A Treatise on Earthy and other Minerals and Mining

Front matter

EARTHY AND OTHER MINERALS AND MINING WORKS BY THE SAME AUTHOR. A TREATISE ON METALLIFEROUS MINERALS AND MINING. Illustrated with numerous Wood Engravings. Third Edition, revised. Crown Svo, 12s. 6d. cloth. (Uniform with, and forming a companion volume to, "A Treatise on Earthy and other Minerals and Mining.") "Without question, the most exhaustive and the most practically use ful work we have seen ; the amount of information given is enormous, and it is given concisely and intelligibly." — Mining Journal. "The author has gathered together from all available sources a vast amount of really useful information. As a history of the present state of mining throughout the world this book has a real value, and it supplies an actual want, for no such information has hitherto been brought to gether within such limited space." — Athenæum.

"The volume is one which no student of Mineralogy should be with out." — Colliery Guardian. A TREATISE ON SLATE AND SLATE QUARRYING, SCIENTIFIC, PRACTICAL, AND COM- MERCIAL. Illustrated with numerous Wood Engravings and Folding Plates. Third Edition. i2mo, 3s. 6d. cloth. " Mr. Davies has written a useful and practical handbook on an important industry, with all the conditions of which he appears familiar."— Engineering. "One of the best and best-balanced treatises on a special subject, having at once scientific, practical, and commercial relations, that we have met with." — Engineers^ , CROSBY L^Jcw^Q)) AND SON, 7, Stationers' Halt-Court, London, E.C. A TREATISE ON EARTHY AND OTHER MINERALS AND MINING BY D. C. DAVIES, F.G.S. MINING ENGINEER; AUTHOR OF "A TREATISE ON SLATE AND SLATE QUARRMNG," "A TREATISE ON METALLIFEROUS MINERALS AND MINING," ETC, ETC. §ecotxb gbitioxx.

LONDON CROSBY LOCK WOOD & SON 7. STATIONERS' HALL COURT, LUDGATE HILL 1888 [All rights reserved] LONDON : PRINTED BY J. S. VIRTUE AND CO., LIMITED, CITY ROAB,

Preface

. The design of this book is to give such a full and intelligible an account of the minerals selected for description in it as shall be useful and interesting to persons engaged in mining pursuits, and in the manufacture of the substances described ; while it is also hoped that it will possess some interest for the general reader. It does not aspire to be a manual of mineralogy, although it is hoped that the classified list of minerals, with a brief description of each species, given at the end of the book, will serve to show the mineralogical position of each mineral described, and form an introduction, for the student who may desire it, to the more elaborate and systematic treatises on mineralogy. It is intended as a companion volume to my work on " Metalliferous Minerals and Mining," and perhaps, in point of time, it should have preceded that volume.

It will be observed that in the present book the distinctively earthy minerals are first considered. Next come those minerals which are compounds of earths and alkalies, some of which have a metallic base ; after which carbon and compounds of carbon are noticed. Sulphur next occupies a place by itself,

PREFACE.

. and then follow a number of metallic minerals distinguished by the extreme difficulty with which their metals have been ex tracted from them, and the rapidity with which those metals, when so obtained, and when unalloyed with others, unite with oxygen. The student is thus led up to the series of useful and noble metals described in the volume on " Metalliferous Minerals and Mining." In both volumes prominence is given to the way in which the minerals described occur in the strata of the earth. Of necessity a work of this kind must to a large extent be a compilation. It may, however, be permitted to me to say that a considerable portion of the information it contains is the result of my own observation and experience in the course of mining travels and work at home and abroad. I have thus been able to supplement the researches of others by my own.

My hope is that the work which is the outcome of these combined researches may prove a useful one, and, with its companion volume, be found of permanent value for information and reference. D. C. Davies. Ebnal Lodge, Gobowen, Oswestry, April \yjh, 1884. CONTENTS.

Chapter I. Silica And Some Of Its Combinations

TAGR Silicon — Oxygen — Silica — Description — Proportions in Rock Masses — Redeposited Silica in Cavities, Cracks, and Beds — Daubree's Experiments on the Decomposition and Crystallisation of Varieties of Quartz, Vitreous, Chalcedonic, Jaspery — Rock Crystal and its Varieties — Chalcedony — Agates — Flint — Chert — Jasper — Opal — Analyses of Rocks containing much Silica and Alumina . 3

Chapter II. Alumina, Magnesia, Lime, With Some Of Their Combina Tions

Aluminium — Alumina — Bauxite — Valued Forms of Alumina — Corundum — Sapphire — Ruby — Topaz — Brazilian Deposits of Emerald — Analyses of Beryl — Emerald Mines of Grenada — Tourmaline — The Precious Stone Deposits of Ceylon — More Massive Forms of Silica and Alumina — Orthoclase — Adularia — Felspar — Mica — Magnesia — Magnesium — Talc — Steatite — Chlorite — Serpentines- Pyroxene — Asbestos — Rock Masses — Granites and Gneiss Rocks — Syenitic and Dioritic Greenstones — Slaty Building Stones — Liverpool Corporation Quarry, Llanwddyn — Felspathic Rocks of North Wales — Lime and Limestones — Varieties of Costs of work- CONTENTS. PAGE 16 38 61 ing Glucina, Zerconia, Thoria — Chemical Composition of various Limestones

Chapter III. Cla Ys

Clays, how derived and formed — Decomposition of Basalt, of Rocks in Iceland — Brick Clays of the Drift — Analyses — Clays of the Tertiary Strata, Bovey Tracey — China Stone and China Clay of Cornwall and Devon — Comparison with other China Clays — Kimmeridge Clay — Permian Marls and Clays — Clays of the Coal-measures — Analyses — Manufactures of, in North of England, North Wales, Shropshire — Colouring of Clays and their Products.

Chapter IV. Sodium, Chlorine, Chloride Of Sodium

(COMMON SALT). Description of Sodium — Of Chlorine — Common Salt resulting from the Combination of the Two — The New Red Sandstone Plains of England — Stratigraphical Position of the Cheshire Salt Deposits — History of Salt-working in Cheshire and Worcestershire — Strata overlying the Cheshire Salt Beds — Analysis of Rock Salt — Of Brines — Details of Cheshire Salt-mining — Brine Springs of Worcestershire — Associated Strata — Detailed Section of — Characteristics of the Brine — Statistics — Brine Springs of Ashby Wolds — Salt Manufacture in the North of England — Manufacture of Sulphate of Soda — Discovery of a Bed of Rock Salt at Middlesborough — Detailed Section of Strata — Analysis of the Rock Salt — Second Boring near Fort Clarence, with Results — Rock Salt Deposits of Carrickfergus, Ireland — Method of Working

Chapter V. Chloride Of

SODIUM— continued. Salt Deposits of France, of Switzerland, of Spain — The Salt Mines of Cardona, on the Ebro, near Burgos — The Sea Salt Gardens of the South-west Coast — Analyses of Sea-water — Salt Deposits of CONTENTS. IX PAGB Si Italy, of Germany, Mecklenburg-Schwerin, Hanover, Anhalt, Wurtemburg, Bavaria — Salt Deposits of Austria, Salzburg, Wieliezka — Description of the latter Mine — The Sea Salt Gardens of Istria and Dalmatia — Salt Mines of Roumania, of Russia, Solikamsk, Tchapatchi, Orenburg — Salt Lake in the Crimea — Salt Deposits of Africa, of Asia, Caspian Sea, Palestine — Chemical Composition of the Water of the Dead Sea — The Salt Deposits of Persia, of India — Bahadur Khel — Table of Strata— Kohat — Salt Range — North America — " Licks " of Michigan — Petit Anse Island, Louisiana — Nevada, Salt Lake of — Dr. Chas. Darwin's Description of a Saline in Patagonia — Inferences and Conclusions .

Chapter VI. Nitrate Of Soda, Borax, Baryta, Gypsum, Fluor Spar, And Alum

SHALE. Composition of Nitrate of Soda — Occurrence in German Salt Mines — Deposits of in Peru and Chili — The Desert of Atacama — Statistics of Production — Boron — Boracic Acid — Composition of the Lagoons of Tuscany — Borax — The Tincal Trade of Thibet — Borax in Nepaul, in Iceland, and in Nevada — Barium — Baryta — Sulphate — Carbonate — Sulphate of Baryta in Snailbeach Lead Mine — The Wotherton Barytes Mine, Shropshire — Statistics of Production — Gypsum, its Composition and Varieties — Geological Position — Statistics of Production — Fluor Spar in Derbyshire and in Devonshire — Native Alum — Alum Shale — Alum Industry on the Yorkshire Coast — Description of the Deposits ioo

Chapter VII. Phosphate Of Lime

Phosphorus — Importance in Vegetable and Animal Life — Use in Agriculture — Mode of Occurrence in Nature — Phosphoric Acid — Apatite — Other Forms of Phosphate of Lime — Professor Henslow and the Coprolites of Suffolk — Modes in which Phosphate of Lime occurs in Nature — The Apatite Deposits of the Laurentian Rocks of Canada — Their Range and Manner of Occurrence — Particular Examples — Analyses — Particulars of Mining — The Apatite or Phosphate Deposits of Norway— Range — Geological Age — Various Modes of Occurrence — Particular Examples — Rutile — Rock Dykes — Analyses — Difficulties of Dressing — Mining Particulars i°9 X CONTENTS. PAGE 129 146 160

Chapter VIII. Phosphate Of

LIME— continued. Phosphatic Matter in Strata between the Laurentian and Lower Silurian — The Phosphorite Deposit of North Wales — Discovery — Range — Associated Strata — Description of Bed — Supposed Origin and Analyses — Compared with other Phosphates — Particulars and Costs of Mining and Dressing — The Phosphatic Deposits of Estramadura, Spain — Position — Discovery— Composition — Description of Particular Deposits — Deposits in Canada, France, Hungary — Bone Bed at Top of Upper Silurian Strata in Shrophire .

Chapter IX. Phosphate Of

LIME— continued. The Greensand and Gault — Position of Bedfordshire and Cambridge Phosphate Beds — Localities — Description of Beds with Fossil Contents — Analyses — Composition of the Phosphate Bed — Derivation of the Phosphate Matter — The Phosphatic Nodules of Suffolk — Conditions of taking Phosphate Lands — Phosphate Digging — Statistics of Production — Phosphatic Deposits of the Ardennes and the Meuse in France and Belgium — Date of Discovery — Geological Position — Extent — Characteristics of the Deposits — Phosphate Deposits of Bellegarde, France — Geological Position and Fossil and Mineral Characteristics — Analyses — Phosphatic Deposits of the Cretaceous Strata of Russia — History of the Discovery of Mineralogical Features — Analyses

Chapter X. Phosphate Of

LIME— continued. Phosphate of Lime in Tertiary Strata — Phosphatic Deposits of Nassau, North Germany — Situation — Geological Structure of the District — Illustrations of Modes of Occurrence — Whence derived — Analyses — Phosphates of Tarn-et-Garonne, France — Growth of the Industry — Geological Position — Modes of Occurrence — Similarity to the German Deposits — Analyses — Phosphatic Deposits of Carolina, America — History of the Discovery of — Geological Position — Characteristics — Land and River Phosphates — Analyses — Recent Phosphates — Alta Vela — Aruba Island — Navassa Island — Pedro Keys — Redonda Island — Sombrero Island — St. Martin's Island . CONTENTS. XI PAGE I83

Chapter XI. Carbon And Carbonaceous Substances

The Diamond — History of Attempts to consume it, by Boordt, Boyle, Cosmo III., Sir Isaac Newton, Sir George Mackenzie, and Sir Humphrey Davy — Diamonds of India, of Brazil, of South Africa — History of the Discovery and Progress of the Industry and Particulars of Mining — Notable Diamonds — Plumbago or Graphite of Borrowdale, of Ayrshire, of North Wales, of Ceylon — Particulars of Production in Ceylon — Graphite in America — Uses for which it is employed — Jet — Origin of Name — Jet Industry of Yorkshire .

Chapter XII

CARBON— continued. Asphaltum, Varieties of — History of the Uses of Bituminous Substances — Of the American Petroleum Industry — The Cannels of Flintshire and Lancashire — Modes of Occurrence — The Torbane Hill Mineral — The Bituminous Deposit of Bovey Tracey — Deposits of Bituminous Matter in Silurian Strata in Ireland — Bitumen in France — Gneiss in Sweden — Bitumen Deposits of France — Asphalte of the South of France — Bituminous and Petroleum Deposits of Germany — The Hanover Oil-well Region . . . 204

Chapter XIII

CARBON— continued. Bituminous Deposits of Spain, Italy, Roumania — Bitumen and Petroleum of the Caucasus and Caspian Regions — Bituminous Springs of the Valley of the Euphrates, of British Burmah, of the Punjab — Pitch Lake of Trinidad — Bituminous Springs of Barbadoes, Cuba, Venezuela — Bituminous Coal Deposits of North America — Geological Age of the various Petroleum-yielding Strata of North America — Particulars of the Oil — Mode of Sinking Wells — Bitu minous Springs and Schists of South America — General Conclu sions CONTENTS. XII PAGE 258

Chapter XIV. Sulphur

Abundance of Sulphur in Nature — Varieties — Sulphur Mines of Sicily — Situation — Geological Position — Details of Strata — Thickness of Sulphur Beds — Percentage of Sulphur contained — Associated Minerals — Methods of Working — Costs — Sulphur Mines of the Mainland of Italy — Cessena — Geological Position — Thickness of Bed — Modes of Working and of the Treatment of the Mineral — Sulphur Deposits of Greece, of Russia, of Iceland — Pyrites, Production of in the British Isles — Growth of the Treatment of on the Tyne — Pyrites of Norway, of Germany, of Spain and Portugal — Description of the Rio Tinto Mines of Spain . . . 232

Chapter XV. Arsenic

Arsenic, Native — Orpiment, Realgar, Mispickel — Production of Arsenic in the British Islands — Modes of Treating the Ores in Cornwall and Devon and in Bohemia — Mispickel of Norway and Sweden, of France, of Germany, of Austria, Transylvania, and Hungary, of Russia, Spain, Turkey, China, and of North and South America 253

Chapter XVI. Cobalt

Cobalt, Origin of Name — Description of its various Ores— Commercial Varieties — Cobalt in the British Islands — Cornwall— North Wales — The Foel Hiraeddog Mine — Norway Skuterud Mine — Indications about Kongsberg and Drammen — Sweden — Mining District, from Nykoping to Westervik — The Cobalt Mines of Tunaberg, of Gladhammar — Processes employed at the latter Mine for the Extraction of Cobalt from the Ores — Mines of Hvena — Germany, Riegelsdorf, Annaberg and Schneeberg — Austria, Joachimsthal — Past Production of Cobalt in Bohemia — Spain — Mine in the Pyrenees, France — America— Imports into England — Suggestions CONTENTS. XIII

Chapter XVII. Mol Ybdenum

— ANTIMONY. Molybdenum, description of its Ores — Commercial Uses — British Islands : Invefness-shire, Charnwood Forest, Calbeck Fell — Norway : Arendal, Numedal — Sweden : Description of the Deposits of Ekholmen, on the Baltic Coast — Germany — Austria — Hungary — America — Antimony, Early Knowledge and Uses of— Story of the Origin of its Present Name — Native Antimony — Ores of Antimony — Uses of the Mineral — Antimony in the British Islands — Cornwall — Sweden: Sala Mine, Ofverrud Mine, Gladhammar Mines — Germany: Hartz and Erzgebirge — Austro-Hungary — Borneo Algeria — America — New South Wales .... 272

Chapter XVIII. Manganese

Manganese in its Native State — Rapid Oxidisation of — Uses of the Ores of Manganese — Alloys of the Metal with Iron and Copper — Description of its Ores — Manganese Ores of Great Britain and Ireland — Cambrian Rocks of North Wales, of Scotland — Silurian Strata of Ireland, of North Wales — Silurian and Devonian Strata of Cornwall and Devon — History of Manganese Mining in those Counties — Devonian Strata of North Wales — Carboniferous Limestone of Derbyshire, of Shropshire — The Manganese Deposits of Nassau, North Germany — Italy : Mines of Val d'Aosta and Tournanche — Spain : Mines of the Huelva District, of Cape de Gata — France : the Romaneche Mines, Cevennes, Vosges — Occurrence of Manganese in the Mines d'Asprieres — America : Manganese Ores of Missouri, Arizona, Canada — Inferences .... 282

Chapter XIX. Classified List Of Mineral Substances

Purposes of the Chapter — Abbreviations — List of Simple Elements, divided into Metallic and Non-metallic — Further divided into Seven Classes — Oxygen — Enumeration of Classes with Included Substances — Table of Strata — Conclusion LIST OF ILLUSTRATIONS. FIG. PAGE i. Common Crystals of Quartz 4 2. Section of Folded Agate I0 3. Perspective View of Folded Agate I0 4. Common Crystal of Corundum . • . . • . . 18 Y Crystals of Carbonate of Lime • 32 7. General Section across the Plain of Cheshire and Shropshire, showing the position of the Salt Deposits 62 8. General View of the Peckforton Hills, Cheshire ... 70 9. Section of Strata at the Wieliezka Salt Mines, Austrian Poland 87 10. Section through Bahadur Khel Salt Locality, Trans-Indus Salt Region, India .......... 92 11. Hill of Salt at Bahadur Khel 95 12.

Order of Laurentian Strata, Canada ...... 112 13. Map showing Position of the Canadian Phosphorite Deposits . 114 14. Map of the Apatite District, Norway 120 15. Section showing General Order of the Strata in the Apatite District, Norway . . 121 16. Veins of Apatite at Tvitrae, Norway 121 17. Apatite Veins, Godfield, Norway ...... 121 18. Section of Double Apatite Lode, Godfield, Norway . . . 122 19. Section of Vuggens Apatite Mine near Kragero, Norway . . 123 20. Sketch of Rich Part of Apatite Lode, showing Pockets of Apatite with Hornblende . . . . . . . . 124 21. Section of Apatite Deposit at Oedegaarden, Norway . . 125 22. Fine Crystals of Apatite in Vuggens Mine, Kragero, Norway . 125 23. Hill-side with Apatite Deposits at Doredalen, Norway . . 126 24. Section of Apatite Deposits at Midbo, Norway . . . . 127 25.

Map of Position of Baia Limestone with Phosphorite Bed, North Wales 130 26. Section across the Berwyn Mountains ...... 131 27. Section of Strata at the Berwyn Phosphorite Mine . . .133 LIST OF ILLUSTRATIONS. XV FIG> PAGE 28. 1 29. [Sections of tbe North Wales Phosphorite Bed with the associ 30. ' ated Strata 136-7 3'- J 32. Section of Strata at Green Hall Park, Llanfyllin . . .138 33. Section of Strata at Cwm-dynewydd, Llanymawddy . . . 138 34. General Section of Strata from the Summit of the Oolite upwards, showing the Positions of various Phosphate Deposits . . 147 35. Section of Phosphate Bed on Sandy Heath, Bedfordshire . . 148 36. Section illustrative of the Geological Structure of Nassau . . 161 37. Section showing Phosphorite in Dislocation of Strata near Staffel 162 38. Section at Cubach, showing Phosphorite and Manganese resting in Hollows of the Limestone ....... 162 39.

Section of Phosphorite near Arfurt ...... 163 40. Section of Phosphorite Working in Opheim, near Limburg . . 164 41. Section of Phosphatic and Associated Strata, Tarn-et-Garonne, France 168 42. 1 / Sections of Phosphatic Deposits, South Carolina . . .173-4 44- '| •?' sFigures of the Usual Forms of Diamonds . .... 183 47- j 48. {Plan and Section of the Plumbago or Blacklead Mine, Borrow 49./ dale, Cumberland ......... 193 50. Section of the Blacklead Mountain, Ticonderoga, New York . 199 51. Section of Yard Coal, Flintshire, showing Position of Cannel . 208 52. Section showing the Position of the Totbane Hill Mineral . 210 53. Section at Millaberg, Wermland, Sweden . . ... 213 54. Section of the Oil-bearing Strata in Pennsylvania . . . 224 55. Section showing Undulations in Oil-bearing Strata of Pennsylvania ........... 225 56.

Section of the Sulphurous Strata, near Caltanissetta, Sicily . 235 57. Section of the Sulphurous Strata, near Sommatino, Sicily . . 236 58. Section of Cupreous Pyrites in Ranenfjord, N*_. way . . 247 59. Section of Pyrites Deposit, Huelva, Spain . . ... 247 60. General View of the Rio Tinto Pyrites Mines, Spain. . . 249 61. Section of Cavity in Limestone, Flintshire, containing Cobaltiferous Iron Ore ......... 262 62. Sketch Section of Nant Uchaf Manganese Mine, near Abergele 289 63. Section of a Manganese Mine at Pant, near Oswestry . . 291 64. 1 Plan and Section of a Manganese Mine near Elbingerode, Hartz, 65. j Germany ... LIST OF ILLUSTRATIONS, FIG. PAGE 66. Plan of Hæmatite Deposit with Manganese, at Steeterwasen, Nassau ........... 295 67. Cross Section of i..e same 295 68. Longitudinal Section of the same ...... 295 69.

Sketch of the Rubin Mine, near Niedertiefenbach . . . 297 70. Section of the Fahrweg Mine, near Niedertiefenbach . . 297 71. Section of the Hochst Mine, near Niedertiefenbach . . . 297 72. Map of the Huelva Manganese and Pyrites Mining District, Spain 300 73. Section of the Manganese Deposits at Romaneche Mine, France 302 74. Longitudinal Section of Workings on the same . . . . 303 75. Manganese Deposit of Cuthbertson Hill, Missouri . . . 306 76. Section of Manganese Deposit on Burioid Mountain, Missouri

Part I. Earthy Minerals

SILICA, ALUMINA, LIME, MAGNESIA, GLUCINA, ZIRCONIA, THORIA, WITH SOME OF THEIR COMBINATIONS. E A TREATISE ON EARTHY AND OTHER MINERALS AND MINING.

Chapter I. Silica And Some Of Its Combinations

Silicon — Oxygen — Silica — Description — Proportions in Rock Masses — Redeposited Silica in Cavities, Cracks, and Beds— Daubree's Experi ments on the Decomposition and Crystallisation of Varieties of Quartz, Vitreous, Chalcedonic, Jaspery — Rock Crystal and its Varieties — Chalce dony — Agates — Flint — Chert — Jasper — Opal — Analyses of Rocks containing much Silica and Alumina. SILICA. Of the sixty-four simple elements of which, as far as we know, the earth is composed, the most abundant are silicon and oxygen. These two, combined in the proportion 51 -96 of silicon with 48*04 of oxygen, form silica, of which mineral it is estimated that two-thirds of the earth's crust is formed. The true nature of silica began to be investigated in the year 1807 ; but it was not understood until a few years afterwards, when Berzelius extracted from it the simple element silicon, which, on combining with oxygen in the proportion just given, forms the white powder known as silicic acid or silica.

The simple element silicon has been obtained, by Wohler and Deville, in transparent crystals as hard as the diamond, to which they bear a certain exterior resemblance; also in metallic crystals imitating graphite, and also in a black non-crystalline powder. The colour of pure silica, as seen in crystallised quartz, is white ; but along with the combination of silicon and oxygen in its composition there is usually a small admixture of other substances, chiefly metallic oxides, iron, manganese, &c, as hereafter described, and these give to it various other colours, including those which make some of its varieties valuable as precious stones. In hardness, silica ranks as 7,1 and it may be easily dis tinguished in this respect from the fact that it cannot be scratched by an ordinary penknife. In a massive form it ranges from opaque to translucent, but in separate crystals it is transparent.

It crystallises into several shapes, the common form being a six - sided column, capped by a pyramid of an equal number of sides, as shown in fig. 1. Of itself it is infusible, but with soda it melts and forms glass. Under certain conditions, as will be seen, it is soluble. It forms the chief constituent of the rock masses of the globe, Fig. 1. — Common Crystals of Quartz. especially among the older rocks. In granitic and gneissic rocks it is present to the extent of 66 to 75 per cent. The imperfectly cleaved slaty rocks of the Cambrian and Silurian strata contain from 60 to 70 per cent. In the greenstone and syenitic rocks of the same formations it forms from 45 to 55 per cent, of the mass, and in the porphyritic rocks of the same groups it ranges from 59 to 75 per cent. In the sandstones of the millstone grit, the Coal-measures and of the New Red Sandstone group of rocks, it is present up to 92 per cent, the cementing matter consisting of small portions of lime, alumina, and magnesia.

Full analyses of several of these rocks are given at the close of this chapter. In these rock masses, besides alumina, which is in them the 1 See Table on ' Haidness of Minerals ' in the concluding chapter of the book. REDEPOSITED AND CRYSTALLISED SILICA. 5 chief associate of silica, there are proportions of soda and potash up to 14 per cent., with small quantities of lime, magnesia, and the oxides of various metals. As we shall see in treating of clays, it is the presence of soda and potash which has, during vast periods of time, facilitated the dissolving of the silica out of the mass preliminary to its being redeposited with a portion of alumina as clays. Besides this great redeposition of the silicious and alu minous portions of the older rocks in beds of clay, another ol a finer and more delicate kind has also been going on, in which silica, variously coloured and combined, has been de posited in veins, cracks, and cavities of those rocks themselves, where, according to the age or other conditions of the rock, it forms, as quartz, the matrix of gold, copper, lead, zinc, or other metallic minerals ; where, in other cracks, the silica has been closely packed, the result is an opaque quartz without much sign of crystallisation.

Where, on the other hand, there has been space for the process, it has become crystallised into the beautiful transparent forms in which it is found. Portions both of the massive quartz, and also of the crystals, are beautifully and variously coloured by the presence in different proportions of iron, copper, manganese, titanium, and other minerals, and these form the source of many of our pre cious stones, which, broken off their parent rock, have been rolled and polished as pebbles in the sea, or have been de posited with less friction, and hence are found in a more perfect state in conglomerates and breccias near the sources whence they were derived. Much light was thrown upon the way in which crystals of silica and alumina are formed naturally by a series of interesting experiments made by M. Daubre"e, in the year 1857, resulting in the artificial formation of crystals of these minerals.

M. Daubree had observed in the mineral springs of Plom bieres, the waters of which contain silicate of potash and soda, and have a temperature of 700 Centigrade, the formation of certain well-known silicates and other minerals usually found in the veins of older rocks. The masonry near the springs was often seen to be impregnated with hyalite (a sort of transparent silica identical with that found in basaltic rocks), and sometimes apophylite (silicate of potash and lime) appeared in nice crystals. The question then arose with M. Daubre"e, If hydrated silicates form slowly in mineral springs at a not very high temperature, may not anhydrous silicates be more quickly pro duced by the action of water at a high temperature ? To answer this question he began a series of experiments which answered it in the affirmative.

The experiments con sisted chiefly in submitting the different substances in the presence of water to a heat of 4000 Centigrade for a month to gether, in a closed glass tube, protected by an iron case. As glass formed part of the apparatus, it naturally occurred to him to determine first of all what result this treatment would have on glass itself. He found that at the above temperature, by the simple action of water, glass undergoes a complete decomposition. It first becomes opaque, earthy, and fragile, resembling kaolin, then gradually and regularly swells and transforms itself into a host of minute crystals, which were found on examination to be wollastonite (silica 52, lime 48), and at the same time the alkalies of the glass were dissolved. Soon the silica was de posited in the form of crystallised quartz.

When alumina was present, the phenomena were modified. When obsidian was acted upon in like manner, minute crystals of felspar were formed, resembling in the mass granular trachyte. Clay and kaolin, which had been previously purified by washing, on being submitted to similar treatment, resulted in felspar mixed with crystals of quartz. The presence of oxide of iron in the de composition of the glass gave pyroxene instead of wollastonite. This resembled the natural crystals found in the Tyrol and Piedmont. The crystals were beautifully crystallised, and possessed both their green colour and transparency. As the result of these experiments, M. Daubr<_e naturally concluded that most, if not all, the silicates found in the early crystalline rocks were formed by the influence of water at a high temperature, this temperature being, of course, much lower than that of the point of fusion of such silicates.

VARIETIES OF QUARTZ. ROCK CRYSTAL. 7 Let us now notice those varieties and combinations of silica which from their shape, colour, lustre, and transparency have been valued as precious stones. Quartz. — I have already described the way in which this variety of silica occurs in veins, lodes, and reefs in the older rocks — massive, partly in a crystalline form, and crystallised usually in six-sided prisms, capped by a pyramid as shown in fig. i. It also occurs in radiated and in granular forms. The clear white varieties are pure silica, but it is tinged yellow, rose, or of a smoky colour, and is, indeed, of all shades of colour through the presence of metallic oxides. It has been divided into the following three varieties, in which are included the precious stones to be described : — I. Vitreous Varieties.

II. Chalcedonic Varieties. III. Jaspery Varieties. I. In the first, or Vitreous Varieties, we have — i. Rock Crystal. — In shape and colour as described above. The crystals are usually rooted in a mass of quartz. It is pro bably the mineral described by the ancients as Krustallos, ice, whence the word 'crystal.' The crystals are found of small size among the mountains of Wales and Scotland, and, indeed, wherever the older granitic, slaty, or felspathic rocks are found. The clearest and finest specimens are brought from the island of Madagascar, where they are frequently found in blocks ranging from 50 to 100 lbs. in weight. Fine specimens also come from Switzerland, and from Auvergne, in France. The rock crystals of this country were formerly known as British or Cornish diamonds. It was formerly sold at from 51*. to 20_*. per lb. for the purpose of splitting and grinding into spectacle glasses, and it was also used for stones for lockets, seals, and rings.