A Text-book of Coal-Mining ... With ... illustrations

Front matter

A TEXT-BOOK OF C OAL-MININ G Stanfcarfc Worfce. ORE AND STONE MINING (A TEXT-BOOK OF), BY C. LE NEYE FOSTER, D.Sc, F.R.S., F.G-.S., Professor of Mining, Royal College of Science, H.M. Inspector of Mines, Llandudno. In Large 8vo, with numerous Illustrations. In Svo, with numerous Illustrations, Third Edition, cloth, Is. %d. MINE SURVEYING (A Text-Book of). For the Use of Managers of Mines and Collieries, &c. By Bennett H. Brough, F.G.S., Instructor of Mine Surveying, Royal College of Science. " No MiniDg Agent will consider his Technical Library complete without it." — Nature. In Large Svo, with numerous Illustrations, handsome cloth, 10*. 6d. BLASTING : A Hand-book for the use of Engineers and others engaged in Mining, Tunnelling, Quarrying, &c. By Oscar Guttsianw, A.M. Inst. CE. " We especially commend it to Mining Fngioeers, to whom it should prove a vademecum." — Iron and Coal Trades Review. ' Thoroughly practical, and a book which we can unhesitatingly recommend."

Industries. In Large Svo, with 43 Lithographic Plates and numerous other Illustrations, cloth, 25s. HYDRAULIC POWER AND HYDRAULIC MACHINERY, for the use of Practical Engineers and Students. By H. Robinson, M. Inst. C.E., Professor of Civil Engineering, King's College, London. " A book of G-EEAT PROFESSIONAL USEFULNESS." — Iron. By W. J. MACQUORN RANKINE, C.E., LL.D., F.R.S. Late Regius Professor of Civil Engineering in the University of Glasgow. In Crown Svo, cloth, with numerous Tables and Diagrams. I. APPLIED MECHANICS. Thirteenth Edition. 12s. 6d. II. CIVIL ENGINEERING. Eighteenth Edition. 16s. III. THE STEAM ENGINE. Thirteenth Edition. 12s. 6d. IV. MACHINERY AND MILL- WORK. Sixth Edition. 12s. ed. V. USEFUL RULES AND TABLES. Seventh Edition. 10s. M. VI. A MECHANICAL TEXT-BOOK. Fourth Edition. 9s. VII.

PROFESSOR RANKINE'S MISCELLANEOUS SCIENTIFIC PAPERS. With Memoir by Professor Tait, M.A., and Fine Portrait on Steel Royal Svo, hand60me cloth, 31s. 6rf. Losdos: CHARLES GRIFFIN & CO., Limited, Exeter St., Stkand. A.SopyrilK^hclo. D arsons, Th.Sc. A TEXT-BOOK OF COAL-MINING. FOE THE USE OF COLLIERY MANAGERS AND OTHERS. 17 Y HERBERT W. HUGHES, ASSOCIATE OF THE ROYAL SCHOOL OF MINES; FELLOW OF THE GEOLOGICAL SOCIETY; ASSOCIATE MEMBER OF THE INSTITUTION OF CIVIL ENGINEERS ; CERTIFICATED COLLIERY MANAGER; PAST-PRESIDENT OF THE BRITISH SOCIETY OF MINING STUDENTS. WITH VERY NUMEROUS ILLUSTRATIONS. LONDON: CHARLES GRIFFIN & COMPANY, LIMITED, EXETER STREET, STRAND, 1892. [AU t'ightt rttervett.)

Preface

. In the preparation of this volume my aim has heen to ■supply a text-book of moderate dimensions, giving all the information with which the student and the practical miner should be familiar. In order, however, to economise space, I have had to omit reference to many appliances which have become obsolete from their antiquity, or by reason of their failure in practice. Although it is impossible within the limits of the book to furnish exhaustive descriptions on all points, yet the details of general colliery work have been fully described, on the ground that collieries are more often made remunerative by perfection in small matters, than by bold strokes of engineering. All modern collieries are practically identical so far as general machinery and arrangements are concerned ; nevertheless, it frequently happens, in particular localities, that the adoption of a combination of small improvements any one of which viewed separately may be of apparently little value, turns an unprofitable concern into a paying one.

At the end of each chapter will be found a carefully selected list of Memoirs in which fuller information can be sought This will, it is hoped, prove a novel and useful VI

PREFACE.

. feature in a treatise on coal-mining, for, scattered through the pages of the Transactions of the Mining Institutes, numerous valuable papers exist ; but, owing to the lack of general indexes, they are unfortunately not consulted so much as they deserve to be. All the figures elucidating the text have been specially drawn for this work, the majority having been reduced from original working drawings. In conclusion, I have to express my cordial thanks to the many friends who have rendered valuable help in the preparation of the work. Especially, I am indebted to Mr. P. H. Prough, Assoc. R.S.M., F.G.S., Mr. H. G. Graves, Assoc. R.S.M., and Mr. H. F. Pulman, for important suggestions and able assistance while the volume was passing through the press. HERPERT W. HUGHES. Coneygke Colliery, Dudley, September, 1892, GENERAL CONTENTS.

Chapter I. — Geology. PAGE The Study of Geology . . . i Rocks ...... i Classes of Rocks i Aqueous and Metamorphic Rocks .... i Igneous Rocks. . . . I Stratification .... 2 Laminæ ..... 2 Intrusive Rocks ... 2 Induration 2 Segregation .... 3 Fossilisation .... 3 PAGE Inclination of Strata ... 3 Faults. ..... 3 Reversed Faults ... 4 Trough Faults .... 5 Conformable and Unconformable Strata .... 5 Joints in Rocks .... 5 Cleavage ..... 6 Order of Succession ... 6 Carboniferous System in Britain 7 Fossils 7 Bibliography .... 8 Chapter II. — Coal. Definition of Coal ... 9 Formation of Coal ... 9 Classification of Coal . . .10 Lignite ..... 10 Bituminous Coal . . .10 Steam Coal . . . .11 Cannel Coal . . . .11 Anthracite . . .12 Commercial Value of Coal . 12 Gases Occluded in Coal . . 1 5 Chapter III. — Search for Coal.

Prospecting 18 Boring 18 Choice of Site . . . . 19 Various Appliances used in Boring . . . .19 (a) Bits 19 (b) Rods . . . .19 (c) Guides . . . .20 (a) Clearing Instruments . 21 (e) Levers . . . .21 (/) Spring Poles . . .21 (g) Frames . . . .22 Devices Employed to meet Difficulties of Deep Boring . 22 (a) Lighter Rods . . . 22 (6) Free-Falling Cutters . 23 Obtaining Cores . . -24 Special Methods of Boring . 24 (a) Mather and Platt's System 24 (b) American System . . 26 (c) Diamond Boring . . 27 Accidents in Boring . . 31 (a) Accidents arising from the Boring Tools themselves . . . . 32 (6) Accidents arising out of the Nature of the Ground 32 Lining 32 Widening Holes . . -33 Withdrawal of Casing . . 33 Record of Boring . . -34 CONTENTS. Chapter III. — Search for Coal — (continued). PAGE Boring — Cost of Boring . . . -34 Surveying Bore-holes . . 35 Uses of Bore-holes . . -36 Tapping Water . . 36 PAGE Releasing Gas . . . 36 Proving Faults . . • 36 Steam and Rope-ways . . 36 Bibliography . . . -37 Chapter IV. — Breaking Ground.

Contracts 3^ Hastening Work . . . .38 Tools Used 39 Shovels 39 Picks 39 Dressers 41 Wedges 41 Hammers 41 Drills 42 Percussive Hand-tools . . 42 Scrapers 44 Tamping or Ramming . . 44 Hand Machine Drills . . 45 Transmission of Power . . 48 Compressed Air . . .48 Air Compressors . . .49 Valves . . -52 Dancing of Valves . . 54 Conduits . . . -55 Receivers .... 55 Motors SS Electricity .... 56 Alternating and Continuous Currents . . . .56 Terms Used . . . - 57 Preventing Sparking . . 58 Efficiency . . . -59 Power Machine Drills . . .60 Ingersoll Drill . . . .61 Adelaide Drill . . . .62 Brandt's Drill . . . .63 Supports 64 Electric Percussive Drills . 65 Forms of Bits . . . .66 Use of Water in Boring Holes . 66 Cost of Machine and Hand Drilling . . . -67 Coal cutting by Machinery . 67 Machines Worked by Compressed Air . . .68 Gillot and Copley . . 68 Rigg and Meiklejohn . . 68 Baird . . . . .69 Harrison . . . .69 Ingersoll-Sergeant . . 70 Legg 70 Machines Worked by Electricity 7 1 Goolden . . . • 72 Jeffrey 72 Van Depoele . . -72 Cost of Coal-cutting . . 74 Stanley's Heading Machine . 74 Boring Cross Cuts . . -75 Explosives 75 Gunpowder . . . -75 Nitro-glycerine . . .76 Dynamite . . . -76 Blasting Gelatine . . -77 Gelatine-Dynamite . . -77 Rackarock . . . -77 Blasting in Dry and Dusty Mines 77 Water Cartridge . . -77 Roburite . . . . .78 Ardeer Powder . . -79 Carbonite . . . -79 Tonite 79 Ammonite . . . -79 Firing the Charge . . .80 Squibs, or Germans . . 80 Fuses 80 Blasting by Electricity . . 82 Tension Fuses . . .82 Quantity Fuses . . -83 Comparison . . . .83 Frictional Machines . . 83 Magneto-Machines . . .84 Simultaneous Blasting . . 84 Bickford's Volley Fuse . . 85 Position of Holes . . -85 Blown-out Shots . . .86 Various Methods to supersede Blasting . . . -87 Elliot Multiple Wedge . . 87 Haswell Mechanical Coal-getter 88 Burnett's Roller Wedge . 88 Hydraulic Wedges . . .88 Lime Cartridges . . .88 Bosseyeuse . . . .89 Prohibition of Blasting . . 89 Bibliography ....

CONTENTS. IX Chapter V. — Sinking. PAGE Position of Shaft . . .92 Form of Shaft . . . -92 Size of Shaft . . . -93 Operation of Getting Down to " Stone Head " . . -93 («) Where the Ground is Moderately Hard . . -93 (6) Where the Ground is Loose 94 (1) Pile Driving . . .94 (2) Drums . . . .07 (a) Wood . . . -97 (6) Iron ... 98 Method of Proceeding Afterwards 99 Keeping the Shaft Vertical . 100 Winding Debris . . .101 Covering over Pit-top . . 102 Guides . . . . .102 Lining Shafts .... 104 Bricks ..... 104 Number of Bricks Required 104 Mortar ..... 105 Thickness of Brickwork . . 105 Ordinary Curbs . . . 106 PAGE Water Rings . . . .106 Walling Stages . . . 107 Supporting Curbs . . .109 Ventilation . . . .109 Lighting ..... 109 Dealing with Water . . .110 Keeping out Water by Tubbing . 1 1 1 Coffering . . . . .111 Iron Tubbing . . . .112 Strength of Tubbing . .116 Corrosion . . . . 117 Cost of Tubbing . . .117 Sinking by Boring . . .118 Kind-Chaudron's Method . 118 Lippmann's Method . . 120 Sinking through Quicksand . 121 Triger's Method . . .121 Poetsch's Method . . .121 Deepening Pits already Sunk . 122 Widening Shafts . . . 125 Cost of Sinking .... 125 Bibliography .... 127 Chapter VI. — Preliminary Operations.

Underground Roads . . .129 Means of Keeping Direction . 129 Means of Keeping Gradient . 130 Operation of Driving . . -131 Ventilation . . . -131 Supporting Roof . . . .132 Timbering . . . . 133 Joints ..... 135 Chocks or Cogs . . . 135 Double Timbering . .136 Driving through Loose Ground 136 Iron and Steel Supports . . 137 Masonry . . . . .140 Arrangement of Inset . . 145 Bibliography . . . .148 Chapter VII. — Methods of Working. The Two Main Systems . . 149 Shaft Pillar and Subsidence . 149 Arrangement of Labour . -151 Bord and Pillar Working . -152 Lancashire Method . . .156 Longwall Method . . .156 Double Stall Method . . .161 Working Steep Seams . .162 Working Thick Seams — South Staffordshire . . .164 (a) Square Work . . . 165 (b) Longwall .... 166 Pennsylvania .... 168 Working Seams lying near Together . . . .169 Spontaneous Combustion . .170 (a) Oxidation of the Organic Constituents . . .170 (b) Iron Pyrites . . .171 (c) Friction from Slippings . 171 Development . . . -171 Prevention . . . .172 Bibliography . . . -173 CONTENTS X Chapter VIII. — Haulage.

PAGE Transmission of Power . . 195 Compressed Air . . • '97 Electricity . . • -198 Different Systems of Haulage . 198 Direct Acting Haulage . .198 Size of Engines Required . 198 Main and Tail-rope Haulage . 199 Devices for throwing Drums In and Out of Gear . . 200 Methodsof Working Branches 201 Endless Chain. . . . 202 Attachment of Tubs . . 203 Driving Pulleys . . . 203 Taking up Slack . . . 204 Working Branches and Curves .... 204 Minimising Breakages . . 205 Endless Rope Haulage . . 205 Driving Appliances . . 205 (a) Clip Pulleys . . 205 (bj C-pulleys . . . 207 (c) Grooved Pulleys . . 207 Taking Up Slack Rope . 211 Clutches for Working Branches . . . .212 Brakes for Branches . .214 Arrangement of Tubs . .215 One or Two Road Systems . 215 Rails at Junctions . .216 Clips 217 Clips for Under Haulage . 217 Clips for Over Haulage . 218 Automatic Detachers . . 220 Threading the Rope . . 224 Comparison .... 224 Locomotives .... 226 Electric Locomotives . . 226 Bibliography .... 227 PAGE Primitive Methods . . . 175 Rails 175 Length of Bails . . . 177 Gauge . . . . .177 Method of Laying Rails . .177 Fish- Plates . . . .178 Sleepers 178 Wood 17S Iron 179 Steel 179 Switches 180 Plates 181 Turntables 181 Tubs 182 Bodies 182 Frames 183 Height 183 Size. ..... 184 Wheels and Axles . . .184 Drawbars . . . .185 Pedestals .... 185 Lubiication . . . .186 Haulage by Horses . . . 187 Feeding . . . .187 Cost of Feeding . . .189 Cost and Life of Horses . .189 Cost of Corn-cutting and Ostlers . . . .189 Shoeing .... 189 Arrangement of Stables . 190 Cost of Horse Haulage . . 191 Self-acting inclines . . . 192 Arrangement of Rails . . 192 Blocks or Stops . . .193 Drums and Pulleys . . . 193 Brakes ..... 194 Rollers . . . . .194 Junctions . . . . 195 Chapter IX. — Winding.

Pit Frames 229 Wood 231 Iron 233 Pulleys 233 Skips and Cages .... 234 Shape and Construction . . 234 Means for Keeping Tubs on Cages 239 Ropes 236 Wire Ropes .... 237 Attachment to Cage . . 239 Cage Chains .... 240 Method of Taking off Strain . 241 Guides 243 Rails 243 Wire Ropes .... 245 Conductors between Cages . . 246 Guide Shoes .... 246 Guide Troughs .... 247 Engines . . . .248 Position of Engine-house . . 250 Drums ..... 250 Brakes . . . . .252 Counterbalancing . . . 254 Tapering Ropes . . . 256 Flat Ropes . . . .2^6 Conical and Spiral Drums . 256 Tail Rope beneath Cages . 2156 Meinicke's System . \ 257 Expansion . 2r- CONTENTS. XI Chapter IX. — Winding — (continued). PAGE Condensation .... 260 Compound Engines . . .261 Special Methods . . . 262 Blanchet Pneumatic System . 262 Koepe System .... 263 Prevention of Over-winding . 266 PAGE Catches at Pit Top . . . 270 Changing Tubs .... 272 Fencing the Pit Top . . . 279 Tub-controllers .... 281 Signalling ..... 283 Bibliography .... 284 Chapter X. — Pumping.

Pumps ..... 286 Bucket Pumps . . . 286 Plunger Pumps . . . 287 Hollow Plungers . . . 287 Stocks or Trees .... 288 Joints ...... 288 Supporting Pipes in Shaft . . 289 Spear Rods ..... 289 Guiding the Rods . . .291 Counterbalancing . . .291 Connections to Rods . . . 291 Valves ..... 292 Quadrants ..... 293 Suspended Lifts .... 293 Cornish Pumping Engine . . 295 Bull Engine .... 296 Davey Differential Engine . . 296 Direct-acting Steam Pumps . 298 Worthington Pumps . . . 300 Pumps for Sinking . . . 300 Arrangement of Supply-pipes, &c. 301 Air Vessels. .... 302 Condensing Arrangements . . 303 Calculations as to Size of Pumps 304 Effect of Acid Water . . . 305 Draining Deep Workings . . 305 Hydraulic Power . . . 307 Moore's Arrangement . . 308 Electricity .... 309 Pulsometer . . . .310 Dams . . . . . 311 Bibliography .... 312 Chapter XI. — Ventilation.

Importance .... 313 Quantity of Air .... 313 Gases Met with in Mines . . 314 Carbonic Acid . . .314 Carbonic Oxide . . .314 Sulphuretted Hydrogen . -314 Light Carburetted Hydrogen . 314 After-damp .... 315 Coal-dust 316 Action of Moisture . . . 322 Laws of Friction. . . . 324 Production of Air Currents . 327 Natural Ventilation . . 327 Furnace Ventilation . . 327 Steam Jet ... 329 Mechanical Ventilators . . 330 Guibal 330 Waddle . . . .331 Schiele . . . -333 Cockson .... 333 CapeU 333 Walker . . . -334 Walker's Shutter . . . 335 Driving by Straps and Ropes 336 Arrangement of Engines . 336 Determination of useful Effect 337 Efficiency of Fans . . . 337 Comparison of Furnaces and Fans ..... 340 Distribution of the Air Current . 341 Stoppings . . . .342 Doors ..... 342 Regulating Doors . . . 343 Air Crossings .... 343 Loss in Circulation . . . 344 Measurement of Air Currents . 345 Anemometers .... 345 Barometer and Thermometer . 347 Water Gauges .... 348 Bibliography ....

CONTENTS. XII Chapter XII. — Lighting. PAGE Wick 3^5 Glasses 365 Locking Lamps .... 366 Magnetic Locks . . . 366 Lead Rivets . . • -3^6 Ryder's Lock .... 366 Casting Rivets . . • 367 Relighting Lamps . . . 368 Cleaning Lamps .... 369 Electric Light Underground . 370 Secondary Batteries . . 370 Primary Batteries . . -371 Delicate indicators . . . 371 Pieler Lamp . . . • 371 Ashworth's Lamp . . . 372 Coloured Glass . . . 372 Liveing's Indicator . . . 372 Bibliography . . . .373 PAGE Naked Lights . . . • 352 Safety Lamps . . . ■ 352 Davy's Invention . . . 352 Clanny 353 Stephenson .... 353 Mueseler 354 Design of Lamps . . ■ 354 Modern Lamps .... 356 Hepplewhite-Gray . . . 356 Bonneted Mueseler . . . 359 Ashworth's Mueseler . . 359 Morgan 3°° Marsaut 36 1 Deflector 361 Tin-can Davy .... 363 Thorneburry .... 363 Sight Lamp .... 364 Conclusions .... 364 Oil 364 Chapter XIII. — Works at Surface.

Boilers 375 Mechanical Stoking . . . 377 Coal Conveyors .... 379 Coating Steam Pipes . . . 380 Workshops 381 Chapter XIV. — Preparation of Coal for Market. General Considerations . . 382 Circulation of Tubs . . . 383 Tipplers 3^5 Front Tipplers . . .385 Back Tipplers . . . .386 Side Tipplers . . . .386 Duplex Tippler . . .389 Screens 390 Movable Bar Screens . . 391 Jigging Screens . . . 394 Revolving Screens . . . 395 Spiral Screens .... 395 Greenwell's Screen . . . 396 Varying the Sizes made by Screens .... 397 Plating . . . .397 Combs 397 Variable Crossbars . . 398 Belts 400 Revolving Tables . . . 402 Loading Shoots .... 403 Typical Illustrations . . . 404 Pemberton Colliery . . . 405 Brinsop Hall Colliery . . 405 Hilda Colliery .... 406 Hewlett Pit . . . . 408 Aniche Colliery, France . . 408 No. 5 Pit, Bascoup . . . 409 Cross Creek Collieries, Pennsylvania . . . .412 Coal Washing .... 414 Sizing Apparatus . . .414 Trough Washers . . . 414 Robinson's Washer . . . 415 Coppee Machine . . .416 Conclusions . . . .419 Dry Coal Cleaning . . . 420 Briquettes ..... 420 Bibliography .... 422 INDEX ABBEEVIATIONS.

The following abbreviations have been used to denote the publications most frequently quoted in this work. The Roman numerals designate the volume, and the ordinary figures the page. For. Abs. = Foreign Abstracts. so. WALES inst. . . Transactions of the South Wales Institute of Engineers. SOC. ind. min. . . Bulletin de la Societe de l'lndustrie Minerale de Saint Etienne. ches. inst. . . . Transactions of the Chesterfield and Midland Counties Institution of Engineers. ted. inst. . . . Transactions of the Federated Institution of Mining Engineers. brit. soc. min. stud. Journal of the British Society of Mining Students. N. e. i. . . . Transactions of the North of England Institute of Mining and Mechanical Engineers. N. staff, inst. . . Transactions of the North Staffordshire Institute of Mining and Mechanical Engineers. inst. c. e. . . .

Minutes of Proceedings of the Institution of Civil Engineers. AMER. inst. m. e. . Transactions of the American Institute of Mining Engineers. MAN. geo. soc. . . Transactions of the Manchester Geological Society. ENG. AND min. JOUR. . The Engineering and Mining Journal, New York. so. staff, inst. . . Transactions of the South Staffordshire and East Worcestershire Institute of Mining Engineers. REV. univ. . . . Revue Universelle des Mines. min. inst. scot. . Transactions of the Mining Institute of Scotland. mid. inst. . . . Transactions of the Midland Institute of Minino- Civil, and Mechanical Engineers. ANN. des MINES . . Annales des Mines.

Chapter I. Geology

The Study os Geology may be divided into two parts, one of which treats of inorganic matter, the laws to which such matter is subject, and the chemical and physical changes through which the crust of the earth has passed ; the other deals with and inves tigates the order, character, and succession of organic life, and the relation which the various forms bear to each other. As no written records exist, which go back to the remote times when life first existed on our globe, the geologist has interpreted the changes which have taken place by careful observations of phenomena met with; and as histories of extinct races have been built up from the interpretation of hieroglyphics on monuments, so by similar results has the order of succession of geological strata been established from observations of the life forms preserved in a fossil state in the rocks which constitute the crust of the earth.

Rocks. — By this term is meant, not only large masses of coherent matter, as limestone, which build up mountains, but also the soft and loose gravels, or clay, which are found associated with them. Classes of Rocks. — Rocks are divided into three classes — aqueous or stratified, metamorphic, and igneous or ejected. Aqueous and. Metamorphic Rocks. — These are made up of regular beds, or strata, and are probably all produced from the denudation of igneous rocks, although they appear to differ greatly from them. The great agent of disintegration is the atmosphere, and the rain which is precipitated from it. Igneous Rocks. — These rocks may be broadly divided into four divisions, according to the quantity of silica they contain. First, they are separated into acid and basic ; a third class is formed A of rocks containing an intermediate amount of silica ; while last of all there is a small, but important, class called " ultra-basic."

To the acid type, containing on an average about 74 per cent, silica, belong granite and porphyry ; while the basic type, containing an average of 50 per cent, silica, is represented by gabbro and basalts. The intermediate class (syenite, diorite, and some obsidians) contain on an average 60 per cent, silica (the ultra-basic, 39 per cent, silica) and a high proportion of alkaline earths and oxide of iron. Glassy varieties are common in the acid series, rarer in the intermediate series, and still rarer in the basic division. Stratification. — When the fragments are large, the stratifica tion, or bedding, is very imperfect, but if the particles are small, it is very perfect. Laminæ. — When we have very close stratification, and get the thinnest paper-like layers in the planes of deposit of a stratified rock, it is said to be laminated.

Intrusive Rocks. — These are sometimes great masses forced up through the surrounding strata in no definite direction, or fre quently, intrusive matter is forced along definite planes, forming dykes, where the sides are fairly parallel ; a good example of this is the great whin-dyke of the North of England coal-field, which proceeds nearly ninety miles in a straight line. These intrusions were originally forced into their present position in a molten condition, evidence of which is afforded by the way they have altered the adjoining strata, coal seams in many instances being charred and rendered worthless for several yards on either side. It may happen that only the upper side of the stratified rocks below the igneous bed will show signs of baking, from which it is seen that the lava-flow was contemporaneous or interbedded with the rocks, while, if both the upper and lower surfaces of the beds are affected, the lava-bed was certainly intrusive.

The rocks of the globe present very different appearances to the gravels and sands which are formed every day on our sea-shores and at the mouth of rivers. All the stratified rocks have been originally deposited in a manner similar to that now going on, but changes have taken place in them subsequent to formation. 1. Induration. — In the depths of the earth's crust, by the long continued pressure of " miles " of strata above a bed composed of finely divided particles, the effect is very great. In this way,. muds pass into finely laminated clays, and finally into shales. The effect of induration is well shown in the white limestone of Antrim, which was originally formed in the same manner as the English chalk, but, owing to the superposition of at least 2000 feet of basalt, has been hardened into a hard splintery rock, showing no trace of chemical action.

Induration is, how ever, greatly aided by chemical action, the particles forming the rock being cemented together by substances deposited from solu- GEOLOGY. 3 tion in water. At great depths the rocks are undoubtedly saturated with water, and this facilitates the deposition of materials round the rock particles, or, as in the case of limestones, &c, the solution of some of the rock materials themselves, which are afterwards crystallised out from their solution in the water. Disintegration usually undoes all this work ; the cementing material first yields, is removed, and the particles of the rock are set free again. 2. Segregation. — Again, segregation may be going on, par ticles of the rock separating from the remainder and segregating together, this being especially well seen in limestone containing silica ; the particles of silica are drawn together by this action, forming the flints and cherts of the chalk.

Fossilisation. — This is merely a case of segregation round organic matter. In many clay ironstones, the nodules of iron have been formed by the segregation of the mineral round fossil remains, and, on breaking open the nodule, the fossil is found inside, generally in a beautiful state of preservation. Inclination of Strata. — Generally speaking, strata were laid down in a horizontal position, this being shown by the lie of pebbles in rocks, and by the position of fossil trees. It is, however, very rare to find the beds retaining this position, though the folding may be of the slightest. If a bed is at all inclined, it must reach the surface somewhere, and the space where this happens is said to be the outcrop of the bed. The nature of the outcrop and its width, depend on the thickness of the bed and the degree of inclina tion ; it cannot be less than the thickness of the bed, and is wider, the smaller the angle of inclination.

In order to define a bed, two things must be known — first, the direction in which the inclined bed reaches the surface, and the inclination of the bed. The angle which beds make with the horizon is called the dip, and the hne in a horizontal plane, the strike, the latter necessarily being at right angles to the dip. When the surface of the ground is horizontal, the lines of outcrop and strike coincide, but, if the strata are inclined, the outcrop is inclined also ; the strike is always horizontal. Angles of dip are usually measured by an instrument called a clinometer, but, in doinf this, care must be taken to distinguish between the true and apparent inclination ; the latter can never be greater than the former, but it may be less to any amount. When the strata are bent in arches, they are said to have a synclinal fold, -when the arch is downwards ; an anti clinal, when the arch is upwards (Fig. i); when the folds are small, they are called troughs and saddles respectively.

Fig. i. . Faults. — When the pressure is too great, or is applied suddenly, or if the rock refuses to yield, and then breaks, instead of bending, a dislocation is obtained ; the divided segments are thrown out of level, and do not fit, one side being higher than the other. This is called a fault. In mining districts, such term is applied loosely to anything which interferes with the seams that are being worked. Generally speaking, when contortions of the strata are numerous, faults are few ; and vice versd. The position of every fault is defined by two directions, as in the case of beds : the strike of a fault is spoken of, but, in the place of the word " dip," the term hade is employed, this being, however, the inclination measured from the vertical. To determine a fault accurately, it is necessary to know two other things — (i) which side is throw-up, and which is throw-down ; (2) the amount of displacement.