The Prospector's Fieldbook and Guide in the search for ... Minerals. Illustrated, etc

Front matter

THE PROSPECTOR'S FIELD-BOOK AND GUIDE. THE PROSPECTOR'S FIELD-BOOK AND GUIDE. IN THE SEARCH FOR AND THE EASY DETERMINATION OF ORES AND OTHER USEFUL MINERALS. BY Prof. H. S. OSBORN, LL.D., AUTHOR OF " THE METALLURGY OF IRON AND STEEL ;" " A PRACTICAL MANUAL OF MINERALS, MINES, AND MINING." ILLUSTRATED BY FORTY-FOUR ENGRAVINGS. PHILADELPHIA: HENRY CAREY BAIRD & CO., INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 810 WALNUT STREET. LONDON: SAMPSON LOW, MARSTON & CO., Limited, St. Dunstan's House, Fetter Lake, Fleet Street. 1892. COPTRIGHT BY HENRY CAREY BAIRD 4 CO. 1893. Printed at the COLLINS PRINTING HOUSE, 705 Jayne Street, Philadelphia, U. S. A.

Preface

. Lsr the following pages we have attempted to present such a view of the whole subject of prospecting for the useful minerals that any liberally educated reader may fully compre hend our meaning. We have therefore ex plained special terms where we have thought it convenient to use them, and where the tech nically educated student would not need an explanation. It must be understood that the subjects of chemistry, mineralogy, and metallurgy are in troduced only for their practical bearing upon the ores in hand, or those sought for, and not for theory, or the philosophy of the operation, much as such theory or philosophy would please and instruct. The prospector must, therefore, refer to larger works if he desire to be instructed in the principles governing the V

PREFACE.

. sciences, the teachings of which we have frequently nuirle use of. We would suggest to any one intending to use this volume for practical work, to become acquainted with the whole book before attempt ing to use any special part alone. The object and construction have made it necessary to treat some special topics Avithout repeating principles and methods already given in some part of the work, but which bear some relation to the topic under immediate consideration. The Table of Contents and Index have both been carefully prepared, and being very full, will make reference to any subject in the volume easy and satisfactory. Oxford, Ohio, Jan. 5, 1892. CONTENTS.

Chapter I. Preparatory Instruction

PAGE Technical mineralogy, the first study of the prospector; Guises of metals . . . . . . .17 Benefit of cultivating a knowledge of minerals by sight ; Examples of the importance of a knowledge of technical mineralogy . . . . . . .18 Definition of technical mineralogy ; Necessity of a knowledge of the recks associated with the minerals 19 Importance of a general knowledge of the manner in which the geologic rocks are laid dowji ; Signs by which the name of the sedimentary rock can be determined ; Horizons of rocks . . . . .20 Movements of the earth's crust illustrated by a section showing contorted strata due to lateral pressure ; Practical geology . . . . . . .21 Horizons sterile in ores ; Horizons in this country which abound in the useful minerals ; Classification o rocks ; Definition of rocks . . . . .22 Reasons for differences in the geological horizons ; Table showing the relations of certain rocks one to another; Igneous rocks ....... 23 Metamorphic rocks . 24 Aqueous rocks ; Sandstone illustrated and described . 25 Shale illustrated and described ; Granite and its varieties ; ...

CONTENTS. PAGE Granite wiih black mica and feldspar crystals with quartz as chief ingredient, illustrated ; The blowpipe 27 Colors of a candle flame illustrated and described . 28 Oxidizing and reducing flame ; Definition of the assay ; Roasting; Illustration showing the characteristic power of the oxidizing and reducing flame . . 29 How to make a blow-pipe ; .Salts required for blow-pipe practice . . . . . . . .31

Chapter II. Crystallography

The composition of minerals indicated by their form ; Systems of crystalline forms ; the cube illustrated and described ....... 32 The isometric system ; Variations of the cube; The octahedron and dodecahedron illustrated . . .33 The tetragonal system ; The prism illustrated and described ; Tetragonal octahedron, illustrated . . 34 The zircon illustrated and described ; The hexagonal system illustrated and described . . . .35 Forms of the hexagonal system ; Calcite hexagonal crystals — three sided termination, illustrated ; The orthorhombic system illustrated ; The monoclinic system illustrated ....... 36 The triclinic or thrice-inclined system ; Illustrations of the different systems of crystallization . . .37 Distinctions between the turquois, lazulite, and lapis-lazuli 38 The topaz and its crystallization ; Meteoric iron . . 39 Ruby and sapphire ; The garnet sometimes mistaken for the ruby ; Serious mistake of a Paris firm of jewelers ; Locality of gems ....... CONTENTS. VIII

Chapter III. Surveying

PAGI! To measure heights which are inaccessible, illustrated 41 To measure areas, illustrated by examples . . .42 To measure an inaccessible line, illustrated by examples 45 The prism compass and its use . . . . .47

Chapter IV Analyses Of Ores Wet Method

Preliminary examinations; Detection of sulphur, arsenic, and silenium ; Determination of native gold and silver; Detection of antimony and tin . . . .49 Determination of manganese, alumina, magnesia, lime, zinc, cobalt and nickel, uranium . . . .50 Determination of titanium and mercury ; Detection of carbonates ........ 51 Qualitative analysis of ores ; Dry method of analysis ; Directions for the wet method of analysis . . 52 Indications of the presence of silver, lead, or mercury in the assay ........ 54 Apparatus for making hydrogen sulphide, illustrated and described ....... 55 The precipitate and its treatment . . . .56 What the precipitate may contain ; Precipitation of chromium oxide ....... 57 Precipitation of alumina ...... 58 Precipitation of manganese, cobalt, and nickel . . 59 Establishment of the presence of mercury oxide and lead sulphate ; Indication of bismuth . . .60 Indication of copper, sulphur, and gold ; Detection of platinum and of arsenic . . . . .61 Indication of antimony and tin CONTENTS.

IX DRY ASSAY OF ORES. PAGE Crucibles; Scorifiers; The cupel; The assay furnace, illustrated and described .... .03 Brasquing ; Method of obtaining the amount of iron in an ore ; Scales, weighing, etc. . . . .64 Pulverization for the dry method; Gold and silver ores; Cupellation ........ 65 Separation of the gold and silver by the wet process ; Flux for melting the ore . . . . .66 Lead ore, galena ; Copper ore ; Tin ore ; Mercury, antimony ........ 67 Bismuth, zinc, manganese, nickel, cobalt . . .68

Chapter V. Special Mineralogy Gold

Gold; Native gold and its impurities . . .69 How gold is distinguished'; Other forms and conditions of gold ; Placer gold ...... 70 Gold amalgam ; Extraction of gold ; Where is gold found? 71 Gold in granitic regions, illustrated by section showing the two conditions under which gold is usually found in rock and drift ....... 72 Change of metamorphic rocks from ordinary sedimentary rock ; Igneous rocks and their composition . . 74 Where the most paying gold is to be found ; Gold in combination ........ 75 To separate gold in metallic sulphides, for instance, in iron pyrites ........ 76 Mode of making fuming nitric acid . . . .77 Another method of detecting and separating the gold . 78 What constitutes profitable gold working . . .79 CONTENTS. X ■ PAGE Method of separating gold which gives very accurate results ......... 80 In review with additional remarks ; Where the prospector may expect to find gold . . . .81 Phillips' rule for ascertaining the amount of gold in a lump of quartz 83

Chapter VI. Platinum, Etc Silver

Occurrence and properties of platinum ; Platinum in the United States ; How to distinguish platinum . 85 Chemical test for platinum ; Separation of platinum from gold and other metals . . . . .86 Preparation of stannous chloride ; properties of platinum ; Geology and occurrence of platinum . . 87 Test for platinum ; Occurrence of iridium, palladium, and platiniridium ; Silver and its occurrence ; Mispickel ; Distinction of native silver before the blowpipe . 88 Chemical test of silver ; Derivation of most of the silver of commerce ........ 89 Other forms in which silver is found ; Silver sulphides; Horn silver ........ 90 Brittle silver ore or stephanite ; Red silver ore or ruby silver ......... 91 Geology of silver ores illustrated by sections across the Comstock Lode and surrounding strata, east and west, and north and south, and showing the mines and the surface ......... 92 Non-metallic and metallic substances of the Comstock Lode ; Extent and value of the Comstock Lode . 95 Occurrence of silver ores at the Eureka Mines ; Peculiarity of the limestone overlying the Eureka Mines 96 Geology of the Emma Mine ; Ore of the Emma Mine CONTENTS. XI

Chapter VII. Copper And How Measured In Ores

PAGE Copper, its occurrence and properties ; Manner of testing mineral containing native copper . . .99 Red copper ore or ruby copper ; Copper glance or vitreous copper ore ; gray copper (tetrahedrite) ; Copper pyrites (ehalcopyrite) . . . . . .IOC Silicate of copper ; Black oxide of copper ; Malachite, green carbonate of copper . . . . .101 Geology of copper, illustrated by section of the copper bed at the Dolly Hide Mine, Maryland; Section of strata in Lake Superior copper region, and section of the Eagle vein, Lake Superior .... 102 Facts for the detection of copper . . . .103 To obtain the per cent, of copper in an ore . . 104 Precautions to be observed in the assay of copper . 106

Chapter VIII. Lead And Tin

Lead and its occurrence ; Order of strata in the lead district of Wisconsin, Illinois, and Iowa ; Test for silver in galena . . . . . . .108 Geology and form of lodes of the galena ores illustrated by lead lode in micaceous slate in mine near Middletown, Conn.; Galena and its associated minerals; Carbonate of lead (cerusite), illustrated by section of strata in California Gulch, Col. .... 109 Sulphate of lead . . . . . . .110 Phosphate of lead ; Chromate of lead ; Lead ochre (massicot) . . . . . . . .111 Geology of lead, illustrated by section of galena limestone ; Galena limestones . . . . .112 CONTENTS. XII PAGE Circulation of water in lead veins .... 113 Deposit of lead in fissures in the limestone, illustrated by a section ; Tin and its occurrence ; Oxide of tin ; Wood tin ; Toad's eye tin 114 Stream tin ; Discovery of tin in Banca and Billiton ; Associations in Wyoming and Dakota tin mines; Pyrites (sulphide of tin) . . . . .115 Bell metal ; Cassiterite or black oxide ; Hearney Peak Mines ; Gold in tin veins . . . . .110 Minerals found in the Etta Mine ; Detection of wolframite . . . . . . . . .117 Phosphate of lime, ;'. e., apatite . . . . .118 Home of the tin deposits . . . . . .119 Cassiterite of the Black Hills, Dakota . . .120

Chapter IX. Zinc

— IRON. Zinc and its chief ores; Zinc carbonate (smithsonite); Zinc silicate (calamine) ; Red oxide of zinc (zincite) 121 Sulphide of zinc (sphalerite or blende) or black jack ; Geology of zinc, illustrated by section of strata near iSparta, N. J., zinc mines . . . . .122 Sulphide of zinc deposits in Colorado and Montana; Zinc blende from a group of mines near Cotopaxi, Col. ; Report by Mr. E. H. Saltiel ; Blow-pipe tests for zinc . . . . . . . .123 Iron and its chief ores ; Magnetite; Franklinite . 124 Specular ore (red hematite); Geological horizons around the iron ores of Lake Superior, illustrated . . 125 Brown iron ore or brown hematite; Spathic iron ore . 120 Black band ore ; Geology of iron ores . . .127 Section of Pilot Knob, Missouri . . . .128 CONTENTS. PAGE The use of the magnetic needle in prospecting for iron ; Mr. W. H. Scranton's summary of the indications from the magnetic needle in searching for ore . .129 Methods of using the compass in searching for ore . 130

Chapter X. Mercury, Bismuth, Nickel, And Cobalt

Mercury; Cinnabar; Native amalgam . . . 132 Bismuth and its geology; Nickel .... 133 Smaltite ; Nickel arsenide (copper nickel, or nicolite) ; Emerald nickel . . . . . . .134 Millerite; Nickel at Sudbury, Canada . . . 135 Analysis of ores for nickel and cobalt ; Preparation of the assay ; Separation of lead . . . .136 To separate the copper . . . . . .137 Apparatus for reducing the oxides to the metallic condition by ignition under a stream of hydrogen . 139 Separation of nickel and cobalt . . . . .142 Analysis of ores for pyrrhotite ; New Caledonia nickel ore 143 Cobalt; Smaltite; Cobaltite . . . . .144 Erythrite; Linnaeite ; Cobalt wad .... 145

CHAPTER XL ALUMINUM, ANTIMONY, MANGANESE, AND OTHER MINERALS.

Aluminum ; Corundum ...... 147 Cryolite; Beauxite ....... 148 R. L. Packard's report on aluminum .... 149 Clays at Gay Head, Martha's Vineyard, Mass. ; Antimony and its geology ; Stibnite ; Manganese ; Classes of manganese ores . . . . . . .150 CONTENTS. XIV PAGE Wad ; Geological position of manganese ; Other useful minerals; Ozokerite ...... 151 Asphaltum ........ 152

Chapter XII. Precious Stones

Diamond and its occurrence in the United States ; Itacolumite . . . . . . . .153 Ruby and emerald ; Beryl, phenacite, and topaz . . 154 Garnets; Epidote ; Fire opal ; Turquois . . . 155

Appendix

. CORRECTION OF WEIGHTS AND MEASURES. English length ........ 157 Peculiar measures of length ; Surface measure ; Surface measure in feet ; Solid measure ; Weight ; Troy weight ......... 158 ■s Avoirdupois weight ; Weights by specific gravity . 159 Specific gravity, how to find . . . . .160 Special weights, etc. ; French measures — Length . 161 Smface ; Solid measure ; Weight ; Specific gravity of metals, ores, rocks, etc. ...... 162 A ton weight will average in cubic feet . . . 164 Prospector's Pointers . . . . . .165 Index . THE PROSPECTOR'S FIELD-BOOK AND GUIDE.

Chapter I. Preparatory Instruction

In preparation for skilful work, the prospector should become thoroughly acquainted with the forms under which useful minerals and metals appear. This should be his very first study. It may be called the study of technical mineralogy. He should be able to detect all the guises, as they may be called, which usually present themselves. Some metals are found native and in some degree of purity, as in the cases of gold, silver, copper, mercury, and platinum, and when so found are readily determined at once by any one who is at all acquainted with those metals as they occur in general use. But frequently native metals appear under such colors and even forms, that the discoverer must possess more knowledge than any one usually possesses who has seen the metal in the arts only. Gold, as an illustration, is frequently found in various shades of yellow, in accordance with the amount of silver or copper it may contain and yet to the practiced eye of a true mineralogist it never loses the true gold hue.

Iron pyrites which is composed of sulphur and iron and called "pyrite," mineralogieally, has a color some what similar to that of gold, and so also has a mineral called ' ehalcopyrite," or copper pyrites, which contains copper, iron, and sulphur. These, with others, vary in the yellow shade and degrees of color, but to the practiced eye are instantly detected. Of course the brittleness of these minerals is unlike the softness of native gold, and this would instantly reveal the fact that they were not gold, but we are now speaking of the practiced eye, alone, and therefore of the benefit of cultivating a knowledge, by sight, of minerals. What we have said of color may also be said of weight and form. A lump of pyrite in the hands of a skilful mineralogist would be distinguished from gold by its weight, since a mass of gold of the same size would weigh at least three times as much.

Three crystalline pieces, the one of barite, the other two of lime carbonate and of quartz, may to the unskilful eye appear equally transparent but the form of the first is tabular, that of the latter two is in six-sided crystals, but the lime carbonate crystals terminate in three sides while the quartz always (like the sides) in six. These distinctions may appear to be only scientific abstractions, but they are sometimes of seriously great practical importance. A large amount of iron ore in Jefferson Co., New York, was condemned as being covered witli quartz from the fact that the minute crystals which appeared had six sides, but the author by means of his pocket lens noticed that none of the terminations were six-sided, and therefore that they could not be quartz, which renders iron ore injurious to the furnace.

They were crystals of lime, which is no detriment, but rather a benefit to iron ore. This simple discovery restored several thousand tons of ore to the market. At another time the author was shown a nearly transparent specimen taken by the finder to be a piece of calcite found the same day on an island in Lake Erie, but calcite, in crystalline shape aud transparent, takes a rhomboidal form and this appeared as though several tablets had been joined together at the edges. It was tabular in form, which form is never taken by lime (calcite), then on handling the specimen its weight, together with its form, showed that it was baryte, or sulphate of barytes. A visit to the island led to the discovery of many tons. It is now a very valuable mine. We have presented these illustrations to show that a knowledge of technical mineralogy is of the first importance to the prospector.

By technical mineralogy we mean only that amount of mineralogical knowledge which will be needed to recognize valuable minerals and metals, and to trace them to their hiding-places, aud this amount of mineralogical skill can be most thoroughly acquired, although, of course, it forms but a small part of the whole subject of mineralogy as a science. Beside a knowledge of the forms under which the minerals we seek present themselves, it is also neces sary to learn the characteristics of some of the rocks which are generally associated with those minerals. The object of this knowledge is to serve in directing us to those regions where we may with greater probability discover the minerals we seek. It also serves to warn us out of a region where we should not expect to find what we desire. To illustrate, we may not expect to find iron ores of a certain kind, brown hematites for instance, in a granitic country.

On the other hand we may find the magnetic ores in such a region, and it is useless to explore a granitic region for black band iron ore, although it may be the proper region to discover red hematite. It is, therefore, important that the prospector should be able to distinguish many of the geologic rocks to help in guiding or in checking him, in his explorations. A general knowledge, therefore, of the manner in which the geologic rocks are " laid down," their order, or succession, in the earth, is important, and the distinction between sedimentary and that which has been, and is usually called " igneous rock," but more properly " azoic rock," that is, rock whicli does not exhibit any remains of fossil or organic life. For often the only signs by which we can, with any degree of certainty, determine what is the name of the sedimentary rock is by finding the remains of former life, that is, the kind of fossil it contains.

Prof. Dana says (The Amer. Journal of Science, Nov. and Dec., 1890) that it is settled that the kind of rock in itself considered is not a safe criterion of geological age. If all the rocks in the world had been laid down in regularly horizontal sequence and had always remained in their own separate " horizons," as every rock of the same age is called, not only should we find them all parallel, one over the other, but we might readily determine to some extent what were the exact order and distance of any one horizon, or geological age. But, although there is a general order, the same in all parts of the world, there have been upheavals and sinkings, dislocations and erosions, during the ages, so that it is necessary that the prospector should become acquainted with the various changes probable in the order and forms of the vast rocks which carry the minerals for which he is seeking.

Some of these movements of the earth's crust are represented in Fig. 1. Section showing contorted strata due to lateral pressure. aa,"an ticlinal axes;" c, the '* synclinal axis." The direction of the arrows ee,ee, is that of " the strike." That of the arrows d d, is that of " the dip" of the strata, always measured from the horizon; gg, are the out-crops. PRACTICAL geology. We repeat that it is of considerable importance that the prospector should have at least some general knowledge of those geological horizons with which his work is specially associated. As we have intimated, useful ■ )■) PROSPECTOR'S FIELD-BOOK AND GUIDE. minerals do not always confine themselves to one horizon ; but there are certain ranges of rock which indicate their vicinity. There are also limits which are never overpassed by some useful minerals, and experience has shown that some horizons are always sterile in ores, and it is therefore useless ever to expect to find them in paying quantities, in certain rocks or beyond them in certain directions.

Gold often occurs where it will not pay to open and work the strata, so also with lead and copper. It is well to learn the relations of such barren regions or horizons as the strata are called. In the following table we have given chief place to those horizons which have been found in our own country to abound in the useful minerals, and we advise the possession of small specimens of the principal rocks mentioned and the special examination of the specimens under a good lens so as to become thoroughly acquainted with their appearance and their minute parts of composition. All rock may be classified as — 1. Igneous. 2. Metamorphic. 3. Aqueous. Speaking geologically, not only the hard consolidated massive and stony substances are called "rocks," but any natural deposits of stony material such as sand, earth, or clay, when in natural beds, are geological rocks.

Very few of the rocks of this earth, at any rate so far as examined, are in their original and primal condition. Even the granites and volcanic rocks are composed of other and more ancient material disinte- STRATIFIED ROCKS. i Between pages '2-2 snd 28.) GENEK VI. DIVISIONS. SUBDIVISIONS. CH IB Vi ITERKM [i 3, BECENT, PLEISTOCENE, os QUARTERN \KV. All its shells and hones are of exieting apecies. 8U g§ SO wo F PLIOCENE. About 50 per cent, of existing apeciea of shells. Contains 80 per cent. Of extinct species. '1'ert iary rocks yield hriek and other idays, gypsum, sand, phosphate of lime deposits such as are in Florida, Soiltli Carolina, and elsewhere. GOLD in the drift and alluvial, al 0 I'l. VTINTM ( Indium, Mi text), and TIN. Coal flelda (brown or lignite) of this Period, occur in India, Indian Archipelago, Japan, New Zealand, Vancouver's Island, and in Europe; also in California, Washington,!

Colorado, etc. The true coal (anthracite and i> it uminous) belongs to the Carboniferous A very bard lignite exists al Gay Head, Martha's Vineyard, in this formation. [only. MIOCENE, EOCENE. Contains fresh water and marine st rala. aid mala all exl Incl . CRET vci'ors. Upper. Middle, Lower. Upper Chalk with flints, bul the t The whole formation contains sea-shells, sponges, Lower Chalk withoul flints. £ sea-urchins, etc. Contains Greensand In England and In New Jersey, used as a marl and fertilizer. There is a supposed Cretais lignite In Alaska. Colorado, California, Utah, etc. i onsists of sand, .day, or marl, the sand used in glass making. X 9 JURASSIC. VVhoalden. Qo "/. >■ - 'Al OS 63 / Port land Stone. Oxford Group. Stoneesleld Slate. I.iniesti in horizontal strata. Some English < I la found In the Oolite.

Eimmeridge (day is found In upper Oolite ; the fine Bavarian lithographic stone In the middle Oolite. Lias plcuoue for the number of ammonites and nautilus shells. Furnishes buildinand )r.i\ Ing st Called by the Germans TRIAS. Connecticut river sandal with footprints. Red clays, marls, shales and sandsl *. The New Bed Sandsi.nn' of England. In Europe great salt beds. ig TRIA8SIC. Keuper, Muschelkalk. Bnnter-sandstone. PERMIAN. l lark red sandstone. Magnesian Limestone. ( longlomerates, Breccias, Marls in all three. v sandstones and marlytes, some Impure magnesian limestone and gypsum. Thii seams of coal, unworkable. With ezceptii f BROWN HEMATITE Ir 'e and il>< metals mentioned above, all the other metals are found in the formations below. 6 3 c w CARBONIFEROUS. Seams ofant hraclte and bil uminous coals of varying thicknesses.

Millstone grit, Subcarbonlserous. The black band iron ore. Limestone from the same mines with the coal iii Great Britain, but not so frequently In America. Anthracite, cannel, and bituminous coal in seams in limestone, sandstone, ami shales, forming tl I'he Coal Measures." Alford- PETROLEUM in Pennsylvania, Ohio, ami else-wbere, ami salines in Michigan. It is the MOUNTAIN LIME8TONE of England. Largely of corals. M c pi < a. DEVONIAN. Catskill Period. ( Iheroung Period, Hamilton Period. ( loriliferoUS Period. Oriskany Sandstone. Lovi er Helderberg Period. Salina Period. Niagara Period. Include-- the OLD BED SANDSTONE OF ENGLAND. Hamilton black Bbalea produce oil, the Hamilton beda afford excellent Bagging stone. Corniferoue called also Upper Helderberg group. Upper Salina Period supplies the sail waters of Salina and Syracuse, N. Y. SILURIAN.

Lower Trenton Period. i lanadian Period, Potsdam Sandstone. The LEAD MINES of Iowa and Wisconsin arc in the Magnesian Limestone of tb< Canadian Period. I amhrian. Lauren tlan. VIM II. KAN grated, ground up, or worn dosvn, settled, buried, aud compressed by ages of enormous pressure, or consoli dated by cementation. Some have been "laid down" under water having been disintegrated into dust carried by the winds of ages out over the oceans and seas and settled down into the form of the present rocks which afterward have been lifted up into mountains and plains above the seas. But by the transporting power of rivers or currents in ancient oceans, aud because of unequal upheaval of some regions where subterranean forces were greater than at distant places, very large differences in the nature of the deposit have occurred, even in limited regions.

These special and limited forces will account for the fact that, although, taking the geological horizons throughout the world, there is a general same ness, differences do occur, and important members of the order of succession are omitted in some regions, and exceptions to general rules occur. We give, therefore, in the table following those uni versally accepted relations of certain rocks, one to an other, in the great geologic arrangement of the svorld, omitting some of the subsidiary limited and unimport ant horizons. 1. IGNEOUS ROCKS are such as have been subjected to sufficient heat to melt the ingredients. Of these rocks — Volcanic rocks are those which have been cooled near or at the surface, as lavas, etc. Trachyte ; a grayish rock of rough fracture ; the same specific gravity as quartz, but mainly con stituted of grains of glassy feldspar.

It is essentially a unisilicate of alumina, with 10 to prospector's field-book and guide. ■24 15 per cent, potash, a little soda and lime. Differs from quartz in that it fuses before the blowpipe, while quartz remains unfused except when soda is used. Basalt ; blackish or dark brown. Traps, greenstone, dolerite, amydolite ; these latter four are only modifications, being all unisilicates with smaller amounts of potash than in trachyte, a little more soda and lime, and some traces of iron and of magnesia, varying in color and form. Obsidian is a glass, something like bottle glass, of a dark shade, and translucent. All these are compact in texture, except where some holes have been worn in by steam or gases. They are frequently found penetrating several strata, having been forced up in columns almost vertically, and some times spreading out horizontally for many miles between the strata or on the surface, and are called volcanic dykes, or intrusive rocks, or lava.

These and suck-like are igneous rocks. It is not certain that granite rocks are of igneous origin, but seem to belong to the metamorphic series. 2. METAMORPHIC; these are of igneous, subsequently to the time when they were of aqueous origin, and have undergone a change through pressure and heat, and, perhaps, in connection with steam or water. Of this class are the following : — Gneiss ; having a composition of small pieces of feldspar, mica, and quartz, like some granites, but laminated or foliated in form, and not equally solid, homogeneous, and continuous throughout its structure as granite is. Mica Schist. This term is given to those laminated rocks composed of mica and quartz in small particles, easily broken up, but more easily broken into tabular or leaf-like pieces because the mica has been deposited in planes allowing of cleavage. 3.

THE AQUEOUS ROCKS are simple water rocks, that is, rocks composed of sediments from the dust or ground-up remains of other rocks. The presence of such sediments is due to the transporting power of rivers, floods, or currents, and also of winds and storms and other agencies, carrying the dust to the ocean waters where it was arrested and became a sediment. Fig. 2. Sandstone. In sandstone (Fig. 2), the grains of sand are rounded, having no sharp edges as in granite. Where the sedimentary material was exceedingly dust- PItOSPECTOR's field-book and guide. like it sometimes is laid down as fine mud and frequently in lamina as in shale (Fig. 3). Fig. 3. Shale. Granite is a term descriptive of rocks generally composed of quartz, feldspar, and mica in grains (hence the name) of a crystalline form.