the degree required by the increased volume necessary to perform that amount of work. 
 
 Suppose now an additional quantity of heat applied until the temperature has been doubled. 
 
 Then bv Law II. the volume will have been doubled also, and the work done upon the piston will be 
 
 13*09 X 2116*8 = 27,709 units, which represents an expenditure of heat to that amount. To 
 
 double the temperature there will be required 67,860 foot-pounds of heat, as already shown, and the 
 
 eflfect produced by this quantity of heat may be called the internal work. Hence the total quantity 
 
 of heat expended will be equal to the internal work -|- the external work = 67,860 + 27,709 = 
 
 96,569 units of work, = Kp521*2 = 183*35 x 521*2 ; and the external work may be expressed as 
 
 c521*2 = c3*15 X 521*2, From this it will be evident that the internal work is always K„ (t^ — t^ 
 
 where t^ and t^ are the temperatures at the beginning and the end respectively of the change 
 
 produced, and that we may readily find the quantity of heat expended in producing any change in 
 
 a pound of air, since : Heat (expended = internal work -f external work = K^ (^j — 4) -f external 
 
 work = K« - ^ Vi~P2 2 _j_ extQj.jja,I work, which is the general equation of the action of heat in a 
 c 
 
 perfect gas. 
 
 Heat Expended in the Expansion and Compression of Air. — We have now to consider the 
 important practical question of the quantity of heat expended in the expansion and compression of 
 air. Let A B, Fig, 331, be a cylinder, in which moves an air-tight piston P ; and let the dimen- 
 sions of the cylinder be such that when the piston is in the position m n, the weight of the con- 
 tained air at mean atmospheric pressure and 60° Fahr. temperature shall be 1 lb. Then, assuming 
 that the temperature is kept constant, when the piston is moved forward to the position to' n' the 
 volume of the air will be reduced to one-halt^ and its pressure increased to two atmospheres. Suppose 
 
174 MINING ENGINEERING. 
 
 now a body X, at a temperature of 60° = tj,, and capable of communicating an indefinite quantity of 
 heat, to be put in communication with the cylinder A B, and the piston to be set in motion towards 
 its first position m n. As the position moves on, the volume of the air increases, and if no heat were 
 communicated the temperature would fall ; but as the body X is in contact with the cylinder, which 
 is supposed to be a perfect conductor, the slightest depression of the temperature below ii causes heat 
 to flow from X into the air, and thus the temperature is maintained constantly at t^. During this 
 operation the air expands at constant temperature, and the question to be determined is : What 
 quantity of heat has been abstracted from the reservoir of heat X ? for this is the quantity expended 
 by the expansion of the air. The expansion curve in such a case being a common hyperbola, it can 
 be shown that this quantity of heat = pv log. r = cti log. r, r being the ratio of expansion, and the 
 logarithm being hyperbolic. Thus, H representing the quantity of heat expended, we have 
 
 a = cti log. r. 
 
 Suppose now the body X to be removed, and another body Xi of the same temperature, and 
 capable of receiving an indefinite quantity of heat, to be placed in contact with the cylinder, and let 
 the piston be again moved ' forward towards m' n'. As the piston travels forward the air is com- 
 pressed, and if no heat were abstracted the temperature would rise ; but as the body Xi is in contact 
 with the cylinder, the slightest elevation of the temperature causes heat to flow from the air into Xj , 
 and thus the temperature is maintained constantly at t^ . During this operation the air is compressed 
 at constant temperature, and the quantity of heat rejected into Xi is equal to that abstracted from X ; 
 that is, it is equal to c ^i log. r. Thus, representing the quantity of heat expended during compression 
 
 by Hi, we have 
 
 Hi = H = c?i log. r. 
 
 In this case, the equality of H and Hi is necessary and evident. And it may be remarked that 
 the quantity of heat Hi rejected during compression, which is equal to H the quantity abstracted 
 during expansion, is the exact equivalent of the work done upon the air in the cylinder by the piston 
 in the forward or compressing stroke. In this example, we have an instance of the conversion of 
 work into heat. The action of an engine working in this way is to pump heat from the body X into 
 the body Xi, and when this view of the action is taken, the equality of the quantities becomes manifest. 
 
 In the case we have supposed, the value of Hi = 19,197 foot-pounds. Let this quantity of 
 
 heat, which has been forced into Xi during the motion of the piston, towards m' n', be restored to 
 
 the air when the piston has reached the latter position, assuming the pressure of the piston to be 
 
 constant. The efi'ect of the application of this quantity of heat will be to raise the temperature of 
 
 H 19 197 
 the air j^ = f^To^ = 104: -7 degrees, that is, from ^i = 521"2 degrees to 4 = 625-9 degrees 
 
 absolute. But as the volume varies as the temperature when the pressure is constant, the volume 
 A7n'n'B will be increased in the proportion of 0*2, which is the ratio of 104*7, the increase of 
 temperature, to 521*2, the original temperature. Thus the original volume being 1, the new volume 
 due to the increased temperature will be 1 ' 2 ; in other words, the piston will be forced back from the 
 position to' n', to the position shown by the dotted lines at o o, and the volume of air at the pressure 
 of two atmospheres will he AooB, instead of A m' n' B as before. Suppose now the cyHnder to be 
 placed in communication with a reservoir R by means of the valve V, the pressure of the air in the 
 reservoir being two atmospheres, and additional force applied to the piston. As the pressure in the 
 cylinder and in the reservoir is in equilibrium, it is obvious that as the piston advances the volume 
 
SHAFT-SINKING. 175 
 
 AooB will be forced into the reservoir, where means are provided for keeping the pressure constant. 
 Now, so far, it matters not whether we force into the reservoir the volume A m' n' B at ti tempera- 
 ture, or the volume AooB at ?2 temperature, since the work of the heat Hi applied is stored up 
 in the increased volume. But as it is practically impossible to keep the temperature of the air in 
 the reservoir above that of the surrounding atmosphere, this quantity of heat Hj will escape, and the 
 greater volume will diminish to the lesser without doing any work. Hence it will be seen that the 
 restoration of the heat abstracted will occasion a loss of work equal to that which is represented by 
 the external work of that quantity of heat. And it is also evident that if the heat be allowed to 
 accumulate during compression, the effect will be practically the same as that produced by restoring 
 it after compression. It follows, therefore, that in the compression of air under these conditions, 
 there must necessarily be an important loss of motive force, and that this loss is greater as the degree 
 of compression is greater. 
 
 In the work of compressing air in practice, the surrounding atmosphere is the body X, from 
 which heat is abstracted by the backward stroke of the piston ; and water, applied in various ways, is 
 the body Xj, into which the heat is forced by the forward stroke. If it were possible to apply 
 water in such a way as to fully satisfy the conditions demanded in the assumed body Xj, there could 
 be no accumulation of heat, and, consequently, no loss of work due to this source. 
 
 There yet remains for consideration a matter of some practical importance. Suppose, again, the 
 piston to travel forward to the position m' n', while the body Xi is in contact with the cylinder. The 
 air occupying the volume A m' «' B will then be of the same temperature as Xj = t^. Let the body 
 Xi be then removed, and the piston allowed to travel back to the position m n. The conditions are 
 now such that no heat can be received by the air, and, consequently, as it expands, its temperature 
 will fall. It is required to know by how much the temperature has fallen when the piston has 
 arrived at the position m n, "When a gas expands at constant temperature, which is the case we have 
 had under consideration, the expansion curve is a common hyperbola ; but when it expands in a 
 non-conducting, non-radiating cylinder, which is the case we have now to consider, the expansion 
 curve is ot a form called the adiabatic, the equation of which is pvy = constant, y being the ratio 
 
 rr 
 
 :r^ 1 • 41 of the specific heat at constant pressure to that at constant volume. Suppose the gas to 
 
 expand from Vi to V2, and let its corresponding pressure and temperature hep^ ti and p^ t^. Then we 
 have />i Vj = c ifi ; />2 ^2 = c ^a ; p^ v^ = p^ v^. Hence c t-^ v^~'^ = ct^ v^~'^ ; or, 
 
 = '■(.)'■' 
 
 This equation, in which r is the ratio of expansion, shows by how much the temperature falls for any 
 given expansion. 
 
 In employing compressed air for driving machinery, as machine rock-drills, for example^ this 
 fall of temperature is attended with important consequences. When low pressures are used, the 
 coolness produced in the atmosphere of underground workings by the expansion of the compressed 
 air is highly conducive to the salubrity of such situations ; and when high pressures are employed, 
 great inconvenience is occasioned by the excessive cold produced, the water contained in the air 
 being frequently frozen and deposited as ice in the exhaust passages of the machine. 
 
 Loss of Work in Compressing Air. — The most important source of loss of work in compressing 
 air is the accumulation of heat. If the foregoing expositions have been fully understood, there should 
 be no difficulty in estimating its precise value in any case. The means of remedying the evil lies ia 
 
17G MINING ENGINEEEING. 
 
 the application of a suitable medium of abstraction. Hitherto water has shown itself to be the most 
 effective and convenient body for such a purpose, and numerous modes of applying it have been 
 devised, in order to obtain the best possible results. To favour the action of the water, the velocity 
 of the piston should be kept low. This would appear from the foregoing considerations to be a 
 necessary condition of efficiency. The mode of applying water as a jet within the cylinder must 
 necessarily be the most effective, and designers of air-compressing machines will therefore do well to 
 direct their efforts to the improvement of the means whereby this mode of application is effected. 
 
 Another source of loss of work, the consequences of which increase in importance with the 
 degree of compression, is the clearance space at the end of the cylinder. These consequences will, on 
 reflection, become sufficiently apparent. Suppose a cylinder in which the compression is carried to 
 six atmospheres. When the piston arrives at the end of its stroke, the clearance space contains air 
 compressed into one-sixth of its volume at atmospheric pressure ; and it is obvious that when the 
 piston recedes, this air must expand into six times that volume, that is, into its volume at atmospheric 
 pressure, before any air from the surrounding atmosphere can enter the cylinder ; that is, in other 
 words, before the suction-valve can open. Thus a volume of air is lost at each stroke equal, at 
 atmospheric pressure, to that assumed by the compressed air in the clearance space when, by 
 expansion, it bas dropped to the same pressure. To remove altogether the necessity for a clearance 
 space, columns or cushions of water have been employed, in a manner which will be described here- 
 after. These fulfil the purpose required very satisfactorily ; but it must be borne in mind that they 
 are themselves a source of loss of work, by the inertia which they oppose to the motive force. It 
 should be remarked that the contents of the clearance space includes the air in the receiver behind 
 the valve, which air returns into the cylinder as the valve closes. This is called the slip of the valve, 
 that is, the quantity of air which the valve as it returns to its seat allows to slip back into the 
 cylinder. When the lift of the valve is great, this quantity may be considerable ; and when the lift 
 is slight, the resistance from friction, due to the contracted passages, may also be considerable. 
 
 Leakage of the valves and pistons and the friction of the moving parts constitute sources of loss 
 of greater or less importance according to the degree of perfection attained in the construction of the 
 machine, and the condition in which it is maintained. As these sources of loss are greatly dependent 
 for their existence upon design, workmanship, and supervision, they are capable of being reduced 
 to narrow limits. It is, however, needful to remark here that the loss of work due to the friction of 
 the air in the valve-ways, and to the influence of the contracted vein, is by no means insignificant. 
 
 There is yet another source of loss of motive force, the influence of which is very great, and 
 which increases with the degree of compression. This source of loss, which has been singularly 
 neglected, exercises an important bearing upon the question of economy relatively to this mode of 
 transmitting force, and is therefore deserving of careful consideration. As the air has to be com- 
 pressed by the application of force, it is clear that the fraction of that force which remains after the 
 important deductions have been made for the losses already described, cannot be fully recovered 
 without working the air expansively down to the pressure of the atmosphere. As this is in all cases 
 impracticable, there must be always a loss of work, the value of which may be determined from the 
 degree of expansion adopted. In the ca^^e of machine rock-drills, which work without expansion 
 altogether, the loss is necessarily very great, and, when high pressures are used, may become enormous. 
 This question is obviously an important one, and it will undoubtedly exert a modifying influence 
 upon the design of machines to be driven by compressed air. 
 
SHAFT-SINKING. 
 
 177 
 
 Loss of Work in Traiismission. — Compressed air has to be conveyed in pipes and tubes from the 
 reservoir into whicli it has been forced, to the machines in position at the various points where 
 operations are being carried on, through distances in many cases considerable. During this trans- 
 mission, a loss of work is occasioned by the friction of the air in the pipes. Numerous and 
 exhaustive experiments have been made to determine accurately the value of the loss thus occasioned. 
 From the results of these experiments, the following three conclusions have been deduced, namely, 
 1, that the resistance is directly as the length of the pipe ; 2, that it is directly as the square of the 
 velocity of flow ; and 3, that it is inversely as the diameter of the pipe. Upon these results and 
 conclusions formulae have been established whereby the value of the loss of force may be ascertained 
 with ease and accuracy. These formula show that for pipes of the diameters usually employed 
 for this purpose, and for distances not exceeding one mile, the loss of motive force due to the 
 friction of the air in the pipe is insignificant when the velocity does not exceed 4 feet a second. 
 And it can be shown that even this loss is notably diminished, and in some cases entirely annulled, 
 by the increased head due to the depth of the shaft, when the compressed air is employed in 
 mines. The influence of this head may often be taken advantage of to diminish slightly the 
 diameter of the pipes, and thereby to effect a considerable economy of cost. As this source of 
 loss of motive force is of small moment when compressed air is applied to ordinary mining 
 operations, so long as the velocity is kept below the limit already mentioned, it is unnecessary 
 and undesirable to discuss here the formula by means of which its value may be determined, or 
 to illustrate the manner of their application. The consideration of this question will therefore be 
 deferred to a subsequent chapter. 
 
 It becomes apparent from the foregoing investigations that compressed air as a medium of trans- 
 mission is, under the most favourable conditions, exceedingly wasteful of the motive force, and that 
 the waste may become enormous if means are not employed to keep it near its minimum limits. The 
 application of such means involves conditions which can be satisfied only when the machinery 
 employed for the compression is designed to form a portion of the permanent plant of a mine. Even 
 with machinery of this character as at present constructed, not more than 30 per cent, of the 
 motive force remains to be utilized when the necessary deductions for loss have been made ; and 
 calculations for practical purposes ought, therefore, to be based upon this, or a smaller proportion. 
 It will be found instructive to compare the results of carefully conducted experiments with a com- 
 pressor constructed on the principle adopted by Sommeiller at the Mont Oenis tunnel, and applied, 
 with improvements of detail, to supply the rock-boring machines employed at the Sarrebruck mines, 
 which results have been tabulated by the engineer, M. Pernolet, as follows : 
 
 No. of the 
 Experiment. 
 
 Kevolutions a Minute. 
 
 No. of Eevolutions in the Engine required 
 
 to give in the Eeeeivers an Excess 
 
 of Pressure of 
 
 Useful Effect of the Compressors at 
 
 Engine. 
 
 Cfcmpresso*. 
 
 One 
 Atmosphere. 
 
 Two 
 Atmospheres. 
 
 Three 
 Atmospheres. 
 
 One 
 Atmosphere. 
 
 Two 
 Atmospheres. 
 
 Three 
 Atmospheres. 
 
 1 
 2 
 3 
 4 
 5 
 6 
 
 14-83 
 21-26 
 29-76 
 35-20 
 44-62 
 48-50 
 
 5-51 
 7-90 
 11-06 
 13-09 
 16-59 
 18-03 
 
 108 
 107 
 109 
 107 
 108 
 109 
 
 230 
 229 
 231 
 226 
 234 
 238 
 
 359 
 356 
 358 
 352 
 367 
 380 
 
 0-94 
 0-95 
 0-93 
 0-95 
 0-94 
 0-93 
 
 0-88 
 
 0-885 
 
 0-88 
 
 0-90 
 
 0-87 
 
 0-85 
 
 ' 0-85 
 0-855 
 0-85 
 0-865 
 0-83 
 0-80 
 
 2 A 
 
1V8 MINING ENGINEEEINa. 
 
 The compression cylinder was in this instance 0"393 metre = 15*47 inches in diameter, and the 
 length of the stroke was 1 • 255 metre = 49^ inches. The ratio of the gear being 29 : 78, one 
 revolution in the compressor corresponded to 2-69 in the engine. During the first four experiments 
 there was no sensible elevation of temperature in the valve-box ; but in the fifth an increase of tem- 
 perature became apparent ; and in the sixth this increase was very marked. It will be remarked that 
 up to thirty-five revolutions of the engine, corresponding to 13-09 of the compressor, = 21-5 inches 
 a second, the useful efiect remains independent of the velocity ; but that beyond this it diminishes 
 notably as the velocity increases. In consequence of the results obtained from these experiments the 
 maximum velocity of the compressors was fixed at eighteen revolutions a minute, = 29^ inches a 
 second. The ordinary speed, however, was hardly more than half this. 
 
 Construction of Machines for Compressing Air. — It now remains to illustrate the foregoing 
 theoretical remarks by a detailed description of the most approved machines for compressing air 
 actually in use. In the fulfilment of the conditions demanded, Continental engineers appear to have 
 been the most successful, and for this reason our descriptions will relate mainly to machines of their 
 design. In consequence of the important tunnelling operations which have heen carried on upon the 
 Continent, more favourable opportunities have been there afforded for studying the requirements of 
 compressed air, and hence arises the superiority of design. If the mechanical properties of air 
 expounded in the foregoing pages be borne in mind, there should be no difficulty in understanding 
 the principles involved in the construction of the machines to be described, or in appreciating their 
 merits and defects. In treating of them, therefore, it will be sufficient to limit our remarks to 
 description only. 
 
 In nearly all recent instances in which compressed air has heen appHed on an important scale, 
 preference has been given to water-column compressors, in which the piston acts upon the air through 
 the medium of a mass of water that rises at each stroke to the delivery valve, and thereby reduces 
 the clearance space to zero, while the air is kept saturated with water during the compression. But 
 such machines, in which there is always a considerable mass of water in motion, must necessarily be 
 driven at a low speed, and hence, when large volumes of compressed air are required, recourse must 
 be had to increased dimensions. This necessity involves a large outlay, and this outlay often consti- 
 tutes an insuperable difficulty in the way of adopting rock-boring machinery. Many attempts have 
 been made to remove this defect by omitting the column of water, and thereby allowing the piston 
 to act directly upon the air to be compressed. Few of these attempts have, however, proved 
 sufficiently successful to justify the adoption of the system. In most of the compressors so designed 
 the air becomes greatly heated, notwithstanding the precautions taken to prevent such a result. 
 There are, however, some notable instances in which success has been achieved in an eminent degree 
 and these instances are deserving of special and careful consideration by reason of the important 
 results to which they lead. Of these, the compressor in use at the St. Grothard tunnel, and known 
 from the name of its inventor, as CoUadon's machine, is the most noteworthy. 
 
 Air- Compressors at the Sarrebruch Collieries. — We have already had occasion to allude to the 
 satisfactory results obtained from the air-compressors used at the Sarrebruck collieries. The desi"-u 
 and construction of these compressors, as well as the general arrangements adopted, are shown in 
 Figs. 332 and 333. The motor is a horizontal expansion steam-engine, the cylinder of which is 
 24f inches in diameter, with a stroke of 43 inches. With a pressure of 45 lb., and a cut-off at half 
 stroke, this engine develops, at fifty revolutions a minute, a nominal foice of 170 horse in round 
 
SH A PT-SINKING. 179 
 
 numbers. But with the compressors at present in use, it is found to be sufficient to drive the 
 engine at twenty-five revolutions a minute under a pressure of only 30 lb., the force developed under 
 these conditions being about 54^ horse. This engine communicates motion to a shaft, from which 
 the compressors are driven by spur gear. This shaft is designed to admit of being lengthened for 
 the purpose of driving two additional compressors when the workings are more fully developed. 
 Besides the compressors, the engine drives, by means of belting, a lathe and a boring machine in 
 an adjoining workshop erected for the repair of the rock drills. The whole arrangement will be 
 understood from the drawings. The advantage of transmitting the force developed upon the steam 
 piston through the medium of gearing lies in the arrangement allowing the engine to be run at a 
 higher speed ; and with a higher speed a less weight in the fly-wheel becomes sufficient. Moreover, 
 when an engine working expansively is connected directly to the compressors, the greatest resistance 
 in the compression cylinder occurs when the tension of the steam is least, and vice versa, a defect that 
 is removed by the adoption of intermediate gear. 
 
 The compressors are constructed upon the principle, first adopted by the Italian engineers at the 
 Mont Cenis tunnel, by which any heating of the air is prevented and clearance space avoided, by 
 interposing a column of water between the piston and the air to be compressed. In this construction, 
 we have upon each of the two faces of a piston moving horizontally a column of water of a certain 
 height, which ascends and descends as the piston advances and recedes. During the descent of the 
 column the air is drawn into the space left free by the water, and during the ascent of the column 
 this air is compressed and forced into the receiver. The water being driven close up to the delivery 
 valve there is little or no clearance space ; and as the water acts as a packing for the piston, as 
 well as a cooling medium, there is no leakage or heating of the piston, cylinder, or valves. 
 Figs. 332 and 333 are a plan and a sectional elevation of this machine, in which the piston is at 
 half stroke. 
 
 The piston of the compressor is 15^ inches in diameter, and 12 feet in length ; its form is that of 
 a hollow plunger, and it has a thickness of cast iron of 1 inch ; it is turned on the outside, and closed 
 at its two ends. This piston moves on each side in a cylinder 5 feet in length, and 20^ inches in 
 diameter. Over the middle of the cylinder is a tubular outlet, 33 inches in diameter and 5 inches 
 in height, upon which is bolted a valve chest or chamber 27 inches in depth. The whole thus forms, 
 at each end of the piston, a column rising to a height of 33 inches above a horizontal cylinder. 
 
 The two cylinders, or pump-barrels, are separated from each other by a horizontal distance of 
 6 feet, measured from stuffing box to stuffing box. In this space travels between guides an iron cross- 
 head fixed upon the piston, to which cross-head the two connecting rods are attached by which the 
 motion is communicated to the piston. The length of the stroke is 4 feet. "Within the valve 
 chamber are two annular spaces, formed by the valve seating and the cover. The space below the 
 seating contains the air drawn in from the atmosphere, and the space between the seating and 
 the cover contains the compressed air. The construction of these points will be best understood by 
 reference to the drawings. It should be remarked, however, that both the suction and the delivery 
 valves are of indiarubber. 
 
 The action of this compressor is as follows : As the plunger recedes, the column of water above it 
 sinks, the suction valve opens, and the space vacated by the water is filled with air. When the 
 piston returns, the suction valve closes, the column of water rises into the space it previously occupied, 
 and compresses the air in it till the pressure is sufficient to open the delivery valve, when the air is 
 
 2 A 2 
 
180 MINING ENGINEEEING. 
 
 forced into the annular space above, and thence into the receiver. The quantity of water is so 
 calculated that when the piston has arrived at the end of its stroke, the column reaches the delivery 
 valve, and consequently the whole of the air is expelled. To replace the water which is carried off 
 by the air, a constant supply is brought in above the suction valve through a pipe | inch in diameter. 
 This water enters the cylinder while the valve is open, and the excess is driven off through the 
 delivery valve along the air-conduit into the receiver. This excess of water serves to cool the air ; 
 the requisite degree of opening of the cock upon the supply pipe for a given piston velocity is soon 
 shown by experience. 
 
 The compressed air enters a horizontal pipe 6 inches in diameter, connecting the two pumps of 
 each compressor. From the middle of this pipe, another of the same diameter rises to a height of 
 6 feet, and then becomes horizontal till it reaches the reservoir. Beneath the point at which the 
 latter pipe enters the former is a well to catch the water carried along by the compressed air. A 
 small tube, half an inch in diameter, conducts the water back to the reservoir. For the purpose 
 of emptying the cylinders in case of repairs being required, a discharge cock is placed near the 
 bottom. As a considerable quantity of the water is carried into the air receiver, the same automatic 
 apparatus is applied to the bottom of the receiver as to the well below the pipe. This apparatus is 
 shown in section in Fig. 334. It consists of a copper float a a open at the top, and capable of motion, 
 in a cast-iron vessel dd, closed by a screwed cover; the motion of this float actuates a double-beat 
 valve by means of the rod b. The water entering through e accumulates in the annular space d d, 
 and the float a a rises and closes the valve. But as the water continues to enter, it flows over and 
 into the float, and thereby causes it to descend again ; the valve consequently opens again, and the 
 pressure of the air acting upon the water inside the float forces it out through the central tube //. 
 This water passes through the valve v, and thence along the passage g to the cold water reservoir. 
 As soon as the float is emptied it rises, and the same effects are reproduced. There is always 
 sufficient water in the float to keep the end of the ascension tube closed. To allow the air to escape, a 
 small opening h is provided. This ingenious contrivance works very regularly, and when the com- 
 pressors are driven at their normal speed the water is discharged in a nearly continuous jet. Thus 
 the only supply of fresh water needed is that which is lost by evaporation. 
 
 It becomes necessary now and then to cleanse this apparatus of the impurities brought in by 
 the water. For this purpose the cock which isolates it from the receiver or the compressor is closed, 
 and the valve removed by means of the screw and stirrup shown at i. This operation occupies less 
 than ten minutes. To clean the apparatus more completely the cover must be removed. 
 
 These compressors, as already shown, work very satisfactorily ; but their construction is some- 
 what expensive, and they occupy a considerable space. 
 
 Air- Compressors at the St. Gothard Tunnel. — Colladon's air -compressor, the general arran ele- 
 ment of which is shown in Figs. 335 to 341, consists of a horizontal cylinder having a hollow 
 piston, the rod of which, also hollow, passes through both ends of the cylinder, the suction and 
 discharge valves being placed in the cylinder covers. The peculiarity in the construction of 
 this compressor consists in the means adopted for cooling those parts of the apparatus which 
 are brought into contact with the compressed air. These means, which are very ingeniously 
 arranged, are : a circulation of water around the cylinder and through the cylinder covers, 
 piston, and piston-rod ; and an injection of water, in the form of spray, into the two ends of tliP 
 cylinder. The circulation of the water in the cylinder covers and around the cylinder is effected 
 
SHAFT-SINKING. 181 
 
 by means of a small pump placed at the side of the cylinder, the plunger of which takes its 
 motion from the cross-head of the compressor piston-rod. This pump forces the water, through 
 copper tubes having an internal diameter of about f inch, into the spaces a a cast in the thickness of 
 the cylinder covers, and into the annular space h b formed between the cylinder and its outer casing 
 or jacket ; and the water passes ojff through similar tubes situate in the bottom of the cylinder jacket. 
 By this means a constant and regular flow is maintained. The circulation of the water in the piston 
 and piston-rod is carried on by the following arrangement. The piston-rod, which is of steel, is bored 
 throughout its whole length to a diameter large enough to receive a copper tube c c and leave a small 
 annular space around it. This tube is nearly equal in length to the piston-rod. Fig. 335, and is 
 fastened to it at its back end by means of a brass screwed plug, into which penetrates, with easy fric- 
 tion, through the glands of the stuffing box, a pipe //, which is firmly fixed to the cylinder by means 
 of an iron strap g g. The water, driven by the pump already mentioned, passes throxigh this pipe 
 into the tube c c. Having reached the forward end of this tube, it returns, through the annular 
 space left between it and the piston-rod, as far as the diaphragm e, which consists of a brass ring 
 fastened to the piston-rod in the same line as the piston. This diaphragm obliges the water to pass 
 into the piston, and to cool successively its two faces, as shown by the arrows in the section. Fig. 335. 
 The water afterwards escapes through the indiarubber pipe i, which is fixed to the back end of the 
 piston-rod. The water is injected into each end of the cylinder by means of two small pipes. Figs. 335 
 and 336, fixed in the upper part of the cylinder, their ends being closed by a metal disc I, and pierced 
 by two inclined holes opening opposite each other, and having a diameter of about one-fiftieth of an 
 inch. The water being forced, under considerable pressure, through these holes by means of the feed- 
 pump, one jet strikes against the other, and is thereby divided into very fine spray. The quantity 
 of water to be introduced by this means is so regulated by experiment as to keep the air completely 
 saturated. Under these conditions, even when the circulation in the interior of the piston is cut off, the 
 temperature of the apparatus will not rise above 25° Centigrade. All the parts, indeed, remain cool 
 with a velocity ot sixty-five revolutions per minute, and with the air compressed to six atmospheres. 
 In each end of the cylinder there are two suction valves and one discharge valve, formed of very 
 thin plates of steel with bronze seatings, the valves being kept in contact with the seating by means 
 of spiral springs coiled round the valve stems, Figs. 335 and 337. The dimensions of these valves are 
 as follows : Suction valves, internal diameter of seating, 4j inches ; external diameter of valve, 
 5 inches. Discharge valves, internal diameter of seating, 3| inches ; external diameter of valve, 
 41 inches. 
 
 At the Airolo end of the St. Gothard tunnel twelve of these compressors have been erected, in 
 ■groups of three on one side of a common driving shaft, which is set in motion by four distinct 
 turbines by means of powerful beveled gearing. The coupling boxes or clutches employed allow the 
 isolation of each of these four groups with its motor, while by another mechanical arrangement, 
 which disconnects the beveled gearing, either of the motors may be stopped, the corresponding 
 group of compressors receiving motion from the common driving shaft. These arrangements 
 greatly facilitate the carrying out of repairs, as they allow of any one group of compressors being 
 stopped without its interfering with the working of any other part of the machinery ; for even if 
 it be necessary at the same time to repair one of the turbines and a compressor, belonging to 
 different groups, the remaining nine compressors can be driven, as already shown, by means of the 
 common driving shaft. In each group the three compressors o, o\ o". Fig. 340, are fixed side bj 
 
182 MINING ENGINEEEING. 
 
 side upon one bed-plate, and connected directly to the three-throw crank-shaft P; this shaft is 
 connected by means of the couplings Q Q' to the driving shafts R R', thus producing a continuity 
 between the shafts of each group. On these driving shafts are keyed massive beveled toothed- 
 wheels s, which are driven by horizontal turbines T, Fig. 341. 
 The dimensions of the compressors at Airolo are : 
 
 Diameter of piston .. .. .. .. .. .. .. ., .. .. 18" 1 inches. 
 
 Stroke of piston .. .. .. .. .. .. .. .. .. .. .. 17"7 „ 
 
 The theoretical volume generated by the compressor at each stroke will be .. .. .. 2*63 cub. ft. 
 
 And at each revolution of the shaft .. .. .. .. .. .. .. .. 5"27 
 
 Which will give for each group of three compressors a volume of .. .. .. .. 15 "SI 
 
 At the normal velocity of sixty-five revolutions per minute this will give, for each group of 
 
 three compressors, a theoretical volume of .. .. .. .. .. .. 1027' 65 
 
 At a pressure of six atmospheres, which is the ordinary working pressure, this quantity will 
 
 be reduced to 171-27 
 
 The actual volume, as proved by experience, will not amount to more than 70 per cent, of 
 
 the theoretical volume, or .. .. .. .. .. .. .. .. .. 119*9 
 
 This apparatus has been in operation during too short a time to enable us to judge of its merits 
 definitively. Nevertheless, the experience of some months' work at Airolo gives authority for 
 stating that Colladon's compressor, notwithstanding the complication of its parts, and the high 
 velocity at which it is driven, does not require more repairs than the ordinary machines with water 
 columns, which are driven at a much lower velocity ; while the amount of its effective work will be 
 fully equal to theirs. It is therefore superior to these latter, as, on account of its greater velocity, it is 
 capable, with a smaller diameter and shorter stroke, and a consequent proportionate reduction in the 
 first cost, of furnishing the same quantity of air at a given pressure. It also possesses the advantage 
 of being able, with a slightly increased velocity, to furnish volumes of air greatly in excess of the 
 normal quantity. This advantage, which is altogether unattainable in a machine with water 
 columns, on account of the great mass of water which has to be put in motion, belongs, however, to 
 all those direct-acting compressors in which the velocity can be increased in proportion as the 
 cooling of the air is more completely carried out. The importance of this advantage can hardly be 
 overrated. 
 
 With regard to the complication of its construction, this exists only in the means adopted for 
 carrying on the circulation of the water in the interior of the piston and the piston-rod ; and although 
 these means of cooling may be indispensable in those cases in which we are precluded from adopting 
 the more simple, direct, and efficient method of cooling by the water jets, as commonly used for 
 compressing gas, it seems to be proved by the experience at Airolo, where the circulation of the water 
 in the piston has not been maintained, that up to a velocity of sixty-five revolutions a minute the 
 water jets suffice perfectly for maintaining the temperature within those limits which are favourable 
 to the proper working of the apparatus. If this circulation be abolished, the machine will become one 
 of the most simple, and, on account of its other advantages, the best of all air-compressors. 
 
 A series of four sizes of these compressors are manufactured, which it may be well to describe in 
 this place. The compressor itself is, with the exception of its dimensions and some few matters of 
 detail, the same as that which we have just described. It consists of a horizontal double-action 
 cylinder, the piston of which is actuated either by a connecting rod, crank, belt, or toothed 
 gearing, when the power is derived from an independent motor ; but when the motor forms a part 
 
SHAFT-SINKING. 
 
 183 
 
 of the apparatus, the motor cylinder is placed on the same bed-plate and in a line with the compressor 
 cylinder, and the two piston-rods are coupled together in such a manner as to form but one rod. A 
 fly-wheel connected to the piston-rods by means of a connecting rod and crank, equalizes their 
 motion ; while a governor, placed upon a small air-reservoir, into which the water carried over by 
 the air flows, acts in such a manner upon the steam-supply pipe as to cause the velocity of the 
 engine to vary according to the pressure of air which it may be desirable to maintain constant. 
 
 The first type A, which is the least powerful, has been designed for the purpose of supplying 
 suflScient air to drive one large size rock drill. 
 
 The second type B is sufficiently powerful to drive two of such drills. 
 
 Types C and D are formed by coupling two or three of type B, of which any number may be 
 joined, in order to meet the requirements of those works in which a large quantity of air is required. 
 As, however, type B is of itself sufficiently powerful to drive four Dubois-Frangois rock drills, it will 
 generally be found the most useful and economical for employment in mines. 
 
 The following table gives the principal dimensions, theoretical and useful effect, power required, 
 and price of each of the four types. 
 
 The prices given include bed-plate, connecting rods, cranks, pulleys, and fly-wheels, and a 
 reservoir for the compressed air, in which the latter is deprived of the water previously used to cool 
 it. The prices with engine include, besides the above, an automatic governor which regulates the 
 velocity of the motor according to the pressure of the air in the reservoirs. 
 
 I Diameter of the piston 
 Stroke of the piston 
 Theoretical volume generated per minute at the mean 
 yelocity 
 
 (Mean .. 
 
 Eevolutions per minute < Minimum 
 
 [Maximum 
 
 Corresponding velocity of the piston per) jy-j^j^^ 
 ^e«°^^ iMaximum 
 
 Power Eequired 
 
 Useful Effect , 
 
 V 
 J Calculated for the different velocities at which I jjjj,i~„Tn 
 
 ' I the machine may be driven 
 
 Mean 
 Minim 
 (Maximum 
 
 Price of the Appa-^ 
 ratus .. 
 
 f Volume of air compressed to six atmospheres TMean .. 
 
 , i which the apparatus will furnish per minute,< Minimum 
 
 [ when driven at either velocity .. .. (Maximum 
 
 Compressors arranged to be driven by an independent 
 motor — steam or hydraulic 
 
 Combined engine and compressors — the engines being 
 horizontal and non-condensing, with variable expansion 
 
 Type A. 
 
 One 
 Cylinder. 
 
 in. 
 
 10-63 
 23-26 
 
 cob. ft. 
 
 181-25 
 
 88 
 
 41-5 
 
 124-5 
 
 ft. 
 
 5-0 
 2-5 
 7-5 
 
 H.P. 
 
 25 
 12 
 36 
 
 cub. ft. 
 
 25-2 
 12-6 
 37-8 
 
 290 
 
 900 
 
 Type B. 
 
 One 
 Cylinder, 
 
 In. 
 15-0 
 30-9 
 
 cub. ft. 
 
 240-43 
 
 60 
 
 30 
 
 90 
 
 ft. 
 
 5-0 
 2-5 
 7-5 
 
 H.P. 
 
 50 
 25 
 75 
 
 cub. ft. 
 
 38-6 
 16-8 
 50-4 
 
 540 
 
 1512 
 
 TypeO. 
 
 Two 
 Cylinders 
 coupled. 
 
 15-0 
 30-9 
 
 cub. ft. 
 
 480-86 
 
 60 
 
 30 
 
 90 
 
 ft. 
 
 5-0 
 2-5 
 7-5 
 
 HJ. 
 
 100 
 50 
 150 
 
 cub. ft. 
 
 67-2 
 
 33-6 
 
 100-8 
 
 1008 
 
 2700 
 
 TypeD. 
 
 Three 
 
 Cylinders 
 
 coupled. 
 
 in. 
 
 15-0 
 30-9 
 
 cnb. ft. 
 
 721-29 
 
 60 
 30 
 90 
 ft. 
 
 5-0 
 2-5 
 7-5 
 
 H.P. 
 
 150 
 75 
 225 
 
 cub. ft. 
 
 100-8 
 
 50-4 
 
 151-2 
 
 1512 
 
 4000 
 
 As the principal advantage possessed by compressors with direct action, and the one which 
 often causes them to be chosen in preference to all others, lies in their being capable of being 
 
184 MINING ENGINEEEING. 
 
 economically worked at velocities varying within wide limits, the above machines have been cal- 
 culated and designed for a maximum piston speed of 7 " 5 feet per second ; they may, however, be 
 driven at any speed below this, the normal velocity depending upon the volume of air which it is 
 wished to compress per minute. In calculating the efifective volumes in the above table, a loss of one- 
 sixth of the theoretical value has been allowed. 
 
 Air- Compressors at the Blanzy Collieries. — At the Blanzy mines, where compressed air is 
 employed on a large scale, there has been adopted for its production, in the place of one of Som- 
 meiller's double compressors, which had long been in use, a compressor with direct action, constructed 
 by EevoUier, Bietrix, and Co., of St. Etienne, which furnishes 423 ' 8 cubic feet of air per minute, 
 compressed to three atmospheres, whilst the Sommeiller compressor gave but 105*95 cubic feet. 
 
 These compressors are composed of two horizontal cylinders, fixed in a line with and upon the 
 same bed-plate as the two steam cylinders, which are fitted with variable expansion on Mayer's 
 system. The piston-rods of the compressors and of the engines are joined by a coupling the pins of 
 which work in guides ; the engine piston-rods being attached by means of connecting rods and cranks 
 to the two ends of the shaft carrying the fly-wheel. Pigs. 342 and 343. By referring to Figs. 342 and 
 344 it will be seen that the cooling is produced by a current of water circulating through an external 
 casing or jacket, as well as by the direct injection, at each end of the cylinder, of a jet of water under 
 great pressure through an ajutage or rose pierced with very small holes. The suction and discharge 
 valves are simple cast-iron clacks faced with leather, the seats being also of cast iron. 
 
 The principal dimensions of this compressor are as follows : 
 
 Diameter of steam cylinder .. ,. .. .. .. .. „ ., ., 25' 6 inches. 
 
 „ compressor cylinder .. .. .. .. ., .. ,. .. .. 21 -7 „ 
 
 Stroke of pistons .. .. .. .. .. ., .. .. .. .. .. 63"0 „ 
 
 „ suction valves .. .. .. .. .. ». .. .. .. .. 59 '0 sq. in. 
 
 „ discharge valves .. .. .. .. .. .. .. .. .. .. 47'74: „ 
 
 Number of revolutions per minute .. .. .. .. .. ,. .. .. 25 „ 
 
 Velocity of the pistons per second .. .. .. .. .. .. .. .. 4 '37 feet. 
 
 Theoretical volume generated by the compression piston at each stroke .. .. .. 13"5cub. ft. 
 
 Which gives for each revolution of the two compressors .. .. .. .. .. 54 '0 „ 
 
 And for the two compressors, running at a velocity of twenty-five revolutions per minute .. 1350 „ 
 
 This reduced to a pressure of three atmospheres will equal a theoretical volume of .. .. 450 „ 
 
 In practice the actual volume will not amount to more than 90 per cent, of the theoretical .. 405 „ 
 
 This compressor, which is more simple in its construction than Colladon's machine, may be 
 employed in all cases where an economy in the first cost is not a matter of grave consideration ; 
 for though its velocity, which is almost double that of Sommeiller's compressor, combined with its 
 larger size, permits it to furnish three or four times the quantity of air given by the latter, without 
 any increase in its cost, its dimensions and mode of direct action prevent it from being driven at 
 velocities equal to Colladon's compressor ; in this latter also, the water jet being more finely divided 
 into spray, the cooling of the air is obtained with a much smaller volume of water, which of itself is 
 equal to an increase in the duty of the machine. 
 
 Air- Compressors at the Ronchamp Collieries. — The compressors in use at the Ronchamp collieries, 
 where compressed air is employed upon a large scale, merit attention by reason of the important 
 improvements in the practical details of construction that have been introduced by the manufac- 
 turers. The principal advantages claimed for these compressors are : 1. That they occasion no loss 
 by clearance space ; 2. That they compress the air to four atmospheres without sensibly raising its 
 
SHArT-SINKING. 185 
 
 temperature ; and 3. That they occupy but little space, and that, moreover, their compactness does 
 not render their parts less accessible for repairs. These repairs, it is stated on the authority of the 
 engineer, amount to a fresh packing for the piston about once a month. 
 
 The construction and arrangement of these compressors, which are very simple in their action, 
 will be seen by referring to Figs. 345 to 351. They consist of a horizontal cast-iron cylinder 17*7 
 inches in diameter, and 39 '37 inches long, firmly fixed to a horizontal bed-plate, in which moves the 
 compression piston, which is packed with a leather packing. At each end of this principal cylinder, 
 and communicating freely with it, is another cylinder or vertical column, which, like the first, is 
 partially filled with water. Two gun-metal clack-valves, faced with leather, opening from the out- 
 side inwards, and having each a surface of about 15 square inches, serve for the admission of the 
 air ; whilst a horizontal valve, placed at the summit of the vertical columns, permits the escape of 
 the compressed air into the conducting pipes and reservoir. The two vertical columns are identical 
 in their construction, and form, with the horizontal cylinder, a double-acting air-compressing engine. 
 The piston-rod is cased with gun-metal, in order to prevent the rapid oxidation of the iron which 
 would take place if it were in contact with the water charged with air at a high pressure. The 
 glands of the stuffing boxes are for the same reason formed of gun-metal. 
 
 The volume of air given at each stroke of the piston is in practice 4 • 9 cubic feet ; theoretically, 
 this quantity should be 5*6 cubic feet, thus showing a loss of from 10 to 12 per cent. This 
 apparatus, therefore, theoretically perfect as it is in all parts of its construction, is, practically, far from 
 being so ; the loss, however, appears to be due more to the presence of a certain quantity of air, 
 which is held suspended in the water, and which at the moment of opening the suction valves 
 expands, and thus prevents the inrush of the air, than to any loss occasioned by leakage or loss of 
 stroke. 
 
 At each stroke of the piston a certain quantity of water is carried over with the air into the 
 reservoir, Fig. 350, which would finally become full if no precautions were taken to prevent it. In 
 order to avoid leaving the conduct of this operation to the care and watchfulness of the workmen, 
 a very simple apparatus is employed. At the bottom of the air-reservoir, the capacity of which 
 is 882-5 cubic feet, is fixed a small copper pipe, which can be closed at pleasure by means of a 
 stop-cock. During the working of the compressors, this cock is slightly opened, so as to allow the 
 water, which is carried into the reservoir with the compressed air, to escape by the pipe into a 
 cistern which receives its water from a common well-pump. The level of the water in this cistern 
 is such that the overflow runs of itself into the tank of the compressors b b, Figs. 346 to 348, where 
 its flow is regulated by cocks provided for that purpose. By these means, if there be only a small 
 quantity of water at disposal, it may be made to serve over and over again indefinitely. The only 
 precaution necessary to be taken is, not to open the cock r. Fig. 350, before there is some water in 
 the reservoir, and so to arrange the discharge pipe that the compressed air may not escape with the 
 water. 
 
 The water in the compressor cylinder being thus constantly renewed, prevents the heating of 
 the air, which otherwise would attain to a very high temperature, a result that would be detrimental 
 to the action and the duty of the machine. When working under ordinary conditions, the tem- 
 perature of the air-pipes remains sensibly the same as that of the surrounding air, even when the 
 latter is as low as 18° to 20° Centigrade. 
 
 As a precaution against the occurrence of accidents, which might occur to the compressors if the 
 
 2 B 
 
186 MINING ENGINEERING. 
 
 pressure became excessive, a safety-valve S, Fig. 345, is placed upon the pipe througla whicli the air 
 passes to the reservoir, and a counterweight on this valve is so regulated as to allow the valve to 
 rise under a pressure of 4~ atmospheres. This safety-valve is altogether independent of that situate 
 upon the reservoir itself 
 
 Sturgeon's High-speed Compressor. — The chief object sought by Mr. Sturgeon in the 
 design and construction of his high-speed air-compressing engine has been to increase the per- 
 centage of the useful effect obtained from the force applied. This object he has endeavoured to attain 
 by the adoption of a new construction of inlet-valves of his own invention, which allows him to run 
 his compressor at high speeds, without danger of these valves becoming unreliable in their action, 
 and without detriment to his machine, allowing for reasonable wear and tear. 
 
 The receiver and steam cylinder in this engine are cast in one piece, the air-compressor cylinder 
 being bolted to the receiver on the side opposite to that on which the steam cylinder is placed, as 
 shown in Figs. 352 and 353, in which a is the air-compressing cylinder, c the steam cylinder, and b 
 the receiver. A fly-wheel shaft d is carried by two pedestals at the other end of the bed-plate or 
 receiver b, and to this shaft are keyed the fly-wheels e e', one at each end ; the crank-pins //' on 
 these fly-wheels are fixed at right angles to each other, and are connected in the usual way to the 
 two cylinder pistons. Now, as in the compressing cylinder the pressure is smallest at the beginning 
 of the stroke, and the greater portion of the work is done in the latter part of the stroke, whereas in 
 the steam cylinder the pressure is greatest at the beginning of the stroke, and least at the end, the 
 setting of the crank-pins at right angles to each other enables the steam crank-pin to be in its best 
 position to meet the increasing resistance in a similar ratio. It is said that by this arrangement, 
 and with equal cylinder diameters on both sides, the air-compressor has registered, at one and the 
 same time, double the steam pressure of the other cylinder. 
 
 To meet the varying requirements of the air-driven machinery in the supply of air, the following 
 arrangement has been adopted, by means of which the steam engine is enabled to vary its speed 
 automatically, so that when the air-driven machinery is stopped, the air-compressor may likewise 
 stop of its own accord. On the fly-wheel shaft d an eccentric k is placed, which, by working on to a 
 combination of levers, is made to actuate the valve of the steam engine in such a manner as to 
 lengthen or shorten the travel of the slide, according as the pressure in the receiver falls below or 
 above the required degree, which will necessarily correspond to an increase or slackening of speed. 
 A plunger q fits air-tight in a recess made in the receiver b, and according as the pressure increases 
 or diminishes, so will the plunger, rise or fall, carrying with it in the same direction the fulcrum o of 
 a lever n, whose centre o is accordingly raised or lowered in the guides pp. Motion is produced 
 in this lever n around its fulcrum o, by its upper end being connected with the before-mentioned 
 rod m. The valve lever s, working from the fixed centre t, has a projecting pin r, gearino- into 
 a corresponding groove cut along the length of the lever n, so that the to-and-fro movement of the 
 lever n is imparted to the valve lever s. From this description it will be evident that the more the 
 centre o rises, the more will the travel of the valve be shortened ; in other words, the less steam will 
 be admitted into the steam cylinder, whereupon a slackening of speed must ensue, and vice versd. 
 In order to regulate the pressure required in the receiver b, a sliding weight u is attached to the 
 rod m, which, according to the position in which it is set, can be made to maintain the degree of 
 pressure desired in the receiver. When the centre of the lever n comes opposite the pin r of the 
 lever s, the motion of the latter is stopped, and the engine automatically comes to a stand. 
 
SHAFT-SINKING. 187 
 
 In order to reduce the heating of the compression cylinder, it is enveloped by a cavity or tank, 
 which is kept constantly filled with cold water. As this water becomes heated, it is used as feed 
 water for the boiler, and thus a portion of the heat generated, which otherwise proves detrimental, 
 is turned to some advantage. The nicety with which all the working parts of this machine are 
 counterbalanced is evident from the fact, that with a speed of two hundred and twenty revolutions, 
 or 440 feet a minute, no further foundation is required than a few wooden logs placed underneath, to 
 keep the fly-wheels from touching the floor. 
 
 The construction of the air-cylinder valves, which form the chief innovation in this type of air- 
 compressor, will be fully understood by a reference to the enlarged section, Fig. 354, and the following 
 description : These valves are fixed in the cylinder covers, and are exactly similar at each end. 
 The inlet-valve i i is placed in the centre of the cylinder cover in the form of a circular ring. The 
 cylinder piston is fitted at each end with stuffing boxes h h, which are securely packed to the piston, 
 so as to have a frictional hold thereon. The inner end of this stuffing box h is made to sit close on 
 the inner surface of the cylinder cover when the two come in contact with each other. Owing to 
 the frictional grip which this stuffing box has upon the piston, as the latter recedes from one end of 
 the cylinder, the corresponding stuffing box becomes drawn in . the same direction, till its travel is 
 checked by the stop, shown in the figure, coming against the outside surface of the cylinder cover, 
 when the piston completes the remainder of its stroke independently, while the air is drawn in to the 
 full extent of the stroke. The return of the piston brings the inlet-valve close on to its inner seating, 
 thus preventing the air from escaping out again whilst it is being compressed. To prevent these 
 valves from coming in violent contact on their inner seatings, when working at high speeds, the 
 crank-pins are further so arranged that, at the moment of contact, the respective crank-pin is almost 
 on its centre, or at its lowest speed, and the valve is thus brought gently on its facings, without 
 violent concussion. It is further evident that the opening of such inlet-valves is altogether indepen- 
 dent of the vacuum formed in the air-cylinder, inasmuch as they owe their actions to the driven 
 piston. Moreover, the compressed air is here turned to account, in preventing the valve from opening 
 until the piston has travelled sufficiently far to allow time for the delivery valves to close. 
 
 The delivery valves j j. Figs. 352 and 363, are distributed over the whole inner surface of the 
 cylinder covers, and are in direct communication with the receiver h, through the passage g. These 
 valves are kept in close contact with their facings, partly by means of a spring thrusting inwards, 
 and partly by means of the back pressure exerted on them by the compressed air in the receiver b. 
 As soon as the pressure in the air-cylinders, acting on their inner surfaces, becomes greater than the 
 counter-pressure before mentioned, the springs become compressed, or, in other words, the compressed 
 air in the cylinder forces its way through the valve openings and the clear passage g, into the 
 receiver b, to be there stored according to requirements. The back pressure on these delivery valves 
 causes them to close again, and the inlet-valves are then ready to open inwards. It will be seen that 
 for the purposes of repairing or cleaning, these delivery valves can be removed without detaching 
 any fast joints. 
 
 If we, therefore, compare the present construction with the usual types which have hitherto 
 prevailed we shall find that, notwithstanding the high speed at which the present engines may be 
 run, friction has been reduced by enlarging the delivery areas, and by preventing as much as possible 
 cross currents of air ; whereas usually these effects have been increased by the introduction of high 
 speeds. 
 
 2 B 2 
 
188 MINING ENGINEEEING. 
 
 Air-Receivers. — As machines driven by compressed air in underground workings do not run 
 continuously, the consumption of air is irregular ; consequently it becomes necessary to store the air 
 as it is received from the compression cylinders, in a reservoir of sufficient capacity to annul the 
 effects of the irregularity existing between the production and the consumption. The minimum 
 capacity of this reservoir should be twenty times the average consumption a minute, when only one 
 compressor is employed ; ten times when the compressors are two in number ; and five times when 
 there are three compressors. The form of the receiver or reservoir is a matter of small importance. 
 Frequently an old boiler is used for this purpose. At the Sarrebruck mines the receiver consists of 
 three old boilers communicating one with another. Two of these boilers are placed side by side, and 
 the third is placed upon and between them, resting equally upon each. Every receiver should be 
 provided with a pressure gauge, in order that the pressure of the contained air may be readily ascer- 
 tained at any moment. The outlet from the receiver should be provided with a cock, for the purpose 
 of cutting off communication between it and the conduit pipes. There should also be a discharge 
 cock at the bottom of the receiver, for the purpose of removing the water which is carried in by the 
 air, and which accumulates at the bottom. A neat and effective means of discharging the water has 
 already been described in connection with the Eonchamp compressors. It is hardly necessary 
 to remark that the receiver should occupy a situation in which it will not be liable to be exposed to. 
 heat, the action of which upon the contained air would occasion a loss of work. 
 
 Air- Conduits. — For the conveyance of compressed air from the reservoir to the points at which 
 the machines are required^ both cast-iron and wrought-iron pipes are used. When cast iron is the 
 material employed, the pipes are cast with a flange, and the joint is made by means of an indiarubber 
 washer inserted between the flanges. In some cases, one flange is provided with a groove, and the 
 other with a corresponding annular prominence, the edges both of this projection and of the groove 
 being beveled. To form the projection, the flange is turned down, and the groove is also cut in 
 the lathe. The ring of indiarubber is placed in this groove, which is I inch broad and | inch deep. 
 
 Wrought-iron tubing is in many cases preferable, especially on account of its lighter weight. 
 This tubing is usually manufactured in 14 feet lengths, and with an internal diameter of 3\ inches. 
 Such a length will weigh about 80 lb. The joints in this case are made by means of flanges 
 7\ inches in diameter, strongly brazed upon the ends of the tube, and pierced with four bolt-holes 
 I inch in diameter. In order to obtain the requisite degree of rigidity, great care is needed in 
 putting on these flanges. Before applying- them a groove is cut in the lathe in the thickness of the 
 flange, and a copper ring of -^ inch on the side inserted. This ring is, by the process of soldering, 
 rendered solid with the flange and tube, and by that means a perfectly air-tight joint is made. In 
 joining the tubes, an indiarubber washer is inserted between the flanges. 
 
 In certain situations, where rapid oxidation of the metal is likely to occur, an air-conduit may 
 be composed of both cast and wrought iron pipes, each material being confined to the locality for 
 which its qualities render it the more suitable. All air-pipes should, previously to their being put 
 into use, be tested by hydraulic pressure up to ten atmospheres, and also by air pressure under water 
 up to seven or eight atmospheres. By such means any latent defects in them are rendered apparent, 
 and confidence in their resisting and retaining powers is created. 
 
 When a considerable length of air-piping is laid down, means must be provided to allow of 
 expansion and contraction under the influence of changes of temperature. In underground workino-g 
 the temperature is sufficiently constant to justify a neglect of such precautions ; though even there it 
 
SHAFT-SINKING, 189 
 
 is well to be prepared against a sudden rise of the temperature. But in the shaft and at surface the 
 conditions are different, and rollers and compensating joints become a necessity. A form of compen- 
 sating joint that has been proved to act satisfactorily in practice is shown in Figs, 355 and 356. 
 It consists of a tube of copper, of the same dimensions as the iron tubes, and bent into the form 
 shown in the drawing. The flanges of this tube are applied in the same manner as those of the iron 
 tubes. In practice it has been found necessary and sufficient to insert one of these compensating 
 joints at intervals of about 100 yards. 
 
 The tubing used to connect the machine drills with the fixed iron tubing is always flexible. The 
 material used is indiarubber, and great thickness is given to the tubing to ensure strength. As a 
 protection from injury caused by friction against the rough surfaces of the rock, such tubing is 
 covered with coarse canvas. The internal diameter of the largest size used is 2 inches, and that of 
 the smallest about | inch. 
 
 Water Reservoirs. — In rock boring by machinery the application of water greatly facilitates the 
 operation, by keeping the bottom of the hole free from the debris, and hence it is highly conducive to 
 rapidity of execution. It has been proved by experience that the rate of boring in a dry and in a 
 wet hole varies as 1 : 1*5 ; that is, it takes one and a half times as long to bore a hole dry, as to bore 
 a hole with the assistance of water. Thus it is possible to reduce the time of boring by one third. 
 Moreover, the great heating produced in the borer bit by the blows upon hard rock causes a rapid 
 deterioration of the tool, and hence it becomes necessary to change and to repair it more frequently. 
 Another great objection to dry boring is the production of a large quantity of fine dust, which is a 
 cause of annoyance to the workmen, and of destruction to the packing and the rubbing surfaces of 
 the machinery. For these reasons a supply of water is desirable ; and when the holes are inclined 
 upwards, it becomes necessary to inject the water into them with considerable force. For this 
 purpose water reservoirs are used. These reservoirs are constructed of galvanized iron, and are 
 made of various dimensions, according to the conditions under which they will have to be used. 
 They are filled through a funnel-cock, which being closed renders them air-tight. By means of a 
 piece of tubing, the water reservoir may be placed in communication with the air-pipe, from which 
 the requisite pressure is obtained ; the water is directed into the bore-hole as a strong jet by means 
 of another piece of flexible tubing provided with a suitable nozzle. When a heavy drill support is 
 employed, capable of running upon tramways, the water reservoir may be conveniently fixed upon 
 the support. But in other cases there is a difficulty in using a reservoir so as not to be an encum" 
 brance rather than a means to rapid progress. 
 
 Reserve Machines and Tools. — In order to avoid the costly delays which might be occasioned by 
 the derangement of the machine drills, there should always be machines in reserve for all important 
 undertakings. The number of the latter required will obviously depend upon their liability to get 
 out of order. When machines of the simplest construction and of good workmanship are employed, 
 one in ten will be sufficient under ordinary conditions of work. 
 
 Also it is highly desirable, to avoid frequent delays, to have at hand a store of the pieces which 
 are most subject to wear and derangement, such as bolts, nuts, unions, packing leathers, flexible 
 tubing of various diameters, and any other parts that are known to require frequent replacing. And 
 besides these, there should be always ready at hand the tools necessary for replacing the parts, and 
 for making any slight alteration in their dimensions which may be required. If such means be 
 provided, the delays incidental to the employment of machinery wiU be reduced to a minimum. 
 
190 MINING ENGINEEEING. 
 
 Explosive Compounds for Mining Purposes. — In the foregoing sections, we have considered 
 the means of perforating rock, for the purpose of placing in a favourable position a charge of explosive 
 compound. It now remains to consider these compounds themselves,, and to show the importance of 
 possessing a- complete and an accurate knowledge of their properties before attempting to apply them 
 to use. Such knowledge is all the more necessary as there is great danger in dealing with a 
 substance of the character in question, of whose particular nature we are wholly or even partially 
 ignorant. 
 
 An explosive compound is a mixture of substances capable of being suddenly transformed into 
 gases by the application of heat. Hence an explosion is a sudden evolution of gases ; and as these 
 gases occupy a much larger volume than the original substances from which they were evolved, 
 pressure will be produced upon the body in which they are retained. It is obvious that the degree 
 of pressure, which represents the strength of the explosive, will vary as the volume of the gases 
 evolved, and thus we have a means of measuring and comparing the strength of the various 
 compounds. Gunpowder being taken as the standard of measurement, and the volume of its gases 
 being assumed as one for a unit of weight of the substance, the volume of gases evolved by the same 
 weight of some other substance, will represent its strength relatively to that of gunpowder. In this 
 way, other things being equal, the value of an explosive may be ascertained when its chemical 
 composition is known. 
 
 The effect of an explosive, however, does not depend wholly upon the volume of gases evolved. 
 The rapidity of their evolution modifies the effects produced in no inconsiderable degree. When a 
 substance in a confined space is slowly converted into gas, this gas will make its escape in the 
 direction in which the least resistance is opposed, and the pressure upon the containing body can in 
 no part be greater than that which is exerted upon the part which yields ; that is, it can never be 
 greater than the resistance of the least resistant part. When, however, the gas is instantaneously 
 evolved, the whole force which it is capable of developing is exerted upon every part of the containing 
 body, because motion requires time, and as no time is allowed for the less resistant parts to yield by 
 moving away before the pressure of the fluid, it follows that the whole force of the latter must be 
 exerted upon all alike. Absolute instantaneity is never obtained in any explosive, but the action of 
 some is so exceedingly rapid as to be practically instantaneous. Thus in measuring the strength of 
 any explosive compound, two things have to be taken into consideration : the relative volume of the 
 gases evolved, and the rapidity with which the evolution takes place. 
 
 The question of rapidity in the evolution of gases by an explosive is one of great practical 
 importance, inasmuch as the effects produced are, as previously stated, very different with different 
 velocities. When the transformation of a substance into its gaseous form is slow, the gases of a charge 
 in a bore-hole do not exert their full energy at once, but they force their way gradually up the hole, 
 and thereby bring their greatest pressure to bear at a considerable distance from the bottom. This 
 is the reason why slow explosives, as gunpowder, do not blow the rock out to the full depth of the 
 hole. Moreover, as time is allowed to elapse during the progress of the explosion, the retaining 
 body, that is, in the case we have assumed, the rock, yields along the line of least resistance, and 
 directly along that line only. The result is that the rock is lifted out bodily, or, as miners and 
 quarrymen express it, " the explosion heaves." When, on the contrary, the transformation of the 
 substance occurs instantaneously, the full force of the enlarged volume is at once exerted in all 
 directions, and the rock is not only blown out to the full depth of the hole, but, being violently 
 strained in every direction, it is blown out in fragments, or, in miner's language, " the explosion 
 
SHAFT-SINKING. 191 
 
 sLatters." Thus, classified according to their action, we have two kinds of explosive compounds, 
 which may be described as " rending " and " shattering " compounds respectively. These classes 
 of explosives are represented by gunpowder and nitroglycerine ; the other compounds will be ranged 
 under one or the other of these classes, according as their properties approach more nearly gunpowder 
 on the one hand, or nitroglycerine on the other. 
 
 It will appear from the foregoing statements that the strength of an explosive compound, or in 
 terms more strictly accurate, its available strength, depends upon two conditions, namely, the 
 relative volume of the gases evolved and the rapidity of the action of evolution ; for it has been 
 shown, that the full force of the expansion cannot be exerted upon the containing body, except when 
 the evolution of the gases takes place instantaneously. Hence it follows that with equal relative 
 volumes of gases, the shattering compounds possess greater available strength than the rending com- 
 pounds, and that, with this condition, the available strength of any compound is as the rapidity of 
 evolution. When, therefore, we know the relative volume of the gases generated by any explosive, 
 and the rapidity with which they are produced relatively to the case of gunpowder, its strength 
 relatively to the latter compound may be accurately determined and clearly expressed. 
 
 The advantages of strength in an explosive compound are sufiSciently obvious to need but little 
 explanation. If, weight for weight, one of two compounds which may be purchased at the same 
 price possesses greater strength than the other, there will evidently result an economy from the 
 adoption of the stronger, since a smaller quantity will be required. But the economy is to be sought 
 mainly in another direction, and it may exist in an important degree even when there is great 
 inequality in the price of the two substances. To produce a determinate effect by means of a blast, 
 whatever the nature of the explosive adopted may be, the centre of action of the charge must be 
 placed at a certain point relatively to the unsupported' faces of the rock. The greater the strength 
 of a given volume of the explosive, the smaller will be the space occupied by the charge ; that is, the 
 space varies inversely as the strength of the explosive. Hence the section of the bore-hole may be 
 varied in the same ratio while keeping the centre of action at the same points ; and by this means 
 the labour of boring may be greatly lessened. For as the area of a hole increases as the square of 
 the diameter, it follows that a small reduction of the latter will materially diminish the cube of the 
 rock to be removed by the boring tool. A limit is, however, placed in this direction by the strength 
 of the tool, the dimensions of which cannot in practice be indefinitely reduced. But in the case of a 
 very small diameter of bore-hole being required theoretically, the condition may be in some degree 
 satisfied by diminishing the depth. So that generally it may be stated that the labour of boring 
 will vary as the strength of the explosive employed. 
 
 Another advantage of the strength due to rapid ignition lies in the nature of the " tamping " 
 required. When the evolution of the gases takes place slowly their force is developed progressively, 
 and in order to restrain this force until it has become suflScient to rend the rock, it is necessary 
 to " tamp " the hole, that is, to fill it above the charge with some strongly resistant substance. This 
 necessity involves considerable labour, and some danger. But when, on the contrary, the evolution 
 occurs instantaneously, any resistance will prevent the gases from escaping through the bore-hole, 
 and therefore the atmosphere alone will be suflScient in many cases, and a very light tamping in 
 all. Thus we have, besides a lessening of the danger, an important economy resulting in this 
 direction from the employment of shattering compounds. The advantage of an effective action 
 without tamping becomes especially apparent when blasting in fissured and vughy rock. In such a 
 case, it is often impossible to bore a hole that is not in communication either with the face or with 
 
192 MINING ENGINEEEING. 
 
 deep fissures or spacious vuglis in the rock ; and under such conditions as these, a slow explosive 
 would exhaust its energy through these spaces. 
 
 It will be justly inferred from the foregoing statements, that the shattering compounds are 
 generally more suitable for blasting purposes than those which are of a rending character. But as 
 circumstances in all cases modify the means employed, so in blasting operations conditions will often 
 occur that will be best satisfied by the latter class of explosives. Thus in dealing with tender and 
 friable rocks the shattering compounds would produce but little effect, inasmuch as such material 
 would be simply crushed within a certain radius of the charge. In general it may be stated that the 
 less hard and tenacious the rock, the less suitable the shattering explosives become. So also the 
 purpose of the blasting will determine the class of explosives to be employed. In building-stone and 
 slate quarries, or in a coal seam, where it is required to extract the produce in a certain condition, the 
 rending class is alone applicable. In such cases, the shattering explosives would render a large 
 jaroportion of the produce useless by breaking it up into small fragments. On the other hand, for 
 the extraction of the substances in large and sound blocks, the lifting and rending action of the slow 
 explosives is particularly suitable. But in ordinary limestone and road-metal quarries, in tunnels, 
 headings, and shafts, and in many metalliferous veins, where the state in which the produce is 
 extracted is of little or no importance, the strong, shattering explosives may, if no other conditions 
 weigh, be advantageously employed. 
 
 Hitherto we have considered explosive compounds solely from the point of view of their 
 efficiency as blasting agents. There are other conditions, however, to be taken into account in 
 determining the suitability of a given compound for any particular purpose. In many situations, but 
 more especially in shafts, there is an abundance of water present. If the nature of the explosive to 
 be used is such as to be readily affected by water, precautions must be taken to protect it from the 
 influence of the water. These precautions, the character of which has been already described, neces- 
 sitate much labour and expense. Moreover, the difficulties of tamping in such situations are 
 enormously increased. Hence a compound whose properties undergo no change in the presence of 
 water will, under the conditions supposed, offer advantages of a weighty character. And if, besides 
 this, it be of the class for which water will serve as a sufficient tamping, another advantage will be 
 added of hardly less magnitude. In subaqueous blasting operations, these qualities of the compound 
 will obviously assume their highest degree of importance. 
 
 There yet remain other considerations respecting the nature and action of an explosive that are 
 of the highest moment. All the merits to which attention has been directed may exist in a compound 
 side by side with defects of a character that will render its employment impracticable. The gases 
 evolved by an explosion are always of a more or less unwholesome nature ; but when they become 
 particularly noxious, the compound becomes unfit for use in confined situations. This circumstance 
 is of weighty importance in mining operations which are carried on in close shafts, or still closer 
 headings. Under such conditions, an explosive that generates a large volume of noxious fumes is 
 altogether unsuitable, and its use, whatever merits it may otherwise possess, ought to be prohibited. 
 Safety in handling is also an essential quality in an explosive. Compounds in which an explosion 
 may be produced by unknown causes, or by causes that can be ill provided against, introduce an 
 element of danger that cannot be compensated by any merits which they may possess. This is a 
 question that bears heavily upon the responsibility of those who have the conduct of operations, and 
 such should be on their guard, particularly in these times of hasty execution of work, lest a desire to 
 
SHAFT-SINKING. 193 
 
 keep pace with the requirements of the times should tempt them to adopt a more dangerous 
 compound, to the risk of human life. 
 
 There is yet another condition which an explosive compound must satisfy to enable it to be of 
 common use, namely, cheapness of production. The exigencies of rock blasting are such as require 
 large quantities of the substance employed, and unless that substance can be obtained at a cheap rate, 
 the cost of excavating by such means will not bear a favourable comparison with that of purely hand 
 labour ; or, where the latter is impracticable, it will render the enterprise unprofitable. This condition 
 reduces a numerous list of explosive substances to the following few, which alone are extensively 
 applied to blasting purposes. 
 
 In the foregoing considerations it has been assumed that the strength of an explosive is 
 dependent upon two conditions, namely, the relative volume of the gases generated, and the rapidity 
 of their evolution. This view supposes the relative volume of the gases to be that existing at the 
 moment of explosion. But as the volume at that moment is dependent upon several causes, it will 
 be well to separate the latter, in order to obtain thereby a fuller and more accurate view of the 
 subject. If, then, we understand relative volume to mean that of the gases when at the same 
 temperature as the substance from which they were evolved, the strength of an explosive wil) 
 obviously depend upon : 1. The relative volume of the gases generated, to which the force developed 
 is primarily due ; 2. The density of the gases, whereby the degree of their expansibility is limited ; 
 3. The heat generated by the chemical change produced in the substance, which heat causes the gases 
 to expand in volume according to a law already explained ; and 4. The rapidity with which the 
 chemical change in the substance takes place. The volume and the density may be expressed by 
 the v:eight of the gases, an expression of more convenient use. The relation subsisting between the 
 weight of the gases produced, their nature, and the heat generated by their production, is a complex 
 one, the three being mutually dependent. If, however, the foregoing remarks concerning these 
 matters have been fully understood, there should be no difficulty in perceiving this relation, nor in 
 applying the practical consequences that result from it. In treating of the combustion of coal, the 
 production of carbonic oxide and of carbonic acid was considered, and it was shown that the heat 
 generated in the latter case was double that generated in the former case. Also in treating the 
 subject of compressed air, it was demonstrated that the volume of any gas is dependent upon its 
 temperature. When these facts are borne in mind, the effects of perfect combustion in the explosive 
 compound, and the importance of the degree of heat attained in modifying the expansion of the 
 gases evolved, become clearly apparent ; and we are enabled thereby to form at least an approximate 
 estimate of the force which any given explosive of known composition is capable of developing. By 
 reason of the difficulty of taking every condition into account, the relation of the strength of an 
 explosive to the volume of its gases, and to the heat generated, has not been determined 
 experimentally with precision. But the researches of Messrs. Eoux and Sarrau have shown 
 conclusively that the simple explosive force of a substance is proportional to the product of the 
 weight of the gases evolved by the heat generated ; and that the detonating force is pro- 
 portional to the heat. The difference between simple explosion and detonation will be hereafter 
 explained. 
 
 Gunpowder. — Grunpowder is the representative of the rending class of explosives, and it is the 
 only one of that class that is extensively employed. It is a compound of sulphur, saltpetre, and 
 charcoal, and exists in a form that is too well known to need description. Until very recent times, 
 
 2 c 
 
194 MINING ENGINEEEING. 
 
 this explosive was the only one applied to blasting purposes. Its slow-burning character renders it 
 admirably suitable for those operations in which a rending action is required. Indeed, in the cases 
 to which allusion has already been made, namely, those of building-stone and slate quarries, and 
 seams of coal, gunpowder is alone admissible. And for these purposes this compound will probably 
 continue to be employed, whatever the modifications introduced into those of the other class may be, 
 since it is difficult to conceive of an explosive more suitable in its mode of action, or capable of being 
 more cheaply produced. But in the cases in which a rending action is not desirable, gunpowder, 
 except under certain conditions to be explained hereafter, is greatly inferior to the compounds of the 
 other class, and its use in such circumstances is being gradually abandoned. Besides the unsuitability 
 which is due to its slow action, gunpowder also possesses the defect, very important for blasting 
 purposes, of being readily affected by moisture. This property renders it difficult of employment in 
 wet ground. By the adoption, however, of fitting precautions, such as the use of waterproof 
 cartridges, and the other means that have been already described, the defect may be overcome, 
 though at the cost of labour and an increased outlay. One immense advantage possessed by gun- 
 powder is the safety with which it may be handled and transported from place to place. This 
 advantage is not unfrequently contested by those who are prejudiced in favour of the newly- 
 introduced shattering explosives ; but the experience of centuries is sufficient to place this quality of 
 gunpowder beyond reasonable dispute. 
 
 The eminent gunpowder makers, the Messrs. Curtis and Harvey, stimulated by the success which 
 has attended the introduction of the nitroglycerine compounds, have lately made an attempt to render 
 their explosive capable of competing with those compounds in the very cases to which the latter are 
 most applicable, namely, to those operations in which a shattering action is desirable. In this attempt 
 they have succeeded in a very remarkable degree. The new compound which they have produced 
 possesses a strength greatly superior to that of the ordinary blasting powder. This increase of 
 strength appears to be due rather to a quickening of the ignition than to an augmentation of the 
 relative volume of the gases evolved. If it can be shown that the velocity of the gases during 
 evolution is capable, in the case of gunpowder, of being notably increased by a change of the 
 chemical composition, much will have been accomplished towards the reintroduction of that safe, 
 convenient, and cheap explosive into those situations from which it has been driven by the nitro- 
 glycerine and nitrocotton compounds. This result, in some degree at least, appears to have been 
 attained by the Messrs. Curtis and Harvey, in their new blasting powder, and it must be acknow- 
 ledged that in this they have done good service to mining. We shall have occasion later, when 
 treating of the most effective means of firing explosives, to show how this new compound may be 
 made to equal in disruptive force the best preparations of dynamite. It may be desirable to add 
 that the manufacturers claim for this compound, which is commercially known as the E.S.M. powder, 
 a strength equal to five times that of the common blasting powder. Such a degree of strength may 
 be undoubtedly attained under the condition of suitable firing to which we have alluded. If this fact 
 be viewed relatively to the foregoing considerations on the advantages of strength, it will be evident 
 that the use of this powder must lead to a notable economy. 
 
 Grunpowder is sometimes employed in a compressed form in cartridges for blasting purposes. 
 The chief object of the compression is to obtain within a minimum volume a given store of force. 
 This object, however, is only partially attained when the firing takes place by the ordinary means, 
 inasmuch as the combustion of the compressed grains proceeds slowly, thereby causing a waste of 
 
SHAFT-SINKING. 195 
 
 energy. But when special means of firing are adopted, a marked economy is to be gained by com- 
 pression. This question will be considered in a subsequent section. 
 
 Nitroglycerine. — Nitroglycerine is the representative of the " shattering " class of explosive com- 
 pounds. This violent explosive was first discovered by Sobrero in 1847, but it was not till the year 
 1860 that it was applied to blasting purposes. Since that time, when it was brought prominently 
 into notice by Alfred Nobel, a Swedish engineer, its use, under various forms, has been rapidly 
 extending. 
 
 Nitroglycerine, or glonoin, exists in its pure state as a nearly colourless liquid ; but usually, 
 owing to the colouring matters contained in the glycerine employed in its manufacture, it is of a 
 light yellow colour, somewhat oleaginous, inodorous, and of a sweetish pungent flavour. "When 
 applied to the tongue, in the most minute quantity possible, the maxillary glands are stimulated, 
 and in a few minutes a violent throbbing headache supervenes. The latter effect is produced by 
 merely touching it with the hands. It has been remarked, however, that the system speedily 
 becomes sufficiently accustomed to the poisonous nature of this compound to allow of its being handled 
 with impunity. The specific gravity of nitroglycerine is 1*6 at a temperature of 60° Fahr. It 
 solidifies at 45° Fahr. if perfectly pure ; at 320° Fahr. it decomposes, giving out red vapours, and at 
 a higher temperature it explodes. It is insoluble in water, but soluble in alcohol — one part to four 
 parts, — ether, and some other organic products; it separates from the alcoholic solution by the 
 addition of water. When in a pure state, nitroglycerine remains for a long time unchanged, even 
 when exposed to the varying influences of the weather ; but if impure, it is subject to rapid change, 
 becoming of an orange-yellow colour, and evolving fumes. When in this state, it does not congeal 
 till a much lower temperature than 45° Fahr. has been reached, and it very readily explodes. Most 
 of the terrible accidents that have occurred from the accidental explosion of nitroglycerine have been 
 due to this change of state. 
 
 Nitroglycerine is produced by the action of nitric acid in the cold upon glycerine, the sweet 
 substance obtained from oils and fats by the process known as saponification, that is, a treatment of 
 these fatty substances with an alkali, or with watef itself at a high temperature, or with steam. 
 The compound may be safely prepared, according to Professor Abel, by adding concentrated glyce- 
 rine gradually to a cold mixture of one part of nitric acid, of specific gravity 1*52, and three parts, 
 of concentrated sulphuric acid, the mixture being kept cold by artificial means. When the proper 
 proportion of glycerine has been introduced, the mixture being stirred during the addition, the latter 
 is poured into water, by which the separation of the nitroglycerine is effected. Nitroglycerine is 
 manufactured as three different preparations, due to differences of chemical composition ; these prepa- 
 rations are known respectively as " Mono-nitroglycerine," " Di-nitroglycerine," and " Tri-nitro- 
 glycerine." The latter has shown itself to be the most suitable for industrial purposes. The most 
 important matter, however, in the manufacture of nitroglycerine is the purity of the materials 
 employed. The glycerine must be free from sugar, fatty acid, or saline impurities ; and the acids 
 required must be used in the due proportions, there being no more water therein, nor in the glycerine, 
 at one time of making than another. It is essential that the resulting compound be of uniform 
 quality, invariable in composition, and free from water, and all other impurities. If these conditions 
 of manufacture be not fully satisfied, the substance becomes a dangerous one to handle by reason of 
 the changes which it is liable to undergo. The impure compounds may be recognized by their deep 
 yellow colour, and also by the low temperature required to congeal them. If all such were rejected 
 
 *» c 2 
 
196 
 
 MINING ENGINEEEING. 
 
 by the persons in charge of blasting operations, the number of accidents from premature explosions 
 would be greatly reduced. 
 
 A description of the mode of manufacturing nitroglycerine would be out of place here ; we shall, 
 therefore, give only the formulae according to which the three several preparations may be produced. 
 These formula, which are due to Liecke, are the following : 
 
 Mono-Nitroglycerine. — Grlycerine, 100 grammes ; nitric acid, sp. gr. 1 ' 3, 200 grammes. Dissolve 
 the glycerine in the nitric acid, and add sulphuric acid 200 cubic centimetres. The product should 
 
 Di-Nitroglycerine. — Sulphuric acid containing 1 eq. water, two volumes •, nitric acid, sp. gr. 1 "4, 
 one volume ; mix the foregoing, reduce the temperature to 32° Fahr., or below, and drop into it : 
 
 Glycerine, pure, one volume. The product should be o-vrnt-nT [ O*- 
 
 Tri-Nitroglycerine. — Sulphuric acid, 3 • 5 parts ; nitrate of potash, 1 part ; cooled to 0° Fahr. 
 This produces KO + 4S0^ + 6H0 ; from this the concentrated fuming nitric acid is separated by 
 decantation. Being maintained at the temperature of 0° Fahr., glycerine • 8 part is very gradually 
 
 added, giving the product ^ 2N0* ^*" 
 
 In combining the glycerine with the acids, a large amount of heat is evolved, and means must 
 be provided for absorbing this heat, so that the mixture shall not under any circumstances exceed a 
 certain temperature. This temperature Sobrero fixes at 32° Fahr. If this condition be not fulfilled, 
 the character of the resulting compound is changed, and may become unsafe for use. From the fore- 
 going remarks concerning the manufacture of nitroglycerine, it appears that safety in handling the 
 compound is, in a high degree, dependent upon the purity of its constituents, and the care exercised 
 in combining them. 
 
 As a blasting agent, nitroglycerine possesses merits which render it greatly superior to gun- 
 powder for many purposes, in company with some grave defects. When ignited in the open air, it 
 burns away rapidly, but does not explode. When confined, however, it explodes, when ignited, with 
 great force. In both cases very little smoke is produced ; and, if the combustion is complete, the 
 resulting gases consist of nitrogen, carbonic acid, and vapour of water. Thus, in confined situations, 
 the fumes produced by an explosion of nitroglycerine are less noxious than those resulting from an 
 explosion of gunpowder. But if the combustion is incomplete, large volumes of carbonic oxide are 
 evolved, and in such a case the products are of a particularly noxious character. Hence it is 
 important, when employing nitroglycerine and its compounds, so to fire the charge that the combus- 
 tion of the substance may be complete. A sharp blow will provoke an explosion in nitroglycerine, and 
 the same result may be produced by the detonation of a charge of fulminate in contact with it. AVhen 
 fired in this way, nitroglycerine explodes with extreme violence, and when applied under such con- 
 ditions to blasting operations, efi"ects are produced that could not be obtained by the use of gunpowder. 
 The enormous force developed by this explosive when fired by detonation allows deep holes of small 
 diameter to be adopted, a consequence that leads to a considerable economy of labour, and to a 
 notable acceleration of the progress of the work. Any explosive compound, even in minute quanti- 
 ties, is capable of producing an explosion of nitroglycerine, and this circumstance renders the latter 
 dangerous for common use. The insolubility of nitroglycerine in water gives it a very great advan- 
 tage over gunpowder by allowing of its use in wet situations, or under water, without any protective 
 
SHAFT-SINKING. 197 
 
 covering. As this property, moreover, renders water tamping sufficient, it must be considered as 
 constituting one of its greatest merits. Though, nitroglycerine may be very readily exploded when 
 in a liquid state, when frozen it can hardly be exploded by the strongest detonators, particularly 
 when of pure composition. This property constitutes both a merit and a defect ; a merit inasmuch 
 as the compound may be safely transported in a frozen state, a defect as it freezes at a high tempera- 
 ture. The latter property is highly conducive to convenience in transport, but it is a somewhat 
 serious disadvantage when the substance has to be applied in use. 
 
 The chief defect of nitroglycerine, however, when employed in its pure state as a blasting agent, 
 is due to its liquid form, and its consequent tendency to leak out of receptacles in which it is trans- 
 ported, stored, or used. In blasting operations, the explosive material with which the hole is 
 charged may flow into fissures in the rock, and thus be conveyed to points where its existence would 
 not be suspected. Afterwards, by the boring of other holes at these points, an accidental explosion 
 may be caused attended with disastrous consequences. Numerous terrible nitroglycerine explosions 
 have occurred in different parts of the world, the majority of which are considered to have been 
 primarily due to the leakage of the substance from the packages in which it was stored and trans- 
 ported, notwithstanding the care exercised in the construction and the filling of these packages. The 
 great susceptibility of nitroglycerine in the liquid form to detonation, especially during hot weather 
 or in tropical climates, would lead to the explosion of portions of the liquid which had escaped from 
 the packages, by accidental concussion, or comparatively light blows. 
 
 Dynamite. — The inconvenient and dangerous character of nitroglycerine in its liquid form led 
 to the abandonment of its use, and, in numerous instances, to the prohibition of its manufacture. To 
 overcome the difficulties thus occasioned, Alfred Nobel, to whom the introduction of the compound as 
 an industrial agent was due, commenced a series of observations and experiments which ended in the 
 very important discovery that the readiness with which an explosion may be produced in nitro- 
 glycerine by means of a detonation is not lessened, but rather increased, by the presence of an inert 
 substance. Nobel recognized at once the immense importance of this discovery, since it afforded 
 a means of removing the principal defects possessed by the liquid nitroglycerine. By mixing the 
 latter substance with a material of a porous character, its form would be practically changed to that 
 of a solid, in which condition it might be handled like any other solid explosive substance, while 
 affording the additional advantage of plasticity. It was clear, indeed, that if nitroglycerine could be 
 presented in this way, all the objections arising out of its liquid form would be completely removed. 
 As it was obvious that the strength of the resulting compound of explosive and inert matters must 
 necessarily be less than that of the pure substance, in proportion to the quantity of inert matter 
 present, it became desirable that the latter should be very porous, so as to absorb as much of the 
 explosive liquid as possible. It was also important that this inert matter should be of a nature 
 incapable of giving rise to chemical change in the nitroglycerine itself. These properties were found 
 combined, and in a high degree of perfection, in a kind of silicious earth, abundant in many parts of 
 Germany, where it is known as " kieselguhr." This earth, or " rotten-stone," was therefore selected 
 as a suitable absorbent medium, and it was found by experiment to fulfil all the conditions required 
 in a very complete manner. The solid compound resulting from the mixture of the liquid nitro- 
 glycerine with this infusorial earth was called by Nobel dynamite, under which name it has since 
 come into common use. Dynamite contains about 75 per cent, of nitroglycerine ; but as the strength 
 of the latter is so much greater than that of gunpowder, this degree of dilution does not occasion any 
 
198 MINING ENGINEEEING. 
 
 important detriment to its usefulness. It may, moreover, be remarked here tliat thougli the strength 
 of dynamite is only 75 per cent, of that of nitroglycerine, regarded from the point of view of the 
 effects which it is capable of producing, it is scarcely inferior to the latter, by reason of the forces 
 developed by its explosion being more widely distributed. 
 
 Dynamite, thus constituted, is a moist pasty substance of a light-brown or pinkish-yellow colour. 
 The only defect to be feared was the exudation of the liquid nitroglycerine from the mass. But 
 experience has proved that the kieselguhr is capable of absorbing and retaining, even under consider- 
 able pressure, the proportion of nitroglycerine already mentioned. Improvements in the mode of 
 preparation have removed any tendency that might have existed towards this source of danger. 
 Dynamite is now supplied in the form of small cylindrical cartridges, consisting of the explosive in a 
 compact condition, enclosed in a wrapping of parchment paper. These cartridges are consolidated by 
 pressure, whereby any excess of the liquid, which the porous earth will not hold absorbed, is expelled. 
 Thus the separation of the nitroglycerine during transport, handling, or exposure to elevated 
 temperatures, appears to have been effectually guarded against. The consistency of the dynamite 
 charges prepared in this way is that of moderately dry putty, and the fingers are scarcely soiled with 
 nitroglycerine when the uncovered substance is handled. 
 
 The plastic character of dynamite constitutes an important advantage in practice, inasmuch as 
 the charge may be made, by pressure, to fill the bore-hole completely, a condition that is essential to 
 the full utilization of the gases evolved by an explosion. This advantage becomes particularly 
 apparent in rugged and uneven holes. 
 
 The explosion of dynamite takes place under precisely the same conditions as that of liquid 
 nitroglycerine. When in a frozen state it explodes with difficulty ; no explosion can be started in it 
 when its temperature is below 32° Fahr. If fired by the ordinary means when exposed to the air, 
 it burns slowly, after the manner of moistened or compressed gunpowder, with a characteristic yellow 
 flame. The products of this combustion are nitrogen, carbonic acid, and vapour of water, accom- 
 panied with traces of nitrous vapours sensible to the smell. If combustion is incomplete, carbonic 
 oxide is produced. The silica remains as a fixed residue. When dynamite is fired in a confined 
 situation, it explodes violently, provided the containing body offers great resistance. Otherwise, no 
 explosion occurs. Thus a strong wooden cask, bound with iron hoops, and containing 11 lb. of 
 dynamite, was on one occasion placed upon a fire and there consumed. At a certain moment the 
 cask burst slowly, and the contents burned as in the open air. The same results were obtained when 
 a thin sheet-iron cask was substituted for the wooden one. The direct ignition of dynamite in 
 confined situations is difficult, and can be satisfactorily accomplished only by means of a strongly 
 detonating priming charge. When fired in this way, whether in a confined situation, or in the open 
 air, dynamite explodes with great violence. If struck with a hammer upon an anvil, the portion 
 struck explodes violently, but unless the blow is very heavy and the resulting detonation severe, the 
 explosion is not communicated to the rest of the mass. The shock of stone upon stone will seldom 
 provoke an explosion in dynamite, and the shock of iron upon wood, or of wood upon stone, has 
 never been known to produce that effect. 
 
 Lithofracteur. — Numerous attempts have been made to substitute combustible and explosive 
 absorbent media for the incombustible silicious earth used in the preparation of dynamite. The 
 purpose of this substitution is to increase the strength of the explosive by rendering the absorbent 
 matters, which in dynamite are wholly inert, themselves explosive, to ensure perfect combustion when 
 
SHAFT-SINKING. 199 
 
 the charge is fired, and to prevent the formation of noxious gases. The first of these objects is unattain- 
 able in the direction in which it is usually sought. No two explosive substances generate their gases 
 with the same degree of rapidity, and it is obvious that if any two be mixed as independent explosives, 
 the resulting compound cannot exceed in strength that of the more rapid substance, since the tardy 
 forces of the other can take no part in the work done. The strength, however, of a compound may 
 be greater than that of either of its explosive constituents when the latter are chosen to act in 
 conjunction in producing an explosion ; in other words, if the several ingredients are of such a nature 
 and in such proportions that they are capable of acting towards each other in a manner that tends to 
 promote rapid and perfect combustion. This condition has been overlooked in many of the nitro- 
 glycerine compounds that have been introduced as improvements upon dynamite. Many of these 
 compounds having failed to evince the superiority claimed for them, while they unmistakably 
 showed themselves to be more dangerous to handle, have never got beyond the experimental stage. 
 Others, having proved in some degree successful by reason of the favourable conditions under which 
 they were brought into notice, are slowly but surely dropping out of use. Among these unsuccessful 
 attempts, however, others of a different character were made. These, based upon a true chemical 
 knowledge, have, in a more or less satisfactory degree, attained the end proposed ; and are likely to 
 assume, in the future, an importance which is not yet accorded to them. These compounds we now 
 purpose to describe. 
 
 Lithofracteur, by reason of its extensive application as a blasting agent, possesses a claim to first 
 notice. It consists, according to Lieutenant Trauzl, of about 52 per cent, of nitroglycerine, 30 per 
 cent, of silicious earth and sand, 12 per cent, of powdered coal, 4 per cent, of nitrate of potash, and 
 2 per cent, of sulphur. These proportions, however, are not always adopted, and frequently an 
 impure kind of gunpowder and sawdust are employed as ingredients. The nitroglycerine is prepared 
 with special regard to purity, and to this circumstance is probably due the immunity from accident 
 which has hitherto marked its manufacture. Thus constituted, lithofracteur presents itself in the 
 form of a dark, blackish-grey, pasty substance. It is made up into cartridges in the same manner as 
 dynamite, and may be used in precisely the same way, and under precisely the same conditions. In 
 the matter of exploding, there is no difierence observable between lithofracteur and dynamite. It is 
 claimed for the former substance that, containing only 50 per cent, of nitroglycerine, it is capable 
 of developing a force equal to that of dynamite containing 75 per cent., and consequently is 
 cheaper than the latter compound; and that its combustion produces fumes of a less noxious 
 nature. 
 
 Horsleys Powder. — Numerous attempts have been made to substitute chlorate of potash 
 compounds for gunpowder, which compounds are capable of more violent action than the latter. But 
 most of these attempts ended in failure, by reason chiefly of the dangerous character of the 
 compound. The property, which they all possessed, of exploding when subjected to comparatively 
 slight friction or percussion, would alone have suflSced to prevent their being adopted as practically 
 useful explosive agents, even if a decided superiority over gunpowder in the matters of efficiency 
 and economy had been shown. To lessen this tendency of the chlorate of potash mixtures to explode 
 prematurely, inert substances were added for the purpose of serving as protective agents by absorb- 
 ing the violence of the blows or concussions to which the mixtures might be subjected. In some 
 instances, the protective action of these agents was such as to render that of the explosive 
 less rapid and violent than that of gunpowder. Other attempts were more successful, and in these 
 
200 MINING ENGINEEEING. 
 
 instances a strong and comparatively safe compound was produced. This result was arrived at by 
 mixing with the salt, substances containing, in addition to carbon, a considerable proportion of 
 hydrogen, such as powdered nut-galls, resins, and tannin. Of the compounds thus prepared, that 
 known as Horsley's may be taken as a typical, and the most successful example. This consisted of 
 a preparation of chlorate of potash and powdered nut-galls in certain proportions; the results of 
 experience showed that when prepared in this way the compound possessed great explosive force, and 
 was of a comparatively safe character. But though Horsley's powder was applied somewhat 
 extensively to blasting purposes, it is as a nitroglycerine compound that it deserves notice here. 
 One of the attempts to which attention was directed in a former paragraph, was that of 
 employing Horsley's powder as the absorbing medium for the nitroglycerine. In this case, the 
 proportion of the latter was about 20 per cent., and the resulting compound was found to possess 
 very violent explosive properties. This compound, which has been extensively applied to mining 
 operations in Norway, is fired, like dynamite and lithofracteur, by means of a percussion fuse. 
 It possesses an advantage over these latter explosives in not losing its susceptibility to detonation at 
 low temperatures. 
 
 Brains Blasting Powder. — The latest and the most successful attempt to produce a nitro- 
 glycerine compound superior in character to dynamite is that of Mr. W. B. Brain, the result of 
 which attempt is seen in the explosive known commercially as Brain's blasting powder. This 
 exceedingly strong explosive compound is remarkable as the outcome of sound chemical knowledge 
 and exhaustive experiments. Its composition has been carefully considered, and the action of each 
 of the constituents, both individually, and in common, accurately determined, in order that the end 
 proposed might be fully and with certainty attained. The intelligence which has been exercised in 
 the production of this explosive is sufficiently manifest in the success which has attended its applica- 
 tion to the purposes for which it was designed. It has shown itself possessed of the qualities 
 necessary in an explosive for common use, not the least of which qualities is its freedom from noxious 
 fumes when exploded in confined situations. The merits, as well as the chemical composition, of this 
 compound are clearly described and fully explained in the following report, prepared at the writer's 
 request by Mr. Linford, consulting chemist, who possesses opportunities of rendering himself fully 
 acquainted with the method of its manufacture, and with its behaviour in store, in transit, 
 and in use : 
 
 " Brain's blasting powder consists of a base of chlorate of potash, or a mixture in varying 
 proportions of chlorate and nitrate of potash, wood-charcoal, and prepared sawdust, which base is 
 combined with 40 per cent., or less, of tri-nitroglycerine. In chemical composition this compound 
 approaches nearest to the powder known as Horsley's, but it is much less costly, and the proportions 
 of oxidizing and oxidable ingredients render it, in its strongest form, more powerful, and admit of 
 greater variation in rapidity if required. It is superior to lithofracteur in having a more easily 
 detonable base, and therefore generating more power with less nitroglycerine. For the same reason 
 it is of course greatly superior to dynamite, which has an incombustible base; in fact, the No. 1 with 
 40 per cent, of nitroglycerine is a more powerful explosive than any dynamite I have yet seen with 
 75 per cent. From a number of experiments, I estimate its force as quite equal to pure tri-nitro- 
 glycerine. This at first sight seems an anomaly, but it is thus explained. The force of an explosive 
 depends upon : 1. The amount of gas formed ; 2. The density of that gas ; 3. The amount of heat 
 generated by the explosion ; 4. The rapidity with which the gas is liberated. Practically we may 
 
SHAFT-SINKING. 201 
 
 talce nitroglycerine and guncotton, when detonated, to be the most rapid explosives in use, and 
 gunpowder to be the slowest, 
 
 " The composition of glycerine and cotton is similar, each consisting of carbon, hydrogen and 
 oxygen, but in somewhat different proportions, and in the nitro-compounds certain atoms of the 
 hydrogen are replaced by NO2. In the tri-nitroglycerine, the proportion of hydrogen so replaced 
 furnishes oxygen sufficient to convert all the carbon into CO2, carbonic acid, and indeed leave a 
 portion in excess as N2O. In the cotton, the proportion being less, the carbon is chiefly converted 
 into CO, carbonic oxide. The remaining elements, oxygen and hydrogen, unite in the same propor- 
 tion as they exist in the cotton, forming H2O, or water in a state of vapour. Now H2O, or water 
 vapour, is not so dense a gas as CO2, or carbonic acid, the relative weights being 9 and 22, and CO, 
 or carbonic oxide, is between the two, or 14, so that it is easily seen that a cubic foot of CO2 
 generated in the same time, and at the same temperature, produces more explosive force than the 
 same bulk of CO, or H2O ; but it is a well-known fact that carbon oxidized to CO2 generates about 
 one-half more heat than the same amount of carbon oxidized to only CO. 
 
 " In Brain's powder we have, as will be seen from the above considerations, the required condi- 
 tions thoroughly fulfilled ; there is nitroglycerine in sufficient quantity to ensure instautaneity of 
 detonation, while the excess of oxygen is also used up, together with all that in the chloi'ate, in 
 producing, with the carbon of the wood and charcoal, carbonic acid ; and, with the exception of the 
 small amount of chloride of potassium formed, the whole is converted into gas as instantaneously as 
 any other explosive. It is a misconception of the nature of a detonation to sujjpose the possibility 
 of the nitroglycerine in such a mixture being detonated first, and the chlorate compound after. The 
 chlorate and charcoal is the more easily detonated of the two, and really ensures the perfect 
 detonation of the other. It is a fact acknowledged by all who use nitroglycerine, both in Europe and 
 in America, that a powerful detonating charge, from 15 to 20 grains of fulminate, is required to ensure 
 perfect detonation, and the same holds good of guncottxjn. Now I have exploded many charges of 
 Brain's powder, never using more than 10 grains of fulminate, and never failed to detonate the entire 
 charge. In fact, looking at the composition of the powder, I do not think it would be possible to 
 detonate part of a charge either in the open air or in untamped holes. Dynan^ite, it is well known, 
 generally leaves a vapour causing severe headache, showing that a portion must have been volatilized 
 unburnt. Guncotton, as shown by an accident which occurred at Woolwich Arsenal, unless detonated 
 with a powerful detonating charge, is often blown away, neither of which sources of loss are, I 
 believe, possible with- this powder, while the small amount of mineral matter, chloride of potassium, 
 is more than compensated for by the density and temperature of the gas generated." 
 
 Guncotton. — Gruncotton, nitrocotton, pyroxilin, or tri-nitrocellulose, was discovered by Schon- 
 bein in 1845, within two years of the discovery of nitroglycerine. The discovery of Schonbein 
 showed that when cotton-fibre, or wood-fibre (cellulose), is submitted to the action of nitric acid, or a 
 mixture of nitric and sulphuric acids, at ordinary temperatures, it becomes endowed with explosive 
 properties, a proportion of the hydrogen in the cellulose being replaced by an equivalent amount 
 of nitric peroxide. The degree of nitration of the cellulose, and the consequent explosive power of 
 the product, vary with the strength of the acids employed, and also with the temperature at which 
 the converting operation is conducted. Gruncotton proper, or tri-nitrocellulose, C6Hj3(N02)05, is 
 the most highly explosive of those substances yet known. 
 
 In the manufacture of guncotton, as in that of nitroglycerine, purity of the constituent sub- 
 
 2 D 
 
202 
 
 MINING ENGINEERING. 
 
 stances is essential to the stability of the product, and, consequently, to the safety with which it may 
 be handled. The means now adopted to obtain the requisite degree of purity in the materials, 
 and the precautions taken to ensure unifoi'mity in the resulting compound, are such as to render 
 guncotton one of the safest explosives in use. The following description of the method of its 
 manufacture, by Professor Abel, shows the nature of these means and precautions, and gives a clear 
 notion of the form in which the explosive is produced. 
 
 " In the production of compressed guncotton, carefully selected cotton-waste is employed, in the 
 place of the cotton-wool used in Schonbein's original process, and of the long staple cotton, spun into 
 loose strands or threads, which was employed in Von Lenk's system of manufacture. The cotton is 
 first carefully picked over, and submitted to a preparatory cleansing process if necessary. It is then 
 opened up in a teasing machine, and cut into suitable lengths, with a view of facilitating its rapid 
 immersion and impregnation in the acid bath. After having been thoroughly dried and allowed to 
 cool in closed vessels, it is immersed, in small quantities at a time, in a perfectly cool mixture of 
 1 part of nitric acid (sp. gr. 1*52), and 3 parts of sulphuric acid (sp. gr. 1'85), and is afterwards 
 allowed to remain for twenty- four hours in contact with about ten times its weight of the mixed 
 acids, to ensure as complete a conversion as possible into guncotton. The vessels containing the 
 cotton and acids are kept closed, and as cool as practicable ; and, at the expiration of the proper 
 period, their contents are transferred to a centrifugal extracting apparatus, by which the guncotton 
 is separated to a great extent from the excess of acid. It is then suddenly plunged, by means of 
 simple mechanical arrangements, in small quantities at a time, into a large volume of water. The 
 object aimed at is to dilute the acid which remains in the guncotton with water so quickly as to 
 avoid the development of heat, and the consequent establishment thereby of a secondary oxidizing 
 action of the nitric acid upon the guncotton — an action which, even if of brief duration, might affect 
 prejudicially the quality, and perhaps also the stability, of the product. The adoption of this pre- 
 cautionary measure, and the long-continued digestion of the guncotton with considerable excess of 
 acids, constitute the prominent improvements which Baron von Lenk effected in Schonbein's process 
 for producing guncotton. After this preliminary washing, the guncotton is drained of water by 
 means of the centrifugal extractor ; it is then rinsed twice in a large volume of water, and passed 
 through the centrifugal machine after each rinsing. It is now transferred to a rag-engine, of the 
 kind ordinarily used in producing pulp for paper-making. By this operation the guncotton is 
 reduced to the state of fine division necessary for its subsequent conversion into homogeneous com- 
 pressed masses : it is subjected, at the same time, to a most searching purification, which is continued 
 in the next operation, the pulp being transferred to ' poaching ' engines, where it is beaten about in 
 a large volume of slightly warm water, which is renewed from time to time. This final washing 
 operation is carried on continuously until the guncotton has passed satisfactorily through a searching 
 test of purity. This method of washing constitutes one of the great advantages of the present system 
 of manufacture. The chief obstacle to the complete purification of the guncotton consisted formerly 
 in the obstinate retention of impurities within the hollow fibres. With a view to their removal Von 
 Lenk prescribed continuous washing during many weeks in running water, and subseqiient boiling 
 with very dilute alkali. But by the application of the pulping and poaching processes, the capillary 
 action of the fibre is greatly reduced, and the washing operation is rendered so searchino- that a 
 decidedly more complete and uniform purification of the material is accomplished in three days, at 
 the outside, than was previously attained by processes which extended over six or eight weeks. At 
 
SHAFT-SINKING. 203 
 
 the conclusion of the washing process, the guncotton pulp is impregnnted with a small proportion of 
 alkaline matter, and is then converted, by a preliminary moulding process, and subsequently by 
 powerful hydraulic pressure, into compact masses of cylindrical and other forms, of about the same 
 density as water, and of dimensions suited to the particular application required. During the whole 
 of these manufacturing operations the guncotton is wet, and therefore absolutely uninflammable. 
 After compression, the finished material is dried either in the open air or in heated chambers, where 
 a rapid circulation of air is kept up. It is then packed ip light wooden boxes for storage or trans- 
 port. The drying process may be deferred for any time, and the damp, perfectly uninflammable 
 guncotton stored in waterproof packages." 
 
 Gruncotton is insoluble in water ; but it is soluble in a mixture of ether and alcohol. The 
 resulting solution is collodion. Guncotton is but little affected by heat until a temperature of 
 300° Fah. is reached ; at that temperature it is decomposed, and burns away with abundant flame, 
 or if confined, it explodes. It does not appear that shocks, however violent, are capable of producing 
 an explosion in it. 
 
 When fired in the open air guncotton does not explode, but burns rapidly away with 
 abundant flame, but without emitting smoke. When, however, it is fired in a confined 
 situation, it explodes without producing either visible flame or smoke, and the violence of the 
 explosion increases as the space within which the substance is confined becomes more limited. If 
 fired in the open air by means of a detonating charge, guncotton explodes with great violence with- 
 out producing flame. This property, which it possesses in common with nitroglycerine, gives it a 
 great advantage over gunpowder in many situations. It is a curious fact that not all fulminatitig 
 substances are capable of producing an explosion in guncotton, and that some of the most violent 
 fail to produce that effect. Thus such powerful explosives as chloride of nitrogen and nitroglycerine 
 are incapable of producing an explosion in guncotton, and the same minimum quantities of fulminate 
 of silver and of fulminate of mercury are required, though the former is a more violent explosive 
 than the latter. A long series of experiments has shown that the fulminate of mercury is the most 
 suitable for the purpose, and that moreover this fulminate must, to produce the full effect, be con- 
 tained by a substance capable of offering considerable resistance to its action. The character of 
 the explosion which occurs in guncotton places this compound in the class of shattering explosives. 
 
 As a blasting agent, guncotton, like nitroglycerine, possesses some important advantages, and 
 some serious defects. The absence of smoke allows the miners to return to their work much sooner 
 after a blast with guncotton than with gunpowder, when combustion has been complete. But if the 
 rock is fissured, or if the resistance opposed is insufficient to develop the full explosive force of 
 the guncotton, the incomplete combustion results in the development of noxious vapours. One of 
 the chief advantnges of compressed guncotton lies in the convenient and safe form in which the 
 charges are delivered to the miners, who may carry the discs about and handle them without much 
 risk of accident. A defect, however, of this form, as compared with the plastic nitroglycerine com- 
 pounds, lies in its inability to accommodate itself to the irregularities of the bore-hole. Other 
 advantages possessed by guncotton are, that it is not at all injurious to handle, that its explosiveness 
 is not affected by cold, and that it may be preserved for any length of time, without deterioration, 
 in the damp and unignitable state. When all the properties of guncotton, physical and chemical, 
 are taken into consideration, that compound appears to be less suitable for ordinary mining operations 
 than those which have a nitroglycerine base. 
 
 2 D 2 
 
204 
 
 MINING ENGINEEEING. 
 
 Cotton Gunpowder. — Recently nitrocotton has been produced in a granulated form under tLe 
 name of cotton gunpowder. For blasting in ordinary mining operations, this form of the compound 
 removes one of the objections to compressed guncotton which, as we have shown, is manufactured 
 in hard and unyielding discs. Beyond this, however, it is difficult to see what advantage is gained 
 by the adoption of the pulverized form. 
 
 Means of Firing Explosive Compounds. — Recent research has led to the very important 
 discovery that, in every explosive compound, two kinds of explosion may be produced. The value of 
 this discovery, from a practical point of view, can hardly be over-estimated , since it opens up a way 
 to very great economy of labour and material, and to increased expedition in the execution of work. 
 The difference in these two kinds of explosion appears to be rather one of degree than of nature. It 
 is probable that, in the one kind, the evolution of gases takes place gradually from one grain or 
 molecule of the substance to another ; while in the other kind, the evolution takes place simultaneously 
 from all the grains or molecules. However this may be, the fact remains that a very important 
 difference is observable in the effetets produced by an explosion of the same quantity of the same 
 substance under the same conditions, when the character of the explosion is changed from that of 
 one kind to that of the other. Messrs. Roux and Sarrau, to whose researches the discovery of the 
 possibility of producing two kinds of explosion is chiefly due, distinguish these two kinds as explo- 
 sions of the first and of the second order. An explosion of the second order occurs when the 
 substance is fired by the simple application of heat, as in applying flame to the substance ; an 
 explosion of the first order may occur when the substance is fired by the application of heat and 
 force, as in the case of an explosion in it of some other substance. As an explosion of the first 
 order is produced through the agency of a detonation, it may itself be called a " detonation," and the 
 term " explosion " reserved for that of the second order. The manner in which a detonating 
 substance operates in determining the detonation of another substance is enveloped in obscurity. A 
 careful investigation of the subject by the most able men has hitherto failed to do more than show 
 that the result cannot be ascribed to the direct action of the heat developed by the chemical changes 
 which take place in the charge of detonating material employed as the exploding agent. Professor 
 Abel remarks on this subject, that an experimental comparison of the mechanical force exerted by 
 different explosive compounds, and by the same compound employed in different ways, has shown 
 that the remarkable power possessed by the explosion of small quantities of certain bodies, as the 
 silver and mercury fulminates, to accomplish the detonation of guncotton, while comparatively large 
 bodies of other highly explosive agents are incapable of producing this result, is generally accounted 
 for by the difference in the amount of force suddenly brought to bear in the different instances upon 
 some portion of the mass operated upon. And that generally, therefore, the degree of facility with 
 which the detonation of a substance will develop similar change in a neighbouring explosive 
 substance may be regarded as proportionate to the amount of force developed within the shortest 
 period of time by that detonation ; the latter being, in fact, analogous in its operations to that of a 
 blow from a hammer, or of the impact of a projectile. These views, however, are not supported by 
 facts ; and nothing remains, in the present state of our knowledge upon this subject, but to determine 
 for every substance by actual experiment the nature and the quantity of the fulminating substance 
 required to produce detonation. For the nitroglycerine compounds and guncotton, the fulminate of 
 mercury has been found to constitute the most effective detonator. This explosive is, however 
 totally incapable of detonating gunpowder. 
 
SHAFT-SINKING. 205 
 
 To produce detonation in any explosive substance, there are four conditions which must be 
 satisfied. These are: 1. That the detonating charge employed shall be suitable in nature, and 
 sufficient in quantity; 2. That the walls enclosing the detonating charge shall offer considerable 
 resistance to the forces developed within them ; 3. That the substance to be detonated shall surround 
 the detonating charge ; and 4. That the particles of which the substance to be detonated is composed 
 shall not be liable to displacement. 
 
 The nature of the detonating substance employed is a question of primary importance. Fre- 
 quently detonators are adopted which do not effect the purpose for which they are intended. With 
 guncotton, which cannot be readily exploded by any substance other than the fulminate of mercurv, 
 no other is likely to be used. But with the nitroglycerine compounds, which may be fired by any 
 explosive substance, there is a strong temptation to use a less costly detonator. It should, however, 
 be borne in mind that such detonators are capable of producing an explosion of the second order 
 only, and that consequently the larger portion of the force which the explosion is capable of 
 developing is lost. It is only by detonation that the full force of an explosive can be utilized. The 
 quantity of the detonating substance is likewise important. If the quantity be insufficient, either 
 detonation does not take place at all in the charge, or it is not propagated throughout the mass ; for 
 it is possible for detonation to occur in one portion of the charge, and simple explosion in the rest. 
 This singular occurrence will be illustrated hereafter. For ordinary small shot charges of the nitro- 
 glycerine compounds dynamite and lithofracteur, a detonator consisting of not less than 5 grains 
 of fulminate of mercury should be used. In deep holes and larger charges, as much as 15, or, 
 in some cases, even 20 grains will be required. For gunpowder, the writer has prepared a special 
 detonator, which has been found to possess all the necessary conditions. 
 
 If the walls enclosing the fulminate of the detonator do not oppose considerable resistance to the 
 forces generated within them by the explosion, detonation will not be produced. A charge of 
 5 grains of fulminate enclosed in a metal capsule is sufficient to detonate dynamite ; but four times 
 that quantity is insufficient to produce that result when paper is substituted for the metal. The 
 action of a detonator upon the blasting charge is similar to that of a blow, and to obtain this sudden 
 application of force, it is necessary to retain the gases evolved until the requisite force has been 
 developed. If this condition be not satisfied, the effect will be the same as that resulting from the 
 employment of an insufficient quantity of fulminate. 
 
 It is also necessary to certain detonation that the blasting charge should surround the detonating 
 charge. If the latter be placed only in close proximity to the former, or even in contact with it, 
 simple explosion may occur^ or a portion of the charge may be detonated and the rest exploded in 
 the second degree. To avoid such an occurrence, the detonator should be inserted to its full length 
 in the charge when practicable. In every case, it must be at least partially inserted. 
 
 The condition which requires that the particles composing the blasting charge shall not be liable 
 to displacement is of essential importance. The action of the forces developed by the detonating 
 charge is to produce vibration in the particles of the charge to be detonated. This vibration is 
 essential to detonation. It has been discovered by experiment that when a motion of translation 
 occurs among these particles, the vibratory motion is not produced, or at least it is not produced 
 in a degree sufficient to cause detonation. Hence it follows that if the particles of the blasting 
 charge which are in contact with the detonator, or in close proximity to it, are free to move 
 before the forces developed by the latter, detonation will not ensue, but only simple explosion. 
 
206 MINING ENGINEERING, 
 
 The experiments of Messrs. Ronx and Sarrau have certainly and clearly established this fact. In 
 these experiments, cast-iron bombs, of equal dimensions, and practically of equal strength, were 
 subjected to the action of an explosive charge fired within them. Repeated trials showed that 
 4 grammes of dynamite sufficed to burst the bomb when the charge was detonated, whereas 
 16 grammes were required to produce that effect when the charge was simply exploded. In 
 continuing the experiments, the dynamite was placed loose in the bomb, and by no means could the 
 latter be burst with a less charge than 16 grammes, a result which showed that the explosive had 
 not been detonated. Next, 2 grammes of dynamite were placed loose in the bomb, and a cartridge 
 also containing 2 grammes of the same substance, and enclosing a detonator, was inserted in it. 
 When fired, this charge failed to rupture the bomb. The loose dynamite was then increased to 
 4 grammes, and with a like result. Finally the bomb burst Avith a charge of 6 grammes of loose 
 dynamite and 2 grauimes enclosed in a cartridge. These results showed that in no instance had 
 the loose dynamite been detonated. The explanation of the failure of the detonated cartridge to 
 cause detonation in the loose dynamite is to be found in the motion of translation produced 
 among the particles of the latter. These particles underwent displacement, and were scattered by 
 tlie forces brought to bear upon them by the detonation of the cartridge, and, consequently, the 
 necessary vibration did not occur. On the contrary, when the explosive was enclosed by the walls 
 of the cartridge, the opposition of these to motion among the particles enabled the latter to resist the 
 f irces of the detonator sufficiently for vibration to be produced. Experiments, leading to results 
 similar to the foregoing, are recorded by Professor Abel, relative to guncotton. A bullet was fired 
 from a rifle at a distance of 50 yards against a slab of compressed guncotton | inch thick, and 
 3| inches in diameter, freely suspended in air by a string ; the guncotton was, in this case, simply 
 perforated by the bullet. A similar result was several times obtained with slabs of the same dimen- 
 sions, and with others twice the thickness. On making the experiment with a slab three times the 
 thickness, the guncotton was inflamed by the heat generated by the impact of the bullet, but not 
 detonated. This experiment was repeated with the same result. But when subsequently the bullet 
 was fired against a slab four times the thickness of that first employed, the result was detonation of 
 the mass. In this instance the increased thickness and weight of the mass occasioned the resistance 
 necessary to cause the requisite vibration. 
 
 It follows from this necessity for strong vibration in the particles and molecules of the substance 
 to be detonated, that the nature of the material used as the absorbent in the manufacture of dynamite 
 will influence, in no inconsiderable degree, the readiness with which detonation may be produced. 
 Thus a plastic material like ochre, for example, must give rise to conditions unfavourable to 
 detonation. On this ground also, the silica of the kieselguhr appears to be the most suitable yet 
 employed. It is moreover evident, from the results of the experiments described in the foregoing 
 paragraphs, that the retention of the grains of gunpowder by the walls of a cartridge will be 
 favourable to the detonation of that substance. This retention, too, must be complete in every 
 direction, for the existence of an empty space within the cartridge will prove an eftectual obstacle 
 to detonation. The required effect is more readily produced when the charge is slightly compressed, 
 so as to put the grains into firm contact with each other. Such compression is besides advantageous 
 in reducing the dimensions of a charge of a given weight. For these reasons the compressed 
 gunpowder, to which attention was directed in a former paragraph, is very susceptible to detonation, 
 and economical in use. 
 
SHAFT-SINKING. 
 
 207 
 
 Tlie following table contains the results of the experiments of Messrs. Eoux and Sarrau, 
 previously alluded to, and shows clearly the relative value of the effects produced by detonation and 
 by simple explosion. In this table the explosive force of gunpowder developed by simple explosion is 
 taken as unity. 
 
 EELA.TIVE STKENGTH OF EXPLOSIVE COMPOUNDS. 
 
 Substance Exploded. 
 
 Fulminate of Mercury 
 
 Gunpowder 
 
 Nitroglycerine 
 
 Guncotton 
 
 Picric Acid 
 
 Picrate of Potasli 
 
 Bimple 
 Explosion. 
 
 1-00 
 4-80 
 3-00 
 2-04 
 1-82 
 
 Detonation. 
 
 28 
 34 
 
 10-13 
 6-46 
 
 50 
 31 
 
 Relative weight 
 of (jases. 
 
 0-414 
 0-800 
 0-850 
 0-892 
 0-740 
 
 Heat disengaged by 1 lb. 
 
 Simple 
 Explosion. 
 
 Units. 
 
 1316 
 3097 
 1902 
 1491 
 1417 
 
 Detonation. 
 
 Unlla. 
 
 1354 
 1318 
 3200 
 1909 
 1563 
 1534 
 
 The evidence afforded by this table is very remarkable, and of the highest practical importance. 
 There are two especially striking features in this evidence. The first is the enormous increase 
 of force obtained by detonation, and the second is the singular fact that this increase is greatest in 
 the common explosive gunpowder. It would be difficult to over-estimate the importance of these 
 facts from a practical point of view. The ability to more than double the explosive force of the 
 shattering compounds by the simple employment of suitable means for firing the substance must tend 
 greatly to promote expedition and economy in the execution of future blasting operations. And the 
 fact that by the adoption of such means gunpowder may be so changed in the character of its 
 explosion as to become a shattering from a rending compound, possessing an available strength con- 
 siderably more than quadrupled in value, will undoubtedly influence the future position of that sub- 
 stance among explosive compounds. Detonation has, it is true, been extensively practised with pure 
 nitroglycerine, nitroglycerine compounds, and guncotton, but want of attention to the conditions of 
 success leads to frequent failure. It is probable that in the majority of cases in which dynamite is 
 fired by the ordinary means, certainly in a large minority of such cases, complete detonation is not 
 produced. Sometimes a portion of the charge is detonated and the rest exploded ; often only simple 
 explosion occurs. To this cause must be attributed, in great part, the wide discrepancies which 
 frequently appear in the results of experiments made with the same quantities of the same substance, 
 and the seemingly anomalous differences between the effects of substances of different composition. 
 By a suitable arrangement of the conditions under which the substance is fired, a dynamite contain- 
 ing 50 per cent, of nitroglycerine can be made to appear more powerful than another in which 
 there is 75 per cent, of the latter substance. In practice, the conditions of detonation are often 
 neglected, the result being the development of a force insufficient for the effect required, or the 
 employment of a superfluous quantity of the explosive, and an evolution of noxious fumes consequent 
 on incomplete combustion. For it should be borne in mind, that detonation is conducive, not only to 
 economy of labour and explosive material, but to the wholesomeness of the atmosphere at the 
 working faces. In close headings and in shafts this is a matter of weighty importance. 
 
 But to whatever extent the advantages of detonation may have been obtained from guncotton 
 and nitroglycerine and its compounds, no such application has ever been made of gunpowder. In 
 
208 MINING ENGINEEEING. 
 
 ordinary practice, gunpowder is never detonated. Seldom, indeed, is any attempt made to produce 
 tbat result ; but even in the few cases in which detonation is sought, the means are frequently 
 incapable of producing the effect desired. When the numerous and great advantages possessed by 
 gunpowder are borne in mind, the importance of increasing its strength four and even fivefold is 
 sufficiently obvious. It will appear from the foregoing table that dynamite containing 75 per cent, 
 of nitroglycerine possesses a relative strength of 3 • 60 in single explosion, and of 7 • 60 in detonation. 
 This is on the assumption that the nitroglycerine in mechanical combination with the absorbent 
 material is capable of exerting the same force as when in a pure state. Thus gunpowder when 
 detonated is much stronger than dynamite simply exploded, and the latter when detonated is 
 superior to the former only in the ratio 1"75. If the merits and defects of the two compounds be 
 fairly weighed, it will hardly appear that this superiority is sufficient to justify the claims often 
 put forward for the nitroglycerine compound. But even this difference in strength may be lessened. 
 Attention has already been directed to the E. S. M. blasting powder of the Messrs. Curtis and Harvey. 
 This compound is, in consequence of its quicker action and the greater amount of heat disengaged, 
 superior to common powder in simple explosion. But when fired by the special detonator, this 
 powder is but little, if at all, inferior in strength to dynamite of the composition indicated above. 
 But even if we admit the ratio of the strength of the No. 1 dynamite to be 1 • 75, the difference is 
 much less than it is generally supposed to be. Notwithstanding this, however, cases will occur in 
 which the superiority of the nitroglycerine compounds will be very marked ; this will happen, for 
 example, in the case of blasting in hard and very tough rock. Also the advantages offered by these 
 compounds in wet ground are by no means to be overlooked. It should be remarked that, when 
 gunpowder is detonated, a light tamping is sufficient. 
 
 Electrical Blasting Apparatus. — The employment of electricity to fire the charge in blasting 
 rock, offers numerous and great advantages. The most important, perhaps, of these advantages, the 
 ability to fire a number of charges simultaneously, will be considered hereafter, when treating of the 
 principles of blasting. But another advantage, of no small moment, lies in the security from acci- 
 dental explosions which this means of firing gives. By the employment of electricity, not only is 
 the charge fired at the exact moment desired, when it has been clearly ascertained that all the work- 
 men are under shelter, but the dangers due to misfires and the use of matches are avoided altogether. 
 There are, it is true, other dangers to be feared, peculiar to the nature of electricity ; but these may 
 be lessened or removed by the employment of suitable means, and the adoption of simple precautions. 
 Moreover, the facility afforded by electricity for firing charges under water constitutes a feature in 
 this agent of no small practical importance. It would, therefore, seem, when all these advantages are 
 borne in mind, that electricity is destined to become of general application to blasting purposes, and 
 hence it is important to consider the means by which this agent is brought into use. It would, 
 however, be beyond the scope of this work to investigate and explain the principles upon which the 
 excitation and application of electricity rest. All that it is desirable to do here is to describe brieflv 
 the instruments commonly employed in the operations under consideration. 
 
 Electric Fuses. — An electric fuse, or, more correctly, an electric " exploder," consists of a charge 
 ©f an explosive compound of a character capable of being acted upon by an electric current in a 
 manner and in a degree sufficient to produce explosion. This charge is inserted in the cartridge or the 
 capsule containing the detonating charge, and provision is made for conveying into it the current of 
 electricity that is to decompose it. The mode in which this current is made to act may be one of 
 
SHAFT-SINKING. 209 
 
 two kinds. In one mode, a very fine platina, iron, or an alloyed metal wire is inserted in the charge, 
 and included in the circuit of a powerful voltaic battery. The resistance offered by the diminished 
 conducting power of the fine wire to the passage of the electric current heats the wire to redness, and 
 the heat thus developed causes an explosion of the compound in contact with the wire. The 
 conditions to be observed in this case are : to develop a large quantity of electricity ; to provide 
 conducting and return wires of sufficient sectional area; and to seal the fine wire to be heated 
 within the charge to be exploded. In the other mode, a sudden discharge of static electricity is 
 made to take place between the terminals of two wires embedded in the compound composing the 
 charge. The conditions to be observed in this case are : to provide means of exciting and accumu- 
 lating static electricity ; to employ suitably placed and, where necessary, insulated conducting and 
 return wires ; and to include between these a compound capable of being exploded by the passage of 
 the spark between the terminal points. The latter is found in practice to require the more simple 
 appliances, and to be in consequence the more certain in action. 
 
 In the design and manufacture of fuses constructed upon the principle of an electric discharge, 
 there are certain difficulties to be overcome, and certain dangers to be avoided. It is essential to 
 isolation that the terminal points of the wires be separated by a considerable space, one-sixteenth of 
 an inch being the minimum distance allowable. But as the electric spark cannot be made to leap a 
 great distance, it is necessary that the compound itself, which is to be exploded by the spark, shall 
 possess some degree of conducting power. It is obvious, however, that the conductibility of this 
 compound must not be sufficient to allow of the passage of the current ; and hence arose a necessity 
 for numerous experiments to determine the composition of the explosive substance. An element of 
 danger, to be as far as possible eliminated, lies in the too great sensitiveness of the compound. 
 Many serious accidents have been occasioned by this property. Several compounds have been proved 
 to fulfil the requisite conditions in a satisfactory manner, and have been largely adopted in practice. 
 Of these, that which was discovered by Professor Abel is perhaps the most widely employed at 
 present. It consists of an intimate mixture of chlorate of potash and subsulphide and subphosphide 
 of copper, in certain proportions, the copper being introduced to give the required conducting power. 
 The proportions adopted are : subphosphide of copper, 10 parts ; subsulphide of copper, 45 parts ; and 
 chlorate of potash, 16 parts. These substances are well rubbed together in a mortar, with the addition 
 of sufficient alcohol to thoroughly moisten the mass. The mixture is afterwards carefully dried, and 
 it may then be safely preserved in closed vessels until required. The following description of the 
 Abel fuse is given by the inventor in a memoir published on the subject. 
 
 " The fuse-head, which is of wood, contains three perforations, as shown in Figs. 357 and 358 ; 
 the one passing downwards through the centre receives about 2 inches of double insulated wire a a, 
 two copper wires of 24 gauge, 0*022 inch diameter, enclosed side by side at a distance -^ inch, in a 
 coating of guttapercha of | inch diameter. The other two perforations, which are parallel to each 
 other on each side of the central one, and at right angles to it, serve for the reception of the circuit 
 wires. The arrangement for securing the connection of these with the insulated wires in the fuses 
 is as follows : 
 
 " The piece of double-covered wire above referred to is originally of sufficient length to allow of 
 the guttapercha being removed from about 1\ inch of the wires. These bare ends of the fine wires, 
 which are made to protrude from the top of the fuse-head, are pressed into slight grooves in the wood, 
 provided for their protection, and the extremity of each is passed into one of the horizontal perfora- 
 
 2 £ 
 
210 MINING ENGINEEEING. 
 
 tions in the head, in which position it is afterwards fixed by the introduction into the hole of 
 a tightly fitting piece of copper tube, so that the wire is firmly wedged between the wood and tlie 
 exterior of this tube; thus it is brought into close contact with a comparatively large surface of 
 metal. It will be seen that it is necessary only to fix one of the circuit wires into each of these tubes, 
 in opposite sides of the fuse-head, in order to ensure a suJficient and perfectly distinct connection of 
 each of them with one of the insulated wires in the fuse. 
 
 " The extremity of the double-covered wire, which protrudes to a distance of about f inch from 
 the bottom of the fuse-head, is provided with a clean sectional surface by being cut with a pair of 
 sharp scissors, care being taken that the extremities of the fine copper wires be not pressed into 
 contact by this operation. A small cap of about ^ inch in length is constructed of thin tinfoil, 
 into which is dropped about one grain of the priming material. The double wire is then inserted into 
 the cap and pressed firmly down, so that the explosive mixture is slightly compressed and in close 
 contact with the surfaces of the wire terminals, as shown in Figs. 358 and 359. The cap is fixed by 
 winding a piece of twine once or twice around its upper parts ; tightening the ends of this, and then 
 removing it. The fuse is then ready for enclosure in the detonating charge. The latter is contained 
 in a paper case tied on to the head, or in a cylinder of sheet-tin tightly fitting on the fuse-head at 
 one end, as shown in Figs. 360 and 361 ; the other end, after the introduction of the charge, is closed 
 with a plug of clay or plaster of Paris. It is advisable to have the fuses ready fitted with pieces of 
 insulated wire about 2 feet in length, and twisted together, as shown in Fig. 362. The ends of the 
 wires, after they have been passed through the connecting holes in the fuse-head, should be tightly 
 fixed in their positions by the introduction of a short piece of copper wire." 
 
 A compound of a character similar to Abel's was used by George Mowbray, an eminent 
 American chemist, in the manufacture of the electrical fuses employed in the Hoosac Tunnel. This 
 compound consisted of sulphide of copper, 9 parts ; subphosphide of copper, 2 parts ; chlorate of 
 potash, 3 parts ; the whole intimately mixed. This chemist subsequently substituted silver for the 
 copper sulphide and phosphide of the Abel composition, as being a better conductor. Thus consti- 
 tuted, the priming compound consisted of: phosphorus, 6 parts; sulphur, 15 parts; silver, 100 parts; 
 mercury, 25 parts ; and chlorate of potash, 30 parts. And still later, a new compound, consisting 
 of 3 parts of mercuric sulphide and 1 part of chlorate of potash, was adopted. Mowbray thus 
 describes the mode of manufacturing his fuses : 
 
 " The priming compound is prepared by myself, to ensure uniformity and a proper combination 
 of the ingredients, and then passed on to the filling house, where it is made up into exploders. Two 
 insulated wires, from 4 to 12 feet long, are inserted into a moulded guttapercha plug, f inch in 
 length and \ inch in diameter at one end, and ^ inch at the other, to which they are fastened by a 
 weld of guttapercha. Immediately before the priming is inserted, an electric spark is passed 
 through and between the wires where the priming is put, to ascertain that the insulation is perfect, 
 so as to prevent the possibility of misfire. This being proved, the priming is put in, and a small 
 paper plug, boiled in parafiine, inserted. Then, a copper cap, f inch in length and f inch in diameter, 
 receives the detonating charge of fulminate mercury, on the top of which a varnish is poured to 
 prevent the fulminate from being shaken out by accident, or affected by vibration. This copper cap 
 having been previously covered with a guttapercha envelope, the electric fuse is inserted about 
 i inch, and cemented tight ; the parts are afterwards painted with asphaltum varnish around the 
 joints, when the exploder is complete and ready for service," 
 
SHAFT-SINKING. 211 
 
 Numerous other compounds are used in electric exploders; indeed, they may be varied in an 
 almost unlimited degree. A common one consists of chlorate of potash and sulphide of antimony in 
 equal parts. The essential conditions to be observed are : that they shall be uniform in their com- 
 position ; that they shall offer neither too great nor too little resistance to the spark ; and that they 
 shall not be so sensitive as to explode from the ambient electricity of the atmosphere, or from a light 
 concussion in handling. 
 
 A very simple, effective, and cheap form of electric fuse is in common use : it is known as the 
 "blasting stick." It consists of a thin lath of wood, 3 feet in length, | inch in breadth, and about 
 \ inch in thickness, armed at one end with a detonator, in which two fine wires, preferably of copper, 
 are lodged. The detonator consists of a metal cap containing the detonating charge and the priming 
 compound into which the wires are led. These wires, insulated by a coating of guttapercha, or of 
 asphaltum applied hot, are lodged in saw grooves made in the face of the stick for that purpose. 
 Instead of the saw grooves being made to receive the wires, the stick is frequently composed of two 
 thin strips glued together, with the wires lodged between them. Fig. 363 represents one of these 
 blasting sticks. 
 
 In using the blasting stick, the detonator is placed in the blasting charge, and the hole tamped, 
 with the stick standing against the sides of the hole. To fire the charge, the end of one of the wires 
 is connected with the conducting wire from the electrical machine, and the end of the other with 
 another wire which connects it with one of the wires on the stick in the next adjacent hole. The 
 other wire of this second stick is connected by the same means with one of the wires of the stick in 
 the third hole, and so on till the whole number of charges are connected. The end of the second 
 wire in the last hole is connected with the return wire from the machine. In this way as many as 
 fifty shots may be fired at once. In making the connections, the insulating coating must be scraped 
 off the ends of the wires for a length of about two inches, and these uncovered portions twisted 
 together in the manner shown in Fig. 364, care being taken to keep the ends close down to the 
 wire, and not sticking out^ in the manner shown in Fig. 365. In wet situations a small gutta- 
 percha tube may be drawn over the joint, the end of one of the wires having been passed through 
 the tube previously to the joint being made. This tube should extend beyond the uncovered 
 portions of the wires, and be bound to them with twine, as shown in Fig. 366. Abel recommends 
 the joint shown in Fig. 367. The ends of the wires in this instance are hooked firmly into each other 
 by the application of pliers. A piece of fine copper binding wire, about 6 or 8 inches in length, is 
 then bound over the whole of the connection, and finally enclosed in a small wrapping of oiled canvas. 
 
 Conducting Wires, Insulators, and Supports. — The conducting wires used in blasting may be 
 either of copper or of iron. The former is the better conducting medium, and as it also possesses the 
 advantage of greater toughness, it is the most commonly employed. The sectional area of the wire 
 is largely concerned in its conducting power ; the resistance is found to vary inversely as the 
 sectional area, and hence it is important to give the conducting or circuit wires a sufficient diameter. 
 As a portion of these wires is necessarily destroyed at every blast, there is a temptation to reduce the 
 weight of the wire used to the lowest possible limits, for the sake of economy. But it will be found 
 more conducive to economy in the end to be somewhat lavish in this direction. A suitable weight of 
 copper wire is 250 grains a yard ; this weight gives a diameter of about ^5- inch. "Wire of this 
 diameter constitutes a good conducting medium, and is inexpensive. When covered with gutta- 
 percha, it is easily portable, very flexible, and capable of being readily coiled upon a reel. Two miles 
 
 2 E 2 
 
212 MINING ENGINEEEING. 
 
 of this wire will easily pack into a cubic yard. The prices range from 10?, to 201. a mile, the 
 difference being due to the greater or less quantity of the guttapercha covering. P'or firing charges 
 upon land, where a return wire is always necessary, the lowest priced wire is suflScient in every 
 case. It is a good plan to compose the conducting wires of three strands twisted together as a rope. 
 The advantage of this form is greater flexibility, and less liability to rupture. A single strand of 
 wire having the same weight per unit would convey electricity equally well ; but it soon becomes 
 hard and unmanageable, and is then very liable to break at the bendings. The twisted wire is less 
 strained by being bent, and even when one of the strands gets broken, the other two are capable of 
 transmitting the current. 
 
 To insulate the circuit wires, tbey are covered with a coating of guttapercha. This substance 
 appears to be the only one suitable for the purpose. Various other materials have been substituted 
 for it, and it has been employed, for the sake of cheapness, adulterated with other substances, such as 
 pitch, clay, and plaster of Paris. But the results obtained were, in every case, of an unsatisfactory 
 character. Besides the guttapercha for insulation, a covering of tape is needed for the protection of 
 the insulating coating. Sometimes a coating of a solution of shellac is laid over the tape covering, 
 and a varnish is put over this again, for the better protection of the wire. 
 
 Not unfrequently ordinary iron telegraph wire is used for the circuit wires. In such cases no 
 covering is applied, and consequently insulators may be required at the points of support. The common 
 stoneware insulators are the most suitable for this purpose; they may be fixed in the usual manner 
 upon a wooden arm, about 2 feet in length, nailed upon the top of a stake or a pole, when the wires 
 have to be carried over the surface of the ground. In headings, the insulators may be fixed to the 
 timbers of the roof. In all cases the circuit wires should be fixed to the roof timbers, because when 
 in that situation they are out of the way of the workmen, and are not liable to be flapped against the 
 sides or dropped upon the floor. 
 
 Electrical Machines. — The apparatus required to excite and to accumulate electricity may be of 
 several kinds. Thus we may have a frictional electrical machine and Leyden jar ; a voltaic battery, 
 with induction coil ; an electro-dynamic machine, such as Siemens', or Gramme's ; or an electro- 
 magnetic machine, as Wheatstone's, or Clarke's. Of these, however, only one, namely, the frictional 
 machine, is suitable for ordinary blasting operations. The conditions of mining are such as to render 
 simplicity of construction and action an essential quality in a machine, and this quality is possessed 
 only by the frictional electrical machine. Many forms and modifications of this machine have been 
 devised, for the purpose of rendering it suitable to the requirements of practice. The main objects 
 of these devices have been the attainment of simplicity and strength of parts, and the provision of 
 means for protecting the parts from the influence of moisture. The importance of such a protection 
 will be obvious, wbeii the usually wet character of the situations in which mining operations are 
 carried on is borne in mind. One of the best of these improved machines is that of A. Bernhardt of 
 Brunswick, which will be found illustrated on Plate XXXII., Figs. 368 to 371. 
 
 The circular friction plate F is of vulcanized guttapercha, and turns upon an iron axle a which 
 is furnished with a pinion b. This pinion is driven by a toothed wheel c four times its diameter to 
 give velocity to the plate. The driving wheel c is turned by means of the handle d on the outside of 
 the wooden case or box in which the machine is contained. The rubber R is held up against both 
 sides of the plate by a spring H. The collecting rings J collect the electricity as it is excited and 
 charge the condenser jar L with it. This jar is set in a wooden base or support fixed to the casing ; 
 
BHAFT-SINKING. 213 
 
 the forward side of the jar is covered with a guard or shield of vulcanized guttapercha, to prevent a 
 discharge of electricity from the plate to the external covering of the jar. The discharge of the jar 
 is effected through the medium of the conductor Gr, which is pressed into contact with the latter by- 
 means of the button K, as shown by the dotted lines, against the pressure of a spiral spring which 
 tends to hold it in communication with the ring C. The ring D is in metallic communication with 
 the external covering of the jar. In order to ascertain easily the normal condition of the machine, a 
 scale of fifteen metallic buttons is provided at X, which scale may be put in communication with the 
 rings C and D through the medium of chains, as shown in the figures. If, after fifteen or twenty 
 turns, the spark leaps the intervals of the scale, when the button K is pressed in, the machine is in 
 good condition. The joints of the wooden casing are made air-tight, to protect the internal parts 
 from the influence of moisture. The outside dimensions of the casing are 20 inches in length by 
 14 inches in depth, and 7 in breadth, and the whole does not exceed 20 lb. in weight ; thus it will 
 be seen that this machine is simple in construction, well protected, easily portable, and not likely to 
 get out of order. It is capable of firing any number of charges up to thirty. 
 
 This machine may be lodged in any suitable place underground. To fire the charges by means 
 of it, the leading wire is hooked into the ring D, and the return wire into the ring C, the other ends 
 being connected to the fuses in the manner already described. The handle is then put on, and from 
 ten to fifteen turns given to excite the electricity. It is then necessary only to press in the button 
 or knob K to produce the discharge, and the consequent explosion of the blast. To give additional 
 security to the men engaged, the handle d is designed to be taken off when the machine is not in 
 actual use, and the end of the machine, into which the circuit wires are led, is made to close with a lid 
 and lock, the key of which is always in the possession of the person in charge of the blasting'.^ 
 operations. 
 
 George Mowbray has introduced into use in America a frictional electric machine, similar in 
 design to that of Bornhardt's, but possessing some improvements in the details of its construction 
 which render it, perhaps, the most perfect of its kind. The patentee has adopted the cylinder for an 
 exciting surface, because " the cylinder machines have a superiority in their exciting power over 
 plate machines of equal surface in the proportion of four to one." 
 
 It may be desirable to add here one word of caution with respect to the use of over-sensitive 
 fuses, and the careless handling of the bare wires. The dangers proceeding from these sources were 
 observed by Mowbray in his experience at the Hoosac Tunnel, and recorded by him in the following 
 words : 
 
 " It is important that the fuses shall not be so sensitive as to explode, either from the ambient 
 electricity of the atmosphere, or from the electricity pervading a tunnel, and caused by the friction of 
 the air from the compressors when it escapes through the vulcanized rubber of the connecting pipe. 
 This source of electricity, I believe, caused an accident in March, 1873, attended with fatal results, 
 which accident was followed by another, similar in every respect, a fortnight later. For as the 
 blaster charging the holes on that occasion observed : 'The moment I touched the bare wire, after 
 the insulated portion had passed through my hand, premature explosion ensued.' It had been the 
 custom, after withdrawing the drilling machines, to allow a pretty free discharge of compressed air, 
 for ventilation ; and assuming a man in his rubber boots to be an insulated jar, the hands, face, &c., 
 would serve as collecting points, whilst the electricity developed by the moist vesicles of the cold, 
 expanding air rushing through a pipe from a reservoir charged up to 50 or 60 lb. to the inch, would 
 
214 MINING ENGINEEEING. 
 
 resemble in its source tliat obtained by the hydro-electrical machine. The blaster, unaware that he 18 
 a walking charge of electricity, proceeds to his work, inserting cartridge after cartridge of the 
 explosive compound, until he comes to the last, which is armed with the electric fuse. The moment 
 his hand touches one of the naked wires the current passes through the priming, and an explosion 
 follows. Let, therefore, a blaster, before he handles these wires, invariably grasp some metal in 
 moistened contact with the earth, or place both hands against the moistened v/alls of the heading. 
 Also, before taking the leading wires to the electric fuse wires, let the bare ends of the leading and 
 return wires be first brought into contact with each other, and then into contact with the moist 
 surface of the heading, or with some metal in good connection with the ground ; and before inserting 
 the armed cartridge, let him unite both of the uncovered wires, and touch them against a metal 
 surface having good ground connection. But, above all, it is desirable not to ventilate, by allowing 
 a free blast of air through a rubber pipe, until after the electric connections have been made and the 
 blast fired." 
 
 The Principles of Blasting. — The principles upon which the operations of blasting are con- 
 ducted are few and simple. Yet it may be doubted whether they be more than imperfectly understood 
 by those who conduct such operations. Yery frequently, holes are bored in certain positions, and 
 the explosive substance is inserted in certain quantities for no better reason than that such things 
 have been done' before. The inevitable consequences of this ignorance are, slow progress in the 
 execution of the work, and a large consumption of material. There are, indeed, few engineering 
 operations offering such a field for the exercise of economy as that of blasting, or one in which the 
 end proposed may be so easily attained. By a skilful application of an accurate knowledge of the 
 manner in which an explosion acts, and of the structure and mineral composition of rocks, a reduction 
 in the number of the bore-holes and in the quantity of the explosive required may be made, and a 
 rapidity of progress attained, no less remarkable and important than the results attendant on the 
 adoption of machine drilling. It is therefore desirable, before quitting the subject of blasting, to 
 point out and explain the principles which should guide the conduct of the operations. 
 
 It has already been said that an explosion is a sudden transformation of a substance from the 
 solid or liquid into the gaseous form. The action is similar to that which goes on in a steam 
 bjoiler. The application of heat to the water contained in the boiler transforms that substance from 
 the liquid into the gaseous form, and as the gases into which the liquid is converted tend to occupy 
 a much larger volume than the liquid from which they are derived, a pressure is caused tending to 
 burst the boiler, and the intensity of this pressure will depend upon the relative volume of the gas. 
 In that case, the transformation of the water into gas proceeds slowly, and the full effects are not 
 obtained until after a considerable lapse of time. If, however, the water could be suddenly flashed into 
 steam, as happens when a jet is directed upon a red-hot iron plate, the full pressure would be pro- 
 duced at once, and a result very much like an explosion would ensue. If, instead of the water, gun- 
 powder were placed in the boiler, and heat applied, when a certain degree of temperature was reached 
 the powder would flash into gas, in the same manner as we have supposed the water to flash into 
 steam, and the same effect of pressure would be produced on the boiler. The pressure of a fluid, it 
 must be borne in mind, is exerted equally in all directions, and, consequently, every square inch of 
 the metal will be subjected to the same strain. Hence it is obvious that if the boiler bursts it will 
 yield in the weakest parts, and the line along which the fracture would run in such a case is called 
 the line of least resistance. It will appear from the foregoing that an explosion is merely the sudden 
 
SHAFT-SINKING. 215 
 
 application of great pressure ; so sudden, indeed, as to partake of the character of a blow. But though 
 the forces developed are thus suddenly applied, their action is in all respects the same as when the 
 application is gradual and slow, and in considering their action, therefore, it is only necessary to 
 assume a slow evolution of gases to determine it with precision. 
 
 As in the steam boiler the full pressure is not attained until the whole of the water has been 
 converted into steam, so in the case of an explosive compound, the full pressure upon the containing 
 body is not developed until the whole of the substance has been converted into gas. When 
 gunpowder is fired in the open air, the gases escape as they are formed, and the pressure developed 
 upon the body upon which the substance rests is equal to the resistance opposed by the air to the 
 escape of the gases. The value of this resistance will obviously increase with the velocity possessed 
 by these gases. It is the pressure due to this cause that forces the rocket to ascend, and it is evident, 
 from the relation subsisting between the pressure exerted and the velocity of evolution of the gases, 
 that the more rapid the combustion of the substance, the greater will be the velocity of ascent. If the 
 rocket-case were made sufficiently strong, and the gases retained within it until the whole of the 
 substance was transformed, the pressure exerted against the inside of the case would continue 
 to increase as the transformation was effected ; and if, when the latter was complete, the gases were 
 allowed to suddenly escape from the end, the rocket would ascend with the maximum attainable 
 velocity, or if retained in its position, the gases would exert upon it their maximum lifting force. 
 These facts explain the difference in the effects produced by the slow and the quick explosives when 
 fired in the open air. When gunpowder, for example, is fired in this way upon a stone, the down- 
 ward pressure developed is not great ; but when nitroglycerine is fired by detonation under the same 
 conditions, the stone is crushed or fractured. Even gunpowder, will produce similar effects if 
 detonated. The different pressures produced in these cases are chiefly due to the differences in the 
 rapidity with which the transformation of the substance takes place. Hence we see the value 
 of detonation. When a substance is detonated, the vibration caused by the detonator produces a 
 simultaneous evolution of gases from each molecule of the substance detonated, and consequently the 
 maximum force is developed at once, instead of gradually, as in simple explosion. 
 
 Suppose now a charge of slow explosive placed in a vertical bore-hole in strong rock, and fired. 
 Here the gases can escape only in one direction ; and as the area upon which the air presses is much 
 less than when the charge was exposed on all sides but one, the velocity of the air must be much 
 greater to allow the same volume of gases to escape in the same time. Consequently the pressure 
 exerted upon the bottom of the hole will be greater than that exerted upon the stone ; and as the 
 pressure is necessarily equal in all directions, the same pressure will be exerted against the sides of 
 the hole. As the action of the explosive is quickened, — assuming this condition possible — the 
 resistance of the air, and consequently the pressure upon the bottom and sides of the hole, will 
 increase until its maximum is reached when detonation or instantaneous transformation is effected. 
 This maximum, it must be borne in mind, is necessarily equal to the resistance opposed by the 
 atmosphere ; and though it may be sufficient to fracture the rock, it does not represent the whole of 
 the force developed by the explosive. A large proportion is expended in giving velocity to the air 
 in the bore-hole, and another portion is lost as heat communicated to the rock. The quantity of heat 
 lost in detonation is less than in simple explosion, because the gases are in contact with the rock 
 during a shorter interval of time. Thus a larger proportion of the force developed is rendered 
 available by detonation. Moreover, as gunpowder, when detonated, may be used in much smaller 
 
216 MINING ENGINEEEING. 
 
 quantities, the surface of rock exposed to the gases will, by such means, be proportionately reduced, 
 and, consequently, the loss of heat will be lessened in a like degree. This constitutes another source 
 of economy of the force developed by the explosion. But as the greatest loss is occasioned by the 
 comparatively slight resistance of the air in the bore-hole, the most important saving is to be sought 
 in this direction. It is obvious that by substituting for the air a more strongly resistant substance, 
 a larger proportion of the force developed may be rendered available ; in other words, a pro- 
 portionately greater pressure will be exerted upon the sides of the bore-hole. By this means, which 
 is known as " tamping " the hole, a suf6cient force may be thrown against the sides of the hole to 
 fracture the rock, which is the end proposed in blasting. It is also obvious that economy of force 
 requires that the materials employed as tamping should be of the most resistant character 
 obtainable. Those which are available for this purpose will be hereafter considered. 
 
 Line of Least Resistance. — As the pressure of a fluid is exerted equally in all directions, the 
 surrounding mass subjected to the force will yield, if it yield at all, in its weakest part, that is, the 
 part which offers least resistance. The line along which the mass yields, or line of rupture, is called, 
 as we have already stated, the line of least resistance, and is the distance traversed by the gases 
 before reaching the surface. When the surrounding mass is uniformly resisting, the line of least 
 resistance will be a straight line, and it will be the shortest distance from the centre of the charge to 
 the surface. Such, however, is rarely the case, and the line of rupture will therefore in most instances 
 be an irregular line, and often much longer than that from the centre direct to the surface. It will 
 be obvious, on reflection, that the line of least resistance will be greatly dependent upon the texture 
 of the rock, which may vary from one point to another ; its structure, which renders it more easily 
 cleavable in one direction than in another ; the position, number, and direction of the joints which 
 separate the rock into more or less detached portions ; and the number and relative position of the 
 unsupported faces of the rock. All of these circumstances must be ascertained, and the position of 
 the bore-hole determined in accordance with them, in order to obtain the maximum effect from a 
 given quantity of explosive. It must not be supposed that this is a labour involving minute 
 examination and long consideration. On the contrary, a glance is generally suflBcient to enable the 
 educated eye to estimate the value of the circumstances before mentioned, and to determine accordingly 
 the most effective position for the hole. The ability to do this is always claimed by workmen. They 
 can see, they say, which is the best position for the charge. To those who possess the requisite know- 
 ledge of rock structure and the action of expanding gases, the determining circumstances are certainly 
 apparent. But in a great majority of cases, this seeing amounts to little more than following the 
 famous rule of thumb. And if there be one operation less subject to this rule than any other, it is that 
 of blasting, in which the conditions vary from hole to hole. The possession of such knowledge should, 
 therefore, be deemed essential. Without it, every blast is necessarily of a tentative character ; and 
 to ensure the attainment of the end proposed in such cases, a superfluous quantity of the explosive 
 compound is employed. Nor is this the only waste due to the same source ; even by the expenditure 
 of an additional quantity of the explosive, the work can seldom be eff'ected without distributing this 
 quantity among a larger number of holes. The object to be aimed at by the blaster is the accomplish- 
 ment of a given quantity of work with the least labour of boring, and the least expenditure of powder. 
 To attain this object, the first condition evidently is, to determine accurately the line of least resist- 
 ance, or in other words, the most effective position for the bore-hole. In practice, the line of least 
 resistance is taken as the shortest distance from the centre of the charge to the surface of the rock 
 
SHAFT-SINKING. 217 
 
 unless the existence of natural divisions or differences of texture shows it to lie in some other 
 direction. 
 
 Force required to Cause Disruption. — When the line of least resistance is known, it remains to 
 determine the quantity of the explosive compound required to overcome the resistance along that 
 line. This matter is also one of great importance, for not only is all excess waste, but this waste will 
 be expended in doing mischief. In mining operations, the dislodged rock is violently projected, to 
 the injury of the sides of the heading or the shaft, and the air is fouled in an unnecessary degree ; 
 and in quarrying, stones are shattered which it is desirable to extract in a sound state. Of course, it 
 is not possible so to proportion a charge to the resistance that the rock shall be just lifted out, and no 
 more, because neither the force developed by the charge nor the value of the resistance can be known 
 with precision. But a sufficient approximation may be easily arrived at to enable us to avoid the 
 loud report that is indicative of what may be called " superfluous " waste. The lavish expenditure 
 of powder which is everywhere made does no honour to the mining engineering profession, and it 
 becomes all interested to direct attention to this matter. The common miner, or quarrymau, acting 
 in accordance with his rule of thumb, fills his bore-hole up to a certain height with the explosive 
 substance, and this condition must be fulfilled irrespective of the diameter of the hole, the nature of 
 the rock, or the length of the line of least resistance along which the rock will be fractured. More 
 than this, the rule must be followed irrespective of the strength of the explosive, for not unfrequently 
 dynamite, even, is made to fill the same portion of the hole as gunpowder. This source of waste 
 claims immediate attention, and opens a wide field to economy. 
 
 Charges of powder of uniform strength produce effects varying with their weight, that is, 
 
 a double charge will move a double mass. And as homogeneous masses vary as the cube of any 
 
 similar line within them, the general rule is established that charges of powder capable of producing 
 
 similar results, are to each other as the cubes of the lines of least resistance. Hence, when the charge 
 
 requisite to produce a given effect in a particular substance has been determined by experiment, that 
 
 necessary to produce a like effect in a given mass of the same substance may be readily determined. 
 
 As the substances to be acted upon are various, and differ in tenacity in different localities, and as, 
 
 moreover, the quality of the powder may vary considerably, it will be necessary, in undertaking 
 
 mining operations, to make experiments in order to determine the constant which should be 
 
 employed in calculating the charges. Grenerally, the charge of ordinary blasting gunpowder requisite 
 
 to overcome the resistance will vary from -^ to jj of the cube of the line of least resistance, the 
 
 latter being measured in feet, and the charge in pounds. Thus, if the material to be blasted be 
 
 moderately strong sandstone, and the length of the Hue of least resistance 3 feet, we shall have 
 
 3 X 3 X 3 = 27, and |f = the weight in pounds of gunpowder required. Also, if the line of least 
 
 4x4x4 64 
 resistance be 4 feet, we shall require ^ ~ on ~ ^^ ^^* ^ Produce rupture, the proportion 
 
 for sandstone being taken as -^. Of course, when a stronger explosive than gunpowder is employed, 
 a proportionately smaller quantity must be taken. Thus, if we assume dynamite to be five times the 
 strength of gunpowder, the foregoing proportion must be reduced in a corresponding degree ; that is, 
 
 instead of jj-, we must take -^ r- = tt?- I* i^ neither practicable nor desirable that such calcula- 
 
 tions and measurements as these should be made for every blast ; their practical value lies in this, 
 namely, that if the principles involved in them be clearly understood, the blaster is enabled to 
 
 2 F 
 
218 
 
 MINING ENGINEEEING. 
 
 proportion his charges ly sight to the resistance to be overcome, with a sufficient degree of 
 precision. 
 
 One pound of gunpowder of average specific gravity occupies, when loosely poured out, about 
 30 cubic inches, and one cubic foot will thus weigh 57| lb. Consequently, a hole one inch in diameter 
 will contain 0'416 oz. for every inch of depth. Hence, to find the weight of powder to an inch of 
 depth in any given hole, we have only to multiply 0'416 oz. by the square of the diameter of 
 the hole in inches; and in this way we may determine, either the length of hole for a given charge, 
 or the charge in a given space. The following table will be found of practical value : 
 
 Diameter 
 
 Powder 
 contained in 
 an inch of 
 
 length. 
 
 Powder 
 
 contained in 
 
 1 foot of length. 
 
 Depth of Hole to contain 
 
 Diameter 
 of the 
 Hole. 
 
 Powder 
 contained in 
 an inch of 
 
 length. 
 
 Powder 
 
 contained in 
 
 1 foot of length. 
 
 Depth of Hole to contain 
 
 of the 
 Hole. 
 
 I lb. of 
 Powder. 
 
 1 lb. of 
 
 Powder. 
 
 i lb. of 
 Powder. 
 
 1 ib. of 
 
 Powder. 
 
 In. 
 
 oz. 
 
 lb. oz. 
 
 in. 
 
 in. 
 
 in. 
 
 oz. 
 
 lb. oz. 
 
 in. 
 
 in. 
 
 1 
 
 0-416 
 
 4-992 
 
 9-615 
 
 38-461 
 
 2| 
 
 3-175 
 
 2 6-100 
 
 1-259 
 
 5-039 
 
 li 
 
 0-650 
 
 7-800 
 
 6-153 
 
 24-615 
 
 3 
 
 3-744 
 
 2 12-928 
 
 1-068 
 
 4-273 
 
 l| 
 
 0-936 
 
 11-232 
 
 4-273 
 
 17-094 
 
 3i 
 
 4-394 
 
 3 4-728 
 
 0-910 
 
 3-641 
 
 If 
 
 1-274 
 
 15-288 
 
 3-139 
 
 12-558 
 
 3| 
 
 5-096 
 
 3 13-152 
 
 0-784 
 
 3-139 
 
 2 
 
 1-664 
 
 1 3-968 
 
 2-403 
 
 9-615 
 
 3| 
 
 5-850 
 
 4 6-200 
 
 0-683 
 
 2-735 
 
 2i 
 
 2-115 
 
 1 9-380 
 
 1-891 
 
 7-565 
 
 4 
 
 6-656 
 
 4 15-872 
 
 0-600 
 
 2-408 
 
 2| 
 
 2-600 
 
 1 15-200 
 
 1-534 . 
 
 6-158 
 
 
 
 
 
 
 Blasting holes are never bored truly circular ; but the variations of the quantity, as determined 
 by the table, due to this circumstance are of no practical importance. 
 
 Tamping. — It will be apparent from the foregoing considerations that the operation of tamping 
 the bore-hole, and the materials to be employed for that purpose, are questions of the highest 
 importance in blasting. The object of tamping is to oppose a resistance to the escape of the gases in 
 the direction of the bore-hole superior to that offered by the rock along the line which has been 
 determined as that of least resistance. That is, the use of the tamping is to prevent the line of the 
 bore-hole being that of least resistance. Hence, a primary condition is that the materials employed 
 shall be of a strongly resistant character. A second determining condition is that these materials shall 
 be of ready application. This condition precludes the use of all such devices as plugs, wedges, and 
 forms of a similar character, which have been from time to time proposed. The only material that 
 has been found in practice to satisfactorily fulfil the requirements demanded is rock in a pulverulerit 
 state. As, however, all rock is not equally suitable, either from the point of view of its resistant 
 character, or from that of convenience of handling, it becomes necessary to consider which satisfies 
 the two conditions in the most complete manner. 
 
 Though it is not easy to assign a perfectly satisfactory reason why one kind of rock substance 
 opposes a greater resistance to motion in a bore-hole than another, yet it is certain that this 
 resistance is due to the friction among the particles of that substance. If a column of solid hard 
 rock, of the same diameter as the bore-hole, be driven down upon the charge, the resistance opposed 
 by the column to the imprisoned gases will be, neglecting the weight of the former, that of the 
 friction between the sides of the column and those of the hole. But if disintegrated rock be used 
 not only is an absolute motion imjjarted to the particles, but, on account of the varying resistances a 
 relative motion also. Consequently, friction occurs amongst the particles, and as the number of these 
 is immense, the sum of the slight friction of one particle against another, and of the great friction 
 
SHAFT-SINKING. 219 
 
 of the outside particles against the sides of the hole, amounts to a much greater value than that of 
 the outside particles of the solid column against the sides of the bore-hole. If this view of the facts 
 alone be taken, it follows that dry sand is the most resistant material, and that the finer the grains 
 the greater will be the resistance which it offers. In practice, however, it has been found that 
 though the resistance offered by sand tamping is very great, and though also the foregoing inference 
 is true when the tamping is lifted by the pressure of a solid against it from below, this substance is 
 notably inferior to some others when acted upon by an explosion of gases. The explanation of this 
 apparent anomaly is that the gases, under the enormous tension to which they are subjected in the 
 bore-hole, insinuate themselves between the particles, and so prevent the friction which would otherwise 
 take place. When the readiness with which water, through the influence of gravity alone, permeates 
 even closely compacted sand is borne in mind, there will be no difficulty in conceiving a similar 
 action on the part of more subtile gases in a state of extreme tension. Under such conditions as 
 these, there is no resistance whatever due to friction, and the only resistance opposed to the escape of 
 the gases is that proceeding from the inertia of the mass. How this resistance may be very great, 
 we have shown in the case of air tamping. Hence, it becomes necessary to have recourse to some 
 other material, of a composition less liable to be thus acted upon, or to seek means of remedying the 
 defect which renders such action possible. 
 
 Clay, dried either in the sun or, preferably, by a fire, appears to fulfil the requirements of a 
 tamping material in the fullest degree. This substance is composed of exceedingly minute grains of 
 silicious matters, bound together by an aluminous and calcareous or ferruginous cement. Thus 
 constituted, there are no voids between the particles as in porous substances, and, consequently, there 
 is no passage for the gases, the substance being impervious alike to water and gas. Hence, when 
 this material is employed as tamping, the forces act only upon the lower surface, friction takes place 
 among the particles, and the requisite degree of resistance is produced. By reason of its possession 
 of this property, clay is generally used as the tamping material. 
 
 In rock blasting, it is usual to prepare the clay beforehand, and this practice is conducive both 
 to effective results and to rapidity of tamping. The latter consideration is an important one, inas- 
 much as the operation, as commonly performed, requires a good deal of time. To prepare these 
 pellets of clay, a lump is taken and rolled between the palms of the hands until it has assumed the 
 form of a sausage, from three to four inches in length, and of the diameter of the bore-hole. These 
 pellets are then baked until they are thoroughly dry, when they are ready for use. In making them 
 up to the requisite diameter, a little excess should be allowed for shrinkage, since it is essential 
 that they fit tightly into the hole. When the charge has been put in, and covered with a wad 
 of hay, or a handful of sand or rubbish, one of these pellets is inserted and pushed home with a 
 wooden rammer. Considerable pressure should be applied to make the clay fill the hole completely, 
 but blows should be avoided. A second pellet is then pushed down in the same way, and the 
 operations repeated until the whole of the hole is tamped. To consolidate the whole, light blows may 
 be applied to the outer pellet. It will be found advantageous to place an undried pellet immediately 
 above the charge, because the plasticity of such a pellet enables it to fill all the irregularities of the 
 sides of the hole, and to securely seal the passage between the sides and the tamping, along which 
 the gases might otherwise force their way. 
 
 In coal blasting, soft shale is always iised for tamping, because it is ready at hand, and heavy 
 shots are not required. It may be desirable to call attention here to an erroneous notion prevalent 
 
 2 P 2 
 
220 
 
 MINING ENGINEEEING. 
 
 relative to plastic clay tamping. It is supposed that clay in a moist and plastic state opposes a much 
 less powerful resistance than when dry. This is to some extent true, and the reason appears to be 
 that less friction is produced among the particles when the latter are lubricated with water. The 
 difference of the effects, however^ is less than that due to difference in friction. The outsides of the 
 dried pellets become granulated by being forced down in rubbing contact with the sides of the hole, 
 and thus a film of porous material is interposed between the latter and the tamping, through which 
 the gases may force their way. It is to prevent such an occurrence, that the plastic pellet next the 
 charge is recommended. But when the whole of the tamping is of a plastic character, no pul- 
 verization occurs, and hence it is that the lessening of the friction is nearly compensated. The 
 plastic clay should be applied in rolled pellets in precisely the same manner as the dried clay, 
 except that no blows should be resorted to. By plasticity, we must be understood to mean only that 
 due to a moderate degree of moisture, such as will allow the clay to yield before considerable 
 pressure without crumbling. 
 
 Broken brick constitutes a fairly good tamping material, especially when tempered with a little 
 moisture; but as it is not readily procurable, its application is necessarily limited. The dust and 
 chippings of the excavated rock are largely employed as tamping in quarries. This material, 
 however, has but little to recommend it for the purpose beyond its readiness to hand. 
 
 It now remains to consider what means are available for remedying the defect inherent in sand 
 as a tamping material. This constitutes a very important practical question, because if the defect 
 can be removed, sand will form by far the most suitable material whenever the bore-hole has a 
 downward direction. It can be everywhere obtained at a low cost ; it may be poured into the hole 
 as readily as water ; and its application gives rise to no danger. Two methods of overcoming the 
 difficulty present themselves : one is to employ means of preventing the gases from penetrating the 
 sand ; the other, to have recourse to detonation. 
 
 The end proposed in the former of these methods may be successfully obtained by means of the 
 plastic clay pellet in the following manner. Immediately above the charge, place a handful of 
 perfectly dry and very fine sand. This may be obtained by sifting, if not otherwise procurable. 
 Upon this sand, force firmly down with a wooden rammer, so as to fill every irregularity, a plastic 
 clay pellet, about four inches in length and of the same diameter as the bore-hole, prepared by 
 rolling between the hands in the manner already described. Above this pellet fill the hole with dry 
 sand ; the impervious nature of the clay prevents the gases from reaching the sand, except along the 
 line of junction of the clay with the sides of the hole. As the depth of clay is at the most four 
 inches, an escape of gases along this line may occur in a greater or less degree, according to the 
 greater or less regularity of the hole, and the more or less care with which the pellet is forced down. 
 To prevent this escape is the use of the fine sand beneath. The particles, taken up by the gases, become 
 closely wedged into the interstice, and completely block the passage. Tamped in this way, a resist- 
 ance is obtained scarcely if at all inferior to that opposed by the most carefully-placed dried clay. 
 
 By the employment of a detonator, the defect due to the porous character of sand is not 
 removed, but its influence is greatly diminished. "When detonation is produced in an explosive 
 compound, the full force of the elastic gases is developed instantaneously ; and it has already been 
 shown that, under sucli conditions, the resistance occasioned by the presence of any substance in the 
 bore-hole, even the air alone in the case of nitroglycerine, is sufficient to throw the chief portion 
 of the force upon the sides of the hole. Loose sand, therefore, may be successfully employed as 
 
SHArT-SINKING. 221 
 
 tamping under these conditions, since its inertia will oppose a suflScient resistance to the escape of 
 the gases. But though the rock may be dislodged when light tampings are used with detonation, 
 there can be no doubt that a considerable proportion of the force of the explosion is lost ; and hence 
 it will always be advantageous to tamp securely by means of the clay pellet, as already described. 
 The highest degree of economy is to be attained by detonating the charge, and tamping in this 
 
 manner. 
 
 Conditions of Disruption. — Having explained the laws according to which the elastic gases 
 evolved by an explosion act upon the surrounding rock, and described the means by which the 
 forces thus developed are made to bear upon the points desired, it now remains to consider the 
 conditions under which disruption may take place. Suppose a block of unfissured rock detached 
 on all sides, as shown in plan, in Fig. 372, and a bore-hole placed in the centre of this block. If a 
 charge be fired in this position, the lines of rupture will radiate from the centre towards any two, 
 or towards all four of the unsupported faces of the block, because the forces developed will act 
 equally in all directions, and the lines of rupture will be those of least resistance. Evidently this is 
 the most favourable condition possible for the charge, since the rock offers an unsupported face on 
 every side, and it is evident that the line of rupture must reach an unsupported face to allow of dis- 
 lodgment taking place. Suppose, again, as shown in Fig. 373, the block to be unsupported on three 
 sides only, and the charge placed at h. In this case, the lines of rupture may run to any two, or to all 
 three, of the unsupported faces ; and hence this will be the next most favourable condition for the action 
 of the charge. The greatest useful effect, however, will be obtained in this case by placing the charge 
 farther back at h', when the lines of rupture must necessarily run to the opposite faces b c, and, 
 consequently, the whole of the block will be dislodged. Assume another case, in which the rock is 
 unsupported upon only two sides, as shown in Fig. 374, and the charge placed at h. In this case, 
 the lines of rupture must run to each of the unsupported faces a b. Thus, it is evident that this 
 condition, though still a favourable one for the good effect of the charge, is inferior to the preceding. 
 As rock is never homogeneous in composition or uniform in texture, the lines of rupture, which, 
 as before remarked, will be those of least resistance, may reach the faces at any point, as at m n, 
 wl n', or any point intermediate between these. But it will be seen that the useful effect will 
 be greatest when these lines, radiating from the charge, make an angle with each other of 180°, or, 
 in other words, run in directly contrary directions, and that the useful effect diminishes with the 
 angle made by these lines of rupture. Suppose, again, the rock to be unsupported upon one side 
 only, as shown in Fig. 375, and the charge placed at h. In this case, the lines of rupture must run 
 to the face a, and the condition must therefore be considered an unfavourable one. As, in the 
 preceding case, the useful effect will depend upon the angle made by the lines of rupture h m and 
 h n, which angle may be very small, and which must necessarily be much less than 180°. A 
 greater effect may be obtained under this condition by firing several charges simultaneously. If, for 
 example, we have two charges placed, one at h, and the other at h', and fired successively, the 
 lines of rupture will run in or near the directions h m, h n, h' n', h! n', and the portion ot 
 rock dislodged will be mhnh' n'. But if these two charges be fired simultaneously, the lines of 
 rupture will he hm, h o, h' o, h' n', and the mass of rock dislodged will be mhh! n '. Simulta- 
 neous firing is in this way productive of a greatly increased useful effect in numerous cases, and 
 the mining engineer, and the quarryman especially, will do well to direct their attention to this 
 source of economy. There is yet another case to be considered, in which the conditions are still 
 
222 MINING ENGINEEEING. 
 
 more unfavourable. Suppose two unsupported faces at right angles to each other, and the charge 
 placed at h, as shown in Fig. 376. In this case, the lines of rupture will run to each of the two 
 unsupported faces ; but as these lines must necessarily make a very small angle with each other — 
 for the length of the lines increases rapidly with the angle — the useful effect will be less than in the 
 last case. It follows, therefore, that this is the most unfavourable condition possible, and as such it 
 should be avoided in practice. 
 
 In the foregoing considerations, the holes have been assumed to be vertical, and for this reason 
 the unsupported face which is perpendicular to the hole, that is, the face into which the hole is bored, 
 has been neglected. For it is evident that, under the conditions assumed, the lines of rupture cannot 
 I'each this face, which, therefore, has practically no existence. Suppose, for example, a bore-hole 
 placed at h, in Fig. 377, and the rock to be supported upon every side except that at right angles to 
 the hole. The forces acting perpendicularly to the direction of the bore-hole are opposed on all sides 
 by an infinite resistance, and consequently the line of the hole becomes that of least resistance. 
 Hence, in this case, either the tamping will , be blown out, or, if the forces developed are unequal to 
 the work, no effect will be produced beyond a slight enlargement of the hole at the base. This, 
 however, is a case of frequent occurrence in practice, and it becomes necessary to adopt measures for 
 roaking this unsupported face available. Evidently this object can be attained only by so directing 
 the bore-hole that a line perpendicular to it may reach the face ; that is, the line of the bore-hole 
 must make with the unsupported face an angle less than 90°. This direction of the bore-hole is 
 shown in Fig. 378, which may be regarded as a sectional elevation of Fig. 377. In this case, the 
 lines of rupture, which will run similarly to those produced in the case shown in Fig. 375, will reach 
 the unsupported face at b, and the length of these lines, and consequently the depth of the excavation, 
 for a given length of bore-hole, will depend upon the angle which the latter makes with the face. 
 This mode of rendering a single exposed surface available is called " angling the holes," and it is 
 generally resorted to in shaft-sinking and driving headings. The conditions involved in " angling " 
 are favourable to the action of strong explosives. 
 
 To show how these principles are applied in practice, we will take a typical case of a heading, 
 7 feet by 9 feet, as shown in Fig. 379. In this case, we have at starting only one exposed face, 
 which is perpendicular to the direction of the driving. Hence it is evident that we shall have to 
 proceed by angling the holes. We might begin in any part of the exposed face ; but, as it will 
 hereafter appear, the most favourable position is the centre. We therefore begin at this point by 
 boring the series of holes, numbered 1 on the drawings. These holes are angled towards each other ; 
 that is, the two sets of three holes vertically above each other converge in the direction of their 
 lower ends, as shown in the sectional plan. In this instance we have assumed six holes as 
 necessary and sufficient. But it is obvious that the number of holes, as well as their distance apart 
 horizontally, will be determined by their depth, the tenacity of the rock, and the strength of the 
 explosive used. When these holes are fired, a wedge-shaped portion of the rock will be forced out, 
 and this result will be more effectually and certainly obtained if the charges be fixed simultaneously. 
 The removal of this portion of the rock is called " taking out the key." The effect of removing this 
 key is to leave the surrounding rock unsupported on the side towards the centre ; that is, another 
 exposed face is formed at right angles, or nearly at right angles, to the first. 
 
 Having thus unkeyed the rock by the removal of this portion from the centre, it will evidently 
 be unnecessary, except for convenience, to angle any more of the shot-holes. The second series. 
 
SHAFT-SINKING. 223 
 
 therefore (numbered 2 on the drawings) may be bored perpendicularly to the face of the heading. 
 "When this series is fired, the lines of rupture will all run to the unsupported face in the centre, and 
 from hole to hole, if the shots be fired simultaneously, and the annular portion of rock included 
 between the dotted lines 1 and 2 will be removed. If the shots be fired successively, the first will act 
 under the condition of one unsupported face, as illustrated in Fig. 375 ; but as another unsupported 
 face will be formed by the removal of the rock in front of this charge, the succeeding shots will be 
 subject to the more favourable condition represented in Fig. 374. The firing of this second series of 
 shots still leaves the surrounding rock unsupported towards the centre, and consequently the same 
 conditions will exist for the third series (numbered 3 on the drawings), the firing of which series will 
 complete the excavation. The longitudinal sectional elevalion;, given in the drawings, show clearly 
 the position of the charges relatively to the unsupported faces of the rock. 
 
 It may be remarked here that, owing to the want of homogeneity in the rock, and to the 
 existence of joints and fissures, in practice, the outer line of rupture will not run so regularly as 
 indicated, in this assumed case, by the dotted lines. This circumstance will influence the position of 
 the holes in the next series, and furnish an opportunity for the exercise of judgment on the part 
 of the blaster. 
 
 There exist also other circumstances which will influence the position and the number of the 
 holes in a very important degree, and which therefore must be taken fully into account at every 
 advance. One of these is the irregularity of the face of the excavation. Instead of forming 
 an unbroken plane at right angles to the direction of the heading or the shaft, this face is broken up 
 by projecting masses and more or less deep depressions. Obviously these protuberances and cavities 
 will influence, in no inconsiderable degree, the lines of least resistance ; the latter being lengthened 
 or shortened, or changed in direction by the presence of the former, which give existence to unsup- 
 ported faces to which the lines may radiate. These conditions must in every case be taken into account, 
 when determining the best position for the bore-hole. Of yet greater importance is the existence 
 of joint planes and bedding planes. It will be evident, from a consideration of the nature and mode 
 of occurrence of these planes as described in the first chapter of this work, that they may constitute 
 unsupported faces to which the lines of rupture may run. A bed of rock may be, and frequently 
 is, cut up by these planes into detached blocks of greater or less dimensions, according to the more or 
 less perfect development of the different sets. Hence it becomes necessary, in determining a suitable 
 position for the blasting charge, to consider such planes as unsupported faces, and to ascertain the 
 direction and the length of the lines of least resistance under such conditions. If a charge be placed 
 in close proximity to one of these planes, not only may the lines of rupture run in unforeseen 
 directions, but the greater part of the force of the explosion will be lost by the escape of the gases 
 along the plane. The same loss of force may be occasioned by the presence of a cavity, such as are 
 of frequent occurrence in cellular or vughy rock. When the joint planes are fully developed, their 
 existence can be ascertained by inspection ; but when their development is imperfect, there may be 
 considerable difficulty in discovering them. In such cases the rock should be carefully inspected, 
 and sounded with a hammer or pick. When a cavity is bored into, it should be rammed full of clay, 
 and the boring continued through the clay ; or if sufficient depth has been obtained, the charge may 
 be placed upon the clay, which will prevent the wasteful dissipation of the gases. As none of the 
 afore-mentioned circumstances recur under precisely similar conditions, no general rules of much 
 service can be laid down: they are matters upon which the blaster must be left to use his ovvn 
 
224 MINING ENGINEERING. 
 
 judgment, and to do this effectively, it is obviously necessary that he j)ossess some knowledge of the 
 materials with which he deals. 
 
 A somewhat different mode of unkeying the face is occasionally adopted when the nitroglycerine, 
 compounds are employed as the explosive substance. In such cases, instead of angling the holes in 
 the centre of the face, these are bored, three or four in number, close together. When fired with a 
 charge of the strong explosive, the thin partitions of the rock between the holes, and the rock 
 immediately surrounding these to a slight depth, are crushed to dust by the force of the explosion, 
 leaving a large hole in the centre of the face, to serve as the cavity caused by the removal of the key 
 in the former case.. The relatively small diameter of the hole, however, affords a less extent of 
 unsupported face than the cavity, and for this reason, as well as that of the small useful effect 
 produced by these first charges, the method must be considered as wasteful of explosive material. 
 The only justification for its adoption is to be found in the increased convenience of execution 
 afforded by the perpendicular direction of the holes, in certain circumstances, when machine drills 
 are used. 
 
 Economical Considerations. — Besides the important economical considerations involved in the fore- 
 going, there are others which claim notice. Foremost among these is the question whether, for a given 
 effect, it is better to augment or to diminish the individual importance of the shots; that is, whether it is 
 better to diminish the number of the holes and to increase their diameter, or to diminish the diameter 
 and to increase the number. It may be readily shown, mathematically, and the results are confirmed 
 by experience, that there is an important gain in reducing the diameter of the bore-holes to the 
 lowest limit allowed by the strength of the explosive and in increasing their depth. The gain is in 
 the direction of a great saving of labour and a no less considerable saving of explosive material. 
 Hence we again see the advantage of strength in the explosive employed, and the necessity of having 
 recourse to deep holes in order to obtain the full benefit of that advantage. 
 
 It has been proposed to increase the useful effect of the charge by mixing with the explosive 
 some inert substance, for the purpose of making the charge extend farther up the bore-hole. It is 
 believed that by thus distributing the force over a larger area, a better effect may be obtained. Within 
 certain narrow limits, this is true. In the case of dynamite, for example, the addition of 25 per cent, 
 of kieselguhr does not diminish the useful effect of the charge in a corresponding degree. Hence 
 the fact that a pound of dynamite, by reason of this wider distribution, will produce nearly the same 
 useful effect in rock as the same weight of nitroglycerine. But it must be borne in mind that, in 
 consequence of the greater surface to which the gases are exposed, and the presence of the silica in 
 the charge, there is a greater loss of heat. To obtain this wider distribution of force, which, in many 
 cases, leads to a greater useful effect, it has been proposed to mix sawdust with the gunpowder 
 employed in blasting rock. The expedient was tried on an extensive scale in Germany, with the 
 result of a notable economy of powder. A further investigation of the matter, however, showed this 
 result to be due to the excessive quantity employed when applied in an unmixed state. The workmen 
 had been accustomed to follow, in every case, the common rule of charging the hole to a heio-ht equal 
 to one-third of its length, and hence it arose that, when the powder was mixed with a large propor- 
 tion of gunpowder, there was still sufficient force to dislodge the rock. To mix an inert substance 
 with an explosive compound is to renounce the advantages of strength. In the case of the very- 
 strong explosive nitroglycerine, the admixture of 25 per cent, of kieselguhr, which otherwise serves 
 a useful purpose, is comparatively unimportant. But it is folly to apply the same expedient to gun- 
 
SHArT-SINKING. 225 
 
 powder for no other purpose than to economize material. The addition of sawdust, besides exposing 
 a larger cooling surface to the heated gases, causes a slow combustion, and the only positive gain to 
 be hoped for from this source is a greatly increased quantity of smoke. 
 
 The simultaneous firing of shots offers several important advantages. It has already been shown 
 how one charge assists another under such a condition, and in what way the line of rupture is 
 affected by it. It must be understood, however, that to produce these effects, perfect simultaneity is 
 necessary. If the shots be fired successively, no matter how rapidly, each will act independently of 
 the others. Thus simultaneity of discharge can be obtained only through the medium of electricity, 
 and hence it becomes important to simplify the means by which electricity may be applied to blasting 
 purposes. There can be no doubt that this mode of firing is destined to come into general use, and, 
 with machine drills, to modify, in no inconsiderable degree, the operations involved in rock excava- 
 tion. Another advantage of simultaneous firing lies in the fact that less delay is occasioned in wait- 
 ing for the explosion of the charges. Where a large number of workmen are employed, this delay 
 may be a matter of considerable importance. 
 
 The Operations of Blasting. — When the positions and the directions of the shot-holes have 
 been determined, the operations of blasting are begun by striking a few light blows with a pick 
 upon the spot from which the hole is to start, for the purpose of preparing the surface to receive the 
 drill. In some cases, this preliminary operation will not be needed, but generally some preparation 
 is desirable, especially if the surface is smooth and the hole is to be bored at an angle. As an 
 illustration, we will suppose the case of a vertical hole, as required in shaft-sinking. In this 
 case, the boring will be double-handed, and the set of tools needed will be that described in a former 
 section. 
 
 Boring. — When the surface has been prepared by the pick, one man sits down, and placing tlie 
 shortest drill between his knees, holds it vertically in both hands. The other man, who stands opposite, 
 if possible, then strikes the drill upon the head with the sledge, lightly at first, but more heavily when 
 the tool has fairly entered the rock. The man who is holding the drill raises it slightly after each 
 blow, and turns it partially round, the degree of turn usually given being about one-tenth of a revo- 
 lution. By this means the hole is kept circular in section, and the accuracy of this form will be 
 dependent upon the regularity and uniformity of the motion imparted to the tool. To keep the 
 latter cool, and to convert the dust and chippings into sludge, the hole is kept partially filled with 
 water. The influence of water upon the rapidity of boring was shown in a former section. To 
 prevent the water from spurting out at each stroke and splashing the man who is holding the drill, 
 a kind of leather washer is placed upon the drill immediately above the hole, or a band of straw is 
 tied round it in that situation. When the hole has become too deep for the short drill, the next 
 length is substituted for it, which is in its turn replaced by the third or longest drill, as the depth 
 becomes greater. Each drill, on the completion of the length of hole for which it is intended, is 
 sent away to be resharpened. In very hard rock the drills may require to be frequently changed, 
 a circumstance that renders it necessary to have several of the same length at hand. The depth 
 of blasting holes varies from 2 feet to 10 feet, according to the nature of the rock, the character of 
 the excavation, and the strength of the explosive to be used. In shafts and headings, the depth 
 varies generally between 2 feet 6 inches and 4 feet, a common depth being 3 feet. 
 
 The debris accumulating at the bottom of the hole must be removed from time to time, to keep 
 the rock exposed to the edge of the drill. The removal of this sludge is effected by means of the tool 
 
 2 G 
 
226 
 
 MINING ENGINEEEING. 
 
 called a scraper, described in a former section. If the sludge is in too liquid a state to allow of its 
 ready removal by this means, a few handfuls of dust are thrown in to render the mass more viscous. 
 The importance of keeping the bore-hole clear of sludge, and of shortening the time expended in 
 using the scraper, has led, in some instances, to the adoption of means for rendering the sludge 
 sufficiently viscous to adhere to the drill. When in this state, the sludge accumulates around the 
 tool rather than beneath it, the fresh portions formed pushing the mass upward till it forms a thick 
 coating around the tool throughout a length of several inches. When the tool is withdrawn from 
 the hole, this mass of de'bris is withdrawn with it, and by this means the use of the scraper is 
 rendered wholly unnecessary. This mode of clearing the hole is commonly adopted by the Hartz 
 miners, who employ slaked lime for this purpose. This lime, which they procure for themselves at 
 their own expense, they reduce to the consistency of thick paste by the addition of water, and they 
 store it, covered with water, in a small tin box, which they carry with them to their work. To use 
 this paste, they take a piece about the size of a walnut, dilute it with water, and pour it into the 
 bore-hole. This lime paste is, for the purpose intended, very effective in friable rock, especially those 
 of a granular structure, as sandstone. As the grains of sand resulting from the trituration of such 
 rocks have no more tendency to adhere to each other than to the tool, each of them becomes 
 covered with a coating of lime, which causes them to agglutinate into a viscous mass, possessing a 
 sufficiently adhesive quality to enable it to cling to the tool in the manner described. 
 
 When the hole has reached the required depth, it is prepared for the reception of the charge, if 
 gunpowder is used, by removing the moisture from the bottom and sides. This is effected by means 
 of a piece of tow, rag, or a wisp of hay passed through the eye of the scraper, or twisted round it, 
 and forced slowly up and down the hole, so as to absorb the moisture from the face of the rock. 
 When water enters the hole through crevices, it may be stopped back by claying the hole by 
 means of the instrument called a " bull." Also, if water is likely to flow into the hole from above, 
 a little^ dam of clay must be made round it to keep out the water. The labour of drying the bore- 
 hole may be saved by the use of greased paper cartridges, and even that of claying may be rendered 
 unnecessary by the use of cartridges of a perfectly water-tight character. It is commonly objected 
 against the use of cartridges that they occasion a loss of the explosive force, by leaving empty spaces 
 between the case and the sides of the hole, where irregularities exist in the latter. For it is a well- 
 ascertained fact that the existence of such spaces is the cause of a notable decrease of useful effect. 
 To this objection, there are several answers. In the first place, it may be replied that the loss of 
 force is, from other causes, greater when the cartridge is not employed. In the dryest hole, the rock 
 contains a very considerable degree of moisture. When the powder is put in loose, the grains, which 
 are very greedy of water, are in contact with the sides of the hole during the time of tamping and 
 the burning of the fuse ; and the necessary consequence of this prolonged contact is a weakening of 
 the charge, due to the imbibition of moisture from the rock by the grains of powder in close 
 proximity to it. For it must be borne in mind that this imbibition or absorption will extend into 
 the charge to a depth of several grains from the outside. When a paper covering is used this injury 
 cannot occur. Again, it may be urged in favour of the use of the cartridge that if the workmen 
 apply a moderate degree of skill and care, such as should be required by every man in charo-e of 
 blasters, the irregularities of the hole will be trifling, and consequently the empty spaces will exert 
 but little influence. But a more cogent argument hes in the fact that such spaces may be easily 
 filled up. If a handful of dry and very fine sand be poured in upon the cartridge, the grains will 
 
SHAFT-SINKING. 227 
 
 enter, some at once, and some during the process of tamping, into the interstices, and tightly wedge 
 the cartridge into the hole. It does not, therefoie, appear, either that the merits claimed for loose 
 charging, or that the objections urged against the use of the cartridge, rest upon a very solid founda- 
 tion ; and when it is borne in mind that the cartridge, besides the advantages already mentioned, 
 offers an effectual check against the employment of powder in wasteful quantities, the superiority of 
 that mode of charging must be acknowledged. As a general rule, therefore, it may be laid down that 
 gunpowder should always be used in cartridges. 
 
 Charging. — When the hole is ready to receive the charge, the latter must be inserted in a 
 manner and by means suitable to the nature of the explosive compound. If this compound is 
 gunpowder, and it is to be employed loose, the requisite quantity is poured down the hole, care 
 being taken to prevent the grains from lodging against the sides of the hole. This precaution is 
 important, since not only is the force of the grains so lodged lost, but they may be the cause of a 
 premature explosion. As it is impossible to prevent this occurrence when the holes are inclined, 
 and difficult when they are vertical, it becomes necessary to have recourse to a tin tube, which 
 should be covered to prevent accidents. This tube is rested upon the bottom of the hole, and the 
 powder poured in at the upper end ; when the tube is raised, the powder is left at the bottom 
 of the hole. In horizontal boles, the powder is put in by means of a wooden spoon. It will be 
 obvious that in holes that are inclined upwards, the powder cannot be inserted loose. This is 
 a serious defect of the loose-charge system. The safety fuse is then dropped down, and its end 
 forced slightly into the powder. If it be required to fire the charge from the bottom, in order to 
 obtain a better effect, the safety fuse must be put in before the powder. A wisp of hay, a piece of 
 paper, or some other substance having been put in above the powder, to separate and protect it from 
 the tamping, the fuse is led up against the side of the hole and the tamping put in. When the charge 
 is enclosed in a cartridge, the end of the latter, if of paper, is opened, and the fuse inserted in the 
 powder ; the paper of the cartridge is then bound to the fuse by a piece of string. If the cartridge is 
 a waterproof one, the fuse is inserted into the hole in. the end, left for that purpose, and a piece of 
 tallow laid on to keep out the water. The cartridge is then inserted into the bore-hole, and forced 
 to the bottom with a wooden rammer ; and the fuse having been laid against the side of the hole, as 
 in the preceding case, the tamping is put in. If the charge is to be detonated, the fuse is inserted 
 into the cap of the detonator, and the open end of the cap pressed into firm contact with the fuse 
 by means of a pair of nippers. The detonator is then inserted into the cartridge, and the paper of 
 the latter tied up to the fuse with a piece of string ; the cartridge is then placed in the hole. When 
 the charge is loose, the detonator is forced into it, or better, if the fuse is good, placed at the bottom 
 of the hole, before the powder is put in. 
 
 When dynamite is used, one or more of the ordinary cartridges, according to the charge required,, 
 are inserted into the bore-hole, and each cartridge forced home separately with a wooden rammer. 
 A moderate degree of force should be applied, in order to put the plastic material everywhere into 
 contact with the rock. A safety fuse is then cut clean, and inserted into a detonator cap down to the 
 fulminate ; and the cap is fixed to the fuse by pressing the open end into firm contact with the latter. 
 This closing of the cap is important, as it not only prevents the withdrawal of the fuse, but it retains 
 the gases of the fulminate when fired. When water tamping is to be used, grease, tar, or white lead 
 must be applied to the junction of the cap with the fuse. A primer cartridge, that is, a small 
 dynamite cartridge designed to explode the charge, is next opened at one end, and the detonator cap, 
 
 2 a 2 
 
228 MINING ENGINEERING. 
 
 witli the fuse attached, inserted into the dynamite to a depth of about three-fourths of its length, and 
 the paper of the cartridge is firmly tied to the cap and to the fuse with string. The primer, with the 
 detonator and fuse attached in this manner, is then dropped down upon the charge in the bore-hole, 
 and loose sand or water poured in as tamping, the fuse being led up against tlie side of the hole, as 
 in the former cases. When the holes have been loaded in the manner described, the charges, whether 
 of gunpowder or of dynamite, are ready for firing as soon as the tamping has been put in. 
 
 The operation of tamping was fully described when treating of the principles of blasting. 
 
 Firing. — When all the holes bored have been loaded in this way, or as many of them as it is 
 desirable to fire at one time, preparation is made for firing them. The first consideration is the safety 
 of those employed, and to ensure this, an unmistakable signal must be given for all in the immediate 
 vicinity to withdraw. When the man to whom is entrusted the duty of firing the blasts has clearly 
 ascertained that all are under shelter, he assures himself that his own way of retreat is clear. If, for 
 example, he is at the bottom of a shaft he calls to those above, in order to learn whether they are ready 
 to raise him, and waits until he receives a reply. When this reply has been given, he lights the ends 
 of the fuses, and shouts to be hauled up ; or if in any other situation than a shaft, he retires to a place 
 of safety. Here he awaits the explosion, and carefully counts the reports as they occur. After all 
 the shots have exploded, a short time is allowed for the ventilation to clear away the smoke 
 and fumes, and then the workmen return to remove the dislodged rock. If one of the shots has 
 failed to explode, at least ten minutes should be allowed to elapse before returning to the place, for it 
 is easy to conceive how many causes may operate to delay the combustion of the fuse. Fifteen 
 minutes is not too long a time to wait in such a case, and a regulation to that effect should be made 
 and strictly enforced. When it has been clearly ascertained that the shot has failed, the men may 
 be permitted to return. But in no case should they be allowed to bore out the tamping for 
 the purpose of inserting another fuse. Numerous fatal accidents have resulted from this proceeding. 
 The unexploded charge should be left untouched, and a fresh hole bored to dislodge the rock. Thus 
 it is evident that careful loading is conducive to economy of time, since a misfire causes a serious 
 delay. In headings, manholes are provided as places of retreat for the blasters while awaiting the 
 explosion ; these manholes are small excavations made at right angles to the sides of the heading. 
 Sometimes it is necessary to erect a shield of timbers in the heading, for the protection of the men ; 
 such a shield is very frequently needed to protect the machine drills from the effects of the blast. In 
 Belgium, it is a common practice to provide manholes in the sides of a shaft for the retreat of the 
 blasters ; these holes are called caponnihres. Instead of caponnieres, a hollow iron cylinder 
 is sometimes used as a protection to the workmen. This cylinder is suspended in the shaft at 
 a height of a few yards from the bottom, and is lowered as the sinking proceeds. The men climb 
 into the cylinder to await the explosion of the shots. 
 
 On returning to the working face, the workmen remove the dislodged rock, and break down 
 evfery block that has been sufficiently loosened. For this purpose they employ picks, wedges and 
 sledges, and crowbars. And not until every such block has been removed do they resume the boring 
 for the second blast. To facilitate the removal of the rock dislodged by the shots, iron plates are not 
 unfrequently laid in front of the face in a heading. The rock falling upon these plates is removed 
 as quickly as possible, to allow the boring for the succeeding blast to commence. It is important, in 
 the organization of work of this character, that one gang of workmen should not be kept waitiug 
 for the completion of the labour of another. 
 
SHAFT-SINKINa. 229 
 
 In the example of blasting under consideration, the holes are vertical, or only slightly inclined 
 from the vertical. But it is evident that the operations to be performed would be similar in the case 
 of horizontal holes, such as are required in headings, the only diiferences being those due to the 
 altered direction, which will modify, in a manner easily imagined, the mode of holding the drill, and 
 of clearing and loading the hole. 
 
 It may be remarked here that, in some places, notably in the Cleveland district, the bore-hole is 
 made triangular in section, rather than circular. This form is preferred on the supposition that it 
 is more favourable to the convenient fracture of blocks of rock. When, however, the action of 
 expanding gases is borne in mind, it is difficult to see how this result can be brought about by such 
 means. The only fact that appears clearly to follow from the adoption of this form is that, under 
 such conditions, the use of gunpowder in cartridges becomes impossible ; that is, all the disadvantages 
 of a badly bored hole are incurred, without any apparent compensating gain. If the action of an 
 explosion be carefully considered, and all the conditions of blasting be taken into account, it must be 
 acknowledged that the more truly circular the hole, the more favourable is it for the charge. It is 
 indeed one of the advantages afforded by machine drilling that the holes are bored truly circular. 
 
 The foregoing description of the operations involved in blasting apply only to hand drilling. 
 "When machine drills are employed, these operations will necessarily differ somewhat in their details 
 from those described, and, in some cases, other methods of procedure wiU be adopted, more suitable 
 to the requirements of machine labour. It may even be inexpedient to follow the principles which 
 lead to economy of the explosive substance employed, since the more restricted conditions under 
 which machine power can be applied may point to more important gains in other directions. Thus 
 it may be found more conducive to rapidity of execution to determine the position and the direction 
 of the shot-holes rather to satisfy the requirements of the machine, than those of the lines of least 
 resistance ; or, at least, these requirements must be allowed to exert a modifying influence in deter- 
 mining those positions and directions. These questions will be considered incidentally in the 
 following section and chapter, where the details of the operations will be fully described ; and some 
 proposed systems of applying machine drills to give the greatest useful effect will be explained and 
 illustrated. 
 
230 MINING ENGINEEEING. 
 
 CHAPTER IV. —continued. 
 SHAFT-SINEING. 
 
 SECTION II. 
 
 In the foregoing section, the tools and other mechanical appliances used in the excavation oi 
 rock have been somewhat minutely described, and the principles upon which the use of these means 
 are based fully explained. It has been shown that an accurate and intimate knowledge of such 
 means must precede any attempt to apply them to the important requirements of practice, since the 
 ultimate success of an undertaking, both from engineering and from, commercial points of view, is 
 greatly dependent upon the possession of this knowledge by those to whom the execution of the work 
 is entrusted. And attention has been directed to the necessity which has arisen for the substitution 
 of machine for manual power to meet the rapidly growing demands for the produce of the mine, and 
 the altered relations subsisting between capital and labour. It now remains to consider and to 
 describe the various operations involved in the important undertaking which forms the principal 
 subject of the present chapter. 
 
 The shaft of a mine constitutes the means of communication between the underground workings 
 and the surface, and as such its importance commends itself at once to the understanding. It would, 
 indeed, be difficult to overrate this importance from whatever point it be viewed. During the process 
 of sinking, the shaft has to pass through all the strata intervening between the surface and the seam to 
 be worked, whatever their nature may be. This nature may be such as to render the operations simple 
 and easy, and they may be such as to render them exceedingly difficult and almost ruinously costly. 
 To the bottom of the shaft, the whole produce of the mine must be brought, and from the mouth, at 
 surface, it must all be conveyed away. Moreover, every particle of this produce has to be drawn up 
 the shaft, and, by the same way, all the material required has to be let down. The same means of 
 communication serves to introduce the air necessary to the ventilation of the workings, and to convey 
 away that which has become unfit for respiration, and through the same passage, the minei's 
 employed in extracting the mineral must every day pass. Hence it is obvious that the shaft Avill 
 claim the most serious attention of the mining engineer, and call for the most careful exercise of his 
 knowledge and judgment. 
 
 Designations of Shafts. — Shafts are classed and described according to one of the several uses to 
 which they are put. Thus we have an engine shaft, up which the water is pumped, and over which the 
 pumping engine is situate, from which it takes its name. A winding or draioing shaft, up which the 
 mineral is raised, and in connection with which the winding engine is erected. An air shaft, which 
 is sunk to a seam for the purpose of providing ventilation. A down-cast shaft, down which the fresh 
 
SHAFT-SINKING. 231 
 
 air passes to the underground workings. And an up-cast shaft, up which the fouled and heated air 
 passes from the workings to the surface. In thus designating shafts, or as they are commonly called 
 in the coal districts, " pits," it is not intended to convey an idea of a special and an exclusive use, 
 but rather to direct attention to that particular one of its several uses which relates to the subject in 
 question. Thus, in reference to ventilation, the shafts are spoken of as down-cast and up-cast ; and 
 in reference to the extraction, of the mineral, or the removal of the infiltering water, as winding or 
 engine shafts. "Winding may be, and usually is, carried on through both the down-cast and up-cast 
 shafts, and the pumping may be performed through either. 
 
 Number, Form, and Dimensions of Shafts. — It was formerly the practice, in mines of small 
 extent, to sink but one shaft to the seam, on account of the costly character of sinking operations. 
 In such a case, this single shaft had to serve all the purposes indicated in the foregoing paragraph ; 
 and to enable it to do this, it was divided into several compartments. One of these compartments 
 was set apart for the pumps, and two others for the winding, while the air was conveyed down one 
 of these and up another, or the two others. This arrangement was, however, a very dangerous one 
 to the lives of those employed, since an accident to the shaft cut off all means of retreat. Under this 
 system many terrible accidents occurred, and at length the Legislature was compelled, in the interests 
 of those employed, to interfere and prohibit the working of a mine with less than two shafts. Two, 
 therefore, is the least number possible. In districts where the seams of coal are accessible at small 
 depths, less effort is made to reduce the number of shafts to the lowest practicable limit. But when 
 great depths have to be attained, the workings are always laid out with this view. In Staffordshire, 
 for example, the shafts are very numerous, and of small diameter, and the winding through these is 
 carried on at a slow speed. In Durham, on the contrary, the shafts are few and of large diameter, 
 and the winding through them is effected at a very high speed. In all cases, however, economy 
 requires that this latter system should be followed ; that is, that the number of the shafts should be 
 reduced to the lowest practicable limit; that their dimensions should be sufficient to supply an 
 adequate quantity of air to the workings, and allow the passage of capacious tubs in properly con- 
 structed cages ; and that the winding should be carried on at a high speed. The actual number of 
 shafts requisite can be determined only by the conditions of the case. 
 
 The form of the shaft varies considerably. Thus we have, in England, shafts circular or 
 elliptical in section in the coal districts, and rectangular in the metalliferous districts. On the 
 Continent, the rectangular and polygonal forms, as well as the circular, are adopted for coal shafts. 
 These various forms of shafts are by no means due to caprice or to custom, but are determined by 
 several conditions. The rectangular section occasions the least waste of space, and the circular the 
 greatest. This consideration, however, does not influence the choice in any very great degree. The 
 determining conditions are, mainly, the strength of the rock passed through and the material 
 available for supporting the sides. When the sinking is through plastic clay or running sand, for 
 example, the pressure upon the lining of the shaft is very great, and this pressure is exerted nearly 
 equally in all directions. To resist this pressure, the circular form is the most suitable, and it is for 
 this reason that it has been adopted whenever the rock is of a weak and unstable character. Another 
 reason tending to confirm the choice of the circular form under such conditions, in localities where 
 stone and brick are the only materials available for lining, is that that form lends itself most readily 
 to the nature of those materials. On the contrary, where wood is abundant, as in some of the 
 Continental and American coal fields, and is therefore preferred to masonry, as a lining to the shafts, 
 
232 MINING ENGINEEEING. 
 
 the circular form is an impossible one, and the rectangular the most suitable. Hence it arises that, 
 while in England the circular and elliptical forms are exclusively adopted for coal shafts, the 
 rectangular and polygonal forms are resorted to in other countries. Similar conditions prevail in 
 Cornwall, where the rectangular shaft is almost exclusively used, and in other metal-mining districts 
 of England. The rocks of those districts, being of a strong character, need but little support, and 
 this support is given by timbering. It may be remarked that rectangular shafts are never made 
 square, and that the length varies from about once and a half to three times the breadth. 
 
 Shafts also vary widely in their dimensions. But the tendency of the present time is in the 
 direction of large diameters, which tendency is, as we have already stated, in accordance with the 
 requirements of economy. Circular shafts should never be less than 9 feet in diameter in the clear, and 
 they may be as much as 16 feet in diameter. In some instances, both in England and on the 
 Continent, elliptical shafts have been sunk, the diameters of which are as much as 18 feet and 20 feet. 
 In France and Belgium, the diameter of circular shafts rarely exceeds 10 feet. Yet there, as in 
 England, the tendency is to increase the dimensions. The up-cast should, for reasons that will be 
 hereafter explained, possess a larger diameter than the down-cast. "When the section is rectangular, 
 the dimensions are very various. In France and Belgium, they are commonly between 4 and 6 feet 
 in breadth, by from 9 to 16 in length. In the Hartz mountains, the dimensions are usually great; 
 many shafts are 10 feet in breadth by 26 feet in length. These dimensions are, however, outside the 
 timbering. In the clear, these shafts would be about 8 feet in breadth by 23 feet in length. In 
 America, where the shafts are usually inclined, and partake more of the character of day-levels than 
 shafts proper, the dimensions adopted are often very large. Of course, the dimensions of a shaft 
 must be determined in accordance with the degree of pressure likely to be thrown upon the walls. 
 Thus in ground of a very unstable character, even a strongly walled shaft oi a circular section may 
 not exceed a moderate diameter. 
 
 Position of the Shaft. — "When the requisite evidence concerning the dip, thickness, and 
 regularity of the seam has been obtained by boring, or by any other reliable means, the position of 
 the sinking may be determined. The selection of the most favourable position for the shafts is, 
 perhaps, the most important duty that the mining engineer is called upon to perform. It is one 
 that requires extensive knowledge and sound judgment, and entails an amount of responsibility that 
 is not to be accepted lightly. An error of judgment in an undertaking of this nature may lead to 
 very serious consequences, which can afterwards be neither remedied nor mitigated. It behoves the 
 engineer, therefore, who is called in to advise on such a matter, to exercise the utmost caution, to 
 obtain complete evidence concerning all the facts of the case, and to weigh this evidence carefully 
 before arriving at a decision, which cannot be revoked. 
 
 There will be in every case two sets of conditions which will determine the position of the 
 shaft, and, in many cases, there will be a third set to influence the question in a considerable degree. 
 The first set of determining conditions to be taken into consideration are those which relate to the 
 seam itself, and the workings in that seam. Foremost among these are the dip of the strata, the 
 degree of their inclination, the quantity of water likely to be met with, and the character of 
 the seam as a source of explosive gas. These are questions determinable by means of surveys, 
 borings, and inquiries in neighbouring mines, and they must be ascertained for every particular case. 
 The other conditions of this set relate to the proposed method of working the seam, and the general 
 plan of the workings. It must always be borne in mind that, the whole of the produce will have to 
 
SHAFT-SINKING, 233 
 
 be brought to the bottom of the shaft, and that, therefore, it is desirable to place the shaft in a 
 position favourable to the conveyance thither of that produce. Also, as it is requisite for the sake 
 of economy to reduce the number of shafts to the lowest possible limit, they should be so situate as 
 to command the most extensive area in the field to be worked out. The extremities of the area 
 apportioned to a shaft should not, however, be so distant as to render the conveyance of the produce 
 of the seam difficult, since this would frustrate the object of diminishing the number of shafts. Other 
 circumstances will also weigh in an important degree, such as the existence of faults, the vicinity of 
 old workings, or the presence of any of the other numerous obstacles that are likely to occur. 
 
 Among the most important of these underground conditions are those which relate to the 
 gravitation of the water and of the loaded tubs towards the pumping and the winding shafts. These 
 questions will be considered in a subsequent chapter. 
 
 The second set of determining conditions relates to the circumstances existing at surface. These 
 are of very great importance ; in all cases, their influence will modify the decision arrived at from a 
 consideration of the first set, and not unfrequently it will preponderate, and determine alone the 
 choice of the position ; that is, the position chosen in accordance with the surface conditions may be 
 unfavourable to the conditions prevailing underground. Of course, the latter cannot be ignored, 
 and it must be borne in mind that the degree to which they may be set aside will be entirely 
 dependent upon their importance. The determining conditions prevailing at surface relate to the 
 disposal of the several products of the mine, namely, the coal, the rubbish, and the water. The first 
 of these, which is the useful product, and which will be raised in by far the largest quantities, will 
 certainly claim the chief consideration, but the removal of the rubbish and the water will influence 
 the choice in some degree. The coal will have to be conveyed to the nearest highway, canal, or 
 railway ; and it is obvious that the situation of the coal-field relatively to these, the surface con- 
 figuration of the locality, and the existence of natural and artificial obstacles, will exert a weighty 
 determinative influence on the position of the shaft, between which and the afore-mentioned means 
 of communication a constant, suitable, and sufficient connection must be kept up. Grenerally, this 
 connection will be made by tramway, and the foregoing circumstances will, therefore, have to be 
 considered relatively to the requirements of such means of transport. Sometimes no railway may 
 exist, but it may. be intended to construct a branch to the colliery from a line a few miles distant. 
 This, however, amounts to nothing more than increasing the importance of the tramway. In all 
 cases, advantage should be taken of gravitation to run the loaded trucks away from the shaft in order 
 to save an expenditure of costly power. But to do this, a position must be chosen for the shaft 
 sufficiently elevated above the railway or the canal, and to make this position accord with the other 
 determining conditions above and below ground is the problem that the engineer is required to 
 solve. It will thus be apparent that the problem is a difficult one, and its solution will demand the 
 exercise of judgment and of skill. It will also be evident that the fulfilment of this condition will 
 be favourable to the removal of the rubbish derived from the excavation of the shaft, and to the 
 discharge of the water, whether the discharge take place from the surface, or through an offtake. 
 
 The third set of conditions which may occasionally supervene to limit the influence of the first 
 and the second, relates to the character of the strata through which the shaft is to be sunk. In some 
 localities, it may happen that quicksands or drift of an unstable nature will have to be passed 
 through, and it then becomes a question of passing through these beds in the most favourable part. 
 In such a case as this, borings afford valuable evidence, and should be deemed indispensable. The 
 
 2 H 
 
234 MINING ENGINEEEING. 
 
 very costly character of sinkings tlirougli water-bearing and unstable beds gives great importance to 
 those conditions, and frequently renders them paramount. Numerous instances might be cited in 
 which altogether unfavourable positions have been selected for the shafts solely for the purpose 
 of escaping the difficulties that would otherwise be encountered in traversing such beds. 
 
 The foregoing remarks on the position of the shaft, or, as it is commonly expressed, the spot 
 for the winning, are necessarily of a general character. It is impossible to give definite directions 
 concerning circumstances that never exist under the same conditions in any two localities. In- 
 structions that might be profitably followed in one case, would be only partially applicable to 
 another, and to give such instructions would be rather to mislead than to guide. It is, however, 
 desirable to point out what the determining circumstances may be, and to indicate their relative, 
 importance. The means by which the end desired may be obtained, in assigning to each condition 
 the influence due to its importance, must be left for individual skill to apply. 
 
 It has been already remarked that the minimum number of shafts to every colliery is two. 
 The legislature provides that these shall be separated from each other by not less than. 10 feet of 
 natural strata ; but beyond this limitation they may be placed at any distance apart, and in any 
 position relatively to each other that best fulfils the foregoing conditions and is most suitable to the 
 system according to which the workings are to be laid out. Sometimes it is found convenient to 
 separate the shafts by long distances ; but generally they are placed only a few yards apart. By 
 bringing the shafts near together, the important advantage is gained of concentrating the points of 
 delivery, and the machinery required at those points, upon one spot at surface. Other advantages 
 will be rendered apparent in describing the operations of sinking, and the modes of laying out the • 
 underground workings. The position of the shafts relatively to each other and to the dip of the 
 strata, will also be determined by those considerations, which will form the subject of the following 
 chapter. 
 
 The OPERATioisrs of SixKiisra. — In the operations of sinking, as in those of boring, rapidity ot 
 execution may be deemed generally essential to the success of the undertaking. It is, therefore, 
 important that every means should be employed to facilitate the several operations involved, and due 
 precautions taken to prevent delays. To this end, the preliminary arrangements should be carefully 
 considered and completely carried out. All the tools and other appliances required should be 
 suitable in character, and of the best design and quality, and means should be always ready at hand 
 for keeping these in a proper condition, and of promptly repairing them in case of damage. This 
 foresight should be exercised throughout the whole of the preliminary arrangements and labour 
 undertaken previously to commencing the actual work of sinking. Every difficulty that may be 
 encountered should be fully provided against, so that valuable time may not be lost in devising and 
 searching for the necessary means when the difficulty has presented itself. Such delays increase the 
 difficulties immensely, and may render the cost of overcoming them ruinously great. Indeed, it may 
 be said that a sinking well considered and fully provided for, is a sinking half accomplished, 
 and, therefore, no pains and no expense should be spared in the measures taken to insure the 
 attainment of this object. It will also be necessary, during the progress of the work, to see that 
 the advantage thus gained be not lost by neglect. A vigilant supervision must be held necessary 
 from the moment of the commencement of operations to that of their .completion, and this supervision 
 should be extended to the minutest and the seemingly most trivial details. When the end to be 
 attained is so important, the smallest matter is not beneath notice. Besides, it should be borne in 
 
SHAFT-SINKING. 23-3 
 
 mind that a habit of inattention to small matters is very apt to extend itself to others of greater 
 importance. 
 
 In order to explain and to describe in an intelligible manner the various operations involved in 
 sinking a shaft, we will assume a pair of circular shafts, one of which is to serve as a down-cast, and 
 the other as an up-cast, the former being 13 feet, and the latter 14 feet in diameter. As the 
 operations in each will be identical in character, it will be sufficient to consider the down-cast alone, 
 merely premising that the two will be sunk simultaneously, and that, consequently, the preliminary 
 arrangements must include provisions for this circumstance. The advantages of sinking both shafts 
 simultaneously are great and obvious. For besides reaching the seam through the two shafts 
 at the same time, whereby the immediate opening out of the underground workings is much facili- 
 tated, the water encountered is more easily dealt with, and one provision of tools, machines, and 
 surface erections is sufficient. 
 
 The preparatory work consists, as we have seen, in providing the tools and other mechanical 
 appliances, the materials of various kinds, and the buildings that will or may be required in the 
 progress of the sinking. The tools chiefly required will be the picks and sinking shovels already 
 described as suitable for working in rock, the stone-blasting gear, also described and illustrated, and 
 wedges for dislodging jointed or fractured rock, and rock-boring machines, when these are to be 
 employed, together with the air-compressors, and the other appliances and materials to be used with 
 them, as reservoirs, tubing, and repairing tools. Besides these tools for dislodging the rock, there 
 will be required corves or kibbles for raising it to surface. It was formerly the custom to 
 construct these sinking corves of wicker work, well-seasoned hazel being used for this purpose. The 
 capacity of one such corf was about 20 gallons. These corves have, however, been almost entirely 
 superseded by " kibbles" constructed of wooden staves bound together by iron hoops like a small cask, 
 and provided with a handle or with three ears to which chains may be attached, to form a kind of 
 bucket, as shown in Fig. 383. When of small dimensions for well sinking, it is called a sinker's 
 bucket. This form of kibble, which is much used on the Continent, is made to " belly " in the middle 
 to make them sheer off from each other should the ascending and the descending one come into contact. 
 For the same purpose, the edges of the hoops are chamfered off. This is a danger to be carefully avoided, 
 inasmuch as the canting of the loaded kibble pours the contents down upon the sinkers. In England, 
 the sinking kibble is commonly constructed of iron, and in that case its form is very similar to that 
 adopted for the wooden barrel-shaped bucket. The kibble is attached to the rope by a spring hoolc, 
 shown in Fig. 384, or by the form of hook represented in Fig. 385. The former is the more convenient, 
 and perhaps the safer form. The kibble is raised at first by means of a common windlass with two 
 handles, which, therefore, will have to be provided for that purpose. Besides the foregoing tools, 
 and appliances of a like nature, an ample supply of curbing and planking should be provided for the 
 support of the sides of the shaft. The construction of this curbing and the method of applying it 
 with the planking will be described hereafter. 
 
 The surface erections required, besides those of a more important and permanent character, 
 which will be described later, are : a carpenter's shed, a smithy, an office for the master sinker and 
 others in charge of the work ; a sinkers' lodge, for drying the sinkers' clothes and other purposes ; 
 a shed wherein to store the materials required ; and a magazine to contain the explosive substance to 
 be employed. In some cases, cottages will be needed for the sinkers, and other erections may be 
 necessitated by the peculiar circumstances of the case. As nearly the whole of these buildings will 
 
 2 H 2 
 
236 MINING ENGINEEEING. 
 
 be required to remain as parts of the surface works, their situation relatively to the shaft and to each 
 other should be chosen ratlier with a view to subsequent convenience than to immediate exigencies. 
 When all of those buildings which will be required during the progress of tlie sinking have been 
 erected, the engine houses may be commenced, and their construction carried on during the sinking 
 of the shafts, so as to be ready for the reception of the engines as soon as the latter are required. In 
 this way, delay in opening out the workings may be avoided. Grenerally the winding engines will 
 be situate between the two sliafts, so as to draw from both. 
 
 Sinking to the Stone Ilead.—When all the preparatory work has been completed, and every- 
 thing likely to be required is i-eady to hand, the operations of sinking will be begun by determining 
 the point that is to be the centre of the shaft, and striking from this centre a circle having a 
 diameter 2 feet greater than that which the shaft is to have when finished. In the case assumed 
 this diameter is to be 13 feet ; the circle will therefore be struck with a diameter of 15 feet 6 inches. 
 When this has been done, the excavation of the soil will be commenced with the pick and the shovel. 
 The nature of the operations from this point will depend greatly upon that of the rock to be passed 
 through. In the case under consideration, it will be assumed that the first 15 or 20 yards will pass 
 through moderately strong clay. 
 
 The firm rock to be met with after the clay has been passed through is spoken of as the 
 " stone head," and this part of the sinking is described as " sinking to the stone head." As the exca- 
 vation during this portion of the sinking is through soft rock, the pick and the shovel will be the 
 only tools required, and the sinking will progress with rapidity. The "stuff" will be raised to 
 surface in kibbles by means of the ordinary jack-roll, and tipped, or, in miner's language, " teemed " 
 around the mouth of the shaft. A matter to which attention must be given at the commencement of 
 the excavation, and continued throughout the whole of the sinking, is the preservation of the verti- 
 cality of the shaft. The axis of a shaft must be kept rigorously vertical throughout its length, the 
 slightest deviation from that direction being attended with evil consequences not easily remedied. 
 In rectangular shafts, each face should form but one vertical plane from top to bottom, and in circular 
 and elliptical shafts, each generating line should be perfectly straight and vertical. This regularity 
 of form must be preserved throughout the subsequent operations of timbering, walling, and tubbing, 
 care being taken to place these supports everywhere in exact accordance with the centre of the 
 shaft. To insure this verticality to the excavation, frequent and careful use must be made of 
 the plumb-line. In rectangular and polygonal shafts, a plumb-line should be suspended in each 
 angle ; and in circular and elliptical shafts, at the four extremities of the two diameters crossing 
 each other at right angles, in the former, and at the extremities of the major and minor axes in the 
 latter. If the section is large, lines may be required at other points also, to be determined by 
 the engineer or the master sinker, according to the conditions of the case. These suspended lines 
 will be lowered as the sinking progresses, and from time to time other lines will be dropped, in the 
 same positions, from the surface to near the bottom of the excavation, to check the accuracy of 
 the work done. All irregularities rendered apparent by this plumbing must be carefully removed. 
 
 Curbing. — During the sinking to the stone head, however, the sides of the shaft cannot be 
 left without support. There is a tendency in soft rock, as we have seen in deep boring, to swell 
 and to close up the excavation. We have also seen that when this swelling has once begun, its 
 progress is rapid, the motion produced in the rock being an accelerated one. Hence it becomes 
 necessary to prevent the swelling action from setting in, by placing a sufficient support to the 
 
RH APT-SINKING. 237 
 
 sides of the excavation as tbe sinking progresses. This support consists, for circular shafts, of 
 rings formed of segments of wood, called " curbs " or " cribs," placed at intervals in the shaft, and 
 backed with deal planking. The curbs should be of oak or elm, and their dimensions should be 
 proportioned to their diameter, and to the degree of pressure likely to be brought upon them. 
 
 These dimensions will vary from 4 to 6 inches square. Care should be given to their construc- 
 tion in order to bring the ends of the segments to bear evenly upon each other, and to make the joints 
 radiate truly from the centre. The best mode of forming the joint is that shown in Figs. 386 to 388, 
 in which the ends of two contiguous segments are made to bear against each other in one vertical 
 plane. When jointed in this way, the segments are prepared at surface with the curved wooden 
 fish-pieces or cleats, and sent down the shaft ready to be put together, as shown in the dra\ving-. 
 Another method of jointing the curbs is shown in Fig. 389. The backing deals used with the curbs 
 should be about 1 inch in thickness, and about 6 feet long ; if desirable, a greater length, sny 
 9 feet, may be adopted. The first length of backing deals set should, in every case, be 9 feet. It is 
 highly important that there should be always ready at hand a sufficient number of curbs, and an 
 ample supply of the planking required to be used with them. 
 
 In the case we have assumed, the curb may be 5 inches square in section, and when put 
 together it should have an inside diameter of 13 feet 9 inches. When the excavation has reached a 
 depth of 6 feet, the first curb is sent down in segments, and put together and placed in position at 
 the bottom. The 9-feet backing deals are then placed vertically behind the curb, their ends passing 
 down to about the middle of the thickness of the latter. If the ground to be supported is very weak, 
 the backing deals must be placed close together; in fairly strong rock, they may be set at small 
 intervals apart. The distance to be allowed between the curbs will be determined by the pressure 
 from the sides of the excavation. If that pressure is very great, the interval should not exceed 
 2 feet, or in some cases even less than that distance. Instances are on record in which 6 inches 
 could not be exceeded. A common distance, however, is 3 feet, and this might be adopted in the 
 case under consideration. A second curb, therefore, having been sent down, and put together upon 
 the first, is raised to a height of 3 feet above the latter, the height being measured from centre 
 to centre, and supported by a few upright props called punch props. A third curb is then put 
 together upon this second one, and, having been raised 3 feet above it, is supported by props in the 
 same manner as the second. A fourth curb is put in at the top of the backing deals, and supported 
 in the same way as the others. This last curb will thus be situate at the height of 3 feet above the 
 surface of the ground. The object of this elevation is to obtain a height for tipping the stuff drawn 
 from the shaft. The curbs inserted in this manner are next strung, or hung together vertically by 
 means of thin deal planks, called on that account " stringing deals." These stringing deals are 
 nailed against the inside of the curb, so as to suspend the latter one from another, and the whole 
 may, if needed, be suspended from balks of timber at surface by means of the stringing deals. 
 Fig. 390 shows a section of the shaft thus supported by curbs and planking. 
 
 When the curbing of the excavation has been completed in the manner described, the sinking 
 may be resumed, and continued down another 6 feet. This part of the excavation is not, however, 
 extended to the full diameter ; but the sides are kept in a line with the inside of the curbs. This is 
 necessary in order to leave a support for the latter. When the depth of the second 6 feet has been 
 reached, the excavation is shorn out to the full diameter, and a level bed provided for the reception 
 of the next curb. This is sent down in segments, as before, put together, and placed in position at 
 
238 MINING ENGINEEKING. 
 
 the bottom. The sides are then shorn out up to the first curb laid, that is, the lowest curb of the 
 first set, and the 6 feet backing deals put in behind this curb and the one just laid. Another curb 
 is sent down, put together upon the bottom one, and raised upon props to a height of 3 feet, that 
 is, midway between the curb last put in, and the lowest of the first set. , Upon this curb, props are 
 set to support the one immediately above it, and the stringing deals are nailed on to hang them all 
 together. It is to be remarked here that the whole length of curbing should be slung by means of 
 the stringing deals to balks of timber at surface. This is necessary to prevent the curbing from 
 slipping down when the support is removed by shearing out the sides from under them. The deals 
 may be suspended from the timbers forming the temporary staging required around the mouth of the 
 shaft for convenience in drawing and tipping the rubbish. When the second 6 feet of excavation 
 has been curbed, the sinking will be again resumed, and continued through the third 6 feet, which 
 length will be curbed in the. same manner as the preceding. These operations will be repeated- until 
 the stone head is reached. In the case under consideration, it is assumed that the clay is of a 
 sufficiently firm character to stand with safety during the excavation of 6 feet in depth. But in 
 weak ground, such a depth may be too great, and in that case the curbing will have to be put in 
 more frequently. 
 
 Walling. — When the stone head has been reached, another set of operations has to be performed. 
 The support afforded by the curbing is intended to be only of a temporary character. The continued 
 pressure of the sides of the shaft against this support would, in a short time, cause it to yield, and 
 when the sides have begun to run, the destruction of the shaft is almost inevitable. Hence it becomes 
 necessary to replace the timbering by masonry, and the substitution of the latter for the former should 
 be made as soon and as speedily as possible. In general, however, the walling, as this masonry 
 support is called, cannot be built until a firm rock foundation has been reached, that is, until the 
 sinking has reached the stone head. Thus it is desirable to push on the sinking to this point with 
 all possible speed, in order to escape the danger which always exists, of the timbering giving way 
 before the enormous pressure to which it is exposed. The walling of this portion of the shaft is, 
 therefore, the next labour to be undertaken. 
 
 On reaching the stone head the excavation is reduced in diameter, and the sinking is continued' 
 until the rock has become sound and strong. When this point has been attained, the sides are 
 shorn back to a greater diameter than the excavation had previously possessed; in the case in 
 question, say to a diameter of 16 feet 9 inches. It is now required to prepare the foundation for 
 another curb of larger dimensions, upon which the walling is to rest, and called on that account 
 the " walling " curb, or sometimes, from the method of fixing it, the " wedging " curb. This curb 
 may be either of metal or of wood. Sound and well-seasoned oak is commonly employed. When 
 iron is used, the curb is open on the inner side. The oak wedging curb will be 13 inches on the 
 bed, as the walling is to be of brick, and 6 inches in depth ; its inner diameter will, of course, be 
 that of the shaft, namely, 13 feet. The rock bed upon which this curb is to rest must be carefully 
 levelled, so as to give it an even bearing at all points. Some half-inch fir sheathing is then laid 
 upon this bed, and the curb laid upon the sheathing. Before proceeding to fix the curb, it is impor- 
 tant to ascertain that its centre coincides exactly with that of the excavation. When the curb has 
 been placed accurately in position, a backing of fir, about 2 inches thick, is put in vertically between 
 the outside of the curb and the sides of the shaft, and firmly wedged. The wedging must be per- 
 formed simultaneously at opposite points in the curb, and it must be continued until no more wedges 
 
SHAFT-SINKING. 239 
 
 can be driven in. The greatest care must be exercised during tbese operations to avoid displacing 
 the centre of the curb. When iron curbs are used, a piece of oak sheathing is placed between the 
 joints ; the thickness of this sheathing should diminish from the outside of the curb inwards. As 
 the pressure thrown upon the curb by the wedges tends to lift the former from its bed, this tendency- 
 must be counteracted by props set upon the joints of the curb, and abutting against the rock above. 
 To avoid repetition, a detailed description of the operations of wedging, with drawings illustrative of 
 them, is deferred to a later paragraph, in which the method of fixing the wedging curb in a durably 
 water-tight manner for the support of tubbing is treated of. 
 
 When the walling curb has been securely fixed, the walling of the shaft may be proceeded 
 with. In most cases, the walling will consist of bricks, which is the cheapest material available, and 
 sufScient for the purpose under all conditions. Frequently these bricks may be made on the spot from 
 the clay necessarily excavated for the surface works. It is essential that the bricks used in the 
 walling be moulded to the form required by the shape and diameter of the shaft. The mortar should 
 be of the best quality and slightly hydraulic in character ; and strict supervision should be exercised 
 to ensure good workmanship. In walling through wet strata, quick setting cement will be required. 
 
 Sometimes stone masonry is adopted for the walling of a shaft. In such cases the material 
 should be carefully chosen, for the adoption of an unsuitable stone entails constant labour in repairs, 
 and it may endanger the very existence of the shaft. Stone of a schistose structure is rapidly 
 disintegrated by the action of atmospheric agencies, and must, therefore, be held to be quite unsuit- 
 able for walling purposes. Sandstone and limestone may be employed ; but the former is somewhat 
 difficult to work, and the latter is usually costly to obtain. In stone walling the blocks should be 
 of moderate dimensions, and, as nearly as practicable, uniform in size. Very small blocks involve 
 the use of a large quantity of mortar, which it is important to avoid, and very large blocks are 
 difficult to work and to handle ; while the mingling of large and small blocl< s occasions an unequal 
 distribution of the pressure. Each of the blocks should be tooled upon five of its faces, that which 
 is in contact with the rock being alone left in a rough state. The two side faces should be prepared 
 with special care, to insure a close joint, everywhere coinciding in direction with the radius of the 
 
 shaft. 
 
 Bricks, when properly prepared, constitute a more suitable and a cheaper material for shaft walling 
 than stone. The quality of the bricks, however, is a matter of essential importance. The clay of which 
 they are made should be rich in alumina, and entirely free from lumps of calcareous matter. If the 
 clay is not sufficiently rich in alumina, the bricks will be porous and crumbly ; on the other hand, if too 
 rich, they are apt to run during the process of manufacture, and are too smooth to hold well to the 
 mortar ; while the presence of lumps of calcareous matter may occasion the destruction of the brick. 
 For these lumps, being converted into lime in the burning, swell, on exposure to moisture, and 
 fracture the brick. If the bricks be insufficiently burned, they will not have that degree of consistency 
 which is necessary to enable them to withstand the pressure to which they will be subjected ; if 
 overburned, their surfaces may become vitrified, a circumstance that will greatly diminish the 
 adhesion of the mortar. The defect of over burning is, however, not so great as that of under- 
 burning. The proper degree of burning may be ascertained, either by the colour for a given clay, 
 or by the soimd emitted when lightly struck. Fireclay is an excellent material for walling bricks, 
 and in some localities it may be procured nearly as cheaply as ordinary clay. Sometimes this 
 material is employed moulded into blocks to the required form. The dimensions of such blocks may 
 
240 MINING ENGINEEEING. 
 
 vary ; commonly they are 24 in. x 9 in. x 6 in. Fireclay prepared in this way is somewhat 
 expensive, but it makes a very excellent shaft walling. 
 
 As before remarked, it is important that the mortar or the cement used should be of the best 
 quality. The hydraulic character of the material requires that it be used immediately after wetting 
 up, and the quicker its setting property, the shorter should be the interval between its preparation 
 and its application. This is a matter that is commonly neglected, to the great detriment of the 
 substance employed. If, for example, a cement is capable of setting in fifteen minutes, and it be 
 allowed to stand ten minutes before using, it will have partially set, and consequently will have to 
 be broken up before being applied. "When this cement has set a second time, it will be found thai 
 its strength has undergone a very serious diminution. In all cases, the value of this reduction will be 
 proportionate to the ratio of the time allowed to elapse after wetting and that necessary to complete 
 setting. Another mistake commonly made is to employ an unnecessarily large quantity of mortar iu 
 walling. In water-bearing strata this practice is a very pernicious one. It should be obvious on 
 reflection that mortar is less capable of withstanding the action of water than stone or brick, and that 
 consequently the employment of a superfluous quantity of that material must weaken, rather than 
 strengthen, the walling of a shaft against which there is the continual pressure of a considerable, 
 sometimes a great, head of water. What is required is to interpose a thin but perfectly continuous 
 film of the cementing material between two faces in contact ; and to do this effectually the mortar 
 should be in a somewhat stiff pasty condition. A common mistake is to apply the mortar too wet. 
 The bricks should be slightly moistened before being laid, to prevent their absorbing the moisture 
 from the mortar. 
 
 The thickness of the walling will be, in some degree, determined by the pressure likely to be 
 thrown upon it. Thus, in passing through compact rock, a single brick may be sufficient, the object 
 of the walling in such a case being rather to protect the rock from atmospheric influences, and to 
 prevent the fall of detached portions, than to resist a pressure from the sides. In loose rock of a 
 fairly strong character, such as we have assumed in the example under consideration, a thickness of 
 13 inches will be required, and will suffice; and in very unstable rock, or where there is a very 
 great pressure of water, 18 inches or more may be necessary. In the assumed example, the wedging 
 curb is designed for a walling of 1 3 inches. 
 
 When the wedging curb has been securely fixed, the walling is commenced upon it, as a 
 foundation, and carried up as rapidly as the exigencies of good workmanship will allow. Until 
 a shaft is walled, it is exposed to the danger of closing in, and therefore no exertion should be spared 
 to complete the walling in the shortest possible time. The labour of walling will have to be 
 performed from a staging or scaffolding, capable of being raised as the work progresses. The staging 
 adopted for this purpose is circular in form, and is commonly known as a " cradle." The cradle is 
 a simple wooden construction, consisting of 2-inch planking nailed upon timbers variously put 
 together. Through these timbers stout bolts with a ring attached are passed^ and secured on the 
 underside by means of a nut. From these rings the cradle is suspended, by means of chains attached 
 to two ropes, from two winches at surface, one on each side of the shaft. Later, when the surface 
 arrangements are more complete, the cradle will be suspended by one rope. It is almost needless to 
 remark that, to avoid accidents, this rope must possess a wide margin of strength, and it must 
 undergo frequent and careful inspection. Such a rope should be 10 inches in circumference. The 
 diameter of the cradle should be such as to leave a space of about 4 inches all round between it and 
 
SHAFT-SINKING. 241 
 
 the shaft. This space is necessary to ensure the ventilation of that portion of the shaft which is 
 below the staging. When a seam of coal is near the bottom of the shaft, or has been entered or 
 passed through, this precaution is of the highest importance, and means must be adopted to promote 
 the ventilation of that portion. Sometimes, besides the space around the staging, a hole is provided 
 in the centre of the latter, to allow the gas to pass up ; through this hole, the tub dips into the sump. 
 If means of escape be not provided, the gas will accumulate beneath the staging, and then a light 
 inadvertently lowered or accidentally dropped may occasion a disastrous explosion. In spite of the 
 precautions taken to avoid an accident of this nature, the accumulation of gas beneath the staging 
 is one of the most fruitful sources of explosion of firedamp. 
 
 As the walling proceeds, the timbering immediately above it will have to be removed, and care 
 must be taken during the removal of this portion not to materially weaken that which is left. If the 
 pressure against the timbering is great, a small portion only of the latter can be taken out at a time, 
 and the remainder must be securely stayed. How much may be removed with safety at one time, 
 the circumstances of the case will determine. The curb immediately below which the timbering has 
 been taken out must be supported by vertical punch props set upon the walling beneath, and some- 
 times, when the pressure is great, by other props placed horizontally or in an inclined position 
 against the sides of the shaft. These inclined props are called " raking " props. Under some difScult 
 circumstances, it may be necessary to build portions of the timbering into the walling; but this 
 should be avoided wherever possible, as the rotting of the wood endangers the masonry. 
 
 The hollow between the walling and the rock must be filled with clay, carefully rammed to 
 form a solid backing, or better, with concrete. This is necessary to distribute the pressure equally 
 over the masonry, and it cannot be neglected without risking the safety of the latter. It is also 
 essential, both to the stability of the work and to the convenience of the operations, that means be 
 provided for getting rid of the water which oozes out from the sides of the shaft, and which would 
 accumulate between the walling and the rock if there were no way of escape for it. Evidently the 
 presence of this water would render it impossible to put in the clay or concrete backing in the solid 
 manner required ; and if it were allowed to flow over the last course of masonry, the latter would be 
 injured, and the work greatly impeded. It is, therefore, sought to make it flow away from below, by 
 providing an outlet beneath the lowest course of the walling. For this purpose, either an iron pipe 
 is built into the bottom course, after the manner of the " weeping " holes in retaining walls, or 
 a horizontal hole is bored with an auger in the wedging curb itself, which hole is made to commu- 
 nicate with the space between the walling and the rock, through another vertical hole bored near 
 the outside of the curb and left uncovered by the masonry. The outlet thus provided for the water 
 is kept in communication with the space above the backing by means of a little triangular channel 
 formed by two pieces of board, placed with their front edges against the walling, and two or three 
 inches apart, and with their back edges in contact ; or, in some cases, by means of a vertical pipe of 
 small diameter, and pierced with holes, which is lengthened as the walling rises. In putting in the 
 backing, care should be taken to make the upper surface incline towards this outlet for the water. 
 By these means, the water soaking from the sides of the excavation may be conveniently got rid of. 
 When the walling is completed and the sinking recommenced, the outlet may be plugged ; or if the 
 quantity of water is considerable, flexible tubing may be afSxed to it, to conduct the water down to 
 the sump, and so prevent it from dripping upon the sinkers. 
 
 A somewhat similar arrangement is adopted for collecting and conveying away the water that 
 
 2 I 
 
242 
 
 MINING ENGINEEEING. 
 
 soaks through the walHng. This water, which trickles down the sides of the shaft, is stopped and 
 collected at one of the wedging curbs in the following manner. The first three or four courses of 
 brickwork upon the curbs which are to serve this purpose are inset for the purpose of leaving a 
 portion of the upper surface of the curb exposed, as shown in Fig. 391. In this portion of the curb? 
 a groove is cut, so as to form a channel round the shaft. The water which runs down the face of 
 the walling collects in this channel, and is discharged through a hole, bored obliquely in the curb, as 
 shown by the dotted lines in the figure, into a small pipe, called the " waste pipe," through which 
 it is conveyed, either to the sump or to a tank from which the pump takes its water. Sometimes, 
 instead of using the wedging curb for this purpose, a wooden curb of smaller sectional dimensions is 
 built into the walling at the points desired ; such a curb is called a " ring curb," a designation that 
 is also applied to the wedging curb when made to serve the same purpose. 
 
 Drawing the Stuff. — The shaft walling is continued up to a convenient height above the surface 
 of the ground ; this height may vary from 5 to 15 feet. The object of thus elevating the mouth of 
 the shaft is to obtain a good lead for the removal and the discharge of the stuff raised from the 
 excavation. The first stuff raised after the completion of the walling is tipped around the latter to 
 support it, and the rest is run away to a convenient spot. The manner of terminating the walling 
 and of fitting up the mouth of the shaft varies in different localities, according to the method of 
 receiving the loaded kibbles. In the north of England, a kind of covering or staging of wood is 
 fixed to partially cover the shaft, as shown in Fig 392. To prevent the ascending kibbles from 
 striking against the under side of this staging, deals are nailed diagonally against the edge of the 
 staging and a bunton fixed against the sides of the shaft, as shown in the figure. These deals are 
 called " striking " or " sliding " deals. When the loaded kibble is raised to a height a little above the 
 staging, a tram is run out to the edge upon rails laid down for that purpose, and the kibble is 
 lowered upon it by being drawn over it by hand during the lowering. To prevent the tram from 
 ruiming off the staging into the shaft, a wooden sill of sufficient depth is nailed along the edge. 
 The loaded kibble is then detached from the spring hook, and an empty one, brought up on the 
 tram, substituted for it. As soon as the latter is raised to be lowered into the shaft, the tram with 
 the loaded kibble is run back, and the contents discharged, after which it is again pushed forward 
 with the empty kibble for the next load. To facilitate these operations, the rails should be laid with 
 a slight inclination from the mouth of the shaft. This inclination is also needed to prevent the tram 
 from striking heavily against the sill. 
 
 In some other coal districts, the manner of receiving the loaded kibbles and the laying out of 
 the shaft mouth are different. This difference will be best understood from a description of the 
 surface arrangements of a shaft in South Staffordshire, on the estate of the Duke of Sutherland. 
 The walling of this shaft, which was sunk under the direction of Mr. C. Bromley, was carried up to 
 a height of about 15 feet above the surface of the ground, and thick brick walls erected to inclose 
 the shaft, in the manner shown in Fig. 394. An inner wall, contiguous to the shaft, forms with the 
 outer walls a rectangular brick foundation for the head-gear. The walls inclosing the shafts carry 
 balks of timber to form a staging on a level with the top of the pit walling. Upon this staging are 
 laid light tram rails, on which runs a wooden tram or movable platform, shown in Fig. 393. This 
 platform is of sufficiently large dimensions to completely cover the mouth of the shaft, when it is run 
 over the latter. In arrangements of this kind, a rail is laid on each side of the shaft to allow the 
 tram to be run over. As it is essential that the mouth of the shaft should be fenced to prevent 
 
SHAFT-SINKING. 243 
 
 accidents, a suitable fence, shown in the figure, is fixed to one end of the tram platform, and 
 supported upon two small wheels on the opposite ^de. These wheels run upon rails laid for that 
 purpose. Two posts are fixed vertically into the platform to afford a hold in pushing it backwards 
 and forwards. During the drawing, the fence stands over the mouth of the shaft, as represented 
 in the figiire. When the load has been raised a little above the level of the platform, the latter is 
 run forwards completely over the mouth of the shaft. The load is then lowered and deposited upon 
 the platform. When the loaded kibble has been removed from the spring hook, and an empty one 
 attached, the latter is raised, and the platform is then run back with the loaded kibble. At the same 
 time, the fence returns over the mouth of the shaft. This particular arrangement of the platform 
 and fence was designed with a special view to the ready removal of the water raised in tubs from 
 the shaft, and we shall have occasion to refer to it again relatively to this use. But as it represents 
 exactly the method adopted in this and other districts for receiving and removing the rubbish as 
 well as the water drawn from the excavation, we have selected it to serve a double purpose. It is 
 obvious that any varieties of detail may be made to facilitate the running away and the tipping ef 
 the stuff raised. The principle of this arrangement is everywhere adopted where that described in 
 the preceding paragraph is not in use. 
 
 When the walling has been completed, a strong and convenient head-gear must be erected to 
 continue the drawing of the stuff on the resumption of the sinking beneath the walling. The con- 
 struction represented in Figs. 396 to 398 will be found suflScient and suitable for the purpose 
 required, a height of 18 or 20 feet being ample for a structure of this provisional character. 
 
 In connection with this head-gear, a steam engine will be required to draw the rubbish and the 
 water from the excavation. During the sinking and the walling of this first portion of the shaft, the 
 most important of the surface work will have been pushed forward, such as the erection of the 
 buildings for the reception of the pumping and the winding engines. It was formerly the practice 
 to get these engines in position as soon as possible, in order to apply them to the work of raising 
 the stuff and pumping the water, during the progress of the excavation. For as the depth increases, 
 it becomes important that these operations should be rapidly performed. Since, however, the 
 introduction of the winding engine of the locomotive type of construction, the more powerful engines 
 destined to the ordinary work of the colliery will not be required for the sinking operations, except 
 under extraordinarily difficult conditions. This new type of engine, which is manufactured by the 
 Messrs. Rdbey and Co., offers very great advantages for the temporary purposes of sinking. No 
 strong foundations or buildings are required beyond a light shed to protect it from the weather ; 
 it is exceedingly compact, and can be brought upon the ground almost in a state to receive steam ; it 
 may be readily removed when its services are no longer required ; it is very economical of fuel ; 
 its first cost is light ; and it may be built of any power up to 200 horse. In all ordinary cases, this 
 engine may be made to do both the winding and the pumping, when pumps are used. The following 
 is a general description of this type of engine, the form and appearance of which is well known. The 
 dimensions are those of the largest size engines, capable of working up to 200 horse-power effective. 
 
 The general arrangement is that adopted for the locomotive ; but the frames are suppressed, 
 and the engine is erected upon a massive cast-iron bed-plate, formed at one end into an ashpit, with 
 damper doors, which carries the fire-box end of the boiler ; the other end is carried by a saddle 
 casting, fixed over the cylinder. The end of the bed-plate under the cylinder constitutes a feed- 
 water tank, into which the cylinder cocks discharge all the condensed water, and into which also 
 
 2 I 2 
 
244 MINING ENGINEEEING. 
 
 a portion of the exhaust is directed to heat the feed-water to near the boiling point before it is 
 forced into the boiler. The latter is bolted to the cylinders at the smoke-box end, and as the 
 fire-box is carried on small rollers, it is free to expand on steam being got up, no strain being 
 thrown upon either the plates or the joints. Upon the bed-plate, is fixed one plummer block and 
 bearing for the winding drum. This drum stands by the side of the engine, the outer bearing 
 being carried on a heavy balk of timber. The drum is 9 feet diameter, lagged with oak, and 
 made up with cast-iron ends. On the end next the engine, is bolted a spur wheel 8 feet 4 inches 
 diameter. On the end of the crank-shaft is keyed a pinion 2 feet 4 inches diameter, which gears 
 with the spur wheel. Both these wheels are shrouded on one side. They are 9 inches wide on 
 the working faces of the teeth, and 4 inches pitch. They work smoothly and quietly at a high 
 velocity, the drum, when winding, running at the rate of twenty-four or twenty-five revolutions 
 a minute, and the engine a little less than four times as fast. Two brakes are fitted to the engine ; 
 ,one to the fly-wheel, which is the one ordinarily used, and an extra one, of great power, round 
 the drum itself This last is provided to avert an accident, should the spur wheel or pinion 
 give way. The whole of the parts of both the engine and the boiler being erected upon one 
 bed-plate, heavy and expensive foundations are rendered unnecessary. The weight of the boiler 
 and its contained water tends to keep the whole machinery firmly in position. All the levers 
 for working the engine and the winding gear are brought together near the fire-box, so that 
 one man may attend to both the driving and the stoking. The principal dimensions of such 
 an engine are as follows: Cylinders, each 16 inches diameter by 24-inch stroke; crank-shaft, 
 bent out of one piece of Lowmoor iron, 6f inches diameter; drum shaft, best scrap, 10 inches 
 diameter; drum, 9 feet diameter by 6 feet wide, cast-iron ends, lagged with best English oak; 
 boiler, 10 feet 10 inches long, by 4 feet 9 inches diameter ; fire-box, 5 feet 9 inches long, and 
 4 feet 9 inches wide ; tubes, seventy-four in number, and 3 inches in diameter ; working pressure, 
 100 lb. to the square inch. 
 
 The engine to which the foregoing dimensions relate is a very powerful one. In most cases, 
 one of much less power will be sufficient. In the case assumed for the purpose of illustration, 
 it is supposed that an engine of this class, capable of working up to 50 H.P. effective, is erected 
 to continue the sinking below the first length of walling. To enable the engine to draw from 
 the two shafts which are being sunk simultaneously, it should be erected between them. The 
 details of such an arrangement are too obvious to need description. 
 
 Drainage. — The sinking having reached a point at which moderate quantities of water will 
 be met with, means must be provided for draining the bottom of the excavation. The streams of 
 water which enter the excavation through fissures in the rock are called " feeders." Surface feeders 
 are such as are in direct communication with the surface ; these, of course, are influenced by the 
 weather. Partial feeders are those which are in communication with a cavity containing water; 
 they gradually decrease after being opened, and in time become entirely exhausted. Permanent 
 feeders are such as derive their water from inexhaustible sources, and, therefore, continue without 
 diminution. Feeders are shut back by means of tubbing, to be hereafter described. The smaller 
 quantities of water that escape from the strata into the excavation must be raised to surface either 
 in tubs by means of the drawing engine, or by means of pumps. When the latter are used 
 they may be worked by the same engine that does the drawing. The question of drainage by 
 means of pumps will be treated in a subsequent chapter ; in this place, therefore, we have only 
 
SHArT-SmKING, 245 
 
 to consider the method of drawing tlie water in tubs. This method is sufficient whenever the 
 quantity of water met with is not great. Even when the quantity is considerable, it may be 
 advantageously removed by this means in many cases where pumps are usually resorted to. 
 Winding is a far cheaper mode of raising water than pumping. 
 
 The tub commonly used for drawing water is of iron, and is similar in shape to the kibble, that 
 is, it is barrel-shaped. The capacity of these tubs varies, but frequently it is about 100 gallons, 
 when it is intended to be drawn by the engine. The tub is suspended by a bow turning on two pins 
 placed a little below the centre of gravity, on the outside of the tub, as shown in Fig. 399, The 
 object of this arrangement is to facilitate the discharge of the contents on arriving at surface. 
 Besides the larger bow which turns upon the pins forming the points of suspension, there is a 
 smaller one fixed to the tub, and passing freely beneath the former. On one side of the tub is 
 a spring catch, which, by laying hold of the larger bow, prevents the tub from tilting in the 
 shaft. When the tub is raised full of water to the top of the shaft, the waiter-on seizes the 
 smaller bow, and, releasing the spring catch, puUs the tub over, discharging the water into a 
 shoot, by which it is conveyed away. The position of the centre of gravity above the axis upon 
 which the tub turns renders the operation of tipping an easy one. When the contained water has 
 been discharged, the man pushes the tub back into the vertical position, where it is seized by the 
 spring catch ; in this state it is ready to be again lowered into the shaft. An objection to this 
 kind of tub is that it does not fill well, the water having to flow into it over the top. 
 
 The objection to the tub described above may be removed by constructing it with a valve at 
 the bottom, through which the water can enter. This arrangement has been adopted in a very neat 
 and effective manner by Mr. C. Bromley, the engineer in charge of the sinking already referred to. 
 Fig. 395 represents a vertical section of the tub or bucket as constructed by that gentleman. The 
 bottom of this tub, which is about 5 feet in height and 3 feet in diameter, is provided with a circular 
 aperture 20 inches in diameter ; this aperture is covered by an iron disc or valve B, mounted on a 
 central spindle A, which moves between guides D and E. The under side of the disc is faced with 
 a ring of vulcanized indiarubber, to enable it to close water-tight. When this tub is lowered into 
 the water, the pressure of the latter forces up the valve B, and the tub fills. When the tub is full, 
 the valve drops upon its seating, and retains the water. The mode of emptying this tub, and 
 conveying away the water, is very simple. In the end wall of the rectangle shown in Fig. 393 is 
 fixed a drain pipe, 2 feet in diameter, leading to a channel provided to convey away the water. A 
 wooden shoot, 0, leads from the flooring to this drain pipe ; and on the platform B rests a trough 
 about 8 feet wide and 2 feet deep, open at the end next the shoot. When the tub is raised to a 
 height slightly above the mouth of the shaft, as in the case of the loaded kibble, the waiters-on push 
 the platform forward over the mouth of the shaft until the closed end of the trough is under the tub. 
 The latter is then lowered gently on to the trough, when the projection F of the spindle coming in 
 contact with the planking, the valve B is forced up till the tub comes to rest upon the stops X X. 
 The water issues through the valve aperture, and flows down the trough into the shoot, and is 
 conveyed away through the drain pipe in the end wall. Thus it will be seen that the apparatus is 
 self-acting, and it has been found in practice to fulfil the purpose intended in a very satisfactory 
 manner. A tub of this construction, and of the dimensions shown, weighs about 900 lb., and 
 contains about 220 gallons of water. 
 
 Ventilation. — When the excavation has attained the depth of from 15 to 20 yards, the ventilation 
 
246 MINING ENGINEEEING. 
 
 will become defective, and means must be provided for directing a sufficient current of air down 
 to the workings. These means may be of several kinds, according to the requirements of the case. 
 The air-box will for some time give an adequate ventilation, and may be advantageously employed 
 until a considerable depth is attained. The air-box is a wooden pipe, generally about 12 inches 
 square, outside dimensions, made of 1 inch, or |-inch deal boards, the joints of which are made to 
 fit truly, and tarred, or if necessary, pitched, to render them fairly air-tight. This pipe is fixed 
 against the side of the shaft, and carried down to near the bottom. In order not to encumber the 
 mouth of the shaft, the pipe, on reaching within a few feet of the latter, is passed through the 
 walling, and carried in an inclined direction to surface, at a convenient spot a few yards distant. 
 Over the aperture of the pipe at this spot a chimney is roughly built of bricks, in which a fire is 
 kept burning, or into which a steam jet is turned. Instead of erecting this special chimney, the pipe 
 may be put into communication with one already existing, the engine stack, for example. The rare- 
 faction of the air in the chimney, occasioned by the fire or the steam, causes it to ascend, by a well 
 known law ; and as this air can be replaced only by that which is in the pipe, a constant current is 
 maintained down the shaft and up the pipe. As the lower end of the pipe cannot be brought close 
 down to the workings by reason of the danger to which it would be exposed from the shots, a 
 flexible canvas tube, called a "bag," is attached, which is dropped lower as the sinking proceeds. 
 "When the workings have receded too far from the wooden pipe, the latter is lengthened. It will 
 be necessary to keep a considerable current of air passing through this pipe ; for besides the large 
 quantities of powder smoke that have to be carried off, carbonic acid gas, or choke damp, may exude 
 from the joints and fissures in the rocks ; and in passing through thin seams of coal, or on approaching 
 the thicker seams, blowers of inflammable gas may be met with. 
 
 When the depth of the shaft has become great, or earlier if the rock is foul with gas, the fore- 
 going method of ventilation will be found insufficient. Recourse must then be had to the plan of 
 " bratticing " the shaft, that is, of dividing it by a wooden partition, called a brattice. The purpose 
 of the bratticing is to divide the shaft into two unequal air-tight compartments, the larger of which, 
 devoted to the drawing of the stuff, may serve as a downcast, and the smaller of which, reserved for 
 the pumps, may serve as an upcast. The arrangement is obviously of the same nature as that of the 
 air-box, previously described ; but the important difference is that the brattice gives a very much 
 larger air-way than the box. When the brattice has been put in, the ventilation will proceed 
 naturally, the current descending on one side, and ascending on the other side of the brattice^ 
 Under such conditions, however, the air current will not always descend through the same com- 
 partment, the direction being dependent upon certain external causes, such as the direction of the 
 wind, and the existence of objects affording shelter. When this natural ventilation has become 
 insufficient, the top of the smaller compartment is planked over, and the space below placed in 
 communication with a chimney, through an inclined passage, as in the case of the air-box, as shown 
 in Fig. 392 ; or, in some cases, with a small fan erected to exhaust the air from the shaft. By such 
 means as these a very efficient ventilation may be maintained. 
 
 In determining the position of the bratticing, the permanent divisions of the shaft must be 
 considered, and the bratticing placed in accordance with them, for this bratticing will form one of the 
 permanent divisions, even if it be at first constructed in a temporary manner with a view to its being 
 replaced by a more substantial structure when the shaft is completed. There are two methods 
 adopted of constructing the bratticing, one of which is known as the " bunton " system, and the other 
 
SHAFT-SmKING. 247 
 
 as the " plank " system. In the former, deal battens, 7 inches x 3 inches in section, are fixed against 
 the sides of the shaft, one on opposite sides, from the top to near the bottom. As these pieces, which 
 are called side, or stringing planks, are to form the support for the bratticing, they must be firmly 
 fixed to the shaft. The method of fixing them is to drill holes in the walling to a depth of not less 
 than 12 inches, and to plug these holes with wood to give a sufficient hold for the spikes to be used. 
 The stringing planks are then fixed to the sides of the shaft by means of spikes driven into these 
 holes. Where the shaft is lined with metal tubbing, the planks are spiked to the joints of the 
 tubbing. At intervals of 3 feet, from centre to centre, the stringing planks are provided with 
 notches to receive the ends of other battens, called " buntons," placed horizontally from stringing 
 plank to stringing plank across the shaft. These buntons are fixed to the side supports with nails, 
 and are intended to support the cleading or sheathing which is to constitute the brattice. This 
 cleading consists of fir boards from 1 to 2 inches thick, according to the character, of the 
 bratticing, whether temporary or permanent, nailed vertically upon the buntons. These boards are 
 planed true on the edges, so as to form air-tight joints, and in nailing them in position care is needed 
 to keep the joints close. When the brattice is to be permanent the joints are " slivered ;" that is, a 
 thin strip of wood, called a " sliver," is inserted into a groove ploughed in the edges of two 
 corresponding boards. 
 
 The " plank " brattice is of more simple construction than the foregoing, and is to be preferred 
 as a permanent structure. In this system of bratticing, two side planks are used upon each side of 
 the shaft, placed at an interval of 3 inches apart, and the buntons are dispensed with. The brattice 
 boards in this case are 3 inches thick, and are placed horizontally, edge upon edge, by being slid 
 down the grooves formed on opposite sides of the shaft by the side planks. The joints in this kind 
 of brattice are kept firm and air-tight by planing the edges of the boards true and dowelling them 
 with iron dowels, or preferably by means of oak slivering, as previously described. Sometimes, 
 when iron tubbing is used, the latter is cast with grooves to receive the boards, in order to dispense 
 with the stringing planks. Whatever the nature of the bratticing, it must not be carried, during 
 the sinking, nearer to the bottom than 20 feet, because of the injury which might be caused to it by 
 the firing of shots. Another precaution which it is very important to observe, to secure the brattice 
 from injury during the progress of the sinking by the ascending kibbles coming into contact with 
 the under side, consists in placing beneath it, at intervals apart so as not to materially impede the 
 ventilation, sliding deals, similar to those placed beneath the covering of the shaft at surface, already 
 described. 
 
 Sinking in Compact Rock. — We have now to consider the operations of sinking below the first 
 length of walling, that is, the continuation of the sinking in the rock. In the case assumed, it is 
 supposed that the rock is of a moderately compact and strong character, yielding but little water, and 
 capable of standing without support. 
 
 On resuming the sinking beneath the walling, the excavation is carried down in a line with the 
 inside of the wedging curb for a distance of about 3 feet, and from that point gradually enlarged to 
 the full diameter. This enlargement should be proportioned so as to make the sides of the excava- 
 tion, from the point at which the enlargement begins to that at which it terminates, form an angle 
 of about 60° with the horizontal. By this means a kind of bracket is left for the support of the 
 walling. Beneath this bracket the excavation is continued down of the full diameter. When a 
 depth has been reached at which walling becomes necessary, a wedging curb is laid in the manner 
 
248 MINING ENGINEEEING. 
 
 already described, and the walling is built up upon it, till the lower portion of the rock bracket is 
 arrived at. This bracket is then cut away in small portions at a time, and the walling carried up to 
 the under side of the wedging curb. During this part of the work, it will be necessary to support the 
 wedging curb of the upper length of walling, at the points from which the rock has been removed, 
 by vertical props set upon the lower walling. The greatest care should be exercised to make the 
 latter join well and closely up to the wedging curb, which will thus divide the two lengths of 
 walling. In some instances, the wedging curb has been removed in small portions at a time with 
 the chisel, and the brickwork made to join ; but this is not often attempted. 
 
 This portion of the sinking being in compact rock, the excavation will be carried on by means 
 of blasting. The details of these operations have been fully described in a former section. The 
 mode of procedure in shaft sinking is precisely the same as that followed in a heading, which 
 procedure is illustrated on Plate XXXIII. The first operation, as therein shown, consists in unkeying 
 the face, which is effected by angling the shot holes, in the manner described when treating of the 
 heading. As in the latter case, the unkeying is from the centre of the face, that is, the bottom of 
 the excavation. "When the strata are highly inclined, however, it is better to unkey from one side 
 of the excavation. The water which flows into the workings must be collected into one place, both 
 for convenience in raising it, and for the purpose of keeping the surface of the rock clear for the 
 sinkers. The depression caused by the removal of the key serves for the purpose of collecting the 
 water, and is called on that account the " sump," or well. Into this sump the tub dips, or, if pumps 
 are used, the suction hose is dropped. When the rock beds are highly inclined, the water gravitates 
 towards the dip side of the excavation, and it therefore becomes necessary to place the sump in that 
 situation. The unkeying of the rock from this direction is, moreover, favourable to the action of the 
 shots under the conditions of highly inclined beds. In putting in the shot holes, care must be taken 
 not to terminate them in, or nearly in, a bedding plane, because when so situate the force of the 
 charge expends itself along this plane. 
 
 When the shot holes are bored by machine drills, the most favourable position for the holes can- 
 not always be adopted. Mention has already been made of this matter, and it will be again consi- 
 dered in the next chapter. In sinking with the machine drill, the tripod support is of very Kttle use. 
 Under such conditions, the stretcher bar should always be adopted. The machine is suspended from 
 this bar, and slid along from one end of the bar to the other, by means of the clamp. Hence arises 
 a necessity for placing the holes in straight rows. When all the holes that may be reached from 
 the bar have been bored, the latter is shifted, and a new series commenced. It will be evident, on 
 reflection, that the labour of changing the position of the stretcher bar will occupy much time, and 
 that, consequently, any attempt to obtain the advantage due to the most favourable position and 
 direction of the shot holes must be useless, since what is gained on the one hand is lost on the other. 
 Hence it becomes necessary to determine the position of the holes rather in accordance with the 
 exigencies of machine labour, than with those of the greatest useful effect. It is, however, of the 
 greatest importance that these conflicting conditions should be fulfilled in the highest degree 
 possible ; in other words, that the greatest possible amount of useful effect should be sought con- 
 sistently with a due satisfaction of the conditions imposed by the employment of the machines. 
 To obtain this result, it is necessary to place the machine so that the required number of holes may 
 be bored with the fewest possible changes of position of the stretcher bar, and then to place and 
 to direct the holes in a manner that will give the best effect to the charges. To unkey the face 
 
SHAFT-SINKING. 249 
 
 from the centre, sometimes several holes are bored near together, and the charges fired to crush the 
 rock between them, after the manner described in a former section. This is probably the very worst 
 method of unkeying a face of rock. A more common method is to angle a single hole in the centre, 
 and to fire it with a heavy charge to take out the key and form the sump. Unkeying from one side 
 will, however, be found generally the most favourable to machine labour. The usual method of 
 setting the stretcher bar in a shaft, and of applying the drill under such conditions, will be under- 
 stood from the drawing. Fig. 401. 
 
 Another method of using the stretcher bar, commonly adopted in France and in Belgium, and 
 recently introduced into England, is shown in Figs. 402 and 403. A central support, or leg A, 
 is placed in the middle of the shaft, and four wooden arms, radiating at right angles to one another 
 from the central leg or support, extend to the sides of the excavation. These arms are fixed firmly 
 in position by means of a lengthening screw, in the same manner as the stretcher bar, and the central 
 support is tightened in position by the same means. A block of wood is usually placed between the 
 points of the arms and the rock, to give the former a better hold. The arms a, h, c, d are shown 
 thus fixed in position in Figs. 402 and 403. Upon the top of the central leg and the inner ends of 
 the arms is an iron plate, provided with holes at e, /, g, h, for the purpose of attaching one end of 
 the stretcher bar. When the bottom of the excavation is ready for boring, the supports are firmly 
 fixed in the manner described, and the stretcher bar is set in position by attaching one end to the 
 centre plate through the hole h, and screwing the other up against the side of the shaft, as at x. If 
 two machines are to be used, the second is set in the same manner on the opposite side, by fixing it 
 into the hole / of the centre plate. The machines being set at the required angle, the necessary 
 number of holes between the centre and the sides of the excavation are bored by sliding the machine 
 along the bar, by means of the ordinary clamp arrangement. When these holes have been bored, 
 the end w of the bar is loosened, and removed to the point ^/, where it is fixed as before, the bar 
 being turned upon h as an axis. When all the holes required in the quadrants formed by the arms 
 a d and b c have been put down, the stretcher bars are detached from the centre plate at h and /, and 
 refixed to the plate at e and g. The holes required in the other two quadrants or divisions of the 
 circular face are then bored in the same manner, and the face is ready for the blasters. The holes 
 bored by this method are necessarily in concentric circles, but the angling may be varied as 
 desired. When the blast is ready for firing, the arms of the support are loosened, and the whole 
 is drawn a sufficient distance up the shaft to remove it beyond the reach of harm from projected 
 pieces of rock. In order not to encumber the shaft when in this position, and to facilitate its with- 
 drawal, the arms of the support are frequently made to hinge in the centre, so as to allow them to 
 drop down when the support is lifted by the central boss. If only one, or if three machines are to 
 be used, three arms, disposed as in Fig. 404, should be preferred to four. 
 
 A method of using the machine drill has recently been introduced by Mr. W. B. Brain, in which 
 it is sought to fulfil the two sets of conditions, namely, those due to the exigencies of machine labour, 
 and those involved in the attainment of the greatest useful efi'ect from a given charge, in the fullest 
 possible degree. This method constitutes, indeed, a new system, both of applying the drill and of 
 placing the charges ; and the success which has everywhere attended its adoption shows that 
 the end proposed has, in some degree at least, been attained. In Brain's system, which is known 
 as the " radial system," the holes of each series, 1, 2, 3, 4, 5, Fig. 406, or as many of them as 
 possible, are made to radiate from some fixed point A, Fig. 405, which point represents the position 
 
 2 K 
 
250 MINING ENGINEERING, 
 
 of the clamp on the stretcher bar. When all the holes in one series have been bored, the clamp is 
 shifted a certain distance along the bar, and the next series is bored in like manner. The distance 
 apart of the holes in a series, and also of the series themselves, that is, the distance between the series 
 1, 2, 3, &c., and 1, 2, 3 ; and also between the series 1, 1, 1, &c., and 2, 2, 2, &c,, is determined 
 beforehand^ in accordance with the toughness of the rock and the strength of the explosive, and 
 afterwards strictly adhered to, irrespective of joints, fissures due to former shots, irregularities of the 
 face, or any other circumstance that may exist peculiar to the case. The angles of the holes in a 
 series 1, 2, 3, &c., are also preserved through all of those series, so that all the holes in a series 
 1, 1, 1, &c., are in the same plane. 
 
 It will be observed that in this system the unkeying of the rock takes place from the side of the 
 face by sharply angling the holes in that position, and that as many of the holes as possible are 
 bored from one position of the stretcher bar. In general, unless the diameter of the excavation is 
 very great, one change of position, from A to A', will be sufficient. Thus it is evident that these 
 changes have been reduced to the lowest limit in this system, and that, consequently, the loss of 
 time due to the labour of changing has been brought to a minimum value. On the other hand, a 
 certain loss of time is incurred in setting the machine to the required angle at each successive 
 boring. It must be remarked, that this system was designed with a view to simultaneous firing, and 
 the use of a strong explosive ; and it is only by the fulfilment of these conditions that all the advan- 
 tages of the system can be obtained. "We shall have occasion to consider and to illustrate this 
 method of machine boring more fully in the next chapter. 
 
 The blasting, especially if the shot holes have been bored by machine drills, leaves the sides of 
 the excavation in a very rough state. These will, therefore, require to be subsequently dressed down 
 by hand with the pick and the wedge. 
 
 Tubbing. — The sinking and walling of the shaft will be continued through the rock in the manner 
 described until, we will suppose, for the purpose of fully illustrating our assumed case, water- 
 bearing beds are met with. Down to this point, all the infiltering water has been raised to surface, 
 without much difficulty, in tubs, or by means of small pumps. But when heavy feeders are met 
 with, it becomes important to stop them back. The means by which this is accomplished consist of 
 a water-tight wooden, or cast-iron lining, called tubbing, which is fixed in the shaft throughout that 
 portion which passes through the water-bearing beds. Brick walling has been applied as tubbing, 
 but its nature is not suitable to this purpose, and it is now very rarely used. Wooden tubbing was 
 formerly employed in England, but its use has been almost entirely abandoned in favour of cast iron. 
 It is, however, still very commonly adopted on the continent of Europe, and in other parts of the world 
 where timber is plentiful. It is therefore desirable to describe this kind of tubbing, and the method 
 of fixing it in the shaft, before considering that more durable kind which is composed of iron, and 
 which is now generally adopted in England, particularly as many of the operations of fixino- the 
 tubbing are identical for both kinds. The operations of sinking through water-bearing beds, and of 
 tubbing the shaft throughout that portion of its length, are beset with difficulties, and their successful 
 accomplishment demands the application of knowledge, skill, and, above all, energy. 
 
 The sinking beneath the last wedging curb supporting the walling is carried down a few feet 
 in a line with the inner face of the curb, to form a support for the latter, as already described, and 
 then gradually laid off to the diameter, in the case assumed, of 15 feet 6 inches, for metal tubbing; 
 and to about the same diameter for wooden tubbing. From this point, the sinking should be carried 
 
SHAFT-SINKING. 251 
 
 down through the permeahle bed to the impervious bed beneath with all possible speed. Promptitude 
 is here one of the conditions of success ; for when a water-bearing bed is pierced, the water, which 
 is often under great pressure, issues in great abundance into the excavation, and this abundance 
 increases as the water clears itself a passage through the interstices of the rock. When the imper- 
 vious bed has been reached, the sinking will be brought into its net size of 13 feet, and continued 
 down till a good foundation is found for the wedging curb. At this point, the sinking, after being 
 carried down 4 or 5 feet farther to form a sump for the water, will be shorn back to receive 
 the wedging curb. The latter is of oak, and similar to that used for the walling, but of somewhat 
 larger sectional dimensions ; the joints require to be fitted with greater care, thin slit deals being 
 placed between them, and the rock bed must be prepared and levelled with perfect accuracy for its 
 reception. As the wedging has a tendency to lift the outer edge of the curb, the bed should have a 
 slight inclination outwards, so that the upper surface of the curb may be perfectly level when the 
 wedging is completed. 
 
 When laid in position, the wedging curb should be everywhere about 2| inches from the sides 
 of the excavation, so as to leave an annular space of that width between it and the rock. Care should 
 be taken to see that the rock be perfectly sound in this part; if joints or small fissures exist here and 
 there, they must be well stopped with clay, or, in some cases, caulked with oakum, A fir sheathing 
 1^ inch thick is placed next the curb in the annular space between it and the rock; the breadth ot 
 this sheathing is a little greater than the depth of the wedging curb, so that when in position it 
 stands a little above the latter. When the shaft is circular, as in the case assumed, saw-cuts at every 
 three inches across the sheathing, that is, at right angles to its length, will be required, to enable it 
 to adapt itself readily to the shape of the curb. The fir sheathing is forced into close contact with 
 the curb by means of wedges driven in at intervals, and the space between it and the rock is filled in 
 with moss or with oakum, usually the former. The moss must be forced in until it is incapable of 
 further compression, when the wedges will have to be withdrawn, and their places also filled with 
 moss in a like manner. At this stage the curbing will appear as in Fig. 407, The prop, which is 
 set upon the joint of the curb, and made to abut against the rock above, as shown in the figure, 
 is needed to prevent the curb from rising during the operations of wedging. 
 
 The curb is now ready for wedging, which is performed in the following manner : Between the 
 curb and the sheathing, carefully prepared wedges are driven in, to force the sheathing and the moss 
 behind it firmly back against the rock, so that the curbing, when finished, shall make a perfectly 
 water-tight joint. The wedges are of soft wood : poplar, where this is readily procurable, as in 
 France ; and fir in other localities. It is essential that these wedges be uniform in dimensions. In 
 form, those first applied will be broad and flat, and called on that account " flat " wedges ; afterwards 
 narrower wedges of a pointed form, sometimes called " spiles," will be required. These flat wedges are 
 inserted close together all round the curb, the edge being slightly driven in to keep them in position. 
 When all the wedges are thus inserted, they are driven in as equally and as nearly simultaneously 
 as possible. This wedging drives the sheathing back from the curb, and compresses the moss 
 tightly against the rock. The next operation is to double the wedges; this is performed in the 
 following manner : An iron wedge, of greater thickness than the wooden ones, is driven in for the 
 purpose of loosening the wooden wedge next to it, by taking the pressure from the sheathing. 
 When this wedge is thus freed, it is taken out, and another one substituted for it, head downwards. 
 A second wedge of the same dimensions is then inserted, point downwards, between the upturned 
 
 2k2 
 
252 MINING ENGINEEEING. 
 
 point of the first and the sheathing. This operation is repeated all round, until all the wedges have 
 been doubled ; after which the driving is continued as long as the wedges will move. At this stage 
 the curbing will appear in section, as in Fig. 408, which shows four concentric lines, consisting of 
 the curb, the wedges, the sheathing, and the moss. 
 
 "When the wedging has been completed up to this point, a quadrangular iron wedge, steeled at 
 the tip, is taken and driven in successively between the flat wooden wedges, for the purpose of 
 inserting the point of a fir spile. These spiles are driven into the interstices between every two 
 wedges, until they refuse to penetrate farther. When these are all driven down, the whole of the 
 curbing is tightly wedged in all directions, and the moss has become so compressed as to be hardly 
 visible ; the heads of all the wedges and spiles are then adzed down. Next, the heads of all the 
 flat wedges are cleaved with a steel-tipped iron wedge, and oak spiles, previously well dried in an 
 oven, are inserted in the cleft, and driven in as far as they will go. This operation of cleaving the 
 wedges is continued as long as a spile can be made to enter. When no more can be got in, the whole 
 is adzed down to form a level surface. The curbing is then complete, and appears as shown in 
 Fig. 409, which represents two curbs superposed for greater security. Sometimes three such curbs 
 are laid ; but commonly there are but two. It is important that the wedges should be put in dry, 
 because when in that state their dimensions are at a minimum, and by swelling, on exposure to 
 moisture, they still further tighten the joint. It is for this purpose that the last wedges inserted are 
 dried in an oven. Fig. 410 shows a plan of the wedging curb when completed; the four concentric 
 circles representing the curb itself, the wedges, the fir sheathing, and the moss. Precisely the same 
 method of fixing the wedging curb is adopted when the shaft is polygonal, as it frequently is on the 
 Continent. Fig. 411 is a plan of the curb as constructed for such a form. The mode of putting in 
 the fir sheathing under these conditions will be understood from the drawing. 
 
 When the wedging curbs have been laid, the tubbing is built up upon them. This tubbing 
 consists of wooden curbs, constructed similarly to the wedging curbs, and built up one upon another 
 throughout the whole length of the shaft to be tubbed. These curbs are generally about 8 inches 
 broad on the bed, and 10 inches in depth. It is by no means essential that they should be all of the 
 same depth, and in practice they are never equal in that respect. Their thickness will be determined 
 by the pressure which they will be required to support ; which thickness will, therefore, diminish as 
 the tubbing rises towards the surface. The beds of the curbs should be truly dressed, in order that 
 a water-tight joint may be made subsequently by merely caulking it. When the height of the tubbing 
 is considerable, a broader curb, called a bearing curb, is put in at intervals of 8 or 10 yards, and firmly 
 wedged against the rock. These bearing curbs take the weight of the tubbing off the wedging curbs 
 at the bottom. Tubbed in this way, the shaft appears as in Fig. 412. The space behind the tubbing 
 is filled up with strong concrete. This concrete backing is an important adjunct to the tubbing, as it 
 penetrates into every hollow and fissure, and on hardening it forms a strong protective casing around 
 the tubbing. The existence of such a casing greatly facilitates the operation of replacing a faulty 
 curb by a sound one after the completion of the shaft. 
 
 It now remains to consider the method of tubbing with cast iron, as generally practised in 
 England, and commonly in other countries where wood is not very abundant. 
 
 In the case of iron tubbing, the wedging curbs are themselves of cast iron, and hollow. Some- 
 times they are open on the outside and sometimes on the inside, and are divided at intervals by 
 partitions to give strength to the curb. The hollows between these partitions are filled with oak. In 
 
SHAFT-SINKING. 253 
 
 some cases, the curb is not open on either side. Generally, these curbs, of which examples will be 
 given hereafter, are about 13 inches broad, and 6 or 7 inches in depth, the thickness of the metal being 
 about Ij inch. Such cast-iron curbs are put together in segments, and laid upon a bed of —inch 
 fir sheathing. Oak sheathing is inserted between the joints, which are made firm by wedging. This 
 sheathing should be cut and placed in such a way that the grain may run towards the centre of the 
 shaft, and it should be made to taper from the outer towards the inner face of the curb, say from a 
 thickness of 1 inch on the outside to | inch or \ inch on the inside. The method of fixing the iron 
 wedging curb is in all respects the same as that adopted for the wooden curb, which has been fully 
 described. Sometimes a wooden wedging curb is first laid, and an iron one then laid upon it ; oftener, 
 two iron curbs are laid one upon the other. 
 
 The plates of the tubbing, like the wedging curbs, are cast in segments, the dimensions of which 
 require from eight to twelve to form a circle of tubbing. These segments vary from 12 inches to 
 36 inches in height, according to the pressure they are designed to withstand, and from | inch to 
 1^ inch in thickness. They are smooth on the inside so as to form a regular surface in the shaft, 
 but on the outside, next the rock, they are strengthened by ribs and flanges, supported by brackets, 
 as shown in Fig. 413. These flanges form the edges of the segment, and they should be cast perfectly 
 true, so as to form a regular joint when two segments are brought into contact. The top and one of 
 the side edges are provided on the outside with a projection or flange, the use of which is to retain 
 the joint sheathing and two adjoining segments in their positions. These flanges may be called 
 " retaining " flanges. Every segment has a hole in the middle, to allow the water to escape during 
 the operations of setting. This hole is made use of in lowering the segments and in placing them in 
 position. It is of essential importance that these castings be perfectly sound in every part. The 
 method of setting the segments is as follows : A sheathing of pitch pine, f inch or ^ inch thick, is 
 laid upon the upper surface of the wedging curb, to form the joint between it and the first course of 
 tubbing ; the breadth of this sheathing will be from 4 to 5 inches. A course of tubbing is then set 
 upon this bed all round the shaft, and fir sheathing, from j inch to | inch thick, is placed between the 
 joints, in the same manner as was required for the wedging curb. In order to close up the joints and 
 to steady the tubbing in position, two strips of Wood, an inch thick and from 4 inches to 6 inches 
 broad, may be placed behind the vertical joints, between the tubbing and the rock ; and a third strip, 
 thinned off towards the end to form a wedge, driven down between them. The space between the 
 tubbing and the rock is next filled in with loose rock from the excavation, or, preferably, with 
 good concrete. When the latter is used, it will be well to remove the wedging strips behind the 
 vertical joints as the concrete is put in. Upon the top of this first course of tubbing, pine sheathing 
 is laid to form the horizontal joints between the courses, and a second course is set up upon this, and 
 fixed in position in the same manner as the first, always taking care that the joints, both horizontal 
 and vertical, be very accurately made. The latter must be broken, that is, the vertical joints of the 
 second course must be over the middle of the segments forming the first course. These operations are 
 repeated until the stone bracket supporting the wedging curb beneath the walling is reached. This rock 
 is then cut away sufficiently to afford room for the tubbing, leaving a portion of the thickness to support 
 the walling, and the tubbing completed up to the wedging curb. The joints have now to be tightened 
 by wedging, which is effected in the following manner : Beginning at the bottom, incisions are 
 mad^ with a broad chisel in the sheathing, and broad flat wedges are driven into the clefts thus 
 made. These wedges are about 4 inches broad and f inch thick at the head. When the joints have 
 
254 MINING ENGINEEEING. 
 
 been filled with these, a square-pointed steel tool is used to make fresh incisions, and spiles or square 
 wedges of the same thickness are driven in wherever it is possible to make one enter. The joints 
 between the top course of tubbing and the wedging curb beneath the walling must also be tightly 
 wedged. The plugging of the holes in the centre of each segment is also commenced from below. 
 When the head of water is great, there is some difficulty in inserting the plug on account of the 
 force with which the water issues. After the plug has been driven in as tightly as possible, the head 
 is cleaved with a chisel, and an oak wedge driven into the cleft to increase the hold of the plug. 
 Care must be exercised in plugging not to proceed too rapidly, because it is necessary that any air or 
 gas that may be imprisoned behind the tubbing should be allowed to escape. 
 
 As the corroding action of water is very destructive to cast-iron tubbing, means must be adopted 
 for protecting it. A thick coating of tar or of paint will be found sufficient in some situations. When 
 the shaft is an upcast, and the mine is ventilated by a furnace, or when there are engine fires under- 
 ground, the destruction of the tubbing may proceed rapidly. In such a case, a lining of brick may 
 be inserted ; but such a lining renders it difficult to repair the tubbing or to stop a leaky joint. 
 Of course, when a lining of this nature is contemplated, the diameter of the excavation must be 
 determined accordingly. Sometimes a lining of wood is put in to protect the tubbing. Such a 
 lining should consist of deals 2 inches thick, having their edges properly beveled to form close joints. 
 
 Cast-iron tubbing is more difficult to construct and to repair than wood tubbing ; but it is far 
 more durable under ordinary conditions, and it is capable of resisting a much greater pressure 
 of water. The wood tubbing may be used with safety down to a depth of 100 yards; and in 
 localities where wood is abundant, its adoption will occasion a notable economy. But for greater 
 depths, iron tubbing is alone suitable. The thickness of cast-iron tubbing will be determined, as far 
 as the exigencies of practice will allow, by the pressure which it will be required to sustain. The 
 following formula gives the maximum thickness for segments not exceeding 2 feet in depth, H being 
 the head of water, and D the diameter of the shaft, in feet, and T the thickness of the plate, in inches : 
 
 T = 0-35 -t- 0-00025 HD. 
 
 Thus, if H = 200 and D = 14, we shall have T = 0-35 + 0-00025 x 200 x 14 = 1-05 inches, as 
 the requisite thickness. In practice, the thickness is generally varied at every 25 feet. 
 
 The following examples of tubbing, which have been executed in England and in difierent 
 localities on the Continent, may be studied with advantage. They constitute the principal types now 
 in use, and for that reason they have been selected as illustrations. It is obvious that in constructions 
 of this character very little modification can be made beyond varying the arrangement of the 
 strengthening ribs and flanges, and the number of segments in a course. 
 
 Some of the earliest examples of a complete system of cast-iron tubbing may be found in the north- 
 eastern coal districts of England. In one of these, to which the following particulars relate, the shaft 
 is 14 feet in diameter ; it is walled down to a depth of about 25 yards, and from this point to a 
 depth of about 172 yards it is tubbed with cast-iron tubbing. This tubbing is composed of eight 
 segments to the circle, 1 foot in height, and li inch thick, in the lower portion ; and 2 feet in height, 
 and f inch thick in the upper portion. Each segment is strengthened by a horizontal rib in the 
 middle, and two vertical ribs ; and the hole in the middle is surrounded by an increased thickness of 
 metal, forming a boss. The overlap or retaining flanges are i inch in depth, and 1^ inch in breadth. 
 The wedging curb is open on the outside, each segment having three vertical diaphragms or 
 
SHAFT-SINKING. 
 
 255 
 
 partitions, which divide the interior into four portions. These are filled with oak, which projects 
 slightly to forma face to wedge against. The depth of the curb is 6 inches, its breadth is 12 inches, 
 and the thickness of the metal is 1| inch. This is the type of tubbing described in the foregoing 
 paragraphs, and generally adopted both in England and on the Continent. 
 
 Another very good example of cast-iron tubbing was erected in 1856, in the Basin of the Ruhr, 
 "Westphalia, by an English engineer. The tubbing in this case is of the same type as that described 
 above. The diameter of the shaft is 12 feet, and the length tubbed is about 120 yards, through 
 strata consisting of sands and marls. As in the preceding example, a course is composed of eight 
 segments ; the height of a segment is 2 feet, and the thickness was begun at ^ inch, and increased g- 
 at every 20 metres — about 22 yards — of depth, reckoning from the surface downwards. Thus the 
 thicknesses are as follows : 
 
 Depth, 20 metres. Thickness, f inch. 
 
 40 
 60 
 
 Depth, 80 metres. Thickness, 1^ inch. 
 
 100 
 120 
 
 1| 
 
 The wedging curb is 6 inches in depth, 14 inches in breadth, and 1 inch in thickness of metal. 
 American pine was used for the joint sheathing, and the same wood was used for the wedges in the 
 joints. The greatest quantity of water to be dealt with was about 265 gallons a minute. This was 
 encountered at a depth of 83 yards. 
 
 A third noteworthy example may be taken from the coal-fields of the north of France, where a 
 length of tubbing was put into a shaft by M. Demilly, chief engineer to the Societe Houillere de 
 Fiennes, in the year 1858. The portion tubbed was from 171 to 182 metres from surface, giving a 
 length of 11 metres. The first 50 metres was tubbed with the solid wood tubbing described in a 
 former paragraph. From this depth to that of 100 metres, no water was met with ; but below 100 
 metres, 5 metres of tubbing had to be put in, and another length of 8 metres, below the depth of 
 120 metres. The sinking was through Jurassic strata, and the upper carboniferous limestone, and 
 the water was met with at the junction of the limestone and the coal measures. The quantity of 
 water did not exceed 70 gallons a minute. The excavation was carried 7 metres into the coal measures 
 to obtain a suitable bed for the tubbing, the height of which was to be 11 metres, 4 metres being in 
 the limestone. Three wedging curbs were laid below and above the tubbing. These curbs are. double, 
 as shown in Fig. 414, the inner one being 12 inches, and the outer one 8 inches broad. Both are 
 8 inches in depth, and are open on the side towards the shaft ; each segment is divided internally by 
 three vertical partitions into four compartments. These compartments are fiJled with oak. The 
 space of 1| inch between the curbs is firmly wedged. The tubbing, which has an internal diameter 
 of 13 feet 4 inches, is composed of twelve segments, constructed as shown in Figs. 415 to 418. The 
 overlap or retaining flanges are represented at ab and cd; the height of the segment is 16 inches ; 
 it is strengthened by two horizontal and one vertical rib, and provided in the middle with a hole 
 1- inch in diameter. The joint sheathing used was of fir, f inch in thickness, and the wedges were 
 also of fir. The horizontal joints are made to taper towards the centre of the shaft, the sheathing 
 being | inch thick on the inside, and | inch on the side next the rock. M. Demilly thinks that two 
 or three shallow grooves in the upper edge of the segment would give a better hold upon the wood. 
 He is also of opinion that it would have been better to have used segments of 2 feet in height, and 
 of 16 rather than 12 to the circle. 
 
 A final example of recent construction may be taken from the coal-fields of Schoeneck, at Styring 
 
256 MINING ENGINEEEING. 
 
 (Moselle). The shaft in "this case is 13 feet 4 inches in diameterj and' it is tiihbed with wood from 
 a depth of 20 metres to that of 105 metres ; and from this depth to that of 130 metres, which is within 
 2 metres of the bottom, it is tubbed with cast iron. The wedging curbs in this case, shown in 
 Figs. 419 to 421, are 14 inches in breadth, 8 inches in depth, and of the same thickness as the 
 bottom courses of tubbing. Each segment is open on the side next the rock, and divided internally 
 into four compartments. These compartments are filled with oak. The upper surface of the curb is 
 not level, but indented, as shown in the drawing, to receive the fir sheathing upon which the tubbing 
 is to be set. The bed of the wedging curb was cut with a slope of | inch towards the sides of the 
 excavation. After the wedging had been performed, the upper face of the curb was found to be 
 perfectly horizontal. The sheathing used for the joints of the curb was of oak, and planed down to 
 a thickness at the four angles of 22, 25, 28, and 30 millimetres = 0-86, 0-98, 1" 10, and 1-18 inch. 
 The sheathing placed behind the curb was of poplar, in pieces of 5 feet 10 inches long, 1 inches 
 broad, and 1} inch thick. Saw-cuts, I inch in depth and 1^ inch apart, were made perpendicularly 
 to the length of the piece, to enable it to assume readily the circular form. The segments of tubbing 
 are shown in Figs. 422 to 424; ten of these constitute a complete course. Each segment is 20 
 inches in height, and it is strengthened by one horizontal and three vertical ribs. The thickness of the 
 plates was varied at every 10 metres. Thus, the thickness at a depth of 100 metres is 30 millimetres 
 = 1'18 inch; at 110 it is increased to 32 millimetres = 1"26 inch; at 120 it is 35 millimetres = 
 1*37 inch; and at 130 it is 38 millimetres = 1*50 inch. The central hole in each segment is 1} 
 inch in diameter. The vertical joints of the tubbing were made with oak sheathing ' 44 inch in 
 breadth, O-'ZO inch thick on the front, and 0*39 inch thick on the back face. The horizontal joints 
 were made with poplar sheathing of the same dimensions. The wedging was done with oak wedges 
 in the vertical joints, and with poplar and oak wedges in the horizontal joints. The flanges forming 
 the edges of each segment were provided with grooves f inch deep and 1 inch apart, to obtain a 
 firm hold upon the wood. Each segment of the tubbing was wedged to the rock, and the space 
 between the tubbing and the rock was filled in with concrete formed of one-third sand and two- 
 thirds cement. 
 
 Backcasing the Shaft. — In the foregoing assumed example of a sinking, the method of sup- 
 porting the sides of the excavation during the sinking to the stone-head, or the " fast," as the firm 
 rock is sometimes called, chosen for illustration, was that system of timbering known as " curbing." 
 This system is generally adopted in the north-eastern coal-field of England, and under ordinary con- 
 ditions it is probably the most economical. There remains, however, to be described another method, 
 adopted in other localities, notably in the Lancashire districts, which dispenses with wood entirely, 
 except for the walling curbs. This method is known as " backcasing," and consists in employing 
 bricks laid dry, in the place of the wood required in curbing. The mode of procedure in back- 
 casing is briefly as follows : 
 
 The shaft is laid out with a diameter 20 inches greater than that required for the permanent 
 walling, and carried down as far as the sides will stand safely. In the case assumed, this depth was 6 feet. 
 A walling curb, similar in construction to those described for the permanent walling, but of larger 
 diameter, and smaller sectional dimensions, the latter being 9 inches x 3 inches, is then laid upon 
 a carefully levelled bed at the bottom of the excavation. A walling of dry bricks, 9 inches, that is, 
 one brick, thick, is built up upon this curb to surface. The bricks used should be of a quality suitable 
 for this purpose, and shaped to accord with the circle of the shaft. The sinking is then resumed with a 
 
SHAFT-SINKING. 257 
 
 diameter eqnal to the inside of the curb, and continued down another 6 feet. At this depth, the sides 
 of the excavation are shorn back at one part for a width equal to the length of one of the segments 
 of the curb, and a segment of a new curb put in. Punch props will be required to support the curb 
 beneath the walling at this point, from which the underlying bed has been removed. Upon this 
 segment, a new length or course of walling is then built up, and tightly wedged to the first walling 
 curb, so as to afford a good support to the latter. The wedges used for this purpose should be broad 
 and thin, and preferably of fir. An adjoining portion of the sides of the excavation, equal in width 
 to the first, is now shorn back, and a second segment of the curb laid and bolted to the first, and the 
 walling carried up upon this segment and joined by wedging to the upper curb, as before. These 
 operations are repeated until the whole of the curb has been laid, and the circle of walling put in. 
 When this has been accomplished, the sinking is carried down in a line with the inside of the curb 
 through another 6 feet, and the sides shorn back or walled as before upon a third curb. This mode 
 of procedure is continued until the stone head is reached. If the work has been carefully executed, 
 this backcasing will be nearly as strong as the permanent walling, to which it will afford great relief. 
 When the stone head has been reached, the permanent walling is built up inside the backcasing, in 
 the manner already described. Thus, unlike the wooden curbing, the brick backcasing is left behind 
 the permanent walling, whence its name. The support afforded by this system of backcasing is 
 notably superior to that obtained from the wooden curbing. 
 
 Sinking through Loose Rock. — In the example chosen for the purpose of illustrating the several 
 methods of procedure in sinking, and in securing the sides of the excavation, the passage through the 
 surface beds was assumed to offer but little difficulty. Frequently, however, these overlying beds of 
 alluvial cover occasion great labour and expense, and demand the application of knowledge and 
 skill. In carrying a sinking down to the stone head through beds of quicksand, or loam saturated 
 with water, an enormous pressure develops itself against the timbering placed to support the sides of 
 the excavation, since the cohesion of the particles of the rock is very little. Hence arises a necessity 
 for very strong timbering. Instead of placing the curbs at intervals apart of 3 feet, as in the 
 example described, it may be impossible to exceed 6 inches, or it may even be necessary to place 
 them in contact with one another. Also the strength of the curbs must be augmented by increasing 
 their dimensions up to a sectional area of 6 inches x 6 inches, and great care will have to be 
 exercised that the wood of which they are formed be perfectly sound and free from defects of every 
 kind. But this excessive pressure is not the only difficulty to be overcome. When, in a bed of 
 sand, the spaces or voids between the grains are filled with water, the cohesion among these grains 
 is destroyed, the film of water surrounding each grain, and the floating action of the fluid present 
 in the interstices, preventing friction. Hence it happens that when an issue is given to the water 
 the grains of sand pass out with it. This fluid character of the sand constitutes a very great 
 difficulty in sinking, because the issue of the sand into the excavation occasions the falling in of the 
 sides and the surface, besides the necessity which it creates of removing an indefinite quantity with the 
 water to be lifted. When the water is under great pressure, this difficulty is immense, and in some 
 cases altogether insurmountable. Thus, at a sinking in the Belgian coal-field recently undertaken, a 
 bed of quicksand was encountered, at a considerable depth from the surface, after passing through 
 the upper beds without difficulty. As soon as this bed was struck, the fluid mass of water and sand 
 rapidly rose in the shafts ; so rapidly, indeed, that the sinkers had barely time to escape. As the 
 prospect of successfully contending with the irruption appeared hopeless, the sinking was abandoned. 
 
 2 L 
 
258 MINING ENGINEEEING, 
 
 Numerous examples of a similar nature might be given from the north-eastern coal district of 
 England ; some of which were finally dealt with successfully, though at an enormous cost. Sinking 
 through such strata is the most costly and the most uncertain of mining operations, and it should 
 never be undertaken without a careful consideration of all the circumstances of the case. 
 
 There are several methods of sinking through quicksand, but the general and most effective 
 method, when the sands exist near the surface, is by piling ; that is, by driving planks close together 
 vertically around the shaft, and supporting these internally with curbs. When this method of 
 passing through the loose rock is to be adopted, the shaft must be laid out of a sufficiently large 
 diameter to allow of the successive reductions which will have to be made at each course of piling. 
 To do this accurately, it is necessary to know exactly the thickness of the beds, which must be 
 ascertained from existing shafts in the locality, or if none be available for that purpose, by borings 
 made on the spot. It is, indeed, seldom that the former source of information is sufficient, and 
 therefore preliminary borings may be regarded as generally necessary. As the curbs to be used are 
 6 inches x 6 inches, and the piling 3 inches thick, every fresh course of piling will diminish the 
 diameter of the excavation by 18 inches. With piles 15 feet long, a fresh course will be required at 
 
 about every 12 feet, so that the reduction of the diameter in a depth of x feet will be feet. 
 
 Thus if the thickness of the overlying water-bearing cover be 100 feet, the reduction at that depth 
 
 virill be — — ^ = 12-6 feet; and consequently, if the diameter of the shaft outside the brickwork 
 
 is to be 15 feet 2 inches, the excavation must be begun with a diameter of 15 feet 2 inches + 12 feet 
 6 inches =27 feet 8 inches. 
 
 When the sinking has been laid out to the requisite diameter, and the surface soil removed to as 
 great a depth as the ordinary method of curbing will safely sustain, a strong wooden curb, about 
 6 inches x 6 inches in section, and of a diameter 6 inches less than that of the excavation, is placed 
 in position at the bottom, and perfectly concentric with it. The piles to be used should be about 
 6 inches x 3 inches in section, and from 10 feet to 15 feet in length; their lower ends should be 
 pointed and shod with iron, to enable them to penetrate the rock, and their edges should be planed 
 true and beveled, so as to form a close joint when placed in contact around the circular curb. These 
 piles are then driven down side by side against the outer face of the curb, care being taken to keep 
 them vertical, that their edges may remain in contact throughout their length. A wooden maul is 
 the most suitable instrument for driving the piles, and where the ground is strong, the latter should 
 be hooped at the head, to prevent them from being crushed and split by the maul. It will not often 
 be possible to drive the piles down to their full length at once ; usually about 5 feet will be practically 
 the limit. Supposing, therefore, the piles to have been driven down to this depth, the earth will be 
 taken out from the inside to a depth of 3 or 4 feet or less, according to its strength, and another curb 
 of the same diameter laid to support the piles. As before remarked, the distance of the curbs apart 
 will be determined, by the pressure to be sustained. When the support of the curbs has been substi- 
 tuted for that of the earth, the piles are again driven down as far as they will readily go, and the 
 earth excavated from the inside, other curbs being placed to support the piles. These operations are 
 repeated until the piles have been driven down to their full length. 
 
 When the earth has been excavated to within, say, 3 feet of the lower ends of the piles, and a 
 curb laid at that depth to support the latter, another curb, 18 inches smaller in diameter than those 
 
SHAFT-SINKING. 259 
 
 previously laid, is placed inside the bottom one, and 3 inches distant from it all round. Into the 
 annular space between these curbs, a fresh course of piles is set, and driven down as far as they will 
 go, and the same operations of excavating, curbing, and driving are gone through as before. On 
 approaching the foot of this second course of piling, another curb, 18 inches less in diameter than 
 those just put in, is laid within the bottom one, and a third course of piling is set in the annular 
 space between them, and driven down as far as they will go. These operations are repeated until the 
 stone head is reached. Piled in this way, a section of the shaft appears as in Fig. 425. When 
 the stone head is reached the wedging curb is laid, and the walling or tubbing erected as quickly as 
 possible. The space between the shaft lining and the piling is filled up, as the walling or the tubbing 
 proceeds, with clay. 
 
 The method of piling followed on the Continent differs somewhat in detail from that just 
 described. The piles used are about 3 feet long, from 4 inches to 5 inches broad, and 1 inch thick. 
 Instead of being driven into the ground vertically, as in the method described, they are driven with 
 an outward inclination of 10 or 15 degrees, as shown in Fig. 426. When these piles have been 
 driven in to their full length, the earth on the inside is excavated to a depth of about 2 feet 6 inches, 
 or 2 feet 9 inches ; and before the thrust of the earth has brought the piles into the vertical position, 
 a second curb is placed to support them. Around this curb, a second course of piling is driven as 
 before, in diverging directions, and the earth again excavated. If the piles preserve their inclined 
 direction, another set is driven vertically behind the curbs, and the space between the two sets is 
 filled in with bits of wood, as shown in the figure. All systems of piling for passing through water- 
 bearing beds are merely modifications of the two foregoing ; and it is evident that these modifications 
 of detail may be extended in an almost unlimited degree. 
 
 Water-bearing drift deposits may frequently be passed through by the method of backcasing, if 
 the details of the operations be made conformable to the exigencies of the case. As the sides of the 
 excavation will not stand alone if the height exceed a few inches, curbs will have to be put in very 
 frequently, at intervals of three or four courses of bricks. Also the length of the segment to be 
 bricked at one time must be reduced in a proportionate degree ; one-tenth of the circumference, or 
 even less, being as much as may be removed with safety. It will, moreover, be necessary to support 
 the curbs from above in ground of the unstable character we are now considering. This may be 
 effected by means of stringing deals spiked to the curbs and to balks of timber at surface, in the 
 manner adopted for the wooden curbing, already described. Iron rods, however, constitute a better 
 means of suspension than the deals. Such rods should be 1| inch in diameter, and there should be 
 one to each segment. The usual mode of fixing the rods is to pass them through the bottom curb and 
 through the b9,lk of timber at surface, and to secure them to those pieces by means of washers and 
 nuts. This mode of suspension will be adopted when the bottom of the course of walhng has been 
 reached, and the sinking is to be continued in some other manuer ; as, for example, by means of a 
 drum, when a bed of quicksand is met with. When the quicksand is encountered at a considerable 
 depth, the lower course of walling may be suspended, by means of the iron rods, from an upper 
 course, instead of carrying the rods up to surface. 
 
 The method of backcasing, though generally successful in even very wet marl, is inapplicable 
 to quicksands, by reason of the tendency, already pointed out, of the sand to flow with the water 
 into the excavation. When such beds are met with, therefore, it becomes necessary to have recourse 
 to piling, or to the " brick " drum, as it is commonly, but incorrectly, called. In describing the 
 
 2 L 2 
 
260 MINING ENGINEEEING. 
 
 method of sinking with the drum, which is generally followed in the Lancashire district, we shall 
 assume that a bed of quicksand is encountered beneath some fathoms of cover, and that the back- 
 casing, which has been put in down to this point, is suspended by means of iron rods from balks of 
 timber at surface. The first operation is to construct the drum. This drum, the use of which is to 
 support the sides of the excavation, may be constructed of wood, of wrought iron, or of cast iron. 
 If it is to be of wood, a sufBcient number of oak curbs, usually 6 inches in breadth by 4 inches in 
 depth, are placed at intervals of 2 feet, or 2 feet 6 inches apart, until a length is made up greater by 
 a few feet than the thickness of the bed to be passed through. Upon the outside of these curbs are 
 firmly bolted, with their edges in contact, pieces of planking, called " lags." This " lagging " is to 
 take the place of the back sheathing, in the method of wooden curbing, and as the pressure against 
 it will be great, it should have a thickness of 3 inches. It is also important that the edges of these 
 pieces should be truly planed to the circle of the excavation, so that when placed in contact they 
 may bear evenly and fully upon each other ; and this equal distribution of pressure may be best 
 attained by limiting the breadth of the lags to 4 or, at most, 5 inches. Constructed in this way, the 
 drum resists like an arch, and it can yield only by the destruction of the material by compression. 
 It will be observed that in this case the arch is composed of the lagging alone, the curbs merely 
 serving as supports to keep the elements of the arch in their places. The true fitting of the joints 
 is also necessary to keep out the water, for the drum is to serve as a short length of tubbing at that 
 portion of the shaft where the quicksand occurs. Around the bottom of the drum, and on the 
 outside, a plate of iron, about 2 feet broad, is bolted so as to project half its breadth beyond the lower 
 end of the drum. This plate is called the " leader," and its use is to enable the drum to cut its wav 
 into the sand or soft clay. The lower edge of the plate should be made sharp, to allow it to fulfil 
 its purpose more effectually. 
 
 When the drum is thus prepared, it is lowered into the shaft and brought to rest with its cutting 
 edge upon the bottom of the excavation. To give the drum weight, the spaces between the curbs 
 are filled up with brickwork. The sand is then carefully excavated from the inside of the drum, 
 which, deprived thus of its support, sinks through the bed, the leader cutting its way down as the 
 resistance is diminished by the removal of the sand. Sometimes the friction against the sides of the 
 drum will cause it to stick, notwithstanding the weight of the bricks inside. In such cases additional 
 weight is applied in the following manner. Four pieces of timber, two bearers and two cross-pieces, 
 are laid upon the bottom curb, so as to leave a rectangular opening in the middle, and pieces of board 
 are laid upon these timbers around the central opening. Upon the staging thus constructed, bricks 
 are built up to the top, or as far as may be needed to give the requisite weight. It is ot essential 
 importance that the drum be placed perfectly vertical in the shaft, and that it be kept in that 
 position during the sinking, for if it once lose its verticality it is almost impossible to rectify the evil. 
 When the drum has sunk through the sand, and a few feet into the clay beneath to form a water- 
 tight junction, the sinking may be resumed in the usual manner, by backcasing to the diameter of 
 the curbs inside ; for it will be observed that the drum, like the piling, will reduce the diameter of 
 the excavation by 18 inches. When the permanent walling is put in, it will be built up inside the 
 drum, which merely serves as a backcasing. In most cases, however, the curbs may be recovered. 
 
 Though a wooden drum may be run to a much greater depth than a course of piles can be 
 driven, it is urged as an objection to this drum that it reduces the diameter of the excavation to the 
 same extent as the piles. To remedy this defect, wrought iron, in the form of finch boiler plate, 
 
SHAFT-SINKING, 
 
 261 
 
 has been substltiited for the wood. But the liability of these to collapse, owing to the absence 
 of inside staying, renders them far more objectionable than the wooden drums. It is, moreover, 
 extremely difficult to keep these drums in the vertical position, or to increase their weight, if 
 necessary. On the other hand, the friction between them and the rock is less. But these defects 
 may be removed by the adoption of cast iron. Drums made of this material are cast in segments, in 
 the same manner as the ordinary tubbing, but with the flanges and strengthening ribs on the inside ; 
 for it is essential that the outside of the drum be smooth to allow it to sink through the sand. Such 
 a drum will seldom need to be weighted, and the reduction in the diameter of the excavation 
 occasioned by it will not be more than half that due to the wooden drum. Besides this, a well- 
 constructed cast-iron drum may be run in so as to constitute a portion of the permanent lining of the 
 shaft, as a short length of tubbing, in fact. When this can be accomplished, the cast-iron drum will 
 afford the most economical means of passing through a bed of quicksand. 
 
 The following example of sinking through a bed of quicksand by means of the cast-iron drum is 
 worthy of careful consideration. In this instance the work was well designed and skilfully executed 
 in the face of great difficulties ; and as Mr. H. Bramall, of Rainford, to whom both the design and 
 the execution of the work are due, has briefly and clearly described the operations in a paper read 
 before the Manchester Greological Society, we quote the following as given by him : 
 
 " The pit referred to is the No. 9 Pit, of the Rainford Colliery, and is situate about 11 miles 
 from Liverpool, on the Lancashire and Yorkshire Railway. The cover, or drift, here consists of 
 
 Soil 
 
 Marl 
 
 Loam 
 
 Wet gravelly clay 
 
 Quicksand .. 
 
 Gravelly marl 
 
 Total 
 
 " This pit was commenced in September I860, with a diameter of 19 feet clear, and was sunk 
 on the usual Lancashire plan of brick-casing, but owing to the slovenly and careless manner in which 
 the work was done, the side of the pit was pushed in by the pressure at a depth of 17 yards; and 
 to save the pit, a ring, 13 feet inside diameter, was laid on the bottom, and a casing of 6-inch brick- 
 work brought up nearly to the surface, the space between the two casings being filled with ashes, as 
 shown in the upper part of Fig. 427. This casing also was put in in a very negligent manner, 
 and proved afterwards a source of considerable trouble to us, the chief aim having apparently 
 been to put in the greatest number of yards in the least time, and for the least money, without a 
 care or a thought about the quality or the safety of the work, or of what was ultimately to be done 
 with the pit. Indeed, the pit was then abandoned, and another commenced at a distance of 40 yards. 
 Here the top, though troublesome, was not nearly so bad, and was passed without very much 
 difficulty, by carrying the pit down in the usual way for 12 yards in the marl, and afterwards 
 running two wooden drums. When I undertook the management of the colliery in October, 1861, 
 I found they had just passed the sand in this new pit, and having found a suitable bottom, I laid a 
 wedging ring, and brought up cast-iron tubbing to stop out the sand-feeders. Having thus secured 
 this pit, I turned my attention to the No. 9 Pit. 
 
 Feet. 
 
 Inches 
 
 1 
 
 6 
 
 34 
 
 6 
 
 15 
 
 
 
 16 
 
 6 
 
 21 
 
 
 
 3 
 
 
 
 91 
 
 6 
 
262 MINING ENGINEEEING. 
 
 " We first proceeded to lay two balks, Fig. 427, across the pit, resting on frames & b at eacli 
 end, and across these two other balks c c, also resting on frames d d, the frames standing on a 
 number of short planks jj, placed crosswise, to spread the weight and prevent the frames from 
 sinking into the ground, as the place had formerly been a marl hole, and having been filled up with 
 loose materials, it was very soft. On the crossed balks, were erected the pulley frame and banking 
 stage. Sinking was then resumed on the backcasing plan, taking out very short segments at a time, 
 and putting in rings at every 18 inches, which distance, as the ground became worse, was reduced to 
 9 inches, or three courses of bricks. We thus carried the work down within a yard of the sand. 
 The whole of the rings were then hung by spiking 2-inch battens along the face of them and to the 
 balks above. The lowest ring was doubled, and three strong bearers placed upon it and across the 
 pit, so as to form a triangle, on which a ring was laid perfectly level to form a stage on which to 
 build the drum, and at the same time allow the water to be wound out of the pit. 
 
 " It was my intention to use the drum as part of a length of water-tight tubbing, with which I 
 purposed to stop out the sand-feeders. The drum was cast in segments, and was 12 feet in diameter 
 outside ; each segment was 2 feet deep, and twelve of them formed a course. They were made as 
 shown in Figs. 428 to 430, with the brackets and flanges inside, so as to leave the back perfectly 
 smooth, in order to receive the least possible amount of frictional resistance from the ground to be 
 passed through. The segments were fastened together by |-inch bolts, |-inch sheeting being put 
 between all the joints. The lowest course of segments had riveted on the back a leader a, Figs. 428 
 and 430, which was simply a plate of iron, 1 inch thick in the upper part, and sharp on the lower 
 edge, so as to cut its way through the ground. The corner or shoulder formed by the leader and 
 lower flange of the bottom course of segments was filled up by a beveled ring of wood b, Fig. 429, 
 to lessen its resistance to the passing downwards of the drum ; this was afterwards removed to 
 allow of segments being bolted below the drum, as shown by the dotted lines in the figure. 
 
 " The lower course of segments, with the leader attached, /, Fig. 427, was then placed upon the 
 ring platform at the bottom of the pit, and fourteen additional courses of segments built upon it, so 
 as to form a drum about 10 yards long. Six sling chains gg were attached to the third flange from 
 the top, |-inch chains carried from these to the surface, and coupled to screws h, 2 inches in diameter, 
 passing through the before-mentioned balks. All preparations being now made, we proceeded to 
 lift the drum by means of the screws, and take out the platform ring and bearers, on which up 
 to this time the drum had been resting. It was then lowered upon the clay, into which it at once 
 sunk. On proceeding to take out the clay, the sand blew up into the pit with considerable force. 
 The screws were slackened and the drum allowed to sink very gradually, the utmost care being 
 requisite to keep it upright. The sand was sent out of the pit, keeping the leader 3 feet below the 
 pit bottom. At the end of a hundred and eight hours from its first entering the clay, the drum 
 had sunk 22 feet. Here it began to stick, and we were compelled to weight it. We constructed 
 a scaffold near the bottom of the drum, with a 6-feet square hole in the centre, leaving room enough 
 between the scaffold and the bottom of the pit for the men to work in. Bricks were then built upon 
 this scaffold. On taking out a little more sand, the drum began to move, and sank 2 feet 2 inches in 
 12 hours, passing through the sand on the rise side of the pit, and entering a gravelly or stony marl. 
 We again added weight, and ultimately forced it 3 feet through the marl, until it lodged upon 
 brown rock on the higher side. The drum had thus run 27 feet from the commencement. 
 
 " The most difficult part of the operation now presented itself. The dip was found to be very 
 
SHAFT-SINKING. 263 
 
 severe, and while the drum on the one side rested on brown rock, rendering it quite impossible to 
 force it any farther, on the lower side of the pit the leader had not entered the clay more than 6 or 
 8 inches. On attempting to remove the clay, a rush of sand and water took place, which speedily 
 drove us out of the pit. In order to overcome this difiSculty, we took a number of piles h, 6 feet long, 
 6 inches wide, and 3 inches thick, made very sharp at the point, and drove them longitudinally into 
 the side of the pit, close together, under the leader, and as far round the pit as could be done. Over 
 these were driven circle wedges m of 1-inch deal, and about 1 foot wide. These kept back the sand 
 suflSciently to enable us to bare the rock and get in a few segments on the deep side of the pit, bolted 
 to the lowest course of the drum. "We then took out the rock so as to allow of this course being 
 completed round the pit ; and having sunk a couple of feet, we bolted another course to the last one. 
 We now felt perfectly secure, and went on sinking and seeking a suitable place for a wedging ring. 
 This we found in a close brown linsey, at a distance of 1 3| yards below the last segments. Here we 
 laid a wedging ring o, and brought up tubbing till we joined that forming the drum, taking the pre- 
 caution of placing an escape pipe in the closing course. Tubbing was also placed upon the top of 
 the drum until the surface-feeders were outset, when the whole was wedged. As the shaft is 
 intended for an up-cast, we have since lined the tubbing with brickwork, as shown in the lower part 
 of Fig. 427." 
 
 In Germany and in Belgium, a method of sinking through quicksands is adopted very similar in 
 character to that of the drum used in England. In this method, a cylinder of masonry is substituted 
 for the wood or iron of the drum, and the masonry is made to rest upon wooden curbs, the bottom 
 one of which is furnished with an iron leader, to enable it to cut its way through the sand. The 
 following description of this cutting curb and walling is given by M. Ponson, in his work on ' Coal 
 Mining in Belgium.' It may be remarked that a similar method of sinking a shaft was adopted by 
 Brunei in excavating the Thames Tunnel : 
 
 After having made secure, by means of sheet-piling, a square excavation abed. Figs. 431 and 
 432, from 6 to 10 feet deep, and sufficiently large to allow the workmen space in which to carry on 
 the work which they have to execute, the sinking is continued of a circular form to a depth of about 
 6 feet, the diameter of the excavation being from 2 feet to 2 feet 6 inches greater than that required 
 for the shaft and its walling. This latter excavation hefc serves to facilitate the vertical descent of 
 the masonry. The sides in this case do not need to be supported, as they are only left a few hours 
 unprotected, and slips, under these conditions, are to be but little feared near the surface of the soil. 
 
 A hollow cylinder of wood A B is prepared beforehand, the base B B' of which is a platform, 
 or circular curb formed of three rings. These rings are of oak, and are from 2 to 3 inches thick. 
 They are placed one upon another, and are doweled and firmly bolted together. The upper ring 
 has an external diameter equal to that of the masonry, and a breadth equal to its thickness ; that is, 
 about 18 inches. The middle ring projects beyond the first about 2 inches, in order to leave exposed 
 an outer edge into which is cut an annular groove 2 inches deep and 1 inch broad, designed to 
 receive the ends of the planks which envelop the column of masonry. The lower ring is slightly 
 inset to receive a steeled leader, three-quarters of an inch thick and from 3 to 4 inches deep, sharp 
 on its bottom edge, and inclined outwards in such a manner that its lower edge projects about three- 
 eighths of an inch, experience having shown that this form is the most suitable for enabling the 
 cylinder to penetrate the soil. 
 
 This platform-curb, which is represented in the figure as having already descended to a certain 
 
264 MINING ENGINEEEING. 
 
 depth, is placed in the first instance at the bottom of the excavation ef, and vertical boards, 12 to 
 20 feet in length, 8 or 9 inches wide, and about 1^ inch thiek, are placed side by side, and inserted by 
 their lower ends into the annular groove in the centre curb or ring. To complete the cylinder, two 
 curbs, each formed of two rings, are introduced, the one A A' at the upper part, and the other C C at 
 the centre of the vertical boards. On the upper surface of each of these are placed horizontal cross- 
 pieces m to', about 6 inches square, by means of which the STiperposed cylinders are bound together. 
 This bollow cylinder serves to contain the masonry, and also as a centering in which to construct it ; 
 it also greatly favours the descent of the walhng by preventing the great friction which would take 
 place if the latter were in contact with the soil. 
 
 The masonry being erected, the circular space b e f c is filled with the de'bris previously 
 extracted, care being taken to guide the cylinder from the commencement of the operation and to 
 ensure its descent in a truly vertical direction. These preliminary operations having been com- 
 pleted, the apparatus is made to penetrate into the sand, by digging in the centre of the shaft 
 a cavity N, in the form of a reversed truncated cone. The sand will then generally, under 
 the pressure of the masonry, slide from under the platform and rise up in the centre of the shaft, 
 allowing the cylinder slowly to descend. If, however, it remains firm, the hole should be enlarged 
 and its form changed from that of a cone to that of a cylinder ; the soil will then offer less resistance 
 to the pressure of the masonry. If these means do not succeed, two workmen, placed back to back, 
 cut holes under the platform curb on opposite sides. Lastly, the ground beneath the leader is 
 completely cut away for a depth of 18 inches or less, care being taken not to shear one side lower 
 than the other, as this would cause the cylinder to descend obliquely. In this latter case, the whole 
 of the curbs should first be bound together, in order to strengthen the masonry and to bind it into a 
 single mass, thus preventing it from separating into two parts, of which one would descend alone, 
 whilst the upper part, retained by the pressure of the soil and the friction, would remain suspended. 
 It is for this purpose that the cross-pieces m to' are provided. These pieces are held by iron bars 
 n n, the upper ends of which pass through them and are fastened by nuts, the lower ends being bent 
 at right angles and passing under the curb below. Finally, if the weight of the masonry is 
 insufficient, the cylinder is weighted with stones, old iron, or other heavy substances, until it sinks. 
 
 When the upper part of the cylinder reaches the level of the bottom of the rectangular exca- 
 vation, it is lengthened in the following manner : The upper ends of the planks g i and h k are 
 cut off at an angle, and nailed to the lower ring of the curb, other planks g p h q, cut in the same 
 manner, are placed on the first, and nailed to the ring A A'. Two curbs are then placed, as in the 
 first length, one at the top and the other in the centre of the planks ; the cross-pieces are placed in 
 position, and fixed, the masonry is erected, the iron tie bars are inserted, and the whole again is made 
 to descend in the manner described. These operations are repeated until the solid rock, or some 
 other impermeable bed, is reached. 
 
 During the operation, the master sinker, by carefully observing the plumb-line, will immediately 
 perceive if the cylinder deviates from the vertical direction ; and as this evil, once begim, increases 
 very rapidly, he will have to apply an immediate remedy. 
 
 The causes of the oblique descent of the cylinders are often a slight slip, or a more rapid fall of 
 the soil on one side than the other ; sometimes it may be attributed to an unequal pressure, caused 
 by an inclined stratification, or by encountering a quartzose pebble, &c. It is in the first few yards 
 of the excavation that these accidents are met with most frequently. In any of these cases, the 
 
SHAFT-SINKING. 265 
 
 miner rapidly cuts away the soil on the side opposite to the slip, and props the side of the wall 
 which has a tendency to advance too fast. He also suspends the whole by means of iron rods, the 
 lower ends of which are furnished with broad straps, to pass under the platform curb, the upper 
 ends terminating in long screws, which pass through balks of timber, placed across the mouth of the 
 shaft. By means of these screws, the masonry may be held in position, or dropped at pleasure. 
 Eopes or chains are also employed, and fastened by one end to stakes, firmly driven into the ground, 
 the other end being suspended in the shaft, and fastened to the cylinder. These arrangements also 
 serve to prevent the too rapid, although vertical, descent of the whole. 
 
 It is always prudent to bore frequently under the platform curb, in order to discover any pebbles 
 that may exist, as at Gr, Fig. 431, as these would either blunt the cutting edge of the leader, or cause 
 the cylinder to incline to one side. When this circumstance happens, the walling will have to be 
 supported. In order to do this, the miner places the cross bearers n, and under them the shores or 
 props 0, which are prevented from sinking into the earth by having their feet placed upon the frame 
 V, which rests upon the soil. Then he excavates all round and under the stone which forms the 
 obstacle, and removes it. If a bed of clay were met with, interstratified with the alluvial sands, the 
 same method of procedure would have to be adopted. 
 
 In the Anzin coal district of France, beds of quicksands, locally known as " torrents," are met 
 with below the chalk marl, at considerable depths from the surface ; generally from 70 to 80 yards. 
 The method of passing through these beds usually adopted in that locality is the following simple 
 one : "When the excavation has been walled down to near the quicksand bed, a wooden curb, of the 
 same diameter as the shaft, is wedged against the rock beneath the walling. The use of this curb is 
 to afford a point of support against which screws may be set during subsequent operations. Besides 
 the wedging, two bearers are placed across the shaft above the curb, and firmly fixed into the rock, to 
 prevent the curb from being forced up by the pressure to be brought against its lower side. An 
 oak curb, of the dimensions of those used for tubbing, is then laid upon the sand, at the bottom of 
 the excavation, and beneath the wedged curb. This oak curb is provided with a cutting edge, by 
 beveling the under side, that is, the outer face is made twice the depth of the inner face. Around 
 the outside of the curb, an iron plate is screwed to form a leader, the heads of the screws being 
 countersunk, to avoid projections on the outside, and the lower edge of the plate being allowed to 
 extend an inch beyond the wood. The segments of the curb are joined by tenon and mortise, and 
 the joints are strengthened by iron straps. Pressure screws, to be applied after the manner of a 
 lifting jack, 4 inches in diameter, and from 8 feet to 10 feet in length, are, then set upon the cutting 
 curb, and made to abut against the wedged curb placed above for that purpose. When the cutting 
 curb has been got perfectly level, and the screws have been tightened, the former is pressed down, 
 by turning each of the latter about one-third of a revolution in succession. As soon as the sand 
 appears behind the descending curb, and on a level with its upper side, means are taken to prevent 
 it from flowing over into the excavation, by driving in pieces of fir sheathing, sometimes preceded 
 by straw bands. The jack screws are then removed, and a second tubbing curb, of ordinary con- 
 struction, is laid upon the first, and bound to it by means of vertical iron straps, nailed on 
 simultaneously at several equidistant points. The screws are then replaced, and the tubbing is 
 again forced down, until the second curb is on a level with the sand. A third curb is then placed 
 upon the second, and strapped to it in the manner described ; the sand displaced by the curb is 
 removed, and the three are again forced down. These operations are repeated, until the lowest, or 
 
 2 M 
 
266 MINING ENGINEEEING. 
 
 cutting curb, has entered the clay beneath, when the shaft, throughout the length occupied by the sand 
 bed, will have been securely tubbed. Great care is needed to prevent the tubbing from deviating 
 from the vertical during the descent, and to facilitate its even motion. Pebbles are picked out from 
 beneath the cutting edge by means of tongs or other suitable tools. When the clay has been 
 reached, the sinking is carried on in the usual manner, until a foundation for a wedging curb is met 
 with, upon which the wood tubbing is carried up to the cutting curb. The beveled edge of the 
 latter, with its iron leader, is then cut away in portions, leaving its under side level, and a curb of 
 suitable thickness is inserted, to join and complete the tubbing. 
 
 Another method of sinking through the upper water beds of this district merits attention ; this 
 method partakes of the character of the preceding, and of that of piling. The excavation having 
 been begun of a sufficient diameter to allow of the subsequent necessary reductions, is carried down 
 till the water is met with, when the bottom is levelled, to receive a wooden curb. This curb, which 
 is generally polygonal in form, is 4 inches in breadth, and 12 inches in depth, and it is strengthened 
 at each of its angles with iron straps. Behind this curb, piles are set, and driven down vertically 
 side by side, so as to form a close joint. These piles are from 6 feet to 7 feet in length, 4 inches 
 broad, and 1 inch thick, and they are first driven down about half their length. The sand or marl 
 is then removed to a depth of 1 2 inches, which is equal to the depth of the curb. A second and 
 similar curb is laid upon the first, and the two are driven down, by means of mauls, to the bottom 
 of the excavation. The earth is again removed to a depth of 12 inches, a third curb is laid upon 
 the second, and the whole are driven down with the maul, as before. During these operations, the 
 piles are kept in advance of the bottom curb. If the curbs become fixed by the pressure against 
 them before the foot of the piles is reached, the remainder are put in from below. When a tubbing 
 of curbs has been put in, in this manner, to nearly the length of the piles, a curb of the same sectional 
 dimensions, but of 10 inches less external diameter, is laid within those already fixed, and on a level 
 with the lowest ; and a second series of piles is driven in between the inner and the outer curb. 
 These piles are not driven in to their full length, but are left to stand out about 12 inches, so that 
 they may be nailed to the first series of curbs, should the forcing down of the second carry the piles 
 with it. This second series of curbs is sunk in the same manner as the first^ and the same operations 
 are repeated for all the subsequent series needed. This method has been successfully adopted in 
 numerous instances. 
 
 The foregoing are the methods adopted in different localities for sinking through water-bearing 
 strata. Of course, each of these is subject to modifications, and some modification will always be 
 necessary to adapt the system to the exigencies of the case. In shaft-sinking, where the conditions 
 are ever changing, much must necessarily be left to the judgment and the invention of the engineer 
 in charge, who will have to adapt the means at his disposal to the end to be attained in a manner 
 that is most in accordance with the circumstances in which he finds himself placed. But to do 
 this successfully, he must at least possess a knowledge of the various methods practised under 
 different conditions in different localities, so as to be able to comUne and to modify them according 
 to the requirements of the case in hand. 
 
 The Kind-Chaudron System. — Within the last few years, a system of sinking shafts through 
 water-bearing strata has been introduced, and adopted with marked success on the Continent. 
 This, which is known as the Kind-Chaudron system, consists in boring out the shaft from surface 
 by means of apparatus similar in character to that used for prospective borings. A detailed descrip- 
 
SHAFT-SINKING. 267 
 
 tion of the Kind-Claaudron system was given by E. Bainbridge, in a paper read before the 
 Institution of Civil Engineers, in 1871 ; and the system vi^as again described later by Warrington 
 W. Smyth, in a paper contributed to the North of England Institute of Mining Engineers. From 
 the latter paper we extract the following : 
 
 " In the year 1849 it was proposed by the eminent master borer, Kind, to bore out pits by 
 apparatus placed at the surface of the ground, and of the same character as that employed for 
 Artesian wells ; to excavatet the rock without removing any of the water, and on arriving at firm 
 ground below the watery measures, to lower down a suitable lining or tubbing. Several shafts 
 were during the next few years sunk by him on this principle, but it did not appear on these first 
 trials that any notable economy was obtained, or that the lining could be so introduced as securely 
 to tub back the water. At the London International Exhibition, in 1862, M. Chaudron, a Belgian 
 engineer, who had joined Mr. Kind in bringing forward an improved process, exhibited a segment in full 
 size of a kind of gland, boite a mousse, or moss-box, which he had devised for the purpose of forming 
 an effectual water-tight joint in the place of the ordinary wedging curb ; and the details which he 
 published in the * Annales des Travaux Publiques de Belgique,' of several pits sunk by this method, 
 seemed to give assurance of its importance. In Paris, in 1867, the colliery company of the Hopital 
 St. Avoid, in the department of the Moselle, exhibited the actual tools with which Messrs. Kind 
 and Chaudron had just succeeded in boring for them two large shafts, one of them about 14 feet in 
 diameter, and fixing under water a thoroughly water-tight tubbing, on foundations at depths of 521 
 and 523 feet from the surface. 
 
 " The coal measures were here overlain by several hundred feet in thickness of the very watery 
 strata of the Grres de Vosges, a part of the new red sandstone series. Various attempts made by 
 different mining companies to sink to the coal measures had already cost, up to the year 1858, no less 
 than 840,000^., and as the ground was confessedly of a very difficult character, and these two pits 
 were put down for a sum not more than one-third of what it was estimated they would have cost by 
 the ordinary method, it was evident that a remarkable step in advance had been taken, and that the 
 combined method of these two engineers now stood on a firm and practical footing. 
 
 " Having learned that a sinking by the new system was in progress in Belgium, in a district that 
 offers peculiar diflSeulties on account of the water-bearing strata to be passed through, the author 
 went over and inspected the process, and informed himself concerning the details of the operations. 
 
 " The coal-field between Mons and Charleroi is overlain uniformly and somewhat irregularly by 
 strata of the cretaceous and tertiary periods, which thin out and allow the coal measures to crop to 
 the surface at Bois-le-duc, an extensive and ancient work east of the station of La Louviere, but 
 which become thicker to the west and south of that station, till they attain to several hundred feet 
 over a large area ; and at Grhlin, near Mons, have been proved by borings to be 230 metres, or 
 754 feet thick. These beds consist in great part of sands, marls, and chalk, with occasional bands of 
 massive flints and loose or running sand ; and with water generally extremely abundant until the 
 excavations reach certain of the more solid lower beds of the cretaceous series, the so-called dieves, 
 or the taurtia, or have penetrated to the coal measures themselves, when scarcely any addition to the 
 water is expected. 
 
 " The pits now in process of sinking a niveau plein, at ' fall level,' or under water, in the 
 concession of Maurage, are situate in a virgin district on the north rise of the basin, and a short 
 mile distant on the west from the railway station of Bracquegnies. At this latter place, the older 
 
 2 M 2 
 
268 MINING ENGINEERING. 
 
 pits, called St. Alexandre, were completed in 1847, after enormous difficulties due to water and 
 quicksands, which were overcome by the perseverance of M. Delaroche ; whilst the new plant, called 
 St. Alphonse, farther south, was fortunately commenced at a much more favourable spot, but never- 
 theless cost a sum of 2,000,000 francs, or 80,000^., inclusive of plant. 
 
 " At Maurage, the thickness of the overlying aqueous beds is known from common borings to be 
 miich greater, and the foundation of the iron tubbing of the shafts is fixed at 194 metres, or 636 feet, 
 below the surface. A branch line of private rails leads to the pit, which, with all the apparatus 
 connected with them, are, as usual in Belgium, under cover. The principal feature of the exterior 
 consists of two wooden towers, about 60 feet high, containing the pulley frames for the boring 
 operations ; and between the two come in the engines, the smithy, and the office ; whilst closely 
 adjoining is the fast-increasing store of tubbing rings, being proved as they are delivered from the 
 founders, in readiness for dropping when the work is a little farther advanced. 
 
 " At each shaft the men employed in the sinking, four or five in number, stand on a working 
 floor 5 metres below the surface, the shaft being here 5 • 75 metres, or close on 1 9 feet, in diameter, 
 but being narrowed immediately below to 4*70 metres, or 15 '4 feet, of which size, and protected 
 by bricking, the shaft is carried down to the water-level, about 30 metres. Below that point it 
 stands full of water, unlined, and is, in fact, a colossal bore-hole. 
 
 " The excavation of these large pits of 14 feet diameter is effected by at least two successive 
 stages. At first, a cylindrical hole of about 4 or 5 feet diameter is bored, and this is usually kept at 
 the least 10 metres farther advanced than the wide or full-sized pit to which it is enlarged by the 
 second or third operation. 
 
 " The cutting of the ground for excavation is by the same kind of means in both stages — the 
 central and the enlarging, whilst the removal of the de'bris is different. In each case the cutting- 
 tool, trepan. Figs. 433 to 439, consists essentially of a horizontal wrought-iron bar, to the under 
 surface of which are attached steeled teeth, so placed that as the bar is rotated round the central axis 
 of the pit, each tooth, in falling with the bar through the requisite length of the stroke, generally a 
 quarter to half a metre, cuts for itself an annular portion of the bottom of the shaft. The tre'pans, 
 both large and small, for, of course, they are worked only at separate times, are lifted and 
 turned by the same rods, these latter being of pine, 20 centimetres square and 18 metres long, and 
 connected as in common boring by male and female screws. Care is taken to preserve the whole 
 strength of the pole ; and the elasticity of the wood, with its buoyancy in the water, are found, as in 
 most deep borings in America and Europe, to give great advantages over iron rods. 
 
 " The lift is effected by means of a simple lever placed at the level of the surface of the ground, 
 to one end of which the rods are attached by a strong flat chain, whilst near the other end it has a 
 direct connection with the piston-rod of a steam cylinder of 39| inches in diameter, and 40 inches 
 length of stroke, placed below the beam ; so that the simple admission of steam above the piston 
 depresses that end and raises the rods and cutter, which then fall by their own weio-ht. This 
 striking beam is 23 feet long, 11 feet on the side of the borer, 12 feet on the side of the engine; it 
 is formed of two superposed logs of wood, the upper one of pine, and strengthened on each side by a 
 stout plate of iron. Beneath the suspension chain is a lengthening screw, and below that a very 
 strong swivelj by means of which the rotating movement is given to the rods and cutter. The 
 upper piece of rod has, as usual in boring, eyes for the insertion of cross-bars, by which the actual 
 "turn is given at each stroke by the workman standing on the wooden flap doors which close all the 
 
SHAFT-SINKING. 269 
 
 shaft, except the central rod-hole at the level of the working floor. The smaller trepan, Figs. 436 
 to 439, is differently constructed, according to the nature of the ground it is intended to cut. When 
 engaged with soft material, the lame or bar to which the teeth are attached is suspended by a fork of 
 wrought iron ; but when hard rock has to be encountered, such as the massive flint at the time of our 
 visit, it is forged in a single piece, and weighs 8000 kilogrammes, or about 8 tons. The working 
 drawings, kindly supplied to us by M. Chaudron, will sufficiently show the details of construction of 
 this powerful instrument, which is capable of advancing, in ordinary ground, 2^ metres, or above 
 8 feet per day. The teeth, which are well steeled, fit into sockets in the lame or main bar, and are 
 additionally secured by a pin, which is readily driven out when the teeth have to be sharpened or 
 renewed. 
 
 " When the cutter has done its work for some hours, usually at the rate of nine to ten strokes per 
 minute, sometimes at about twenty, it is raised by bringing into action a small capstan engine, with 
 a flat hempen rope of 14 j inches wide by 2f inches thick, and the successive unscrewing of the rods 
 in the usual manner. The hole is then cleared by means of a shell, sludger, or pump, cuiller, a sheet 
 iron cylinder of some 6 feet in length, with two valves in the bottom, which is lowered and raised by 
 the rods. 
 
 " The large cutter or trepan. Figs. 433 to 435, which weighs in all 16 tons, is similarly formed of 
 a lame or bar of wrought iron, having teeth attached for that portion of its length which exceeds the 
 diameter of the small pit ; and it is guided below by a cradle of iron bars, which fit loosely within 
 that smaller diameter. The teeth are so formed and set that they always cut the bottom of the shaft 
 into a sloping surface, so as to allow the fragments to roll into the smaller pit, and there they are 
 caught in a sheet-iron bucket which is previously lowered into it. The rate of progress, in 
 ordinary ground, when all is going well, is about 1 metre, or 3 • 28 feet, per day, but in hard rock 
 this is reduced to a quarter of that amount. 
 
 " In order to obviate the tremendous vibration which would be imparted to the rods by 
 implements of this unusual weight, a special joint is necessary, in order to detach to a certain extent, 
 from the mere suspension rods, the heavy rod and the cutting tool, which together are 36 feet long. 
 The ingenious ' free-falling ' apparatus, devised by Kind, and found so applicable in bore-holes of 
 moderate diameter, was proved in former experiments to be unsuited to these great dimensions, and 
 a slide piece, glissiere, of great strength is now always applied, in a manner analogous to the " jars " 
 commonly used in the oil borings of America. 
 
 " The vertical position of the boring rods throughout the sinking process is additionally secured 
 by guides attached to the upper part of the instrument. In the smaller trepan, these are formed of 
 two strong iron bars set at right angles, and having teeth at their extremity, which slightly enlarge, 
 and at the same time smooth down the sides of the bore-hole. With the large trepan, one cross- 
 piece only is rigid ; the other one at right angles to it is hinged on both sides of the main rod in 
 such a way as to be lowered or raised during the shifting of tools, through a comparatively narrow 
 opening in the working floor. It is afterwards, by aid of ropes wound on small windlasses, brought 
 into position when the tool reaches its proper position for working. The guide then forms a cross, 
 through the central opening of which the rod of the boring tool slides freely up and down. 
 
 " The most remarkable part of the operation is the fixing of the tubbing, Fig. 440, without the 
 use of pumping engines, in such a manner that it shall securely dam back the water in the measures 
 sunk through. The lowermost ring of the tubbing is, like all the upper portion, cast in a single piece. 
 
270 MINING ENGINEEKING. 
 
 Its bottom flange A, which comes to rest on the bed or seat cut in wafer-tight ground, is turned 
 outward, its upper flange B inward. Upon the lower flange and all round the ring a wall of well- 
 picked moss C is packed tightly against it, and secured in its place by a net placed at the back of it. 
 To aid in the forcing of the moss against the side of the shaft, small shee1>iron springs D D are 
 placed above and below, as seen in the drawing, which have the effect of giving the pressure a 
 definite direction. On the moss cushion rests, by a flange also turned outward, the next ring B, large 
 enough to slide down outside the bottom piece, as soon as the moss is pressed down by the weight, 
 and upon this sliding piece the ordinary rings of tubbing are built. Each flange is planed, and 
 between them a ring of sheet lead of one-eighth of an inch thick is laid, which, after screwing up by 
 the bolts, is beaten on both sides with hammer and chisel. The tubbing is of extra thickness, and 
 each ring, generally about 4y to 5 feet high, is tested on the spot by hydraulic apparatus. The 
 lowermost simple ring is 2| inches thick, and weighs llf tons. The upper ones are made gradually 
 lighter, but the total weight of the tubbing to be lowered in each shaft is no less than 800 tons. 
 In order to facilitate the gradual lowering of this enormous weight, by means of the six rods 
 and screws used for this purpose, a diaphragm or false bottom P is attached by screw bolts near 
 the bottom of the tubbing, which causes it to float on the water. A centre equilibrium tube Gr 
 passes up the shaft, and through cocks, placed at intervals, allows of water being poured into 
 the middle of the tubbing in such measure as may help to aid its descent. In this way they 
 contrive never to have a greater weight than 40,000 kilogrammes, or 40 tons resting on the 
 suspension rods. 
 
 " When at length the moss-box, hanging by light rods H from the flange of an upper ring, 
 comes to occupy its position on the seat or bed, the weight of the tubbing above begins to bear on 
 the moss and squeezes it down and against the sides in such wise as to form a thoroughly 
 water-tight joint. 
 
 " For additional security, the annular space between the rings and sides of the pit is filled, by 
 means of spoons discharged by pistons, with beton or concrete, which is allowed to consolidate 
 before the water is drawn out of the interior of the pit. Much, of course, depends on the perfection 
 with which the seat of the moss-box is cut and smoothed ; and for the purpose of ensuring its 
 proper condition, a gigantic pair of pincers, grapin, I, with arms on the principle of a lazy-tongs, is 
 lowered with and underneath the whole of the tubbing with a rod passing up through the central 
 or equilibrium pipe. The ends of this tool can, by working the rod up and down, be made to expand 
 to the full size of the shaft, and brought together so closely as to pick up fragments of stone or iron 
 which may be lying on the bed of the shaft, and then in its contracted form it may be passed out of 
 the way into the smaller central shaft. 
 
 " The water being, after the setting of the be'ton, pumped out of the pit, the false bottom is 
 removed by unscrewing the bolts which attach it to a flange, the moss-box foundation is examined ; 
 and to make everything thoroughly safe, a lower seating is cut a few feet deeper, a wedging curb put 
 in by hand in segments, and a length or two of tubbing built up to the moss-box, and securely 
 wedged against it. The shaft is then free from water and ready for further sinking by the ordinary 
 methods." 
 
 Journal of the Sinking. — It is important that a register be kept of everything of importance that 
 occurs during the sinking of a shaft. In this register or journal, an intelligible and a full description 
 of the strata passed through should be given, so that the " section " thus recorded may be of use sub- 
 
SHAFT-SINKING. 
 
 271 
 
 sequently. The best manner of describing strata was pointed out and explained in the chapter 
 devoted to boring. But it is not suflScient to illustrate the section only. The journal should be 
 a record of all the important details of the work of sinking, and any observations that may subse- 
 quently possess a practical value should find an entry in its columns. If this were generally done, 
 the published sections or records of sinkings would have a value which at present they seldom 
 possess, and by affording, at the moment when required, precise information concerning past 
 experience, such records would tend in no inconsiderable degree to lessen the hazardous and costly 
 nature of sinking operations. The following arrangement of the page may be taken as a guide in 
 preparing the journal, though it is by no means intended to confine the information to the subjects 
 here indicated. The wider and more detailed the information, the greater will be the value of the 
 record. That which we have suggested should be considered as indispensable in every case; more 
 may profitably be added : 
 
 JOUENAL. 
 
 SinMng executed at 
 
 Begun 
 
 in the County of 
 May 1, 1874. 
 
 
 
 
 On the Estate o£ 
 
 Completed June 5, 1875. 
 
 Date. 
 
 Description 
 Strata. 
 
 No. of n,™l,i„ 
 
 Thick- 
 ness. 
 
 Depth 
 
 from 
 
 Suiface, 
 
 Angle 
 
 of 
 Dip. 
 
 Time 
 
 occupied in 
 
 passing through. 
 
 Quantity of 
 
 Water 
 met with. 
 
 Nature and ' Nature and 
 Dimensions of the Dimensions of the Eemarks 
 timbering used. Shaft Lining. 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Cost, and Arrangements with Contractors. — There is probably no kind of work that varies so 
 widely in cost as shaft-sinking. The conditions under which the work has to be executed are so liable 
 to change from one spot to another, even in the same locality, that no estimate, not even an 
 approximate one, can be given that shall be generally applicable. But a rough approximation may 
 be arrived at of the cost of the important operations of timbering, walling, tubbing, and bratticing, 
 by taking an average from a number of sinkings, from 13 feet to 15 feet diameter, executed under 
 different conditions. Thus obtained, the cost of the wooden curbing generally adopted in the north 
 of England will be from Al. 10s. to bl. a yard; and that of the backcasing commonly employed in 
 the Lancashire district will be about the same. The cost of the permanent brick- walling will be from 
 5^. to Ql. a yard, and that of stone walling from 7^. to 8/. a yard.. The cost of cast-iron tubbing is 
 more difficult to arrive at, by reason of the greater variations that occur in the price of the material ; 
 but taking a general average, it may be stated roughly as varying between 30?. and 40Z. a yard. 
 The cost of the permanent bratticing will be from 21. to 21. 10s. a yard. These prices include all 
 labour of preparing the materials, and of putting them into the shaft. 
 
 Sinking is usually done by contract, the contractor agreeing to provide all labour and material, 
 or a certain portion of the material, and to sink and line the shaft for a fixed price per yard or per 
 fathom. This price will be determined according to the evidence of the nature of the strata to be 
 passed through, afforded by boring or by any other available and trustworthy source. The cost of 
 sinking through water-bearing strata is so uncertain that this portion of the sinking will not be 
 undertaken by contract, but will be done by day work, according to a scale of charges previously 
 
272 MINING ENGINEEEING. 
 
 agreed upon. Generally, the sinking to the stone head wiJ] form a separate contract. In drawing up the 
 terms of a contract, the work to he performed should be precisely indicated and clearly described, so as 
 to avoid causes of subsequent disputes. The chief points to be clearly defined are, the diameter of 
 the shaft when finished ; its depth from surface to floor of seam, and to bottom of sump ; the nature 
 of the lining, and the dimensions and quality of the materials of which it is to be composed ; the 
 supply of all the material and machinery required in sinking, — if a portion is to be supplied by 
 the owner, such should be clearly stated ; the arrangements to be adopted when large quantities of 
 water are met with ; the nature of the bratticing to be put in ; the number of sinkers to be employed 
 in the shaft ; and the number of hours in the week during which operations may be suspended. In 
 addition to this, there will be required the customary clauses respecting the periodical measurement 
 of the work, and the control to be exercised by the engineer or viewer. It will also be well 
 to require the contractor to furnish the engineer, as the sinking proceeds, with proper samples of all 
 the beds passed through. 
 
 Slmft Fittings. — When the shaft has been sunk to the required depth, and lined throughout, it 
 remains to prepare it for the various purposes which it is intended to serve. The permanent 
 brattice must be put in, and the shaft divided into compartments for the work of winding and 
 pumping. Figs. 441 to 445 show the various ways of dividing a shaft for these purposes. The 
 fitting up of each of these compartments will be treated of in the chapters devoted to winding and 
 drainage. In these chapters also, the construction of the head-gear will be described and illustrated. 
 it will be necessary to fence the shaft mouth, in compliance with the law on this matter, to prevent 
 accidents, and the laying out of the surface immediately around the mouth of the shaft, or the pit- 
 bank, as it is technically called, will demand attention. These matters will be fully considered in the 
 chapter devoted to surface works. The bottom of the shaft, which part is known as the pit-eye, must 
 be laid out to receive the loaded tubs as they arrive from the workings, and to despatch the empty 
 ones to the working faces. As all the roadways of the mine will converge here, it is of the highest 
 importance that this part be laid out in a convenient manner. The roadways, or " levels," enter the 
 shaft at the bottom by means of brick arching run into the shaft walling ; and as the necessity for 
 great strength here is imperative, great caution and care will be required in designing and executing 
 this portion of the work. The way in which the levels lead into the shaft will be understood 
 from the drawings which illustrate the next chapter. The bottom of the shaft is laid with iron 
 plates, called " tram plates," to facilitate the motion of the tubs ; and the tramways upon which the 
 tubs are run from the workings lead up to this plated floor. If the shaft is to be used for pumping 
 the water from the mine, the excavation is continued down below the floor of the seam to form a 
 sump, over which a wooden flooring covered with tram plates is laid. When the water is to be 
 drawn in tubs, a portion of this flooring is made removable, so that the tubs may dip during the 
 night, or some other convenient time. When pumps are used, the suction pipe of the lower lift is 
 dropped into this sump. As it is desirable that this sump should be capable of containing some 
 hours' drainage, its depth should not be less than 20 feet ; in some cases the depth required will be 
 greater. With a diameter of 13 feet, and a depth of 20 feet, the sump will be capable of containing 
 16,587 gallons of water, a quantity considerably in excess of the daily drainage of many mines. In 
 order to be able to store up the drainage of several days, in case of an accident to the pumps, another 
 reservoir of large capacity is made on the course of the water flowing towards the sump ; this 
 reservoir is called a " standage." Means must, of course, be provided tor placing the standa'ge in 
 
SHAFT-SINKING. 273 
 
 communication witli tlie sump. The staudage as well as the sump should be lined with brick, as 
 prolonged contact with water promotes the disintegration and the fall of the rock. 
 
 While the sinking of the shaft and the laying out of the pit-eye are in course of execution, the 
 surface work will be pushed on, so that the engines may be ready for winding and pumping when 
 the opening out of the underground workings is begun. 
 
 Examples of Sinking. — In concluding the present chapter, attention is invited to the two 
 following examples of sinking, executed as long ago as the years 1829 and 1838. These examples, 
 which are quoted from Dunn's * Winning and Working of Collieries,' are specially interesting, and 
 that from several points of view. The former was the first application of metal tubbing in Scotland, 
 and one of the earliest examples of the use of that kind of lining ; and the second is conspicuous, as 
 being the most difficult and the most costly on record. Both of these sinkings were executed 
 according to the designs, and under the direction of experienced and skilful engineers ; and they, 
 therefore, exhibit the most approved methods of dealing with the difficulties encountered. More- 
 over, they are interesting and instructive, as showing how little the means employed and the 
 methods of procedure have changed during the last fifty years : 
 
 " The Preston Grange Pit, East Lothian, remarkable as being the first example of metal 
 tubbing in Scotland, was sunk in the year 1829. The main shaft was 10 feet in diameter; 4^ feet 
 being bratticed off for ventilation and the pumping apparatus ; and the sinking was commanded by 
 a pumping engine, capable of raising 400 gallons of water per minute ; also with an associate 
 winding engine. Grins, crabs, five-fold ropes, and sheaves, and other apparatus for hanging and 
 working the pumps were duly provided. 
 
 " No sooner had the sinking arrived at the depth of 7 fathoms, than a feeder of water, of 200 
 gallons per minute, was met with, which required to be tubbed off, and which was accordingly done, 
 by affixing wedging curbs,, after the manner previously described, with a suitable quantity of 
 tubbing, in segments 4 feet long by 2 feet high, and f inch thick ; the whole being outset by walling. 
 As was expected, the water, which had forsaken the neighbouring wells, again returned to its 
 channel, and discharged itself at the surface. 
 
 " The sinking was then resumed ; and at a depth of 22 fathoms the shaft intersected the fissure 
 of a ' trouble,' which gave out a new feeder, consisting of 300 gallons per minute. It was not till the 
 shaft had reached the depth of 28 fathoms that a suitable water-tight stone could be selected, 
 wherein to fix the two wedging curbs for another tub ; but as there was reason to believe that this 
 water also would rise to the surface level, it became necessary either to join it to the other tub, or to 
 affix it, top and bottom, in water-tight stone, by means of wedging curbs, which latter mode was 
 adopted, the shaft being first widened, to receive the tub and wedging curbs, so as to preserve an 
 uniform finished size. The curb which surmounted the tub was held firm by a succession of wooden 
 stays against the superior rock ; after which the wedging was completed, and all this water was 
 stopped, except a few small streamlets, which were collected into boxes and conveyed down the 
 shaft. On account of the additional pressure, the thickness of this tub was increased to half an 
 inch. 
 
 " The sinking was then resumed with little interruption till, at the depth of 36 fathoms, a 
 similar feeder demanded the application of a third tub, 4 fathoms in length. 
 
 " At this period, the sinking set had been hung upon ground ropes ; but a thin seam of coal 
 caused it to be converted into a standing set, 31 fathoms long, which was done by excavating a space 
 
 2 N 
 
274 
 
 MINING ENGINEEEING. 
 
 for the reception of a cistern, fixed upon strong buntons across the shaft. At the same time the 
 hitherto common pump was replaced by a forcing set, with ram ; the barrel being bestrode by a pair 
 of iron rods, for the working of the intended hanging pumps underneath the forcing barrel. 
 
 " The second column of pumps now became the hanging set, and the sinking proceeded to the 
 depth of 44 fathoms, where 4\ fathoms of tubbing were again required, to stop back water to the 
 extent of 350 gallons per minute. These segments were increased in thickness to five-eighths and six- 
 eighths, with still deeper flanges. 
 
 " Here a new difficulty occurred from a considerable discharge of carbonic acid gas with the 
 water, which affected the eyesight of the sinkers ; and it so operated against the tightening of 
 the tub, that at one time it was feared that air-pipes to the surface would have been necessary to 
 discharge the gas, 
 
 " As all the waters were derived from an origin considerably above the level of the shaft top, 
 the pressure upon the last-mentioned tub, at 264 feet perpendicular, exceeded 120 lb. upon every 
 square inch of its surface ; and as the surface contained an area of 768 square feet, it sustained a 
 pressure of 6000 tons. 
 
 " Little additional water was met with below this point ; but at the depth of 55 fathoms the 
 second column of pumps was converted into a fixed set, by establishing another cistern, and the third 
 column was attached in its turn, as the sinking set. At the end of two years the coal was sunk 
 through 70 fathoms in depth, at which period the total water did not exceed 50 gallons per minute, 
 or one-eighth part of the engine power. 
 
 TABLE OF THE DIPrERENT TUBS AND THEIE EFFECTS. 
 
 Ist Tub 
 2nd „ 
 3rd „ 
 4th „ 
 
 Weight 
 per Segment. 
 
 cwt. qr. lb. 
 
 2 
 
 2 2 
 
 2 3 
 
 3 2 
 
 Weight 
 
 per 
 Fathom. 
 
 cwt. 
 
 48 
 60 
 66 
 80 
 
 Length. 
 
 fathoms. 
 8 
 
 64 
 4 
 4* 
 
 23 
 
 Quantity of 
 
 Water per Minute 
 
 stopped. 
 
 gal. 
 
 200 
 
 300 
 
 300 
 
 350 
 
 1150 
 
 Depth of 
 Bottom of Tub 
 from Surface. 
 
 fathoms. 
 
 9 
 
 28 
 
 36 
 
 44 
 
 The Dawdon Winning, in the Hetton district of the county of Durham, remarkable as being the 
 most arduous and costly on record, was commenced in the year 1838. 
 
 " The South Hetton Company, having considerably increased their tract of coal under lease, 
 decided on the propriety of also increasing their powers of working. A site for a new winning 
 was fixed upon, and the necessary borings commenced, to ascertain the thickness of the sand under- 
 lying the magnesian limestone. This having been accomplished, the ground was broken for the 
 first shaft on the 19th February, 1838. Two months afterwards another shaft was begun, and 
 they were carried forward simultaneously, both pits being 14 feet in diameter. 
 
 " The upper stratification consisted of : 
 
 Soil, gravel, and strong blue clay .. .. ., .. .. ., 
 
 Soft marl, mixed with beds of craggy limestone 
 
 Strong brown limestone 
 
 Blue metal, soft 
 
 Quicksand 
 
 Total 
 
 fa. 
 
 ft. 
 
 in. 
 
 7 
 
 4 
 
 9 
 
 48 
 
 4 
 
 9 
 
 19 
 
 
 
 
 
 
 
 2 
 
 6 
 
 5 
 
 4 
 
 6 
 
 81 
 
 4 
 
 6 
 
SHAFT-SINKING. 275 
 
 " Little or no water was met with till the pits readied the depth of 32 fathoms, after which the 
 quantity gradually increased until the sand-feeders were encountered, which were successively tubbed 
 off whenever favourable foundations were met with ; so that, previous to the sand being tapped, the 
 shafts were freed from water. On the 26th June, 1839, the sand-feeders burst away from the bottom 
 of the shaft, throwing up, with gigantic force, 4 feet of strong limestone which intervened between 
 the bottom of the shaft and the top of the sand. With such violence did this eruption take place, 
 that before the capstans could heave the pumps up from the bottom they were all choked, and 
 upwards of 10 feet of sand deposited in the pit. 
 
 " The difficulties of this gigantic and critical undertaking now commenced in earnest. The 
 engine power placed on the shaft which first pierced the sand not being able to make any impression 
 upon the water, several large bore-holes were made through the bottom of the other shaft, then close 
 upon the sand, so that the united engine power might be applied. This being accomplished, every 
 nerve was strained to make the application most effective : 4678 gallons per minute were drawn to 
 bank for some time, without making any sensible impression upon the feeders, and which thus 
 effectually prevented the further progress of sinking. 
 
 " This difficult and unpromising state of things would have allayed the ardour of less adven- 
 turous speculators ; but the company were determined, cost what it might, to brave every obstacle, 
 notwithstanding the warnings and condolence of many sage persons in the trade. 
 
 " A third shaft, of greater diameter than any hitherto sunk, was commenced and furnished with 
 an unprecedented force of engine power, as applied to one shaft. This new pit was urged forward 
 with every despatch, and in six months reached the depth of 73 fathoms, being completed with 
 walling, metal tubbing, brattice, pumps, cisterns, &c. Two pumping engines and two winding 
 engines, constructed also to pump, were likewise erected upon this shaft, and were set to work 
 simultaneously with the sinking. The total amount of engine power thus brought into action was 
 as follows, viz. : 
 
 Horse-Power. 
 3 Pumping engines of 350 horse-power each .. .. .. .. .. ., .. 1050 
 
 2 Winding engines, also employed in pumping, of 130 each 
 2 „ for drawing stones, of 25 each 
 
 1 u » » 
 
 260 
 
 100 
 
 60 
 
 18 
 
 Total horse-power ., .. .. 1478 
 
 " To maintain this enormous engine power thirty-four boilers were required, and also twenty- 
 seven columns of pumps, viz. eighteen columns of 19^ inches, and nine of 16 inches diameter. 
 
 " When the necessary preparations were completed, the sand was broached in the last-mentioned 
 pit, and the operation of sinking the whole of the shafts through it was commenced. The sand, 
 although tolerably firm when dry, was found to be so disintegrated by the action of the water, that 
 it was necessary to suspend the men whilst working in it. The scouring effect of this mixture of 
 sand and water upon the buckets of the pumps as well as upon the working barrels, was found to be 
 a serious impediment to the progress of the work, the buckets being frequently ' worn off' at the end 
 of from two to four hours. The engines at this time drew 10,000 gallons per minute. Every 
 expedient which the ingenuity of the persons in charge of this difficult work could devise was put in 
 requisition. Success at length crowned their exertions, by the completion of all the shafts through 
 this formidable quicksand. 
 
 2 If 2 
 
276 MINING ENGINEEEING. 
 
 " The whole of the feeders of water were effectually stopped back by metal tubbing', of 
 from f inch to 1\ inch in thickness, and the shafts rendered perfectly dry. 
 
 " The two original pits were then sunk to the several seams of coal usually found in the district, 
 and which in this locality consist of twenty-three beds, five of which are found to be of workable 
 thickness. 
 
 " The Hutton seam, lying at the depth of 248 fathoms from the surface^ was sunk to on the 15th 
 April, 1843. 
 
 " The thicknesses of the three principal seams of coal recognized in the Wear district were found 
 here as follows, viz. : 
 
 ft. in. 
 
 The Main Coal .. .. 6 2 
 
 The Low Main Coal 4 7 
 
 The Hutton Seam .. ., .. .. „ „ .,5 " 
 
( 277 ) 
 
 CHAPTER V. 
 
 DEIVING OF LEVELS, OE NAEEOW WOEK 
 
 When the staft has been sunk to the coal, and completed for all the purposes which it is intended to 
 serve, there remains much important work to be done before coal can be extracted. To proceed at 
 once to the excavation of the mineral would be to endanger the safety of the shaft, and to create 
 serious obstacles to the subsequent working of the seam and the efficient ventilation of the working 
 places. The extent to which the preliminary operations of opening out a mine should go will be 
 determined by local conditions, and more especially by the amount of capital to be expended and the 
 limit of time allowed by commercial and other considerations. But whatever these considerations may 
 be, a certain amount of preparatory work must necessarily be performed in laying out the workings in 
 a manner suitable to the nature of the subsequent operations of extracting the coal. And it should be 
 borne in mind that the more systematically and completely this preliminary opening up of the 
 ground is performed, the more economically and safely may the extraction of the coal be effected. It 
 is an altogether false economy that leads to a curtailing of the time and expense requisite to the 
 opening out of a new colliery, or portion of a colliery, since the consequent difficulties, which can never 
 be removed subsequently, or even modified in an important degree, far more than compensate the 
 first expenditure of money, or the inconsiderable gain of time. 
 
 As the work incident to the opening out of a mine is not immediately remunerative, it is 
 generally described as " dead " work, or frequently, on account of the narrow width of the working 
 face, as compared with the ordinary working places, as " narrow " work. The excavations which 
 constitute the dead or narrow work consist of drifts, headings or roadways, called " rolley-ways," 
 " way-gates," " gate-roads," " water-gates," and " levels," driven out from the mass of coal left to 
 support the sides of the shaft and called, on that account, " shaft pillars." These levels are the 
 principal roadways, airways, and waterways of the mine ; through them all the produce of the mine 
 will have to be conveyed, and the whole of the air which is to ventilate the workings, as well as the 
 water flowing therefrom, will have to pass. It is therefore obvious that these excavations are of 
 essential importance in the economy of a mine, and that their design, execution, and maintenance 
 demand the most careful consideration and attention. The mode of laying out these pioneer 
 excavations will be in the main the same, whatever the system of working adopted may be. But 
 modification may be required to conform to the exigencies of the case, due to the angle of dip, 
 the existence of faults, or any other of the numerous circumstances that may accompany the occur- 
 rence of a seam. In the example which we shall assume for purposes of illustration, the seam will be 
 supposed to dip at a small angle, and to be free from disturbing circumstances, in order to form a 
 typical case, that shall involve a syste in its entirety. 
 
278 MINING ENGINEERING. 
 
 Shaft Pillars. — A large mass of coal must be left unwrought around the shaft, as a support, 
 which mass will be cut through only by the narrow excavations that constitute the roadways to 
 the shaft. These drifts divide the mass into detached blocks, which are called the shaft pillars. It 
 is hardly necessary to remark that these pillars are of essential importance, since they support the 
 shaft which forms the highway between the mine and the surface. It is easy to see that the 
 slightest movement in that portion of the beds through which the shaft passes must necessarily 
 be destructive to the latter ; and hence it becomes essential to the very existence of the mine to 
 provide sufficient means for preventing such a movement from taking place. In view of the 
 inevitable destruction which must result to the shaft from the yielding of the shaft pillars, it is 
 surprising that in some instances these have been laid out with dimensions utterly incapable of 
 resisting the forces brought to bear upon them, and that frequently their dimensions are reduced, for 
 economical considerations, to a limit which leaves no margin for safety. 
 
 The dimensions of the shaft pillars are determined by four conditions, namely, the depth of the 
 seam from surface ; the angle of inclination of the beds ; the strength of the coal ; and the nature of 
 the thill or floor. In no case can safety be obtained with pillars less than 35 yards square ; these 
 may, therefore, be considered as the minimum dimensions in the shallowest mines, when the other 
 conditions are favourable, say up to a depth of 150 yards. Beyond this depth the dimensions may 
 be increased by 5 yards for every 25 yards of increase; that is, the pillars of a shaft 175 yards deep 
 will be 40 yards square ; those of a shaft 200 yards deep, 45 yards, and so on. These dimensions 
 are given as sufficient, on the assumption that the other conditions are favourable. But it is evident 
 that those conditions may be such as to require an augmentation of the dimensions, as determined 
 according to the depth alone. Thus, if the strata are highly inclined, the tendency of the pillars to 
 yield is greater than when the strata are flat. The difficulty of preserving the shaft through steep 
 measures is, in Belgium, often found to be a serious one. The strength of the coal will also 
 materially affect the resistance of the pillars to compression. The difference in the strength of coal, 
 as pointed out in a previous chapter, is very considerable, and this difference must be taken into 
 account in determining the dimensions of the pillars. But perhaps the most important of these 
 determining conditions is the nature of the thill or floor of the coal seam. When this floor consists 
 of soft underclay, the pressure of the pillar upon it tends to force it to rise in the roadways between 
 the pillars. This tendency of the floor to rise between the pillars is often very observable in the 
 workings, when it is known as the " creep." Of course, the displacement of the floor in this way 
 causes the pillars to sink ; and the downward movement of the superincumbent beds is accelerated 
 by the crushing effects which take place in the pillars, by reason of the unequal strain thrown upon 
 them. .The only way of counteracting this tendency is by increasing the diinensions of the pillars, 
 so as to distribute the pressure over a wider area. The amount of increase demanded by each 
 of these conditions cannot be stated in a general manner. It is a question that will have to be 
 determined for every individual case, in accordance with the circumstances by which it is surrounded, 
 and the degree in which the conditions are modified. The proper method of procedure, in dealing 
 with this question, is to determine the dimensions required by the depth alone, and then to augmen" 
 these, if necessary, for each of the other conditions, in a proportion adequate to its requirements. 
 The experience of the district will in this matter be of great avail. 
 
 The Levels.— When the dimensions of the shaft pillar have been determined, the levels may 
 be set out, the designing and driving of which constitute the work of opening out the mine. The 
 
DRIVING OF LEVELS, OR NARROW WORK. 279 
 
 direction of these levels is determined by that of the dip of the strata, and, as remarked in the pre- 
 ceding chapter, the relative positions of the downcast and upcast shafts will be dependent upon the 
 same conditions. As the levels are to be driven in the seam of coal, it is evident that the horizon- 
 tality of their floor, whence their designation of level is derived, can be obtained only by driving 
 them in the direction of the strike of the beds, which, as already pointed out, is at right angles to 
 their dip. In this direction, therefore, which is known among miners as the water-level direction, is 
 that of the levels to be driven out from the shaft. Those so-called levels are, however, not 
 perfectly horizontal, for reasons that will hereafter appear, but their deviation from the horizontal is 
 made as little as the conditions will admit, and in no case is it more than trifling in amount. A 
 consideration of the conditions which determine the position and the direction of the levels will show 
 that these must greatly influence the choice of the position of the shafts. The relation of the levels 
 to the shafts and to the coal to be wrought, in position and in direction, will be understood by a 
 reference to the plan shown in Fig. 446. This plan represents typically the method of laying out 
 the workings generally followed in England. 
 
 The direction of the dip of the seam is shown in the plan by the arrow upon the coal to be 
 wrought C. The downcast shaft is shown at D, and directly to the rise of the dawncast, and 
 distant 15 yards, is the upcast shaft U. When these shafts have been carried down to the requisite 
 depth, the first step in opening out the workings is to connect them by a headway or drift driven 
 through the coal. This connection will provide for the ventilation by enabling each shaft to serve 
 the purpose for which it was ultimately intended. For the current of air, instead of passing down 
 and up each shaft on opposite sides of the brattice, will now descend through the downcast D, and 
 ascend through the upcast U. It now remains to set ofi" the levels perpendicularly to the direction 
 of the dip of the seam, as shown &i ab, ac, d e, df. These are driven out from the shafts in opposite 
 directions, and as they will be in all respects identical on each side of the shafts, it will be sufiScient 
 to describe those on one side only. Before describing these levels, however, it should be observed 
 that in extensive collieries a third level is usually added, mainly to ensure a more efficient ventilation ; 
 and also that the shafts may be situate farther apart than in the example chosen for illustration. 
 Under such conditions, the shaft pillars will be laid out, and the levels driven out from them some- 
 what after the manner represented in Fig. 447, in which plan the levels a and b correspond to the 
 levels ab, de, in Fig. 446. 
 
 In driving the levels out from the shafts, care must be taken, as before remarked, not to weaken 
 the ground in that part. This condition will generally necessitate a walling to sustain the sides and 
 the roof of the level, timbering being insufficient in all but exceptional circumstances. Whenever 
 timbering is used to support the roof in such situations, it will be well to wall the sides. But an 
 arching of brick is far preferable ; and if the floor is of a weak character, the walling should rest upon 
 an invert. 
 
 Of the levels a b and d e, the former or lower is the drain, water-level or water-gate, one of its 
 uses being to convey the water, which gravitates towards it from the workings situate above, to the 
 pumping shaft. The upper level de is the main road, roUey-way, or way-gate, through which the 
 mineral will be conveyed to the shaft. As these are the main outlets to the mine, and as, moreover, 
 they constitute the air-channels through which the workings will be ventilated, it is obvious that 
 their design and construction demand careful attention to render them convenient and durable. The 
 lacilities which these roads afford for the easy and rapid transport of the coal from the working faces 
 
280 MINING ENGINEERING. 
 
 to the shaft will very materially influence the quantity of the output and the cost of delivery at 
 surface, or " bank," as the surface around the mouth of the shaft is technically called. And the con- 
 sequences of an accident resulting in the blocking up of these roads are of too serious a character to 
 leave any precaution unnecessary. 
 
 Form, Dimensions, and Inclination of the Levels. — The section of a level, unlike that of the shaft, 
 offers but little variation in form. Wlien timbered the sides are generally vertical, and the top or 
 roof horizontal, the section in such a case being rectangular. The sides may, however, incline 
 towards each other, thus giving a greater width at the floor than at the roof. When walled, the sides 
 are vertical, and the roof is arched. 
 
 The dimensions will be determined by three conditions : the thickness of the seam through 
 which the levels are driven, the strength of the roof, and the requirements of the means of transport. 
 If the seam be of moderate thickness, say from 6 to 8 feet, the level will be driven between the roof 
 and the floor ; that is, the whole of the seam will be removed, and the height of the level will be 
 equal to the thickness of the seam. When the thickness exceeds 8 feet, the level is driven from tlie 
 floor to a height of 7 feet or 7 feet 6 inches, and the remainder is left to form the roof. When, on 
 the contrary^ the seam is too thin to afford a convenient height for a horse-road, either a portion o£ 
 the roof must be stripped down, or a portion of the floor removed to give the necessary height; and 
 as such labour is altogether unproductive, the minimum height demanded by convenience will not be 
 exceeded. Under some conditions this may be as little as 5 feet. The width of the excavation will 
 be determined according to the strength of the roof, and the requirements of the means of transport. 
 If the roof be of a very weak character, it may be necessary, to insure safety, to limit the width to 
 5 feet. If, on the contrary, the roof be very strong, this width may be increased to 10 feet. Thus 
 the limits of height and width of a level may be stated as 5 feet and 8 feet, and 5 feet and 10 feet 
 respectively. The width necessary to convenience of transport will be determined by the extent of 
 the workings, and the degree of activity to be developed in them. In most cases, the roUey-ways 
 will have to be laid out to a width sufficient for a double line of tram rails, so that a train of empty 
 tubs may be returning to the workings while a train of loaded tubs is running out towards the 
 shaft. In general, the width which best fulfils all the requirements of the case is from 7 feet to 
 8 feet, when the strength of the roof is sufficient. An important use of the levels, to be borne 
 in mind when determining these dimensions, is that of conveying air to and from the workings. The 
 large quantity required necessitates a large sectional area in the ways, and on this ground, as will 
 more clearly appear when we treat the subject of ventilation, ample width is desirable. For 
 economical reasons, the sectional area of a level is frequently reduced to its lowest practicable limits ; 
 but to assume that the cost of driving a level diminishes as its sectional area is an error. When the 
 miner is compelled to work in a space insufficient to allow freedom in his movements, there is a very 
 notable loss of useful effect due to the restrictioi), which loss, by prolonging the labour, increases the 
 cost of the work. Also the labour of driving a heading of small sectional area is relatively greater 
 than that required by a heading of larger dimensions, since the amount of side cutting is propor- 
 tionally greater in the smaller section. Besides this, the coal extracted from the smaller face is more 
 broken, and consequently less valuable, than that hewn from the larger face. The only advantage 
 offered by the smaller section lies in the diminished labour of conveying away the dislodged mineral. 
 
 It has already been remarked that the levels are not driven truly horizontally. There are two 
 important circumstances which require them to have a slight inclination towards the shaft. The 
 
Plate 1 
 
 /Vx^ 
 
 
 
 Enxpta/0^ Disrupttvej arudj IntJiosive/ lanetrujs RocJos. 
 
 Fvg . 2 
 
 InterhecLded aruL Overb/in/i Iqneaue Mocks 
 
 Fvg . 3 
 
 ThcUvrvmn ozct of Rocky Beds. 
 
 E ifc.r N.SpanXcmdon iScNew^fork. 
 
Plate 2. 
 
 IF ij g 4 
 
 IrudinatuTrv of Rode Bedti Market' Dr-aytorv, Salop. 
 Fvg 6. 
 
 AntCdinaL and SyuiLnaL dcrves _ SecCunv thnnujli. (J B. 
 
 Fvg. 7 
 
 Antucbirwd,' and SyrtdinaL/ Curvet' Plarv. 
 
 c 
 
 JbvddtrwL(xixdy^mjd]uwiLOArve/S—Sactwn t)v(jwqh C D. 
 
 B 
 
 Fvg . 5 
 
 Contortioyui:^ Ijouqlislwnrcy (h. Ihxbbin/. 
 TvQ 10. 
 
 Jiock Jauits. _ MaUjyH, Cv. Ccrk. 
 
 Fvg . 9 
 
 jbiUcltnaL. ^ Frodehanv, Cheshire/. 
 
 E (ib'F.lSl. Spon. London & New York 
 
Ylst/i 3 
 
 J^V^ 11 
 
 Fig 12. 
 
 Swell or- Horseis Bark.'. 
 
 Fig . 13 . 
 
 Flan, of Jotrvbs iroRock Bwrreri/, Co. Cirire-'. 
 
 F tcj 14-. 
 
 TrcugJh near Fdrvs . 
 
 Fault' of FrO'SzOTi/- Stoiwtonj. S^toFfbrcUhjiTe>. 
 
 Fiq 15 
 
 Fvg 16 
 
 Fault' of Ftosiotv. 
 
 FaitlX' of IKslocxvaorv- 
 
 E &. F.TSI.Spcin.Lon3Dn&;TJew York. 
 
Plate 4 
 
 ITwan til Hari^zoritaJj £ed^ 
 
 TJlTVw TTu Iriclijieci' Bed . 
 
 P-9 ^.9 
 
 F i-a 20 
 
 \ ^^^^yj^Tl^-s" 
 
 Apparent Lateral ■Shxft I^an/. 
 
 dr- 
 
 
 North. 
 
 LateraL Shift' _ Sectioru 
 
 A 
 
 F Lg.\ .22. 
 
 Sozuth. 
 
 e/-. i 
 
 NortJv 
 
 V\ 
 
 \r 
 
 \ \ \a>- 
 LatfraL ShaJh _ SextiMnj. 
 
 F ij a . 23 ■ 
 
 Lateral/ Skufi - Plan 
 
 F vg 24 
 
 / — / 
 
 Step Fault/. 
 
 E <fcF.N.Span.Lan3i3n.&i{ew"K!rk. 
 
Hate 5. 
 
 T i^^ . 7/5 . 
 
 Trough/ Fca4lt6 
 
 JrouaJv jFaults. 
 
 J'^g ■ ^7, 
 
 I' tci 2S 
 
 Trau^Tv FaiUiy in/ Staffbrdshxre/ ITiicJo CoaL. 
 
 Direction/ of Throw. 
 
 E & F.IT , Spon..Landcm. & I^evr"S)rk . 
 
Bate 6. 
 
 Fug. 30. 
 
 Faults of IHslvccvtwn/. Veckforton/JHV^, Cheshire^ 
 
 JSffects of SercudaZioru ^ Wewtcn/, ISnicshxre/^ 
 
 F i,g 33 . 
 
 Fffecte of FctuJts and' Dervujdattoru Trervthanv ParlCj Staffbrdshire^ 
 
 F i/g . 34- . 
 
 T/jiayrifbrrnabilitv. QiesWarcUne/j Salop. 
 
 E&J.N Spon Lonaon fcNewYork. 
 
HateT, 
 
 CHARACTERISTIC FOSSILS OF THE SILURIAN PERIOD. 
 
 Ftg.36 . 
 
 Fi/Q.3& 
 
 Ftg.S7. 
 
 Ftg.SS. 
 
 Rastritee 
 Peregrinjus 
 
 F-vg .40. 
 
 SedgwukL 
 
 JFi^Q. 41. 
 
 GraphtoUthes 
 
 IkpLograpsws 
 
 Ttg.39. 
 
 .DiplcgmJfy^u^ 
 
 Ftg.42.. 
 
 Ortkus 
 Virgateu 
 
 Ftg . 43 . Fvg. 44. Fz^g .45. 
 
 jtmpyx/ 
 
 PccrvuJzLs CaJynww 
 
 FqjUxrijcu 
 Serixxay 
 
 Fentamerus 
 Oblongus 
 
 E ifcTN. Span, London. &I>Iew "York. 
 
Tlabe 8. 
 
 JFtg.64-. 
 
 Mjcrddsomxi' 
 (^Tvqoruw 
 
 Fvg.G9. 
 
 Ftg. 65. 
 
 B'UpmplwLhi.g 
 
 Fig. (i<J ^ 
 
 Ft a. 67 
 
 Ihintnfj/,s 
 
 FVQ.W. 
 
 Danbyt 
 
 Orthrrcrd.i 
 Aniinlntinn 
 
 Fvg. 
 
 68. 
 
 
 
 m 
 
 
 Br 1 
 
 Ptiit/nrcenjus' 
 Kniiijlaii 
 
 CHARACTERISTIC FOSSILS OF THE DEVONIAN & OLD RED SANDSTONE PERIODS. 
 Fig. 71. Fig. 72-. Fig.7.> f ' g 7 --I 
 
 Cal/xolu 
 Sandnlma 
 
 Fig . 76 . 
 
 Gfynvmicv 
 Xinearxe 
 
 Megalodni 
 Ciihdlatua 
 
 MurchMOiua' 
 BiJ.incata 
 
 ■Spirtfer 
 DijspirutiAjs 
 
 Fig. 
 
 Strinrii'i ■ yV/. izoi' 
 
 DipteriLs MacrolepifloWji 
 
 yldx.azitites 
 J/iiierracus 
 
 Fvq.79. 
 
 CHARACTERISTIC FOSSILS OF THE CARBON PERIOD. 
 
 Ftg.S'Z. 
 
 jirvJdyrLedipora.- 
 Archiiwcidetu 
 
 Fig. SO. 
 
 Ftutna/ 
 
 Ftg.Sn. 
 
 FerijestrelLa/ 
 Membroowucxou 
 
 Fixhostrctijow \ 
 Sasaltiforrw 
 
 It n S3. 
 
 Lidwdci idi'cri 
 iregulare/ 
 
 I! &T N. Span. London fclsTewYork . 
 
Plate ^ 
 
 M 
 
 Fvg. SS 
 
 F,.u. sn 
 
 J (rUranites 
 FJavalL-f 
 
 Fig. S7. 
 
 Aj/tplexu.s 
 QtriillcufcA- 
 
 Fi CI a( 
 
 RrtiridaUc 
 Fia dF 
 
 ArcucLfjx- 
 Fi(, OS 
 
 Prlci 
 
 x.ocrjtuu 
 
 Fug. y? Fiq. 33 
 
 DiBivivcam 
 
 T\iJlPiI(IIIII_.'. 
 
 iSjjIrd'nrU't^ 
 
 WccdocPUUiS 
 Maavduchiuii 
 
 3eUvrajj'^ 
 
 Scuuleri :BdlLLlu.< 
 
 .Arrhaccidcr' ? ^'{ 
 FriA, 
 
 FOaiK 'hi II fill c 
 VI a I red an 
 
 FiQ .')6 
 
 7 
 
 Lr-ircitiila. 
 Haslata 
 
 SpuFfera 
 ijb'uxtrx 
 
 Fi n 10'> 
 
 At/a-ris 
 Fiq. IC3. 
 
 PrvdxictiJ.s 
 Gzqar(t£ios 
 
 hicuTcjjeetert 
 
 Fcsidcruriua 
 BerdterL 
 
 Fig. 104 
 
 Fia 105 
 
 Posidr.-i_i)i 
 (ri/i.<ri/:l 
 
 Vi q IC7 
 
 j-liithrciccpti 
 Bjti\ rm.nuf 
 
 Fin. ICS 
 
 BcUrri'iilirii 
 ('(;■</ 1 diu< 
 
 'la ConulaTKi Euon<.j)li<d_us 
 
 Qiuuh •(sidaibi Paihmqrlatii.'S 
 
 Fiij. IC") Fig. IK 
 
 Lear III "Id 
 JicffJriirci 
 
 .\ (iiili/ccrnis 
 
 iTirm'TfH^r.< 
 JTni.dnvi 
 
 ('rducci'^ 
 
 LateraTc 
 
 Flci '!•"('( intlnts 
 Fji-MSninvia 
 
 Ccclddtlns 
 Centering 
 
 K ?tP TV Spon London >s. iNe-.. 
 
J-lcOeiC 
 
 1 
 
 Fiy. ne. 
 
 Fig . 1)8 
 
 JPeccpteris 
 
 Odantcpterif; 
 
 ixrcfH 
 
 E & F N Spon uoiidoi, & NevrT-;-:. 
 
Plate 11 . 
 
 CHARACTERISTIC FOSSILS of the PERSIAN PERIOD. 
 
 Fig 150. Fzg. 131 Fig 132. Fiy.m. 
 
 FLeurvphorLLs Macrochaliis 
 
 CostxdjuLS Svmmetricus 
 
 F^cU^'scrmis 
 
 Scaler of Pygopterij^ 
 
 MandibvJLari^ CErdcLrgeoL.) 
 
 Scale rfAcrolepis 
 SedgwickvC 
 (Enlarged.) 
 
 LABYRINTHODON REMAINS of the TRIASSIC 
 
 F i q 146 
 
 ■PERIOD. 
 
 Footprmts vf LahyraiBwdjDn, Gigoaitetcnt 
 
 Ftg m 
 
 Tooth of 
 Labyrmdwdon 
 
 E &F N Spon London &, "New York 
 
Plate 12 
 
 CHARACTERISTIC FOSSILS OF THE LIAS. 
 
 J^ig. J48 
 
 Fiff. M9. 
 
 I-'ig loO 
 
 lahyosannis 
 Carrnrturtzs 
 
 
 Dapecbxis 
 Iktrajgottolepts 
 
 Jtesinscacrue 
 
 ■^ DoUchodexrus 
 
 E&F N Spon London &, New Tori: 
 
PJatt 1-3 
 
 i% 161. Fig. 162. Fig. 163. Fig. 164. Fig. 165. Fig. 166 Fi^. 161. Fi^. 168-. 
 
 mt 
 
 "\) 
 
 Jl 
 
 r^ ill 
 
 "tF 
 
 h 
 
 Fig. 169. Fig. 110. tig. m. Tig- ^3. 
 
 Fig. in. Fig. 115. Fig. 116. 
 
 Fig. 114-. 
 
 SCALE. FIGS. 173 It 174.. 
 
 1234-56789 10 M 12 INCHES 
 M.l' l .lil M- I .l I I . l il 
 
 SCALE. 
 
 Fig. /7Z 
 
 INCHES 12 9 6 3 
 
 |_j M U 1-1 l-l M 1= 
 
 3 FEET 
 
 G.G.ANDRE. 
 
 JE 3c!F.!N'.Spctn..XoLndon. &Kew-"Ybrfc. 
 
?Iat^ A 
 
 Fi;^ 173 . Ftg . 173. 
 
 
 U 
 
 & ! 
 
 t< 
 
 F-vg. 18C. Fig. W. Ftg. 182. 
 
 li^l 
 
 fl 
 
 
 U 
 
 
 J:-A 
 
 
 
 F-ucf. 183. Fvg. 184- 
 
 ■- -s 
 
 
 u 
 
 Ftg .736 
 
 Fta . 185 
 
 Fig 188 F-Lg . 180 
 
 Ftg. IdC Fvg. 191 
 
 SCALE FIGS l'B6 TO 191 
 
 'NCHES ' liJ u_, u-^ !_. ^-, -.^JP FEET 
 
 INCHES I ? 9 6 3 
 
 I — L I— i I — ^ I — ^ I — 1 I — c: 
 
 SCALE 
 
 3 FEET 
 
 6 G ANDRE 
 
 E 8<.F. W Span. London &. New l(ark. 
 
=1 
 
 Fxg. 134- 
 
 Fig. 1&5 
 
 FLg ZCI 
 
 SCALE- is 
 
 ^ 
 
 E 8iFI'J.S3on Lcmdon &. TTew /crK 
 
Plate 16. 
 
 Ftg 136 . 
 
 Ftg 197 
 
 Ftg 199 
 
 Fi^g '^CP 
 
 
 INCHES I ? 6 
 Mfc 
 
 SCALE 
 
 5 ip 15 20 26 60 
 
 i — li — ^1 — II — II — ll IJ — II — ll — ^1 — I T — I I — I I— I 
 
 G G. ANDRE 
 
 E & F. N- Span. London. &. New York 
 
F:a^e i; 
 
 Ftg 20 Z 
 
 Fig. Z08. 
 
 J^_ 
 
 -xS^ 
 
 I r^p^p^^ 
 
 /■^y^'C^ 
 
 
 ifti 
 
 x^ 
 
 
 LJ 
 
 ^t:^. W5. Fig. 209. Fvg. 210. 
 
 Ft a Z11. 
 
 Ftg. Z08. 
 
 ruv 
 
 Fvg ZIZ. 
 
 F-9 2X)6. @^x^ 
 
 Ftq. Z13 Fvq . Z14- Fvq. Z15 
 
 ■.0. 
 
 '9 
 
 n 
 
 \ 
 
 SCALE 
 
 vg. 
 
 A 
 
 INCHES I? 3 6 
 
 i-i h-i 1-1 -i=r 
 
 3 FEET 
 
 JB &.F W.Spon London 8<.Newli&A. 
 
Plate 1 6 
 
 Fi.g ZJ6. 
 
 I 
 
 Fig 213. 
 
 Fx.g . ZZ1 
 
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Plate 29 . 
 
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