A Popular and Practical Exposition of the Minerals and Geology of Canada, etc

Front matter

CHAPMAN'S MINERALS AND GEOLOGY OF CANADA. A POPULAR AND PRACTICAL EXPOSITION OF THE MINERALS AND GEOLOGY or CANADA. BY E. J. CHAPMAN, Ph.D. PEOPESSOE IN UNIVERSITY COLLEGE, TORONTO, (LATE PBOKSSOR IN UNIVERSITY COLLEGE, LONDON, ENGLAND.) WITH OVER TWO HUNDRED WOODCCJTS, AND A COPIOUS INDEX. TORONTO: fa. C. CHEWETT AND CO. 1864. TORONTO : PRINTED BY LOVELL & GIBSON, YONGB STREET. TO SIR W. E. LOGAN, F.R.S., .fee, <fec, 4c, Qirrrtor ot ttjc (Scalogical Surbr*** of Canatia, THIS WORK (BASED LARGELT ON THE EXPLORATIONS OF THE SURVEY) IS INSCRIBED, IN ALL HOMAGE AND RESPECT, BY HIS SINCERE FRIEND, THE AUTHOR.

Preface

. The subject matter of this volume was originally published in the form of a series of papers, in the pages of the Canadian Journal of Science nnd Art. In its present shape, the work is intended to fulfil two purposes : first, to supply the general reader with a popular, and, at the same time, a practical, or really useful, handbook of our minerals, fossils, and .geology ; and secondly, to serve as an explanatory introduction to the enlarged Eeport on the Geology of Canada, and other publications, issued by the Geological Survey. The term " popular," in its application to works of this kind, is so frequently abused, that I may perhaps be allowed to explain, at the outset, the sense in which it is employed in the present volume. This will be done most readily, by an explanation of the scope and general character of the work.

"With this view, it may be observed that the subject of the present Essay is arranged under five divisions or parts. The two first, of these, relate to the minerals of Canada ; the other three, to our fossils and rock groups. i\ sow, if it were designed to draw up a description of Canadian minerals for the perusal of the mineralogist, these substances might be arranged in a chemical or chemico-physical order, and an analysis of their crystallographic peculiarities, chemical relations, and other allied points of inquiry, at once entered upon ; but as this work is intended to meet the wants of the general reader, another method — a popular or explanatory treatment — is rendered necessary. The object here, moreover, is not only to describe the characters, uses, localities, &c, of these minerals, in general terms; but to enable the reader, whilst acquiring this information, to recognise these bodies, or, in other words, to make out their names, whenever subsequently met with ; and thus to convey to him, as far as it goes, a really practical knowledge of the subject.

The more common characters or properties, consequently, by which minerals are distinguished from one another, are first passed under review. These, discussed in Part i, are considered.

PREFACE.

. however, only in their simpler or more practical bearings, so as to occasion no difficulty in their application. In Part ii, our Canadian minerals are arranged in groups and sections, founded on these easily-observed characters, in such a manner as to lead at once to the recognition of any species : see pages 20 — 22*. During the publication of this portion of the work in the Canadian Journal, many amateurs and others, previously unacquainted with Mineralogy, availed themselves of this plan, and always succeeded, by its use, in discovering the name of any specimen presented to.them. In the descriptions of the minerals, thus arranged, all the more important characters, uses, Canadian localities, &c, are fully given ; and at the close of the division (page 62), these substances are re-arranged in groups according to their chemical composition.

In order, moreover, to facilitate still further, the recognition of the more common minerals of Canadian occurrence, a synoptical view of the distinctive characters of the latter, is also given at the conclusion of this Part, (page 64). The third part of the work is devoted to a brief but sufficiently detailed analysis of the classification, structural characters, composition, modes of formation, and other allied points, relating to rocks in general. In this division, the various technical terms employed in geological descriptions, are fully illustrated and explained — reference being made, as frequently as possible, to Canadian examples. An introductory section of this kind — together with the general sketch of the typical characters and natural relations of organic remains, in the succeeding division of our subject — is absolutely necessary to ensure a proper understanding of the geology of Canada, as developed in Part v. Persons unacquainted with these details, can have no clear conception, for example, of what is implied by the term " metamorphic " in its application to rocks, or by that of "Silurian strata," "trap dyke," "anticlinal axis," "unconformable stratification," and so forth.

As a general rule, the term Silurian is associated in their estimation with some particular kind of rock, as limestone, sandstone, or the like ; and experience shews that there are many readers of geological books, who have but a very confused idea * The Reader is recommended to mark the number of the pa-ze to which the Sections refer, immediately after each of these, on pages 21 and 22. Thus : after " Aspect metallic : Hard ness sufficient to scratch glass : A :— write, page 22. After " Aspect metallic : Hardness in sufficient to scratch glass: B :— write, page 27— and so on with regard to the other sections and sub-sections.

PREFACE.

. IX of some of the commonest principles of geological reasoning. It is next to useless, in like manner, to inform a person, unacquainted with the more general details of Zoological classification, that a particular set of strata contains many examples of Orthis testudinaria, or of Calymene Blumenbachii, oroth er fossil species : or even to state that the strata in question are characterized by the presence of particular brachiopods and trilobites — since he can have no idea of the true nature and existing relations of these forms. Por this reason, I have tried to put myself, throughout, in the position of the uninitiated reader ; and I have given in Part iv, a general view of the leading classes and groups of the Animal Kingdom, with the fossil relations of these, as regards Canadian strata, fully explained.

I have also taken care, whenever it seemed necessary, to prefix to each group a few explanatory observations on the structural characters of the shell or other parts found in a fossilized condition, as will be seen more especially under the corals, brachiopods, cephalopods, trilobites, &c. The reader will thus be rendered familiar \-tith most of the technical terms employed in the descriptions of fossils in other works ; and the examination of these bodies, when their peculiar characters and conditions of occurrence, and their relations to existing types, are thus known, will present an interest altogether new. A fragment of fossil-marked shale, picked up on the lake shore, on the road, or in the quarry, becomes to us something more than a mere piece of stone, if we can read aright the strange record of life and death, of ancient shore and sea, and Nature's ceaseless changes, thus impressed upon its surface in some far distant epoch of the Past, between whose day, and ours, immeasurable ages must have come and gone.

But apart from this, a practical interest is also at tached to the study of these organic remains : inasmuch as certain fossils are characteristic of certain strata, and serve to define the geological position of these in the rock series generally. Hence the necessity of tbe study in even geological investigations of a purely technical character. Finally, in Part v., after these introductory sections, the various geological formations of Canada, including their economic materials, fossils, instructive exposures, &c, are brought under review. In this part of my work, more especially, I am bound to record my obligations to the Reports and other publications of Sir William Logan and the assistant officers of the Geological Survey. I have b X

PREFACE.

. been careful, throughout, to acknowledge my special obligations to these geologists, as well as to Dr. Dawson, the able Principal of McGill College, Montreal, and others ; but it is only just that I should prominently express also, in this place, my indebtedness to the researches and publications of the Survey, generally. In justice to myself, however, it should be stated, that the materials of this part of the work, though largely, and, in places, essentially, derived from the sources in question, have been put together, as regards generalizations, &c, in at least an original spirit. They are interwoven, also, with various notices drawn from my own field books, and are accompanied by no inconsiderable amount of explanatory observation. The engravings given in the work are of somewhat rude execution ; but there is at least this merit connected with them : a small number only — under ten or twelve, at the most — have been copied from other publications.

The rest are either original diagrams, or figures that I have drawn directly from the objects which they represent. For the use of the greater part of these woodcuts, I am indebted to the Canadian Institute of Toronto. In order to render the volume especially useful as a book of reference, an exceedingly copious index has been added to it. A glance, at this, will shew the large amount of matter condensed within the book. In conclusion, I may observe that the earlier portions of this Essay were printed in 1861 ; and that the entire work was completed, as now given to the Public, at the commencement of 1863. Various circumstances huwever, over which I have had no control, have pre vented its final publication until the present time. E. J. C. University College, Toronto, February 1, 1864. CONTENTS.

Pagi Introductory Notice 1 Part I. — How Minerals are distinguished from one another Aspect or lustre (3) ; Colour(4); Streak(5); Form(5); Structure (101 ; Hardness (11); Specific^Gravity (13) ; Relative Malleability (14); Magnetism (14); Taste (14); Action of Acids (15); Action of the Blowpipe (16) ; Trial of Fusibility (17) ; Water Test (19). Part II.— The Minerals of Canada 19 Introductory Notice 19 Index to the classification 21 Chemical Arrangement of Canadian Minerals 62 Simplified Grouping of more Common Species 64 Part III. — How.Rocks are classified and distinguished : with special reference to the Rocks of Canada 65 Eruptive Rocks 68 Lavas(67); Obsidians (67); Trachytes (67) ; Traps and Greenstones (68) ; Serpentines (70) ; Granites and Syenites (70). Metimorphic Rocks 72 Sedimentary Rocks 77 Composition of Sedimentary Rocks (78); Formation of Sedimentary Rocks (80) ; Action of the Atmosphere (81); Action of Streams and Rivers (81) ; Action'of the Sea (82); Consolidation of sediments (84) ; Changes to which the^Sedimentary Rocks have been subjected (85) ; Elevation above the'Sea (85) ; Denudation (87) ; Tilting up and Fracturing of [Strata (88)); Metamorphism and Cleavage (91).

Classification of Rocks in accordance with their Relative Ages 91 Part IV. — Some Remarks on Organic Remains, with special reference to Canadian'Forms 95 Fossilized Vegetable Remains 97 Fossilized Animal Remains 97 Protozoa 98 Infusoria (9S and 224) ; Sponges (99 and 224) ; Rhizopods or Foraminifera (99). Radiated Animals) " Corals (Graptolites, 100 ; Corals proper, 101) ; Acalepha (105) ; Echinodermata (Crinoida, 106 ; Blastoida, 107 ; Cystidea, 108 ; Thyroida, 110 ; Asterida, 110 ; .Ophiurida, 111 ; Echinida, 111 ; Holothurida, 112). Molluscous Animals I12 Bryozoa (112); Brachiopoda (113); Lamellibranchiata (119); Pteropoda(122); Heteropoda (122) ; .Gasteropoda (123); Cephalopoda (126). CONTENTS. XII Page Articulated Animals ' 32 Annelida (132) ; Cirrhopoda (133) ; Crustacea, including Trilobites, &c, (133).

Vertebrated Animals 1**1 Part V. — Canadian Rock Formations : their Sub-divisions, Fossils, Economic Materials, and Topographical Distribution 141 Introductory Notice 141 Azoic Rocks of Canada 143 Laurentian Series 143 Mineral Charaeters (144); Structure (14S); Intrusive Rocks (148); Economic Materials (149) ; Area (151); Agricultural Capabilities (152). Huronian Series 153 Mineral Characters (153) ; Intrusive Rocks and Mineral Veins (155) ; Economic Materials (155) ; Topographical Distribution (156). Palæozoic Rocks of Canada 157 Silurian Series 157 Lower Silurian Series 157 Potsdam Group (157); Calciferous Group (161); Chazy Formation (167); Trenton Group (168); Utica Formation (175) ; Hudson River Formation (177). Middle Silurian Series 180 Medina and Clinton Formation (180) ; Niagara Formation (182) ; Guelph Formation (187).

Upper Silurian Series - .. 188 Onondaga Formation (188) ; Lower Helderberg Group or Eurypterus Formation (190). Devonian Strata 191 Oriskany Formation (191) ; Corniferous Formation (192) ; Hamilton (or Lambton) Formation (195) ; Petroleum Springs and Wells (196); Portage and Chemung Group (200). Carboniferous Strata (Bonaventure Formation) 201 Sketch-Map of the Geological Formations of Western Canada 202 Post-Tertiary Deposits of Canada 204 Drift Formation (204); Post-Glacial Deposits (205) ; Conditions under which tbe Drift and Post-Glacial deposits were accumulated (209) ; Recent deposits (211) ; Economic Materials (212). General Outline and Recapitulatory Sketch of the Geology of Canada 213 Canadian Rock Formations (213) ; Azoic Series (213) ; Laurentide Mountains (214); Great Northern Basin of Canada (214) ; Great Southern BaBin of Canada (215); The Basin of the Lakes (215); The St. Lawrence Basin (219); The Eastern or Metamorphic Basin of Canada (22 1).

Corrections and Additions 223 Index MINERALS AND GEOLOGY or C /^N Js, DA.. Introductory Notice. In attempting to convey to the general reader a practical or really useful knowledge of the Minerals and Geology of Canada, it is ac - visable to consider the subject under the following heads : 1. How minerals are distinguished from one another. 2. The minerals and metallic ores met with in Canada. 3. How rocks are classified and distinguished. 4. Organic Eemains : their use and teachings. 5. Subdivisions and distribution of Canadian rocks. The term " Geology " comprises, strictly, a knowledge of the phy sical history of the Earth, as revealed to us by the study of the rock masses which lie around and beneath us ; and by a comparison of B the results of ancient phenomena, with the forces and agencies still at work in modifying the surface of the globe.

As geology is thus essentially based on the study of rocks and their contents, and as rocks are made up of a certain number of simple minerals, it is necessary, or at least advisable, to obtain a knowledge of these latter (so as to be able to recoguize them when met with), before proceeding to the discussion of the rocks into which they enter. With these minerals, also, it is convenient to consider a few others of economic application and common occurrence, including the more important metallic ores. In this consideration, the characters or properties by which minerals are distinguished from one another will first be explained, introductory to a Tabular Distribution of Canadian minerals. The latter will be so arranged as to enable the reader to make out the name of any one of the included species, with great facility.

I. How Minerals are distinguished from one another. Minerals are distinguished from one another by certain characters or properties which they possess : such as form, degree of hardness, fusibility, &c. Hence, it is to these characters that our attention must be first directed. Mineral characters are of two kinds -. physical or external characters, and chemical characters. The former are exhibited by the mineral under ordinary conditions ; the latter, only when the mineral is expos ed to the action of heat or mineral acids, by which, .in general, a certain degree of chemical decomposition is effected. Hence the term " chemical " as applied to these latter characters. The physical properties of minerals are somewhat numerous ; but many, although of the highest interest in indicating the existence of natural laws, and in their relations to physical science generally, are not readily available as a means of mineral discrimination.

These, consequently, will be omitted from consideration in the following pages ; and the other characters will be discussed only in so far as they admit of direct application to the end in view — namely, the practical discrimination of minerals one from another.* • In the explanation of these various characters, it ia occasionally necessary to refer, as examples, to a few substances of foreign occurrence. The reader will therefore understand. that the present Part of this Essay makes no special mention of the minerals of Canada, bufe is simply an Introduction to Part II, in which these minerals will be found arranged together. The following are the characters in question : 1. Aspect or Lustre. 2. Colour. 3. Streak. 4. Form. 5. Structure 6. Hardness, 7 • Specific Gravity. 8. Relative Malleability. 9.

Magnetism. 10. Taste, &c. 1. Aspect or Lustre. — We have here to consider, first : the kind ; and, secondly, the degree or intensity of the lustre, as possessed by the mineral under examination. The kind of lustre may be either metallic, as that of a piece of copper, silver, &c. ; or sub-metallic, as that of most kinds of anthracite coal ; or non-metallic, as that of stones in general. Of the non-metallic lustre there are several varieties, as, more especially : the vitreous or glassy lustre — example : rock-crystal ; the resinous lustre — ex.: native sulphur ; the pearly lustre — ex. : talc ; the silky lustre (usually accompanying a fibrous structure) — ex. ; fibrous gypsum ; the stony aspect ; the earthy aspect, &c. These terms sufficiently explain themselves. Occasionally, two kinds of non-metallic lustre are simultaneously present, as in obsidian, which exhibits a " resino-vitreous " aspect ; and the lustre in some zeolites is pearly within, and vitreous externally.

In mica, and some few other minerals, there is frequently a pseudo-metallic lustre. This may be distinguished from the metallic lustre properly so-called, by being accompanied by a degree of translucency, or by the powder of the mineral being white or light-colored : minerals of a true metallic aspect being always opaque, and their powder being always black or dark-colored. So far as regards the metallic and the non-metallic lustres, there are very few minerals which exhibit (in their different varieties) more than one kind. Thus, galena, the common ore of lead, copper pyrites, &c, always present a metallic lustre ; whilst, on the other hand, quartz, feldspar, calc-3par, gypsum, &c, are never found otherwise than with a non-metallic aspect. Hence, by means of this easily-recognized character, we may divide all minerals into two broad groups ; and thus, if we pick up a specimen* and wish to ascertain its name, we need only look for it amongst the minerals of that group with which it agrees in lustre.

The first step towards the determination of the substance will in this way be effected. The degree of lustre may be either splendent, shining, glistening, glimmering, or dull ; but tbe character i3 one of comparatively little importance. 2. Colour. — When combined with a metallic aspect, colour becomes a valuable character in the determination of minerals, because it then remains constant as regards a given substance. Thus galena, the common ore of lead, is always lead-grey ; copper pyrites, always brass-yellow; native gold, always gold-yellow; and so forth i When accompanied, however, by a vitreous or other non-metallic lustre, colour is, practically, a character of no value ; as iu that case, the mineral may present, in its different varieties, every variety of colour. Thus, we have colourless quartz, amethystine or violet quartz, red quartz, yellow quartz, &c, just as in the vegetable kingdom, we have red, white, and yellow roses; and dahlias, &c, of almost every shade.

When combined with a metallic aspect, the colour issaid to be metallic ; and of metallic colours we may enumerate the following W! ite $ Silver-white ex. Native silver. I Tin-white ex. Pure tin ; cobalt ore Grey J Lead-grey ex. Galena. . Steel-grey ex. Specular iron ore. Black Iron-black (usually with sub-metallic lustre) ex. Magnetic iron ore. s Gold-yellow ex. Native gold. Yellow.. A Brass-yellow ex. Copper-pyrites. ( Bronze-yellow (a brownish-yellow) ex. Magnetic pyrites. Red Copper-red ex. native copper. These metallic colours are often more or less obscured by a black, brownish, purple, or iridescent surface-tarnish. Hence, in noting the colour of a mineral, a newly-fractured surface should be observed. The non-metallic colours comprise, white, grey, black, blue, green, red, yellow, and brown, with their various shades and intermixtures ; as orange-yellow, straw-yellow, reddish-brown, greenish-black, &c. In minerals of a non-metallic aspect, the colour is sometimes uni form ; and at other times, two or more colours are present together, in spots, bands, &c, as in the varieties of quartz, called agate, bloodstone, jasper, and so forth.

In Lahradorite, or Labrador feldspar, a beautiful play or change of colour is observed in certain directions. The finer varieties of Opal also exhibit a beautiful and well-known iridescence. 3. Streak. — Under this technical term is comprised the colour of the powder produced by drawing or " streaking " the mineral under observation, across a file or piece of unglazed porcelain. The charac ter is a valuable one on account of its uniformity ; as, no matter how varied the colour of a mineral may be in different specimens, the streak will remain of one and the same colour throughout. Thus, blue, green, yellow, red, violet, and other specimens of fluor spar, quartz, &c, exhibit equally a white or " uncoloured " streak. The streak is sometimes "unchanged," or ofthe same tint as the external colour of the mineral ; but far more frequently it presents a different colour.

Thus, Cinnabar, the ore of mercury, has a red colour and red streak ; realgar, a sulphide of arsenic, has a red colour and orange-yellow streak ; copper pyrites, a brass-yellow colour, and greenish-black streak ; and so forth. In certain malleable and sectile minerals, whilst the colour remains unchanged in the streak, the lustre is increased. The streak is then said to be " shining." Finally, it should be remarked, that in trying the streak of very hard minerals, we must crush a small fragment to powder, in place of using the file ; because otherwise, a greyish-black streak, arising from the abrasion of the file, might very possibly be obtained, and so conduce to error. It may be observed, however, that all minerals of a non-metallic as pect, and sufficient hardness to resist the file, have a white streak. 4.

Form. — The forms presented by minerals, may be either regular or irregular. Regular forms are called crystals, whether the minerals which present them be transparent or opaque. The term " crystal " was first applied to transparent vitreous specimens of quartz or rock crystal ; but, as it was subsequently found that opaque specimens of quartz presented exactly the same forms, and that opaque as well as transparent forms of other minerals existed, the term gradually lost its original signification, and came to be applied to all regular forms of minerals, whether transparent, translucent, or opaque. Minerals of a metallic lustre are always opaque ; and many of these, as iron pyrites and galena, occur frequently in very regular and symmetrical crystals. Crystals originate in almost all cases in which matter pas se from a gaseous, or liquid, into a solid state ; but if the process take place too quickly, or the matter solidify without free space for expansion, crystalline masses, in place of regular crystals, will result.

If a small fragment of arsenical pyrites, or native arsenic, be heated at one end of an open glass tube (five or six inches long and one-fourth of an inch in diameter), the arsenic, in volatilizing, will combine with oxygen, and form arsenious acid, which will be deposited at the other end of the tube, in the form of minute octahedrons (Fig. 3, below). In like manner, if a few particles of common salt be dissolved in a small quantity of water, and a drop of the solution be evaporated gently (or suffered to evaporate spontaneously) on a piece of glass, numerous little cubes and hopper-shaped cubical aggregations will result. Boiling water, again, saturated with common alum, will deposit octahedral crystals on cooling : the cooled water not being able to retain in solution the full amount of alum dissolved by the hot water.

In like manner, sugar, sulphur, and other bodies crystallise by slow cooling from the molten state. The study of crystal-forms constitutes the science of Crystallogra phy. To enter into the details of this science would extend our present discussion beyond its proposed limits, and carry us altogether beyond the object in view — the simple determination of the names of commonly-occurring minerals — and hence we shall confine ourselves to the general statement, that crystals admit of being arranged in six groups, or " systems ;" the forms of each individual group passing into one another by simple transitions, but having no relations to the forms of the other groups.* The names of these respective groups, * The reader desirous to take up the study of Crystallography in a more extended manner, may attend the author's special courses of lectures which include that subject.

In these, the use of crystallographic instruments is shewn, and the lectures are illustrated by numerous wood and porcelain models, drawings, and natural crystals. The following is ex tracted from the syllabus of the advanced course on Mineralogy : CET3TALLOGEAPHY, Part I— Crystals, how defined. Formation of Crystals. Elements of Crystals: planes, edges, angles; diagonals, axes. Forms and combinations. Replacing pianos. General nomenclature of Forms and simple Crystals. Law of constant Angles. Measurement of Angles. Laws of Symmetry: Holohedral, Hemihedral, and Tetartohedral Forms. Classification of Crystals. Dimorphism. Isomorphism. Compound Crystals. Distortions. Pseudomorphs. Paet II.— The six systems of Crystallization. The Monomctric system. The Dimetric system. The Hexagonal system. The Trimetric system.

The Monoclinic system. Tha Triclinic system. Method of ascertaining the system of a given Crystal. Paet III.— Optical and other physical relations of Crystallography. with figures of a few of their more common forms and combinations are given in the annexed tabular view. The Monometric or Regular System. — This group includes th? cube (Fig. 1), the rhombic dodecahedron (Fig. 2), the regular octahedron (Fig. 3), trapezohedrons or leucitoids (Fig. 4), pentagonal dodecahedrons (Fig. 5), <fec. Fig. 6 is a combination of the cube and Fig. L Fig. 2. Fio. S. Fio.*. Fig. 5. Fig. 6. Fig. 7. octahedron ; Fig 7, a combination of the cube and pentagonal dodecahedron. Native gold, silver, copper, iron pyrites, galena, magnetic iron ore, garnet, fluor spar, rock salt, and numerous other minerals, crystallize in this system.

The Dimetric or Square-Prismatic system. — This includes, principally, square-based prisms and pyramids (or octahedrons), and their combinations. Figures 8 and nine are examples of Dimetric crystals. Fig. 8. Fig. 9. Amongst minerals, Copper Pyrites, Tin-stone, Zircon, and Idocrase, may be cited as belonging to the group. The Hexagonal system. — Regular six-sided prisms (Fig. 10) and pyramids (Fig. 11), combinations of these (Fig. 12), rhombohedrons (Figs. 13 and 14), and scalenohedrons (Fig. 15), are included under this system. Graphite, Red Silver ores, Cinnabar, Specular Iron Ore, Corundum, Quartz, Beryl, Apatite or phosphate of lime, Cal- Fig. 12. Fig- 10. Fig. ll. Fig. 13. Fig. 14. Fig. IS. careous Spar, Dolomite, and Carbonate of Iron, are some of the principal minerals which belong to it.

The Trimetric or Rhombic system. — This system includes right rhombic prisms, rectangular prisms, rhombic octahedrons, &c, and their combinations. Fig. 16 is a rhombic prism ; figs. 17 and 18 are Fig. 17. fig. 16. Fig. 18. combinations belonging to this system. White iron-pyrites, mispickel or arsenical pyrites, native sulphur, topaz, staurolite, arragonite, heavy spar, celestine, and Epsom salt, are some of the principal minerals which belong to this group. The Monoclinic or Oblique Rhombic system. — Rhombic prisms and pyramids, and rectangular prisms and pyramids, with oblique or sloping base, belong to this system. Figs. 19 and 20 are monoclinic combinations. The principal minerals comprise : Augite, Horn blende, Epidote, Orthoclase, or potash feldspar, Stilbite, and Gypsum. Fig. 19. Fig. 20.

The Triclinic, or Doubly Oblique system. — The forms of this system are oblique (or they incline) in two directions. The crystals in general are more or less flat and unsymmetrical in appearance. No two planes meet at right angles; and there are never more than two similar planes present in any crystal belonging to the group. Axi nite, Albite or soda feldspar, Lahradorite or lime feldspar, and sulphate of copper, are the principal triclinic minerals. Such is a brief exposition of the six crystal systems. For present purposes it will only be necessary for the student to impress upon his memory the following forms, so as to be able to recognize them when met with. The cube (Fig. 1), the regular octahedron (3), the rhombic dodecahedron (2), the pentagonal dodecahedron (5), the cubo-octahedron (6), the regular six-sided prism (10), a combination of a six-sided prism and pyramid (12) a rhombohedron (13 and 14), a sealenohedron (15), a rhombic prism (16).

The irregular forms presented by minerals are of very subordinate importance ; so that a few of the more common need only be men tioned. Most of the terms used in reference to these, explain themselves. Irregular mineral forms : — Globular or nodular, ex. quartz, iron pyrites ; reniform or kidney-shaped, ex. quartz, &c. ; botryoidal or mammillated : a form made up of a series of rounded elevations and depressions, or otherwise exhibiting a surface of this character, ex. red and brown iron ore, calcedony, &c. ; stalactitic, ex. calc spar, &c. ; coralliform, resembling certain branching corals, ex. arragonite ; dendritic or arborescent, a branching form, often made up of small aggregated crystals, ex. native silver, native copper, &c. ; filiform or wire-like, ex. native silver : acicular, in needle-like crystallizations, ex. many varieties of augite, hornblende, epidote, &c. When a mineral has a perfectly indefinite shape it is said to be " massive " or " amorphous."