The metallurgy of silver, a practical treatise on the amalgamation, roasting, and lixiviation of silver ores; including the assaying, melting, and refining of silver bullion

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Preface

The object of this volume is to give a practical out¬ line of the Metallurgical Treatment of such Silver Ores as are adapted to Amalgamation — that is, of ores whose character allows them to undergo treatment with quicksilver, with which metal silver forms an amalgam.

The processes of amalgamation may be classified as the Wet Process and the Dry Piocess. Ores which require no preliminary chemical preparation are adapted for direct amalgamation by the wet process. Ores which have to be treated by the dry process have to be crushed dry, and are roasted before being submitted to amalgamation — treatment which involves some very delicate manipulation and skill.

Professor Clarence King (in one of his Reports to the United States Government, to which, as will be mentioned presently, I have to acknowledge my in¬ debtedness) has given an excellent account of amalga¬ mation by the wet process ; and from this report I extract a description of the Washoe process, as practised on the Comstock lode.

VI

PREFACE.

I then follow with a description of the application of the Washoe process in working ores from the Golden Chariot Mine in Idaho, as practised by me when in charge of the works.

In the description of the dry process I give my experience, at various mines, when dealing with such ores as require roasting, and I describe in detail the metallurgical operations at the works of the Mineral Hill Silver Mines Company, which were in my charge from 1870 to 1873; and although for several months I followed there the system adopted by my predecessor, who roasted the ore in a Stetefeldt furnace before amalgamation, I subsequently abandoned the dry process, as I found that the ores could be more profitably worked by the Washoe process, and I was thus able to effect a saving to the company of many thousands of pounds sterling every year.

For the roasting of ores many new furnaces have from time to time been introduced, which have greatly contributed to the development of the silver¬ mining industry by cheapening the cost of treatment, and thereby rendering productive mines which other¬ wise would have lain dormant.

Of late years a new science has been developed in the treatment of silver ores which cannot be worked profitably by amalgamation, and are too poor in lead, or of such character as not to smelt. I refer to the Lixiviation Processes, which are being successfully carried out in many localities. I have gathered in this volume the latest information

PREFACE.

Vll obtainable on this very important branch of Silver Metallurgy, as no doubt in the near future the lixiviation of ores will be more generally practised. Indeed, there is open here for inventors and investi¬ gators a very wide field, w’-hile success will mean large returns in money.

In describing in the following pages the several methods of treatment, full particulars, with illustra¬ tions, of the machinery employed for crushing, grind¬ ing and amalgamating are given.

The various processes included in Concentration of argentiferous minerals, by sizing, jigging, huddling, and vanning, will also be found fully explained and illustrated. Although concentration has not as yet been extensively introduced in the metallurgy of silver, I have devoted a portion of this volume to the subject, as I am convinced that in the near future large bodies of low-grade refractory silver ores will be worked by this system, recent experiments at mines having demonstrated that it pays better to con¬ centrate than to submit a large quantity of unreduced ore to roasting, amalgamation, or lixiviation direct.

In this matter I have freely drawn on the ex¬ perience and methods of English and German metal¬ lurgists, who have so largely contributed to bring concentration to its present state of perfection in the tin, lead, and copper districts ; and I am more especially indebted to the interesting and detailed descriptions of some of the machinery employed which are given in the standard work of the late Air. Robert Hunt, F.R.S., on “British Alining;’' to

Vlll

PREFACE.

IMessrs. Rittinger & Goetschman’s “ Aufbereitungskunde ; and to the Reports to the United States Government on the Mining Industry of the Pacific Coast, which were prepared several years ago by Professor R. W. Raymond and the eminent American geologist, Mr. Clarence King. I am also indebted to the kindness of Messrs. Fraser & Chalmers, of Chicago, of Mr. Krom, of New York, and of Messrs. Commans & Sons, of London, for specifications and drawings of improved modern machinery. Informa¬ tion as to the Russell process and the working of ores at Tombstone, in Arizona, and at the Ontario Mine, in Utah, has been gleaned from papers read before the American Institute of Mining Engineers.

The work concludes with an article on the Assay¬ ing of silver bullion, as practised by me when Assistant- A.ssayer in the United States Mint of San Francisco, and when in charge of mines and metal¬ lurgical works during a period of eighteen years.

17, Belsize Crescent,

South Hampstead, London, N.W.

AUTHOR’S NOTE TO SECOND EDITION.

I AM much gratified by the speedy sale of a large impression of the First Edition of this work ; and I have taken the opportunity afforded by a Second Edition to add a Supplementary Chapter.

Johannesburg, South Africa.

Section I. — Silver Mines of the Western States of America

— First Discovery of Silver in the United States — Comstock Lode — War Eagle Mountain Mines — Golden Chariot and Ida Elmore Mines — Contests betv een Miners — Burnt Wagon District — Eureka Silver Lead Mines — White Pine and Pioche Mines — Panamint and Death Valley — Arizona and New Mexico — Author’s Sources of Information — Mr. Clarence King on the Silver Regions of the Pacific Coast .......... i

Section II. — SILVER ORES. — Forms of Native Silver — Varieties of Ore — Their Geographical Distribution — Chemical Properties of Silver . . . . . . . . . . . -13

Section III. — Treatment of the Ore. — Methods considered in this volume ; Amalgamation and Lixiviation — Other Methods — Mexican or Patio Process — Stove Amalgamation — Hot Process . 19

Chapter II. The Washoe Process Of Free Milling On The

COMSTOCK LODE.

Classification of Okes — Separate Treatment — Crushing in Rock-breaker and Stamps — Grinding and Amalgamation in Pans — Use of “Chemicals” — Settlers and Separators — Straining the Amal¬ gam — Retorting and Melting — Tailings — Results of the Process . 31

X

Chapter III

MACHINERY EMPLOYED IN CRUSHING AND A M A L G A M A TING.

PAGH

Rock Breakers — Blake’s and Krom’s described — Stamps — Tulloch’s Ore Feeder — The Battery — Mortars — Dies — The Stamp Head — The Shoe — The Tappet — The Gui ’es — The Cam — Num¬ ber of Stamps — Weight and Drop of Stamps — Quantity of Water used in the Battery — Amalgamating Pans : Wheeler’s, Greeley’s, Hepburn and Peterson’s, Wheeler and Randall’s, McCone’s —

The Combination Pan — Fountain’s Pan and Horn Pan — Separa¬ tors — Agitators — Clean-up Pans — Retorts — Melting Furnace — General Arrangement of Mills . . . . . . *4*

Chapter IV. Cost And Results Of Milling Operations

Cost of Labour and Materials — Staff required in Mill — Cost of Treatment per Ton of Ore — Relation of Mines to Mills — Sampling the Ore — Yield of the Mills — Cost and Results at the Virginian Mills 89

Chapter V. Treatment Of Slimes And Tailings

Slimes and Tailings on the Comstock Lode — Amalgamation of Slimes in Pans — Concentration of Tailings — Tailing Reservoirs — Successful Concentration of Slimes and Tailings — At Tombstone —

At the Montana Company’s Mills — Amalgamation of Raw Tail¬ ings in the Washoe District . 97

Chapter VI. The Washoe Process As Applied In Other

MINING DISTRICTS.

Milling in Owyhee District, Idaho, as practised by the Author — Passing the Ore through the Rock-breakers — Crushing in the Battery — Settling of the Pulp in the Vats — Amalgamation in the Pans — Working the Settlers, Agitators, and Concentrators — Gathering the Amalgam and Retorting it — Saving of Slimes and subsequent Treatment — Milling in While Pine, Nevada — Milling at the Montana Mines — At Silver Reef, Utah — At Pioche, Nevada . . . . ^ • • • • .it*

CONTENTS.

XI

Chapter VII. Chemistry Of The Washoe Process

PAGB

Constituents of the Comstock Ores — Mr. Hague’s Experiments on Action of Mercury and other Reagents— Chemical Action of Sulphate of Copper and Salt — Irt^n as a Reducing Agent — Action of Quicksilver — Practical Conclusions . . . . • *135

Chapter VIII. The Dry Process : Chloridising, Roasting, And Amalgamation

Rebellious Silver Ores — Operation of Roasting — Treatment of First-class Ores on the Comstock by Barrel Amalgamation — Treatment of Silver Ores at Mineral Hill — Introduction of Mechanical Roasters — Ore Elevator — Amalgamation of the Roasted Ore — Oakes’ Quicksilver Strainer — Change to Wet Pro¬ cess— Taylor Alill at Mineral Hill— Treatment of Tailings from the Roasted Ore — Sampling — Working Ores at the Ontario Mine — At the Silver King Mine . . . 145

Chapter IX. Roasting Furnaces And Kindred Appliances

The Stetefeldt Furnace — Automatic Feeder — Bruckner’s Roast¬ ing Cylinder — The Improved Bruckner Cylinders, as described by ICr Raymond — The Advantages Claimed — The Improved White Furnace — The O’Harra Roasting and Chloridising Furnace — Re¬ volving Ore Dryer — Krom’s Dry Kiln . , , .178

Chapter X. Sundr Y Appliances For Sil Ver Milling

Sectional Machinery for Mule-back Transportation — Amalgam Safes — Quicksilver Elevator and Tanks — Quicksilver Pumps — Krom’s Improved Crushing Rolls ..... 207

CONTENTS.

XU

Chapter XI. Concentration And Ore Dressing : Sizing

, PAGE

Or^s as they come from the Mine — Separation of the Ore — The y/" Theory of Separation — Sizing Apparatus — Coarse and Fine Con¬ centration — Sizing of equal-falling Particles — Continuous Cylindri¬ cal Trommels — Single Conical Trommel — Revolving Screens — Separation without Sizing — Pyramidal Troughs — Triangular Double Troughs — -Conical Apparatus — Bilhaiz Spitzgerinne . 221

CHAPTER XH.

CONCENTRATION AND ORE DRESSING (continued) :

CONCENTRA TING.

Jigging Machines or Jigs — Coarse and Fine Sand Continuous Jig — Wimmer’s Continuously Working Jig — Rittinger’s Continuously Working Jig — Huet and Geyler’s Self-Acting Jig — Argali's Jig — Collom’s Jig — Concentrating on Buddies — The Convex Buddie —

The Concave Buddie — The Percussion Table — The Rotating Table — The Embrey Concentrator — The Krom Dry Concentrator 241

CHAPTER XHL

EXTRACTION OF SILVER BY LEACHING PROCESSES.

Treatment of Silver Ores by Solutions — Augustin’s Process — Ziervo gel’s Process — Von Patera Process as improved by Russell—*

Mr. Stetefeldt’s Account of Russell’s Process — Lixiviaiion and Amalgamation compared . . . * , . , .279

CHAPTER XIV.

MELTING AND ASSAYING.

Section I. — Assaying Alloys and Ores of Silver by the Dry Method. — Process of the Assay — Classes of Or s tor Assay, according to Mitchell — Sconfication — Cupellation — Melting Fur¬ nace — Muffle Furnace . 297

Section II. — Melting and Refining of Silver Bullion. — Melting the Amalgam for Bullion — Melting Room and Bullion Weighing Room at Consolidated Virginia Mine — Assaying of Silver Bullion — Assaying of Dore Bullion . . . . • 311

Section III. — Assaying Silver by the Wet Method. — Process of the Assay — Measurement of the Salt Solution — Temperature of the Normal Solution of Salt — Calculating the Standard of Alloy — Assay of Silver Alloys containing Meicuiv — The Agitator . 321

CONTENTS.

Xlll

SUPPLEMENTARY CHAPTER.

PAGE

The M. P. Boss Plant — The Boss One-Level System — Boss Amal¬ gamating Pan — Brunton’s Ore Sampler — Roasting with Salt — What Roasting Furnace to adopt — The W. H. H. Bowers Fur¬ nace — The R. L. Thompson Furnace — Comportment of other metals in the Amalgamation of Silver Ores . 331

LIST OF ILLUSTRATIONS.

FIG.

PAGE

I. The At rastra

The Patio .

— 4. Blake’s Rock-breaker

— 6. Krom’s Rock-breaker

Tulloch’s Ore-feeder . .

P'ront Elevation of Battery

Section of Battery . . .

Double - discharge Wet-

crushing Moi tar . . .

II. The Die

The Stamp Head or Boss .

The Shoe .

14. The Tappet .

15 & 15a. The Guides . . .

Wheeler Pan .

Shoe in Wheeler Pan .

Hepburn and Peterson’s

Wheeler and Randall’s Pan

Elevation of McCone’s

Pan .

McCone’s Pan ....

-25. ,, Section and Plan

Combination Pan . . .

Settler or Separator . .

„ Plan .

Amalgam Strainer . . .

30. The Agitator .

3^-

The Clean-up Pan . . .

-33. Retort .

FIG. PAGE

34. Retort Lid . 84

35. Liebig’s Condenser ... 84

36. Amalgam Trays .... 84

37 — 38* Bullion Melting Fur¬ naces . 85

39. Melting Tongs .... 86

40. Ingot Moulds . 86

41. Section of Silver Mill . . 87

42. View of California Pan

Room . 95

43. Montana Mill, Elevation \

45- j) Section . /

46. Roasting Furnace, Plan . 148 47* » Section . 149

48. Freibei g Barrel . . . .150

49. „ Transverse Section 150

51. „ Steam Pipes. . . 151

52. Dry Crushing Mortar . .155

53. Ore Elevator . 156

54. Pan with wooden sides . 157

55. Oakes’ Quicksilver Strainer 1 59

57. Retort and Melting Fur¬

nace . r6i

58. The Taylor Mill .... 164

59. Stetefeldt Furnace . . . 179

61. Bruckner Roasting Cylinder 187

62. „ Longitudinal Section 188

LIST OF ILLUSTRATIONS.

^iv

FIG. PACE

63. Bruckner Roasting Cylin¬

der, End Elevation . 189

64. Bruckner Two - Cylinder

Roaster . 192

65. ,, Elevation B ick iq

67. White Roasting Cylinder 200

68. O’JHarra Roasting Fur¬

nace . 202

69. Revolving Ore Dryer . 204

70. Krom Dry Kiln . . . 205

71. Sectional Moitar . . . 207

72. Quicksilver Safes . . . 208

72A. Quicksilver Elevator. . 209

73. Quicksilver Pump System 210

74* 5 ’ >> 2 1 1

75. Quicksilver Pump Section 213

76. Krom’ s Crushing Rolls . 214

79. Cylindrical Trommel . . 228

80. Single Conical Trommel . 229

81. Revolving Screens . . 230

82 — 84. Pyramidal Troughs . 231 85 — 87. Triangular Double

Troughs . 235

88. Conical Separator . . . 238

89. Bilharz Spitzgerinne . . 239

90. Continuous Jig .... 243

93. Rittinger’s Jig .... 246

94. Huet and Geyler’s Jig . 247

96. Argali’s Jig . 249

97* >> . 230

98. Collom’s Jig, Longtitudi-

nal Section . 251

99. ,, Transverse Section 251

100. ,, Horizontal Section 252

101. ,, Perspective View . 252

102. Convex Buddie . . . . 255

103. Concave Buddie . . .237

FIG.

104. Concave Buddie, Plan .

105. Percus-ion Table . .

106. Rotating Table . .

107. Embrey’s Concentrator,

Longitudinal Section .

109. ,, End Elevation .

110. Krom’s Pneumatic Jig .

111. ,, ,,

1 12. Ore Assay Crucible . .

113. Crucible Tongs . . . .

1 14. Ore Assay Mould .

1 15. Mortar .

1 16. Scorifier .

1 1 7- Scorifying Tongs . .

118. Cupel Triiy .

1 19. Ore Assay Furnace .

120. Muffle furnace . . . .

121. Bullion Melting Room .

122. Bullion Weighing Room

123. Pipette .

124. Agitator for Silver Assay¬

ing .

125 — 127. Boss Amalgamating Apparatus . . 332—

[28 — 9. Boss One-Level System 130 — 132. Boss Pan -driving Gear and Clutches .

133. BooS Amalgamating Pan,

Section . .

134. ,, Bottom View .

135 — 136. Brunton’s Ore Sam¬ pler .

137. The Bowers Furnace ;

Elevation . .

139* Plan of Dust

Chamber . . .

140. ,, Sectional Elevation

145 147* >> ....

148 — 150. The Thompson Fur¬ nace .

PAGE

277 299 299 299

317 323

THE

METALLURGY OF SILVER.

- • -

Chapter I

Section T. — Silver Mines of the Western States of America. — First Discovery of Silver in the United States — Comstock Lode — War Eagle Mountain Mines — Golden Chariot and Ida Elmore Mines — Contests between Miners — Burnt Wagon District — Eureka Silver Lead Mines — White Pine and Pioche Mines — Panamint and Death Valley — Arizona and New Mexico — Author’s Sources of Information — Mr. Clarence King on the Silver Regions of the Pacific Coast.

Section II. — Silver Ores. — Forms of Native Silver — Varieties of Ore — Their Geographical Distribution — Chemical Properties of Silver. Section III. — Treatment of the Ore. — Methods considered in this volume : Amalgamation and Lixiviation — Other Methods — Mexican or Patio Process — Stove Amalgamation — Hot Process.

I. — Silver Mines of the Western States of America.

On many occasions, when acting (as I did for a period of eighteen years) in charge of mines and metallurgical works in the Western States of America, it fell to my duty to visit pro¬ fessionally new mining districts, as they were opened up to civilization by intrepid prospectors, who had penetrated into unexplored mining fastnesses, inhabited only by wild Indians. To these pioneers — the advance guard of an ever-changing and shifting Western mining population — we owe numerous disco¬ veries ; and the world at large is indebted to them for a large amount of the stock of precious metal now available.

B

INTRODUCTORY CHAPTER.

A warm tribute is due to the prospector for the services he has thus rendered, and is still rendering, to his fellow-men. Hardened by prolonged outdoor life they are noted for their indomitable courage and bravery, and their readiness to face hardships and privations of all kinds ; and although their out¬ ward appearance, like their manners and diction, may be rough and uncouth, I have discovered among them traits of a noble character worthy of men in the highest ranks of life.

A party of these pioneers, who were located in 1859 in one of the mountain ranges east of the Sierra Nevadas, on what they supposed to be gold “ placer ” mines, while washing the auriferous earth found intermingled with their scales of gold dust, a black earthy substance which so seriously interfered with their method of gold extraction that it was decided that one of their party of five should go to Sacramento to ascertain what this black substance was. Examination of the “ black stuff” re¬ vealed it to be pure sulphide of silver ; and these five prospec¬ tors, it appeared, were “ground-sluicing” on the much-de¬ composed outcrop of the Ophir mine, a portion of the now famous Comstock lode, which was subsequently so named after Comstock, the leader of the party. This was the first discovery of silver in the United States of America; and it is hardly necessary to say that it created almost unbounded excitement among the miners of California. Shortly afterward the open¬ ing of the Esmeraldas, farther south in Nevada, led to the production of large amounts of silver ; and these same mines are now being reopened by some London mining companies.

At the outset of metallurgical operations difficulties were experienced in the treatment of the ores, but in spite of all drawbacks, the quantity of gold and silver produced from the Comstock, within a short time after the discovery, was enor¬ mous, demonstrating the great wealth which was hidden in hose mines, which are productive even now.

Thanks to the efforts of some metallurgists with European raining and experience (amongst whom special notice is deserved by the Hungarian engineer, Guido Kiistel), the treat¬ ment of the ores gradually improved, and it eventually de-

DISCOVERIES OF SILVER IN AMERICA. 3

veloped into the now perfect Washoe Process, named after the district in which the Comstock Lode is located.

The next discovery of silver of any note was the deposit on War Eagle Mountain, in Idaho Territory ; and in spite of the distance of the spot from any centre of supply — located, as it was, in an inhospitable region, difficult of access on account of roving Indians — a most prosperous mining district quickly sprang up. As one of the early settlers there, I became in¬ terested in some valuable finds ; and I was probably one of the youngest of the mine and mill-owners in that region, having then barely passed my twenty-second year.

Most noted among the mines of the district were the Golden Chariot and Ida Elmore. Their working shafts were barely one hundred feet apart ; but the short intervening piece of ground contained such riches that both mines coveted its possession, and came into frequent collision as to the exact boundary line. Their disputes culminated in armed contests deep under¬ ground, men armed with repeating rifles being sent down the shafts to protect the miners from behind breastworks built up in the tunnels and drifts, while the diggers were blasting out the rich ores from the disputed bonanza. As the working galleries of the mines were connected, several men were killed and wounded on both sides before this unsatisfactory state of things was brought to an end. It was costly work, for the companies had to pay their “ fighters ” from to ^£200 a

day for doing patrol duty in the mines.

Matters were brought to a crisis by the killing of Mr. Marion Moore, the largest shareholder of the Ida Elmore ; and the country becoming terrorized, the governor of the territory came upon the scene with a battalion of United States soldiers, and taking possession of the mines, proclaimed martial law and restored order. That was in March, 1868. This was not the only instance of a bloody conflict for the possession of rich ore, similar scenes having been enacted in other districts.

Now followed discovery after discovery, and news reached us from the sandy deserts of Nevada that rich silver ore had been found in the Reese river regions. From that point a

INTRODUCTORY CHAPTER.

party of prospectors started in 1869 the Burnt Wagon District, seventy miles north-west, a country which took its name from the remnants found there of burnt wagons, which had belonged to a party of emigrants attacked and killed by Indians, the latter finishing their work by burning the wagons. Near by was a spring, and here the party of prospectors camped. Their search for minerals was rewarded by a most magnificent find of bold and rich outcroppings, which were located on what they designated “ Mineral Hill.” Their re¬ ward was the sum of ;£‘ioo,ooo, which they received from the Californian purchasers. When these mines were sold to an English company, in 1870, I was appointed metallurgist of the works. My engagement at this concern gave me the oppor¬ tunity to examine and study the Eureka Silver Lead Mines, sixty miles farther south and thirty miles beyond the then cele¬ brated White Pine Mines ; and, to crown fhe brilliant silver period, the famous Pioche Mines were “ located ” by some soldiers, while in pursuit of hostile Indians, another hundred miles farther on in the south-eastern corner of Nevada. Mean¬ while, and simultaneously, the western escarped ridges of the bold Wahsateh ranges were being closely searched. There large bodies of silver lead ore were uncovered, rivalling the Eureka Mines in extent. Such mines as the Emma, Flagstaff, and many others were also being developed, and the comple¬ tion of the great Central and Union Pacific Railways, which crossed the continent, assisted the early explorers in the active prosecution of their enterprises.

Meanwhile, also, explorations were pushed farther south, and in 1874 the discoveries at Panamint, in Suprise Canon, Inyo County, attracted me to that region. While there I had occa¬ sion to investigate the New Coso Silver Lead Mines, the Argus Range with its noted Modoc Mines, Wild Rose Springs and adjacent territories, including Death Valley, some portions of which are no feet below sea-level.

When I look back to those days, when I underwent priva¬ tions and hardships such as were not known to me in a more congenial northern clime, I cannot but commiserate those poor

DISCOVERIES 015 SILVER IN AMERICA.

fellows who, falling a prey to hunger and thirst, lost their lives in their struggles to acquire wealth in those mountain fastnesses, and whose bones are bleaching among the desert sands of Panamint and Death Valley. Beyond California and Nevada, still farther south, among the more dreary and desolate reaches of Arizona, the indomitable energy and perseverance of the prospector opened up new countries and fields for enterprise. Arizona and New Mexico, although very sparsely settled and little known as far back as 1870, have since risen to the rank of great silver-producing countries, and the Silver King, the Tombstone Mines, and others too numerous to mention, have contributed their quota to the world’s stores of silver and gold.

In the course of my explorations, I visited over twelve hundred mines and every individual district possessed distinct geological features of its own, and in no case did I observe two distinct districts, which, as to formation and character of ores, were entirely similar in structure. No amount of geological knowledge alone, therefore, will enable an observer to determine, as it were by rule of thumb, the possibilities or probabilities of a newly discovered mine ; and I accordingly recommend the mining engineer or metallurgist who is in charge of a mine to thoroughly explore his ground and open up his ore bodies before launching into large expenditure in the erection of reduction works. Let him first satisfy himself that he has

plenty of grist for his mill.”

Silver on the Pacific Coast of America. — As the demon¬ strations given in this work mostly refer to mining regions located on the Pacific coast, I will here quote an interesting account given by Mr. Clarence King* of the geological features of the mining districts and the mode of occurrence of the precious metal ores : —

“ West of the hundredth meridian, and bordering the Pacific Ocean from Southern Mexico to the Arctic Sea, stretches a series of mountain chains and elevated plateaux. From a width of 400 miles on the Mexican line it rapidly widens to

* In his “ Geological Explorations of the Fortieth Parallel.”

INTRODUCTORY CHAPTER.

the north, reaching its greatest expansion on the fortieth parallel, where the actual mountain zone is over i,ooo miles wide. Fron^this point it again narrows toward the north, diminishing to 400 miles upon the north-west boundary line.

“ The central portion of this area is embraced under the general name of the Great Basin, and includes all that barren middle ground between the California mountains and the Rocky system.

“ The Great Basin is walled up upon the west by the Sierra Nevada range. Its eastern boundary is the Wahsatch chain. A section across the 500 miles of intervening country, along the fortieth parallel, shows a rapid descent from the Sierra summit, whose elevation at this point is about 10,000 ft., to a depressed zone of country which skirts the great range for 1,000 miles and spreads out to the east in comparatively level deserts, its surface here and there interrupted by abrupt chains of mountains. From this area of desert lowland, averaging in altitude about 4,000 ft. above sea-level, the country gradually ascends to the eastward, the surface being occupied by a suc¬ cession of meridional ranges separated by trough-like valleys.

“ Where the fortieth parallel intersects the one hundred and sixteenth meridian of west longitude the rise culminates, and passing thence eastward the general profile of the plateau sinks gradually to a second belt of depressed plains, whose aridity rivals those of the Nevada Basin. The desert basin of Utah is still further suggestive of Nevada since the lofty Wahsatch rises abruptly from its level, scored by sharp canons closely resem¬ bling the eroded front of the Sierra. The average altitude of the entire system of parallel ranges, which trace themselves from north to south across the Great Basin, is not far from 9,000 feet.

“ The plains, from a level of 4,000 feet, which is about the height of the basins of Nevada and Utah, rise to a mean eleva¬ tion of 6,000 feet in the middle of the system.

“ If a circle be traced from this central point, latitude 40 and longitude 116, with a radius of 250 miles, the circumference will be found to mark a continuous chain of depressions. The

SILVER ON THE PACIFIC COAST. 7

middle plateau of Nevada is, then, an important centre of elevation and of drainage.

“ The depressions of the ring are dreary reaches of desert where fields of sand alternate with alkaline plains, where, in the brilliant dry air, the eye may range over expanses of deso¬ late lowland, naked and devoid of all vegetation except those blighted-looking forms of life, the sages, which rather intensify than relieve the deathly aspect of the scene. The central plateau region is somewhat more favoured ; occasional grassy valleys interrupt the sage plains, and the mountains are less sterile and forbidding. Trees, which were almost wholly absent in the lowland, occur on the loftier ranges, and near the per¬ petual snow which here and there caps the higher summits an extraordinary fertility is developed.

“ A glance at any physical map of this region shows a general parallelism of ridges with a prevailing north-west trend. The materials of this immense mountain area are infinitely varied, ranging from the earliest to the most recent deposits, and em¬ bracing almost all known species of sedimentary and eruptive products. The greater part of the rock is a series of conform¬ ably stratified beds, reaching from the early Azoic up to the late Jurassic period, when these level beds were compressed into vast mountain corrugations and elevated above the sea in a general wide and high plateau. Accompanying the upheaval and crumpling of this great oceanic family, and bursting from its fractured folds, are important masses of granite, penetrating the axis of the flexures and breaking through lateral fissures. Quartz-porphyries, felsite, and, notably, syenitic granite, with occasional occurrence of granulite and greisen, accompany the ejections of granite.