NRLF PUKL.ISHER & IMPORTER UNIVERSITY Of CALIFORNU THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA BEQUEST OF Alice R. Hilgard V LITHOLOGY. LOIfDOK FEINTED BY SPOTTISWOODB AITI) CO. NBW-STEEBT 8QITABE ROCKS CLASSIFIED AND DESCRIBED. Iwatitt on i BY BEENHAED VON COTTA. AN 'ENGLISH EDITION BY PHILIP HENRY LAWRENCE. WITH ENGLISH, GERMAN, AND FRENCH SYNONYMS. REVISED BY THE AUTHOR. LONDON : LONGMANS, GREEN, AND CO. 1866. LITHOLOGY, or a Classified Synopsis of the Names of Kocks ar-d Minerals, also by Mr. LAWKENCE, adapted to the present work, may be had, price 5s. or printed on one side only (interpaged blank) for use in Cabinets, price 7s. 7 GIFT TRANSLATOR'S PREFACE. IN presenting this work to English readers, I wish to acknowledge the kind assistance I have received from Professor Jukes and Mr. Bristow in my own country, from M. Daubree and M. Guyerdet in France, and last, but not least, from the distinguished author, Professor Cotta himself, and from Mr. Stelzner, of Freiberg, to whose valuable assistance I owe most of what is good in the new arrangement of the Mineralogical part of the work. For the many imperfections which, in spite of much care, will probably be found, I am alone responsible. Never- theless, I hope that this work may in some measure supply a want which has been long felt in our geological literature. I trust that allowance will be made for the difficulties of a translator if, in some instances, terms have been used in this work in a slightly extended or even different sense from that of some English authors. This has never been done without much consideration, and what appeared to me absolute necessity in rendering the meaning of my author, and in the absence of an exact equivalent for the German term in our accepted geological language. M860773 vi TKANSLATOK'S PKEFACE. The juxtaposition of the English, German, and French equivalent names for each rock, although frequently pre- senting doubts and difficulties, will, I trust, in the main meet with acceptance, in which case it cannot fail to prove useful. Scientific names are the coin in which enquirers must exchange their ideas ; and if they can be made to corre- spond in different countries, the gain to science will be great. Such correspondence is as important in its way as the assimilation of currency for the operations of commerce. Should this object have been in any way promoted by the present work, my most sanguine expec- tations will have been fulfilled. I may here mention that, in furtherance of the same object, I have published, separately, a catalogue of the names of Rocks in the three languages. This catalogue, which is an outline of this work, may, perhaps, prove useful to collectors. P. H. LAWRENCE. LONDON : January 1866. AUTHOR'S PREFACE TO THIS EDITION. BEFORE my friend the Translator undertook the transla- tion of this work, I had collected materials and made certain alterations with a view to a third edition. The Translator himself, in the course of his labour, proposed jcertain alterations, which were adopted with my entire concurrence. As far as my knowledge of the language enables me to judge, after a careful perusal, the translation appears to me to be very accurate. . This English edition may therefore be considered as the third edition of my original work, although, if the appearance of a third German edition should be delayed for some time longer, there will doubtless be new matter and fresh alterations to be introduced; for Science marches with uninterrupted steps towards new fields of discovery, mid every year alters its aspect. In a system of Lithology, however, most of the names viii AUTHOR'S PREFACE. which are in use will probably remain, and one chief object of this book is to define these so as to render intelligible the ideas which each name should convey ; and both Author and Translator are actuated by the desire and ambition of arriving, as far as may be possible, at a common ground for all nations in respect of the important matter of rock-nomenclature. B. COTTA. FBEIBEKG : January 1866. CONTENTS. PART I. CHAPTER I. PAGE MINERALS ...... 1 I. Oxygen Compounds . . . . .5 A. Oxides of Silicon and Aluminum (Earths) . . 6 B. Silicates ..... a. Felspar Section ..... 8 Orthoclastic Felspars . . . , 9 Plagioclastic Felspars . . . .10 Leucite and Nepheline Group . . .14 b. Augite Section . . . . . K> c. Mica Section . . . .22 d. Hydrous Magnesian Silicates (Talc Section) . 24 e. Zeolite Section (Non-Magnesian Hydrous Silicates) 28 The Monometric Zeolites Hexagonal Zeolites . . . .30 Trimetric Zeolites . . . .31 Monoclinic Zeolites . . .32 f. Andalusite Section . . .34 g. Garnet Section ... .38 C. Tantalates (or Columbates), Titanates, Vanadates . 46 D. Sulphates .... a. Anhydrous Sulphates . .47 b. Hydrous Sulphates . .49 E. Borates . . . -62 CONTENTS. I. Oxygen Compounds continued. PAGE F. Phosphates . . ... .53 a. Anhydous Phosphates . -. . .53 b. Hydrous Phosphates . . .54 G. Nitrates ... ... . . 55 H. Carbonates . . . . . .56 a. Anhydrous Carbonates . . . .56 b. Hydrous Carbonates . . . .59 I. Oxides of the Elements of the Hydrogen Group . 60 a. Anhydrous Oxides . . . . .60 b. Hydrous Oxides . . . . .66 II. Fluorides and Chlorides . . . . .67 III. Sulphurets. Arseniurets . . . . .69 IV. Native Elements . . . . . .74 V. Kesins. Organic Compounds . . . .76 CHAPTER H. ANALYSIS OP ROCKS . . . . . .78 Microscopic Analysis . . . . . .78 Magnetic Analysis . . . . . .78 Chemical Analysis . . . . . .79 CHAPTER III. PHYSICAL STRUCTURE OP ROCKS . . . .87 Texture ....... 87 Particular States of Rocks . . . . .95 Concretionary Structure . . . . .98 Special Forms of External Structure . . . .99 Jointed Structure . . . . . . 103 STRATIFICATION OP ROCKS . . . . 105 SHAPE AND BEDDING OP ROCK MASSES . . . . 106 CHAPTER IV. GEOLOGICAL FORMATIONS AND GROUPS OF Roczs . . Ill CHAPTER V. TRANSITIONS AND TRANSMUTATIONS 120 CONTENTS. X PART II. THE ROCKS. INTRODUCTORY CHAPTER. PAGE CLASSIFICATION . . /'" . . . .123 CHAPTER I. IGNEOUS ROCKS . . ', * 127 Basic Igneous Rocks ...... 131 (1) Volcanic . . . ." '. . 131 Basaltic Rocks ..... 132 (2) Plutonic . . . . . . .144 Greenstones ...... 146 Porphyrite Group ..... 168 Mica Trap Rocks . . . . .173 Syenite Group ; . ,. ^ .176 Acidic Igneous Rocks . . . . 182 (1) Volcanic . . . . . .182 Trachyte Group . . . , .183 Phonolite Group ' .. >, . . . 198 (2) Plutonic . . . . .201 Granitic Group . .... 201 CHAPTER H. METAMORPHIC CRYSTALLINE SCHISTS .... 227 Felspar Group . . . . . 229 Quartz Group . ..... 241 Chlorite, Talc, and Hornblende Group . . 249 Schists indistinctly Crystalline . . . 264 CHAPTER HI. SEDIMENTARY AND FRAGMENTAL ROCKS . . 259 Argillaceous Group . . . 263 Marl Group . . . Limestone Group . 274 Gypsum and Anhydrite . 290 Fragrnental Rocks . .294 Conglomerates . 302 Xii CONTENTS. CHAPTER IV. PAGE ROCKS OF SPECIAL CHARACTER OK BEDDING . . . 313 Serpentine Group -,' '.^ . . 314 Garnet Group . .318 Greisen and Schorl Group . . . . 320 Carbonaceous Group . . . r \ . 324 Ironstone Group . . . . . 340 CHAPTER V. MINERALS AS ROCKS . 347 PAKT III. OBSERVATIONS ON THE PROCESSES OF ROCK FORMATION IN NATURE . . . . .- A-. . 359 Igneous Rocks ... u? v . 361 Sedimentary Rocks . . . "> .' :. - . 374 Metamorphic Crystalline Schists . . ; > . . 378 Mineral Veins and Veins of Ore 392 CONCLUSION , 393 LITHOLOGY. PART L CHAPTER I. MINERALS. THE SEVERAL SUBSTANCES which form the materials of the earth's crust are termed 'Rocks,' the idea of a solid rocky substance not being necessarily implied. Most of what we call rocks are no doubt of a firm and solid character, but some consist only of soft or loose aggregates or accumulations of their component parts. These component parts are always minerals ; that is to say, all rocks are mineral aggregates, consisting of minute mineral parts more or less solict and more or less intimately and firmly united, knit, or cemented together. By this definition it will be seen that we exclude the animal and vegetable kingdoms ; it may therefore be well to add that under the term mineral we include all mineralised remains of organic bodies. Most rocks are made up of parts of two or more different minerals, in which case they are termed composite. Some rocks, however, consist essentially of particles of one mine- ral only, such for instance as limestone ; these, in contra- distinction to the composite, are termed simple rocks. The composite as well as the simple rocks not unfre- quently contain subordinate ingredients, besides those which are essential to their character. These subordinate ingredients are termed accessory or non-essential. In most cases they are inconsiderable in quantity, or they only occur locally and do not appreciably alter the nature B 2 MINEKALS. of the rock ; but sometimes these accessory ingredients impart a special character to it, and so to a certain extent pass into essentials. Their presence creates the varieties of species. The constituent minerals (whether accessory or essen- tial) of any given rock either occur in separate crystals or particles distinguishable by the naked eye, or they consist of small finely divided particles so intimately blended to- gether as apparently to form a homogeneous mass ; never- theless, in the latter case, their separate existence may be generally recognised by magnifying power. The first and principal requisite for the student of Lithology is to be able to recognise and determine the minerals of which a given rock consists. This is in many cases no easy task ; he must therefore have a competent knowledge of mineralogy. Not with a view adequately to supply the want of such knowledge, but by way of intro- duction to our subject, rnd for the purpose of reference in the absence of more comprehensive works, we propose to give in this chapter a brief notice of the principal minerals with which we have to do in examining the structure of rocks, adding such particulars as are more especially useful for our present purpose. The number of these principal minerals is relatively very small. They may be classed under the following comprehensive names : FELSPAR, QUARTZ, MICA, HORNBLENDE (Amphibole), PYROXENE (Augite), CALCSPAR, and DOLOMITE. The following occur less frequently : CHLORITE, TALC, LEUCITE, NEPHELINE, OLIVINE, TOURMALINE, GARNET, GYPSUM, COAL, some SULPHURETS, and some IRON ORES. The number of the accessory ingredients is very much greater, and indeed almost unlimited; that is to say, under certain circumstances almost every known mineral may occur as an accessory in any rock, and the essential ingredients of one rock frequently occur as accessories in another rock. But although we may say with truth that the number of the accessory minerals is without limit, yet in fact only about a quarter of the number of hitherto known minerals occur in rocks so abundantly and fre- quently as to be specially noticed in a treatise of Lithology. One consideration is particularly deserving the atten- MINERALS. 3 tion of the scientific observer of rocks ; we refer to what is termed by Breithaupt the ' Paragenesis ' of minerals. By this is meant the law of mutual association or repulsion of certain minerals. It is well known to mineralogists that the presence of one mineral very frequently denotes the neighbourhood of another, and, vice versa, that the presence of some minerals forbids the simultaneous pre- sence of certain others. In 1849 Breithaupt first treated this subject, and pub- lished in his ' Paragenesis der Mineralien ' a great number of remarkable instances of this law. We may, for the sake of illustration only, select the following as examples : 1. Minerals which are usually associated together: Quartz and mica ; orthoclase, quartz, and mica ; ortho- clase and oligoclase ; labradorite and augite ; orthoclase or oligoclase and hornblende ; hornblende and epidote. 2. On the other hand, quartz and augite appear each to exclude the presence of each other ; also (according to Both) labradorite and hornblende (?). We are unable to pursue this important subject in this place ; we have been compelled to confine ourselves, in the following notice, to appending a few of the more im- portant instances of paragenesis to the description of some of the principal mineral classes. As to the much-debated question of classification of the minerals, we have adopted one which appeared to us best suited for our present purpose ; it is not exactly that of any one author. We have -placed a few of those minerals first which are of the most frequent occurrence ; otherwise, the arrangement adopted will be found to correspond in several respects with Dana's ' System of Mineralogy.' The following are the abbreviations we have used : H. for hardness; S.G. for specific gravity ; Cp. for chemical composition ; Bp. for before the blowpipe. The quantities of the chemical elements we have given in round numbers, as being sufficient for our present pur- pose. In the chemical formula? we have, for the sake of convenience, adopted the abbreviations usual on the Con- tinent, of expressing the oxygen atoms by dote, and a stroke to denote a double atom ; thus, Fe' 2 O 3 is written Fe. W"e subjoin the following list of formulae for the elementary bodies and their simple compounds: B 2 MINERALS. CHEMICAL SYMBOLS. Al Aluminum, Aluminium Al Alumina Ag Silver As Arsenic As Arsenic Acid Au Gold Ba Barium Ba Baryta B Boron B Boracic Acid Ca Calcium Ca Lime C Carbon C Carbonic Acid Cb Columbium, Niobium Cb Columbic Acid Ce Cerium Ce Protoxide of Cerium Cl Chlorine HC1 Hydrochloric Acid Cr Chromium Cr Oxide of Chromium Cr Chromic Acid Co Cobalt Co Oxide of Cobalt Cu Copper Cu Oxide of Copper Fe Iron Fe Protoxide of Iron Fe Peroxide of Iron F Fluorine HF Hydrofluoric Acid G Beryllium or Glucinum G Glucina Hg Mercury H Hydrogen H Water K Potassium K Potassa La Lanthanum La Protoxide of Lanthanum Li Lithium Li Lithia Mg Magnesium Mg Magnesia Mn Manganese Mn Protoxide of Manganese Mn SesquioxideofMangane.se Na Sodium Na Soda Ni Nickel Ni Protoxide of Nickel N Nitrogen N Nitric Acid Oxygen P Phosphorus P Phosphoric Acid Pb Lead Pb Oxide of Lead Se Selenium Si Silicon Si Silica Sn Tin Sn Oxide of Tin Sr Strontium Sr Strontia S Sulphur S Sulphuric Acid Ta Tantalum Ta Tantalic Acid Ti Titanium Ti Oxide of Titanium ti Titanic Acid V Vanadium Y Yttrium Y Yttria Zn Zinc Zn Oxide of Zinc Zr Zirconium Zr Zirconia QUARTZ. 5 I. Oxygen Compounds. A. OXIDES OF SILICON AND ALUMINUM (EARTHS). 1. Quartz. Rhombohedral crystals, usually combinations of two rhombohedrons and hexagonal prism. Cleavage accord- ing to the planes pf one rhombohedron, but imperfect. Frac- ture conchoidal to uneven and splintery. H.=7. S.G.=2'5 2 '8. Colourless and limpid, or variously coloured, forming many varieties. Lustre vitreous, sometimes resinous, especially on the surfaces of fracture. Cp. = Si, with admixture of minute particles of colouring oxides. Two modifications of chemical composition are distinguished by their different degrees of solu- bility. The one is insoluble in water and in every acid, except hydrofluoric acid ; the other is soluble in water at high tem- peratures, especially in the presence of other acids and alkalies. The insoluble variety of quartz may, in process of time, be- come converted into the soluble by the contact-influence of infiltrated moisture. The soluble variety of quartz, in small proportions, is found in many waters of springs and rivers, and in the sea, e. g., at the Geysers in Iceland, up to T8 | 00 per cent, and in sea- water to -nrurjuir P er cent - Bp. infusible ; with soda fusible to a clear glass with effervescence. Not affected by phosphoric acid. (a) Common Quartz, the most abundant of all minerals. It is found : (a) As an independent rock. (See post.) (ft) As essential ingredient of many crystalline rocks, espe- cially the plutonic. In most kinds of granite, in greisen, and in the crystalline schists it is found in crystalline grains. In quartz-porphyry, rhyolite, and, excep- tionally, in some kinds of granite (e.g. St. Austell, Cornwall), it is perfectly crystallised. r MINERALS. (y) As accessory constituent mass of some rocks (snch as crystalline schists), in form of veins and swellings, or clothing the interior of geodes in other rocks (e.g. in the granites of Switzerland, Carrara marble, the variegated sandstone of the Schwarzwald, &c.) The quartz of the geodes is frequently in the form of transparent crystals (rock crystal), or in greyish- brown to black crystals (smoky quartz, false topaz). (S) As principal ingredient of many fragmental rocks (sandstones, conglomerates). As sand and gravel in beds of deposit. (It) Amethyst. Violet, coloured by the oxide of manganese. (c) Chalcedony. An intimate admixture of crystalline and amorphous silica. (d) Agate. A variegated combination of common quartz, amethyst, jasper, carnelian, and other varieties of quartz, arranged in alternate stripes or layers, or irregularly mixed together. \b, c, and d chiefly occur in the geodes of volcanic rocks (in Iceland, Faroe Islands, the Brazils, &c.), or in metallic veins (e.g. in Saxony).] . (e) Jasper. Very frequently in globular masses (ball-jasper) coloured red by the peroxide of iron ; found in the bog iron-ore of Briesgau, in Germany, and elsewhere, or coloured yellowish-brown by the hydrated oxide of iron. (Occurs in form of pebbles, e.g. in the sand of the Nile and Desert.) Jasper sometimes forms subordinate layers in other rocks. (/) Flint. Coloured greyish-blue, or black, by presence of carbon. Occurs as a concretionary formation in sedi- mentary limestone rocks, e.g. in the Chalk of England and France, in the Upper White Jurassic of the Fran- conian Switzerland in Bavaria. OPAL. 7 (g) Chert, Homstone is distinguished from flint by its more splintery fracture, by its transparency, and colour, which is grey, yellow, green, red, or brown, resembling jasper. It frequently furnishes the material of fossils, especially of fossil wood (woodstone). There are at least three different processes in nature which have contributed to the formation of quartz. Quartz has been formed: 1. By organic agency. The siliceous needles (spiculae) of sea-sponges, the siliceous shields of certain Protozoa (kieselguhr, tripoli), and many plants (especially grasses) either contain quartz, or consist entirely of quartz. 2. By agency of water. The concre- tionary formations of flint, jasper, &c., the crystals and amorphous quartz contained in geodes, and many formations at springs which consist of pure quartz, and are termed freshwater quartz. 3. By hydroplutonic agency. Daubree has actually produced quartz, by way of experiment, through the agency of steam on chloride and fluoride of silicon. Many kinds of quartz have no doubt been produced by pure plutonic agency. 2. Opal. Amorphous, massive. Fracture conchoidal to un- even; friable. H.=5-5 6-5. S.G.=1'9 2-3. Colourless or variegated with rich play of colours. Transparent to opaque. Lustre vitreous, also resinous. Possesses many varieties, dis- tinguished by their different colours and degrees of trans- parency. Cp. amorphous Si combined with water, in varying proportion (up to 13 per cent.), and small quantities of colour- ing matter. It is distinguishable from quartz by being almost entirely soluble in potash ley, in matrass yields water. Bp. most kinds of opal decrepitate ; otherwise behaviour like quartz. Occurrence and Mode of Formation. Opal is never an essen- tial ingredient of rocks, but is of very frequent occurrence 8 MINERALS. as a secondary product, furnishing the interior of small nests, and filling vesicular cavities in volcanic rocks, or cloth- ing the surfaces of clefts in the same rocks. In these and similar cases the opal is a product of exfiltration from the rock in or near which it occurs. Thus, the precious opal found in the trachytic rocks of Hungary, the colourless hyalite in clefts of basalt and lava (Bohemia, Auvergne). In rare cases, however, opal forms independent layers of small extent (riband opal) in siliceous rocks, e. g. in the tripoli of Bilin. The variety known as menilite occurs in knobs and layers embedded in the adhesive slate of Menil Montant, Paris. 3. Corundum. Occurs in rhombohedral crystals, or gran- ular aggregates (emery). Cleavage basal, also rhombohe- dral in various degrees of perfection. Fracture conchoidal to uneven and splintery. H. 9. S.G.=3'9 4*2. Colour- less or coloured blue (sapphire), red (ruby), or cloudy (corundum). Lustre vitreous, and frequently, on the basal cleavage surface, mother-of-pearl lustre. Transparent to translucent. Cp.=Al, with small quantities of Mg, Ca, Si. Bp. infusible when alone, perfectly fusible with borax, but not without difficulty ; not affected by acids. Occurs as an original product accessorily in many rocks (granite of Silesia, basaltic lava of Medermendig on the Rhine, dolomite of the St. Grotthard). The precious varieties are chiefly found in alluvial beds (Ceylon, China). Emery forms separate masses of deposit in the talcose schist (Naxos, Saxony) . B. SILICATES. (a) FELSPAR SECTION. The felspars are, after quartz, the most important of all ingredients of rocks. We distinguish two principal kinds of felspar, the orthoclastic (monoclinic), the two most per- FELSPAR. 9 feet cleavage planes forming an angle of 90, and the pla- gioclastic (triclinic) with an angle of less than 90. All felspars have a great tendency to form twin crystals, and this duplication occurs in them in a very marked manner, and according to six different laws. Orthoclastic Felspars. 4. OrtJioclase. Monoclinic. Cleavage basal and clinodia- gonal, very perfect in both directions, hemiprismatic, im- perfect. Fracture conchoidal to uneven and splintery. H.=6. S.G. = 2*4 2*62. Colourless, sometimes limpid, more frequently coloured, especially reddish, yellowish, rarely green (amazon stone coloured by copper). Lustre vitreous, frequently with mother-of-pearl lustre on the most perfect cleavage surfaces. Possesses every degree of transparency, sometimes with iridescence or play of colours. Cp.=KSi + AlS'i 3 with 65Si, 18AJ, and 17K. A portion of the Al is frequently replaced by Fe, or Mn, and a portion of the K is sometimes replaced by Na or Ca. Bp. fusible with difficulty, and only at the edges, where it forms a dull porous glass. The varieties which contain soda colour the flame yellow. In microcosmic salt it is only soluble with difficulty, leaving behind a skeleton of silica. With cobalt solution the fused ''dges are coloured blue. Not susceptible to the action of acids. Varieties of Colour and Lustre. (a) Adularia. Colourless, or only slightly coloured, with bright lustre, transparent to semi-transparent. Essen- tial ingredient of the adularia-granite and adularia- gneiss abundant in the Alps, also frequently found in the geodic cavities of granitic rocks (St. Gotthard). (6) Common Felspar (Pegmatolite, Microdine). Variously coloured, less lustrous than adularia, translucent to 10 MINERALS. opaque. A characteristic ingredient of very many rocks, especially amongst the phitonie, such as granite, .gneiss, syenite, porphyry. Frequently large felspar crystals (such as the so-called Carlsbad twins) occur porphyritically embedded in an otherwise regularly constituted rock (e.g. in the granite of Carlsbad in Bohemia, and of Cornwall, porphyry of Ilmenau), or larger crystals clothe the sides of geodes (as in the granite of Baveno and the rocks of the Mourne Moun- tains, in Ireland). (c) Sanidine. Colour greyish- and yellowish-white, also grey. Lustre vitreous, very bright, transparent, trans- lucent. The crystals are very often split and creviced. It forms a very characteristic ingredient of genuine volcanic rocks, and only occurs in these. Thus it is found in phonolites, trachytes, pitchstones, obsidian, and lavas. Sometimes it occurs porphyritically in large tabular crystals, as in the trachyte of Dra- chenfels. Plagioclastic Felspars. All plagioclastic felspars are triclinic ; they cleave perfectly according to the base and the brachydiagonal, imperfectly according to the hemiprism. 5. Albite. Fracture uneven. H.=6 6'5. S.G. - 2'59 2 ! 65. Colourless or light red, yellow, green, or brown. Lustre vitreous ; mother-of-pearl lustre on the basal cleavage sur- faces. Transparent, translucent. A white and usually semi-opaque variety termed pericline, is distinguished by its constant crystallographic habitus. Cp.==NaSi + AlSi 3 == 69Si + 19AH-12;N"a. The Na is frequently in part replaced by Ca, K, or Mg. Bp. it fuses with difficulty, colouring the flame yellow. It is scarcely affected by acids. Albite is FELSPAR. 1? frequently found associated in parallel growth with ortho clase. It is likewise a characteristic ingredient of many diorites and granites. Exceptionally crystals of albite are found in compact limestone (Col du Bonhomme). 6. Oligoclase. Fracture uneven. H.=6. S. G. = 2'58 2*69. Colour greyish, yellowish, or greenish. Lustre upon the principal cleavage surface vitreous, otherwise resinous. Usually is much weathered, and in that state dull ; in its fresh state translucent at the edges. Cp. = NaSi-i- AISi 2 = 62S1 + 24Al + 14Na, The Na replaced in part (up to 6 per cent.) by Ca, K and small quantities of Fe or Mn. Bp. fuses much more easily than orthoclase and albite, forming a clear glass. Little attacked by acids. Oligoclase is an essential con- stituent of diabase, diorite, and kersantite ; it is frequently associated with orthoclastic felspars as a constituent of many kinds of granite (Stockholm), syenite (Dresden), porphyry (Southern Tyrol), and trachytes (Hungary). Andesine may be considered as an oligoclase rich in lime. It has much the outward appearance of albite. It is an ingredient of many trachytic rocks of the Andes, and likewise of many crystalline rocks of the Vosges. 7. Labradvrite. H. = 6. .S.G. = 2'67 276. Barely co- lourless, usually grey, reddish, bluish or otherwise coloured ; usually displays a rich play of colours. Lustre vitreous, sometimes resinous ; translucent, but usually only at the edges. Cp. = RSi + AISi = 53Si + 30A1 + 12Ca + 5Na. Bp. fuses somewhat more readily than oligoclase to a colour- less glass. Unlike other felspars, its powder is thoroughly soluble in heated muriatic acid. Labradorite is an essential constituent of many, and especially of the augitic, rocks, e. g. dolerite, basalt, gabbro (Isle of Skye), hypersthenite, and many lavas of Etna. Saussurite (jade) is probably only an impure labradorito. 12 MINERALS. bearing somewhat the same relation to it as felstone to orthoclase. It remains unchanged by acids, occurs only in compact or finely granular masses, and forms an essential constituent of many kinds of gabbro and greenstones. 8. Anorthite.H.= 67. S. G. = 2'66 278. Colour- less, white. Lustre, mother-of-pearl on the cleavage surfaces, otherwise vitreous; transparent to translucent. Cp.= R/ 3 Si + 3A1S1 = 43Si + 37Al + 20Ca. The Ca replaced by Mg, K, and Na to the extent of 5 per cent. Anorthite is completely soluble by concentrated muriatic acid, without gelatinising, but is distinguished from labradorite by its being more diffi- cult of fusion. It is an essential constituent of the orbicular diorite (Kugeldiorit) of Corsica and of many ancient lavas (Monte Somma). It is also found in meteoric stones. Some Aids for distinguishing the Felspar Species. (a) Crystallographic Signs. When the light is brought to play on the basal cleavage plane of the orthoclastic fel- spars it presents an unbroken surface, or in case of twin crystals (according to the Carlsbad law) is double ; whereas in the case of the plagio clastic felspars a fine parallel striping is usually observed, occasioned by the parallel growth of numberless individual crystals as thin as leaves of paper. This striping, when observable, is a very characteristic sign, but its absence is not equally so. (/3) Signs of Paragenesis. The following minerals are fre- quently found in comparing : Orthoclase with oligo- clase ; orthoclase and oligoclase with hornblende ; labradorite with pyroxene. On the other hand, we seldom or never find together : the alkali felspars (Nos. 4. 5, 6) and the calcareous felspars (Nos. 7, 8) ; or orthoclase with pyroxene ; oligoclase with leucite and nepheline ; labradorite with FELSPAR. 13 hornblende ; labradorite or anorthite with quartz or leucite. (y) The weathering of felspars is noteworthy, and is parti- cularly useful for purposes of distinction where two species are found together in one rock. Labradorite and oligoclase weather more readily than orthoclase, orthoclase more readily than albite. Bearing this law in mind, if we have determined the species of the un- changed felspar, we may usually determine the other with a high degree of probability. (3) The chemical and physical characteristics of felspars have been already noted as above. As regards the origin of felspars : They are sometimes clearly the result of wet process ; evidence of which is their appearance in veins and clefts, also the pseudomorphs which we find after leucite, analcime, laumontite, &c. Sometimes metamorphic, for Daubree succeeded in pro- ducing sanidine-like crystals by subjecting obsidian to the influence of overheated steam. And sometimes plutonic, as is proved by the presence of felspars in lavas and many other rocks of undoubted igneous origin, as also in the slags of smelting furnaces. Finally, some are the result of process of sublimation. Thus, crystals of felspar have been found in blown-out furnaces, and, reasoning from analogy, we may suppose the same process to have taken place in nature. 9. Kaolin may be put as an appendix to the felspar group, as it is a product of the disintegration of orthoclase, albite, and other felspars. Its chemical formula may be stated as AJSi + 2H or Al 3 Si 4 + 6H. Occasionally kaolin is the result of the decomposition of whole rock masses (granite of St. Stephen's in Cornwall, gneiss of St. Yricux, near 14 MINERALS. Limoges, graimlite near Passau). It occurs only in primary formations. On the other hand, the clays (which, in a che- mical point of view, may be called impure kaolin) always occur in secondary formations. More or less allied to kaolin are the following minerals, all of whose composition is, however, more or less indefi- nite, viz. lithomarye, myelin, halloysite, bole or bolus, rock- soap, and agalmatolite. These sometimes occur as separate independent mineral deposits, but principally are found filling cavities and nests in various rocks, in which latter case they are to be regarded as products of exfiltration from those rocks. Chemically they are all hydrous aluminous silicates, and in appearance may easily be mistaken for soapstone, talc, &c. Leucite and Nepheline Group. The minerals of this group, which in many respects are closely allied to the felspars, are without doubt of contem- poraneous origin with the volcanic (or plutonic) rocks, in which they occur as essential constituents. They are, there- fore, almost always, if not always, igneous products. "We do not, however, mean to dispute the possibility of some having arisen by wet process. The most questionable of all in respect of origin is probably lapis lazuli. 10. Sodalite. Monometric in dodecahedrons ; cleavage, accordingly, also massive. Fracture conchoidal to uneven. H. r= 5-5-6. S.G. =2-26. Colour yellowish, greenish- white, greenish-grey, and blue. Lustre on crystal sur- faces vitreous ; on fracture surfaces resinous. Translucent. Cp. = Na s Si + SAlSi + NaCl. Bp. fuses, with more or less difficulty, to a colourless glass, sometimes with intumescence. Gelatinises with muriatic and nitric acids. Sodalite is an essential constituent of miascite, and an accessory in other igneous rocks (dolerite at the Kaiserstuhl) . LEUC1TE AXD NEPHELINE. 15 11. Lapis lazuli (ultramarine). Monometric in dodeca- hedrons ; cleavage accordingly, usually massive. H. = 5*5. S. G. = 2'4. Colour azure-blue. Lustre glassy, resinous. Translucent at the edges to opaque. Cp. a silicate of Al with Na and Ca, containing also NaS. Bp. loses its co- lour and fuses to a white vesicular glass. Gelatinises with muriatic acid, and evolves HS. Lapis lazuli is found as an accessory in granite, limestone, and dolomite. 12. Haiiyne. Monometric in dodecahedrons ; cleavage, ac- cordingly, usually in crystalline grains. H.= 5'5. S. G. = 2 '4 2 '5. Colour blue, rarely green or red. Lustre vi- treous to resinous ; semi-transparent to translucent. Cp.= Na 3 Si + 3AlSi + 2CaS. Bp. decrepitates violently, and fuses to a blue-green vesicular glass. Gelatinises with muriatic acid. It occurs in single crystals imbedded in the lavas of active volcanoes (Volturara, near Melfi), or in the basaltic lavas of extinct volcanoes (Niedermendig, on the Rhine), in which latter it is characteristic as an accessory mineral, and occasionally occurs in such quantity as to have given rise to the name of Hauynophyre for those rocks. Nosean is very similar to haiiyne in its mineralogical character and geological habitat, usually yellowish-grey or greyish- white. In Brava, one of the Cape Verde Islands, there occurs a porphyry rock, consisting of very numerous small crystals of nosean in a felsitic mass. Cp.= Na 3 Si4- SAlSi+NaS. 13. Leucite. Monometric, only known in trapezohedrons (embedded). Cleavage cubic, imperfect. Fracture con- choidal. H. = 5'5 6. S. G. = 2'48. Colour greyish or reddish- white, also ashen-grey. Lustre vitreous, in fracture resinous. Semi-transparent to translucent only at the edges ; brittle. Cp. = K 3 Si 2 -I- 3AlSi 2 . Bp. unchanged ; with cobalt solution coloured a beautiful blue; with borax melts to a 16 MINERALS. clear glass. Gelatinises with muriatic acid. Lencite is a frequent and very characteristic constituent of recent ig- neous rocks, in which it appears to some extent to be a sub- stitute for felspar. It is especially frequent in basaltic lavas (leucitophyre), in which it always appears porphyritically imbedded. In the older rocks leucite is unknown. 14. Nepheline (Davyne, Elceolite). Hexagonal. Crystals with imperfect basal and prismatic cleavage, or massive. Fracture conchoidal to uneven. H.= 5'5 6. S. G. = 2*5 2*64. Colourless, white and usually crystallised (nephe- line), or green, red, brown, and then massive (elaeolite). Lustre on crystal surfaces vitreous ; on fracture surfaces pre-eminently resinous. Transparent to translucent at the edges. Cp. = (]STaK) 2 Si + 2A1S1 = 44Si + 33A1 + IGlSTa + 5K (with small quantities of Fe and Ca). Davyne, which is very similar, both chemically and mineralogically, contains, in addition to the above, some Cl and C. Bp. nepheline fuses with difficulty, and elseolite readily to a vesicular glass. Slowly dissolved in borax and phosphor- salt. The fused edges are coloured blue in cobalt solution. Gelatinises with muriatic acid. It occurs in geodic cavities of lavas, and as an accessory constituent of dolerite and basalt. In these rocks it sometimes forms a complete substitute for the fel- spar, producing nepheline rock. Finally it appears as an essential constituent of some of the older plutonic rocks (miascite, zirconsyenite) . In dolerite it may be recognised by its forming short thick columns, whilst the apatite, which is associated with it in those rocks, assumes the form of acicular hexagonal columns. (&) AUGITE SECTION. 15. Hornblende (Amphibole). Monoclinic. Crystallised or massive, in stalklike or granular aggregates. Cleava ge pris- LEUCITE GROUP AUGITE. 17 matic, very perfect ; in other directions imperfect. Fracture uneven. H. = 5 6. S.G.=2'9 3*4. Colour passing from white through various shades of green and brown to black. Streak either colourless or lighter than the colour of the mineral. Lustre vitreous, on cleavage surfaces mother-of- pearl ; the fibrous varieties silky. All degrees of trans- parency to the opaque. Cp. variable. We may give as a normal formula, R 3 Si' 2 + RSi, in which B = Mg, Ca, and Fe, and Si is sometimes partially replaced by Al. Bp. these minerals usually fuse, with intumescence, to a grey, greenish, or black glass, and the more readily the more iron they con- tain. The varieties richest in iron are partially decomposed by muriatic acid ; other varieties are little affected by that acid. (a) Tremolite (Grammatite, Calamite). Of light colour, semi-translucent. Iron not an essential ingredient. Cp. = Mg'S'i 2 + CaSi=60Si + 27Mg + 12Ca. Usually imbedded in granular limestones and dolomites, in the form of long columnar crystals, or long stalklike or fibrous masses. (6) Actinolite (Strahlstein, Glassy Actinolite). Colour green. Cp. like tremolite. Occurs as an accessory in talc- schist, chlorite-schist, &c. also as an independent rock (actinolite-schist) . (c) Hornblende (proper). Colour dark-green or black; opaque. Cp. rich in iron and alumina. Forms an independent rock of itself, or occurs as an essential constituent of many compound rocks (syenite, diorite, many kinds of gneiss and porphyry). Occurs in the form of very perfect brownish-black crystals, imbedded in basaltic and trachytic rocks. A variety of the mineral is termed gamsigradite, and forms an essential constituent of the rock timazite. C 18 MINERALS. (d) Uralite has the same cleavage, structure, and composition as hornblende, but the exterior form of augite. Crystals of this mineral occur in many greenstones (uralite- porphyries). (Predazzo.) (e) Asbestus and amianthus are fibrous varieties of tremolite and actinolite. In the variety known as Mountain leather the fibres are closely interlaced, or woven like felt. These minerals fill cavities and clefts in lime- stone and serpentine. (/) Nephrite and Jade may be here added. They consist of a compact white or light-green translucent mass, with splintery fracture. Cp. very variable, sometimes that of tremolite. It is not a rigidly- defined mineral ; forms independent layers as deposits between talcose rocks (in Turkey, New Zealand, &c.). 16. Pyroxene (Augite). Monoclinic. In crystals imbedded or attached, or in stalklike, scaly, or granular masses. Cleavage prismatic, but usually less perfect than hornblende. Fracture conchoidal to uneven. H.=5 6. S.Gr.^3'2 3'5. Rarely colourless. Colour usually grey, green, or black. Lustre vitreous, sometimes mother-of-pearl. All degrees of trans- parency. Cp.=R, 3 Si 2 , but very variable. Si partly replaced by Al ; R. Ca, Mg, Fe, Mn. Bp. the pyroxenes fuse (some quietly, others with some effervescence) to a white, grey, green, or black glass. Usually they are with difficulty re- ducible by microcosmic salt ; those that contain Al almost not at all. Almost all exhibit the reaction for iron, the white and light-coloured varieties manganese. Imperfectly decom- posed by acids. The following mineralogical varieties are distinguished : (a.) Diopside. Light- coloured, transparent and translucent varieties, and (5) Salite. Green, translucent only at the edges ; usually AUGITE SECTION. 19 foliated. This and the last are without much geological importance. A sahlite, termed malakolite, is however found separately imbedded in the granular limestone. (c) Augite. Green to black, opaque. Occurs as an essential ingredient in basalt, dolerite, diabase, and many lavas. Frequently in the form of perfect crystals porphyriti- cally imbedded. Also found in meteoric stones. (d) Omphazite. Grass-green, always accompanied by garnet, and together with it forming eklogite. (e) Hypersthene (Paulite). Reddish-brown, greenish-black, or black, with metallic mother-of-pearl lustre on the faces of most perfect cleavage, and sometimes a change of colours showing a copper-red tinge. Lustre other- wise vitreous or resinous. In thin lamellce translucent. Cp. very poor in lime, rich in iron and manganese. Hypersthene is an essential constituent of the rock hypersthenite (Penig in Saxony, Isle of Skye, Southern Tyrol). Otherwise it is usually an accessory, and is especially frequent in gabbro. Appendix to Pyroxene. Diallage (Smaragdite), which is an essential consti- tuent of many gabbro rocks, is only a peculiar variety of pyroxene or hornblende, or perhaps a mixture of both. The following are hydrous products of the decomposition of pyroxene : Schiller spar. An essential constituent of schiller rock (Baste, in the Harz), accessory in serpentine. Palagonite. The principal ingredient of the tufa of that name (Sicily, Nassau). Green Earth. Frequent in vesicular cavities of amygdaloids and in basaltic tufas. c 2 20 MINERALS. The distinction between hornblende and pyroxene is ex- tremely important lithologically, but is often attended with considerable difficulty. Some assistance may be derived from the following remarks : (a) As to Grystallograptiic Differences. Only recognisable in cases of granular texture, where the crystals are tolerably perfect. One of the most essential and best-marked differences consists in the different angles of the cleavage prisms of the two minerals (and those are usually identical with the angles of the exterior faces of the crystal.) In hornblende the larger angle of the prism is 124 30' (giving a complement of 55 30') ; in pyroxene the angles are 87 5' to 92 55'. (/3) Differences of Par agenesis. Rocks containing free quartz, felspars rich in silica (such as orthoclase and albite), or potash-mica as essential constituents, seldom likewise contain augitic minerals, but if the latter occur, they are almost invariably hornblende, and not pyroxene. In pyroxenic rocks, quartz especially is very rarely found, and if present is only accessory (eklogite, hypersthenite). On the other hand, labra- dorite and magnesian micas are very frequent in such rocks, though not exclusively there found. Pistacite and pyrites are more frequent accessories in hornblendic than pyroxenic rocks. The pistacite is found adhering to the surfaces of clefts, or in geodic cavities, and would appear in most cases to be a pro- duct of the decomposition of amphibolite. Leucite and olivine are characteristic as accessory minerals in pyroxenic rocks. As a very general rule, we may characterise horn- blende as the constituent of the plutonic, pyroxene as AUGITE SECTION. 21 that of the volcanic igneous rocks. Nevertheless, sometimes both are found together in the same rock (basalt, omphacite, trachyte of Etna). In this latter case the pyroxene is the older formation of the two, i.e. it has cooled and become solid more rapidly than the hornblende. (y) The chemical differences between pyroxene and hornblende are not marked. It would appear as if one or the other might have resulted from the same identical mass ac- cording to the conditions under which it cooled and solidified. The origin both of hornblende and of pyroxene may be of various kinds. The possibility of their formation by wet process during the development or the transmutation of a rock's mass has been proved by Daubree, who actually produced diopside by subjecting glass to the influence of the thermal waters of Plombieres. Many of the crystals which are found disseminated in limestone rocks would appear to be the result of metamorphosis (Pargas, Tyrol). Again, both these minerals may be products of sub- limation (Elie de Beaumont, Sacchi), or they may be simple products of igneous action, since we find in the slags of smelting furnaces products of precisely similar form and composition. 17. Spodumene (Triphane). Monoclinic, isomorphous with pyroxene; crystallised or massive in broad fibrous or scaly masses. Cleavage orthodiagonal and prismatic. Fracture uneven. H.=6'5 7 S.G. = 3'1 3'2. Lustre vitreous, with mother-of-pearl lustre on the cleavage surfaces. Colour greenish-grey to apple-green. Translucent, but frequently only at the edges. Cp. = Li 3 Si 2 + 4AlSi 2 frequently with some Na, K, or Ca. Bp. intumescent ; colours the flame red, but 22 MINERALS. weakly and transitorily. Fuses easily to a clear glass. When mixed with Ca F and KS 2 , it gives a purple-red flame. Is not affected by acids. Spodumene is found imbedded in gra- nite (Uto in Sweden ; Killiney Bay, Ireland ; Peterhead, Scotland). It also occurs in the quartz veins of mica-schist (Massachusetts) . Killinite is a product of the weathering or decomposition of spodumene. (c) MICA SECTION. This is a section of minerals distinguished by their pre- eminent foliation (basal cleavage) to a degree not known in any other mineral. As regards origin, they are in part purely plutonic, being found even in the most recent igneous rocks. In part however, they are products of wet processes, and we find pseudomorphs after felspar, tourmaline, and other minerals. 18- Potash-Mica (Phengite, Muscovite, Binaxial Mica), Trimetric with monoclinic aspect. The crystals usually appear as rhombic or hexagonal plates. Sectile, and its thin laminse elastic. H.=2 2'5. S.G.=275 31. Colourless, frequently white, and various shades of yellow, green, or red. Light colours are characteristic. Metallic mother-of-pearl lustre. Transparent to translucent. Optically very distinctly binaxial ; the angle of the optical axes =45 75. Cp. variable average formula==mAlSi + KSi ; in which formula ra=2, 3 or 4. A portion of the Al may be replaced by Fe, Mn, Cr ; a portion of the K by Fe and Mn. Strange to say no Ca is to be found in any species of mica. The K is usually =8 9 per cent. There is usually from 1 5 per cent, of water and some fluorine. Bp. fuses, with more or less readiness, to a cloudy glass or a white enamel. Not affected by muriatic or sulphuric acid. Potash-mica is an essential ingredient of many rocks, and especially characteristic for the older plutonic or metamor- MICA SECTION. 23 plilc rocks, thus for many kinds of granite, gneiss, and mica- schist. Damourite, Margarodite, and other similar minerals of very limited frequency, are, in part at least, products of transmu- tation of potash-mica. They occasion a transition to the chlorites. The same may be said of Sericite, a green mineral, of silky lustre, which is said to form the base of several crys- talline schists and clay-slates ; but it is not .yet free from doubt whether or not sericite is entitled to be regarded as an independent mineral. List gives the following account of sericite H.=l. S.G.=2'89. Foliated in one direction ; planes undulated. Lustre silky. Colour greenish or yellowish- white. 19. Lithia-Mica (Lepidolite, Lithionite). Trimetric, corre- sponds with potash-mica in many crystallographic and phy- sical properties, except that its colour is frequently red. H. = 2'5 4. S.G.=2'84 3. The angle of the optical axes = 70 78. Cp. very variable, may be generally expressed by the formula mRSi+7&RSi; m = w=l; or ra=2, n=3 ; or some- times m=3, n=.2. Again, a part of the bases, as well as of the acids, are compounds of fluorine, not oxygen. The content of lithia is usually 2 5 per cent., and of fluorine 2 10. Bp. fuses very readily, with efflorescence to a colourless, brown, or black glass. The flame is coloured purple-red ; with acids it is imperfectly soluble, but completely decomposed. Lithia-mica is an essential ingredient of Greisen, very fre- quent in some kinds of granite, and in metalliferous veins, especially those of tin. In all these cases this mineral is usually associated with other fluorides, such as topaz, tourma- line, apatite, &c. 20. Magnesia-Mica (Biotite, Hexagonal or Uniaxial Mica). The name of uniaxial mica is now found to be incorrect, as 24 MINERALS. all magnesia-mica is "binaxial, if only slightly. The angle of the two axes is for the most part less than 5. Trimetric (?) crystals, usually tabular ; usually sectile, and in thin plates, elastic. H.=2'5 3. S.G. -- 27 31. Green, brown, black, in general colours usually dark. Metallic mother-of-pearl lustre. Translucent to opaque. Cp. very variable; chiefly =AlSi + K, 3 Si, in which Al is in part replaced by Fe, and R--Mg, K, Fe. The Mg=9 25 per cent. Some fluorine, chlorine, and water likewise enter into the composition. Bp. fuses with greater difficulty than the before-mentioned species of mica, to a grey or black glass. It is little attacked by muriatic acid ; on the other hand, unlike potash-mica, it is completely de- composed by concentrated sulphuric acid, leaving a white residue of silica. The geological area of biotite is far more extensive than that of potash-mica, for it is not only found in the older plutonic rocks and crystalline schists (granite, porphyry, gneiss), but also in more recent and the most recent volcanic products (trachyte, basalt, and the corresponding lavas). Rubellan and Phlogopite are minerals closely allied to mag- nesia-mica, of which rubellan is perhaps only a transformed product. (d) HYDROUS MAGNESIAN SILICATES (TALC SECTION). These have many characteristics and properties in common. Some minerals which contain Fe instead of Mg belong to the same group. We may make three principal divisions : the Chlorites (21), the Serpentines (2225), and the Talcs (26,27). The chlorites under certain circumstances may be regarded as hydrous mica ; the serpentines and talcs appear chiefly to be products of metamorphosis, perhaps occasioned by percolating water. The most important species are : 21. Chlorite (Ripidolite). Ehombohedral ; the crystals TALC SKCTIOX. -25 grouped in the form of comb or botryoidal shape, usually in massive, foliated, or scaly aggregates. Cleavage basal, very perfect; sectile. Its thin lamellae flexible, but not elastic. H.=l 1-5. S.Gr.=2'65 to 2'85. Colour green, in various shades. Its crystals are frequently translucent, and of red colour when regarded in the direction of thfc principal axis. Streak greenish-grey. Lustre mother-of-pearl. Thin laminae trans- parent to translucent. Cp.=3R 3 Si-f E 3 Si-f 12H=30 31 Si + 1419 Al + 32 37 Mg+5 6 Fe. In matrass it gives out water. Bp. fuses on charcoal ; with borax it melts and shows uhe reaction of iron. Thin laminae are decomposed by concen- t rated sulphuric acid. Chlorite forms the most important and essential elements of chlorite- schist, also of chlorite mica-schist, both frequent in the Alps. In the protogine-granite and protogine-gneiss it is a substitute for mica. It is also a characteristic constituent of diabase, and many kinds of syenite-porphyry (Altenberg in Saxony). Delessite is a mineral closely allied to chlorite, but richer in iron. It is frequent in vesicular cavities of melaphyres. Pennine, Ripidolite, and Clinochlore are minerals resembling chlorite, but not yet accurately denned. They are of frequent occurrence in chloritic schists as essential ingredients. Some of the minerals which we have already noticed as having arisen from transmutation of augite, such as schiller spar, green earth, &c., are externally very similar to chlorite. 22. Saponite (Soapstone) . Massive, sectile, and very soft. S.G.^2'26. Colour white or light grey, yellow or reddish brown, dull, with lustrous streak. Greasy feel, not adhesive to the tongue. Cp. = 2Mg 3 Si 2 + Al *Si + 10H. In the matrass it gives out water and becomes black. Thin laminae melt with difficulty at the edges. It is readily and completely decomposed with sulphuric acid. 26 MINERALS. Saponite occurs in fissures of serpentine rock (Lizard's Point, Cornwall). 23. Serpentine. Usually compact, sometimes granular or fibrous ; in the latter case it is called chrysolite or serpentine- asbestus. Fracture conchoidal, flat, or uneven, splintery, fine-grained, or of twisted fibres. H.=3 4, rarely 5 ; S.G.= 2 '2 2 '6. Bright coloured and translucent varieties are termed precious serpentines to distinguish them from the ordinary serpentine, which is usually of dark colour green, red, or brown. Cp.=the general formula Mg 9 Si 4 H (i =43 Si + 42 Mg + 12 H, with a trifling percentage of Al and Fe. In matrass gives out water and becomes darker in colour. Bp. almost infusible, exhibits the reaction of iron ; easily soluble in borax, in microcosmic salt with effervescence. When powdered, soluble in muriatic acid, and still more readily in sulphuric acid. Serpentine is found disseminated in rocks, usually massive, sometimes in broken masses, plates, and veins. It likewise forms a rock of itself. The right of serpentine to the character of an independent mineral is open to doubt, as it frequently appears to be only a pseudomorph of other minerals, e. g. hornblende, augite, garnet, spinel, &c. The rock serpentine also appears to be usually, if not always, a product of transmutation derived from other rocks, such as granite, gneiss, gabbro, chlorite- schist, &c. ; and only to resemble the mineral, not to con- stitute, strictly speaking, an aggregate of it. (Yide post, p. 314.) 24. Ottrelite. In small thin hexagonal or rounded laminae ; cleavage parallel to the lateral faces. Hard; is capable of scratching glass. S.Gr. =4'4. Greenish grey to blackish-green. Lustre vitreous; translucent. Cp. = (Fe,Mn) 3 Si 2 + 2AlSi + 3H. In matrass gives out water. Bp. fuses with difficulty TALC SECTION. 27 at the edges to a black magnetic globule ; with borax, iron reaction ; with soda, that of manganese. Ottrelite is found disseminated in various kinds of clay- slate, which have received the name of Ottrelite Slate (Lux- embourg). 25. Glauconite. Small, round, dark-green grains, which when recently exposed are frequently very soft, but in time assume about the hardness of gypsum. S.G.=2'29 2'35. Cp.=a hydrous silicate of Fe and K (5 10 per cent. K), moreover Al and small quantities of Ca and Mg. Glauconite is found in the form of grains or nuclei of minute fossils (Foraminifera) imbedded in clay-marl and sandstone rocks. Very characteristic for rocks of the Chalk formation (Upper Greensand, Isle of Wight; Chalk of Calais). Occurs also in other sedimentary formations (Muschelkalk of Berlin ; Calcaire grossier, Paris ; Browncoal Sandstone of the North-eastern Alps). 26. Talc. Trimetric (?) ; rarely crystallised, usually mas- sive, in granular, foliated or scaly aggregates. Cleavage basal, very perfect. Very sectile with greasy feel. Thin laminae flexible, but not elastic. H.=l 1-5. S.G. = 2'56 2-8. Colour white, grey, and green, in various shades. Lustre mother-of-pearl, or resinous. Translucent to opaque. Opti- cally binaxial. Cp. = Mg 6 S> + 2H=62 Si + 32'9 Mg-f 4'9 H. The Mg is partly replaced by Fe. Bp. shines brightly and loses its colour ; exfoliates ; becomes hard ; does not fuse. If heated with cobalt solution, becomes pale-red. Is not at- tacked by acids. Varieties especially noticeable are : (a) Foliated Talc. The purest crystalline talc. (6) Steatite. Amorphous. Frequently pseudomorphous after other minerals. Decomposes with boiling sulphuric acid. 28 MINERALS. Talc is a very widely diffused mineral. Talc-schist and many beds of rock in the regions of crystalline schists con- sist almost exclusively of this mineral. Talc-mica-schist, protogine, and some sandstones contain it as an essential ingredient. 27. Meerschaum. Massive and in nodules. Fracture flat conchoidal, and fine-grained, earthy; sectile. H. = 2 2 '5. S.G.=0'8 1. Colour yellowish or greyish- white, dull. Streak little lustrous. Opaque. Greasy feel ; adhering strongly to the tongue. Cp. (probably) MgSi + H, usually with some C. Bp. contracts, becomes hard, and fuses at the edges to a white enamel. Forms separate beds, which are the result of a process of transmutation, probably of Magnesite. (e) ZEOLITE SECTION (NON-MAGNESIAN HYDROUS SILICATES.) The minerals which are grouped under the name of Zeolites are an extensive family of the silicates, having both as to che- mical composition and crystallographic form much in common with the Felspar group, as well as with the Augite and the An- dalusite groups but their chief distinguishing feature is that they invariably contain a large proportion of water, varying from 4 22 per cent. The following properties are common to all zeolites. Before the blowpipe they froth up and melt to a glass, which owing to the many bubbles never becomes very clear or trans- parent. They are all decomposed by muriatic acid, under which process the Si is precipitated to a gelatinous or slimy mass. Again, they all have a colourless streak, which circum- stance is owing to the small proportion of colouring oxides (not above 2 per cent.) which they contain. The geological character of the zeolites is very uniform. They are principally found in the volcanic rocks. They are ZEOLITE SECTION. 29 either found in the vesicular cavities, veins and fissures of those rocks in the form of crystals and foliated and radiated masses, or they sometimes form an essential ingredient of the rock's mass (in basalt, phonolite). In either case they are not original products, i. e. not of contemporaneous formation with the rock in which they are found ; they are products of exfiltration or of the internal decomposition and transmutation of the mother rock. It is interesting to notice with reference to those zeolites which are the products of what we have termed exfiltration, that Daubree has shown them not to be simple deposits of substances held in solution by the per- colated water to which they owe their origin, but rather products of the chemical action of that water at a high degree of temperature on a portion of the rock's mass which had already oozed out ; and thus that the same rill of water percolating through different rocks will produce different species of zeolite. As regards zeolite forming part of the composition of the rock's mass, this is so frequently the case in basalt, that it has recently been put forth as a universal rule that no rnr.k can be a genuine basalt without zeolite. Nevertheless we think this assertion too general, and it is possible that nepheline, which enters largely into the com- position of basalts, may by reason of its great solubility in muriatic acid, have been sometimes mistaken for zeolite. Zeolites are seldom found in metalliferous veins, or in the fissures of the older plutonic rocks. The most convenient arrangement of the individual species for our present purpose will be the crystallographic. We begin with The Monometric Zeolites. 28. Analcime. Usually in trapezohedrons ; more rarely a combination of these with the cube. The crystals usually 30 MINERALS. found grouped together in geodic cavities. Sometimes mas- sive, granular. Cleavage cubal, imperfect. Fracture uneven. H. 5'5. S.G. = 2'1. Colourless, white to grey, or flesh-red. Lustre vitreous. Transparent to translucent at the edges only. Cp. =JSTa3Si 2 + 3AlSi 2 + 6H. Analcime is found in geodic cavities of basaltic rocks (Giant's Causeway, Ireland ; Dumbartonshire ; Seisser Alp) ; in metalliferous veins (Kongsberg ; Andreasberg in the Harz) ; and as a recent formation at the mouth of springs (Plom- bieres). It is especially frequent in the old dolomitic lavas of the Cyclopean Islands near Sicily, and those have been named Analcymite accordingly. The observer must avoid confound- ing the crystals of analcime with those of leucite. 29. Apophyllite (Ichthyophthalmite, Albine). Crystals py- ramidal, columnar, or tabular. Usually grouped together in geodes ; occasionally in scaly aggregates. Cleavage basal, per- fect. Fracture uneven. H.=4'5 5. S.G-. = 2'33. , Colour- less, or yellow, greyish, or reddish- white. Lustre vitreous, on the cleavage surfaces mother-of-pearl. Transparent to translucent at the edges. Cp. -8CaSi-|-KSi 2 + 16H, with sometimes 1 per cent, of fluorine. Apophyllite is found in the geodic cavities of volcanic rocks (Iceland, Faroe, Fassa Thai) in metalliferous veins (at Utoe in ' Sweden, at Andreasberg, and in the Bannat associated with wollastonite). In the Tertiary limestone near intruded basaltic rocks at Puy de la Piquette, in Auvergne. Finally as a recent deposit from spring water at Plombieres. Hexagonal Zeolites. 30. Chabasite (Phacolite). Rhombohedral. Crystals often of twin growth. Cleavage rhombohedral. Fracture uneven. H.=4 4-5 S.G.=2-08 2-17. Colourless, white, or red- ZEOLITE SECTION. 31 dish. Lustre vitreous. Transparent to translucent. Cp.=. (Ca,Na,K)3'Si 2 + 3AlSi 2 + 18H. It occurs in geodes of volcanic rocks (Faroe, Fassa Thai, Giant's Causeway) ; in syenite (Massachusetts) ; ^in gneiss (Connecticut). Trimetric Zeolites. 31. Prehnite. Crystals tabular or short columnar. Grouped in geodes in fan-shaped or spheroidal aggregates. Cleavage basal, perfect. H. = 6 67. S.G.=2'8 2'95. Earely colour- less, usually green. Lustre vitreous ; on the cleavage surfaces, mother-of-pearl lustre. Transparent to translucent at edges only. Cp. Ca 2 Si + AlS'i + H, frequently with some Fe. Occurs in basaltic amygdaloids (Fassa Thai) ; in the trap rocks of Dumbarton. 32. Thomsonite (Comptonite) . In geodes, the crystals in sheaves or fan-shaped groups, or in fibrous aggregates. Cleav- age, according to the brachy- and macro-diagonal, almost equally perfect. Fracture uneven. H. = 5 5*5. S.G.=2'35 2 '38. Colour white. Lustre vitreous, sometimes mother-of- pearl. Translucent, but usually clouded. Cp. = (Ca v N"a) a Si + 3AlSi + 7H. Thomsonite occurs in amygdaloids at Kilpatrick, in Dum- bartonshire, and Lochwinnock, in Renfrewshire, in the vesicular cavities of Vesuvian lavas, in the analcimite and phonolite of Bohemia. 33. Natrolite (Soda-Mesotype) . Crystals usually thin, co- lumnar, acicular, or capillary. In geodes, also in bunches or reniform masses. Cleavage prismatic, perfect. H.=5 5*5. S.G.-=2-17 2-24. Colourless, greyish-yellow or reddish- white. Lustre vitreous, occasionally mother-of-pearl. Trans- lucent, or only at the edges. Cp. = NaSi * AISi -f- 2H, occa- sionally a small quantity of Fe. 32 MINERALS. Natrolite occurs in vesicular cavities of basaltic and phono- lite rocks (Kilmalcolm in Renfrewshire, Aussig in Bohemia) . 34. Pliillipsite (Lime-Harmotome) . Columnar crystals, sometimes long and sometimes short, frequently twin, growth cross-shaped. Cleavage brachy- and macro- diagonal. EL 4 4'5. S.Gr. = 2'2. Colourless, white, yellowish or reddish. Lustre vitreous. Transparent to translucent at the edges only. Cp. = (Ca,K)Si+AlS> + 5H. Phillipsite is found in the basaltic lavas of Capo di Bove near Rome, County Antrim, in Ireland, &c. 35. Harmotome (Baryt-harmotome). Columnar crystals almost always twins, shaped in form of a cross. Cleav- age imperfect, the brachydiagonal more perfect than the macrodiagonal. H.=4'5. S.G.=2'39 2*5. Colourless, or different shades of white. Lustre vitreous, little translucent. Cp.=BaSi+AlSi 2 + 5H, with some K and Ca. Harmotome occurs in the metalliferous veins of Andreas- berg, in nodules of agate from the melaphyre of Oberstein, Zweibrucken, under like circumstances in Dumbartonshire, where its crystals are simple. Monoclinic Zeolites. 36. Laumontite (Laumonite). The crystals usually in colum- nar combinations, also in granular and fibrous masses. Cleav- age prismatic, perfect ; very friable and brittle. H. = 3'5 4. S.G.=2'29 2*36. Colour yellowish, or greyish- white, also reddish. Lustre vitreous, on the cleavage surfaces mother-of- pearl. Transparent to translucent on the edges only. Cp.= Ca 3 Si 2 + 3AlSi 2 + 12H. It loses a portion of its water very quickly on exposure, and then falls to powder. Laumontite is found in vesicular cavities of basaltic rocks (Dumbartonshire, Faroe), in clefts and fissures of syenite (Dresden), or quartz-porphyry (Botzen). ZEOLITE SECTION. 33 37. Scolecite (Lime-Mesotype) . Crystals long or short prisms or acicular ; also massive, radiated, and fibrous. Cleavage prismatic, tolerably perfect. H. = 5 5'5. S.G.=2'2 27. Colourless, greyish, yellowish, or reddish- white. Lustre vitreous, the fibrous clusters silky. Transparent to trans- lucent at the edges only. Cp. = CaSi + AlSi + 3H. Scolecite occurs in the vesicular cavities of basaltic rocks (Auvergne, Staffa), or in the fissures of the same rocks (Kil patrick hills). t 38. Heulandite (Foliated Zeolite, Stilbite, in part). Crystals usually tabular, rarely prismatic, either single or clustered in geodes, also massive, in radiated, foliated, or globular aggre- gates. Cleavage clinodiagonal, very perfect. H.=3'5 4. S.Gr.=2'2. Colourless, white, usually red to brown. Lustre vitreous, on the cleavage surfaces, mother-of-pearl. Transpa- rent to translucent at the edges only. Cp. =CaSi + AlSi 3 + 5H. Heulandite occurs frequently in the vesicular cavities of basaltic rocks (Faroe, Iceland, Skye, Fassa Valley) ; rare in metalliferous veins (Andreasberg). 39. Stilbite (Desmine, Radiated Zeolite). Its monoclinic character is questionable. The crystals are broad prisms, frequently clustered into sheaves or bundles ; also massive and fibrous aggregates. Cleavage brachydiagonal, very perfect, macrodiagonal imperfect. H.=3'5 4. S.G. = 2'1 2'2. Co- lourless, white, grey, yellow, or red. Lustre vitreous, on the most perfect cleavage surfaces, mother-of-pearl lustre. Trans- lucent, perfect or only on the edges. Cp. - CaSi + AISi 3 + 6H. Stilbite is a frequent inhabitant of vesicular cavities or fissures of volcanic rocks (Fassa-Thal, Faroe, Iceland) also occurs in metalliferous veins (Andreasberg, Kongsberg). 40. Smitlisonite (Hydrous Silicate of Zinc, Galmey, in part) may be added here by way of appendix, although geologically it is very far removed from the zeolites, since chemically it 34 MINERALS. agrees with them in being a hydrous silicate free from magnesia. It crystallises trimetrically, hemimorph. The crystals are nsnally small, tabular, and prismatic, independent or in geodes, frequently grouped in fan-like, grape-like, botryoidal, or reni- form clusters ; also fine fibrous to felt- like varieties occur. Cleavage prismatic, very perfect, macro- domatic perfect. Frac- ture uneven. H.=4'5 5. S.G. = 3'16 3'9. Colourless, white and variously coloured (but always light coloured). Lustre on crystal surfaces vitreous. Semi-transparent to opaque. Cp.=2Zn 3 Si + 3H. When heated in matrass gives out water. Bp. decrepitates a little, shows green phospho- rescent light, but does not melt. Gelatinises with acid. Smithsonite takes no essential part in the composition of rocks, but both alone and with other zinc-ores and galena forms separate beds of ore of considerable extent. These ores are usually associated with dolomites and limestones (Raibl and Bleiberg in Carinthia, Aachen, Tarnowitz in Silesia, Mendip hills). Smithsonite occurs in veins of lead-ore at Matlock in Derbyshire, and many other English localities. (/) ANDALUSITE SECTION. With respect to the minerals grouped under this head, we must remark that they are allied together more by their chemical and physical properties than their geological affinities. 41. Andalusite (Chiastol/ie, Hohlspath). Trimetric. The crystals are usually combinations of the prism and base, hence columnar, attached, also imbedded ; also in radiated, fibrous, and granular clusters. Cleavage prismatic, imperfect. Frac- ture uneven and splintery. H. - 7*5. S.G. - 3'1 3 P 2. Colour grey, greenish, or reddish-^ ; ev. Lustre vitreous, usually weak. Barely transparent, and in that case showing trichroism ; ANDALUSITE SECTION. 35 usually translucent, or translucent only at the edges. [The variety chiastolite fluctuates in hardness between 3 and 7'5. This difference is attributable to foreign substances contained in its crystals. These foreign substances are arranged in some sort symmetrically about the edges and axis so as to give a tes- selated appearance in the section. The crystals are mostly twins or fourfold.] Cp.= Al 3 fii 2 , sometimes Al 4 Si 3 , usually with some Fe and Mn. Bp. infusible. When reduced to powder, fuses with difficulty in borax to a transparent colour- less glass ; with cobalt solution coloured blue. Not affected by acids. Andalusite occurs as an accessory in granite and crystalline schists (gneiss, mica-schist), Devonshire and Aberdeenshire. The variety chiastolite occurs exclusively in clay-slate, and usually in the neighbourhood of granites or other igneous rocks. It probably is the product of a metamorphosis result- ing from percolated water. 42. Topaz. Trimetric. Crystals sometimes hemimorphous, always prismatic. Single crystals attached or imbedded, or clusters incrusted in geodes ; also coarse or fine-grained masses. Cleavage basal, very perfect. Fracture conchoidal to uneven. H. = 8. S.G.=3'4 3*6. Colourless and transpa- rent, but usually yellow, red, or blue. Lustre vitreous. Trans- parent to translucent at the edges only. Cp. = 5Al 3 Si 2 + (3AlF 3 + 2SiF 3 ) shows reaction of fluorine. Bp. infusible, but soluble in microcosmic salt, leaving a skeleton of silica. Not affected by muriatic acid. With sulphuric acid, some hydrofluoric acid is formed. Pycnite is a fibrous variety of topaz. Topaz is an essential constituent of topaz-rock, an accessory of granite (imbedded, or incrusting geodic cavities) : Mourn e in Ireland, Mursinsk in Siberia, Greifenstein in Saxony. Very frequently associated with other minerals which contain fluo- D 2 36 MINERALS. rine, and with beryl and tin ore. Also in separate localities, associated with the like minerals (Cornwall, Saxony). Although the topaz crystals which are found imbedded in granite appear to be of simultaneous formation with that rock, and therefore of plutonic origin, Daubree has succeeded in producing topaz by subjecting alumina to the action of fluoride of silicon. 43. Staurotide (Staurolite). Trimetric. Crystals always imbedded, prismatic, frequently cruciform. Cleavage brachy- diagonal, perfect. Fracture conchoidal to uneven. H. = 7 7'5. S.Gr.=3'5 3*7. Deep red to blackish-brown. Lustre vitre- ous. Translucent to opaque. Cp. variable =(AlFe) 2 Si, or R, 3 Si 2 , or R 5 Si 4 . Bp. infusible. With difficulty soluble in borax and microcosmic salt. Not affected by muriatic acid. Staurotide occurs in association, sometimes twin growth, with the next named species ; accessory in mica- schist and gneiss (Switzerland, Tyrol, Brittany). 44. Ky unite (Disthene,Rhoeiizite'). Triclinic. Crystals usually long and broad-shaped (bladed), without terminal faces, fre- quently in twins ; imbedded singly or grouped in fibrous masses. Cleavage prismatic, very perfect, brittle. H.=6 7'2. S.G. =3*56 3'67. Colourless or common blue. Lustre vitre- ous, on the most perfect cleavage planes, mother-of-pearl. Transparent to translucent on the edges only. Cp. = Al 3 Si 2 , with little Fe. Bp. infusible ; dark blue if heated with cobalt solution. Not affected by acids. Kyanite occurs as an accessory ingredient in granulite, also in gneiss and mica-schist similarly to staurotide. 45. Lievrite (Tlvaite^Jenite) . Trimetric. Crystals long prisms. Crystals attached or incrusting geodic cavities ; also massive, usually in fibrous, rarely in granular aggregates. The crystals usually coated with brown iron-ochre. Cleavage indistinct. Fracture conchoidal to uneven. Brittle. H.=5'5 6. S.Gr.=: ANDALUSITE SECTION. 37 3'8 4'2. Colour brownish to greenish-black. Streak black. Lustre resinous. Opaque. Cp.=2Fe 3 Si + Ca 3 Si + Fe 2 S'i. Bp. fusible to a black magnetic globule; with microcosmic salt shows the reaction of iron, and leaves a skeleton of silica. With muriatic acid gelatinises. Lievrite is found associated with pyroxene in subordinate masses in the mica-schist of Elba, also (according to Dana) in the granite of Predazzo in Tyrol. 46. Tourmaline (Schorl). Rhombohedral, eminently hemi- morphous. Crystals mostly columnar, imbedded or attached, also massive, fibrous, or granular aggregates. Cleavage rhom- bohedral, very imperfect. H. = 7 7'5. S.Gr. = 2'94 3'3. Colourless, seldom transparent, most usually black, also brown, red, blue, green, &c. Lustre vitreous. Every degree of pellu- cidity from transparent to opaque. Very eminently polar electric. Cp.= very various and complicated. The following ingredients take part in its composition : Si, B, P, F, K, Na, Li, Ca, Mg, Fe, Mn, Al, Fe, Mn. The oxygen ratio of all the bases in this compound (including boracic acid as a base) to the silica is constant, and is =4 : 3. Bp. very variable, in part fusible (in different degrees), in part intumescent, and in part not. All kinds of tourmaline, when mixed with fluor-spar and sulphate of potash, exhibit the reaction for boron. Not affected by muriatic acid. Sulphuric acid almost completely decomposes the powder of fused tourmaline after lengthened digestion. Tourmaline is of very frequent occurrence ; but is almost exclusively confined to the plutonic-igneous and the meta- morphic rocks. It is an essential constituent of schorl rock ; accessory in granite, granulite, mica-schist, topaz-rock, and it sometimes appears in such quantity in these rocks as to cause varieties to be specially named after it. [See post.] It is unknown in augitic and volcanic rocks. In dolomite it ap- pears exceptionally (Capo Longo, south of St. Gotthard) ; also 38 MINERALS. in sandstone, but only in neighbourhood of intruded plutonic rocks. -, K The origin of tourmaline is sometimes contemporaneous with that of the mother rock, sometimes it is a secondary product occasioned by metamorphism (percolation of fresh- water springs ?). It has not yet been artificially produced. Tourmaline is also known in pseudomorphs after felspar (in the granite of Trevalgan, Cornwall), and on the other hand pseudomorphs of mica, chlorite, and steatite after tourmaline, occur in many places. (#) GARNET SECTION. The affinity of the different minerals of this section to each other consists in their containing the like ratio of oxygen between the acids and bases. 47. Chrysolite (Olivine, Peridot). Trimetric. The crystals usually columnar and imbedded (chrysolite), but very often massive, in granular aggregates, and disseminated (olivine). Cleavage brachydiagonal, tolerably distinct. Fracture con- choidal. H. =67. S.G. = 3'3 3-5. Lustre vitreous. Co- lour green, asparagus-green, olive-green, also yellow and brown. Transparent to translucent. (Chrysolite usually in- cludes the transparent crystals of paler colour, while olivine, so called from the olive-green tint, is applied to imbedded masses and grains of inferior colour and clearness. Dana.) Cp. = (Mg,Fe) 3 Si, with some Mn, Ca, Ti, and H. Bp. only the varieties containing much iron are fusible. All varieties are easily decomposed by sulphuric acid. The most beautiful crystals of chrysolite are said to come from granitic rocks of Upper Egypt. Fayalite, a variety very rich in iron, is found in granite of Mourne Mountains. Other- wise this mineral is known as essential ingredient of the rock called eulisite. It is an accessory constituent of hypersthene GARNET SECTION. 39 rock (Elfdalen) in talc-schist (Katherinenburg). All these occurrences are insignificant compared with the abundance and frequency in which both grains and crystals of olivine occur in basalts and lavas. In basalt, olivine is almost an essential constituent. It is also found in meteoric stones. Olivine is, doubtless, usually a purely igneous product. If additional proof of this were wanted, it may be found in the crystals of an olivine rich in iron which occur in the slags of smelting furnaces. A rock of New Zealand, which has been called Dunite, consists of granular olivine. 48. Beryl (Emerald, Smaragd). Hexagonal. Crystals co- lumnar, either singly attached or imbedded, or clustered in geodes ; also fibrous aggregates. Cleavage basal, tolerably perfect. Fracture conchoidal to uneven. H. = 7'5 8. S.G.=2*68 2'73. Colourless, limpid, but usually green or blue. Lustre vitreous. Transparent to translucent at the edges only. Cp.=(jrSi' 2 + Ai8i 2 , with some Fe and Cr. Bp. fuses with difficulty at the edges to a clouded scoriated glass, completely soluble in microcosmic salt. Not affected by acids. Beryl occurs as an accessory in mica-schist (Salzburg), in granite (Mourne Mountains, Bodenmais in Bavaria), in black limestone (Muzo in Columbia), and with tin-ore (Saxony). PJicnaleite or Phenacite. Cp. GSi. Rhombohedral crys- tals, and occurs under precisely similar conditions to beryl. t 49. Garnet. Monometric, in rhombic dodecahedrons or trapezohedrons or in combinations of both. Crystals singly attached or imbedded or clustered in geodes, also massive, in granular to compact aggregates. Cleavage indistinct, do- decahedric. Fracture conchoidal, or uneven and splintery. ][.=6-5 7'5. S.G.==3'15 4-3. Seldom colourless, usually green, yellow, red, brown or black. Lustre vitreous to 40 MINERALS. resinous. Transparent, translucent, opaque. Cp. extremely manifold, so that six groups may be distinguished of essen- tially different composition, passing over, however, one into the other. The common formula may be thus given : B 3 Si-f RSi, in which formula E,= (Ca, Fe, Mn, Mg), and R=(A1, Fe, Cr). Bp. fuses with considerable ease to a green, brown, or black glass, which is frequently magnetic. With phosphor- salt gives a siliceous skeleton, otherwise iron and manganese reaction. In raw state little affected by muriatic acid, but after fusion easily and completely decomposed by that acid, with a gelatinous precipitate of silica. Almandine, Grossularite, Essonite, Common or Aplome Garnet, Colophonite and Melanite are varieties chiefly distinguished by their colour and different degrees of transparency. Garnet occurs as an essential, and sometimes sole ingredient of the following rocks : garnet rock, eklogite, eulisite, kinzi- gite. It likewise is a very frequent accessory in granite, granulite, vitreous trachyte and perlite (in which it would appear to be a contemporaneous formation with the mother- rock), and in metamorphic rocks (e.g. chlorite- schist, mica- schist), where it is probably a product of the very process of metamorphism. In limestone and sandstone rocks (Killan and Wexford in Ireland), and in lavas of Vesuvius. 50. Pyrope. Monoclinic, crystals almost always rounded off at the edges, imbedded, or scattered loose in alluvial soil. Fracture conchoidal. H.=7'5. S.G.=3'69 3'8. Colour deep hyacinth to blood-red. Lustre vitreous. Transparent or very translucent. Cp. a magnesian alumina- garnet, with a considerable portion of the magnesia replaced by Fe and Cr. Bp. becomes black and opaque at a red heat, but re- sumes its transparency and red colour on cooling. With borax, gives the reaction of chromium. Not affected by acids unless previously fused. GARNET SECTION. 41 Pyrope is a very characteristic accessory constituent of many kinds of serpentine (Saxony), and of the opal-rock termed vitrite (Bohemia). 51. Zircon {Hyacinth). Dimetric. Crystals columnar or pyramidal, singly imbedded or attached. Cleavage pyramidal and prismatic, imperfect. Fracture conchoidal to uneven. H.=7'5. S.G.=4 47. Colourless, rarely white, usually coloured yellow, red or brown. Lustre adamantine, vitreous. Every degree of transparency. Cp. = ZrSi, with little Fe. Bp. infusible, only soluble with borax. Partially decomposed in sulphuric acid after long digestion. Not affected by any other acid. Zircon occurs in many rocks (more or less abundantly), usually as an accessory ingredient only, viz. in zirconsyenite (Norway, Ural) ; in granite (Criffel, Kircudbright and New Jersey) ; in basaltic lavas of extinct volcanoes (Rhenish Prussia) ; and in volcanic tufa (Auvergne) ; in granular lime- stone (Hammond). 52. Idocrase (Vesuvian, Egeran, Wiluit). Dimetric. Crys- tals usually columnar or pyramidal, imbedded and attached ; also massive in fibrous and compact aggregates. Cleavage prismatic, imperfect. Fracture uneven and splintery. H.= 6'5. S.G. = 3*45. Colour yellow, green or brown. Lustre vitreous or resinous. Transparent, translucent, opaque. Cp.= R 3 Si + RSi, and R= principally Ca, Fe, Mg, with H up to 3 per cent. R=A1, Fe. Bp. fuses easily, with effervescence, to a yellowish-green or brownish glass. With microcosmic salt it produces the reaction of iron and a siliceous skeleton. In raw state, imperfectly decomposed by muriatic acid, but after fusion, completely decomposed with a gelatinous precipitate of silica. Idocrase occurs as an accessory in old lavas of Vesuvius ; in serpentine (Mussa Alp, Piedmont) ; in dolomite (Fassa Thai, 42 MINERALS. where it is an unmistakable product of metamorphism) ; and in metalliferous veins (Swarzenberg, Saxony). Its igneous origin, at least in part, is proved by the appear- ance of similar products in slags of furnaces. 53. Scapolite (Wernerite). Dimetric. The crystals columnar, attached and imbedded, also clustered in geodes, or massive and granular. Cleavage prismatic, tolerably perfect. H.= 5 5*5. S.Gr.= 2'6 2*7. Colourless, or coloured pale green, green, or reddish. Lustre vitreous to resinous. Semi-trans- parent to opaque. Cp. very fluctuating, in part answering to the formula : B 3 Si 2 + 2AlSi, with Ca, Na, some H and Fe. Scapolite is an essential constituent of wernerite rock ; it also occurs as an accessory in granite and other crystalline rocks, likewise in limestone, but in that case usually near the margin of intruded granites. Finally in veins of ore ( Arendal) . Heionite and Mellilite. Limpid crystals found in the marble blocks of Somma, and Mellilite, dirty yellow, found in nepheline rocks at Capo di Bove near Rome, are two minerals very closely allied to scapolite. 54. Epidote (Pistacite, Zoisite). Monoclinic. Crystals co- lumnar, extended in the direction of their horizontal axis, usually in geodes, also massive and in fibrous, granular, or compact aggregates. Cleavage orthodiagonal, very perfect, hemidomatic perfect. Fracture conchoidal to uneven. H. = 6 7. S.G. = 3'2 3*5. Almost always coloured, viz. green, yellow or grey. Lustre vitreous, and on the cleavage surfaces adamantine. Transparent to opaque. Cp. = R 3 Si-f 2RSi, in which formula R Ca, with some Mg and up to 2 per cent H ; R=A1, Fe. Bp. variable ; after being subjected to strong heat or melted, all varieties may be decomposed by muriatic acid and they become gelatinised. Zoisite is grey, with Ca and Al ; it occurs as an accessory in granular limestone and granite (Fichtelgebirge). GARNET SECTION. 43 Pistacite is green and rich in Fe. It occurs as an accessory and very frequently in hornblende rocks, and is probably the product of decomposition of hornblende. It also occurs in beds of iron-ore (Arendal). 55. Orthite (Allanite, Cerine). Monoclinic, isomorphous with epidote, but seldom occurs in distinct crystals. More usually massive, in granular and short fibrous aggregates. Fracture conchoidal to uneven. H. 5 5*6. S.G. = 3'3 4'2. Colour, pitch-brown to black. Streak greyish or greenish. Lustre imperfect, metallic to vitreous and resinous. Trans- lucent at the edges to opaque. Cp. variable. In part, R :} Si + JiSi, in which R= Al and R=Ce, Ca, Mg, with little La and H, and in the variety orthite, Y. Bp. on charcoal, puffs up slightly and fuses to a black glass ; with borax fuses easily and makes with oxidising flame a bead of blood-red colour in the heat and yellow on cooling ; with the reduction flame the bead is green. Orthite occurs as an accessory in granite, especially in cer- tain narrow dykes of granite, rich in felspar, which traverse hornblendic rocks (Greenland, Dresden) ; in zirconsyenite (Hitteroe in Norway), where the crystals are a foot in height ; sometimes in porphyries (Totun Fjeld in Norway). 56. Gadolinite. Monoclinic, but seldom in crystals, usually massive and imbedded. Fracture conchoidal to uneven. H.== 6-57. S.G. = 4 4-3. Pitch- and raven-black. Streak greenish-grey. Lustre vitreous, resinous. Translucent at the edges to opaque. Cp. various, in general R 3 Si ; and R= Y, Ce, Fe, Ca. Bp. puffs up slightly without fusing, glows vividly and burns to a light-grey colour. Gelatinises with muriatic acid. Gadolinite occurs chiefly in granite, and as an accessory, imbedded (Fahlun in Sweden, Hitteroe in Norway). 57. Axinite (Thumite). Triclinic. Crystals singly at- tached, or clustered in geodes, also massive, in scaly aggre- 44 MINERALS. gates. Cleavage indistinct. H. = 6'5 7. S.G.=3'3. Colour clove-brown, grey, or plum-blue. Transparent to translucent at edges only. Exhibits trichroism in an eminent degree. Cp. very complicated = B, 3 Si + 2RSi + JB Si; and R = Ca, Mg, K ; R = Fe, Mn. Bp. melts easily, and with intumescence, to a dark green glass, which becomes black in the oxidation flame ; with fluor-spar and sulphate of potash gives the reaction of boracic acid. After fusion it gelatinises completely with muriatic acid. Axinite occurs in the geodes of granite (Oisans, St. Gotthard), or in metalliferous veins (Botallack in Cornwall ; Kongsberg in Norway). 58. Cordierite (Dickroite, Peliom, lolite). Trimetric. Crys- tals usually columnar, hexagonal, also massive and dissemi- nated. Cleavage brachydiagonal, tolerably perfect. Fracture conchoidal to uneven. H. = 7 7*5. S.G. 2*6. Colourless, but usually coloured bluish-grey, violet-blue, or brownish. Lustre vitreous ; in fracture eminently resinous. Transparent to translucent, beautiful trichroism. Cp. R 3 Si 2 -f 3AlSi ; and R=Mg, Fe, Mn and H. Bp. fuses with difficulty at the edges to a glass ; dissolved with difficulty in borax. Little affected by acids. Cordierite occurs as a substitute for quartz, and an essential ingredient in several granites and in metamorphic gneiss, under circumstances pointing to an igneous origin, or to an origin from contact with igneous masses (Saxony). It also occurs in beautiful crystals in metalliferous veins (Bodenmais in Bavaria). FaMunite and Finite are products of transmutation from cordierite, or (according to some authors) from nepheline. They occur porphyritically in granite. Liebnerite and Oosite are like products. They occur chiefly in porphyry rocks. TANTALATES, TITANATES, VANADATES. 45 C. TANTALATES (OR COLUMBATES) TITANATES, VANADATES. The minerals here grouped occur very frequently as acces- sory ingredients in plutonic and igneous rocks, and are for the iinost part of contemporaneous origin with the rocks in which they occur. 59. Pyrochl&re. Monometric, usually in octahedrons (cry- stals or grains imbedded.) Fracture conchoidal, brittle. H.= 55-5. S.G.=3'8 4-3. Colour dark reddish- and. blacjdsh- brown. Streak light brown. Lustre vitreous. Translucent at the edges to opaque. Cp. = (Ca,Fe,Ce,Mn)(Cb,fi) with some NaF and H. Bp. becomes yellow and fuses with diffi- culty to a brown slag, previously (sometimes) emitting an intense light. When powdered, it is decomposed in concen- trated sulphuric acid. Pyrochlore occurs as an accessory in granite and syenite (imbedded), (Miask, Brevig in Norway), also in granular limestone (Kaiserstuhl in Baden). 60. Perofskite. Monometric, usually in cubes or octahedrons. Crystals attached or imbedded, also massive. Cleavage cubal. H. =5'5. S.G.=4. Colour greyish- to iron-black, or reddish- brown. Streak greyish-white. Lustre metallic-adamantine. Opaque. Cp.^CaTi, with small quantity of Fe. Bp. in- fusible. Scarcely affected by acids. Perofskite occurs as an accessory in chlorite schist (Slatoust, in the Ural) in talc schist (Zermatt), and in granular limestone (Kaiserstuhl). 61. Tantalite. Trimetric. Crystals usually columnar, also massive and disseminated. Fracture conchoidal to uneven. H.=6 6-5. S.G.=7'1 7'9. Colour iron-black. Streak brown. Lustre adamantine metallic. Opaque. Cp. = (Fe,Mn)(Ta,Cb 2 ), w ith sometimes some Ca and up to 16 per 46 MINERALS. cent, of Sn. Bp. unchanged. Not affected, or very little affected, by acids. Tantalite occurs as an accessory in granite, imbedded, and is usually associated with beryl and tourmaline (Finland, Sweden). 62. Columbite (Nwbite). Trimetric, usually in thick tabular or broad columnar crystals. Cleavage macrodiagonal, very distinct, brachydiagonal distinct. Fracture conchoidal to un- even. H.=6. S.G. = 5'4. 6'4. Colour brownish-black to iron-black. Streak reddish-brown to black. Lustre metallic adamantine. Opaque. Cp. = (Fe,Mn) 3 Cb 2 , with little Ca and Sn. Bp. infusible, unchanged. Not affected by acids. Columbite occurs as an accessory in granite, associated with beryl and tourmaline (Bodenmais in Bavaria, Connecticut and Massachusetts), also imbedded in cryolite (Greenland). 63. Wolilerite. Trimetric. Distinct crystals very rare, usually massive and disseminated. Fracture conchoidal. H. = 5'5. S.G. - 3*4, Colour wine-yellow to honey-yellow, or yellowish-brown. Lustre resinous in the fracture. Trans- lucent. Cp.=a silicate of Ca, Na, Ta, Zr. Bp. at first un- changed, after some time fuses to a yellow glass. Decomposes in concentrated muriatic acid. v Wohlerite occurs as an accessory in zirconsyenite (Brevig in Norway), in syenite and miascite (Ditro in Transylvania). 64. Titanite (Sphene, Menochine ore). Monoclinic, frequently crystallised, prisms and tabular, imbedded and attached, twins frequent, also massive and in scaly aggregates. Cleavage indistinct. H. = 5 5'5. S.G.=3'4 3'56. Colour grey or brown. Lustre adamantine, often resinous. Semi-transparent to opaque. Cp.=2CaSi=CaTi :{ . Bp. fusible only at the edges. With microcosmic salt and metallic tin gives the reaction of titanium in the reduction flame. Incompletely decomposed by muriatic acid ; completely decomposed by sulphuric acid, gypsum being formed. SULPHATES. 47 Ghreenovite is red-coloured titanite containing Mn. Titanite occurs as an accessory in the mica-schist of the Alps, and there usually in cruciform twin crystals, in gneiss (Massachusetts), in granite (Greenland), in syenite and zir- consyenite (Strontian, Argyleshire ; Arendal), in volcanic rocks, rich in felspar (Laachersee, Andernach on the Rhine), in phonolite (Bohemian Mittelgebirge), in beds of iron-ore (with pyroxene in Arendal), finally in granular limestone (in many localities in North America). 65. Volborthite. Hexagonal. Crystals are small, often only scaly particles on an earthy incrustation. H.=3 3'5. S.G.= 3'45 3'86. Colour olive- or grass-green, also yellow. Streak almost yellow. Lustre mother-of-pearl, vitreous. Translucent in thin plates. Cp. = (Cu,Ca) 4 V + H. When heated in glass tube gives out water. Bp. fuses easily on charcoal, and at a higher temperature consolidates to a slag, resembling graphite, which slag contains grains of metallic copper. It is soluble in muriatic acid. Volborthite occurs as an accessory ingredient in many sand- stones of the Permian formation of Russia, or as incrustation on the walls of clefts in the same rocks. D. SULPHATES. (a) ANHYDROUS SULPHATES. 66. Barytes (Heavy Spar). Trimetric. Crystals tabular or columnar, very various; also lamellar, fibrous, granular, or compact. Cleavage perfect in the planes of the brachy- and macro-diagonals. H.=2'5 3'5. S.G.-4'3 47. Colour- less, limpid, or variously coloured, white, yellow, brown, or red. Lustre vitreous or resinous. Transparent, translucent, opaque. Cp.=BaS, with admixture, in small quantities, of other bases, such as Ca, Sr, and Fe. Bp. decrepitates, and fuses 48 MINERALS. with difficulty. Colours the flame yellowish-green. Not affected by acids. Barytes seldom occurs as an independent rock. It occurs as an accessory in the form of lamellar nodules in the clay strata of Monte Paterno near Bologna, where it is called Bologna-spar or Bolognese stone. It also occurs in the cavities of fossils in the Swabian Jurassic formation ; also very frequent in veins of ore. 67. Celestine. Trimetric, isomorphous with barytes, also the same cleavage, frequently fibrous, granular, or compact. H. 3 3-5. S.Gr. = 3'9. Colourless, limpid, but usually white, rarely blue. Lustre vitreous to resinous. Transparent, translucent. Cp.=SrS. Bp. decrepitates and fuses without difficulty to a milk-white bead. If moistened with muriatic acid, it colours the flame carmine-red. It is only slightly affected by acids. Celestine only occurs as an accessory constituent in rocks. Sometimes it is found in layers of a fibrous texture imbedded in marly limestone (Jena), in lamellar or radiated nodules in dolomite (Seisser Alps), or in fossils (Swabia), also in many metalliferous veins. 68. Anhydrite (Muriacite, Karstenite) . Trimetric. Crystals thick, tabular, but rare ; usually massive, in granular or com- pact aggregates. Cleavage macro- and brachy- diagonal, very perfect, basal perfect. H. = 3 3'5. S.G. = 2'8 3. Colour- less, white, but most frequently light bluish-grey or reddish- grey. Lustre vitreous, on the faces of basal cleavage, resinous. Cp. = CaS. Bp. fuses with difficulty to a white enamel ; with borax effervesces, and fuses to a transparent glass, which on cooling becomes yellowish. Little soluble in acids. Anhydrite occurs as an independent rock, associated with gypsum and rock-salt (frequent in the Alps). It also occurs in metalliferous veins (Andreasberg). SULPHATES. 49 69. Glauberite. Monoclinic, also massive, in thin lamellar aggregates. Cleavage basal perfect. H.=2*5 3. S.G.= 2*6 2 - 8. Colourless and coloured, greenish, yellowish or reddish-white. Lustre vitreous to resinous. Translucent. Taste salt and bitter. Cp. = NaS + CaS. Bp. decrepitates violently, and fuses readily to a transparent glass. Colours the flame reddish-yellow. Glauberite occurs as an accessory in rock-salt (Villa Rubia in Spain, Berchtesgaden in Bavaria, Tarapaca in Peru). (>) HYDROUS SULPHATES. 70. Gypsum (Alabaster, Selenite). Monoclinic. Crystals prismatic and tabular, various, frequently twins, also massive, fibrous, lamellar, granular, or compact. Cleavage clinodiagonal, very perfect, hemipyramidal less perfect. Sectile. In thin plates flexible. H. = 1'5 2. S.G.=2'3. Colourless, limpid, or white, sometimes variously coloured grey, flesh-red, yellow, &c. Lustre mother-of-pearl on the faces of most perfect cleav- age, silky on the hemi- pyramidal faces, otherwise vitreous. Transparent, translucent, opaque. Cp. = CaS=2H. In matrass yields much water. Bp. becomes dull and white, exfoliates and fuses with difficulty to a white enamel, which has an alkaline reaction. Soluble in 460 parts of water, in acids somewhat more easily. Gypsum occurs as an independent rock in sedimentary for- mations, or in metamorphic schists (mica-schist of the Alps). It occurs accessorily in the form of crystals or nodules in clay-marls, rarely in metalliferous veins or dykes ; sometimes, however, in mines as a recent product. The origin of gypsum may be either by wet or dry process, or by metamorphism. It is formed (1) in volcanic districts by fumes of sulphuric acid and sulphuretted hydrogen issuing from cracks or other openings in the ground, and act:'ng upon E 50 MINERALS. lavas previously containing pyroxene and labradorite ; (2) by wet process, where pyrites is decomposed in the neighbour- hood of lime, or as a sediment from the evaporation of sea- water. The latter process may be observed taking place arti- ficially in salt pans ; (3) by metamorphism from anhydrite by simple absorption of water. 71. Alunogen (Hair Salt). Occurs in capillary or acicular crystals or crystalline masses of irregular form, usually in crystalline crusts or reniform aggregates of fibrous structure. H.=1'5 2. S.G.=l-6 1-8. Colour white and yellowish, or greenish. Lustre silky. Cp. = AlS 3 + 18H. Easily soluble in water. If heated in test tube, it intumesces and gives out water. Alunogen is sometimes the product of volcanic action (vol- cano of Pasto, Milo Isle), sometimes a result of the decom- position of pyrites in coal districts, and in alum-shales (Bonn, Dresden) ; sometimes is found as an efflorescence in numerous places in the United States. 72. Native Alum. Chemically speaking there are several subspecies. Crystallographically all monometric, and usually in octahedrons ; also occurs in fibrous masses. Fracture con- ohoidal. H.=2 2-5. S.G. = 1 -61-9. Soluble in water. Taste sweet-astringent. Cp.=RS + AlS 3 -i-24H. According to the various bases, different species are distinguished, viz. : Potash-alum, soda-alum, magnesia-alum, iron-alum, manganese- alum, and ammonia-alum. Bp. on charcoal, efflorescence ; with cobalt solution blue. Alum is found in the vicinity of the crater of ^tna, filling clefts in the Coal and Browncoal formations, especially in pyritous shales (Saarbrucken, Bohemia), and as an efflorescence on other minerals or rocks. In fresh alum-slate no alum is contained, but the latter is only developed in that rock by weathering and the consequent decomposition of the pyrites contained in it. SULPHATES. 51 73. 'Epsomite (Epsom Sa.lt). Trimetric. Crystals columnar, usually in granular, fibrous, or earthy aggregates. Cleavage brachydiagonal. H.=-2'25. S.G.=175. Colourless. Trans- parent. Taste saline bitter. Cp.=2MgS + 7H. Easily soluble in water. Bp. if heated in test tube gives water, fuses, and then remains unchanged. On charcoal it effervesces violently, and shows alkaline reaction ; if heated with cobalt solution, becomes rose-pink. Epsomite occurs as an efflorescence from marshy ground (Steppes of Siberia), and from many kinds of rock (gneiss near Freiberg, alum-slate at Idria), also in solution in spring waters (Epsom, Saidschutz in Bohemia). 74. Glaubersalt (Mirabilite). Monoclinic, usually incrusted. H.=1'5 2. S.G. = 1-48. Colourless, transparent. Taste cooling, and saline bitter. Cp.=NaS + 10H. Easily soluble in water, quickly decomposing, and falling to powder in the atmosphere. Bp. in test tube it melts in its water of crystal- lisation. It colours the flame reddish-yellow. Glaubersalt occurs as an independent rock (Guipuscoa in Spain), accessory in rock-salt strata (Berchtesgaden) ; also in mineral springs (Carlsbad in Bohemia), and salt lakes. 75. Alunite (Ahimstone) . Bhombohedral. The crystals mostly very small, and clustered in geodes. Usually massive, in granular, earthy, and compact aggregates. It occurs mixed and interlaced with quartz, hornstein, and felsite. Cleavage basal. H. = 3-5 4. S.G. = 2'6 27. Colourless, white, yel- low, or reddish. Lustre vitreous, with mother-of-pearl lustre on the basal cleavage faces. Translucent. Cp. = KS-f 3A1S-J- 6H. In test tube gives out water. Bp. decrepitates violently and is infusible. Not affected by muriatic acid ; soluble in heated concentrated sulphuric acid. Alum is manufactured from this mineral by heating and adding water to it. Alunite is met with in the largest known quantities at La 2 52 MINERALS. Tolfa near Rome, where it occurs in small geodes in decom- posed trachytic rocks, and owes its origin to the action of sulphuric acid (a product of volcanic agency) upon the rock during long periods of time (Muzay, Hungary ; Montdore, Auvergne). E. BOKATES. 76. Boracite. Monometric, tetrahedral. The crystals some- times show combinations of the cube, the rhombic dodeca- hedron, and tetrahedron. Always porphyritically imbedded. Cleavage imperfect. Fracture conchoidal. Brittle. H. = 7. S.Gr. = 2'97. Colourless, white or greyish, yellowish, greenish. Lustre vitreous to adamantine. Transparent to translucent at edges only. Cp.=Mg 3 B 4 . Bp. intumesces, fuses with diffi- culty, forming a pearl which, whilst hot, is transparent and yellowish, and when cooled is white and crystalline, acicular. It colours the flame green when fused with sulphate of soda and fluor spar. In muriatic acid it is perfectly soluble. Boracite occurs, as an accessory only, in gypsum, anhydrite, or rock-salt (Liineburg in Hanover, Seegeberg in Holstein, Luneville in France ; in the last place in radiated fibrous masses). A fine-grained to compact rock, which occurs in subordinate masses in the salt mountains of Stassfurt near Magdeburg, consists essentially of boracite with some chloride of magnesium. It is called stassfurtite. 77. Borax (TinkaT). Monoclinic, isomorphous with pyrox- ene. The crystals usually broad and short, columnar. Cleavage clinodiagonal and prismatic. Fracture conchoidal. H. = 2 2'5. S.G.=:1'72. Colourless, or more usually yellowish and greyish- white. Lustre resinous. Translucent. Cp.= NaB 2 -f 10H ; usually impure. Bp. decrepitates with rapid heating, pufis up violently, becomes black, and finally melts to a transparent colourless powder. It tinges the flame reddish- PHOSPHATES. 53 yellow. If moistened Avith sulphuric acid, it tinges the flame green. Borax is met with in loose crystals and crystalline grains or incrustations, associated with rock-salt, on the shores of several lakes in Thibet, where it is a recent formation. Clear lake in California, in crystals several inches long. F. PHOSPHATES. (a) ANHYDROUS PHOSPHATES. 78. Apatite (Spargelstein, Phosphorite). Hemihedral hexa- gonal. The crystals short, columnar, or tabular ; also massive, in granular, fibrous, or compact masses (phosphorite). Cleav- age prismatic and basic. Fracture conchoidal to uneven, and splintery. Brittle. H.=5. S.G.=3'25. Colourless, white, but more usually light green, blue, or grey. Lustre vitreous on crystal faces ; resinous on fracture or cleavage surfaces. Cp.=3Ca 3 P + Ca(Cl,F), with sometimes Mg and Fe. Bp. only fusible in thin laminae. If moistened with sulphuric acid, colours the flame bluish-green. Soluble in muriatic and in nitric acids. Apatite is met with (1) as an independent rock or in con- cretions, principally in strata of the Browncoal formation, more rarely in the Chalk formations, always massive (phosphorite) ; frequent in the Oberpfalz of Bavaria : (2) as an accessory con- stituent of rocks, especially the volcanic (nepheline-dolerite at Lobau in Saxony ; basalt in Bohemia ; volcanic rocks of Tumilla and in meteorites) ; in talc-schist (Zillerthal), and in limestone (Gouverneur in North America, Arendal, Pargas) ; (3) very frequent in veins of tin-ore. It will be therefore seen that apatite in many cases must be a formation by wet process, and in others a plutonic product. Daubree has succeeded in producing artificial crystals of 54 MINERALS. apatite by conducting fumes of chloride of phosphorus over heated quicklime. 79. Turquois (Calaite). Amorphous in cavities and veins, reniform or stalactitic. Fracture conchoidal to uneven. H. = 6. S.Gr. 3=2*6 2*8. Colour sky-blue to verdigris-green. Streak greenish- white, Lustre feeble. Translucent at the edges to opaque. Cp. = Al 2 P + <5H, with some Cu up to 3 per cent. If heated in test tube, it gives water, decrepitates violently, and becomes black. Bp. infusible ; tinges the flame green. Soluble in acids. Turquois is met with as an incrustation in the fissures of Lydian stone ; very precious varieties in Persia. Also occurs in sandstone in Arabia. (6) HYDROUS PHOSPHATES. 80. Vivianite (Blue Iron-Earth). Monoclinic. The crystals usually single, attached, also fibrous, divergent, earthy. Cleav- age clinodiagonal, very perfect ; in thin laminae, flexible. H. = 1*5 2. S.Gr. 2*66. Colour indigo-blue to blackish- green, sometimes white, and becoming blue by exposure. Lustre on cleavage surfaces, mother-of-pearl. Translucent. Cp.=Fe 3 P + 8H. Bp. in matrass gives out much water, pufis up, and becomes particoloured grey and red ; on charcoal burns and becomes red, and then fuses to grey, lustrous, and magnetic globule. Readily soluble in muriatic and nitric acids. Vivianite is usually a product of decomposition from magnetic pyrites, in veins traversing the clay slate (St. Agnes, Corn- wall), or in granite (Bodenmais in Bavaria). The earthy variety is very frequent as an accessory constituent of turf mosses and Tertiary clays. Pseudomorphous in form of oysters and belemnites in New Jersey, U. S. 81. Wavellite (Lasionite). Trimetric. The crystals usually small, acicular, and clustered to reniform aggregates of radiated NITRATES. 55 structure. H.=3'25 4. S.G.=2'34. Colourless, white, or coloured greyish, or a beautiful green or blue. Lustre vitreous. Cp. = (Al 4 P + 18H)+JAlF. Bp. in matrass gives cutwater and traces of hydrofluoric acid. In the forceps puffs up and tinges the flame bluish- green, especially if moistened with sulphuric acid. Wavellite is met with as an accessory and a secondary product in fissures of a soft clay-slate at Barnstaple in Devon- shire ; in Lydian stone at Langenstriegis, near Freiberg ; and in Devonian sandstone at Zbirow in Bohemia. G. NITRATES. 82. Nitre (Saltpetre). Trimetric. The crystals prismatic, isomorphous with aragonite, but usually only very thin, capillary, and acicular. Fracture conchoidal. H.=2. S.G. = 1'9. Colourless, white and grey. Lustre vitreous. Taste saline, cooling. Cp. = KN. Readily soluble in water; defla- grates vividly on glowing charcoal. Bp. fuses easily on pla- tinum wire, tinging the flame violet. Nitre occurs as a separate formation in the caverns of several limestone mountains (Ceylon, Calabria), as an efflores- cence from the surface of the ground, especially in hot weather after rain (Aragon, Hungary, East India) ; also in springs. 83. Nitratine (Chili saltpetre). Rhombohedric. In crystals, and crystalline grains ; cleavage, rhombohedric. H. = 1*5 2. S.G.=-2'1 2'3. Colourless or light coloured. Transparent to translucent. Taste saline, cooling. Cp. = NaN. Soluble in water ; deflagrates in glowing charcoal, but less vividly than saltpetre. Bp. fuses, tinging the flame yellow. Nitratine is a marine product, found in grains mixed with the sand, and associated with gypsum, rock-salt, and glauber- salt, occurring at many parts of the coast of Chili. 56 MINERALS, H. CARBONATES. (a) ANHYDROUS CARBONATES. The most important of the carbonates are those comprised in the Calcite group. The calcspar and dolomites form whole mountain ranges (limestone and dolomite) as well as isolated mineral formations of minor extent in cliffs, fissures, and veins. They are chiefly of neptunian origin, partly crystalline or compact precipitates ; partly formed by springs ; and partly the result of organic processes (chalk, coral). There are probably no limestone rocks of plutonic origin, although carbonate of lime under high pressure is capable of fusion without chemical decomposition. The minor mineral forma- tions in clefts, veins, dykes, and geodes are doubtless, for the most part, the result of infiltration. All calcites are rhombohedral in crystallisation. Calcspar alone presents great variety of form. Its crystals are grouped and interlaced in almost every conceivable shape and fashion, and the uncrystallised varieties are fibrous, granular, compact. The cleavage of the crystals is rhombohedral, very perfect. The angle of the cleavage rhombohedron is the most charac- teristic distinguishing feature of the different species, which can only be determined in many cases by an accurate measure- ment of that angle. Fracture conchoidal, but in the crystal- lised varieties it is somewhat difficult to obtain a genuine fracture. The colour is usually white, grey, yellowish, reddish, or brownish. Lustre vitreous, sometimes resinous. Calcspar and magnesite alone are sometimes perfectly transparent, the other calcites at most only attain translucence. The Cp. of all calcites comes under the general formulae E/C. The following are the principal species of this important group of minerals : CARBONATES. 57 84. Calcspar {Calcareous Spar, Calcite). H.=2'5 3*5. S.G. = 2'5 2-8. Cp. = CaC, usually with small quantities of' Fe, Mg, Mn. Bp. infusible, but burns to quicklime with a bright light. Readily soluble in muriatic acid, even in large pieces, with effervescence, caused by the evolution of carbonic acid. Limestone, marble, chalk, oolite, pisolite, coral, are some of the most important of the very numerous varieties which form independent rocks, and will be described hereafter as such. Marl is a mixture of clay and lime. Iceland spar is a pure transparent variety of calcspar. Anthraconite is coloured black by admixture of carbon. It would lead us too far to attempt to enumerate all the varieties of this very abundant mineral. Calcspar stands next to quartz in importance, as consti- tuting the mineral of the greatest frequency after it, and forming nearly as large a portion of the earth's crust. 85. Magnesite (Talc-spar). H.=3'5 4*5. S.G.=2'8 3. Cp. = MgC, usually also some Fe. Bp. becomes red if heated with cobalt solution. Soluble in acids, if powdered and heat applied. 86. Dolomite (Bitter Spar, Brown Spar, Ankerite). H.= 3-5-^. S.G. =2-85 2-92. Cp.=CaC + MgC, usually with admixtures of Fe and Mn. Ankerite is particularly rich in iron. Bp. infusible, burns to caustic. Does not usually effer- vesce with muriatic acid, and is only soluble in that acid if powdered and heat applied. 87. Breunnerite (Bitter and Brown Spar, in part ; Mesitine Spar). Cp.=FeC + 2MgC. H.=4'5. S.G.=3 3'63. 88. Spathic Iron (Sparry Iron-ore, Siderite). H. = 3'5 4'5. S.G. 3'7 3'9. Colour always yellowish-grey or yellowish- brown. Cp. FeC, with some Mn, Mg, and Ca. In matrass decrepitates and gives out carbonic acid. Bp. infusible ; but 58 MINERALS. becomes black and magnetic. Soluble in acids without heat applied (effervescing). In the compact state, or when occurring in reniform masses or concretions, this mineral is termed SpJicerosiderite, and if, moreover, combined with play, Clay Ironstone. 89. Zinc Spar (Calamine, Galmey, in part). H. =5. S.G. =4 4'3. Cp.=ZnC, with small quantities of Fe, Mn, Ca, Mg. Bp. loses its carbonic acid, and then shows reaction of oxide of zinc. Readily soluble in acids, with effervescence. 90. Aragonite. Trimetric. Crystals usually columnar, with inclination to twin formations. Singly imbedded or clustered in geodes ; also occurring in divergent and fibrous aggregates and stalk-like, coralloidal shapes (flos ferri), or in the form of peastone (pisolite). Cleavage brachydiagonal, distinct ; pris- matic, and brachydomatic, imperfect. Fracture, conchoidal to uneven. H. =3'5 4. S.G.=2'93. Colourless and coloured yellow, wine-yellow, reddish. Lustre vitreous. Transparent to translucent. Cp.=CaC, very often with SrC (up to 2 '4 per cent.), also some CaF. Bp. in matrass decrepitates violently, and falls to a white coarse powder ; on charcoal burns to caustic lime ; if containing strontian colours the flame carmine. Soluble both in muriatic and nitric acids, with effervescence. Aragonite occurs as an accessory in clay and gypsum (Molina and Valencia in Aragon). In clefts and veins of vesicular cavities of basaltic rocks (Bilin, Bohemia). Flos- ferri is formed in great perfection in the Styrian iron mines. A fine fibrous variety called satinspar is found in thin silklike veins traversing the shale at Alston Moor. Peastone (sprudel- or erbsenstein) occurs in great beauty at Carlsbad. Aragonite is entirely a watery product. It is said that whereas cold springs can only produce calcspar, hot springs give birth to aragonite. Moreover, according to Becquerel, aragonite . CARBOXATES. 59 is formed by the action of a saturated solution of NaC 2 on gypsum, but calcspar if the solution of NaC 2 be much diluted. (6) HYDROUS CARBONATES. 91. Trona (Urao). Monoclinic. Crystals broad, columnar ; in direction of horizontal axis, also in fibrous and divergent aggregates. Cleavage orthodiagonal, perfect. H. =2 '5 3. S.G. =2*1. Colourless or grey. Lustre bright vitreous. Transparent. Cp. = Na 2 C 3 + 4H. Sometimes with some NaCl. Does not alter by exposure in a dry atmosphere. Yields water in matrass. Soluble in dilute muriatic acid with brisk effervescence. Trona forms an independent rock (Figzan, North Africa). It forms a crust on the ground on mountain slopes at Mara- caibo in Peru ; and occurs as an efflorescence near Sweetwater River, Rocky Mountains, mixed with sulphate of soda and common salt. 92. Natron {Carbonate of Soda). Monoclinic. Is only known in nature in form of incrustation, or mealy efflorescence on the surface of the ground, or various rocks. H. = 1 1'5. S.Gr. 1'4. Colourless, white or grey. Lustre vitreous, dull. Taste alkaline. Cp. NaC-f 10H. Unlike trona it weathers rapidly on exposure to the air. Liquifies at a moderate tem- perature, and dissolves in its own water of crystallisation ; otherwise, however, has the same attributes as trona (Egypt, Hungary, Vesuvius). 93. Malachite. Monoclinic. In aggregates composed of minute crystallisations, acicular and capillary, lamellar, botry- oidal, and stalactitic, fibrous to compact. Cleavage when crys- tallised basal and clinodiagonal, very perfect. H. = 3'5 4. S.G 3*7 4. Colour emerald- to verdigris-green. Streak verdigris- to apple-green. Lustre of crystals adamantine and vitreous ; of aggregates silky to dull. Translucent to opaque. Cp. = Cu 2 C + H. In matrass yields water and blackens. Bp. 60 MINERALS. - fuses on charcoal, and is finally reduced to copper. Soluble in acids, with effervescence. Malachite occurs as an accessory in various rocks. It is doubtless usually, if not always, a product of the decomposition of copper-ores (Siberia; Chessy near Lyons; Cornwall). It very frequently is found in the form of a pseudomorph of azurite and red copper-ore. 94. Azurite (Lasurite, Blue Copper-ore). Monoclinic. Crys- tals columnar or tabular, usually in clusters or geodes ; also massive and earthy varieties. Cleavage clinodomatic, toler- ably perfect. Fracture conchoidal to uneven, and splintery. H.^3'5 4-25. S.G-.=3'5 3-8. Colour azure-blue, in earthy varieties smalt-blue. Lustre vitreous. Translucent, opaque. Cp. Cu 3 C 2 + H. Bp. similar to malachite. Azurite resembles malachite in the places where it is found in nature, and in the mode of its occurrence in other respects. The earthy variety of azurite may, from its outward appearance, be easily mistaken for vivianite. V. I. OXIDES OF ELEMENTS OF THE HYDROGEN GKOUP. The oxides collected under this head properly speaking belong more justly to the family of earths (Nbs. 1 3). We have, however, postponed their consideration in order to give place as far as possible to those minerals which are more im- portant to the geologist. (a) ANHYDROUS OXIDES. 95. Spinel (Ceylonite, Pleonaste, Automolite, Gahnite). Monometric, usually octahedrons and rhombic dodecahedrons. Crystals singly imbedded and attached, seldom gathered into geodic clusters. Cleavage octahedral. Fracture conchoidal. H. = 8. S.Gr. 3-5 4-9. Usually coloured, red-blue, green, yellow, brown, or black. Lustre vitreous, sometimes ANHYDROUS OXIDES. 61 resinous. Transparent, translucent, opaque. Cp.=RAl; R = (Mg,Fe,Ca,Zn,Mn), and a part of the Al is sometimes replaced by Fe and a little Cr. The varying composition gives rise to distinguishable varieties of the mineral. Thus MgAl, red, transparent, is spinel proper ; (Mg,Fe)Al, black, translucent at the edges, is pleonaste ; ZnAl, greenish-black, translucent at the edges, automolite. Bp. the red varieties infusible, but lose their colour ; on cooling the colour returns. The black varieties fuse to a dark-green bead. The zinc-spinels with soda give oxide of zinc. Not affected by acids. Spinel occurs as an accessory in granular limestone (pleon- aste at Monzoni ; blue spinel in North America in several places), in gneiss and talc-schist (the automolite of Fahlun) ; in the vesicular cavities of volcanic rocks (Somma), and in allu- vium (Ceylon). Sometimes spinel is a product of metamor- phosis, e.g. of the action of syenite on limestone, at Monzoni. Ebelmen has also succeeded in producing spinel artificially by igneous means. 96. Magnetic Iron-ore (Magnetite, Oxydulated Iron). Mono- metric, most usually in octahedrons and rhombic dodeca- hedrons. Crystals imbedded and attached, and clustered in geodes ; very generally massive in granular or compact aggre- gates, also earthy (eisenmulm). Cleavage octahedral. Frac- ture conchoidal to uneven. Brittle. H.=r5'5 6*5. S.G.= 4*9 5 '2. Colour iron-black. Streak black. Lustre metallic. Opaque. Yery strongly magnetic. Cp.=FeFe, sometimes with some Mg. Bp. fuses with difficulty, and with borax gives iron reaction. The powder completely soluble in muriatic acid. Magnetic iron-ore is found in separate beds (Arendal, Dannemora) ; it also occurs as an accessory in many rocks, especially in chlorite-chist, talc-schist, serpentine, granite, syenite, basalt, and limestone. 62 MINERALS. 97. Chromic Iron-ore (Chromite). Monometric in octa- hedrons, usually massive, in granular aggregates, and dis- persed. Cleavage octahedral, imperfect. Fracture conchoidal to uneven. H.=5'5. S.G. =4'3. Colour brownish-black. Streak brown. Lustre semi-metallic. Opaque. Sometimes magnetic. Cp.=FeCr, with some Fe replaced by Mg and some Cr by Al. Bp. infusible. With borax it fuses to a green globule. If fused with saltpetre and dissolved in water, it yields a yellow solution, which shows the reaction of chromic acid. Scarcely affected by acids. Chromic iron very frequently occurs as an accessory in serpentine (Islands of Unst and Fetlar, Shetland), rarely in dolomite (Hoboken, New Jersey). 98. Hematite (Specular Iron, Red Iron-ore}. Rhombo- hedral ; in rhombohedrons, pyramidal or tabular crystals, which are singly imbedded or attached in groups (Specular Iron, Micaceous Iron), or subcrystalline, frequently fibrous in botryoidal, reniform, or stalactitic masses ; also granular, lamellar, compact, and earthy textures (Bed Hematite, Fibrous Red Iron, Scaly Red Iron, Red Iron Froth, Reddle, or Red Chalk, &c.) The crystallised varieties have : Cleavage basal and rhombohedral, imperfect. H.^5'5 6'5. S.G. = 4'5 5'3. Fracture conchoidal to uneven. Colour iron-black to dark steel- grey. Streak cherry- or blood-red. Lustre metallic. The subcrystalline varieties have: H.=3'5 only. S.G. 4*5 4'9. Colour blood-red to brownish-red, sometimes pass- ing over into steel-grey. Streak blood-red. Lustre dull. Cp. Fe, sometimes with some Ti. Bp. both varieties become black and magnetic in the reducing flame. In acids but slowly soluble. Specular iron (eisenglanz) includes the varieties with perfect metallic lustre ; red iron-ore the amorphous varieties. The sub- crystalline varieties of hematite frequently contain impurities, ANHYDROUS OXIDES. 63 siliceous, argillaceous, &c. Itabirite is a granular variety of the same mineral containing quartz, jaspery clay -iron ; reddle, argillaceous iron. Hematite forms independent rocks and beds, sometimes horizontally imbedded between the strata of other sedimentary rocks. It also forms an essential constituent of micaceous iron-gneiss and micaceous iron-schist. It is like- wise met with as an accessory in many other rocks. At Vesuvius and ^Etna it fills clefts in lava, or is found in vesicular cavities of lava, where it is probably the result of the decomposition of fumes of chloride of iron by the vapour of water (steam). In other cases it is usually a product of metamorphism from spathic iron and brown hematite. Again, it is sometimes pos- sibly a direct hydrogenic formation (especially where it is pseudomorphous of other minerals or dendritic on the surfaces of rock clefts). 99. Titaniferous Iron (Titanic Iron-ore, Ilmenite, Crichtonite) . Rhombohedral, isomorphous with specular iron. Crystals imbedded singly, or attached in groups. Also massive, in granular lamellar aggregates, or dispersed in grains. Cleavage sometimes rhombohedral. Fracture conchoidal to uneven. H.=5 6. S.Gr.=4'5 5. Colour iron-black to brown or steel-grey. Streak black to brownish-red. Lustre semi- metallic. Opaque. Cp.=Ti and Fe in various and probably indefinite proportions, sometimes with some Mn, or Mg. It will be seen that this composition admits of a near approach to that of hematite, and in truth the division between the two is not very definitely marked. Bp. infusible, with fluxes gives the reactions of iron and titanium. If heated in concentrated sulphuric acid, it gives a blue colour. Soluble with difficulty in muriatic or nitric acid, titanic acid being separated. Titaniferous iron is an accessory ingredient in many rocks, especially in basalts and dolerites, also in talc-mica-schist (Gastein), miascite (Ilmensee near Miask), granite (Aschaf- 64 MINERALS. fenburg). Very frequent in river deposits (Menaccan in Cornwall). 100. Braunite. Dimetric. Crystals usually small and in pyramids resembling the octahedron, clustered in geodes and in granular aggregates. Cleavage pyramidal, tolerably per- fect. H.=6 6-5. S.G. =475 4-82. Colour iron-black to brownish-black. Streak black. Lustre metallic, resinous. Opaque. Cp. = Mn or MnMn. Bp. infusible. With borax, phosphor- salt, or soda gives the reaction of manganese. Soluble in muriatic acid, chlorine being evolved in the process. Braunite occurs sometimes as an accessory in other rocks, chiefly, however, in veins. (In the porphyry of Oehrenstock near Ilmenau, Elgersburg in Thuringia.) This mineral and similar manganese products very frequently form dendritic coatings to the faces of clefts in rocks. These dendritic forma- tions are usually exfiltrations from the mother rock. 101. Hausmannite (JBraunstein) . Dimetric. Crystals always pyramidal, grouped in geodes. Cleavage basal, tolerably per- fect, pyramidal less distinct. H. = 5 5*5. S.G.=47. Colour iron-black. Streak brown. Lustre bright metallic. Opaque. Cp. = MnMn. Bp. like oxide of manganese. Soluble in muriatic acid, with disengagement of chlorine. In concen- trated sulphuric acid, after a short time, assumes a bright red colour. Hausmannite is usually found in separate beds (Ilmenau in Thuringia, Ihlefeld in the Harz), and would appear to be in almost all cases a hydrogenic product, Mn having been first dissolved in spring and other water, and having afterwards absorbed more oxygen from the air. Daubree has, however, shown the possibility of producing hausmannite by the reaction of water in the state of steam upon chloride of manganese at a red heat. 102. Polianite. Trimetric. Crystals usually in short prisms, ANHYDROUS OXIDES. 65 vertically striped. Also massive in granular aggregates. Cleavage brachydiagonal. H.=6'5 7. S.G-.=4'84 4'88. Colour light steel-grey. Streak black. Lustre black metallic. Opaque. Cp.=Mn. Bp. infusible ; on charcoal changes to brown MnMn. Soluble in muriatic acid, with brisk effer- vescence of chlorine. Pyrolusite is sometimes a modification of polianite, sometimes a product of the transmutation of manganite, a mineral which we shall presently notice. The manganite is a compound of Mn and water, and it has a strong tendency to part with its water and absorb oxygen. Polianite is frequently found in beds of the manganese- ores (Flatten in Bohemia, Johanngeor- genstadt, Saxony). Pyrolusite is found in the same localities, or associated with iron-ores (Siegen, in many parts of France). 103. Cassiterite (Tin-ore, Tinstone). Dimetric. Crystals in short prisms or pyramids, very often twins, imbedded or at- tached ; also massive, granular, or fibrous (wood- tin). Cleav- age prismatic, imperfect. Brittle. H.=6 7. S.Gr.=6'3 7'1. Colour usually yellowish-, reddish-, or blackish-brown ; rarely colourless. Streak colourless or brownish. Lustre adaman- tine or resinous. Translucent to opaque. Cp. = Sn, usually with some Fe, Mn, Si, and Ta. Bp. unchangeable, on charcoal with carbonate of soda reducible to metallic tin. Not affected by acids. Tin-ore is principally found in metalliferous veins, also as an accessory, and especially so in plutonic rocks (greissen, granite, and tourmaline rocks). Wolfram, tourmaline, beryl, and topaz are almost always associated with this mineral. Tin-ore in nature is doubtless in many cases a product of wet processes (we find pseudomorphs after felspar in Corn- wall) ; but Daubree has also proved that crystallised oxide of tin may be formed by the action of steam on fumes of chloride of tin. F 66 MINERALS. 104. Rutile (Nigrine). Dimetric. Crystals always columnar, frequently very thin, acicular and capillary, imbedded and at- tached, frequently twins ; also massive, compact, or granular. Cleavage prismatic, perfect. Fracture conchoidal. H.=6 6*5. S.Gr.=4'18 4'25. Colour yellowish- or reddish-brown to black (nigrine). Streak yellowish-brown. Lustre metallic adaman- tine. Translucent to opaque. Cp.=Ti, with small quantity of Fe. Bp. unchangeable ; with borax gives reaction of titanium. Not affected by acids. Rutile occurs only as an accessory ingredient in rocks ; chiefly in greenstones and diorites, rarely in granite ( Warwick in America) ; gneiss and mica-schist (Barre and Shelburne in Massachusetts) ; or in granular limestone (Edenville in New York). Daubree has produced crystallised titanic acid by the action of steam upon fumes of chloride of titanium. (&) HYDROUS OXIDES. 105. Manganite. Trimetric, sometimes hemihedral. Crys- tals always columnar and distinctly marked with vertical stripings, frequently grouped in bundles or clustered in the form of geodes. Also massive in fibrous, divergent, rarely in granular aggregates. Cleavage, brachydomatic very perfect, basic and prismatic imperfect. Somewhat brittle. H. = 4. S.G.=4'2 4*4. Colour dark steel- grey to nearly iron-black, frequently brownish-black. Streak brown. Lustre imper- fectly metallic. Opaque. Cp. MnH. Bp. in matrass yields water, with borax gives reaction of manganese. Perfectly soluble in concentrated muriatic acid, chlorine being disen- gaged. Slightly soluble in sulphuric acid, which colours it pale red. Manganite is found in separate beds with other manganese- ores (Ihlefeld in the Harz, Ilmenau and Oehrenstock in HYDROUS OXIDES. 67 Thuringian Forest). We have already noticed the tendency of manganite to change into pyrolusite. Psilomelane and Wad are two hydrous ores of manganese, occurring frequently with other manganese ores, or as acces- sories in rocks. They are crystalline, also amorphous, some- times massive, in reniform, stalactitic, lamellar, and earthy varieties. Cp. (of psilomelane) = RMn 2 + H, with Mn, Ba, K ; (of wad) very variable, so that it is hardly to be called an independent mineral : consists principally of Mn, Mn, and H, with variable proportions of Ba, Ca, Cu, Co (earthy cobalt or asbolan). 106. Limonite (Brown Iron-ore, Brown Hematite). Subcrys- talline. In fibrous masses of globular, reniform, or stalactitic shape. Also compact or earthy. H. = 5 5*5. S.G.=3*6 4. Colour, clove-brown to yellowish- or blackish-brown, black. Lustre silky, shining or dull. Opaque. Cp. = Fe 2 H 3 . Bp. becomes black and magnetic, is fusible in thin laminae. With borax it gives reaction of iron. Soluble in heated nitric acid. Limonite is a very abundant mineral, sometimes in inde- pendent beds, sometimes as an accessory. Gothite or Stilpnosiderite (FeH) is a mineral very closely allied to limonite and frequently associated with it. ii. Fluorides and Chlorides. 107. Common Salt (Rock-salt). Monometric. Crystals always cubic ; usually in granular or fibrous aggregates or massive. Cleavage cubic, very perfect. Fracture conchoidal. Slightly brittle. H.=2'5. S.G.=2'1 2'2. Colourless or grey, or yellowish, or reddish ; rarely blue or green. Lustre vitreous. Transparent. Taste pure saline. Cp.=NaCl, very often impure, containing F, Br, KC1, MgCl, and other F 2 68 MINERALS. salts. Soluble in 3" 7 parts of water. Liquefies on exposure to moist atmospheres. Bp. decrepitates in matrass ; fuses on charcoal and evaporates with strong heat ; tinges the flame reddish-yellow, and if combined with microcosmic salt and oxide of copper, it gives a beautiful blue flame. Rock-salt is frequently met with as an independent rock in sedimentary formations of every age. It also occurs as an accessory ingredient in clay marls of the salt mountains (Berchtesgaden) where it is in the form of cubic crystals porphyritically imbedded. In each case it is a neptunian product. It is found in a state of solution in sea- water, which contains about 2'5 per cent .of salt. It occurs in the steppes, in the sand of the Desert, in inland springs and lakes, and finally as a sublimation at the craters of volcanos. We shall have occasion to mention rock-salt again amongst the rocks. 108. Sal-ammoniac. Monometric, usually in uncrystalline crusts, stalactites, or as an earthy coating. The crystals have conchoidal fracture. H.=l 1'5. S.Gr.=l'5. Colourless, or coloured yellow or brownish. Taste saline and pungent. Cp.= NH 4 C1. Easily soluble in water. Bp. in matrass evaporates entirely ; with soda emits a strong smell of ammonia. If melted with phosphor-salt and oxide of copper, it colours the flame a beautiful 1blue. Sal-ammoniac occurs as a product of sublimation in the clefts and fissures of volcanic rocks, and many lavas, also in burnt seams of coal. 109. Fluor (Fluor-spar). Monometric, Cubic form very frequent. Crystals single or in groups, attached, also massive, in coarse granular and radiated aggregates, or amorphous and earthy. Cleavage octahedral, perfect, so that the conchoidal fracture is seldom observable. Brittle. H. = 4. S.Gr.= 3'14 3'19. Colour blue, yellow, green, and various. Some- times colourless and limpid. Lustre vitreous. Transparent, FLUORIDES AND CHLORIDES. 69 translucent, opaque. Cp.=CaF. Bp. decrepitates violently, shows phosphorescence, and in thin laminae fuses to a clouded mass, tinging the flame red. In a stronger flame the fused product becomes infusible, and acts like lime. Is completely decomposed by concentrated sulphuric acid, giving forth hydro- fluoric acid. Fluor-spar forms independent rocks of subordinate extent. It occurs most frequently in metalliferous veins, from which it has occasionally spread into the mother rock. In dolomite it sometimes occurs as an accessory (St. Gotthard), and in geodic cavities of the variegated sandstone at Waldshut. It is also met with as a recent deposit from springs of water (Plom- bieres). The last mentioned case proves that fluor-spar may be produced by purely wet chemical process. 110. Cryolite. Trimetric (?). Hitherto only known in amorphous single masses or thick crusts of coarse granular texture. Cleavage basal, tolerably perfect. Brittle. H.= 2'5. S.G.=2'9 3'0. Colourless, greyish- white, or reddish. Lustre vitreous, on the basal cleavage face mother-of-pearl. Translucent. Cp.=NaF+Al 2 F 3 . Bp. very readily fuses to a white enamel, tinging the flame reddish-yellow. In glass tube gives the reaction of fluor ; on charcoal also it fuses easily, but is decomposed, and leaves a deposit of alumina. In con- centrated sulphuric acid it is perfectly soluble, giving forth hydrofluoric acid. Cryolite occurs in a separate bed or layer in the gneiss of Arksutfiord in West Greenland. in. Sulphurets. Arseniurets. 111. Galena (Blue Lead-ore). Monometric. Very usual in cubes, more rarely in rhombic dodecahedrons, octahedrons, and other forms. Crystals usually attached, clustered in geodes, also botryoidal and reniform. Chiefly massive in coarse 70 MINERALS. and fine grained or compact aggregates. Cleavage cubic, very perfect. Sectile. H.=2'5 275. S.G.=7'25 77. Colour lead-grey, sometimes with tinge of reddish colour, sometimes iridescent on the surface. Streak greyish-black. Lustre me- tallic. Opaque. Cp.^PbS, with frequently a small quantity of silver, or also of Fe, Se, Sb. Bp in glass tube, evolves sulphur and a sublimate of PbS. On charcoal decrepitates, fuses after the sublimation of the sulphur, and finally yields a lead globule and lead fumes. Soluble in nitric acid, with development of nitrous acid and precipitate of sulphur. Galena is met with as an accessory in many rocks, e.g. sandstones (in the form of disseminated grains Commern in the Eifel) ; in the argillaceous sphserosiderite of the Coal for- mation, and elsewhere. Very frequently in veins of ore (in the gneiss of Freiberg, in the Devonian strata of the Harz, in mountain limestone of Derbyshire and Cumberland, in granite of Linares) ; also in nests and irregular masses im- bedded, which are usually met with in limestone or dolomite (Tarnowitz in Silesia, Bleiberg in Carinthia, Alpuj arras in Spain). Although galena may very frequently be of hydrogenic origin, it is not less certainly in many cases a product of sublimation ; artificially it is formed in the cracks of furnaces. Gralena has given rise to many secondary products, such as cerusite (PbC) ; pyromorphite (3Pb 3 P + PbCl) ; and mime- tisite (3Pb 3 As + PbCl). 112. Blende (Zincblende, Sphalerite). Monoclinic, tetra- hedral. The crystals frequently irregularly twisted, some- times twin growth ; often massive, in granular, rarely in fibrous or radiated aggregates. Cleavage very perfect ac- cording to the rhombic dodecahedron. Very brittle. H.= 3'5 4. S.Gr. = 3*9 4'2. Colour, most frequently brown or SULPHURETS. ARSENIURETS. 71 black, more rarely yellow-red, white or colourless. Lustre adamantine to resinous. Semi-transparent to opaque. Cp.= ZnS, sometimes combined with considerable quantities of FeS (up to 23 per cent) and a little cadmium. Bp. decrepitates violently, but is only fusible at the sharp edges. On charcoal in the oxidation flame gives zinc fumes. Soluble in concen- trated nitric acid, with precipitate of sulphur. Its place and mode of occurrence in nature are similar to those of galena, which is almost always associated with it. It has been likewise found in the cells of ammonites of the brown Jura and Lias formations, a fact which proves its partial formation by wet processes. 113. Cinnabar. Bhombohedral. Crystals in rhombohedrons or thick tabular, small and in geodes. Usually massive, in granular, compact or earthy aggregates, dispersed or incrust- ing. Cleavage prismatic. Fracture uneven and splintery. Sectile. H.=2'25. S.G. = 8'99. Colour cochineal-red and scarlet ; streak scarlet. Lustre adamantine. Translucent ; opaque. Cp. = HgS. Bp. in matrass burns black; in open tubes sulphur burns with a blue flame, and sublimes, yielding fumes of sulphurous acid with black sublimate and a mirror of metallic mercury. Soluble in nitro-muriatic acid (aqua regia). Cinnabar forms independent beds, appears as impregnation of bituminous shale, or in veins (Idria), also forms incrustation on clefts of many kinds of rock (granite, clay-slate). 114. Magnetic Pyrites. Hexagonal ; m rarely crystallised, usually massive and disseminated, in lamellar, granular or compact aggregates. Cleavage basal, perfect ; prismatic im- perfect. Fracture conchoidal. H. = 3'5 4'5. S.G.=4'4 47. Colour between bronze-yellow and copper-red ; streak grey-black. Magnetic. Lustre metallic. Opaque. Cp.= Fe 7 S 8 , sometimes contains Ni. Bp. unchangeable in matrass ; 72 MINERALS. in glass tube gives out S, but no sublimate ; on charcoal fuses in reduction flame to a greyish black and highly magnetic bead. Soluble in muriatic acid, sulphuretted hydrogen being developed, and sulphur precipitated. Magnetic pyrites occurs with metallic ores, also as an acces- sory ingredient in many igneous rocks, especially diorite, in Vesuvian lavas and in meteorites. 115. Pyrites (Iron Pyrites). Monometric, in various hemi- hedral combinations. Crystals singly imbedded, or combined in geodes and various groups ; also in globular and reniform or fibrous aggregates, or massive. Cleavage cubic, imperfect. Fracture conchoidal to uneven. Brittle. H.=6 6'5. S.Gr.= 4' 8 5. Bronze-yellow to gold-yellow. Streak brownish- black. Lustre metallic. Opaque. Cp.=FeS 2 , with occasion- ally small quantities of Au or Ag. Bp. in matrass gives out sulphur and sulphurous acid, and afterwards acts like magnetic pyrites. Scarcely affected by muriatic acid. Soluble in nitric acid, leaving a precipitate of sulphur. Pyrites is found in independent beds. It is also an essential constituent of the species of granite called beresite. It is a very frequent accessory ingredient in many rocks ; very fre- quent in the crystalline schists, in diorite, limestone, in clay rocks, in coal. It is no less frequent in metalliferous veins. Pyrites is sometimes formed by the action of a solution of copperas on organic substances, and this will account for its often being found in the form of fossils. Wohler has produced artificial pyrites by slowly heating oxide of iron, together with sulphur and sal-ammoniac. 116. Marcasite (White Iron Pyrites, Hydrous Pyrites). Trimetric. Crystals tabular or columnar, usually clustered into groups termed radiated pyrites, spear pyrites, hepatic pyrites, cockscomb pyrites, cellular pyrites, according to vary- ing texture. Cleavage prismatic, indistinct. Fracture uneven. SULPHURETS. ARSEXIURETS. 73 Brittle. H. = 6 6-5. S.G.=4'6 4'8. Colour greyish bronze- yellow, inclined to green ; tarnishes very readily. Streak dark greenish-grey. Lustre metallic. Opaque. Cp. like pyrites, but more prone to decompose and turn to vitriol. Bp. like pyrites. Marcasite is found in separate beds, and as an accessory mineral (Browncoal formation of the Carlsbad region, dolo- mites of Tharandt in Saxony, and Cornwall). 117. Leucopyrite. Trimetric, usually massive and dissemi- nated, granular, or fibrous. Cleavage basal. Fracture uneven. Brittle. H.=5 5'5. S.G. = 7 7'4. Colour silver-white, merging into steel-grey. Streak black. Lustre metallic. Opaque. Cp.=FeAs 2 , almost always with some sulphur, owing to admixture of mispickel. Bp. in matrass yields sub- limate of metallic arsenic ; on charcoal strong smell of arsenic, and a black magnetic residuum. Soluble in nitric acid, with a separation of arsenious acid. Leucopyrite is an accessory in many rocks, especially in serpentine (Reichenstein in Silesia), and in metalliferous veins. 118. Mispickel (Arsenopyrite) . Trimetric. Crystals usually short prisms, or tabular, singly imbedded, or attached in groups; also massive, in granular or fibrous aggregates. Cleavage prismatic, rather distinct. Fracture uneven. Brittle. H.=5 - 5 5'6. S.G. = 6 6*4. Colour silver- white, inclining to steel -grey. Streak black. Lustre metallic. Opaque. Cp. = FeS 2 + FeAs. Several varieties contain Ag (Weisserz), Au, or Co (Kobalt-arsenkies). In matrass gives first a red, afterwards a brown sublimate of sulphuret of arsenic, finally a sublimate of metallic arsenic. On charcoal the arsenic is dissipated, and leaves a black magnetic bead, which acts like magnetic pyrites, and sometimes gives cobalt reaction. Soluble in nitric acid, with separation of arsenious acid and sulphur. Mispickel is frequently met with in veins of ore, is also an 74 MINEKALS. accessory ingredient in many rocks, e.g. the crystalline schists (Kongsberg in Norway, Freiberg, Franconia in New Hamp- shire), and serpentine in various localities. 119. Chalcopyrite (Copper Pyrites) . Dimetric. Tetrahedral. Crystals usually small, frequently of regular twin growth, often massive. Cleavage pyramidal, sometimes distinct. Fracture conchoidal to uneven. Unlike pyrites, is very little brittle. H.= 3*5 4. S.G.=4'1 4'3. Colour brass-yellow, sometimes with tarnish of gold colour and iridescence. Streak black. Lustre metallic. Opaque. Cp.= Cu 2 S + Fe 2 S 3 . Bp. becomes black on cooling, red, and fuses at a strong heat to a magnetic bead of steel-grey colour ; with borax and soda gives a copper bead ; when moistened with muriatic acid tinges the flame a beautiful blue. Soluble in nitro-muriatic acid (aqua regia) with separa- tion of sulphur. Chalcopyrite is a very frequent associate of pyrites. Is accessory in many rocks, e.g. tourmaline-granite, Predazzo, Tyrol. iv. Native Elements. 120. Sulphur. Trimetric. Crystals usually pyramidal, singly attached, or clustered in geodes ; also globular, reni- form, stalactitic ; with fibrous or compact structure. Cleavage basal and prismatic, imperfect. Fracture conchoidal to uneven, and splintery. Not very brittle. H.=1'5 2'5. S.Gr.=2. Colour sulphur-yellow to straw-colour, or yellowish-grey. Lustre resinous ; on crystal surfaces adamantine. Transparent, translucent. Cp. = S, frequently mixed with clay or bitumen. Bp. sublimates in matrass ; inflammable, and burns with blue flame to sulphurous acid gas. Sulphur occurs as an accessory in rocks, and also as a sepa- rate formation in beds. It is formed by sublimation in the clefts of volcanoes, also in the neighbourhood of burning coal NATIVE ELEMENTS. 75 seams. Sometimes it is the product of the decomposition of metallic sulphurets, or of the sulphuretted hydrogen of some spring waters, which are decomposed by contact with the atmosphere, and form deposits of sulphur. Artificial crystals of sulphur may be produced in great per- fection by dissolving sulphur in sulphuret of carbon, and set- ting it to crystallise at ordinary temperature. Monoclinic crys- tals of sulphur, which have not as yet been observed in nature, are obtained on the cooling of melted sulphur. 121. Graphite (Plumbago). Hexagonal, rhombohedral, usu- ally in six-sided, thin tabular or short prismatic crystals ; also massive, in radiated, lamellar, or compact aggregates. Cleav- age basal, very perfect, prismatic imperfect. Very sectile, flexible in thin laminae. Feel greasy. H.=l 2. S.G.= 2 '09. Colour iron-black to grey. Streak black, with metallic lustre, soils paper, used for pencils to draw and write with. Opaque. Cp.=C, with some iron, and often containing im- purities of Si, Ca, and AL Bp. burns with difficulty . If heated with saltpetre, puffs up slightly. Graphite is sometimes found in separate beds, and is then probably the final product of the transmutation of vegetable remains. It is, however, also found as an accessory ingredient in igneous rocks (in trap at Borrowdale, Cumberland, in por- phyrite at Elbingerode in the Harz, in granite boulders, Green- land) ; in limestones (Lower Styria, Fichtelgebirge), or in metalliferous veins (Arendal) ; finally as an essential consti- tuent of graphite-granite, graphite-gneiss, graphite-mica-schist. The igneous origin of some graphite may be inferred from its presence in furnace slags, where it sometimes occurs in the form of thin lamiiui'. 76 MINERALS. v. Eesins. Organic Compounds. 122. Amber (Yellow Mineral Resin). It is exclusively found in rounded masses of the shape of drops or fluid substance, and frequently insects and fragments of plants are enclosed in it. Fracture perfectly conchoidal. Little brittle. H.=2 2 '5. S.G. = 1*1. Colour yellow or brown in various shades, fre- quently with flame-shaped pencilling^. Lustre resinous. Trans- parent, translucent. When rubbed,, becomes negatively electric. Cp.=C 10 H 4 0. Bp. fusible y burns with a clear flame, and agreeable smell. Amber is a fossil gum-resin, the product of conifers or ter- tiary lignites. It is found as an accessory in strata of the Upper Chalk formation (Lemberg), the planercoal (Skutschin Bohemia), in pebbles in the diluvium and alluvium of North Germany, on the coast of the Baltic, and of Yorkshire and Essex. 123. Bitumen (Asphalte, Naphtha, Petroleum, Mineral Pitch, Mineral Oil). Under the term bitumen are included a whole series of olea- ginous and pitch-like substances, of which the most important are naphtha and asphalt e. (a) Naphtha, a volatile, and, when pure, colourless, oil with bituminous smell. S.G.=07 0'84. Cp.=C 6 H 5 , fre- quently mixed with paraffine, asphalte and the like. (6) Asphalte, a hardened mineral pitch without oil ; massive with perfect conchoidal fracture. Colour pitch-black. Lustre resinous. Opaque. When rubbed gives a strong bituminous smell. Cp. = C, O, and H in un- certain proportions. Easily ignited, burning with a bright flame and thick smoke. Naphtha flows from the ground in considerable quantities RESINS. ORGANIC COMPOUNDS. 77 (Persia, Pennsylvania, Amiano in Parma, Canada, Cali- fornia, &c.). Asphalte is found in many localities (e.g. at the Dead Sea ; Trinidad, where there is a complete pitch-lake ; at Poldice in Cornwall it occurs in granite). An intermediate substance between naphtha and asphalte is elastic mineral pitch or elat&rite (Castleton in Derbyshire). All these bituminous substances are of vegetable or animal origin, partly products of distillation of organic remains. They frequently occur as admixtures in shales and other rocks, which have received the name of bituminous ( Autun in France, Bonn, Markersdorf in Bohemia, &c.) 124. Mellite (Mellilite, Honey Stone). Dimetric, usually in pyramidal crystals, singly imbedded. Cleavage pyramidal, very imperfect. Fracture usually conchoidal. Somewhat brittle. H.=2 2-5. S.G. = 1'5 1-6. Colour honey-yellow to wax- yellow, seldom white. Lustre resinous. Semi-transparent to translucent. Cp. = A1(C 4 3 ) + 18H. Bp. it carbonises with smell of burning ; on charcoal burns to a white ash, which acts like pure alumina. It is readily and completely soluble in nitric acid. Mellite occurs as an accessory ingredient in Browncoal (Artern in Thuringia, Luschitz in Bohemia). 78 ANALYSIS OF EOCKS. CHAPTER II. ANALYSIS OF ROCKS. MICKOSCOPIC ANALYSIS. IT not unfrequently happens that the various mineral ingredients of a composite rock are so small and inti- mately blended together as to be entirely undistinguish- able even to the practised eye unaided by magnifying power. A simple lens will often render great service in this respect, but the aid of magnifying power may be carried much further with the microscope. For the mi- croscope very thin plates of a rock, so thin as to be somewhat transparent, are cemented on glass, and by the aid of a powerful instrument, textures apparently quite compact are frequently resolved into a web of minute crystals, or we find individual crystals become prominent (porphyritic) in an actually compact matrix. The form of these minute crystals is sometimes to be recognised, and so serves as a guide to the determination of the mineral in doubtful cases. If we further call in the assistance of polarised light, we are enabled to pronounce, with greater certainty, on the amorphous or crystalline character of the compact mass, and on the character of the crystals which by these means are brought to view. Delicate investigations such as these no doubt require the assistance of complicated apparatus and demand time, so that they are quite out of the question for the geologist on his travels ; but as we have said, much may be dis- covered by a simple lens, which for the practical geolo- gical purposes of the general inquirer is in most cases sufficient. MAGNETIC ANALYSIS. An admixture of magnetic iron-ore makes many rocks magnetic in their entirety, so as to affect the magnetic CHEMICAL ANALYSIS. 79 needle, or if the iron-ore be present in small quantities only, it may be discovered by abrasure with a sharp- edged magnet, the magnetic particles of the powder so formed clinging to the magnet like a beard. As, how- ever, magnetic iron-ore occurs in many very different rocks, its discovery does not often afford much help to the geologist in determining the character of any given rock. Fostemann and Delesse have made careful investiga- tions of the magnetism of many different rocks. The former is of opinion that by means of careful magnetic experiments, we ought to be able to ascertain whether a rock be of volcanic or neptunian origin, whether it has been rendered metamorphic by heat, whether it has re- tained its original position or been subsequently displaced (vide Poggendorff's Aimalen^ 1859, vol. cvi. p. 106). Delesse had previously discovered that almost all igneous rocks were somewhat magnetic as well as many sedi- mentary ana 1 metamorphic rocks. (Annales des Mines, 1849, vol. xv. p. 1, and Bulletin de la Soc. Geol. de France, 1850, vol. viii. p. 108.) CHEMICAL ANALYSIS. The geological interest attaching to the chemical ana- lysis of rocks is chiefly in respect of the nature of their origin. In the early stages of the science the analysis of com- posite rocks was conducted by mechanically separating, as far as possible, their several mineral ingredients, and analysing each mineral species individually ; and this method is still sometimes adopted where the parts are very distinct and easily to be separated. Compact rocks, such as basalt, were mostly considered as simple mineral substances, and so analysed. When, however, it came to be recognised that many apparently homogeneous rocks were but mechanical compounds of several minerals, chemical analysis was directed to the discovery of these mineral constituents too intimately mixed to be distin- guished by the eye. Gmelin introduced the method of treating a powdered mass of rock with muriatic or other acid, and so sepa- 80 ANALYSIS OF ROCKS. rating it into a part soluble, and another part insoluble in such acid. These two parts he separately analysed, and reduced the results into chemical formulas. The object he had in view was chiefly to discover the mineral con- stituents of the rock. But this mode of analysis is in- adequate for the purpose, since few minerals are wholly soluble, or wholly insoluble, in acids, and therefore, in- stead of the several minerals being separated from each other, a part of each is dissolved and a part of each left, and no definite result as to the original structure can be attained. It is found that even the elementary consti- tuents cannot be successfully so divided ; but that some elementary substances are only partly dissolved and partly precipitated by the process. Nevertheless, as a rough approximate, and somewhat empirical mode of suggesting rather than proving the constituents of a rock, it is still sometimes employed, and may in certain cases be of use. As the chemical character of minerals came to be better known, less reliance was placed on chemical analysis as a means of ascertaining and distinguishing the mineral ingredients of rocks. A small number of elements are so universal in their character that they enter into the com- position of a very large proportion of the whole series of mineral bodies, a very slight variation in their propor- tionate quantities or combination serving to produce en- tirely different minerals, or even the very same elements in the same relative quantities wearing a totally different mineral aspect according to slight differences in the con- ditions of their original formation. Therefore it is that chemical analyses have always hitherto failed, and it would appear that they must always fail, to detect many important mineral differences. For instance, a rock containing 72 silica, 11 alumina, 2*8 oxide or protoxide of iron, 1 lime, 1*2 magnesia, 1*2 potash, 2 soda, and 0*4 water, may either be a granite, or a gneiss, protogine, granulite, quartz-porphyry, felsite, petrosilex, pitch-stone, trachyte-porphyry, obsidian, or pearlstone ; and if we take a wider margin for the propor- tion of silica, say from 62 to 72, increasing some of the other ingredients in proportion, then a rock, such as we have described, may be a trachyte, phonolite, or minette, for in all the rocks we have named similar values of their CHEMICAL ANALYSIS. 81 elementary constituents occur. Again, a rock, containing 49 50 silica, 12 alumina, 5 10 oxide or protoxide of iron, 5 lime, 2 3 magnesia, 1 potash, 2 soda, and 1 water might just as well be a dolerite as a basalt,, or a nepheline rock, leucite rock, diabase, diorite, gabbro, hypersthenite, melaphyre, or porphyrite, for in like manner those values occur in all these rocks. On the other hand rocks, the same in mineral composi- tion, may vary in the values of their chemical or elementary ingredients 10, 20, or even 40 per cent. The mineral character of rocks is therefore now sought to be determined in doubtful cases by microscopic rather than chemical analysis, or by tracing the different stages of a rock's transition from a compact into a distinctly composite state ; for many rocks (as we shall later have occasion to show) are found to pass by gradual stages from an apparently homogeneous mass into states where their mineral ingredients become distinctly and separately developed so as to be readily recognised. Whilst chemical analysis was thus found insufficient for determining the mineral character of a rock, it derived a new importance from the igneous theory of the consti- tution of the primary rocks, when these came to be con- sidered as the products of the consolidation of a general molten mass once the sole material of the earth's structure. The different minerals then came to be regarded as of subordinate importance in inquiring into the origin of rocks, and their differing forms of crystallisation or structure to be regarded but as accidental consequences of slightly different circumstances attending the consolidation of the formerly fused mass. In this view even the sum of a separate analysis (if it were possible) of all the minerals constituting a rock would fail to present a complete picture of its aggregate chemical character, unless the exact proportionate quan- tity of each mineral could be also ascertained, which is practically impossible, although it has been sometimes roughly attempted. These considerations led to the present mode of analy- sis, which is now usually adopted in the case of all rocks indiscriminately, whether compact or granular, homo- geneous or distinctly composite. This is what is termed 82. ANALYSIS OF KOCKS. In German the ( Bausch analyse ' (or collective average analysis). It consists in pulverising a number of repre- sentative specimens carefully selected from various parts of the rock, and in mixing the powder thus obtained so thoroughly as to make the portion taken for the analysis a fair average sample of the whole rock. The results of these analyses are sometimes combined into chemical formulae such as those by which minerals are described. For instance : 3(B)Si + 2KSi, or(R) 2 Si 3 In such formulae we need hardly say there is always more or less of speculation or theory involved. The idea is to arrive at a view of the chemical consti- tution of the original molten mass, and chiefly in the first instance of the preponderance of the silica or other acid in the compound. In other words, the object is to ascer- tain if the original compound forming the rock, when in its previous molten state, were acidic or basic in its chemical character. It has been sought to express the same idea more simply by giving the proportion of the oxygen contained in the acids to that contained in the bases of the compound. Thus if, in a compound say of silica, alumina, peroxide of iron, potash and soda, the silica contain 3 parts of oxygen to 1 of silicon, and the alumina and peroxide of iron 1-J oxygen to 1 of aluminum and iron respectively, the potash and soda 1 of oxygen to 1 of potassium and sodium respectively, the oxygen quotient in a neutral compound would be 3 : 11 I 1 (a proportion which has been actually found to obtain in some rocks), and any variation of this proportion on either side would cause the compound to assume an acidic or a basic character ; thus, 5 : 1J : 1 would constitute an acidic compound, and 3:312 would constitute a basic compound. Bunsen endeavoured to set up two typical rocks, to be CHEMICAL ANALYSIS. 83 termed the trachytic and the pyroxenic, the former con- taining much silica (acidic), the latter a preponderance of bases (basic). He endeavoured to bring all the igneous rocks under one or other of these two heads, but soon found many rocks of intermediate character. These he regarded as mixtures of the two, or rather as the result of a combina- tion of the two kinds of original material which he believed to have existed at their formation. He suggested the idea of the existence of two great furnaces in the interior of the globe, containing these two different mixtures in a molten state ; an idea which has, however, not met with much general favour or acceptance. Others have suggested, with more plausibility, that at the time when the whole earth was fluid, its component parts would be in some degree separated according to their specific gravity, and the silica being the lightest of the very abundant ingredients of the mass, would prevail in greatest quantity at and near the surface, so that the rocks which were first consolidated and the earlier volcanic rocks would be acidic, the next formed igneous rocks would be more basic, containing chiefly the lighter bases, such as alumina, potash, soda or lime ; whilst the latest or most recent igneous rocks would contain the least silica, and principally the heavier bases, e.g. iron. It has also been suggested that the older igneous rocks, as having been formed nearer to the surface of the globe, would probably contain more water than those of later origin. These, then, are the chief problems which have been suggested for solution by chemical means. The most simple and useful of the chemical differences is that of the varying proportion of silica. This quantity when ascer- tained forms a clue to the proportion of the other ingre- dients and general chemical character of the rock. Scheerer has lately proposed that all the igneous rocks should be divided into nine or ten classes, according to their quan- tity of silica, without regard to their mineral character. He has pointed out an easy mode of ascertaining the proportion by fusing the portion of the powdered rock selected for analysis with a certain proportion of carbonate of potash or soda (about five times its weight). So much of the silica as is more than the proportion required for a o 2 84 ANALYSIS OF KOCKS. neutral compound will combine with the potash or soda of the carbonate salt, and drive off a proportionate quantity of carbonic acid so that from the quantity of carbonic acid so driven off, the quantity of silica contained in the original rock may be calculated. Without pronouncing on the correctness of any of the foregoing speculations*, we may however confidently say that for the purpose of lithological classification, an ex- clusively chemical grouping of rocks. would be utterly impracticable. How should the geologist pursuing his labours in the field, or on the mountain, wait for the tedious and uncertain process of a chemical analysis before naming the rocks which come under his ken ? We must, therefore, still adhere in the main to a mineralogical designation and nomenclature, and all the more, as in general we find the mineral characteristics of rocks very much coincide with geological phenomena. We need not, however, on this account disregard the results of chemical analysis, which are doubtless of the highest geological interest, and must prove of still greater value when they shall have been more fully and exten- sively carried out. We propose, moreover, to use these chemical properties for the purposes of our classification to the extent pro- posed by Bunsen of dividing the igneous rocks into two great classes, the acidic and the basic, merely warning our readers that there is, so far as our present knowledge extends, no rigid boundary between the two, and that the state of our analytical knowledge in general is still very imperfect. With these remarks we present the reader with the following extract from the analyses of Roth, as given in his masterly work on this subject ( e Gesteinsanalysen '). For the sake of brevity, the decimal figures have in some instances been omitted or shortened to one figure. * See post, pp. 367 et seq. CHEMICAL ANALYSIS. 85 ll Bi 3 OJ 3 00 ^ ,-< <* f~ CO n j-iai eo 6 6 b 6 rH 4* j e. ^>^(Mf-H In id i 1 33 ii *COOSOSOO l6 6-^rH rHO :1 1 1 1 1 I J Ui 1 w5 ^i tooq-^t^b-^ II 1 1 1 1 O CO r-t O CO t^ 3 1 1 1 O O O O .-i O - * I I-HCO * (Mrjieooooco OO rH rH =U cliliJ, I 0-*(N (N- .t- (M > Jl -L .81 i 8!i35 gq 5 3&& < Ji*i* 1- II I Nil i II 1 1 1 1 1 OO rH O rH CN O OO*O O rH O O 0 CO 00 - ICrHrHrHCO'O . (M^OrH 5 rH C^ ^O OO 00 C^ OO p p C M C^ (M rH rH i 1 O O O O TH rH lO 1 CO CO II Mill O O CO CO O CO 5 CO !>. TH rH O O O CO N O O5 O O rH O O Dolerite t--COt>- COTHOSCO'OCO nrH rH i i O ) Porphyritic with granular matrix. Rocks exhibiting this texture are not called porphyries, but only por- phyritic; such for instance as many porphyritic granites, with large crystals of felspar in the gra- nular matrix. (e) Porphyritic with shaly or schistose matrix. Mica- schist for instance, if it contains garnets, thereby becomes porphyritic. The crystals thus porphyritically disseminated in a rock may either belong to its essential constituents or they may be accessories only. SCHISTOSE (FOLIATED), SLATY (CLEAVED), SHALY (LAMINATED), FISSILE are terms expressive of different kinds of internal parallel texture of rocks. The German geologists have the one term ' Schiefrig ' for all these varieties of texture, the common element in all of which is their tendency to split in the direction of a given plane. This tendency may, however, be the result of very dif- ferent causes, viz : (a) By the parallel arrangement of certain minerals, such as mica, chlorite, talc, &c. eminently cleavable in one direction. Mica-schist is a rock of this character, and the texture is termed schistose or foliated. (b) By some cause or causes, not to be discovered by mere 90 PHYSICAL STRUCTURE OF ROCKS. ocular observation, the invisibly small mineral con- stituents or particles of the rock are arranged so as to produce a fissility or cleavage in the direc- tion of a given plane, which very often cuts at a considerable angle the plane or curved surfaces of stratification. The rock itself has frequently a compact appearance. The ordinary roofing slate is an eminent instance of this texture, which is termed slaty texture or cleavage. (c) By very thin parallel superposition or lamination of the fine particles of the rock. Thus a fissile tex- ture is developed in mud deposits, whether of marl, clay, or sand. This is in truth nothing but a kind of stratification on a small scale. The thin layers of the rock are not in themselves of a fissile tex- ture. Ordinary flagstones are of this character. Or a similar texture may be occasioned by the parallel juxtaposition of thin plates or lenticular particles of the ingredients of the rock, thus for in- stance the laminated texture of certain browncoals may be traced to their construction from an accu- mulation of actual leaves of trees, and a similar texture of certain amygdaloids is owing to the shape and position of the amygdaloidal particles. These and similar textures more or less origin- ating in the act and mode of deposition, and all of which have a tendency to split in the direction of their bedding, are called laminated or shaly, the rocks themselves shales. (d) Occasionally two of the above descriptions of texture occur together ; fissile is a general term which may be applied to all or any of the above-named textures.* * When we wish to be precise, we speak of the ' foliation of schist J the 'cleavage of slate ,' and the l lamination of shale? Jukes. See Jukes's Student's Manual of Geology (2nd edit.), pp. 265277. See also Phillips's Manual of Geology (1855), p. 43, and in Glossary, under heads of slate, schist, shale, laminated, flagstone, fyc. See also Page's Advanced Text-Book, 3rd edit. pp. 74, 81 ; also in Glossary under heads slate, schist, fissile, laminated, flags, shale. See also Dana's Manual of Geology, pp. 71, 93, 95, 96, 100, 101, All the above-named authorities agree, with very trifling excep- TEXTURE. 91 As respects the different causes of the above mentioned varieties of the fissile texture, we have seen that the thin stratification productive of the laminated texture is in- variably the consequence of the original construction of the rock. But if rocks exhibit a slaty texture, which is not parallel to their bedding, this must have another origin than stratification. According to the opinions of Sharpe, Haughton, Sorby, and Tyndall, slaty texture or cleavage, when not iden- tical with stratification, has in most cases been caused by pressure in one direction (viz. at right angles to the cleavage plane), applied to the rock either during or sub- sequent to its formation that is to say, during consolida- tion in the case of igneous rocks, during process of trans- mutation in the case of the crystalline schists, and after their deposition in the case of the sedimentary rocks, in which it therefore seldom coincides with the plane of stratification. (Vide Journ. Geol. Soc. of London, 1848-1849, and Phil. Mag., 1856.) On the other hand, the conjecture of Poulet Scrope, that lamination and cleavage may have arisen from friction of some kind appears to us improbable. Nor can we subscribe to the view advocated by Sedgwick, in his otherwise masterly treatise on the structure of large mineral masses (Trans. Geol. Soc. 1835, vol. iii. p. 469), namely, that this texture is the result of a crystallising force, although his view has been partially adopted by Sharpe and Murchison. (Vide Siluria, edit. 1859, p. 34.) Many rocks exhibit, variously developed, a marked texture, consisting of parallel fibrous lines or particles, with a parallel linear arrangement, called by Naumann, Linear Parallelism. This linear parallelism is of two kinds essentially differing from each other. It is either a delicate zig-zag pencilling of slaty or schistose rocks, or an elongation or extension of the particles or vesicular cavities in one direction. The linear foldings or pencilling of frequent occurrence tions, in the nomenclature as laid down by Jukes, and which is adopted in this translation throughout. It is almost identical with that first proposed by Sedgwick in 1835. See his ' Structure of Large Min -ml .Masses' in'Trans. of Geol. Soc. of London: 2nd series, vol. iii. p. 480. TRANSLATOR. 92 PHYSICAL STRUCTURE OF ROCKS. in gneiss, mica-schist, and clay-slate have the appearance of having been occasioned by lateral pressure, although such an explanation of the phenomenon is open to great and various difficulties. Transitions are found from the most delicate pencilling to the coarsest foliation. Linear elongation or fibrous texture consists of a kind of an apparent extension or elongation of individual parts, or of all the particles of a rock in one principal linear direction, by which a texture resembling the fibres of wood is sometimes occasioned ; or else the vesicular cavities of a rock, either empty or filled (amygdaloids) are elongated in one prevailing direction. In the latter case, we may easily explain the origin of the texture by supposing the mass of the rock, during the period of its consolidation and whilst yet soft, to have been flowing in one direction. But it is much more difficult to ascribe a cause to the linear extension of the particles in other rocks, as, for instance, in some kinds of gneiss. VESICULAR, SconiACEOUs(or Slaglike\ PUMICEOUS, are textures of rocks containing cellular cavities more or less rounded, and which are evidently the result of gas bubbles, developed whilst the rock was in a soft state either at the time of its original formation, or at a subsequent period. If these cavities are only few and isolated, then the rock is termed vesicular. If, however, they are so numerous as to occupy an equal space with the solid part of the rock, then the texture is scoriaceous, and if the hollow part predominates over the solid, then pumiceous (bimssteinartig). The shape of the cellular cavities is most usually irregular, but sometimes very re- gularly spherical, or pear-shaped, lenticular, and occasion- ally the cavities are uniformly elongated in a particular direction, as if stretched. All these differences of shape may be easily explained by the circumstances under which the vesicular mass attained its solid state, whether it was in a state of quiescence, or was subjected to pres- sure, or whether it was in motion, and whether such motion was flowing or irregular. This vesicular condition is most frequently found in those igneous rocks which possess a compact, or at least a very fine-grained or porphyritic principal mass occasioned by rapid cooling. It never occurs in coarse-grained TEXTURE. 93 igneous rocks, probably because these being always sub- jected to a high pressure, crystallised very slowly. But even sedimentary and metamorphic rocks sometimes con- tain genuine vesicular cavities, in which case we must always infer the rock to have been in a soft state during the development of the gas which caused the bubbles. Many rocks are porous without being vesicular, that is, they are penetrated with irregular and often even angular cavities, not the consequence of the development of gas, therefore not to be termed vesicular. The differences between porous and vesicular textures are sometimes very difficult to determine. To a certain extent almost all rocks are porous, although not so to the naked eye, in the sense that they admit of the percolation of water, even if but slowly. Daubree has made many experiments upon this kind of porosity, the result of which is communicated in the Bullet, de la Soc. Geol. de France, 1861, vol. xviii. p. 183, and Delesse has investigated the moist condition of rocks arising from this cause. (Ibid. vol. xix. p. 64.) A rock is said to be AMYGDALOIDAL when the vesicular cavities are filled either wholly or in part with new mineral substance. The filling of these cavities is always a process subsequent to the formation of the rock. The material for this purpose appears, as a rule, to have been derived from the rock itself by a species of exfiltration, and usually consists of chalcedony or quartz, or different kinds of carbonic spars or zeolites, or sometimes of green- earth, varying according to the character of the rock itself. The arrangement of these mineral substances is often very interesting ; concentric or horizontal layers, stalactites, and stalagmites, are formed within the cavities, or we find a crystallised geode or a compact mass. We infer from all the attendant circumstances that the formation of these amygdaloids must have been a very slow process, and therefore have occupied a considerable time in their completion. Hence, we may explain the fact that the most recent of all the igneous rocks, the lavas, although they are very often vesicular, are never amygda- loidal ; whereas the frequency and completeness of the filling up of the cavities increases almost in direct ratio with the age of the rock. 94 PHYSICAL STRUCTURE OF ROCKS. Such igneous rocks as are rich in silica are not only less frequently vesicular, but their cavities, when they occur, are less frequently amygdaloidal than those with little silica in their composition, which probably arises from their con- taining fewer soluble substances adapted to the formation of amygdaloids, in particular, less lime and magnesia. There are some appearances which may be easily mis- taken for the amygdaloidal texture, but which only arise from a concretion of separate mineral parts without previous cavities. We shall mention these below under the names of spherulite, globuliferous, nodular) and variolitic. OOLITIC texture is only found in limestones and iron- stones, and it consists either in the entire mass being composed of small globules, or a great number at all events of such being contained in the mass. The glo- bules are very much of the size and shape of peas or grains of millet or lentils, and when broken exhibit a concentric or radiated structure. Sometimes many very small globules combine to form a larger ball. In the so- called roestune the globules are grey, and usually inter- nally compact, or somewhat radial in the common oolitic limestone or oolite. They are more frequently white or yellowish, and sometimes formed of concentric layers, or they show an organic origin. In pisolite or peastone they sometimes contain a nucleus of foreign substance, covered with concentric layers or coatings of calc sinter, and these layers also show a fibrous radial structure, so that we may distinctly recognise the process of structure to have been a repeated coating of a grain of sand. In oolitic ironstone the grains are partly spherical, partly lenticular. In bog-ore they exhibit a concentric structure, and sometimes attain considerable size, culmi- nating in reniform iron-ore. The origin of this texture is only to be recognised with certainty in the case of pisolite ; in the other similar formations it is more or less wrapped in obscurity, and especially in the Great Oolite beds it is still very pro- blematical. L. von Buch observed a kind of oolite for- mation on the shores of the Canary Isles very analogous in its apparent origin to the pisolite. Virlet d'Aoust found a species of oolite in the Gulf of Mexico produced by the coating of minute insects' eggs with lime (Comptes PARTICULAR STATES OF ROCKS. rather rare - (d) VESICULAR or SCORIACEOUS DOLERITE. ) This texture only BLASIGER (or SCHLACKIGER) DOLERIT. (Germ.) f occurs in the tine- grained varieties (anamesite) ; frequent at volcanoes Stein- heim, near Hanau. (e) AMTGDALOIDAL DOLERITE. ) With filled-up cavities. MANDELSTEINARTIGER DOLERIT. (Germ.) r This variety is rather more AMYGDALOIDE. Brongniart. (Fr.) ) __ rdi t/. (f) DOLERITE-WACZK. ) Can in general only be recognised as DOLERIT WACKE. (Germ.) \ belonging to dolerite by tracing the WACKE DOLERITIQUE. (Fr.) j sequence of transition states, or by its immediate juxtaposition in nature with fresh dolerite. Variety in Composition. (g) NEPHELINE-DOLERITE. ] A crystalline granular compound NEPHELIN-DOLERIT, Von Leon- I of nepheline and augite with ti- ' taniferous magnetic iron-ore. BASALTIC ROCKS. 137 Spec. grav. . . . . 2-22-6 Contains silica .... 41 61 p. c. This rock, formerly taken for common dolerite, was first sepa- rately described and named by v. Leonhard. It is a dolerite in which nepheline takes the place of labradorite. As accessories we find it to contain thin acicular crystals of apatite, some sanidine, olivine, and titanite. In becoming compact it passes into nepheline-basalt, which is hardly to be distinguished from common basalt. Subvarieties of Texture. (a) Porphyritic Nepheline-dolerite, the porphyritic texture being created by crystals of nepheline. Xatzenbuckel in the Oden- wald. (/J) Vesicular and amygdcdoidal and wackenitic varieties occur; as also fine-grained ones, answering to anamesite, e.g. in the Lobauer mountains. Perhaps much of what has hitherto been called dolerite is more properly nepheline-dolerite. The rock is now very distinctly recognisable, e.g. near Meiches in Hessen, at the Lobauer Berg in Upper Lausitz and near Tichlowitz on the Elbe in Bohemia. Dolerite is found irregularly massive, or of columnar, tabular, or globular jointed structure. It forms lava streams, isolated cones, and veins in other rocks. This rock is so frequent in all countries, especially in volcanic districts, that particular localities need not be further enumerated. We will only add that the doleritic trachytes of G. Rose, which are mentioned in the fourth volume of his ' Kosmos,' as occurring at Etna, Stromboli, &c., appear to be dolerites rather than trachytes. References. v. Leonhard, Basaltgebilde. 1832, vol. i. Nepheline in Do- lerite, 1822. Bunsen in Poggendorf s Annalen, vol. Ixxxiii. p. 197. Abich, Vulkanische Erscheinungen, 1841, p. 74. liergemann in Karsten's Archiv. 1847, vol. xxi. p. 1 and 41. /leusser in Poggend. Annalen, 1852, vol. xxxv. p. 299. G. Hose, On Dolerite, in Neumann's Zeitsch. f. Erdkunde, 1859, vol. vii. p. 265. Deluxe in Ann. des Mines, 1858 [5], vol. xiii. p. 369. Durocher in Ann. des Mines, 1841 [3], vol. xix. p. 659." Hartung, Die Azoren, 1860, p. 97. v. Roth in the Zeitschr. der deutsch geol. Ges. 1860, vol. xii. p. 40. Zirkel in the Zeitschr. der deutsch geol. Ges. 1859, vol. xi. p. 539, on Nepheline-Dolerite. Gumprecht in Poggend. Ann. voL xlii. p. 177. 138 BASIC IGNEOUS EOCKS. (l) VOLCANIC. G. Rose in Karsten's Archiv. 1840, vol. xiv. p. 261. Schitt in v. L. andBr. Jahrbuch, 1857, p. 43. Lowe in Poggend. Annalen, 1836, vol, xxxviii. p. 158. Girard in Poggend. Annalen, 1841, vol. liv. p. 559. Heideprim in d. Zeitschr. d. d. geol. Ges. 1850, p. 149. Hesse in Journ. f. prakt. Chem. 1858, vol. Ixxv. p. 216. Mitscherlich, Basalt u. Nephelindolorit am Rhein. Zeitsch. d. deutschen geol. Gesellsch. 1863, p. 372. Otto Prolss, Analysen einiger Dolerite von Tava. Neues Jahrb. f. Miner. 1864, p. 426. v. Rath, Dolerite der Enganeen. Zeitschr. d. deutsch. geolog. Gesellsch. 1864, p. 496. A. Knop, Nephelindolerit von Meiches. Neues Jahrb. f. Mineralogie, 1865, pp. 674 and 682. Appendix. THOLEITE. Steininger has given the name of Tholeite to a rock found at the Schaumberg near Tholei, which he took for a compound of albite and titanite. But according to Berge- mann's analysis this rock consists of 70 labradorite, 5 augite, 3 magnetic iron-ore, 11 of undetermined silicate, and 9 of carbonate of lime and protoxide of iron. It must therefore from its composition be considered a dolerite or basalt unless indeed it be considered as plutonic and classed with melaphyre. ANALCTMITE. ) Bergemann in Karsten's Archiv. 1847, CYCLOPHYRE, lle de Beau- [ vol. xxi. pp. 4, 12. Gemellaro has given mont. (Fr.) ) the name of Analcymite to a rock found in the Cyclades which appears originally to have been a dolerite containing nepheline, but two-thirds of its mass now consist of analcime, although the latter chiefly fills clefts and cavities. We may here also mention two kinds of volcanic rock which might collectively be called OLIGOCLASE-DOLERITE. We refer to the AKDESITE of L. v. Buch, and the TRACHYDOLERITE of Abich. Both are compounds of oligoclase, augite, hornblende, mag- netic iron and some mica, the latter generally of dark colour. But as their silica contents often exceed 60 per cent., and as they are frequently found in vitreous state but of trachytic ap- pearance, we have arranged them according to universal custom amongst the trachytes; but no doubt they stand on the boundary between the trachytic and basaltic rocks, and may be considered as transition states between the two. 2. BASALT. Nepheline Basalt, Trap in part BASALT. (Germ.*) BASALTE. (Fr.) A compact rock, nearly or quite blacky with dull con- choidal fracture ; an apparently homogeneous com- pound^ of which the essentials are labradorite (or nepheline), augite, and magnetic iron-ore, frequently BASALTIC ROCKS. 139 united with carbonates and zeolitic substances. In the compact mass there often occur prominently dis- tinct grains or even crystals of olivine, labradorite, augite, and magnetic iron-ore. Spec. grav. . . . . ,' ' . 2'9 3-1 Contains silica . . . . . 40 5G p.c. The mineral ingredients of basalt are too small and intimately blended to be separately recognised with the naked eye ; formerly it was taken to be a simple mineral substance, but it is now shown to be only the compact state of dolerite or nepheline-dolerite. We must, however, observe that olivine and magnetic iron-ore is of much more frequent occurrence in basalt than in the two last- named rocks. Cordier was the first who, by means of microscopic examination, thought he recognised in basalt a similar composition to dolerite. Hessel confirmed this view by deduction from analysis, and many instances of the gradual transition from basalt into dolerite also coincided. But that basalt was in fact a compound of the above- named minerals was afterwards established beyond doubt by the more accurate analyses of Gmelin, Lowe, Girard, v. Bibra, Grager, Binding, Petersen, Ebelmen, Baumann, Rammelsberg, Schmid, and Bergemann. Gmelin first found that a portion of the mass of basalt was soluble in muriatic acid, and another portion not. The insoluble part he considered must be chiefly augite and olivine, perhaps also labradorite ; the soluble part, mag- netic iron-ore, a sparry carbonate and zeolitic substance (and sometimes nepheline). The proportion between the two parts (as in the case of dolerite) is very different in different kinds of basalt. The quantity of the soluble por- tion fluctuates between 36 and 88 per cent. The propor- tion of the individual mineral constituents, and also that of the elementary ingredients, appear to be equally variable. Like dolerite, basalt very often contains some carbonate of iron, calcspar, and zeolitic substance (probably arisen from decomposition, and of later date than the rock itself) and some kinds of basalt likewise contain nepheline instead of labradorite. Girard first discovered this com- position in the basalt of Wickenstein in Silesia. It is not easy from outward characteristics alone to distinguish 140 BASIC IGNEOUS ROCKS. (l) VOLCANIC. the nepheline-basalt from the ordinary species, unless we are assisted by finding a transition into a distinct nephe- line-dolerite, as is the case, for instance, at the Lobauer Berg. For this reason it is hardly practicable for the geologist to separate nepheline-basalt from labradorite- basalt as a distinct rock, although the difference between them, in a purely mineralogical point of view, is of more importance than that between dolerite and basalt, which are only varieties of texture of the same mass. Besides the more or less essential ingredients of basalt (to which we therefore reckon nepheline), other minerals also very often occur as accessories porphyritically dis- seminated through the mass. Thus, for instance, basaltic hornblende, oligoclase, dark brown mica, rubellan, zircon, (hyacinth), sapphire, apatite, garnet, bronzite, micaceous iron, titaniferous iron-ore, pyrites, &c. These minerals may, in consequence of special local circumstances, have either developed themselves into crystals during the original cooling of the rocks, or (such as pyrites and micaceous iron) they may have arisen from later processes of transmutation. Similar internal transmutations aided by gases or water have most probably produced the car- bonates, zeolites, and water concealed in the compound. The same influences have, doubtless, also produced the minerals which have arisen in the vesicular cavities and narrow fissures of the rock, such as hyalite, chalcedony, zeolites, sparry carbonates, glauconite, &c. The essential texture of basalt is compact ; if it becomes crystalline-granular it passes into anamesite and dolerite. But we frequently find porphyritically disseminated in the compact base, numerous single crystals or crystalline grains of augite, hornblende, olivine, magnetic iron-ore, and the like, or the rock is penetrated with vesicular cavities, and these are filled with those newer mineral formations of which we have already spoken. There also often appears a kind of round-grained or spotted conformation which seems to be the result of decomposition. Varieties in Texture. ( " } Very frequent e.g., at SchlossHerg, (Germ.) near otolpen, Saxony. BASALTE LTTHOIDE. (Fr.) BASALTIC EOCKS. 141 (6) PORPHYRITIC BASALT, or BASALTIC \ .. _ PORPHYRY I Aiso f re( l uent Leschtma, BASALTE poRpHYRotoE. (Fr.) ) Q ear Tetechen, in Bohemia. PORPHYRAKTIQER BASALT. (Germ.) ' (c) VESICULAR or SCORIACEOUS BASALT. ) Often called, par excel- SCORIES BASAL-PIQUES. (Fr.) [ Icticc, Basaltic Lava, as BLASIGER ODER SCHLACKIGER BASALT. (Germ.) J t his j s usua lly vesicular at the surface Kammerbiihl and Wolfsberg, in Bohemia. (d) AMYGDALOIDAL BASALT, or BASALTIC i Never of recent origin AMYGDALOID. J Schlachenwerth, near BASALTE AMYGDALOIDE. (Fr.) I Carlabad MANDELSTEIXARTIGEH BASALT. (Germ.) (e) SPOTTED AND GRANULAR BASALT \ Usually has dark grains in (RESEMBLING DOLERITE). I lighter green mass. It is KORXIOFLECKIGERODERDOLENTAHNLICHER [ a Stage of decomposition J E.g. between Arnsdorf and Steinschonau, in Bohemia, as Stoppels Kuppe, near Eisenach. (f) BASALT- WACKE. ) (Werner's Eisenthon) a dark brown \V.\CKK BASAI.TIQCE. (Fr.) \ OT grev, almost earthy mass, in which BASALT- WACKE. (Germ.) ) sometimes the textures (a) (6) (c) and (d) are distinctly repeated. Pascepole, near Teplitz. Sometimes, but quite exceptionally, a vitreous state also occurs, which Breithaupt has named Trachylyt, as a separate mineral formation. It is found, e.g. near Dransfeld, in the Vogelsgeberg and skirting basalt-veins in Iceland. Here may be also fitly mentioned a number of varieties of composition, some of which, if they were always dis- tinguishable, might even be separately classed as distinct rocks. Varieties in Composition. (c/) COMMON (or LABRADORITE) BASALT. ) Consisting of labradorite, LABRADOR BASALT. (Germ.) i augite, magnetic iron- ore, and usually also some olivine. (A) NEPHELINE-BASALT. \ In which nepheline is substituted for la- NEPHELIN-BASALT. I bradorite ; according to Girard, it shows BASALTEAVEC NEPHE- ( traces of a resinous lustre, and thereby dif- LINE. (Fr.) ) fers somewhat from ordinary basalt. But there must be intermediate gradations or transitions between the two which cannot be distinguished as separate varieties. () HAUYNOPHYRY. \ Is the name given by Rammelsberg HAUYNOPHTR, Rammel&erg. f to a rock from Vulture, near Melfi, HAtJ^oP^RE. (fr.) f not far from Naples, which essentially / consists of augite and haiiyne, with some olivine, mica, and leucite, in which also the haiiyne ap- pears to be the substitute for the labradorite of basalt or dolerite. The simultaneous occurrence of leucite, however, causes it to resemble leucite rock. The basaltic lava of Niedennendig on the Rhine contains a considerable quantity of haiiyne distinctly prominent, but it has been conjectured that this rock according to its conipo- 142 BASIC IGNEOUS ROCKS. (l) VOLCANIC. sition should belong to the nepheline-basalt. On account of its vesicular conformation it is well adapted for millstones. (&) ALLOGOVITE. -j Is the name given by Winkler to certain ALLOGOVIT, Winkler. \ dark grey or reddish rocks of the Allgau, ' which according to him are formed of an intimately blended compound of labradorite with the basalts, although their colour is somewhat different. This may, how- ever, be the consequence of a slight difference in composition or an incipient decomposition. Regular jointed structure is very frequent in basalt, usually columnar, sometimes however tabular or spherical, with concentric layers spheroidal, or even irregularly massive. It forms streams of lava and layers in the basaltic tufa. It is very characteristically and variously developed in the Bohemian Mittelgebirge ; in the columnar form it may be seen with great regularity and beauty at the Giant's Causeway in Ireland, at Staffa, &c. ; but these approach dolerite in their character, and may be more accurately described as transition states between that rock and basalt. References. v. Leonhard, Basaltgebilde, 1832, vol. i. A. Madelung, Metamorphosen von Basalt und Chrysolith. Jahrb. der geol. Reichsanst. 1864, vol. xiv. p. 1. Abichj Vulkanische Bildungen, 1841. Bergemann, Analysen in Karsten's Archiv. vol. xxi. p. 88, 1847. Surtorius v. Waltershausen, Physik. geogr. Skizze v. Island, p. 64. Schmid, Analysen in der Zeitschrift d. d. geol. Gesellsch. vol. v. p. 280, 1853 ; and Poggend. Annalen, vol. xcix. p. 291, 1853. Rammelsberg in der Zeitschrift d. d. geol. Ges. p. 493, 1859 j p. 273, 1860 ; p. 4, 1861, iiber Hauynophyr. Schitt in v. Leonhard u. Br. Jahrb., p. 44, 1857 (Hegau), and in G. Leonhard's Beitr. z. miner. Kenntn. von Baden, No. 3, p. 43, 1854 (Kaiserstuhl). Hartung, Die Azoren, j). 97, 1860. Girard, Ueber Nephelinbasalt in Poggend. Annalen, vol. liv. p. 562, 1841. 3. LEUCITE ROCK. Leucite- Porphyry, Leucito- phyry, Leucilite, Sperone. LETJCITFELS. (Germ.) LEUCITOPHYRE, Coquand. (Fr.) A more or less distinct compound of Icucite and augite, with some magnetic iron-ore porphyritic or compact. Spec, grav 2-5 2-9 Contains silica. . . . . . 45 54 p. c. BASALTIC EOCKS. 143 Leucite rock may be regarded as a dolerite, in which the labradorite is replaced by leucite. This difference of composition is also usually accompanied by other differ- ences easily to be recognised. The colour of the compact mass or matrix of the rock is more grey or reddish-grey than either dolerite or basalt, and, moreover, the charac- teristic crystals of leucite are frequently to be found dis- tinctly and prominently developed. It is a distinguishing feature of this mineral in general, that it rarely occurs otherwise than porphyritically imbedded, and not clus- tered in geodes. Sometimes distinct crystals of augite lie near the leucite in the compact matrix. As acces- sories leucite rock also contains the following minerals : dark magnesia-mica, sodalite, sanidine, labradorite, ne- pheline, olivine, haiiyne, garnet, and traces of apatite. Zeolites also very frequently occur in the clefts or vesi- cular cavities of this rock. Where the proportion of nepheline is greater, a transi- tion takes place into nepheh'ne-dolerite or nepheline- basalt. Varieties in Texture. (a) PORPHYRITIC LEUCITE, LEUCITOPHYRY. LEUCITOPHYRE PORPHYROXDE. (Fr.) (6) COMPACT LEUCITE. LKUCTTOPHYRE LITHOKDE. (Fr.) (c) VESICULAR or LEUCITE-LAVA. LEUCITOPHYRE VACUOLAIRE. (Fr.) (d) AMYGDALOID. AMYGDALOlDE. (Fr.) Leucite rock forms old and recent lavas, e.g. at Monte Somma and at Vesuvius (eruptions of 1828 and 1832); it also occurs at volcanoes long extinct, for instance at Roccamonfina, in the Albanian Mountains, at Bieden, and at Bell near Andernach. Not long since, a leucite- porphyry was discovered at Bohmisch-Wiesenthal, on the highest ridge of the Erzgebirge, with decomposed wack- enitic matrix, and crystals of leucite, more than an inch in length, but for the most part changed into orthoclase (or kalioligoclase). This last named occurrence involun- tarily suggests the question whether the felspar of many older rocks may not originally have been leucite, whose form has become indistinct or entirely altered so as to be no longer recognised. It certainly is somewhat remark- able that hitherto no ancient leucite rock has been found. 144 BASIC IGNEOUS ROCKS. (2) PLUTONIC. Appendix. NOSEAN-MELANTTE ROCK is the name recently given by vom Rath to a rock consisting of a fine-grained compound of nosean, vitreous felspar, and melanite, with some hornblende, augite, and titaniferous iron-ore. Zeitsch. der deutsch. geol. Ges. p. 655, 1862. Von Fritsch uses the common name of TEPHRITE to include leuci- tophyry, hauynophyry, and nepheline rock. Neues Jahrb. f. Mineral. 1865, p. 663. DUNITE is the name given by von Hochstetter to a granular rock which occurs in New Zealand, consisting almost exclusively of olivine. Zeitschr. d. deut. geol. Ges. 1864, p. 341. Sand- berger has described a similar rock as occurring in the Tring- stein in Nassau. Neues Jahrb. f. Mineral. 1865, p. 449. References. ie la Soc. d. Dufrenoy, Mem. p. s. a un descr. geol.'d. Fr. vol. iv. p. 368. Devitte in the Bullet, de la Soc. d. Fr. [2] vol. xii. p. 612, 1856. E. s. a un descr. geol. d. Fr. vol. iv. xxi. p. 326, 1845. Wedding in d. Zeitschr. d. d. geol. Ges. vol. x. p. 395, 1858. v. Rath in d. Zeitschr. d. d. geol. Ges. vol. xii. p. 37 (Zittau), 1860. Leucitophyr von Rieden : Zeitschr. d. deutschen geol. Gesellsch. 1864, p. 73. Naumann in v. L. und Br. Jahrbuch, p. 61, 1860 ; p. 59, 1861 (Wiesenthal). Rammelsberg in d. Zeitschr. d. d. geol. Ges. vol. xi. p. 493, 1859 ; vol. xiii. p. 96, 1861 (Vesuv. and Wiesenthal). 2. Plutonic. These rocks are compounds of various felspars with pyroxene, hornblende or mica. Besides these essential ingredients they frequently contain some chlorite, nephe- line and magnetic iron-ore, quartz only exceptionally ; the greater number are free from quartz. Mineralogi- cally as well as chemically, therefore, the composition of these rocks is very similar to that of the basaltic rocks. The chief differences consist in the greater frequency of hornblende as an essential ingredient, and the frequent occurrence of chlorite and the more rare occurrence of quartz as accessories ; and in the development of slaty or schistose texture in many of these plutonic rocks. All these differences may be accounted for by the greater depth at which these rocks probably attained the solid state, and by their having remained a longer time under the pressure of superincumbent masses. The same causes may have given rise to many transmutations or GREENSTONE GROUP. 145 new formations, such for instance as the formation of chlorite, a characteristic (if not altogether essential) in- gredient of the augitic greenstones, and to which they chiefly owe their green colour, and which also usually serves to distinguish them from the basalts. TVe divide the plutonic basic rocks into GREENSTONES, MELAPHYRES, PORPHYRITES, MICA-TRAPS and SYE- NITES. Some of these, however, approach the acidic rocks in the proportion of silica which they contain. GREENSTONES (trap in part). These rocks are compounds of some species of felspar with pyroxene or hornblende as essential ingredients ; their prevailing dark green colour they apparently owe partly to hornblende and partly to a small admix- ture of chlorite. They are usually divided according to their mineral character into three classes, under the following heads : Diabase, consisting of felspar and hypersthene or augite and chlorite. Gabbro, consisting of felspar and pyroxene. Diorite 9 consisting of felspar and hornblende. Besides these principal divisions, there are several subordinate varieties of composition which have distin- guishing names, such as Calc-diabase, Eukrite, Teschi- nite, Augite-rock, Malakolite-rock, Euphodite, Norite, Hypers thenite, Timazite, Calc-diorite, and Anorthite- diorite. Aphanite is the compact state of greenstone rock in which the several ingredients are not to be distin- guished with certainty ; and if the compact aphanitic mass contain distinct individual grains or crystals porphyriti- cally disseminated through it, then we employ the names of Calc-aphanite, Labradorite-porphyry, Oligoclase-por- phyry, Augite-porphyry, and Uralite-porphyry, for the different varieties. Greenstones of all kinds occur frequently in subor- dinate masses, dykes, or stratified veins in the schists or slates of the grey-wacke or transition period, and even alternating with tuff-formations of the same period which contain characteristic fossils, so that we may conclude that many greenstones were contemporaneous with those formations. This association with the transition-forma- L 146 BASIC IGNEOUS EOCKS. (-2) PLUTONIC. tions may be observed in the Voigtland, Fichtelgebirge, Hartz, and the Rhine district, also in the Silurian district of Bohemia, in Germany, and many other parts of the world. Greenstones are likewise met with which have broken through and penetrated much more recent forma- tions; the timazite of Hungary and Transylvania for instance is found to have even penetrated sandstones of the tertiary period. But the most recent tertiary for- mations are nowhere found to have been broken through by genuine greenstones, although very frequently by basaltic rocks. Greenstones are never found in the form of genuine lava, but always more or less show their plutonic origin, in which probably consists the whole difference (not very considerable after all) between them and the basalts. It is very possible that the same basic compound which, consolidating near the surface, has pro- duced the basaltic rocks, when it attained the solid state at a greater depth formed the greenstones, whose pyrox- ene and hornblende may have been partly an original product and partly produced by subsequent transmu- tation. The basalts and greenstones in general very much resemble each other both in chemical composition and mineral character. The chlorite, by which some of the augitic greenstones are alone distinguishable from the basalts, is most usually a product of transmutation. 4. DIABASE. Hyperite, Scandinavian Trap. DIABAS. (Germ.} DIABASE, Brongniart. (Fr.} A crystalline-granular compound of oligoclase, labra- dorite, albite, or anorthite, with pyroxene and some chlorite in its fresh state dark green. Spec.grav 2-72-9 Contains silica . . . . . , 43 56 p. c. Diabase was first raised to the rank of a separate rock, and distinguished from other greenstones, by Hausmann. It is often very fine-grained, and in that case it be- comes difficult to determine the , species of the felspar or of the pyroxene, or to recognise the chlorite as such. The felspar seems in most cases to be a white or greyish- green, oligoclase or labradorite. The pyroxene is most ge- nerally hypersthene, but sometimes common augite. The green colour of the rock is chiefly owing to its chlorite, GREENSTONE GROUP. 147 the quantity of which is however small. As accessories the following minerals very frequently occur : magnetic iron-ore, magnetic pyrites, pyrites, sometimes also some chalcopyrite (copper pyrites). As accessory accompaniments (in clefts, veins, nests and vesicular cavities) are found quartz, actinolite, asbestus, cat's-eye, pistacite, prehnite, axinite, calcspar, brownspar (dolomite), talcspar (magnesite), &c. The prevailing texture of diabase is fine-grained; it passes over into the compact (aphanite) ; it is also some- times porphyritic, slaty, variolitic or amygdaloidal. Diabase bears a strong relationship to dolerite, the most marked feature of its difference from the latter is its chlorite and its consequent green colour. If this chlorite be a product of transmutation, then all the original dif- ference between diabase and dolerite probably consists in the level or depth of solidification. The vesicular cavities of diabase (where they occur) are almost always filled up (amygdaloids), and this circum- stance may be explained by the rock having long lain in the interior of the earth under modifying hydro- plutonic influences. Varieties in Texture. (a) GRANULAR DIABASE j Frequent near Berneck, Saalburg, SSSZS!^ a 3ti [ both* in the Fichtelgebirge, &c. (6) FINE-GRAINED (TO COMPACT) DIABASE.) Merging into aphanite, FKiNKoijvioERBisDicHTEnDxABAs. (Germ.) > generally occurs with DIABASE LrraoStDE. (Fr.) j (a). (c) PORPHYRITIC DIABASE. ) In fine-grained base, crystals of PonpHYRARTiGERDiABAR.(G'erm.) I labradorite, DZABAHK POKPHVHO^ (Fr.) is compact, then these varieties are also sometimes designated labrador-porphyry, augite-porphyry, or uralite-porphyry (com- pare with aphanite, post, p. 157). (d) SCHISTOSE DIABASE, or DIABASE- ) Indistinctly foliated, going SCHIST. I over into aphanite-schist : DiABAs-ScHiEFKR. (Germ.) [ occurs together with (a) and SCHISTE DIABASIQUK. (f*r.) ) /\ (e) AMYGDALOIDAL DIABASE, or\ The vesicular cavities are filled DIABASE AMYGDALOID. I with calcspar, chlorite, glauconite, AM^l^iL^ 1 ^; (Germ ' ) > chalcedony and the like. Berneck in Fichtelgebirge. (f) VARIOLITIC DIABASE (VARIOLITE) In the principal mass round in part). I concretions occur of a com- VARIOI.ITISCHER DIABAS. (Germ.) [ pact or radial-fibrous or con- (Fr.) J centric felsite (labradorite), L 2 148 BASIC IGNEOUS KOCKS. (2) PLUTONIC. very characteristic near Berneck, where the small felsitic glo- bules have a violet-coloured nucleus and a white ring. 0) WACKEIQTIC DIABASE, or ) Decomposed, discoloured, earthy, DIABASE WACKE. L an d can only be determined to be DIABAS-WACKE. (Germ.) \ such by its juxtaposition with other WACKE DIABASIQTJE. (Fr.) J diabase. The following rocks are varieties of diabase in respect of their composition, or are to be classed under the head of diabase on account of their close approximation. Varieties in Composition. CALCAREOUS DIABASE. } In the fine-grained or compact matrix KALKDIABAS. (Germ.) [ O f diabase rock are found small rounded . ) (h) COMMON DIABASE. (0 DIABASECALCAIKE.(/V.) to be the fillings-up of cavities. This somewhat proble- matical variety has been called calc-trap by Oppermann. By others it has been called blatterstein, calc-aphanite, diabase, and amygdaloid, and if somewhat slaty, schalstein. (Loben- stein in the Fichtelgebirge.) (&) EUKRITE. ) A crystalline-granular compound of anor- ETJKRIT. (Germ.)) thite and augite, occasionally with some olivine, hornblende, and epidote. The latter appears to have arisen from decomposition. This rock, according to its mineralogical composition, would almost appear to be better classed with dolerite than diabase, but according to Tschermark and Kraff't, its geological cha- racter is plutonic. It appears at Gumbelburg near Neutschin in Moravia. Some meteorites have precisely the same composition. (I) TESCHINITE. \ Is the name given by Hohenegger to a TESCHINIT, Hohenegger. f rock whose mass is chiefly felsitic, and in which hypersthene forms long black needles ; it sometimes also contains fine needles of apatite. This rock has broken through chalk formations and even eocene strata in the neighbourhood of Tetschen, where it some- times forms irregular masses, sometimes veins. According to von Hochstetter, hornblende and augite form part of its com- ponents, also sometimes augite and labradorite with subordi- nate admixtures of iron pyrites, magnetic iron-ore, mica, and chlorite. These therefore are compounds which might partly be classed with the diorites and partly with diabase, hyper- sthenite, or even dolerite. More by way of appendix than as properly inclusive in this class, we here add : (m) AUGITE ROCK (LHERZOLITE). j A granular to compact ag- AUGITFELS, LHERZOLITH. (Germ.) i grearate, chiefly consisting of LHERZOLITE. (Fr.) ) l n ^ dttk^tt^ brown, or grey ; as accessory components it contains some talc, steatite, GREENSTONE GROUP. 149 schorl, hornblende, or calcspar. This rock can only be said to be allied to diabase ; it forms subordinate masses at the Lake Lherz, near Vicdessos in the Pyrenees. [According to Damour, however, this rock of the Lherz is not thus composed, but consists of olivine, eustatite, and diopside. See Neues Jahrb. f. .Mineral. 1863, p. 95.] (ti) MALAKOLITE. j Found in granular limestone near MALAKOLTTHFELS. (Germ.) \ Rocklitz at the foot of the Rie- PvRoxfiNrrK, ^uand. (Fr.)> sengebirge) where> according to Herter and Porth, it forms subordinate masses, containing copper-ore and consisting essentially of compact salite (rnala- kolite). The diabases and the last mentioned rocks, which are related to them, are either found in indefinite masses or with columnar, spherical, or irregular spheroidal jointings. The genuine diabases are most frequently found in the Devonian, Silurian and Cambrian formations, so for instance in the Voigtland, Fichtelgebirge, and Hartz mountains, where sometimes the immediately adjoining clay -slate is transfonned into a kind of hornstone. References. G. Rose on Greenstones in Poggend. Annalen, 1835, vol. xxxiv. p. 1. Oppermann, Dissertation iiber Schalstein und Kalktrapp, 1836. IIiiHsmann, Ueber die Bildung des Harzgebirges, p. 22. v. Rodham u. Canaval, Kalktrapp oder Schalstein in Karn- then in v. L. u. Br. Jahrbuch, 1855, p. 584. Genth on Eukrite in the Annalen der Chemie u. Pharm. 1848, vol. Ixvi. p. 17. II(i/f(/hton on Eukrite in the Quarterly Journ. of the Geol. Soc. 1856, vol. xii.j). 197. Tschermack u. &rafft., on Eukrite in the Berichten der Wiener Akademie, pp. 40 and 127. Hoheneyyer on Teschinite in Die geog. Verhaltnisse der Nordkarpathen, 1861, p. 43. v. Hochstetter on the same subject on the Jahrbuch d. geol. Preichsanst, 1853, p. 319. V. Charpentier on Augite Rock in his Essai sur la const. gtSol. des Pyrenees, 1823, p. 245. Marrout on Augite Rock in the Ann. des Mines, 1828 [2] vol. iv. p. 307. Herter u. Porth on Malakolite in the Jahrbuch der geol. Reichsanst, 1859, p. 10. Kjenilf (Diabase) in Christiania Silurb. 1855, p. 26. Delesse (Diabase) in the Ann. des. Mines, 1858 [5] vol. xiii. p. 374. Modelling. Uber Teschinit. Neues Jahrb. fur Mineral. 1865, p. 345. 150 BASIC IGNEOUS KOCKS. (2) PLUTONIC. 5. GABBKO. GABBRO, von Such. (Germ.} GABBRO. (-Fr.) These rocks are compounds of labradorite or saus- surite, with diallage, smaragdite, or hypersthene, and usually some other minerals. They are distin- guished by the irregularity oj their composition and texture. Spec. grav. '. ' . . , . . 2-8 3-1 Contains silica ...... 43 46 p. c. The Italian name of Gabbro, which L. v. Buch first applied to a distinct class of rocks, has a broad and a narrow signification ; but as even the narrower meaning is not very definite, the name is more serviceable in its comprehensive sense, and in which it is more generally understood. Naumann, using the term in its narrower sense, de- scribed gabbro as a compound of labradorite or saussurite with diallage and smaragdite, and he separates from it hypersthene rock or hyperite, which essentially consists of labradorite and hypersthene ; and there are some very similar rocks which have received the names of norite and euphotide. All these in fact only form varieties of the same rock ; they are very difficult to distinguish from each other when they occur in a somewhat fine-grained state ; and when they pass over into the quite compact state, as is often the case, they all become aphanite. Since the texture of these rocks frequently changes very rapidly, that is within a small area, from very coarse- grained to fine-grained, compact, or slaty, their division into varieties of texture cannot serve any useful purpose. We shall therefore only enumerate the varieties of com- position, which are the following : Varieties in Composition. (a) GABBRO, DIALLAGE ROCK, GRANITONE. } Consists of labra- GABBRO. (Germ.) L dorite or saussurite DIALLAOITE, Descloizeaux. (/>.) ragdite irregularly combined, also sometimes of all those mi- nerals together. It is very coarse-grained, fine-grained to compact, sometimes slaty or spotted (variolitic). GREENSTONE GROUP. 151 The felspar if in the form of labradorite is coarse-grained to fine-grained ; colour white, grey, or violet. If it be saussurite it is compact and white or greenish. The diallage occurs in white individual crystals of half metallic lustre, grey to green. The smaragdite is grass-green, and has a mother-of-pearl lustre. Small quantities of sparry carbonates are often also contained in the compound frequently ; not visible, but recognisable through effervescence with acid : they are probably of secondary origin. The visible accessory ingredients are mica, talc, hornblende (especially at the mar- gins of the diallage), actinolite, garnet, iron pyrites, magnetic iron-ore, titaniferous iron-ore, specular iron, and apatite. Many of these also may be secondary formations. Calcspar and quartz occur in nests or veins. This rock passes into serpentine by transmutation (as near Siebenlehn in Saxony) into aphanite by becoming compact, and apparently it also even passes into diorite, diabase, granite, and granulite. The prevailing character of gabbro is massive. It penetrates older rocks and formations in a massive form, or in the form of veins forms apparent parallel strata in such. But it is also fre- quently penetrated by veins of granite, which in that case gene- rally contain some orthite, as near Rosswein and Bb'hrigen in Saxony. In the Radauthal in the Hartz, where it may be easily mistaken for diabase, it also contains wollastonite, schillerspar, and rutile, and in fissures also desmine, prehnite, and albite, near La Prese in Upper Italy. It consists, according to Breit- haupt, principally of hornblende with metallic pearly lustre (schillerspar), and a felspar of the highest spec. grav. with some brown mica. If the felspars have become much wasted from weathering, then the pyroxenic ingredients often appear above the surface in strong relief. (6) EUPHOTIDE. | The euphotide of French geologists is Kri-Honrr. (Germ.) according to Delesse, essentially a com- BupH. compact compound of labrado- (FrT } J. rite ^ d hypersthene. Labradorite is the prevailing ingredient, coarse to fine- grained, grey, greenish or bluish. The hypersthene appears dark-brown, to green on its cleavage surfaces, has a metallic pearly lustre, its outer edges sometimes coated with horn- blende. The labradorite is the most strongly affected by weathering, and it decays away, leaving the hypersthene to protrude. The following minerals occur as accessories in this rock : Titaniferous iron-ore, garnet, hornblende, olivine, brown mica, needles of apatite, iron pyrites, and magnetic iron-ore. It usually is of a massive structure, and forms veins or irregular masses between other rocks. It occurs characteristically in Hollenmiihle, near Penig in Saxony, Neurode in Silesia/ Isle of Skye, Elfdalen in Sweden. The monzon-hypersthenite of v. Richthofen differs slightly from the ordinary kind. It consists of a very distinctly crys- talline granular compound of dark-green to black hypersthene with greenish-white labradorite. The hypersthene is usually the principal ingredient ; sometimes, however, the labradorite is entirely predominant, and in that case distinct crystals of common black augite occur in the mass. The hypersthenic varieties also sometimes contain the like in small quantities, also dark -brown mica-plates and crystals of titaniferous iron-ore are found. At Monzoni in Southern Tyrol, this rock has broken through genuine syenite (free from quartz) and formed veins in it. References. v. Such in the Magaz. d. Gesellsch.-naturforsch. Freunde zu Berlin, 1810, vol. iv. p. 128. v. Rath in Pogg. Annal. 1855, vol. xcv. p. 535 (Silesia). Delesse, Bullet, de la Soc. geol. de France, 1849 [2] vol. vi. p. 410, 435, 547, and Ann. des Mines, 1849 [4] vol. xvi. p. 323. Scheerer in the Gaea Norwegica, vol. ii. p. 313. v. Richthofen, Geogn. Besch. von Siid-Tyrol, 1860, p. 146. Keibel, Zeitschr. d. d. geol. Ges. 1857, vol. ix. p. 573. Koch, Jahrb. d. Ver. f. Naturk. in Nassau, 1858, vol. xiii. p. 123. Kjerulf, Christianias Silurbildungen, 1855, p. 23. Streny, Zeitschr. d. d. geol. Ges. 1858, vol. x. p. 174; Neues Jahrbuch fiir Mineralogie, 1862, pp. 513 and 932, 1864, p. 257. Drysdale, London and Edinb. Phil. Journ. 1833, vol. xv. p. 386. EMmen, Ann. des Mines, 1847 [4] vol. xii. p. 629. Jenzsch has analysed the hypersthenite of Neurode in Silesia, which contains bright shining spots and distinct particles of chlorophoeite in dark brown-green matrix, and pronounces both from chemical and microscopic analyses that the matrix consists of about 27 oligoclase and 25 augite, and of 39 vitreous felspar, 5 magnetic iron-ore, 2 chlorophoeite and GREENSTONE GROUP. 153 2 apatite. He found the content of silica very high, viz. 66-5. Poggend. Ann. 1855, vol. xcv. p. 418, and v. L. u. Br. Jahrb. 1857, p. 436. Websky, Gabbro von Neurode. Zeitschr. der deutschen geol. Gesellsch. 1864, p. 530. 6. DIORITE. DIORIT. (Germ.) DIORITE, Haiiy. (JFV.) A crystalline-granular compound of felspar and horn- blende. The felspar is not orthoclase. In fresh state it is usually dark green. Spec, grav . 2'6 2-9 Contains Silica ...... 47 58 p. c. Diorite was first so named by Haiiy. Its texture is often so fine-grained that it is difficult to determine the species either of its felspar or hornblende, although the minute particles of the former in most cases shew the fine parallel striae which are characteristic of albite, oligoclase, anorthite, or labradorite, and which forbid the idea of orthoclase. Gustav Rose in his first work on greenstones held the felspar of diorite to be albite. Sub- sequently he embraced the view that albite never occurs at all in crystalline rocks. Although this latter opinion is shared by few, yet all observers now agree that the felspar in diorite which was formerly taken for albite is usually oligoclase. Delesse again has recognised labra- dorite and anorthite as essential ingredients in many kinds of diorite. Thus the difference in the species of the felspar constitutes one class of varieties of the rock. The hornblende is also various : generally it is the ordinary hornblende ; sometimes, however, a variety more approaching to actinolite, and Breithaupt lately disco- vered an entirely new species of hornblende as an essential ingredient in many greenstones of Servia, Transylvania, and Hungary. It has a black colour and greenish-grey streaks. He named it gamsigradite after the name of the place where he first found it. But inasmuch as it is not easy, and in the fine-grained state of the rock impossible with certainty, to recognise the different species of felspar and hornblende, it does not appear to us desirable on their account to dignify these different varieties of diorite with the character of indi- 154 BASIC IGNEOUS EOCKS. (2) PLUTONIC. vidual rocks, although it is well to distinguish them where possible, since they are somewhat mineralogically dif- ferent. The gamsigradite variety has been named by Breithaupt timacite, from one place where it occurs. This timacite has also a geological importance, as it is found to have broken through the older tertiary strata of Hungary and Transylvania, whereas the greater number of diorites are much more ancient. All these mineralogical differences are very trifling in a chemical point of view ; so that we may well consider them but as the result of somewhat unequal cooling of the same original mass. We do not mean that they should therefore be disregarded, on the contrary we consider that it would be an inquiry of the greatest geological interest to endeavour to trace their causes. Such an inquiry, to be successful, however, would demand a comparison of many special and accurate observations of the rock taken from various localities. The following minerals sometimes occur in diorite as accessories ; mica (brown and black) pyrites, magnetic pyrites, magnetic iron-ore, titaniferous iron-ore, titanite, garnet-pistacite, and quartz. Some of these may be of secondary origin, e.g. the pyrites and the pistacite, which latter appears to have proceeded from the hornblende, and sometimes contributes to the green colour of the rock. The fine-grained varieties of syenite may be easily mistaken for diorite, the only essential difference between the two being that orthoclase is a necessary ingredient of syenite. The following characteristics may assist in dis- tinguishing the two rocks, although not always to be re- cognised in them, nor universally to be relied on. Diorite is more frequently fine-grained than syenite, and gene- rally (owing to its hornblende) more green in colour. In diorite the felspar decomposes sooner than the horn- blende, and therefore on weathered surfaces the latter often protrudes prominently, whereas syenite weathers more evenly and falls into a kind of sandy grit. Diorite usually contains more pyrites than syenite, and the latter more frequently contains titanite or wohlerite than the former. Their variations of texture and their outward structure, as well as their place in nature, are usually somewhat different, as will appear from the short ac- GREENSTONE GROUP. 155 count which we shall give of each under their respective heads. As varieties of texture without regarding varieties of composition, the following kinds of diorite may be distin- guished : Varieties in Texture. (a) GRANULAR DIORITE. \ The most normal variety, e.g. at the KORXIGER DIORTT. (Germ.) \ Klumpsen mountain, near Ebers- DIORITEGRAMTOIDE. (Fr.) ) (6) FINE-GRAINED DIORITE. \ Passing into compact (aphanite) FEIXKORXIGER BIS DICHTBR ! Belmsdorf, near Bischofswerda, in DIORTT. (Germ.) [ nV^loneU* DIOKITK UTHOIDE. (Fr.) ) Oberlausitz. (c) PORPHYRITIC DIORITE, or DIORITE- j with crystals of felspar or PORPHYRY. I amphibole, going over into PORPHYRARTIGER DlORTT. (Germ.) nnhamtif nnmhvrv DIORITE PORPHTROIDE. (Fr.) ) a lc P or P n y r y- (d) SLATY DIORITE, or DIORITE-SLATE. j The slaty texture usually DIORIT-SCHIEFER. (Germ.) [ imperfect, passing into DIORITE SCHISTOSE. (Fr.) } apfanite slate. (e) ORBICULAR DIORITE, or ] The globular conformation is only NAPOLEONITE. ! a local appearance in diorite. It (Germ.) f occurs very characteristically and 1111 ' BrOH9 ~) Beautifully near Sautina and Ajac- cio, in Corsica. The rock consists, according to Delesse, of a combination of anorthite, blackish- green hornblende, and some quartz, so that it is a distinct variety in respect of its composition no less than its texture. The constituent minerals form alternating concentric layers round kernels. The kernels themselves consist (almost exclu- sively) either of the anorthite or hornblende (not of both), and they likewise exhibit a radiated texture. Thus we find balls of from one to three inches in diameter, whose section shews rings of alternate light and dark colour. At Schemnitz (Stephen-shaft) orbicular timazite occurs, but the spherical masses are not in concentric layers. (/) AMYGDALOIDAL DIORITE. ) Only occurs rarely, and with MAXDELSTEIXARTIGERDIORIT. (Germ.)) a fine-grained to compact matrix, which passes into the state of aphanite. , O) WACKENITIC DIORITE, or\ This decomposed discoloured, and DIORITE-WACKE. L somewhat earthy state can only be SSSSStfSfU.) I rg^h certainty as belong- ing to dionte by tracing its transi- tion from distinct rocks. The foregoing differences of texture are however repeated in it. Varieties in Composition. (A) COMMON DIORITE essentially consisting of oligoclase and horn- blende, the diorite of the Huhnberge, in the Thuringian Forest, is somewhat differently composed, inasmuch as its felspar con- tains lithia, and very many small needles of apatite occur disseminated through the whole mass. This rock, which is 156 BASIC IGNEOUS BOCKS. (2) PLUTOXIC. sometimes very coarse-grained, has broken through the rothlie- gende and becomes quite compact near the surfaces of contact. () AsroRTHiTE-DiORiTE. i In. which the oligoclase is partly or AXORTHIT-DIORIT. (Germ.) f wholly replaced by anorthite. As for instance in the orbicular diorite of Corsica, which likewise contains some quartz. (k) TIMAZITE (TRACHTTIC GREENSTONE). } Consists, according to TIMAZIT, Breithaupt. (Germ.) ] Breithaupt, of a grey or greenish-grey felsitic base, in which are imbedded crystals of white felspar (albite or mikrokline), black hornblende (gam- sigradite), some mica, magnetic iron-ore, and iron pyrites. The base, which is tine-grained to compact, corresponds most closely with labradorite. The cleavage-prism of gamsigradite shews an angle of 124 26', its hardness is 7, and spec. grav. is 3 1' ; it has a greenish-grey streak. The mica forms hexagonal brown plates. The magnetic iron-ore forms very small grains or crystals, the iron pyrites very small cubes. According to an analysis by Dr. Rube the tirnazite of Gam- sigrad, in Servia, contains about 50 per cent, of silica. We have already stated that this rock is frequently met with in Transylvania and Hungary, especially in the mining districts, and that it has penetrated through the Eocene sandstones. We have elsewhere described a rock occurring in Borsabanya, in the Marmaros, in the north of Hungary, which we named labradorite -rock, because its prevailing base consists of labra- dorite. According to Breithaupt this is essentially the same as timazite j but we find from Dr. Rube's analysis that it con- tains above 63 per cent, of silica, and therefore it belongs to the acidic rocks. As, according to Delesse, the diorite of Pont Jean, in the Vosges Mountains, also contains labradorite, it is very possible that it is a timazite. (T) CALCAREOUS DIORITE. ) ls the name g iven b 7 Senftto a dark- KALK-DIORIT, Senft. (Germ.) \ green, more or less distinct compound HEMITHRENE. (Fr.) ) O f hornblende, oligoclase and mica, penetrated with calcspar, and which near Ruhla, in the Thurin- gian Forest, forms a stratum in mica-schist. The jointed structure of the diorites is usually irre- gular ; but sometimes columnar or globular. Diorite frequently occurs in subordinate masses, veins, or dykes in the schistose or slaty rocks of the Silurian or Devonian age, and (exceptionally) sometimes in much newer formations ; sometimes also in granite, gneiss, or mica-schist. Appendix. The NORITE of Esmark (different from that of Scheerer) very widely spread in Norway, appears only to be a variety of diorite containing quartz and mica. The OPHITE of Palassou is, according to its description, a tolerably GREENSTONE GROUP. 157 compact diorite. The MiCA-DiORiTE of Delesse on the other hand ought rather to be classed with Syenite than here, on account of its containing orthoclase. References. G. Rose on Greenstones in Poggend. Annal. 1835, vol. xxxiv. p. 1. Keibel, Analysen in d. Zeitschr. d. d. geol. Ges. 1857, vol. ix. p. 575, and v. Leonhard u. Br. Jahrhuch, 1859, p. 445. Riviere, Bullet, de la Soc. ge"ol. d. Fr. 1844, vol. i. p. 528. Hunt in Sillim. Amer. Journ. 1859 [2] xxvii. p. 340. v. Richthofen, Geogn. Beschreibung v. Siid-Tyrol, 1816, p. 111. The diorite at Klausen contains actinolitic hornblende with oligoclase. Delesse on Orbicular diorite, which was first described in 1785 bv Besson, in the Journ. d. Phys., and on the Diorite of the v osges, Ann. des Mines, 1859, vol. xvi. pp. 160 and 339 : 1851, p. 149. Brctihaupt on Timazite, in the Berg- u. Hiittenm. Zeitg. 1861, p. 51. On the Diffusion of Timazite. Compare Cotta's Gangstudien, vol. iv. pp. 28, 56, 65, and 85. Senft on Calc-diorite. In the Zeitschr. d. d. geol. Ges. 1858, p. 308. Esmark on Norite in the Magaz. for Naturvidenskabern, vol. i. p. 207. Charpenticr on Ophite, Constit. g6ol. des Pyrenees, 1823, p. 481. Dufrenoy on Ophite, Ann. des Mines, 1832 [3] vol. ii. p. 21. v. Rath. The diorite of Neurode, in Silesia, consists of 56 parts of hornblende, and 44 saussurite. The former has been formed from augite according to G. Rose, Pogg. Ann. 1855, vol. xcv. p. 655. Herm. Vogclgesang, as to globular diorite, Berggeist, 1862, Nos. 90 and 91. 7. APHAKITE. Trap in part, Melaphyre in part. APHANIT. (Germ.} APHANITE, Hauy. (Fr.) A compact, apparently homogeneous mass ; usually dark green to black ; of about the hardness of felspar ; very tough ; sometimes porphyritic by reason of crys- tals of felspar, hornblende, or pyroxene ; also vesicular or amygdaloidal. Spec, grav 2-62-9 Contains silica .... 43 58 p. c. The separate ingredients of the principal mass of this rock are not to be recognised with the naked eye, hence the name of aphanite, given by Haiiy. Wehave already shown that transitions take place into aphanite from diabase, gabbro, or diorite ; proving it to be but a com- 158 BASIC IGNEOUS ROCKS. (-2) PLUTONIC. pact state of one or other of those rocks, bearing the same relation to them as basalt to dolerite; a view which is entirely confirmed by chemical analysis. The minuteness and intimate union of the individual constituent ingredients of aphanite when quite compact, no less than their general resemblance to each other, make it impossible with the ordinary aids to discover from the appearance of the rock whether it belongs to diabase, gabbro, or diorite. We can only draw conclu- sions in this respect from finding it in conjunction with one or other of those rocks. If, however, the aphanite be porphyritic, then the minerals porphyritically enclosed in the compact matrix may give a clue to the composition of the latter ; for instance, we frequently find labradorite, oligoclase, pyroxene, or hornblende thus porphyritically im- bedded in aphanite. It is dangerous, however, to rely too implicitly on conclusions so drawn, and on every account, therefore, in describing the varieties of aphanite we refrain from the attempt to keep up distinctions corresponding to the three normal rocks of diabase, gabbro, and diorite. Possibly by careful microscopic observations we might succeed in determining the special mineral character of every aphanite. But such observations are attended with considerable labour, and the appliances are not always within reach; on a journey they would be out of the question. We may, however, state that the microscopic observations which have been made of aphanite entirely confirm what we have already said respecting its nature, and show that even the accessory ingredients of the three normal rocks are represented in its composition. The greater number of aphanites appear to belong to the pyroxenic greenstones, or we might rather say that these latter have more frequently assumed the compact state than the hornblendic varieties. Many varieties of texture and composition which are found in the three granular rocks are likewise repeated in the compact rock. Varieties in Texture, (a) COMMON COMPACT APHANITE. GEMEINER DICHTER DIORIT. (Germ.) APHANITE LITHOIDE. (Fr.) -VTT-.LT- j. i /i i i ,. T (6) PORPHYRITIC APHANITE or With crystals of labradorite, oli- APHANITE-PORPHYRY. I goclase, hornblende, augite, or PORPHYRARTIGER DIORIT. (Germ.) uralite. Accordingly we dis- APHANITE PORPHYROIDE. (Fr.) ) tinguish labradorite - porphyry, GREENSTONE GROUP. 159 oligoclase-porphyry, augite-porphyry, or uralite-porphyry, of which we will treat more at large hereafter. Near Manebach, Herges, and Tabarz, in the Thuringian Forest, there occur aphanitic porphyries whose felspar crystals are not yet accurately determined. (C> Sl s ATT T ^ PHANITEOrApHiNIIE -) Usually only indistinctly AnumttMm. (Otrm.) \ slaty, or of thick cleavage. APHANITE scrasrolDE. (Fr.) (d) VESICULAR APHANITE. ) Rather rare ; sometimes it would BLASIGER APHAXTT. (Germ.) \ appear that the vesicular cavities APHANITE VACUOLAIRE. (Fr.) ) have been once filled, and their contents weathered out. We often find them empty at the weathered surface, but still remaining filled in the fresh in- terior of the rock. (e) AMYGDALOIDAL APHANITE. -\ The vesicular cavities are most APHANIT-MANDELOTEIN. (Germ.) [ usually filled with calcspar or APHANITE AMYGDAixtfDE. (Fr.) ) zeo litic substance. (/) WACKENITIC APHANITE, orj Discoloured and earthy through APHANITE-WACKE. ( decomposition, its petrographic APHANIT-WACKE. (Germ.) character only to be determined WACKEAPHANITIQUE. (Fr.) ) byitssurrou / dings . As varieties of composition the following species may be distinguished in addition to the usual quite compact form : x Varieties in Composition. ( greenish or violet grey- ish colour, either of stringy, radiated, or concentric texture from the size of a grain of mustard-seed to that of a walnut, firmly grown in, and not very sharply defined. They consist of a felsite (probably labradorite), but frequently also contain some pistacite in concentric layers. As accessories in the matrix of the rock we find iron pyrites and magnetic iron-ore, in its clefts and cavities quartz, pistacite, calcspar, and chlorite. Delesse has narrowly investigated and described the vario- lites of the Durance, and he also mentions those of the Fichtel- gebirge, and of Savoy, &c. (Ann. des Mines, 1850, vol. xvii. p. 11(3.) Their spherical concretions often exhibit a reddish, violet, or grey kernel, round that a lighter coloured rind, and round the latter a green shell of a somewhat lighter colour than the enclosing matrix of the rock. In the latter, with the aid of the microscope, he also discovered small laminae of felspar. (*) LABRADORITE-PORPHYRY(BLACK PORPHYRY).) The black matrix LABRADORPORPHYR. (Germ.) [incloses crystals MELAl'HYHE fKLD.Sl'ATHiyUE. (Fr.) 1 / i r j S j oi laDraciorite and 160 BASIC IGNEOUS EOCKS. (2) PLUTONIC. small particles of a dark green mineral not yet determined ; spec. grav. 2-7, content of silica 56-58 p. c. By aid of the magnifying glass Streng found the apparently compact matrix to be dis- tinctly crystalline, consisting of one mineral of dark-green in- clining to black, and another of a lighter green colour. Probably they are the same as the minerals which also occur in a distinct form. The crystals of labradorite often shew a dark dull-green kernel, surrounded by a light and shining margin. The striae of twin crystallisation are continued equally through both. Sometimes the reverse is the case, the kernel is light and shining, and the margin dull and of a darker colour. As acces- sories, but rarely, and only in small particles, brownish-black, mica plates, pyrites, and magnetic iron-ore. Near Elbingerode at the Hartz, this rock penetrates Devonian slates and lime- stones. To this class belong the rocks described by Delesse, found by him at Belfaly and Ternuay, in the Vosges ; these contain augite, and are amygdaloidal in part. Also the rock described by Kjerulf as melaphyre from Barnekjern, near Christiania, as well as many other so-called melaphyres and porfido-verde-antico. Streng in v. L. u. Br. Jahrb. 1860, p. 397. Delesse in Ann. des Mines, 1847 [4] vol. xii. p. 228. Kjerulf, Christiania Silurbecken, 1855, p. 28. (&) OLIGOCLASE-PORPHYRY. \ Is the name given by G. Eose to a OLIGOKLASPORPHYK. (Germ.) J diabasic or aphanitic rock in the Ural Mountains, which has a dark green compact or nearly compact matrix containing crystals of oligoclase. Much porfido-verde- antico is of this character ; also the rock described by Delesse, as found by him at Lescines, in Belgium, containing some pyrites, and some copper pyrites (unless it belongs to mica- diorite) and several rocks from the neighbourhood of Christiania described by Kjerulf. G. Rose, Keise nach dem Ural, vol. ii. p. 571. Delesse. Bulletin de la Soc. geol. d. Fr. 1849 [2] vol. vi. p. 386 ; 1850 [2] vol. vii. p. 310. ) Christiania Silurbecken, 1855, p. 9. ATJGITE-PORPHYRY. | (Often called Melaphyre,) A com- AUGITPORPHYR. (Germ.) \ p ac t matrix, usually dark green, MELAPHYRE PYROXENIQUE. (Fr.) ) Containin c ' rsta ls of auite! Fr. v. Richthofen reckons to this division the most of the rocks of the Fassa region, which are usually designated as melaphyres. These contain crystals of augite and labradorite (or sometimes oligoclase), inclosed in a matrix resembling basalt. Titaniferous iron-ore is also disseminated through the mass in small par- ticles. They are very variously developed ; most frequently we find them vesicular and amygdaloidal. V. Richthofen, Southern Tyrol, 1860, p. 128. (jri) URALITE-PORPHYRY. \ Is the name given by G. Rose to URALITPORPHYR,^. Rose. (Germ.) \ rO ck containing crystals of uralite PORPHYRE 1 OURALITE. (Fr.) ) ^ ft CQmpact dark; pro bably diabasic GREENSTONE GROUP. 161 matrix. This uralite has the form of augite, and the substance of hornblende. G. Rose, Reise nach dem Ural, vol. ii. p. 370. The four last-named varieties may be indifferently termed aphanitic porphyries, or greenstone-porphyries ; and they are sometimes classed together under the name of melaphyres. The timazites of Hungary likewise fre- quently have a compact aphanitic base, for instance, those in the neighbourhood of Schemnitz, in which single crys- tals or crystalline particles of hornblende (gamsigradite) or felspar may be clearly distinguished. Aphanite is usually of jointed structure, or very dis- tinctly cleft.; generally the blocks are irregularly massive, sometimes, however, regularly columnar, or regularly or irregularly spherical. The aphanites occur in nature under the same circumstances as diabase, diorite, and gabbro ; and very often in their company. We have already sug- gested that they should be regarded as mere modifications of those rocks, differing from them chiefly in the greater rapidity of their original cooling process. The Saxon Oberlausitz affords striking instances in illustration of this opinion. The granite region there is found to have been broken through by diorite, and accordingly numerous dome-shaped hills of the latter rock protrude from the surface ; near to these the same eruptive mass has pro- duced narrower dykes (from 5 to 20 ft. thick), whose texture is fine-grained, nearly compact. Near Belmsdorf, not far from Bischofswerde, we observed a diorite dyke 20 to 30 ft. thick, which in the centre was fine-grained, but almost compact towards the walls of the cleft, where it must have cooled more quickly. The offshoots from the same vein into the granite, and the narrow parts of the principal vein of only two inches thick, consist of a com- pletely compact mass, which might easily be taken for basalt, as it is almost quite black. These differences of texture are there manifestly the consequence of different degrees of rapidity of cooling caused by the different volume or thickness of the mass. On this subject see Erlauter. z. geog. Karte von Sachsen, 1839. No. 3, p. 24. Also on the subject of aphanitc, Dclesse in Ann. des Mines, vol. xvi. p. 350. M 162 BASIC IGNEOUS ROCKS. (2) PLUTONIC. 8. MELAPHYRE. Augite-Porphyry in part, Trap in part. MELAPHYB. (Germ.') MELAPHYHE, Brongniart. (Fr.) The rocks which we include under this name are dark- coloured, greenish, brownish, or black ; compact, por- phyritic, vesicular, or amygdaloidal ; always free from quartz. They are compounds (intimately blended) of felsite, pyroxene, hornblende, and magnetic iron-ore. Spec. grav. 2'6 3-1 Contains silica ..... 54 62 p. c. The name melaphyre has ceased to bear a distinct character, having been successively used by different geologists, ever since the time of Brongniart, who first introduced it, for many and various igneous rocks having nothing in common with each other, unless it be a pre- valent compact texture, dark colour, and absence of quartz. Hence the name conveys no definite idea, unless qualified by the name of a particular author, and that is not always sufficient without the name of the locality. There are many and various rocks of uniform dark colour, of a prevailing compact or amygdaloidal texture, close compounds of some kind of felspar with pyroxene, hornblende, and magnetic iron. We have already spoken of several such under the heads of basalt and aphanite. Much of what has been called melaphyre cer- tainly belongs to our basalts and greenstones. The rocks of which we shall treat under the name of porphyrite have often been called melaphyre, and if we take away all that may be ascribed to basalt, greenstone, and por- phyrite, little will be left to which to apply the name of melaphyre. Under these circumstances the name can only be use- fully retained as a sort of provisional term for any basic igneous rocks of prevalent compact texture and dark colour, whose composition is not so definitely marked as to entitle them to be included under any other more distinct species ; much in the same way as we are often compelled to use the general name of greenstone for rocks whose mineral character is not sufficiently decided, or has not been sufficiently investigated, to enable us to class them as diorite, gabbro, or diabase. MELAPHYRE. 163 In dealing thus, for our own part, with the name of melaphyre, we here subjoin a quasi-historical account of the mode in which it has been used by different authors. \Ve think the divergence of their readings will be a sufficient justification, if any be needed, for the way in which we propose that the term should in future be accepted. (a) Al. Branrjniart, the inventor of the name melaphyre, described it as l Pate noire d'aniphibole pe"trosiliceux enveloppant des cristaux de feldspath ; ' what is here meant by 'amphibole pe"tro- siliceux ' is very uncertain, the more so as at that time (1813) the differences Between hornblende and pyroxene were not so well established or known as they are at present. (b) L. von Bttch lirst applied Brongniart's name of melaphyre to certain black-coloured rocks of the Fassa Thai and the Seisser Alp (see ante, p. 162). He, however, also called these rocks black porphyries or augitic porphyries, because they contained crystals of augite, and their matrix was also black and rich in augite. He also included under the same designation many rocks of the Hartz and Thuringian Forest, &c., whose compo- sition he presumed to be similar, and which he considered to be the original cause of the upheaval of those mountains. To them he also ascribed the formation of dolomite in several localities. As the principal characteristics of this rock, he enumerated dark colour, great content of augite, and complete absence of quartz. See von Leonhard's Taschenbuch, 1824, vol. ii. pp. 289, 372, 437, and 471. (c) Xatnnann says on this subject, ' The rocks which Al. Brong- niart has introduced under the somewhat singular name of melaphyre are for the most part identical with those which Faujas de Saint Fond collected under the Swedish name of trap, and of which Warmholz, Steiniger and others have made use in the same sense. Werner called them trap-por- phyries or trap-amygdaloids ; Zobel and v. Carnal, porphy- rite. Freiesleben called them pseudo-porphyries ; v. Raumer, basaltite ; and in many French writings they ara also in part called spilite. Trap and melaphyre are probably the most usual names at the present day ; for although the Swedish trap, ac- cording to Erdrnann is a diabasic rock, whereas the rocks which bear the same name in the Faroe Islands and Iceland are basaltic formations, it nevertheless appears to be most useful to retain (with L. von Buch) the name of melaphyre for the rocks which we are about to treat.' These are tnen described as compounds of labradorite, and (probably) augite in small or invisible crystals (therefore compact), but alone recognisable, and frequently in the form of scattered crystals, the rock very much inclinecl to the amygdaloidal in 'texture. They are further described as always containing magnetic iron-ore, car- bonate of protoxide of iron, and carbonate of lime, in invisible particles, as well ns some rubellan and mica. Their petro- H 2 164 BASIC IGNEOUS ROCKS. (2) PLUTONIC. graphic difference from the basalts, according to Naumann, is confined to the want of olivine, and to the circumstance that the augite is not to be recognised with certainty. Geognosie, and in v. L. u. Br. Jahrb. 1860, p. 1. (0) Von Richthofen attempted to put an end to the confusion which the name of melaphyre had gradually introduced by restoring the definition of Brongniart, and he believed that he had discovered the identical rock in various places ; for instance, at Schneidemiillersberg near Ilmenau, in the Schleusenthal, in the Thuringian Forest, between Landshut and Glatz in Silesia, near Oberstein, and between Botzen and Colmann in the Tyrol. He describes the rock thus : Compact matrix, dark-green or brown to black. Fracture uneven, inclining to conchoidal ; lustre shining ; hardness that of felspar or less; spec. grav. 2*7; contains crystals of felspar (oligoclase or labradorite), other minerals only exceptionally to be recognised. In his large work on the Tyrol he also reckons the rock of which the summit of the Margola is formed to this compound of oligoclase and hornblende, with much oligoclase, labradorite, augite, and hornblende, and partly of a fine-grained species ; it consists partly of an intimate compound of oligoclase, and few crystals of augite. This latter variety was termed by v. Klipstein mulatt-porphyr. From the results of the chemical and microscopic analyses of these rocks, from the minerals which they contain in a dis- tinctly crystalline form, and from their specific gravity, von Richthofen framed conclusions respecting the mineralogical composition of the compact matrix, and pronounced it to con- sist essentially of oligoclase and hornblende, with subordinate quantities of apatite, titaniferous iron, sometimes also some magnetic iron-ore, and chlorophseite, or magnesia-mica. In it often labradorite crystals lie imbedded exceptionally, perhaps, also similar ones of augite, hornblende, epidote, or mica, but never quartz or olivine. In vesicular cavities there occur quartz and chalcedony, car- bonic spars and zeolites. (Vide Zeitschr. d. d. geol. Ges. 1856, pp. 589 and 593, which gives a very complete catalogue of the literature on this subject; Sitzungsb. d. Wiener .Akad. d. Wissensch. 1857, vol. xxvii. p. 293 ; Remarks upon the dis- tinctions between melaphyre and augite-porphyrj^, Vienna, 1839, and Geogn. Beschreibung v. Siid-Tyrol, I860. p. 141.) (e) E. Sochtinff, on the other hand, attempts to show that Richt- hofen's definition of the matrix is unfounded ; that accord- ing to the results of the analyses, it might just as well consist of labradorite and augite, and that Brongniart was not to be depended upon as to the determination of hornblende (Zeitschr. d. d. geol. Ges. 1857, p. 427). Sb'chting himself had formerly described the so-called melaphyres of the Thuringian Forest as an intimate compound of labradorite and augite in the Zeitschr. d. ges. Naturwissenschaften, 1854, p. 197. (/) Girard starts with the principle that the geological character of rocks is the principal thing to be determined, and that they MELAPHYRE. 165 should always be classed and named accordingly, rather than according to their mineralogical or chemical composition. He combats von Richthofen's view in respect of melaphyre, but seems somewhat to have misunderstood his meaning. For Richthofen merely sought to avoid the uncertainty into which the term melaphyre had fallen by keeping as strictly as possible to Brongniavt s first definition, and thereby excluding many rocks which had been called melaphyres. Girard, on the other hand, seeks to show that many of these excluded rocks really contain augite and no hornblende, a fact not disputed by Richthofen, but one which according to him did not entitle them to be called melaphyres. We may, perhaps, think von Richthofen's narrowing of the sense of melaphyre impractical or inconsistent : unpractical because, being too much opposed to prevailing ideas, it is little likely to be adopted ; inconsistent if taken in connection with the enlargement of the meaning of the term trachyte which he himself advocated. Nevertheless it does not follow that it is in itself inaccurate, even if we choose to acknowledge Girard's premised principle to be the ri^ht one. Girard himself considers the melaphyre of Ilfeld to be a compound of a mineral containing felspar with augite, the augite forming only one-fifth or one-sixth of the entire mass. Whether the prevailing ingredient be labradorite or oligoclase, he leaves undetermined. Small black grains in the same mass, he takes for magnetic or titaniferous iron. He compares also some other .melaphyre with that of Ilfeld. (v. L. u. Br. Jahrb. 1858, p. 173.) (g) Streny distinguishes three kinds of rock in the neighbourhood of Ilfeld by the names of melaphyre, porphyry-melaphyre, and melaphyre-amygdaloid. The first, which should belong to our porphyrite, is a grey or brown-coloured rock with matrix re- sembling hornstone, and containing small crystals of felspar not longer than the tenth part of an inch, white or greenish with twin strise (labradorite or oligoclase) associated some- times with crystals of an undetermined dark-green mineral grown into the felspar crystals ; the matrix likewise contains small reddish-brown garnet grains, also a light-green mineral, perhaps only the product of decomposition and very small par- ticles of magnetic iron-ore. In the melaphyre of Streng the principal mass is of dull ap- pearance, a'nd in its fresh state is blue-black, distinctly crystal- line, of wavy lustre and friable by weathering it becomes greenish-grey or brown. It is probably a compound of felsite and augite or hornblende, or a yet undefined mineral of the nature of diallage and some magnetic iron-ore. In the matrix occur very small crystals of the same diallage-like mineral, also hirircr columns of the same mineral which exhibit a growth of t win crystals, crossing each other regularly at an angle of 60, and distinct small plates of rubellan. In a second essay Streng described the diallage-like mineral as a schillerspar which con- tains alumina. The melaphyre-amygdaloid of Streng consists of a homo- 1G6 BASIC IGNEOUS ROCKS. (2) PLUTONIC. geneous brown matrix, of the hardness of 5-6, and contains small amygdaloidal cavities filled with glauconite, chalcedony, and carbonate of lime. The specific gravity of these varieties fluctuates between 2 '6 and 2-7. Their content of silica, taking the mean of a consider- able number of analyses, is for the melaphyre-porphyry 61'3, for the melaphyre and melaphyre-amygdaloid 54'4. They form together a plateau of considerable size between the lower and upper Rothliegende districts (Zeitschr. d. d. geol. Ges. 1858, p. 99, and 1859, p. 78). Upon the position and bedding of these rocks see Bantsch in Abhandl. d. naturf. Ges. zu Halle, 1858. (h} G. Hose defined the Ilfeld melaphyre as follows : a fine-grained almost compact mass of black or brown colour, sometimes con- taining small acicular crystals, or greenish-white crystals, (likewise small). The texture is often vesicular or amygda- loidal. According to the known analyses, both microscopic and chemical, the matrix most probably consists of an intimately blended crystalline compound of oligoclase, with augite or hornblende, magnetic iron-ore, and some apatite; the fine acicular crystals appear to be augite transformed into schil- lerspar; the greenish white crystals Rose could not determine. In local varieties also small crystals of mica occur and irregu- larly shaped grains of some other mineral. The vesicular cavities, often very regularly shaped (for in- stance pearshaped), contain concentric layers of chalcedony and quartz as well as calcspar. The following are varieties more especially distinguished by Rose. Black melaphyre, from the Raben Klippen, at the Hartz. A compact compound in which transparent prismatic crystals are prevalent ; between them lie larger white crystals, very small grains of magnetic iron-ore. Black melaphyre from Wieprersdorff. Matrix under the mi- croscope less distinct than the last-named ; in it lie diallage-like crystals of augite. Red melaphyre from Wiegersdorff. Matrix under the mi- croscope less distinct than the last-named; in it lie diallage- like crystals of augite. Red melaphyre from the Birkenhoff. The matrix reddish- brown, and containing green acicular crystals of augite. Ro^e considers these melaphyres to resemble chiefly those of Lowenberg, Lahn, and Landshut in Silesia. (Zeitschr. d. d. geol. Gesellsch. 1859, p. 280.) (f) THE OBERSTEIN AMYGDALOID. This rock, celebrated for its beautiful agates, is considered by many geologists to belong to the melaphyres ; thus (e. g.) : von Dechen, Dufrenoy, Elie de Beaumont, and Naumann. Its principal mass, usually brown or greenish, no doubt consists chiefly of felsite, and often contains small crystals of felspar, and amygdaloidal cavities filled with agate and other minerals ; accordingly we should term the rock a porphyrite. Delesse was the first to give a careful analysis of it. Its spec. grav. is 2-68. Chemically it contains 51-13 MELAPHYRE. 167 silica, 29-73 alumina and peroxide of iron, 473 of lime, 4073 magnesia and alkali, 3*68 water and carbonic acid. From these data, as well as its mineralogical characteristics, Delesse con- cludes that the principa. mass essentially consists of labra- dorite ; in fact, there frequently occur in it a great number of small labradorite crystals, white and translucent : its frequent green colour appears to be owing to an admixture of chlorite. Sometimes some aueite is observable, also small flakes of brown mica. Magnetic iron-ore in very finely divided particles appears to be uniformly dispersed through the whole mass. In the numerous amygdaloidal cavities, whose diameters vary from one-tenth of an inch to a foot, Delesse found agate, opal, quartz, chlorite, calcspar, different kinds of zeolite, hy- drated oxides of iron and manganese. The amygdaloid of Oberstein possesses compact fine-grained and porphyritic varieties, and occurs in the coal formation of that district, sometimes forming dykes and masses of consider- able size, sometimes parallel seams. It appears to have been t lirust up about the time when the deposit of the rothliegende began. Perhaps its character is the same as that of the rock, previously described under the name of tholeite. (See ante, p. 138.) (Delesse in Ann. des Mines, [4] vol. xvi. p. 511 ; Steininger, Geogn. Beschreib. d. Landes. zu Saar. u. Rhein, 1840, p. 110.) (k) Senft designates as melaphyres almost all dark quartzless igneous rocks of the Thuringian Forest ; according to him, they consist principally of a compact mass of labradorite, combined with in;i \vrnx. (Germ.) KlillSANTON. (Fr.) In a grwnuk-grty fekpathic matrix are contained hexagonal tabular crystals of mica, broion to black. Less frequently the matrix is granular, and contains crystals of felspar. Contains silica about 53 p. c. In the matrix, felspar usually predominates, which is not orthoclase, but most likely oligoclase. The distinct crystals of felspar are generally oligoclase. The mica is magnesian mica, which is not only an ingredient in the matrix, but some- times forms a coating round small globular grains (amygda- loids) of calcspar or quartz. Marcasite and magnetic iron-ore occur as accessories. Delicate veins of calcspar often run through the whole rock. The name of kersanton was first given by Riviere. The rock is evidently closely allied to the inica-porphyiite, minette, and kersantite. It abounds in the district of Brest, and Quimper in Brittany, where it is applied to building purposes. References. Riviere, intheBullet.de laSoc. gSol. deFr.,1844, [2] vol. i. p. 528. Dufrenoi, Expl. de la Carte ge"ol. de la France, 1844, vol. i. p. 198. Delesse, Ann. des Mines, 1851, vol. xix. p. 175, (D) KERSANTITE. KERSANTIT. (Germ.) \\ KKSANTITE (OlJGOCLASITE). ( Fr.) A fibrous or porphyritic compound of oliyoclase and mica, fre- quently containing some hornblende and quartz. Contains silica, about 64 p. c. Oligoclase generally predominates in the compact or fine- grained matrix of the rock, which sometimes is entirely com- 176 BASIC IGNEOUS ROCKS. (2) PLUTONIC. posed of that species of felspar, sometimes of oligoclase and mica. In this mass are enclosed crystals of oligoclase with brown stripings, and of white or greenish colour, or tinged with red by decomposition ; dark laminae of magnesia-mica, some small grains of quartz, and frequently some fibrous hornblende, espe- cially in the narrower veins formed by this rock, and, dispersed through the whole rock, very minute particles of magnetic iron -ore. Carriere also found some red garnet combined with horn- blende in places where the latter was more prevalent and the rock somewhat fissile. At Viesembach, in the Vosges Moun- tains, where the rock is broken through by metalliferous veins, it contains magnetic iron pyrites and common pyrites. It is amygdaloidal. In some places the amygclaloidal cavities are filled with quartz, chlorite, epidote, and calcspar. The porphyritic varieties of this rock (which owes its name to Delesse) are evidently closely allied to the porphyrites, or perhaps also to granite-porphyry; in other respects it very nearly corresponds with kersanton, from which it is, perhaps, only to be distinguished by its containing hornblende, and also more quartz than that rock, and by its texture being sometimes fissile. Near Viesembach and Sainte Marie, in the Vosges, this rock forms subordinate masses and veins in gneiss. The veins are often quite compact at their borders. Fournet observed a similar rock in the granite near Francheville in Brittany. Reference. Delesse, in the Ann. des Mines, 1851, vol. xix. p. 165. SYENITE GROUP. It has been a frequent practice to include under the name of syenite all granites containing hornblende. But as the genuine syenites contain little or no quartz, we consider it more accurate to exclude the first-named rocks from the syenite group, and range them under the head of granites (syenite-granites), confining the term syenite to those rocks which consist essentially of orthoclase or microcline and hornblende, such as the rock of the Plauenschen-Grund, near Dresden. Nevertheless there is no precise boundary to be drawn between these and the syenite-granites. As accessories, some mica and even quartz may occur in syenite, but they are not essential ingredients. This narrowing of the meaning of the term syenite appears to us the more justifiable, as these genuine quartzless rocks only contain 50-60 per cent, of silica, and therefore can be included in the basic group ; SYEXITE GROUP. 177 whereas those containing quartz have 60 70 per cent, of silica, and so belong to the acidic group. It so happens that the derivation of the name presents no obstacle to our definition, since it is well known to have originated in the erroneous belief that the antique stones which first received the name of syenite came from Syene in Egypt, which was not the case. Roziere therefore proposed to alter the name to Sinaite, from Mount Sinai, where genuine syenite is found, whereas at Syene only granite occurs. Werner, who first introduced the name into scientific petrography, applied it to the quartzless rocks of the Plauenschen-Grund ; although afterwards, in his ' Klassification der Gebirgsarten ' (1787), he called the same rock a greenstone. In the syenite group we also include miascite, zircon- syenite, and foyaite, as being closely allied to the genuine syenite. 11. SYENITE. SYEXIT, Werner. (Germ.) SYENITE. (Fr.) A crystalline granular compound of orihoclase or micro- dine and hornblende, and usually some titanite. Spec, grav 27 2-9. Content of silica in the rock of the Plauenschen-Grund, near Dresden, 55 60. The orthoclase or microcline is usually the principal ingredient, and being in general red, it gives that colour to the whole rock, deepened into a brownish-red by the hornblende. There are, however, syenites whose orthoclase is nearly white, and others containing an admixture of oligoclase. The andesine, which Delesse considered he had found in some syenites of the Vosges^ is held by Rose to be a decomposed oligoclase. An indistinct fissile texture is sometimes occasioned by the parallel disposition of the felspar crystals (sometimes twins), and a porphyritic texture by the prominence of separate and larger twin crystals. The hornblende is occasionally developed in separate columnar crystals, but it usually only forms part of the general crystalline granular mass of the rock. Be- sides these, its two principal ingredients, syenite usually contains some titanite (or wohlerite), forming minute N 178 BASIC IGNEOUS KOCKS. (2) PLUTONIC. brown crystals of adamantine lustre, dispersed through the general mass, often only to be recognised with the lens. Some mica, quartz, elaeolite (nepheline), zircon, magnetic iron-ore, and pyrites, are also to be found in the general mass, but only as accessories and in small quantity. Epidote, which also occurs partly in the ge- neral mass, and partly in the crevices of the rock, is probably the product of a decomposition of hornblende ; and an invisibly small proportion of carbonate of lime, causing a slight effervescence with acids, is traced by Bischoff to the same origin. A larger proportion of mica and quartz occasions transi- tions into syenite-granite or syenite-gneiss ; an increase of elasolite and zircon, transitions into miascite and zircon- syenite. Again, many syenites contain oligoclase as well as orthoclase or microcline, opening up a transition into diorite, which latter is essentially nothing but a syenite containing oligoclase instead of orthoclase. This trifling difference, which is usually connected with a coarser tex- ture of the rock, may possibly only be a consequence of the different level at which it attained the solid state. We find, indeed, syenite in its bedding to be more decidedly plutonic than diorite. Varieties in Texture. (a) COMMON SYENITE. \ Uniformly granular, as in the Plau- ( $KH enschen-Grund, near Dresden. (6) POBPHYRITIC SYENITE. \ With separate and larger crys- PORPHYRARTIGER SYENIT. (Germ.) > f -i f nr fi inP i Qca SYENITE PORPHYROIDE. (Fr.) J tals Ol rtnodase. Frh. von Richthofen has given the name of syenite-porphyry to a rock of this class found hi the Visena Valley, near Predazzo, in Tyrol. He desciibes it as consisting of a granular matrix of orthoclase, with little hornblende, and sometimes oligoclase in small quantity. The matrix enclosing twin crystals (three inches long) of orthoclase. It would be too much to say that there are no compact, vesicular, or amygdaloidal varieties of syenite ; we are only unable directly to trace any rocks of such textures through transition states from genuine syenite so as to show a direct connection with it ; and therefore we con- fine the name to the distinctly granular compound of felspar and hornblende, as above described. But amongst the aphanites there are certainly compact and vesicular SYEXITE GROUP. 179 rocks, whose chemical composition, at least, is so exactly that of syenite, that under a slower and more plutonic process of cooling, they might well have become syenite. They bear the same relation to it as petrosilex to granite. That these compact rocks do not occur in geological con- nection with syenite may be owing to the thoroughly plutonic origin of the latter, causing it always and every- where to have cooled uniformly and very slowly. The same observation applies to granite. Properly speaking, there are no varieties of composition to adduce, unless we consider as such those transitions into granite and diorite which are occasioned by the occurrence of mica, quartz, and oligoclase. The zircon- syenite is rather a variety of miascite than of syenite proper. But this seems a fitting place in which to in- troduce the rock which Delesse has termed MiCA-DioRiTE. ] It consists of a crystalline granular (,!.!MMi.i;!)[oitrr. (Germ.)\ compound of hornblende, orthoclase, Ditmrr^MiCACi, Beta*, t oligocla5e) mica> md very little ^^ ' generally of a dark colour, almost black. Content of silica only 48. From this composition we may regard this rock as something between diorite, syenite, and granite. In the Vosges it occurs in dykes in granite. Syenite is usually jointed into large irregular or thick tabular masses ; it forms entire mountains and occupies extensive regions ; only seldom forms distinct veins or dykes in other rocks, but is not unfrequently traversed by granitic veins, or it often contains granitic concre- tions. It is often associated v with great tracts of granite, and then passes over into syenite-granite, and finally into granite. The syenite of the Plauenschen-Grund, near Dresden, is eminently characteristic. Near Ditro, in Tran- sylvania, instead of titanite it contains much wohlerite. References. Xinimtmn on the Saxon Syenite, Erlauterung zur geog. Karte von Sachsen, 1845, No. 6, p. 116. L. van Such on the Monzon-syenite in v. Leonhard's Taschen- buch, 1824, p. 345. von Richthofen on Monzon-syenite, in Geogn. Beschr. v. Siid- Tyrol, 1860, p. 144, which contains, besides orthoclase and hornblende, some oligoclase, mica, and pyrites; ibid. p. 150. Zirkflj Syenit des Plauenschen-Grundes. * Poggendorf s Ann. vol. cxxii. p. 621. N 2 180 BASIC IGNEOUS KOCKS. (2) PLUTONIC. Delesse on Mica-diorite, in which he also includes rocks from the Kuhlenberg, near Harzburg, (gabbro ?) and from the Felsberg, near Darmstadt, in the Ann. des Mines, 1851, [4] vol. xix. p. 150. Karsten's Archiv. 1851, vol. xxiv. p. 280. Bullet, de la Soc. geol. de Fr. 1850, vol. vii. p. 524. The syenite rose cFEgypte here described is granite, Ann. des jnsyenit in v. L. u. Br. Jahrb. 1848, p. The following works on Syenite relate partly to rocks rich in quartz, which we class under the head of syenite-granite, viz. : v. Dechen in v. L. u. Br. Jahrbuch, 1858, p. 339. v. Rath in v. L. u. Br. Jahrbuch, 1858, p. 339. Streng in Poggend. Ann. 1853, vol. xc. p. 132. Kjerulfj Christiania Silurbecken, 1855, pp. 8, 12, and 15. 12. MIASCITE. MIASCIT. (Germ.) MIASCITE. (Fr.) A crystalline compound of orthoclase, nepheline, socialite, and black mica ; coarse-grained to fine-grained (in the different varieties other minerals also occur). This rock was first discovered by G. Rose in the Ural Mountains. Its orthoclase is Breithaupt's Mikrokline, and is white or grey ; the nepheline is yellowish-white (elaeolite) ; lustre only slightly resinous ; the sodalite is grey or a fine blue ; the black mica is nearly unaxial. Besides these principal ingredients, the following occur, but frequently" only as accessories : davyne, wohlerite, zircon, magnetic iron-ore, pyrites, pyrochlore, cancrinite, apatite, monazite, even quartz, hornblende, &c. By means of these minerals, transitions take place into granite, syenite, and especially zircon-syenite. At Miask the texture of this rock is sometimes fissile ; at Ditro, in Transylvania, where miascite occurs at the margin be- tween syenite and mica-schist, and intimately blended with the former, the blue sodalite is frequently arranged in layers, and the texture is generally very unequal, sometimes quite coarse, sometimes fine-grained. References. G. Rose, Eeise nach dem Ural, vol. ii. pp. 47, 93, and 535, and Poggend. Ann. vol. xbii. p. 375. SYENITE GROUP. 181 firrithaupt, Berg- u. Huttenin. Zeit. 1861, p. 493. t'otta, ibid. 1862, p. 73. Varieties in Composition. A. ZIRCON-SYENITE. ZJRKONSYENIT, Von Buch. (Germ.) SYENITE ZIRCONIENNE. (-fV.) A crystalline-granular compound of orthoclase, nepheline (elaolite), zircon, and usually only little hornblende. This rock is closely allied to miascite, both in respect of its essential and accessory ingredients. However, its composition varies so much in different places, that it is frequently difficult to decide what are essential and what accessory ingredients. The principal place where it occurs is the district of Laurvir and Brevig, in Norway: here there also occur eukolite and eudialite as accessory ingredients. References. L. v. Buch, Reise nach Norwegen, vol. i. p. 133. Ifamsmann, Reise nach Skandinavien, vol. ii. p. 103, and vol. x. p. 235. B. FOYAITE. FOYAIT. (Germ.) A crystalline granular compound of orthoclase-mepheline (elaolite), and hornblende. Spec. grav. . ** 2*6. The orthoclase is white or greyish-white, forms long tabular crystals with twin growth^(but not very perfectly developed), and is decidedly predominant. The reddish elaeolite of greasy lustre occurs in single hexagonal crystals. The greenish-black hornblende forms columnar crystals or small grains and parts of grains. The varieties of texture are the coarse-grained, fine-grained, compact, and porphyritic ; the latter contain crystals of orthoclase and elaeolite in a fine- grained matrix. The orthoclase crystals themselves some- times contain elaeolite and hornblende. The texture often changes very rapidly, as in gabbro. As accessories there occur titanite and magnetic iron-ore (very frequent), hexagonal brown laminae of mica, and iron-pyrites. This rock forms the mountains Foya and Picota in the pro- vince of Algarve in Portugal, where it is jointed in irregular masses. Blum has named it after the first mountain. Blum in von Leonhard's Jahrbuch, 1861, p. 426. 182 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. ACIDIC IGNEOUS EOCKS. These rocks are compounds of orthoclase, sanidine, or oligoclase, with quartz, mica, or hornblende. They also contain many other minerals as accessories. Their proportion of silica is almost always above 60 per cent., and extends in some cases to upwards of 80 per cent. Their texture is generally granular or porphyritic, but sometimes compact or vitreous, seldom vesicular, and never amygdaloidal. Frequently they have a somewhat fissile or foliated structure, and so they even form transitions into certain of the crystalline schists. Like the basic rocks, they are divisible into the volcanic and the plutonic. 1. Volcanic. In the rocks of this division the prevailing species of felspar is sanidine or oligoclase ; the labradorite (rich in lime), so often found with pyroxene in the basic rocks, is very rare in the acidic. The felspar is combined with some hornblende, and more rarely also with quartz, yet the rock always contains a large proportion of silica ; augite is only an accessory ingredient. The volcanic acidic rocks fall into two principal groups ; the trachytes and phonolites. The trachytic group, how- ever, contains many varieties both of composition and texture, and hence a great number of separate names, such as pearlstone, obsidian, &c. The trachytes occur as lava at active volcanoes of the present day, which is rarely, if ever, the case with the phonolites. Perhaps the latter are, to a certain extent, products of transmu- tation from compact or porphyritic trachytes. Although the trachytes, when characteristically deve- loped, differ very widely from the basalt, so that these two may be called the extreme products of volcanic agency, yet there are many volcanic rocks of intermediate character, which, to a certain extent, form transitions between the two groups, and prevent any very definite TRACHYTE GROUP. 183 line of distinction between them. In many individual cases it is, in fact, difficult to distinguish trachytic from basaltic rocks. THE TRACHYTE GROUP. The term trachyte, signifying rough stone, was first introduced by Hatiy, to denote a crystalline granular com- pound, in which sanidine, as the predominant ingredient, is combined with some other felspar, with hornblende (or augite), mica, or even quartz, in subordinate quantities. The principal mass is sometimes fine-grained, or even compact, with distinct minerals porphyritically prominent. Soon after Haiiy had first called attention to this rock, many other rocks came to be observed, having the same mineral composition, differing somewhat from it in tex- ture, but connected with the normal trachyte by inter- mediate transition states. These were called trachytic rocks, without being reckoned as actual trachytes ; thus, for instance, trachyte-porphyry, pearlstone, obsidian, pumice-stone, and many compact as well as porous tra- chyte-lavas. Then it was discovered tfyat many of the rocks which, without accurate mineralogical investigation, had been taken for trachyte of the 'prescribed composition, con- tained an oligoclase-felspar instead of the sanidine for- merly considered so essential an ingredient ; but in other respects their trachytic character was preserved. Ac- cordingly, the trachytes came to be divided into sanidine- trachyte and oligoclase-trachyte ; these two varieties are, however, connected with each other by many transition states, and their geological position and character are identical. In compact or fine-grained states the difference between them is scarcely to be recognised ; the varieties of texture appear likewise to be essentially the same in both. It may be useful, before going on to the description of the individual trachytic rocks, to take a general survey of what have been described under that name, and the mode in which different writers have dealt with the different varieties. Before the difference as to the species of felspar was re- cognised or known, the following varieties of the rock were 184 ACIDIC IGNEOUS KOCKS. (1) VOLCANIC. distinguished by Beudant (in his Voyage en Hongrie), and by Bur at (in his Description des Terrains vole, de la France centr. 1833), and also by Naumann. (a) TRACHYTES. Trachyte granitoide (granitic trachyte), e. g. at Handerlo, near Schemnitz. Fibrous or gneiss-like Trachyte, e. g. on the Pontellaria. Trachyte schistoide (schistous trachyte), e. g. at the Pas de Compain, department of Cantal in France. Trachyte a gros crystaux, a trachyte rich in felspar, at Dra- chenfels, near Bonn. Trachyte amphibolique, a trachyte rich in hornblende, e. g. near Schemnitz (perhaps the same as Breithaupt's timazite). Trachyte micace (micaceous trachyte), Monte Catini, in Tuscany. Domite, or Trachyte terreux (domite or clay stone-like tra- chyte), e. g. at the Puy de Dome. Trachyte porphyrolde (porphyritic trachyte), Schemnitz and Kremnitz in Hungary. Trachyte homogene (simple trachyte), frequently resembling phonolite, Monts Dores in Velay. Trachyte semi-vitreux (semi-vitreous trachyte), Tokay in Hungary; Iceland. Masenga, according to Naumann, the genuine trachyte of the Euganean Hills in Lombardy. Nenfro of Brocchi, according to Naumann, genuine trachytes of the Cimini Mountains. Nekrolite of Brocchi, according to Naumann, trachyte from Viterbo and Tolfa. (6) TRACHYTE-PORPHYRIES CONTAINING QUARTZ. Perlite-like Trachyte-porphyry. Hungary. Porous Trachyte-porphynj . Hungary. Vesicular Trachyte-porphyry (with globular cavities). Hun- gary. Millstone porphyry, or cavernous trachyte-porphyry. Miih- lensteinporphyr, or cavernoser Trachytporphyr. Porphyre meulier. Hliniker valley, in Hungary. Clay stone-like Trachyte-porphyry. Thonsteinahnlicher Tra- chytporphyr, Ponza Islands. (E. (Fr.) ) Also somewhat porphyritic. 190 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. (d) VESICULAR TRACHYTE. ^ often, par excellence, called Tra- BLASIGER TRACHYT. (Germ.) r T , / TRACHYTE VACUOLAIRE. (Fr.) ) ch V te iam ' (e) DECOMPOSED TRACHYTE. \ Manv decomposed varieties are ZERSETZTER TRACHYT. {Germ.) called Alumstone, on account of TRACHYTE DECOMPOSE. (Fr.) ) their containing alum. Varieties in Composition. (A) SANIDINE-TRACHYTE. SANIDIN-TRACHYT. (Germ.) An aggregate of sanidine crystals, with some hornblende or mica as subordinate ingredients. Texture coarse or fine- grained to compact. Spec. grav. . ... . . . . 2 -4 2-6 Contains silica - . : . . / . - r 59 60 p. c. In this compound, principally consisting of sanidine, horn- blende, and magnesia-mica, occur, as accessory ingredients, magnetic iron-ore, sodalite, olivine, titanite, and augite or quartz. It further appears probable, from the frequent pre- ponderance of the proportion of soda over the potash in the whole rock, that the compact matrix which permeates the whole nias?, cementing the distinct and recognisable minerals, contains, in addition to those we have mentioned, some mineral rich in soda, such as oligoclase, sodalite, or nepheline. The sanidine often occurs in a porphyritic form. The colour of the rock fluctuates between greyish-white and dark-brown grey. In most cases the texture is porphyritic, with granular or sometimes compact matrix ; some varieties are vesicular, and at the surface even scoriaceous, but not amygdaloidal. By decomposition a state is produced, not wackenitic, but more resembling claystone. The mass then appears almost white, whereas, in fresh condition, it is often very dark-coloured. The rock is generally of irregularly jointed structure. To this species belong, according to Roth, the trachytes of Rabertshausen, in the Grand Duchy of Hessen ; of Kappellen- berg (which contains some pyrope) ; of Mondhalde and Silber- brunnen, at the Kaiserstuhl j of Gleichenberg, in Styria ; of Monte Olibano, near Pozzuoli. Likewise the lavas found at Monte Nuovo, and those of the Azores, &c. The grey porous sanidine-trachyte, which occurs at the Laager lake, contains a good deal of haiiyne. (B) SANIDIXE-OLIGOCLASE-TRACHYTE (DRACHENFELS TRACHYTE). SANiDrsr-OLiGOKLASTRACHYT. (Germ.) A crystalline compound of sanidine and oligoclase with mag- nesia-mica and hornblende, also some augite, magnetic iron-ore, and titanite. Spec, grav 2'6 2-7 Contains silica . . . . 60 67 p. c. This very characteristic rock of the Drachenfels, near Bonn, with its large sanidine crystals porphyritically enclosed in granular matrix, served a long time as the principal type of the TRACHYTE GROUP. 191 trachytes, and all the felspar in that rock was assumed to be sanidine. Now, however, it appears, from the very consider- able quantity of soda contained in the matrix (up to 5 per cent.), that tlie latter probably consists principally of oligoclase. It is especially worthy of remark tnat in this porphyritic trachyte the large sanidine crystals frequently assume a parallel position to each other ; they are also sometimes broken in two, but both pieces still lie close together imbedded in the matrix. According to Roth, to this class belong the trachytes of Kiihlsbrunnen, in the Siebengebirge, and Freienhauschen, in the Eifel ; also, according to Richthofen, many trachytes of Hungary and Transylvania. (C) OLIGOCLASE-TRACHYTE (DOMITE). OLIGOKLAS-TRACHYT. (Germ.) DOMITE. (Fr. ) In this rock oliyoclase is the only recognisable felspar, as it con- tain* no xaniiliitc. The oligoclase is combined with some horn- blende or anyite and dark-coloured mica. These trachytes have been the least accurately analysed of any. They contain many other accessory minerals. *If the quantity of hornblende be above the average, then they pass into greenstones, e.g. into the greenstone-trachyte of Richt- hofen, or the timazite of Breithaupt. Whether andesite and trachydolerite should be included here may be doubtful. We prefer to treat them separately. This variety occurs in a tolerably fresh state at Stenzelberg', and at Wolkenburg, in the Siebengebirge. At the Puy de Dome, on the other hand, it is much decomposed, rough, almost crumbly, and is there called domite. It would be hazardous to attempt to distinguish varieties of texture. At Stenzelberg this rock exhibits a singular cylindrical jointed structure, in so-called 'outliers,' which consist of round columns, composed of concentric layers. Usually its structure is massive. (D) ANDESITE. ANDESIT. (Germ.) ANDESITE. (Fr.) A fine-grained or compact, and sometimes mtreous matrix, usually of dark-grey to black colour; contains crystals which, accord- ing to G. Rose, are oligoclase and augite. According to Abich, on the other hand, they are albite or oligoclase; and Abich adds, that some sanidine and hornblende, and always tiwyni'tic iron- ore, are likewise found in the rock. Dark-coloured mica frequently also occurs. Spec. grav. ,.;.. . . . 2-62-7 Contains silica 50 67 p. c. Roth distinguishes an amphibole-andesite and a pyroxene- andesite, but as the latter likewise contains some hornblende, this distinction would be difficult to maintain. To the amphi- bok-endesites, according to him, the localities which we have 192 ACIDIC IGNEOUS ROCKS. (1) VOLCANIC. above given under the head of * oligoclase- trachyte ' apply ; to the pyroxene-andesite, many volcanic rocks of Iceland and Tenerifte. This rock was first named by L. v. Buch, and its felspar was taken to be entirely albite. G. Kose could only discover oligo- clase in it. Doubts have also arisen respecting the other in- gredients. The matrix is sometimes easily to be reduced to powder. Known localities of its occurrence are : Pinchincha, Chimborazo, Antisana, and Cotopaxi j according to Abich, also the Caucasus and Mount Ararat. (E) TRACHYDOLERITE. TRACHYDOLERIT. (Germ.} TRACHY-DOLERITE. (Fr.^ A compound of oligoclase (or labradorite) with hornblende or augite, some magnetic iron-ore, and frequently also mica. These minerals lie imbedded in a grey or brown matrix. Spec, grav 2-72-8 Contains silica . . . . . 54 61 p. c. We may here distinguish the varieties which contain horn- blende from those which contain augite j the latter are very nearly related to dolerite. Vesicular varieties also occur. Abich, who first distinguished this rock and gave it its name, designates the following places where it is found : The Peak of Teiieriffe, the Schivelutsch in Kamtschatka, the island of Liscanera, near Stromboli, and the older lavas of ./Etna, for the varieties which contain hornblende ; and the top of the crater of Stromboli, and the central cone of the Rocca Monfina, for those containing augite. Deiters recognised in the rock of the Lowenburg, in the Siebengebirge, a complete transition grade between trachyte and dolerite. Under the microscope its principal mass appears to consist of crystalline felspar (either oligoclase or labradorite), imbedded in which lie scattered crystals of striated felspar, of hornblende, augite, magnetic iron-ore, and even some olivine. The content of silica here diminishes to 52 per cent. References. Beudant, Vovage en Hongrie, translated (into German) by Kleinschrod, 1825. Abich, Vulkanische Erscheinungen, 1841 j Vulkanische Bil- dungen, 1849; Natur des armenischen Hochlandes, 1843, p. 25 j and Poggendorf 's Annalen, 1840, vol. 1. p. 345. Bunsen, in Poggendorf 's Annalen, vol. Ixxxiii. p. 197. Sartorius v. Walterhausen, Die vulk. Gesteine in Sicilien und Island, 1853. Schill, in G. Leonhard's Beitr. z. mineral. Kenntn. von Baden, 1854, No. 3, p. 46. Deville, Sur le Trachytisine d. Eoches, in Compt. rend. 1859, vol. xlviii. p. 16. Enyelbach, in the Erlauter. d. geogn. Karte von Hessen. Sect. Schotten. Darmst. 1859, p. 43. TRACHYTE GROUP. 193 Rammehberg, in Zeitschr. d. d. geol. Ges. 1859, vol. xi. p. 434. Zirkel, Die trachytischen Gesteine der Eifel, in Zeitschr. d. d. geol. Ges. 1859, vol. xi. p. 507. L. v. Buch on Andesite, in Poggendorf 's Ann. vol. xxxvii. p. 189. v. Dechen gives eight divisions of trachyte in his Geogn. Beschr. des Siebengebirges (Verhandl. d. nat. Ver. d. Rheinlande, 1852). He appears, however, to have abandoned these in his more recent ' Geogn. Fiihrer durch d. Siebengebirge.' Zehler observed, in 1837, as many as forty different trachyte varieties in his l Siebengebirge.' Vom Rath, in his treatise, ' Die Trachyte des Siebengebirges,' 1860, makes the following divisions : 1. Drachenfels trachyte, whose white or grey matrix con- tains crystals of vitreous felspar and oligoclase, and some magnesia-mica and hornblende; accessorily, titanite, mag- netic iron-ore, augite, and apatite. Content of silica, 65 66. 2. Wolkenburg trachyte. 1 he colour of the matrix from grey to black, or sometimes reddish. It contains crystals of oligo- clase, no vitreous felspar, but some hornblende and magnesia- mica. Accessorily, augite, olivine, magnetic iron-ore, pyrites, and perhaps some quartz. Content of silica, 59 62 per cent. 3. Trachyte of Rosenau (not in connected rocks, only found in blocks). The base contains crystals of vitreous felspar, no oligoclase, more rarely some magnesia-mica, hornblende, sphene, and magnetic iron-ore. Content of silica, 78*8. The matrix appears in all these three varieties to be prin- cipally felsitic. Acid produces a weak effervescence, which may well be owing to carbonates of later origin than the rock itself, and the small quantity of zeolite which occurs is in all probability the result of decomposition. Vom Rath, Ueber Trachyt d. Enganeen. Zeitschr. d. deutschen geol. Ges. 1864, pp. 254-498. Deitei-s, Die Trachytdolerite des Siebengebirges, in Zeitschr. d. d. geol. Ges. 1861, p. 99. v. Richthofen, in the Jahrbuch d. geol. Reichsanst. 1860, Sitz- unjrsber. p. 92; extract in von L. u. Br. Jahrbuch, 1859, p. 304, and 1861, p. 98 ; Jahrb. d. geol. Reichsanst. 1864, p. 7. Stache has given the name of DACIT to a quartzose trachyte of Transylvania. Geogn. Beschr. von Siebenbiirgen. 14. KHYOLITE. RHYOLITH. (Germ.) A compact, enamel-like, or vitreous matrix enclosing grains or crystals of sanidine, oligoclase, mica, or even quartz. Spec. grav. . , , * 2'3 2-6 Contains silica 67 82 p. c. The matrix, which should, strictly speaking, always be of a prevailing felsitic character, varies however from the o 194 ACIDIC IGNEOUS KOCKS. (l) VOLCANIC. simple compact to the vitreous state. It is distinguished from that of the trachyte proper by its larger proportion of silica; and the same difference in the proportion of silica is found to obtain between the trachytes and rhyo- lites in the collective analysis of each rock in its entirety. Hence in rhyolite free quartz appears much more fre- quently than in genuine trachyte ; on the other hand, the former contains no hornblende or augite, or, at least, those minerals are much more rarely found in it than in trachyte. Under the common name of rhyolite we comprehend the following principal varieties : Trachyte-porphyry, perlite, obsidian, and pumice-stone, all of which possess sub-varieties. A. TKACHYTE-PORPHYKY. Liparite. TRACHYTPORPHYR, LITHOIDIT in part. (Germ.) PORPHYRE TRACHYTIQUE. (Fr.) A compact felsitic matrix containing crystals of felspar, and sometimes also mica or quartz. But as this general definition essentially agrees with that of many porphyrites and quartz-porphyries, it is per- haps better to say : Trachyte-porphyry is the name given to those rocks (prevalently felsitic and porphy- ritic with a compact matrix) which are geologically allied to the trachytes. Spec, grav 2-42-6 Contains silica ...... 67 81 p. c. The trachyte-porphyries are, as a rule, much richer in silica than the trachytes proper which we have described above. Their matrix is of prevalent felsitic composition and character, scarcely to be distinguished from that of the quartz-porphyries, and it only very rarely and exceptionally contains some traces of hornblende. Some trachyte-porphyries even contain grains or crys- tals of quartz or mica, or of both those minerals together, and thereby their resemblance to quartz-porphyry, gra- nite-porphyry, or mica-porphyrite, becomes still greater, and in fact so great, that occasionally, in the form of single specimens, it is impossible to tell the difference. In these cases, the only real difference consists in their geological connection with genuine trachytes or their TRACHYTE GKOUP. 195 petrographical transition into perlite or pumice-stone. The felspar of the distinctly developed crystals in trachyte-porphyry is most usually oligoclase, but some- times also sanidine ; both of these also occur in quartz- porphyries. The most important varieties in texture, but which may almost all be divided into those with, and those without, quartz, are t (a) COMMON TRACHYTE-PORPHYRY. ) Its felsitic matrix is compact GEMEIXER TRACHYTPORPHYR. (Germ.) > i n fresh fracture, and fre- quently somewhat shining ; usually light-coloured, containing (more "or less plentifully dispersed) crystals of sanidine or oligoclase, mica, or sometimes quartz. At the Schlossberg of N'-usohl the matrix is of greenish colour, compact, with crystals of felspar, mica, and quartz, ^n the Hliniker valley, near Schemnitz, the matrix is yellowish, and especially distinguished for its crystals of mica. (/>) PERLITE-LIKE TRACHYTE-PORPHYRY. ) The matrix is often PERUTAHNLICHER TRACHYTPORPHYR. (Germ.) f somewhat enamel- like, and contains, besides those crystals which we have men- tioned, small compact balls of felspar (spherulites), frequently with radial fibrous texture, sometimes also grains of quartz and mica. These rocks pass over by transition into perlite. (e) ARGILO-TRACHYTE-PORPHYRY. ) The matrix is dull THOXSTKIXAHXUCHER TRACHYTPORPHYR. (Germ.) J or earthy, and usu- ally penetrated with firm veins or nests of harder texture. Bereghasz in Hungary. (d) VESICULAR or CAVERNOUS TRACHYTE-] The matrix contains PORPHYRY, MILLSTONE PORPHYRY, (round vesicular cavi- BLASIGER oder CAVI:IL\OSKK TRACHYTPOR- f ties, or 18 entirely pene- PHYR, MUHLSTEINPORPHYR. (Germ.) J * regularly shaped cavities, whose sides are sometimes partly coated with cnalcedony or quartz. These cavities, however, are never entirely filled, so as to form genuine amygdaloids. Hliniker valley near Schemnitz. (e) PUMICEOUS TRACHYTE-PORPHYRY. ) Forms a transition BlMSTEDCAHNLICHER TRACHYTPORPHYR. (Germ.) J f rom the Vesicular variety into pumice-stone. ( f) SLATY TRACHYTE-PORPHYRY. ) The slaty texture is pro- SCHIEFRIGER TRACHYTPORPHYR. (Germ.) j duced by the manifold alternation of their layers of somewhat differing composition. Forchhammer has designated certain varieties of trachyte-porphyry which occur in Iceland by the special names of Krablite and Baulite. According to Bunsen, these are compounds of orthoclase and quartz. All these varieties abound in certain trachyte regions, as, for in- stance, in the neighbourhood of Schemnitz in Hungary, in the Euganean Hills, on the Ponza Islands and the Lipari Islands. They are usually irregularly cleft into angular masses, with columnar or tabular jointed structure. o 2 196 ACIDIC IGNEOUS ROCKS. (l) VOLCANIC. References. Beudant, Voyage en Hongrie, 1822, in many places. Poulet Scrope, Ponza Islands, in Transact, of the Geol. Soc. [2] vol. ii. p. 195. AUch, Vulkanische Bildungen, 1849, p. 23. Vulkanische Er- scheinungen, 1841, p. 20; Geol. N. d. armenischen Hoch- landes, 1843, p. 44. K. v. Hauer, Jahrbuch d. Geol. Keiclisanst. 1859, p. 466. Forchhammerj in the Journ. f. prakt. Chemie, 1843, p. 390. Bunseri, in Poggend. Annalen, 1851, vol. Ixxxiii. p. 201. B. PEKLITE. Pearlstone, Pearlstone-porphyry. PERLIT. (Germ.} PERLITE. (Fr.} An enamel-like matrix containing round grains, several of which are constructed with concentric layers. Spec. grav. . . . . .' . 2-32-4 Contains silica . . " . . . - 70 77 p. c. The whole mass of the rock perlite is of the same com- position as that of trachyte-porphyry, except that, on an average, it is somewhat more rich in silica. The state, however, of this compound, which is distinguished as perlite, often alternates with the simple compact obsidian state, or that other state which has become porphyritic by the occurrence of sanidine crystals. It also forms transition states into pumice-stone. Occasionally there occur, in addition to the sanidine crystals, some small mica flakes, red garnets, and even crystals of quartz. According to texture, Beudant distinguishes the follow- ing varieties : (a) GRANULAR SHELLY PERLITE. KORNIGSCHALIGER PERLIT. {Germ.) TRACHYTE TESTACE. (Fr.) (b) SPIUSRULITIC PERLITE. ^ with compact or radial striped ICHER PERLIT. Germ. SPHAROLITISCHER PERLIT. (Germ.) PERLITE GLOBULAIRE. (Fr.) (c) PERLITE-PORPHYRY. PERLITPORPHYR. (Germ.) PERLITE PORPHYROIDE. (Fr.) (d) VITREOUS, WITH RESINOUS LUSTRE. PECHSTEINARTIGKR PERLIT. (Germ.) (e) ARGILLACEOUS PERLITE. THONSTEINARTIGER PERLIT. (Germ.) (/) PUMICEOUS PERLITE. PERLTTBIMSTEIN. (Germ.) All these varieties are found (for instance) in the trachytic regions of Hungary, near Schemnitz, Tokay, Telkebanya, &c., near Zimapan in Mexico, on the Lipari Islands, &c. TRACHYTE GROUP. 197 References. Beudant, Voyage en Hongrie, vol. ii. p. 363. v. Pettko, in Haidinger's Abhandlungen, 1847, vol. i. p. 298 ; and as to Schemnitz, in the Abhandlung. d. geol. Reichstanst. 1853, vol. ii. No. 1. He names the variety with felsite balls ' Spherolite rock.' Erdmann, Journ. f. tech. Chemie, 1832, vol. xv. p. 38. Delesse. Bullet, de la Soc. ge*ol. 1864, [2] vol. xi. p. 109 ; v. L. u. Br. Jahrb. 1856, p. 195. C. OBSIDIAN and PUMICE-STONE. OBSIDIAN und BIMSTEIN. (Germ.} OBSIDEENNE et PONCE. (Fr.) Obsidian is a volcanic glass, sometimes porphyritic by reason of sanidine crystals : this glass, however, when it becomes vesicular, passes over into the most exquisite foam-like pumice-stone. Spec. grav. . ' . ' . . " . " . 2*3 2*5 Contains silica . , . , . . . 7182 p. c. This glassy or frothy texture belongs only to the rocks of the trachyte group, and more especially to the tra- chyte-porphyries or rhyolites. Their colour is (in the case of obsidian) usually dark black, brown, or greenish ; in the case of pumice-stone, on the other hand, white or yellowish-grey. According to differences of texture, we may distinguish : (a) COMMON OBSIDIAN. ) GEMEINER OBSIDIAN. (Germ.) \ A mere glass. OBSIDIENNE COMMUNE uraotDE. (Fr.) ) (6) OBSIDIAN-PORPHYRY \ with sanidine crystals, or some- OBSIDIANPORPHYR. (Germ.) [ t: mpa n l sn mi nlatps OBSIDIENNE PORPHYROIDE. (Fr.) ) Umes al80 mica P lates - (c) SPH^RULITIC OBSIDIAN. \ With felsite balls, passing SPHAROLITISCHER OBSIDIAN. (Germ.) } nvpr intr nprlifp OBSIDIENNB GLOBULAIRE. (Fr.) j over " to P er lte ' . {This rock is often of such long fibre and so nnrniid that it will PVPTI porous tnat it will even float on water. These species of volcanic glass are only found in trachytic volcanic regions. They are very characteristically developed at the Peak of Tenerifle, the Lipari Islands, in Iceland, in Mexico, &c. References. Beudard, Voyage en Hongrie, vol. iii. p. 389. Erdmann, Journ. f. techn. Chem. 1832, vol. xv. p. 36. K. v. Hauer, Jahrb. d. g. Reichsanst. 1854, p. 808. Damour, Poggend. Ann. 1844, vol. Ixii. p. 287. 198 ACIDIC IGNEOUS EOCKS. (l) VOLCANIC. Mundoch, Phil. Mag. and Journ. 1844, [2] vol. xxv. p. 495. v. d. Boon-Meesch, Pogg. Ann. 1828, vol. xii. p. 616. Herter, Perlstein. Zeitschr. d. deutschen geol. Gesellsch. vol. xv. p. 459. PHONOLITE GKOUP. 15. PHONOLITE, CLINKSTONE. PHONOLITH, KLINGSTEIN, PORPHYKSCHIEFER. (Germ.) PHONOLITHE. (Fr.} A compact base or matrix, in its, fresh state dark greenish-grey, showing here and there single cleavage surfaces of a vitreous felspar. The mass is as a rule somewhat slaty or schistose in texture, or of thinly tabular jointed structure gives a clear sound when struck by the hammer ; on weathering a sharply defined white crust is formed. Spec. grav. . . ..'.". 2-4 2'6 Contains silica . . , , , / 50 62 p. c. Klaproth proposed the name of phonolite for this rock, as having a more scientific air than that of klingstein, previously in use, of which it is the translation, and the new name has been very generally accepted. The peculiar properties of the rock had long been recognised, its difference from basalt, trachyte, felsite rock, &c., but its exact ingredients had not been investigated. Gmelin first drew attention to its analysis by muriatic acid, in which it is partly soluble and partly insoluble. The soluble part was considered to be a zeolitic substance, the latter a felspar, and the whole was considered to be an intimately blended compound of zeolite and felspar (sanidine). By the more exact microscopic and chemical investi- gations of later times, however, it has appeared that the composition of the phonolite mass is not so simple, and is in some part wholly different from what was supposed. It is even questionable whether in its fresh state it con- tains any zeolitic substance at all ; certain is it that the nepheline crystals which both Breithaupt and Rose early recognised in phonolite, as well as the mineral forming part of the matrix which Rammelsberg also judged to be nepheline, have frequently been mistaken for zeolite. Gr. Jenzsch ventures to give the following as the mine- ralogical composition of this rock, after investigating mi- croscopically and chemically several very characteristic phonolites of Bohemia : PHOXOLITE GROUP. 199 Per cent. Sanidine, estimated at 63-55 Nepheline, do 31-76 Hornblende (arvendsonite) . . . . 9-34 Titanite ,. > 3-67 Pyrites , . .* . . . 0'04 These proportional values must, of course, vary greatly with locality. As accessories, the following minerals occur, and are sometimes distinctly to be recognised in the rock ; viz. oligoclase, augite, magnetic iron-ore, olivine, hatiyne, brown mica, leucite, and nosean ; the last two minerals are the least frequent. It is possible that the zeolite (natrolite) which sometimes fill^ the crevices of the rock may also occur in the principal mass, but if so, it is probably the result of decomposition. In respect of the proportion of silica contained in pho- nolite, we might equally well group it with the basic as the acidic igneous rocks ; it forms one of the intermediate links between the two. As it never contains quartz dis- tinctly and separately developed, it might seem to be more allied mineralogically to the basic rocks ; but geo- logically its character is nearer that of the trachytes than the basalts. Where it occurs together with the latter, as is very frequently the case, it seems to play the same part as the trachytes under similar circumstances. Its small content of water (0-6 0*8 per cent.) appears to be (at least in part) a secondary product, the result of a commencing decomposition ; and in the same manner the occurrence of many accessory minerals in the mass, more especially those appearing in the clefts and vesicular cavities. Phonolite often acquires a porphyritic texture from the prominence of distinct crystals of sanidine and acicular hornblende. The most marked porphyritic varieties are as a rule little slaty and somewhat decomposed. As de- composition progresses, the crystals become more promi- nent, and even the titanite then is frequently to be easily recognised. Many phonolites are dark-spotted, or they contain round grains of peculiar composition and colour ; these, however, as in the case of basalt, appear chiefly to arise from commencing decomposition. Many are en- tirely decomposed (kaolinised), and show an earthy frac- 200 ACIDIC IGNEOUS KOCKS. (l) VOLCANIC. ture, with a light colour. Whole mountains of phonolite have, apparently at least, decayed in this manner, with scarcely a trace of slaty texture remaining. Naumann calls this variety Tr achy tic phonolite \ it is almost the only variety in which vesicular and amygdaloidal texture is found ; it never occurs in the fresh, dark, and slaty kinds. Jenzsch is even of opinion that the apparent vesicular and amyg- daloidal cavities of the phonolite are not genuine bubbles of the original rock, but have arisen subsequently by a kind of corrosive process of decay. This view certainly agrees with the absence of cavities in the perfectly fresh rock. Yet in some few phonolites are found very decided vesicular cavities. These cavities, as also the clefts and fissures, most usually contain zeolites ; especially apo- phyllite, chabasite, comptonite, desmine, natrolite, anal- cime, or calcspar and hyalite. Varieties in Texture. (a) COMMON PHONOLITE. ^ Dark-coloured, compact, schistose, GEMEINER PHONOLITH. (tar.) > O r imperfect slaty cleavage, and PHONO COMMUNE. (Fr.) ) ^ * the hammer. Mileschauer in Bohemia; Milzburg on the Ehon Mountain. (6) PORPHYRITIC PHONOLITE. ) The same mass with dis- PORPHYRARTIGER PHONOLITH. (Germ.) [ tinct crystals of hornblende, PHONOLITHE PORPHYROIBE. (Fr.) J au ^ te / or sanidine . Aussi ^ and Jakuben, near Tetschen in Bohemia. (c) TKACHYTIC PHONOLITE. ) Not slaty, not clinking, TRACHYTAHNLICHER PHONOLITH. (Germ.) j rough, of a rather light- grey colour ; frequently porphyritic, geodic, or amygdaloidal. Aussig, in JBohemia. (d) SPOTTED PHONOLITE. ] Luschwitz. near Aussig. in Bo- GEPLECKTER PHONOLITH. (Germ.) Y i^ arn : Q PHONOLTTHE TACHETEE. (Fr.) ) L lld< (e) VESICULAR PHONOLITE. j Blattendorf, nearHaida, in Bo- BLASIGER PHONOLITH. (Germ.) \ V.Q:,, PHONOUTHE VACUOLAIRE. (Fr.) ) " (/) AMYGDALOIDAL PHONOLITE. ^ Marienberg, near Aus- MANDELSTEINARTIGER PHONOLITH. (Germ.) [ -R^p,.,:,, PHONOLITHE AMYGDALOIDE. (Fr.) } S1 ?? m -t>0&emia. The slaty or schistose phonolites are those which are most usually of tabular or columnar jointed structure. Those which are not slaty are usually only irregularly massive. This rock forms isolated conical hills, even more per- fectly than basalt, especially so in the Bohemian Mittel- gebirge and in the Oberlausitz. Much more rarely does it form great connected mountain ranges, and it is more GEANITIC GROUP. (2) PLUTONIC. 201 rarely found in the form of dykes than basalt. On the continent of Europe, phonolite is only known as of ter- tiary or of still more recent origin, and never as a genuine plutonic rock. It is, on the other hand, also unknown as actual lava at active volcanoes, and from this it would appear that its state must be more or less the result of cooling under pressure or of transmutation. In favour of the latter supposition (of transmutation) is the presence of zeolite, which is, however, not a constant ingredient. Lyell, in his Geology, has instanced the occurrence of a phonolite of the Devonian period in Forfarshire. If this be a genuine phonolite, it is the only recorded instance of such being found of earlier than tertiary origin, but as the notice is quite incidental, and has reference to a different subject, and is moreover very brief, we can- not, without further explanation, accept it as authority in contravention of a law which otherwise appears uni- versal. References. Gmelin, in Poggend. Ann. 1828, vol. xiv. p. 259. Stntve, in Poggend. Ann. 1826, vol. vii. p. 348. Meyer, in Poggend. Ann. 1839, vol. xlvii. p. 192. Redtenbacher, in Poggend. Ann. 1839, vol. xlviii. p. 494. Schill, in G. Leonhard's Beitr. z. miner. Kenntn. von Baden, 1854, vol. iii. p. 59. Schmid, in Poggend. Ann. 1853, vol. Ixxxix. p. 295 ; v. L. u. Br. Jahrb. 1856, p. 845. Jenzsch, in the Zeitschr. d. d. geol. Ges. 1856, p. 167 ; and Poggend. Ann. vol. xcix. p. 417. v. Rath, in the Zeitschr. d. d. geol. Ges. 1856, p. 291, and 1860, p. 29. Enqelbach, in the Erl. z. geogn. Karte v. Hessen, Sect. Schotten, 1859, p. 45. Fischer, Die Trachyte u. Phonolithe des Hohganes, v. L. Jahrb. 1862, p. 356. Rammekburg, Analysen von Phonolithen, Zeitschr. der d. geol. Ges. 1862, vol. xiv. p. 750. v. Fritsch has lately set up a distinction between nepheline- phonolite, nosean-phonolite, leucite-phonolite, and felspar- phonolite, Neues Jahrb. fur Mineral. 1865, p. 663. 2. Plutonic. Granite is the principal rock of the plutonic division of the acidic igneous rocks, as trachyte is of the volcanic division of the same rocks. 202 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. The other plutonic rocks rich in silica may all be classed with granite as subordinate varieties of the same com- pound. The principal of these are quartz-porphyry, felsite rock, and pitchstone, all of which may be almost regarded but as different states of the same substance, bearing somewhat the same relation to granite as the rhyolites to the trachytic rocks. We therefore describe them all as granitic igneous rocks, although the idea of a granular texture is usually conveyed by the name of granite. In the composition of all these rocks, orthoclase, or an orthoclastic substance, is predominant (frequently asso- ciated with other felspars), and is combined with quartz, mica, chlorite, talc, some hornblende, &c. ; never with augite. The various combinations of these mineral ingredients give the following specially named rocks each with their subordinate varieties. 1. Granite. A compound of felspar, quartz, and mica ; granular, and sometimes also porphyritic, or other variety of texture. The following are varieties in composition : protogine, syenite-granite, schorl-granite, adularia-granite, granitite, ferruginous granite, graphite-granite, beresite, aplite. 2. Granitic porphyry and (so-called) syenitic porphyry. A rock containing the same ingredients as granite. The matrix is usually compact, enclosing distinct crystals or grains of felspar, quartz, and mica, or chlorite. 3. Quartz-porphyry. A compact matrix of the same chemical composition as granite, with separate individual crystals of felspar and quartz. 4. Felsite rock, or petrosilex. The matrix of quartz- porphyry without its crystals. 5. Pitchstone and pitchstone-porphyry. The same sub- stance as the above in a vitreous state, sometimes with crystals of felspar and quartz. It may appear to be inconsistent to treat the four last- mentioned rocks as distinct species, instead of mere varie- ties of the same species, as in the case of the rhyolites in the trachytic group. Our only reason for a different treatment is, that in general they are capable of being more easily distinguished from each other. GRANITIC GROUP. 203 16. GRANITE. GRANIT. {Germ.) GRANITE. (Fr.) A crystalline granular compound of felspar, quartz, and mica. In certain varieties there occur chlorite, talc, hornblende, and schorl. Spec. grav. ...... 2-6 2-7 Contains silica 62 81 p. c. The several mineral grains or particles are firmly knit together by their crystalline surfaces, without any uniting medium. They are of a size to be individually recognised, but their size is very various, and the rock is accordingly coarse-grained, fine-grained, or medium-grained. The so- called giant granites have grains larger than a walnut, other varieties not larger than mustard-seed. If the grains are so small as to become indistinct, and the rock assumes a compact texture, then it is no longer granite according to the usual meaning of the term. We shall treat of these compact states hereafter under the names of felsite rock and petrosilex ; they form states of transition between granite and other rocks. The felspar is usually the predominant ingredient, and the mica occupies the smallest place in granite. The felspar is chiefly orthoclase, very often accompanied by some oligoclase. Oligoclase alone has not yet been observed with certainty. It is also uncertain if albite or labradorite ever occur in the granitic compound. The orthoclase is somewhat various ; it is usually the common opaque species of yellowish-white or reddish colour ; more rarely grey or greenish. At many places (as, for instance, in the central chain of the Alps), it is principally that transparent vitreous variety, frequently split and cracked, which is termed adularia. The ortho- clase of granite is most readily to be distinguished from the oligoclase by its fresher state, its mother-of-pearl lustre, and simple twin growth ; whereas the oligoclase is somewhat of resinous lustre, and has delicate parallel stria? arising from multiform twin growths, or it is more decomposed, dull, paled in colour, or even transmuted into a totally different substance resembling steatite. Sometimes a thin coating of oligoclase is found incrusted round the grains of orthoclase. 204 ACIDIC IGNEOUS ROCKS. (-2) PLUTONIC. Orthoclase not only occurs as an ingredient in the normal granitic compound, but sometimes prominently in distinct twin crystals imbedded in the granitic mass, in which case the rock is termed porphyritic granite. These crystals are sometimes several inches long, and they enclose particles of quartz and mica, so as to form inside the crystal small kernels or parallel streaks of fine-grained granite. In the granite of the Fichtelgebirge, very large twin crystals of orthoclase are sometimes found broken, their several parts lying imbedded close together, just as in the case of the sanidine crystals of the Drachenfels trachyte. The quartz in granite is seldom in the form of perfect crystals ; it usually forms grains of irregular shape, or masses grown in with the other mineral ingredients of the granite, chiefly with the felspar. It is tolerably trans- parent and colourless or white, dark-grey, vitreous, most easily recognisable by its hardness. The granite of Rum- burg in Bohemia contains a dark-blue variety of quartz. It is remarkable that this, the most difficult of fusion of all the ingredients of granite, is often found hemmed in between the felspar and mica, and to have received impres- sions from the felspar at least ; whence it follows that the quartz must have solidified somewhat later than it. The mica of granite occurs in the form of thin laminae or small hexagonal plates, whose cleavage-planes lie in various directions, and therefore do not occasion a foliated texture. Sometimes they are clustered in small bunches ; or sometimes long continuous rays of mica run through the whole rock. Most usually it is potash-mica or mag- nesia-mica ; sometimes margarodite ; or lithia-mica, white, grey, brown, black, more rarely yellow or green in colour. Occasionally different coloured micas occur in the same rock, or a narrow border of white potash-mica envelopes the dark magnesia mica. But it is often difficult accu- rately to determine the species of mica in these thin laminae ; the easiest test is generally the optical. It is worthy of remark that potash-mica and tourmaline (schorl) appear only to occur (as original products) in plutonic-igneous or metamorphic rocks, and in plutonic dyke formations ; never in volcanic rocks. The ingredients which we consider as essential for granite are nevertheless sometimes replaced by others. GRANITIC GROUP. 20,5 This species of substitution occasions varieties in composi- tion which will be more particularly described below. It occurs especially with the mica, whose substitutes are, talc, chlorite (in protogine), schorl (in schorl-granite), graphite (in graphite-granite), micaceous iron (ferruginous granite). Sometimes a fourth ingredient appears in local but characteristic varieties of granite; e.g. hornblende (in syenitic granite) or pyrites (in beresite). The following minerals occasionally occur in granite, but only as accessories ; viz., tourmaline, garnet (always in the form of trapezohedra), andalusite, topaz, beryl, pinite, apatite, fluorspar, pistacite, corundum, zircon, titanite, gadolinite, orthite, pyrorthite, allanite, cordierite, magnetic iron-ore, tin-ore, mispickel, molybdenite, and native gold. We find many transitions from granite into other rocks. These are partly occasioned by variations of composition, and partly- by variations of texture. The accession of talc, chorite, schorl, or hornblende to the granitic com- pound occasions transitions into protogine, schorl rock, or syenite. If the felspar of granite disappears, we obtain gr lessen, or if the quartz disappears, mica-trap (minette), or if the mica disappears, aplite, and a kind of granulite. If the laminae of mica assume a parallel direction, then the texture becomes foliated, and gneiss is the result. If the matrix of a porphyritic granite becomes very fine-grained to compact, then we have a transition to granitic porphyry ; and if in that case the mica also disappears, then the rock becomes quartz-porphyry. Finally, if the whole granitic compound becomes very fine-grained to compact, then the rock isfelstone. Varieties in Texture. (a) COMMON GRANITE. \ Coarse, medium, or fine-grained, pro- GEMEiNERGRANrr.^rro.) f bably the most extensively diffused of GBAKTTE COMMUN. (/*.) J ^ ^^ ^ j f ^ ^^ ^ very coarse, it is sometimes called giant granite. Trebendorf, near Eger. Very fine-grained varieties, on the other hand, occur at Kerbersdorf, near Eger, in Bohemia, at Welsau, near Redwitz, and in the Vienna paving-stone. (6) PORPHYRITIC GRANITE. \ The porphyritic texture is usually GEBIROS-GRAIOT, r. Leonhard. I caused by large orthoclase crys- G JS^RPHTRotoE. (Fr.) I tals, more rarely by quartz crys- ' tals. The principal mass is granular. Carlsbad and Ellenbogen, Ochsenkopf and Gop- fersgriin in the Fichtelgebirge, &c. As a subvariety of this class, we may cite the rappakivi of Finland, the principal mass 206 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. of which is usually much decomposed ; it encloses rounded masses of red felspar often half an inch across, enclosed by orbicular envelopes of green oligoclase a quarter of an inch in diameter. (c) GKEISSIC GRANITE. | A granite with foliated texture. In GNEISSGRANIT. (Germ.) L a geological point of view, much of GRANITE GNEISSIQUE. (Fr.) ) what ^tterly has been called red gneiss (gneissite), and which appears to be eruptive, must be here included. Perhaps some grey gneiss too. (d) GRAPHIC GRANITE. j The orthoclase is altogether predomi- SCHRIFTGRANIT. (Germ.) L nant in large crystals, and is penetrated GRANJTEGRAPHIQUE.OPV.) * Iccording to a singular PECHMATIT, Naumann. (Germ.) PEGMATITE, ffaily. (Fr.) crystallographic law, so that in certain cleavage-planes it pro- duces figures resembling writing. The mica (usually white) is accumulated separately in groups. This remarkable variety usually only forms subordinate masses or dykes of small extent in the ordinary granite or in gneiss or mica-schist, but such dykes' are very frequent, e. g. in the Schloitzbachthal, near Tharand, in Saxony. (e) PEGMATITE. \ This rock Naumann separates from the graphic granite, and he understands by it a variety, very coarsely and irregu- > larly constituted, of orthoclase, quartz, and silvery-white mica. It often contains tourmaline, and occurs under the same conditions as the graphic granite, and frequently together with it. This seems the proper place for certain other granites of irregular composition very rich in felspar. Some are traversed by dark continuous rays of mica, in others the felspar assumes a form resembling flowering stalks (Blumengranif). In the granite of Ballybrack, near Dublin, the mica (Marga- rodite) assumes this plumose form, occurring in branches of Prince of Wales' feathers, one inch across and several inches long. Jukes. The granites of this class are all of very small extent, and their particular character is probably owing to special circum- stances. They all usually contain many accessory minerals, such as albite, tourmaline, topaz, beryl, garnet, gadolinite, orthite, &c. They are sometimes so imbedded between strata of crystalline schist that they can scarcely be regarded as of eruptive origin. (/) MIAROLITE. \ Is the name given by Fournet to MIAROLITH. (Germ.) > a o-eodic granite, rich in oligoclase, MIAROLITE, Fournet. (Fr.) J in " tlie nei | hbour h ood o f Lyons, and at Baveno in the Alps. The following are varieties in composition ; in them we find many of the varieties in texture repeated. ( With adularia ADULARGRANIT und ADULARPROTOGIN. (Germ.) I in the place of the ordinary felspar ; very extensively developed in the Alps. (1) GRANITITE. ' ) Is the name proposed by G. Rose for all GRAxrnr. (Germ.) \ granites containing much oligoclase with red orthoclase, quartz, blackish-green magnesia-mica in small quantity, and no white mica. This rock forms the principal material of the Riesen Gebirge; it occurs in the Brocken of the Hartz Mountains, Brixen in the Tyrol, &c. In composition it is identical with the mariolite of Foumet. (m) RTJMBURG GRANITE. > With blue quartz, occurs at Rum- RUMBURGER GRAuiT. (Germ.) \ burg in Bohemia, also at Pic Blanc in the Monte Rosa chain, (n) GRAPHITIC GRANITE. > With graphite in the place of mica, GRAPHITGRANIT. (Germ.) \ e . g. near Passau, on the Danube. (0) FERRUGINOUS GRANITE. ) With micaceous iron instead of the EISKNGRAXIT. (Germ.) \ ordinary mica. Occurs at several places in the Fichtelgebirge, also in iron-mines near Dossenheim in the Odenwald. (p) BERESITE. ) A granite containing pyrites and very little BERESTT. (Germ.) \ niica ; forms considerable dykes in the clay- slate near Beresowsk in the Ural. These dykes are themselves traversed by quartz veins containing gold. (q) APLITE or SEMI-GRANITE. ^ Is the name given to a variety APLTT oder HALBGRANTT. (Germ.) } O f very subordinate extent, consisting only of quartz and orthoclase, and therefore mine- ralogically allied to granitite. GREISEN might also be reckoned as a variety of granite without felspar. It does actually pass over into granite. . Its special geological character seems, however, to entitle it to be men- tioned as a separate rock. (See post, No. 50.) (r) TONALITE. ) The name given by Vom Rath to the TONALTT, Foro Rath. (Germ.) I roc k which forms the principal mass of the Adamello group of mountains in Southern Tyrol, and 208 ACIDIC IGNEOUS EOCKS. (2) PLUTONIC. which has hitherto always been described as granite. It is a crystalline granular compound of triclinic felspar with quartz, magnesia-mica, and hornblende. The triclinic felspar belongs to an entirely new species not yet named. The quartz forms at least one-third of the whole mass. It contains as accessories, orthoclase, orthite, titanite, and magnetic iron-ore. It contains 67 per cent, of silica. Many dark-coloured concretions are contained in the rock. In Tyrol this rock has broken through the mica-schist. (Zeitschr. d. deutsch. geol. Ges. 1864, p. 249.) All the varieties of granite are most commonly of irre- gularly massive or else of thick tabular jointed structure. By weathering, elliptical bodies are sometimes formed which fall off in concentric layers, the interior remaining fresh and firm. Granite is often found in large blocks and boulders on the surface of the ground. Granite is unquestionably one of the most extensively prevalent of rocks, and its mineral compound, which is also that of gneiss, is without doubt the most important and frequent of all the rock substances of the earth. Moreover, we find granite in all regions of the globe assume the same or analogous bedding in relation to other rocks. It frequently occupies extensive tracts, and sometimes forms the backbone of whole mountain re- gions. It also frequently forms dykes, and these some- times penetrate the larger granite masses (from which they may be distinguished by their texture) ; sometimes the crystalline schists or older sedimentary formations : granite dykes having been exceptionally found as late as the Jurassic formations, e. g. in the Alps. The greater part of the granites accessible to observation appear, however, to be older than the coal formation, and to be of deep plutonic origin. These granitic dykes are occa- sionally accompanied by so-called contact formations ; such as friction breccias ; silicification of the neighbouring rock ; chiastolite-schist ; nodular schist (see post, p. 257) ; granulation of limestone, &c. The usual bedding* of granite, and its relation to the bedding of adjoining rocks, unmistakably prove its erup- tive character, except, perhaps, in some special cases. Some doubts, however, which deserve our notice, have been raised as to its former state of igneous fusion. * The term ' bedding ' applied to igneous rocks, especially to granitic rocks, must be taken as equivalent to ' mode of occurrence ;' and l erup- tive' as only meaning 'intrusive' or 'irruptive.' TRANSLATOR. GEAXITIC GROUP. 209 These rest chiefly upon the fact of the quartz having solidified later than the felspar and mica, and on the want of distinct traces of the effect of heat on the rocks which the granite appears to have broken through. These ob- jections, it appears to us, may be satisfactorily answered by supposing the granite always to have consolidated at great depth, and under genuine plutonic influences, per- haps even with the aid of water. The great resemblance which granite bears to the trachytic rocks speaks, at all events, for a similar process of formation for both. That there are no new granites of volcanic origin is a necessary consequence of the assumed fact that the granitic compound can only have originated in the depths of the earth. We must likewise assume that great periods have elapsed in every instance from the time of the formation of granite rocks before they have become exposed to view. We may well assume that the trachytes represent the vol- canic part of the same igneous formation which gave birth to the granites. The name of granite (according to Emmerling's Lehrb. d. Mineralogie) was first applied to rocks by Tournefort in the year 1698. But according to Breislack's Lehrb. d. Geologic, it had been used by Caesalpinus as early as 1596. For a long time it was, doubtless, used to desig- nate every coarse-grained compound rock. The meaning of the term was first more definitely fixed by Werner. It has from the first been felt to be a geological necessity to group with granite many other rocks bearing a close affinity to it, but it has always been no less difficult to say where the line should be drawn. In 1849, G. Hose proposed the following new division and grouping of granitic rocks (see Zeitschr. d. d. geol. Ges. p. 352) :- 1. Granite (proper), essentially consisting of orthoclase, white (potash-) mica, black (magnesia-) mica, and oligoclase ; as accessories, hornblende, orthite, titanite, apatite, and iron pyrites. 2. Granitite, essentially consisting of orthoclase, oligoclase, quartz, and magnesia-mica ; as accessories, hornblende, orthite, zircon, titanite, pyrites, chalcopyrite, and molybdenite. Now as Rose himself subdivides his granite (proper) into several varieties whose composition differs as much from each other as granitite from granite, no sufficient reason appears for this violent division and new nomenclature. 3. Syenite, essentially consisting of orthoclase, oligoclase, hornblende, P 210 ACIDIC IGNEOUS EOCKS. (2) PLUTONIC. magnesia-mica, and quartz ; as accessories, titanite, apatite, magnetic iron-ore, &c. The difference "between this and the granitite also consists in the greater frequency of the hornblende, in its being named as an essential instead of an accessory ingredient. This is our syenitic granite. The genuine syenite of the Plauenschen- Grund does not agree with this definition because it seldom contains mica and, perhaps, contains no quartz at all. There- fore Rose sets up varieties of composition differing, however, more from each other than his syenite from granite. 4. Porphyry, essentially consisting of orthoclase, oligoclase, quartz, and magnesia-mica; as accessories, cordierite, garnet, ortliite, and pyrites, its essential difference from his granite or granitite consisting only in texture. Now, as oligoclase and mica entirely fail in many rocks which Hose reckons as porphyries, he has been driven again to make varieties which differ almost more from each other than his porphyries from the other granitic rocks. 5. Syenitic Porphyry, with a matrix enclosing crystals of orthoclase, oligoclase, magnesia-mica, and hornblende; as accessories, garnet, nepheline, titanite, quartz, magnetic iron-ore, specular iron, and pyrites. This is a very different rock from that which has received the name of syenitic porphyry ever since Werner's time. It is our porphyrite, which as we have seen may be divided into (A) a rock essentially felspathic, (B) containing felspar and horn- blende, and (C) containing felspar and mica. The literature respecting granite is, as we might ex- pect, a very rich one we will only cite a few treatises on the more special phenomena. References. G. Rose, On the Granitite of the Riesengebirge, Zeitschr. d. d. geol. Ges. 1857, p. 513. Cotta, On the Rumburg Granite with blue Quartz. Erlauter. z. geogn. Karte v. Sachsen, 1839, No. 3, p. 14. Four-net, On Miarolit, Mem. sur la Geol. des Alpes, part. 2, p. 24, and Bullet, de la Soc.^ geol., [2] vol. ii. p. 495. Sothlinkff, On Rappakivi a granite which,' however, often contains no quartz, and then is very similar to mica-trap, v. L. u. Br. Jahrb. 1840, p. 613. v. Rosthorn and Canavd, On Albite-granite and Tourmalin- granite in the Alps. v. L. u. Br. Jahrb. 1855, p. 584. v. Richthofen, On Granitite, Tourmalin-granite, and Tourmalin- syenite, Geogri. Beschr. von Siid-Tyrol, 1860, pp. 108 and 148. Axel- Gadolin distinguished two kinds of granite dykes in the gneiss of Ladoga Lake, viz. : older dykes, with albite from two of more recent formation, containing much oligoclase. Verhandl. der k. russ. mineral. Ges. zu Petersburg, 1857-8, p. 85. GRANITIC GROUP. 211 Svanberg comes to the conclusion from analysis that besides orthoclase other orthoclastic felspars occur in granite. Journ. f. prakt. Chem. 1844, vol. xxxi. p. 161. I)('l<-sse distinguishes in the Vosges Mountains protogine from '(iranite sye*nitique des Ballons.' Bullet.de la Soc. ge*ol. 1852, [2] vol. xi. p. 464. Also, ' Granite des Ballons,' ' Granites des Vosges/ and ' Filons de Granite.' Ann. des Mines [5] vol. jii. p. 369. On the Pegmatite with Tourmalin of Saint Etienne in the Vosges. Ann. des Mines, 1849, [4] vol. xvi. On Pegmatite of Ireland. Bullet, de la Soc. g(ol. 1853 [2] vol. x. p. 568. Haw/hlon, Quart. Journ. Geol. Soc. 1856, vol. xii. p. 177 ; and 1858, vol. xiv. p. 300. Address delivered before the Geol. Soc. of Dublin, 1862. .R. Scott, The Granites of Donegal. Journ. of the Geol. Soc. of Dublin, vol. ix. p. 285. Scheerer, Granite Tyrols. Jahrb.'f. Min. 1864, p. 385. Sir W. E. Logan, Classification of Eruptive Rocks. Rep. Geol. Surv. Canada to 1863, p. 645. G. LconJiard distinguishes between older and newer granite veins in the Heidelberg mountain granite. Gegend um Heidelberg, 1844. Bunsen, On Granite formation. Zeitschr. d. d. geol. Ges. 1861, p. 96. C. Rothe, iiber die krystallinischen Gesteine des Ries. Jahrb. fiir Mineralogie, 1863, p. 169, contains many new analyses of granite. v. Helmersen has described the Rappakivi of Finland, of which the Alexander column of St. Petersburg is formed, as a por- phyritic granite with a flesh-red felspar predominant. n/8on treats of the supposed neptunic origin of granite in the Edinb. New Philos. Journal, 1861, vol. xiv. p. 149. Fuchs on the granite of the Ilartz in the Jahrb. fiir Mineralo- gie, 1862, pp. 769, 807. H. C. Sorby. On the Microscopical Structure of Mount Sorrel Granite : Proc. Geol. and Polytech. Soc. W. Riding of Yorksh., 1863-4, pp. 301-4. On "the Microscopical Structure of Crystals, indicating the Origin of Minerals and Rocks : Quart. Journ. Geol. Soc. 1858, vol. xiv. p. 453. Sorby and (later) Zirkel have made interesting dis- coveries by microscopic analysis of granites and several other igneous rocks. The quartz and the felspar of Granite are found to en- close numerous very small vesicles filled with water and air, and also many minute particles of glass. The quartz also contains some very minute crystals of felspar. The mi- croscopic structure of the Trachytes very closely resembles that of the granites ; their compact matrix Zirkel recog- nised as a compound of felspar and quartz. In the compact mass of fresh Basalt he recognised a compound of felspar p 2 212 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. and magnetic iron-ore with very Mttle olivine, and traces only of augite. The vitreous mass of Pitchstone resolved itself under the microscope into a confused compound of very delicate acicular crystals. The same thing with Obsidian. Even the newest Lavas exhibited in their mass very minute pores filled with water. 17. GRANITIC PORPHYRY and SYENITIC PORPHYRY. GKANITPORPHYR und SYENTTPORPHYR. (Germ.} A compact or fine-grained felsitic base, enclosing crystals or crystalline grains of felspar, quartz, and mica, or chlorite. Spec. grav. < . . Y , . . 2-6 27 Contains silica , . . . . 61 64 p. c. The matrix is yellowish, brownish, or dark green. When not quite compact, its material may be recognised as consisting principally of felspar, combined with quartz, mica, or chlorite in small proportion. The presence of chlorite occasions transitions into porphyritic granite or protogine ; but in distinguishing and naming these transi- tion rocks, their geological relations must always, to some extent, be taken into account. The distinct crystals of felspar are very numerous in this rock, and are usually of large size. They are for the most part twin crystals of orthoclase, and these are often coated with a different species of felspar, probably oligo- clase, crystallographically combined (grown together) with the orthoclase. There sometimes occur also separate and smaller felspar crystals and grains ; these latter, as well as the crust of the larger crystals, show delicate stripings, and therefore both, probably, consist of oligoclase. The quartz most usually forms small grains or crystals of a smoke-grey colour, often, however, larger diplohe- drons (which were formerly mistaken for double pyramids) very distinct and prominent. The dark mica usually only occurs in small delicate flakes or thin hexagonal plates. If the rock contains chlorite instead of mica, as in the variety termed syenitic porphyry, the chlorite forms small dark green scaly grains, or else it is intimately blended with the matrix, to which it imparts a green colour. GKANITIC GROUP. 213 The above-mentioned modifications give rise to several varieties of the rock. Varieties in Texture. (a) COMMON GRANITE-PORPHYRY. The matrix is compact through- out ; often dark-coloured. It contains separate crystals, grains, or laminae of orthoclase (and sometimes oligoclase), quartz, and mica. If the mica faiis ; the rock passes into ordinary quartz-porphyry. Frequent in the Thuringian Forest, e.g. near Schmiedefeld, and in the Drusenthal, where it forms dykes of great thickness. (b) GRANITIC GRANITE-PORPHYRY. i The matrix resembles GiiAxn-AHNLicHER GRANITPORPHYK. (Germ.) I" j n part a fine-grained granite, but distinct crystals of orthoclase, and large grains of quartz, and also laminae of mica, are separately and prominently developed. Frequent in the neighbourhood of Schellerhau and Biirenburg in the Erzgebirge. The composition of this rock is very similar to that of porphyritic granite. The geological character in these doubtful cases should determine the nomen- clature of each particular rock. At Niederschona, near Freiberg, where a rock belonging to this class forms a vein in gneiss, it contains large light- coloured twin crystals of orthoclase, whose exterior appears fresh, but inside each crystal is a decomposed nucleus frequently changed into a greenish substance like lithomarge. It would almost seem as if the nucleus of the orthoclase crystal had originally consisted of oligoclase or a compound of oligoclase and quartz. The magnificent columnar granite-porphyry of Altenhain, near Frankenberg, in the Erzgebirge, is a rock of the same class, but the orthoclase crystals do not exhibit the same phenomenon as those of Niederschona. Near Liebenstein in the Thuringian Forest, a granitic porphyry traverses and forms dykes in the ordinary granite. It possesses a very fine granitic matrix, and very distinct white crystals of orthoclase, with brown edges ; also dark spots or fragments (which are still compact) of greenstone which the porphyry has broken through. (c) MICACEOUS GRANITE-PORPHYRY. \ This rock, which Kit- GUMMERREICHER GRANTTPORPHYR. (Germ.) } tel first described under the name of granitic porphyry, and which occurs at Aschaffen- burg, interposed between syenite rocks, consists of a fine-grained to compact felsitic mass rich in mica (a kind of minette) in which numerous grains or crystals of quartz and somewhat fewer, but much larger crystals of felspar are imbedded. According to Kittel, the quartz crystals often show prismatic surfaces. The orthoclase crystals are partly single, partly twins, very fresh, without marginal crust, and have well-defined edges, but strange to say, completely rounded off, so that their cross-section always appears elliptical. (d) CHLORITIC GRANITE-PORPHYRY. \ Often called syenitic por- GRANrmjRpHYR. (Germ.) ) phyry, probably because 214 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. the. particles of chlorite which it contains have been mis- taken for hornblende ; but in some places the rock appears actually to contain some hornblende as an accessory. The matrix is compact or fine-grained, .brown or dark green, often very rich in quartz, and contains chlorite, and some- times mica also. The chlorite forms little flakes or grains, the quartz is in the form of diplohedrons, and the twin crystals of orthoclase are sometimes more than an inch long. In the syenitic porphyries of the Erzgebirge (the rocks ori- ginally so named by Werner) these orthoclase crystals are often enveloped in an outer coating of oligoclase, of about one-tenth of an inch thick, showing distinct twin stripings. The oli- goclase is sometimes lighter in colour than the orthoclase (greenish-yellow) sometimes darker (brown), and it is gene- rally more decomposed than it. This rock near Frauenstein and Altenberg has broken through gneiss, mica-schist, granite, and quartz-porphyry, and forms very important and extensive dykes in those rocks many miles in length. Near Frauenstein it contains, according to Rube, about 64 p. c. of silica. Naumann has described a rock of somewhat different cha- racter under the name of green porphyry. It occurs in the neighbourhood of Wurzen in Saxony, where it forms small rocky hills. Its matrix is dark-green, probably from chlorite, and it also contains some magnetic iron-ore. Dr. Rube determined its proportion of silica at about 61 p. c. This rock is likewise more recent than the quartz-porphyry of the same district. ( ferent colour and texture from the matrix. This variety has also been called Kattun-porphyry. Leukersdorf near Chemnitz, Saxony. (d) POROUS, CAVERNOUS, OR ] A rock penetrated by numerous MILLSTONE PORPHYRY. I small irregular cavities or geodes, POROSER, DRUSIGER, oderMt^Hi^ f which are seldom vesicular, more STEINPORPHYR. (Germ.) ) usuftlly the regult of weathering> Tannebergsthal in the Erzgebirge, Regenberg near Frie- drichsroda, in the Thuringian Forest, where it is combined with pyromeride. 218 ACIDIC IGNEOUS ROCKS. (2) PLUTONIC. This rock in addition to the usual quartz crystals, contains balls of felsite (either small (e) PYROMERIDE (BALL-PORPHYRY).' KUGELPORPHYR oder PYROMERID. (Germ.) PYROMERIDE, Monteiro. (Fr.) ' and numerous, or large and isolated. The small balls are frequently marked internally with radial streaks. The interiors of the larger ones are usually split after the manner of septaria, or they contain a geodic cavity. The clefts or cavities in the balls are wholly or partly filled with hornstone, chalcedony, agate, quartz, ame- thyst, calc-spar, fluor-spar, micaceous iron, &c. These balls, as we have already mentioned, frequently occur in combination with a geodic structure of the matrix. Regenberg and Schnee- kopf in the Thuringian Forest, the island of Corsica. (/) PORPHYRY WITH ] Forms a transition into felsite rock FEW CRYSTALS. I (petrosilex) or into porphyrite. The KRYSTALLARMER POR- f matrix alone, without crystals, is some- CYR. (Germ.) ) timeg foimd towar( J s tne o uter mar gi n o f masses of very distinct quartz-porphyries thus e.g. at the Weissritz, close above Dippoldiswalde in Saxony, The Frei- berg porphyry dykes are also mostly very poor in crystals of felspar and quartz, but they often contain, in their stead, small cubic crystals of pyrites. Varieties in Composition. (.) J ^ DreS den. A rock of this description is met with at Castelruth in Southern Tyrol ; it contains a felspar resembling sanidine and round grains of quartz, and v. Bichthofen describes it as a quartz-porphyry. (c) ARGILLACEOUS 'PITCHSTONE. \ The Pitch-claystone of Nau^ PECHTHONSTEIN, Naumann. (Germ.) I ma nn, a Stage of decompo- J sition not unfrequent near Meissen. Pitchstone is for the most part of irregular massive structure. It usually occurs associated with quartz-por- phyries, and traverses them in dykes ; probably, however, its geological age is not very different from that of the quartz-porphyries, and it would seem to bear somewhat the same relation to the porphyries as perlite and obsidian to the trachyte porphyries. The vitreous state of pitchstone is somewhat enigma- tical, inasmuch as that rock usually occurs with rocks of decidedly plutonic origin, and moreover contains a large proportion of water : Bischof and Jenzsch consider the glassy texture to be the consequence of transmutation by aqueous process, and only to be apparently vitreous. But it is very possible that under special circumstances in the interior of the earth, eruptive igneous masses may have cooled very rapidly, perhaps in consequence of the sudden accession of a large quantity of water, and so have become converted into a vitreous state containing water. 226 ACIDIC IGNEOUS KOCKS. (2) PLUTONIC. References. Knox discovered a bituminous substance in pitchstone. Transact, of the Geol. Soc. 1811, vol. i. p. 278, and Ann. d. Phys..et Chem. 1823, vol. xxii.^ p. 44. Necker de Saussure. Voyages en Ecosse et aux lies Hebrides, vol. ii. p. 455. The pitchstone of the Hebrides exhibits under the lens a fine granular texture resembling basalt. Macculloch, Descr. of the Western Islands, vol. i. p. 520, on the pitchstone of the Hebrides. v. Oeynhausen and v. Decken, on the Pitchstone of the He- brides, in Karsten's Archiv. vol. i. p. 50. Haughton concludes from his analysis of pitchstone, that it con- sists of a combination of about 62 felspar, 30 stibite, and 7 quartz. Naumann, on Pitchstone and Pitch-claystone from Meissen, in the Erlauter. zur. geogn. Karte v. Sachsen, 1844. No. 5, p. 184. Cotta, on the Pitchstone of Meissen and Tharand, Geognostiche Wanderungen, 1836, vol. i. pp. 40 and 104. Scheerer, Analysen u. Folgerungen in the Art. Pechstein in Liebig's Handworterbuch der Chemie, 1854, vol. vi. p. 105, and in v. L. u. Br. Jahrbuch, 1855, p. 60. Jenzsch considers pitchstone to be fine crystalline, and a pro- duct of transmutation and the balls of felsite in it, for re- mains of porphvry not yet transformed. Zeitsch. d. d. geol. Ges. 1856, p. 257. Rentzsch, Die Pechsteine, 1860. H. Fischer, on Pitchstone and Pearlstone, Zeitschr. der deutsch. geol. Ges. 1862, vol. xiv. p. 312. 227 CHAPTER II. METAMORPHIC CRYSTALLINE SCHISTS. THE term Metamorphic as applied to these rocks implies that they are the product of the metamorphosis of rocks originally sedimentary, and, although several gneiss rocks may have had another origin, they cannot be lithologically separated from those of undoubted metamorphic character. The designation of Crystalline Schist on the other hand rests solely on petrographical characteristics. The mineral composition of these rocks most resembles that of the plutonic division of the acidic igneous rocks, i.e. they consist (like those) chiefly of compounds of fel- spar, quartz, mica, talc, chlorite, and hornblende, and do not essentially contain pyroxene. We might indeed have anticipated the resemblance of the metamorphic rocks to the plutonic rather than the volcanic division of igneous rocks (whether basic or acidic) as their transmutation has probably taken place deep in the interior of the earth, therefore under plutonic influences ; and the fact that they contain more silica and less lime and magnesia on the average than the basic igneous rocks, is accounted for by the separate beds of carbonate of lime and magnesia (limestones and dolomites) which interlie the metamorphic rocks, whence we should expect to find the last mentioned rocks somewhat deficient in those bases. But we shall find that some of the crystalline schists are in fact rich in lime and magnesia, and therefore are more allied to the basic rocks. Those of prevailing acidic character are principally granulite, gneiss, mica-schist, quartz-schist, itacolumite and argillaceous mica-schist. The basic on the other hand are : chlorite-schist, talc-schist, and hornblende- schist, and others. All the rocks of this class are to be distinguished from the igneous by their foliated texture, and yet more by their alternate bedding in parallel layers or strata, and the 228 CRYSTALLINE SCHISTS. traces which they often very distinctly show of internal stratification. These phenomena it is true are sometimes exceptionally met with in the igneous rocks, but in them they are the reverse of characteristic ; their foliated tex- ture, when it occurs, is usually to be explained by local pressure, their stratification by successive overflows of fused matter; as a general rule the igneous rocks also differ very widely in the character of their bedding from the metamorphic schists. Nevertheless there are actual petrographic transitions between the two, and in some in- dividual cases where the nature of the bedding is not very distinctly marked it is difficult to decide the character of a given rock. The properties which the crystalline schists have in common with the sedimentary rocks are stratification, fissile texture, and parallel alternating bedding ; on the other hand the schists are wanting in organic remains (fossils) and in mechanical aggregates. In their com- position they differ from the sedimentary rocks by the crystalline state of their mineral ingredients. There is, however, no very definite boundary between the two ; on the contrary there are series of distinct transitions from one to the other just as we might expect to find if the crystalline were really as we suppose them to be, the offspring of the sedimentary rocks. We moreover find that the greater part of the sedimentary rocks, and espe- cially the older ones, are no longer in their original state but are somewhat changed, doubtless by the identical influences which at last have transmuted them into crys- talline rocks and which are probably still in operation, viz. heat and pressure. The term Metamorphic, however, is in practice only applied to the extreme products of this slow process of transmutation, such as by assuming a crystalline state have entirely departed from that of their original deposit, although their connection with it may still be traced through stages of transition. This is simply a matter of usage, for looking to the meaning of the term., we might just as well call every clay-slate or firm sandstone metamorphic (transmuted) since they were not originally formed in the state in which we find them at the present day. Por these and other reasons it is difficult to prescribe FELSPAR GROUP. 229 a definite and consistent limit to metamorphic rocks. From a geological point of view we ought to include in that term most granular limestone, serpentine, gra- phite, magnetic iron-ore, &c., and reject many kinds of gneiss and granulite as being irruptive ; but in a system of lithology this treatment, however logically correct, would lead to so many inconveniences and difficulties as to render it impossible in practice. For these reasons we have not made use of the general designation Metamorphic rocks as the title for this chapter, but chosen the more restricted term of Metamor- phic crystalline schists. These for the most part are compounds rich in silica, which, in their chemical com- lHition approach Bunsen's formula for the normal trachytic rocks. Some few, however, are poor in silica and resemble the basic igneous rocks in composition. We do not propose to divide the metamorphic schists into basic and acidic groups ; we prefer to group them accord- ing to their leading mineral ingredients without attempting a strict scientific arrangement, except that we begin with those which in their mineral character bear the greatest resemblance to the granite rocks and place those last which approach most in character to the unchanged sedimentary rocks. CRYSTALLINE SCHISTS, RICH IN FELSPAR. (Granulite and Gneiss.) 21. GRANULITE, LEPTYNITE. GRANULTT, WEISSSTEIN. (Germ.) LEPTYNITE, Haiiy. (Fr.) A fine-grained to compact fissile compound of felspar and quartz ) usually with some mica. Spec. grav. . ... . 2-62-7 Contains silica . . 70 80 p. c. This rock, oil account of its frequent white or light- yellowish colour, was formerly called weissstein (white stone) ; but as the same mineral compound also occurs of a dark colour, Weiss proposed to substitute the name of granulite, which has now been generally adopted. Its mineral composition is for the most part that of a granite or gneiss (a red gneiss), with very little mica. Its cha- 230 CRYSTALLINE SCHISTS. racteristic varieties are nevertheless easily to be distin- guished from granite and gneiss, as will appear from a more special description of the rock. Intermediate grades of uncertain character and transitions are, however, frequent, and if these occur in the midst of gneiss or granite, we reckon them without hesitation, to those rocks, and call them granulitic gneiss, or granulitic granite ; but if found in granulitic regions the same rocks would be properly termed gneissic granulite, and reckoned to the granulites. The felspar of granulite is mostly orthoclase ; some- times, however, in part oligoclase. It is intimately blended with the quartz, which is Jess in quantity, or at all events is less apparent, than in granite or gneiss. The free quartz forms few and very thin sepa- rate layers, or flat lenticular grains, which are to be most distinctly seen when the rock is weathered. The mica appears in small scattered laminae, disposed in parallel planes, or if sometimes found connected, scaly seams en- tirely dividing the rock, which otherwise is an intimate compound of felspar and quartz. In both cases the mica increases the fissile texture of the rock. It is usually a white variety of mica seldom black. The felspar, which is always predominant, is usually white, yellowish, or light-red ; and these are, therefore, the prevailing colours of the rock. The quartz is never dark-coloured, seldom transparent, and usually white. In a section of the rock the seams of mica sometimes produce riband stripings of dark colour. There are, however, varieties of granulite in which the whole mass is of a blackish-green to almost quite black colour (owing perhaps to protoxide of iron); for these the old name of weissstein is inappropriate. We repeat, then, that the essential constituents of the rock are its felspar and quartz, and a small proportion of mica. In addition to these, red garnets often appear disseminated through the mass in small grains or crystals ; where little or no mica is present, then these garnets are especially frequent, and this is the most characteristic composition of granulite. Where much mica is' found, the garnets appear to fail, and varieties of this latter kind form the transitions into gneiss. Another characteristic accessory ingredient of granulite, though but * sparingly FELSPAR GROUP. 231 distributed, is blue disthene (kyanite). Schorl and horn- blende also occur, but more locally. This rock forms transitions into granite by assuming a more distinctly granular, and less fissile texture, into gneiss, by the increase of its mica, and into felsite-schist, when its mica disappears and the mass becomes quite compact. Varieties in Texture. (d) COMMON GRANULITE. ) White, yellowish, or flesh-red, GEMEINER GRANULIT. (Germ.) I with little or no mica, contains LEPTYNITK COMMUN. (Fr.) J ^^ g^et^ ^d frequently some disthene. It is more laminated than properly speaking foliated or slaty. Rosswein in Saxony. (b) RIBAND-STRIPED GRANTJLITE. ) Striped by parallel seams of BAXDSTREIFIGER GRANULIT. (Germ.) L mica, interlying the main J mass of felspar and quartz. On the Zschopau between Sachsenburg and Schonborn in Saxony. (c) MICACEOUS GRANULITE or GNEISS-GRANULITE. ) With few or no GLIMMERRHICHER oder GNEISSGRANUUT. (Germ.) I garnets. Mitt- LKPTYNITE MICACE. (Fr.) J we id a in Saxony. (d) GRANITIC GRANULITE. ] More granular than fissile. This GRANrrGRANULrr. (Germ.) I variety passes into a kind of granite LEFTYNITE GRENU. (Fr.) j w hich contains little mica, and where it occurs in the form of dykes or veins, it may be considered as a granite. Neighbourhood of Herrnhut in Saxony. . protoxide LEPTYNITE NOIR. (Fr.) I of iron. Tenig in Saxony. (/) SPOTTED GRANULITE. ) "With dark spots caused by horn- GEFLECKTER oder FORELLKN- f blende. Glocknitzer Schlossberg, ORAKUZ^T. (Germ.) ) Wiener Neustadt. (0) SCHORLACEOUS GRANULITE. ] With considerable quantity TOURMALINGRANULIT. (Germ.) [ o f 8C horl in its composition. ) W of *) Ac LEPTYNITE TOURMAJJMFERE. (Fr.) T TT ') According to v. Hochstetter, it occurs near Krummau in Bohemia, Granulite is usually of very regular tabular-jointed structure, disposed parallel to the foliation or lamination of the rock ; but besides this more or less horizontal jointing, it is also usually intersected at right angles by cross joints, somewhat crooked, but whose surfaces are smooth. This latter jointing is characteristic of granulite, which by its means may sometimes be distinguished from gneiss at a considerable distance. In Saxony, Bohemia, and Moravia, this rock fills con- siderable regions of elliptical shape, surrounded by other 232 CRYSTALLINE SCHISTS. crystalline schists. The granulite region of Mittweida in Saxony is surrounded and overlayed with mica-schist and dichroite-gneiss, of which latter it contains large frag- ments. It is also penetrated in all directions by numerous often very distinct, but narrow dykes or veins of granite. JSTaumann considers this region to be of eruptive origin. Metamorphic rocks may possibly in some cases have become eruptive here. References. JEnyelbrecht, Kurze Beschreibung des Weisssteins, 1802. Weiss, Neue Schriften naturf. Freunde in Berlin, vol. iv. p. 350. fforniff, Analysen des Kremser Granulits, in den Sitzimgs- berichten der k. k. Akademie zu Wien, 1851, vol. vii. p. 586. v. Hochstetter, Granulit von Krummau, in Jahrb. d. geol. Reichsanst. 1854, vol. v. p. 11, and the Corresp.-Bl. d. geol. mineral. Ver. zu Eegensburg, 1853, p. 157. Naumann, in Erlauter. z. geogn. Karte v. Sachsen, No. 1, p. 9, and 1838, No. 2, p. 19 ; Karsten's Archiv, 1832, vol. v. p. 393, and Jahrb. d. geol. Reichsanst. 1856, p. 766. Zirkel, Granulit-analysen, in Poggendorff's Annalen, vol. cxxii. p. 624. 22. GNEISS. GNEISS, GNEUSS. (Germ.} GNEISS. (Fr.) A crystalline-granular compound of quartz, felspar, and mica; texture foliated. Spec. grav. . . . * . 2-6 27 Contains silica 64 76 p. c. The mineral composition of gneiss is precisely the same as that of granite ; the only petrographic difference be- tween the two rocks consists in the foliated texture of the former. We may, therefore, say that gneiss is the name given to schistose granite. The term gneiss originated with the Freiberg miners, who from ancient times have used it to designate the rock in which their veins of silver ore were found, and more especially such parts of the rock as were much decomposed. The felspar of gneiss is usually orthoclase, sometimes with oligoclase, and perhaps even albite. The orthoclase is white, grey, yellow, or reddish, and on fresh cleavage surfaces has mother-of-pearl lustre. Usually it occurs FELSPAR GROUP. 233 only in small grains, sometimes larger crystals or lentil- shaped masses so called, swellings or eyes (Schwielen, Augen), with the regular twin growth peculiar to ortho- clase (porphyritic gneiss, augen-gneiss). The oligoclase which occurs with and subordinate to the orthoclase or (more rarely) as its substitute may usually be recognised by its twin stripings, more resinous lustre, or more advanced decomposition. The quartz forms small white or grey lentil-shaped grains or irregular excrescences upon the felspar ; more- over it often appears in separate larger and irregular masses. The mica is usually potash-mica (more rarely magnesia- mica), brown, black, white, or dark-green ; and some- times in the same gneiss different coloured micas occur together. Gneiss occasionally contains accessory ingredients of various kinds, such as chlorite, talc, graphite, micaceous iron, dichroite, garnet, tourmaline, andalusite, pistacite, zircon, disthene, rutile, titanite, pyrites, magnetic iron- ore, &c. Sometimes one or other of these minerals is abundant, and assume the character of an essential ingredient ; thus, for instance, the prevalence of hornblende occasions a tran- sition from ordinary gneiss into syenite-gneiss, the presence of chlorite or talc into protogine-gneiss, &c. These different varieties in composition are easy of recognition. It is more difficult in many cases to recognise the perhaps more important difference between the so-called ' red ' and * grey ' gneiss. It was formerly considered that all gneiss was of metamorphic origin, but it has of late years been established beyond a doubt that many kinds of gneiss are irruptive, and some geologists have gone so far as to regard all gneiss as of igneous origin. In the mining districts of the Erzgebirge it had been observed that the veins in the red varieties of gneiss were usually non-metalliferous, although within a short distance the same veins traversing grey gneiss were rich in ore. Previously to the year 1844, we ourselves had observed red gneiss of a distinctly eruptive character, forming veins in the grey gneiss, which latter is the prevalent rock of the mining districts of the Erzgebirge ; the result of 234 CRYSTALLINE SCHISTS. these observations we published in von Leonhard's Almanack. (Vide v. L. u. Br. Jahrb. 1844, p. 681.) Subsequently Professor Scheerer received a commission from the Saxon mining authorities, to analyse several kinds of gneiss, with a view to discover the cause of the superior richness of the metalliferous veins in the grey gneiss ; and he found amongst other chemical differences that the red gneiss usually, if not always, contained a considerably larger proportion of silica than the grey. Accordingly the gneiss of the Erzgebirge came to be divided into two principal classes of distinct mineralogical as well as chemical characters, termed respectively red gneiss and grey gneiss. The red gneiss is not, however, always to be easily dis- tinguished from the grey gneiss, as the colours of the two distinct classes do not in every case correspond with the names that have been given to them, and some so-called grey gneiss is of red colour, and vice versa ; and although in several instances the bedding of the red gneiss shows it to be of distinctly irruptive character, yet the bedding of both kinds of gneiss is frequently indistinct and un- certain, or might be capable of various interpretations, and therefore would not alone serve the purposes of litho- logical distinction. The recognised and only reliable distinction consists in the proportion of silica, only to be arrived at by chemical analysis of the rock. These con- siderations compel us, regardless of origin, to retain the usual classification for all gneissic rocks, and notwith- standing the irruptive character of some varieties, to treat them collectively in this place amongst the metamorphic rocks. We proceed to define these two principal classes of gneiss, and (to avoid attaching an undue importance to their mere colour) we propose the name of gneissite for the variety formerly known as the red gneiss : A. GNEISSITE, or RED GNEISS. (Rother Gneiss oder Gneissit. Germ.) The felspar of the compound appears to be always orthoclase, and to be the predominant in- gredient. The mica is always white, or at all events not dark-coloured, not abundant in quantity, but usually scattered through the mass in thin straight laminae. The rock contains 74 76 per cent, of silica. FELSPAR GROUP. 235 According to Scheerer,it is an acidic compound, a sesqui- silicate. Its extreme varieties are easily to be recognised, and may be better distinguished from the grey gneiss than gneiss from many varieties of granulite. Its felspar is usually reddish, exceptionally, however, white or greyish. In the Erzgebirge this gneissite is found in irregular tracts, and sometimes forming distinct dykes or veins in the ordinary gneiss, of which it frequently encloses frag- ments. We may therefore say that there it comports itself as an eruptive igneous rock towards the common gneiss, and geologically speaking should perhaps properly be considered a granite. But as its bedding is frequently indistinct and the character of single specimens is often not to be recognised with certainty, and as some kinds of gneissite may very possibly be of metamorphic origin, we cannot usefully separate it lithologically from every other gneiss by taking it out of the class of the crystalline schists. B. GREY GNEISS. (Grauer Gneiss. Germ.) The felspar of the compound is principally orthoclase, some- times, however, with the orthoclase some oligoclase or albite is associated. The mica is partly dark-coloured (ferruginous and more basic than that of the gneissite), it is moreover abundant, whence the rock usually assumes a dark or grey colour. The rock contains 64 67 per cent, of silica. According to Scheerer, it is a neutral silicate. The normal Freiberg variety is granular, scaly, and unevenly foliated. The felspar is usually white or grey, but some- times of a reddish colour. The mica is mostly dark- coloured, but some white. Mica occasionally occurs in the compound. Accordingly, the differences between these two normal varieties (the gneissite and the grey gneiss) may be stated as follows : Gneissite, or Red Gneiss. Content of silica, 74 76 p. c. Felspar orthoclase only. Mica in small quantity and li tervals large egg-shaped crystals of orthoclase (usually they are twin crystals, sometimes they are amorphous), round which the foliated texture bends itself with a wavy sweep. This is very characteristically developed near Schwartzenberg in the Erzgebirge, Kedwitz in the Fichtelgebirge. (c) STANGEL GNEISS, COARSELY FIBROUS GNEISS. I The ingredients STANGELGNEISS oder HOLZGNEISS. (Germ.) > are disposed in a fibrous manner towards one direction, so that a peculiar linear parallel conformation is produced. The stalks or fibres may consist of felspar and quartz, or of stripes of mica. In the extreme development of this texture a wood-like confor- mation is produced, which almost supersedes the schistose texture. Lippersdorf, Lengefeld, Weissenborn, and Weig- mannsdorf, near Freiberg, Saxony, Sonnenberg in Bohemia. (d) VERY FINE SLATY GNEISS | All the mineral parts small 5 the or SLATE-GNEISS. j- numerous parallel flakes of mica SCHIEPERGNEISS. (Germ.) j occasion very distinct slaty texture. In the cleavage, mica alone is usually seen. (e) VERY FINE-GRAINED, ALMOST ) With only indistinct foliated tex- COMPACT GNEISS. Y ture. Radegrube, near Freiberg, GNEISS A GRAINS FINS. (Fr.) J Radeberg, near Dresden. (/) LAGEN GNEISS. j Quartz and felspar on the one hand, and LAGENGNEISS. (Germ.) L the mica on the other, form thin parallel GNEISS RUBANE. (Fr.)] ^ mutuaJ Q y altera ating seams or layers, which, in the cross section, occasion a ribbon striping. (g) GRANITE-GNEISS or GRANITIC GNEISS. \ With very GRANTTGNEISS oder GRAXITAHNLICHER GNEISS. (Germ.) } granular and only indistinctly foliated texture, forming a transition state between gneiss and granite. Sageritz near Grossenhain, Boxdorf near Moritzburg, Brambach in the Voigtland, Hofles near Eiger. Naumann has collected into one class, under the name of ' CORNUBIATES,' several exceptional varieties of gneiss, some compact, or of very indistinctly compound texture, others of contorted foliated texture. They occur variously, usually as contact formations at the margins of more recent igneous rocks. Saussure called them ' PALAIOPETRE,' Boase ' PROTEOLITE.' Properly speaking they belong only geologically, and not pe- trographically to gneiss, and they can only be classed as gneiss where their position and bedding give them that character. FELSPAE GROUP. 239 Varieties in Composition. (ft) GRANULITE-GNEISS. \ With very little mica, and that usually GKAxcuKiNKiss. (Germ.)) white. Felspar predominates, and is often intimately combined with quartz. Always belongs to the gneissite or red gneiss. Grosswaltersdorf near Freiberg, Lauterbach near Marienberg, Mautern near Molk, Poppenreut near Miinchberg. Hochberg near Eger; and a variety with dark-coloured mica, Fahrnleiten, near the Schneeberg, in the Fichtelgebirge. (0 MICACEOUS GNEISS. | Forming a transition state into mica- GLIMMEROXEISS. (Germ.) } schist, with much mica, chiefly dark- coloured, and little felspar ; usually of a line foliated texture. Near Kabenau and Dippoldiswalde in Saxony, where it occurs between strata of ordinary gneiss ; also, in like manner, at Gastein in the Alps. (k) GM;ISS VKUV RICH IN QUARTZ, and going over into a kind of quartz-schist. (/) SYENITIC GNEISS. ] With characteristic admixture of horn- SYENITGNEISS. (Germ.) I blende. Neighbourhood of Aschaffen- Fichtelgebirge. (m) PROTOGINE-GNEISS. ] With chlorite or talc instead of mica. PROTOGINGNEISS. (Germ.) ^Oberhasli and Mont Blanc in the Alps. Fr.) )M tle Q oldber near Fichtelgebirge, a somewhat indistinct protogine-gneiss encloses fragments of clay-slate, and from this would appear to be of igneous (irruptive) character. (n) ADULARIA-GNEISS. \ With adularia in the place of the usual ADULARONEISS. (Germ.) \ orthoclase. Very widely spread in the Alps, e.g. St. Gotthard. (o) OLIGOCLASE-GNEISS. ^ With oligoclase in the place of ortho- OLIGOKLASGNEISS. (Germ.) \ c lase. According to v. Hochstetter, the lofty Adam's Peak of Ceylon (7,000ft.) consists of this rock. It contains many garnets, and is found in alternate layers with syenite-gneiss, granulite-gneiss, granulite, and hornblende-slate. (p) GNEISS WITH TWO KINDS OF MICA, white and black, occurs very frequently. Seerenbach near Tharand, Lauenstein in the Erz- gebirge, Steingriin near Eger. (q) DICHROITE-GNEISS. | With dichroite in the place of mica. DICHROITGNEISS. (Germ.) Found in the margin of the Saxon 0*1088 AVEC DlCHKOrTK g selburg. (r) MICACEOUS IRON GNEISS. | With micaceous iron instead of com- i-:.>KxLiMiaROKEi.7rm.) } mon m i ca . i n the southern Fichtel- gebirge. (a) GRAPHITE-GNEISS. \ With graphite in the place of the mica. &BU*puBM.(0*m);Neax Passau, on the Danube. (<) ALPIXITE. | Is a name given by Simler to a schistose com- ALP (6?i Simler ' [pound of quartz, 'felspar (oligoclase), and a j flaky green mineral, probably belonging to the mica species, but certainlv not chlorite or talc (liber die Petro- geneses. Berne, 1862). Very frequent in the Alps. 240 CRYSTALLINE SCHISTS. The above are the principal varieties of this very im- portant rock ; it would neither be possible nor desirable to enumerate every modification of differing texture and composition. Gneiss, in addition to those of its accessory ingredients which have been already mentioned, sometimes contains irregular concretions or minute veins of quartz, felspar, or a kind of granite resembling the graphic granite. The foliated texture of gneiss is a universal charac- teristic. Gneiss is also usually stratified or jointed in a direction parallel to its texture. At all events a divergence from this direction has not been hitherto observed. Be- sides this tabular jointing there is sometimes a tolerably regular oblique parallelopipedic jointing dividing the rock into irregular rhombs, two of whose faces correspond with the stratification of the rock. Gneiss is found in extensive regions in many mountain districts. The mountains which it forms are of very various shapes, according to the position and direction of the foliated texture. If this be horizontal then we have fiat undulating table-lands where valleys appear like cuts in the otherwise uniform surface. If, however, the bed- ding of the rock has been upheaved so that the parallel planes of the texture assume a vertical position, then it forms jagged alpine heights. Both the bedding and the texture are frequently very much contorted. Gneiss, wherever we can approximately determine its geological age, is found to be of high antiquity. It occurs with granite rocks usually lying above them, but often penetrated and traversed by them. The oldest sedi- mentary rocks usually overlie the gneiss, but there are some exceptions where, as in the Alps and the Fichtelge- birge, the gneiss is found uppermost ; these exceptions are capable of being explained by disturbances of the original bedding. References. Scheerer, Chemische Untersuclmiigen des Gneisses im Jahrb. d. k. sachs. Bergakademie z. Freiberg, 1858, p. 210, 1861, p. 252, 1862, p. 188 ; Berg- u. Hiittenm. Zeitung, 1861, p. 188 ; and v. L. u. Br. Jahrb. 1861, p. 613 ; Zeitsch. d. d. geol. Gesells. 1862; also separately published under the title of ' Die Gneusse des Erzgebirges.' QUARTZ GROUP. 241 Naumann, Erlauter. z. geogn. Karte v. Sachsen, No. 2, p. 265, and No. 5, p. 51. Cotta, Rother u. Grauer Gneiss, in v. L. u. Br. Jahrb. 1844, p. 681, and 1854, p. 39. Credner, Syenitgneiss, in v. L. u. Br. Jahrb. 1850, p. 549. Peters, Syenitgneiss, in Jahrb. d. geol. Reichsanst. 1853, p. 236. Kittel, Syenitgneiss, Umgegend v. Aschaffenburg, 1840, pp. 11 and 27. v. Rath, Gneiss in Graubiindten, Zeitschr. d. d. geol. Ges. 1858, p. 199. Fournet, Gneiss der Alpen, Me*m. sur la Ge*ol. de la part des Alpes, p. 29. Boose, Transact, of the Geol. Soc. of Cornwall, vol. vi. p. 390. Quincke, Schonfeld and Roscoe, Analysen in Ann. der Chem. u. Pharm. 1854, vol.xci. p. 306, and 1856, vol. xcix. p. 239 ; v. L. u. Br. Jahrb. 1855, p. 453. v. Hochstetter, Oligoklasgneiss, Novarra-Reise, 1861, Th. i. p. 324 CRYSTALLINE SCHISTS RICH IN QUARTZ. (Mica-schist, Quartz-schist, Itacolumite.) 23. MICA-SCHIST. GLIMMERSCHIEFER. (Germ.) MICASCHISTE, Brvngniart. (Fr.) A crystalline schistose compound of mica and quartz. Spec. grav. . . . V ; . 27 3-1 Contains silica . .. > . . ' 6982 p. c. Its texture is always foliated, but with many varieties of modification. Its composition varies between two ex- tremes ; one consisting almost entirely of mica, the other (quartz-schist) almost entirely of quartz. The mica is most usually the optically biaxial potash- mica, but sometimes dark magnesia-mica, damourite, or paragonite. Two different kinds of mica occasionally occur together in the same rock. Usually the laminae, whether large or small, all lie in planes approximately parallel to each other, and thereby occasion the foliated texture of the rock ; it is rare to find them in diverging directions. The mode in w^ich the mica and quartz are united is somewhat various. In those varieties which contain the most mica the small grains or lenticular particles of quartz usually lie hidden in it, and the rock appears almost exclusively to consist of mica. If the quantity of quartz be greater, then its larger lenticular masses are dis- tinctly prominent amongst the mica in a cross fracture of to 242 . CRYSTALLINE SCHISTS. the rock. Again, these lenticular bodies extend and are elongated into thin parallel layers of granular com- position, and sometimes themselves enclose small flakes of mica of divergent direction. Those varieties which are very rich in quartz consist almost entirely of that mineral, and only receive a foliated texture from the thin parallel layers of mica imbedded in the quartz. Sometimes (and even in varieties very rich in mica) in addition to the quartz contained in the main mass of the rock, irregularly swollen-shaped masses and veins of quartz occur, round which the foliated texture bends itself, or there are found actual seams of quartz in the rock. Garnets frequently occur in such abundance as to be characteristic for certain varieties. They are red or brown, and occur porphyritically as isolated crystals, un- usually rhombic dodecahedrons, from the size of a scarcely visible grain to that of an apple. In each individual rock, however, these are usually nearly of a uniform size. The flakes of mica bend round these crystals as if they had been pushed on one side during the process of their formation. Near Fahlun, in Sweden, there is a magnesian variety of mica-schist containing very large dodecahedrons of garnet, which are sometimes split into two parts which have become joined together again in a displaced position. Mica-schist also frequently contains some or other of the following as accessory ingredients : schorl, staurolite, disthene,andalusite, hornblende, chiastolite, beryl, chlorite, talc, and felspar less frequently, also graphite, micaceous iron, cordierite, pyrites, or cinnabar, &c. Some of these accessory ingredients are characteristic for certain varieties of mica-schist, and they also occasion transitions from mica-schist into other rocks. Thus the presence of chlorite occasions a transition into chlorite- schist,of talc into talc-schist, of felspar into gneiss, of schorl into schorl-schist, of graphite into graphite-schist, of mi- caceous iron into ferruginous mica-schist. If the mass becomes compact, and especially if the mica should be- come indistinctly blended with the other ingredients, then the rock passes over into argillaceous mica-schist, and finally into clay-slate, so that we have thus a complete series of transitions from the most distinct gneiss through mica- schist into clay-slate. But we know of no transition from QUARTZ GROUP. 243 mica-schist into the granular greisen, although the com- position of those two rocks is mineralogically the same. Varieties in Texture. (a) COMMON MICA-SCHIST. \ Somewhat unevenly fo- GEMEINEH GLIMMBBSCHIEFER. (SCHTTPPEN- f liated, of a scaly ap- GLIMMKKM-HIKFEU.) (Germ.) .,1 V r , MICASCHISI-E COMMUN ou NORMAL, (Fr.) J pearauce with very much mica, but the quartz nevertheless distinct. Of very frequent occurrence. (6) MICA-SCHIST, VERY FINE AND] EVEN IN TEXTURE. Y Also frequent. PLANGLIMMERSCHIEFER. (Germ.) ) (c) MICA-SCHIST OF WAVY TEXTURE. ) A delicate wave-like tex- FAI/TENGLIMMERSCHIEFER. (Germ.) L ture. occasions a very dis- J tine? linear parallelism. Sometimes there occur larger and more irregular foldings, windings, and contortions of the texture, but these are fre- quently very parallel in their main direction. E. g. at Schwarz- enbach, near Hof in the Fichtelgebirge. (d) MICA-SCHIST WITH WOOD-LIKE OR \ Or as if the different par- COARSELY FIBROUS TEXTURE. I tides had been elongated GEOTRECKTER GLIMMERSCHIEFER oder f by stretchino- This pe- HOLZGUMMERSCHIEFER. (Germ.) J c il iar textlire is caused by a special conformation of the quartz stripped into thin and long strips or stalks. (e) MICA-SCHIST WITH CONTORTED AND \ The disturbances of the IRREGULAR TEXTURE. I parallel texture are partly VKUWORREXSCHIEFRIGER oder WULST- r occasioned by external GLIMMKUSCIUEKER. (Germ.) ,. , J ,, 1 TEXTURE FROISSEE ou PUSSES (Fr.)) forces, and partly by many tuberous swellings of the quartz contained in the rock. Very frequent. (/) STRATIFIED MICA-SCHIST. j. Thin seams of mica with slaty LAGBNGLIMMERSCHIEFER. (Germ.* cleavage, alternate with fine- grained layers of quartz, in which last are sometimes dissemi- nated flakes of mica not parallel to the stratification. This rock is very characteristically developed near Eger, in Bohemia, and between Korbach and Gefrees in the Fichtelgebirge. (y) MICA-SCHIST OF KNOTTY TEXTURE. I Small nodules or concre- KjfOTENGLiMMERscHiEFER, (Germ.) > tions pervade the mass and occasion a knotty texture, disturbing the otherwise parallel layers of the mica. Occurs in the Fichtelgebirge, between "W alpenreuth and Hiihnerhof. Varieties in Composition. (A) GARNETIFEROUS MICA-SCHIST. \ Rich in garnets. Ofveryfre- (iHANATGLIMMERSCHIEFER. (Germ.) f nll - nf n^n-rpn-p MlCASCHIOTE GRENATIFERE. (Fr.) I ^^^ OCCUirCnCC. (t) GNEISSIC MICA-SCHIST. I With some felspar in the GNEIBSGUMIDJRSCHIEFER. (Germ.)> compound; forms a transition state between gneiss and mica-schist. Frequent in the Erzge- birge. R 2 244 CRYSTALLINE SCHISTS. (K) CHLORITIC MICA-SCHIST. ] With some admixture of chlo- CHLORITGLIMMERSCHIEFER. (Germ.) r rite ; forms a transition into MICASCHISTE AVEC CHLOMTE. (Fr.) c hlorite-schist. Frequent in (/) TALCOSE MICA-SCHIST. ) With an admixture of some talc; TALKGLIMMERSCHIEFER. (Germ.) \ forms a transition into talc- MICASCHISTE AVEC TALC. (Fr.) j sc hi s t. Occurs in the Alps, (m) MICA-SCHIST WITH TWO KINDS or MICA (dark and light- coloured). Zschopau in Saxony. () GRAPHITIC MICA-SCHIST. \ With admixture of graphite ; GRAPHITGLIMMERSCHIEFER. (Germ.) r forms a transition into gra- MlCASCHISTE AVEC GRAPHITE. (Fr.) ' 1 (o) MICACEOUS IRON-SCHIST. \ Forms a transition into ElSENGLIMMERHALTIGER GlJMMERSCHIEFER. f femiginOUS Schist. (Germ.) ) (p) SCHORLACEOUS MICA-SCHIST. ] Forming a transition into SCHORLGLIMMERSCHIEFER. (Germ.) I schorl-schist. Eibenstock MICASCHISTE AVEC TOURMALINE. (Fr.)) in S axonv> (q) HORNBLENDIC MICA-SCHIST. } Forming a transition into HORNBLENDEGLIMMERSCHIEFER. (Germ.) I hornblende-schist. E. g. MICASCHISTE AVEC HORNBLENDE. (Fr.) J between Goldmiihl and Brandholz, near Berneck in the Fichtelgehirge. QTJARTZOSE MICA-SCHIST, forming a transition into quartz-schist. CALCAREOUS MICA-SCHIST. \ This is either a granular lime- KALKGLIMMERSCHIEFER, BLAU- [ stone, very rich in mica, and SCHIEFER. (Germ.) ) therefore of fissile texture (ci- polline), as it, for instance, occurs in the limestone beds in the neighbourhood of Zaunhaus in the Erzgebirge, or it is a rock composed of thin alternate layers of mica-schist and granular limestone, as is frequently found in the Eastern Alps. The following varieties differ in the species of their mica : (t) PARAGONITE-SCHIST. j The name given by Schafthautl PARAGONTTSCHIEFER, Schafthautl. j to certain mica-schist of the Alps (Germ.) n -^r^j^ -j^g ordinar mica is replaced by paragonite or damourite. To this belongs, e. g., the beautiful variety found at St. Gotthard, and is distinguished by its containing many cyanites and staurolites. (u) AMPHILOGITE-SCHIST. ) The name given by Schaft- AMPHILOGITSCHIEFER, Schafthautl. r hautl to the delicate 'flaky and (Germ.) somewhat greenish-white mica- slate of Zillerthal in the Tyrol, which only contains 40 p. c. silica. (v) NACRITIDE. j The name given by Schill to a schist oc- NACRITID, Schill. j curring at Pike's Peak in Kansas, consisting (Germ.) Q f q uar ^ z ^fo bi ac k an( j w hite mica. Per- haps it is the same as the Saxon variety described ante (m) . Mica-schist is usually more or less stratified or laminated independently of and more or less parallel to its schistose QUARTZ GROUP. 245 or foliated texture. Sometimes many different varieties alternate and are stratified in thin beds or layers one above the other. Mica-schist is extensively developed in many mountain districts, and there it is usually accompanied by gneiss or talc, and chlorite-schist ; it frequently also contains sub- ordinate intermediate layers of quartz-schist, hornblende- schist, granular limestone, or dolomite, ironstone, or even graphite. The distinctly sedimentary formations usually overlie the mica-schist, but to this rule there are excep- tions, as in the case of gneiss. From its bedding and the rocks with which it is usually associated, we must con- clude that mica-schist has chiefly been formed by trans- mutation from very ancient argillaceous and arenaceous deposits. During this process the quartz has undergone the least change, the clay has for the most part become mica, the superfluous substances in the sedimentary rock appearing, as accessory minerals in the mica-schist. A clay-slate very poor in quartz might produce a mica- schist very rich in mica ; and a clay-slate very rich in quartz (or very sandy) might produce a mica-schist very rich in quartz. An argillaceous sandstone might perhaps produce that variety of mica-schist which forms a tran- sition into quartz-schist. If the original rock contained lime, then garnet, hornblende, and other minerals might also be formed. If the original rock contained subordi- nate strata or layers of limestone, ironstone, coal, or the like, these would be changed into granular limestone, ferruginous mica-schist, graphite, &c. We must assume that these processes of transmutation have always taken place deep in the earth under the influence of great pressure, high temperature, and per- haps that they have been aided by the presence of water in other words, that they were plutonic or hydro- plutonic processes. If there were sufficient alkali in the argillaceous deposit, or if alkalies happened to be within reach (possibly in a state of solution), then gneiss and not mica-schist would be the result. If these hypotheses are well founded, they explain the possible mode of formation of some mica-schists, which appear to be of considerably more recent origin than the greater part of those rocks. The process of transmutation may have been hastened in 246 , CRYSTALLINE SCHISTS. these exceptional cases by an extraordinary degree of pressure. Cases of this kind are met with in the Alps, where between strata of mica-schist certain beds of a sandy calcareous composition occur containing distinct remains of Belemnites. Although mica-schist has been very frequently analysed and described, there are but few treatises which make it their principal subject. The following describe certain special forms of this rock. References. Beudant and Naumann (the former in Hungary, the latter in Scandinavia) have both observed apparent pebbles of quartz in mica-schist a circumstance which forcibly suggests a me- chanical origin (Naumann's Geognosie, 2nd. ed. vol. i. p. 527, Anm.). We have also ourselves observed distinct pebbles of quartz in beds of limestone lying between parallel beds of mica-schist at Jakobeni in the Bukowina. Jahrb. d. geol. Keichsanst. 1855, p. 7. Schqfthautl, on the peculiar varieties of the Alps, Ann. d. Chem. u. Pharm. 1843, p. 733. (Schonfeld and Roscoe, ibid. 1854, vol. xci. p. 305.) Schittj on Nacritide, Ann. d. Chern. u. Pharm. 1857, vol. ciii. p. 119. 24. QUAKTZ-SCHIST. QUARZSCHIEFEE. (Germ.) QUARTZ SCHISTEUX. (-Fr.) A rock chiefly consisting of quartz, but usually contain- ing some mica. We regard this rock as more or less belonging to the mica-schists. It is found to pass over into genuine mica- schist through the transition grade of quartzose mica-schist. Mineralogically, this rock has greater affinity to the siliceous or quartz rocks. Geologically, however, it undoubtedly belongs to the metamorphic crystalline schists, with which it is usually interstratified in parallel but subordinate beds ; and, like the other crystalline schists, appears to have originated in metamorphosis of sedimentary rocks (probably sandstone). We ought, perhaps, on the same principle to include some other rocks in the metamorphic series (granular limestone, for instance) ; calcspar, however, does not oc- cur as an essential ingredient of any crystalline schists, whereas quartz is contained in most, and we must con- QUAETZ GROUP. 247 stantly remind our readers that a logically consistent system of classification is impossible with rocks. We shall again allude to this rock under the head of quartz rocks, No. 69 post. Varieties in Texture, (a) COMMON QUARTZ-SCHIST. \ Consists principally of com- CKMKINBB QUARZSCHIEFER. (Oerm.) [ pac t imperfectly - foliated QUAIO* scm^x COMMUN. (/v.) ) U it 'e qua rtz, containing only little mica; sometimes with very distinct parallel elongations. Occurs in the gneiss of Freiberg. (6) GRANULAR QUARTZ-SCHIST, j Fine-grained, resembling sand- or QUARTZITE. I stone. QPARZIT. (Germ.) Jukes says, l Quartz rock or > quartzite is a compact fine-grained but distinctly granular rock, very hard, frequently brittle, and often so divided by joints as to split in all directions into small angular, but more or less cuboidal, fragments. The colours are generally some shade of yellow, passing occasionally into red, and at other times into green. When examined with a lens it may be seen to be made of grains, which appear some- times as if they had been slightly fused together at their edges or surfaces, and sometimes as if imbedded in a purely siliceous cement. This cementation or semi-fusion of the grains shows at once that it is a sandstone which has been altered and in- durated by the action either of heat alone or of heat and water.' 25. ITACOLUMITE. ITAKOLUMIT. (Germ.) ITACOLUMITE. (Fr.) A fine-grained and at the same time schistose compound of quartz with some mica, talc, or chlorite. In thin plates it is sometimes flexible. This rock first received its name from Von Eschwege. Its principal mass consists of grains of quartz, and re- sembles a sandstone. The grains of quartz, however, are bound together by thin crystalline Iamina3 of mica, chlorite, or talc, and these often assume a parallel arrange- ment and form thin seams through the rock. Thus its foliated texture is occasioned, and the somewhat elastic properties of the mica, chlorite, or talc occasionally give a flexibility to thin layers or plates of the rock. But not all varieties of itacolumite are flexible. The prevailing colour of the rock is yellowish ; sometimes, however, it has a white-reddish or bluish-grey colour. As subordinate ingredients, there occur in it mica- 248 CKYSTALLINE SCHISTS. ceous iron, magnetic iron-ore, martite, native gold, and even diamond. The quartz also occurs locally in the form of rounded stones or pebbles enclosed in the rock's mass, showing clearly the mechanical arenaceous or con- glomeratic origin of the rock. If the specular or magnetic iron-ores occur in considerable quantity, then a transition takes place into ferruginous mica-schist or itabirite (vide post, No. 62 K) ; and if the quartz be altogether pre- dominant, into quartz-schist (No. 24). We may take it as proof of the variable character of this rock that it has received many different names. Alexander von Humboldt called it itacolumite or quartz chloriteux ; Clausen termed it gres rouge, micaschiste quartzeux, and gres itacolumite ; Von Martius, elastischer Sandstein (elastic sandstone), Quartz-schist and Gelenk- quarz (articulated quartz) ; Walchner, quartzose talc- schist ; Jacquemont, gres schisteux ; Shepard includes it under the head of mica-schist ; Tourney terms it quartz rock or the f quartz of the mica slate? and indicates that it may be a hornstone ; Yan Uxem even appears to have considered it in South Carolina as a variety of Greissen. Jukes describes Itacolumite as being a genuine un- altered sandstone, more or less micaceous like other sand- stones, but the mica in worn spangles, not in connected flakes. Varieties. (a) COMMON ITACOLTTMITE. \ Firm, not flexible, resembling a GEMEINER ITAKOLUMIT. (Germ.) L fi rm and somewhat fissile sand- ITACOLUMITE COMMTJN. (Fr.) ) (6) FLEXIBLE ITACOLUMITE. . Usually very fine-grained, and j? thin lars or Plates-very flexible. (c) CONGLOMERATIC ITACOLUMITE. , ^ , . , , , CONGLOMERATARTIGER ITAKOLUMIT. (Germ.)\ Enclosing rounded peb- ITACOLUMITE GRENu. (Fr.) ( bles of quartz. Yon Eschwege informs us that in the Brazils itaco- lumite forms whole systems of strata of great thickness, extending for several hundred miles in length. The mountain Itacolumi, near Villa Eica (5,400 feet high), consists almost entirely of this rock. Shepard and Lieber found it very extensively developed in North and South Carolina, where it generally lies between lime- CHLORITE, ETC., GROUP. 249 stone and clay-slate, and contains subordinate layers or beds of talc-schist, ferruginous mica-schist, itabirite, ca- tawbarite, and fine-grained limestone. Von Helmersen and Hofmann also found the rock in the Ural Moun- tains ; Von Eschwege in Portugal ; Schulz in Spain ; Gergens in the slate region of the Rhine. References. v. Eschwege. Beitr. z. Gebirgskunde von Brasilien, 1832, p. 174. O. Lieber, Gangstudien, vol. iii. p. 323. Shepard, Report of South Carolina, 1854. Schuh, Bullet, de la Soc. ge*ol. de la France, 1834, p. 416. Gergens, in v. L. u. Br. Jahrb. 1841, p. 566. Lucas (as early as 1815) found diamonds in it in the Brazils. Nouveau dictionnaire d'hist. nat., art. Diamant. The same fact was confirmed by Heusser and Claraz, in the Zeitschr. d. d. geol. Ges. 1859, vol. xi. p. 448. r. Hnmboldt. Gisement des Roches dans les deux Hemispheres. p. 89. v. Martius, Reise in Brasilien, vol. ii. Clausen, Bullet, de 1'Acad. de Bruxelles, 1841. Walchner, Handbuch d. Geognosie, p. 38. Tourney, Report on the Geology of South Carolina, 1848, p. 6. Jacquemont, Voyage dans 1'Inde. CHLORITE, TALC, AND HORNBLENDE GROUP. These rocks have been severally termed Chlorite-schist, Talc-schist, and Hornblende-schist, from the prevalence of those respective minerals in their composition. In their chemical composition they resemble the basic rather than the acidic igneous rocks ; that is, they contain more magnesia and lime, and, for the most part, less silica than the acidic rocks. They occur as subordinate beds in the mica-schist, or they entirely take the place of mica-schist in some for- mations. Serpentine might also be included in this group, by reason of its chemical and frequently also its geological character. Nevertheless, inasmuch as serpentine often occurs under other and very different geological rela- tions (appearing as the product of igneous rocks), we prefer to class that rock separately amongst the special rock formations. By introducing this group of rocks between the mica- schists and the argillaceous mica-schists, we interrupt a 250 CRYSTALLINE SCHISTS. connected series of transition between those two groups, but such interruption only represents similar inter- ruptions actually occurring in nature. 26. CHLOKITE-SCHIST and POTSl?ONE. CHLORITSCHIEFER imd TOPFSTEIN. (Germ.) SCHISTE CHLORITIQTJE. (Fr.} A schistose aggregate of chlorite, usually combined with quartz, sometimes also with felspar, mica, and talc. It has a greenish colour and scaly appearance. Spec. grav. . ? ',''- ~- . r V 2-7 2-8 Contains silica V . \ /. * ' 31 42 p. c. The principal mass of this rock is composed of chlorite of green or blackish-green colour and greyish-green streak. It is usually of coarsely foliated texture and soft. The quartz sometimes transfuses the whole mass, and so makes the rock hard ; sometimes it only occurs in the form of thin scattered lamina?, lenticular or irregular swellings ; sometimes again it traverses the rock in thin veins. Felspar, mica, or talc are only occasionally to be distinctly recognised as ingredients ; many other minerals are, however, found as accessories, and often in very per- fectly formed crystals ; the most frequent of these are mag- netic iron-ore, garnet, talcspar, actinolite, and tourmaline. This rock forms transitions into talc-schist, protogine gneiss, mica-schist, clay -mica-schist, and slaty serpentine, and it often lies in alternate strata with these rocks. It is widely spread in the central chain of the Alps, is very characteristically developed in the Fichtelgebirge, near Schwarzbach, Wiersberg, &c., and also in the Eastern Carpathians. It very often contains subordinate beds or layers of magnetic iron-ore, ferruginous mica-schist, copper and iron pyrites, granular limestone, quartz, &c. It is usually very distinctly stratified. Chlorite-schist can scarcely be divided into separate varieties, which have not found a place under other heads, but some analogous rocks may be annexed to it, and may almost take the place of varieties. (a) THE CHLORITE-SCHIST OF HARTHATT (near Chemnitz). The principal mass of this rock consists of an imperfectly foliated chlorite-schist of dark-green colour, traversed by many layers and veins of quartz. Numerous very distinct yellow spots appear CHLORITE, ETC., GROUP. 251 prominently arranged in certain zones. These were for a long time taken to be flakes of talc. A. Knop has, however, ana- lysed this rock more narrowly, and discovered that the spots do not consist of talc, but mostly of a yellowish-green micaceous substance, a kind of pinite, which, however, itself appears to be a product of transmutation from oligoclase (or labra- dorite), and in many places has preserved its crystalline form and distinct cleavage. Strange to say, these felspar crystals, in the process of their transmutation into aggregates of mica, have even changed their outward shape, and accommodated themselves somewhat to the foliated texture of the rock. This rock frequently contains some pyrites, brownspar, and titanic iron as accessories/ It divides into plates or wood-like fibres. It forms subordinate beds in the clay-mica-schist of the same district. ^ (6) CHLORITOID SCHIST is the name given by Hunt to a certain dark-coloured schist, very extensively developed in Canada, principally consisting of chloritoid, a mineral closely allied to chlorite, and also to ottrelite. (c) POTSTONE. \ Consists of a felt-like web of chlorite ; LAVKZOTEIN, it is only rarely foliated. Specific gra- I vity, 2-8 (?) ; content of silfca, 30-60 ) p. c. (?) The mass is greenish-grey to blackish ; its streak greenish-white. It is soft, sectile, and quite infusible. It sometimes contains mica, calcspar, dolo- mite, and magnetic iron-ore or iron pyrites scattered through its mass, and hence it sometimes effervesces on the applica- tion of acid. In fire it loses 7'21 per cent, of its weight, pro- bably in consequence of the large quantity of water which it contains (sometimes as much as 11 per cent/). This rock is easily manufactured into firebricks and fire- proof utensils. It is found in very characteristic form in the Alps, together with serpentine as a subordinate stratum in chlorite-schist, and it forms transition states into serpentine Chiavenna, Drontheim in Norway (?), Boston in Massachusetts, Potton in Canada. References. Varrentrapp, Poggend. Annalen, 1849, vol. xlviii. p. 189. Knop, Progr. der Chemnitzer Gewerbschule, 1856. (?) Neues Jahrb. f. Min. 1863, p. 808. finish, on Chloritoid Slate, v. Leonhard's Jahrbuch, 1861, p. 574. Delesse (Potstone), Bullet, de la Soc. ge*oL de France, 1857, [2] vol. xiv. p. 281. Studer (Potstone), Bibl. univers. de Geneve, 1856, [4] p. 213. 27. TALC-SCHIST. TALKSCHIEFER. (Germ.) TALCSCHISTE (STEASCHISTE, Brongniarf). (jFV.) A schistose aggregate of talc, usually combined with some quartz or sometimes with felspar, yellowish or greenish colour and soft greasy feel. 252 CRYSTALLINE SCHISTS. Spec, grav 2-62-8 Contains silica 50 57 p. c. ; at Zebernick, in Hungary, only 27-6 j at Hinterbriihl, even 62-1. The principal mass of these rocks consists of talc, of light-yellow, yellowish-green, or greenish-grey colour, with a mother-of-pearl varying to resinous lustre. As it contains less silica than the mineral talc (which has 64 per cent.), we may infer that some chlorite enters into its composition. It contains little quartz ; and only in grains, flat lenti- cular particles, laminae, or irregularly shaped masses, or irregular veins, all subordinate as to size and quantity. Felspar is only to be seen in delicate particles scattered here and there ; it is not more frequent than several of the following accessory minerals : chlorite, mica, talcspar, garnet, actinolite, asbestos, magnetic iron-ore, and iron pyrites. This rock forms transitions into chlorite-schist, clay-slate, mica-schist, and protogine-gneiss. Varieties, (a) COMMON TALC-SCHIST. ] Not unusual in the Alps. At GEMEINER TALKSCHIEFER. (Germ.) [ Ochsenkopf, near Schwarzen- TAX.CSCHISTE COMHUN. (Fr.) j berg ^ the Erzgebirge, a variety (with corundum) occurs imbedded between strata of mica-schist. (6) LISTWENITE is the name which has been given to a variety in the Ural Mountains, which contains much quartz combined with talcspar or calcspar, and from that combination assumes a somewhat granular slaty texture. The same rock, at Bere- sowsk is displaced and penetrated by veins of Beresite, which are again penetrated with quartz veins containing some gold. (c) DOLERINE is the name given by Jurine to a talc-schist with es- sential ingredients of felspar and chlorite, and according to Favre this rock is extensively spread in the Pennine Alps. Talc-schist is almost always stratified, and forms alter- nating beds with other crystalline schists. References. G. Rose, on Liswanit, Reise n. d. Ural, vol. ii. p. 537. Jurine, on Dolerine, in the Journ. des Mines, vol. xix. p. 374. Favre, on Dolerine, in v. L. u. Br. Jahrb. 1849, p. 41. Scheerer, Analyse des Talksch. von Fahlun, in Poggend. Ann. 1851, vol. Ixxxiv. p. 345. Richter, Anal. d. Talksch. von Gastein, in Poggend. Amu 1851, vol. Ixxxiv. p. 368. CHLORITE, ETC., GROUP. 253 Ferjentsik, Anal d. Talksch. v. Zebernick, in Jahrb. d. geol. Reichsanst. 1856, p. 807. Raysky, Anal. d. Talksch. v. Hinterbriinl, in Jahrb. d. geol. Reichsanst. 1854, p. 642. 28. HORNBLENDE-SCHIST and HORNBLENDE ROCK. HORNBLENDESCHIEFER und HORNBLENDEFELS, AMPHIBOLTT. (Germ.) SCHISTE AMPHIBOLIQUE et AMPHIBOLITHE, Brvngniart. (Fr.) A schistose or fine-grained to compact rock, consisting chiefly of hornblende, combined with small quantities of felspar, quartz, or brown mica. Always dark-green to black. Spec, gray , 3 3'1 Contains silica ..... 48 54 p. c. This rock is most usually of foliated texture. Its prin- cipal mass is granular and sometimes also fibrous, and consists of common dark-green hornblende as its principal ingredient, with which some felspar, quartz, or mica is usually combined. If the latter are present in considerable quantity, then transitions take place into diorite (6), dio- rite-schist (No. 6 a), or syenite-gneiss (No. 22). As accessories there also occur garnet, pistacite, iron pyrites, magnetic iron-ore, &c. The varieties of prevailing schistose character are usu- ally imbedded between strata of other crystalline schists, to which they clearly belong, and into which they pass over by grades of transition. They also sometimes pass into rocks not of a fissile tex- ture, such as hardly can be classed with the argillaceous schists, and which may perhaps be of igneous (eruptive) origin, especially as they form transitions into diorite. Varieties of Texture. (a) HORNBLENDE-SCHIST. ] Usually thickly foliated, and at HoRNBLENDisscHiEFEB. (Germ.) L the same time fibrous : this tex- SCHIKTK AMPHXBOLXQUE. (Fr.) J ture being ^j^ V ^ pft _ rallel position of fibres of hornblende of various thickness. Quartz and felspar occur as a part of the compound of the principal rock, but also in nests or veins. This rock is often found (subordinate) in strata of gneiss, mica-schist, and <-lil< rite-schist ; e. jr., Miltitz, near Meissen, and the district of Munchberg in the Fichtelgebirge. 254 CEYSTALLINE SCHISTS. At Hanover in North America hornblende-schist is found, containing large dodecahedrons of garnet. (6) HORNBLENDE EocK. ] Without fissile texture. E. g. in HORNBLENDEFELS. (Germ.) \ the district of Hof in the Fichtel- AMPHIBO. ^ J gebirge. Variety in Composition. (c) ACTINOLITE-SCHIST. \ Chiefly consisting of actinolite, and STRAHLSTEIN oder ACTING- (therefore entirely fibrous, otherwise LITHSCHIEFER. (Germ.) f . , ,., , ,, J-. -. . , ' -^ J just like hornblende-schist. Found to the south of Oberwiesenthal in the Erzgebirge ; also at Clau- sen in the Tyrol. We might also include eklogite (No. 44) under this head, but as it is at least doubtful if its origin be that of the metamorphic schists, and as it belongs to the rocks of exceptional character, and by 'reason of its richness in garnets may be conveniently placed with the other garnet rocks, we have so classed it. References. Eischof's Geologie (1st edition) contains almost the only de- tailed account of hornblende-schist. See II. p. 130. On actinolite-schist, see Reuss in v. L. u. JBr. Jahrb. 1840, p. 41. SCHISTS INDISTINCTLY CRYSTALLINE. These form the connecting link between the extreme metamorphic crystalline schists (especially gneiss and the mica-schists) and the clay-slate and slate-clay rocks, which latter being much less changed are still distinctly sedimentary. We therefore term them argillaceous mica- schists. 29. ARGILLACEOUS MICA-SCHIST, PHYL- LITE. THONGLIMMERSCHIEFER, PHYLLIT, URTHONSCHIEFER. (Germ.} PHYLLADE, D'Aubuissoti. (Fr.} A schistose aggregate in which mica is usually to be recog- nised as the chief ingredient^ or in which the peculiar structure of mica rocks is apparent. Sometimes the whole mass appears homogeneous, differing only from clay-slate by its superior lustre. Spec, grav 2-62-8 Contains silica . . . . 45 74 p. c. Argillaceous mica-schist is but a transition state between ARGILLACEOUS MICA-SCHIST. 255 mica-schist and clay-slate, as is apparent from its passing over into both these rocks. We might term it an imperfect mica-schist or a very much transformed and somewhat crystallised clay-slate. Its chemical analysis also agrees with this definition. But its chemical composition varies as much as that of mica-schist or clay-slate. Its principal ingredients are always quartz and mica (or some mineral of the same character as mica), but the quantitative pro- portions of these ingredients are very different in different rocks. With these principal ingredients are associated chlorite, talc, felspar, hornblende, garnet, &c., which occa- sion transitions into chlorite-schist, talc-schist, hornblende- schist, and gneiss. The colour of these rocks is usually grey, greenish, or bluish-grey, but sometimes yellowish, reddish, brownish, and violet. Their lustre varies between the mother-of- pearl, the silky, and the half metallic. They always have a distinctly fissile texture, but not by any means a perfect cleavage. Sometimes they show fine parallel foldings, or sometimes there occurs a second fissile texture obliquely traversing the principal direction, occasioning a rough fibrous cleavage. When the slaty cleavage is perfect, it is usually not parallel to the stratification. In the apparently homogeneous principal mass, we dis- cover grains or irregular lenticular swellings or masses of quartz, or else veins of quartz or flakes of mica (or sericite), chlorite, talc, hornblende, felspar, chiastolite, andalusite, iron pyrites, magnetic iron-ore, or graphite. When these minerals are considerable in quantity, there arise varieties in composition. But these varieties are not peculiar to this rock ; they are necessarily repeated in mica-schist, as well as in clay-slate. Varieties in Texture. (a) COMMON ARGILLACEOUS MICA-SCHIST. IKINKK THOXGLIMMERSCHIEFKR. (Germ.) PHYLLADB COMMUN (SATIXE). (Fr.) (6) FOLDED OR CONTORTED. I.IKTKR THOXGLIMMERSCHIEFER. (Germ,) (c) FIBROUS OR WOODY TEXTURE. HOLZARTIGER THOXGLIMMERSCHIEFER. (Germ.) (d) VERY MUCH CONTORTED. SKHR VERWORREX SCHIEFRIGER oder WULSTIGER THOXGLIMMERSCHIEFER. (Germ.) PUBSE, FROIS8E. (Fr.) 256 CRYSTALLINE SCHISTS. 0) NODULAR SCHIST. j Which we also enumerate below, as (} * a iet ? in comosition. a iet ? in compositi Varieties in Composition. (f) RICH IN MICA. \ Gu ?R. T So M ' Transition into mica-schist. MICACE. (/>.) Forms transitions into quartz. SCHIEFKR. (Germ.) schist. QTJARTZEUX. (A) CH CHZmscH E H THoxGUMMEB-l Fo n ? transitions into chloritic SCHIEFER. (Germ.) SChlStS. CHLORITIQUE. (Fr.) (t) TALCOSE. ) TALKIGER THONGLQIMER- I Forming a transition into talc-schist. SCHIEPER. (Germ.) TALQUEUX. (Fr.) (k) A VARIETY CONTAINING HORNBLENDE. HORNBLENDEHALTIGER THONGLIMMERSCHTKFER. (Germ.) (I) A VARIETY CONTAINING FELSPAR. x Form i nff a transition FELSPATHHALTIGERTHONGLIMMERSCHIEFER. I J (Germ.) j into gneiss. . (6?erm.) j into garnet-mica-schist. GRENATIFERE. (/V.) / (w) SERICITE-SCHIST. ] The name given by List to a variety SERICITSCHIEFER. (Germ.) Iwhose principal mass consists of seri- SCHISTEASERICITE. (j fr.)) cite ( green m i cace ous mineral, re- sembling damourite, with a silky lustre, see ante, p. 23), and which usually also contains quartz and felspar (albite according to List). The colour of this rock in the Taunus, where it is very extensively developed, is greenish with green and yellow spots, or violet. It is often penetrated by veins which contain quartz and albite. The very considerable quantity of alkalies which it contains, especially of potash, is remarkable. List further distinguishes three sub-varieties, according to their colour. (a) Violet, very soft, with thin slaty cleavage. Spec. grav. 2-88. (j8) Green, harder, with thick slaty cleavage (folded), with little albite, and a microscopic quantity of magnetic iron-ore. Spec. grav. 2-79. (y) Spotted, soft ; often decomposed j with much albite and quartz. Spec. grav. 2-68. (o) OTTRELITE-SCHIST. ] The principal mass foliated, and usually OTTRELITSCHIEFER. (Germ.) I grey. It contains greenish laminae of SCHISM loirsft. (/v.) Jott^^te. This variety is frequently found in the Ardennes. It has also been discovered by Giim- bel in the district of Ebnat in Bavaria. (p) CHIASTOLITE-SCHIST. \ The mass is slaty, and usually CHIASTOUTHSCHIEFER. (Germ.) ( dark-coloured. It contains many SCHISTE MACI^ERE. (Fr.) j crygtals of cMastolite disseminated ARGILLACEOUS MICA-SCHIST. 257 through it in the most opposite directions. The chiastolite- schist (which also forms a variety of clay-slate) is found on the contact margins of plutonic igneous rocks, e. g. next to irranite. Near Gefrees in the Fichtelgebirge. Also abundant about Skiddaw, Cumberland. (q) No DULAR or SPOTTED SCHIST. \ This schist contains small con- KNOTENSCHIEFER, FLECK- oder cretions of different structure, ScHS C xo^SS R ou ((7 ^^. hardness, and colour to that of (Fr.) J the general mass. They are, for the most part, harder and darker, and they either form small knots or only spots with indistinct margin ; sometimes they resemble the currants in a fruit-pudding, hence their different names. Their composition has not vet been determined with accuracy by the various mineralogical chemical analyses which they have undergone, according to which they have been suc- cessively taken for a kind of fahlunite, for hornblende, serpen- tine, chiastolite, or andalusite. It is very possible that at different places they are somewhat differently composed. In reference to their origin, it is of special interest that according to the careful investigations of Carius, the schist with nodules does not differ in the quality or proportionate quantity of its ingredients from the same schist without nodules farther re- moved from the contact, so that no new substance appears to have been added to form those concretions, but they appear rather to have arisen from a new arrangement of the previously existing ingredients. At the margin of the granite in the AVestern Erzgebirge and Voigtland, these nodular schists are very frequent, and are observed there just as much in the clay- mica-schist as in the ordinary clay-slate. A similar appearance occurs at Wechselburg in Saxony, in a rock which is decidedly mica-schist. (r) ALUM-SCHIST. \ This schist contains much carbon, and ALAUNSCHIEFER. (Germ.) I i s thereby rendered black. Pyrites is semen ALUMIXEUX. (Fr.) j alwayg mixed with it in fine particles, through whose decomposition alum and iron- vitriol are formed. In the case of this variety, we can only decide from the bedding whether it belongs to argillaceous mica-schist or tq clay-slate, for the carbon which it contains thoroughly oblite- rates the slender landmarks by which the difference might otherwise be established. It is characteristic of most of the alum-schists, that they are of very much contorted or displaced texture, and are frequently pervaded by irregular swollen- shaped fragments of quartz and lustrous but bent laminae (mica), and sometimes also lenticular concretions of bitu- minous limestone or anthraconite. lieichenbach in Voigtland. (s) CARBONACEOUS SCHIST, BLACK CHALK. ] In the case of this ZKICHNENSCHIKKER, SCHWARZE KREIDE. (Germ.) I yarietv verv rich in J carbon, we can only determine by its bedding whether it belongs to argillaceous mica-schist or to clay-slate. It is a quartzless and very soft slate, which, from admixture of carbon, is of a black colour, and also imparts a black streak, so that it may be used for S 258 CRYSTALLINE SCHISTS. drawing or writing. Ludwigstadt in the Thuringian Forest, where it belongs to clay-slate. All the above-mentioned varieties in composition are equally applicable to the ordinary clay-slate as to the argillaceous mica-schist, and we shall therefore have to enumerate them again when we come to consider that rock, but our previous descriptions will suffice for both. Argillaceous mica-schist is usually also distinctly stra- tified in addition to its foliated texture, which, as already said, is not parallel to the stratification ; otherwise, as to its bedding and extent, it exactly resembles mica-schist, with this only difference, that it more usually than that rock is interstratified with the oldest sedimentary and dis- tinctly fossiliferous rocks. By the name of argillaceous mica-schist we do but seek to establish a stage of transmutation between clay- slate proper and mica-schist. References. Frick, Pleischl, Sauvage, and Kjeridf have contributed various analyses to Poggend. Ann. 1835, vol. xxxv. p. 188 ; in the Journ. f. prakt. Chemie, 1844, vol. xxxi. p. 45 ; and 1855, vol. Ixv. p. 192. List, on Sericitschiefer, in the Jahrb. d. Vereins f. Naturk. in the Duchy of Nassau, 1850, No. 6, p. 128. Lipold, on Sericitschiefer in the Alps, Jahrb. d. geol. Keichs- anst. 1854, pp. 201 and 359. Giimbel, on Ottrelitschiefer, inCorresp.-Bl. d. zool. mineral. Ver. z. Regensburg, 1853, p. 53, and on Phyllit, in the same, 1854, p. 12. Naumann, on Knotenschiefer, Erlauter. z. geogn. Karte v. Sach- sen, 1838, No. II. p. 264, and 1845, No. V. p. 50. Kersten, on Knotenschiefer, in Journ. f. prakt. Chemie, vol. xxxi. p. 108. Carius, on Knotenschiefer, in the Annalen d. Chemie. u. Pharm. 1855, vol. xciv. p. 45; and in v. L. u. Br. Jahrb. 1856, p. 595. Miiller, on Knotenschiefer, in the Berg- u. Hiittenm. Zeitung, 1858, p. 107. Durocher, on Chiastolith and Knotenschiefer, in Bullet, de la Soc. geol. de la France, 1846, vol. iii. p. 546. 259 CHAPTER III. SEDIMENTARY AND FRAGMENTAL ROCKS. ALL sedimentary rocks are stratified ; or at least, their beds lie one above the other in parallel planes. The greater part consists of the debris of older rocks mechani- cally washed together and deposited from a state of sus- pension in water. A few only are the result of chemical precipitate of mineral substances. Many contain organic remains (fossils) more or less distinct ; some consist entirely of such. As a consequence of their origin, the sedimentary rocks are rarely of genuine crystalline conformation. Some, however, which appear to be actual chemical precipitates from aqueous solutions, such as gypsum and rock-salt, usually possess a crystalline structure. Following the different origin of these rocks, we may divide them into (a) Mechanical deposits. (b) Chemical precipitates. (c) Rocks resulting from organic processes. (a) Phytogenic, caused by the accumulation of vege- table matter. ($) Zoogenic, caused by the accumulation of animal remains. The minerals which chiefly predominate in sedimentary rocks are not the same as those which are most abundant in the igneous and the metamorphic rocks. We find in the sedimentary rocks little or no felspar, hornblende, or pyroxene. The following are those which occur with greatest frequency : Quartz, which in general terms we may call the most abundant mineral of the earth ; clay (itself, however, a compound rather than a distinct mine- ral) ; carbonates of lime and magnesia, as calcspar (lime- stone) and dolomite ; sulphate of lime, as gypsum and anhydrite ; chloride of sodium, as rock-salt ; finally, coal and iron-ores. Gypsum (or anhydrite), salt, coal, and iron, usually form distinct and separate beds of comparatively small 8 2 260 SEDIMENTARY ROCKS. extent : the principal and most important sedimentary rocks are composed chiefly of the first-named of the above minerals, quartz, clay, and carbonate of lime (or magne- sia). They may be accordingly divided into argillaceous rocks, calcareous rocks, and quartzose rocks. The marl rocks occupy an intermediate place between the calca- reous and argillaceous. The quartzose rocks may be divided into the arenaceous or sandstones, and the con- glomerates, to which we may add certain other fragmental rocks containing less quartz, usually termed tufa or tuff. The material for all these several rocks was mostly derived from the disintegration of more ancient previously existing rocks. The igneous rocks, by the decay of their felspar, hornblende, augite, and mica, have supplied the following substances towards the formation of the sedi- mentary rocks : argillaceous mud, and weak solutions of lime, magnesia, silica, potash, soda, oxide of iron; their quartz has furnished grains of sand ; in some cases their mica has remained undecomposed, and is found as mica in minute Iamina3 in the sedimentary rocks. The older sedimentary rocks have also in process of time be- come disintegrated, and have furnished similar materials to form the more recent, and every solid rock has at times furnished pebbles, and other fragments for the formation of conglomerates. The several sedimentary deposits have been divided into so-called formations, according to the order of their superposition, and consequently of their age, and these again have been gathered into groups, which answer to longer periods of deposit. It may therefore be useful here to present the following TABLE OF GEOLOGICAL PERIODS.* C Recent Formations of every kind. '^ | Mud, sand, gravel, calcareous and volcanic tuff, coral reefs, bog iron-ore, turf, peat, &c., guano, infusorial beds. Pleistocene) or Post-Pliocene Formation. Diluvial or glacial deposits, loam and breccias of bone- caverns, brick-earth and fluviatile loam or loess, valley gravels, bog iron-ore, calcareous tuff, coral-reefs, &c. ' 1! * In different countries these are somewhat differently divided and named. SEDIMENTARY ROCKS. 261 ENGLAND. Pleiocene Formations. Red and coralline crag. Miocene Formations. Absent in England. Eocene Formations. Fluvio-marine strata of Isle of Wight and Hampshire. Bagshot series. London clay and Bognor beds. Plastic clay or Woolwich and Reading beds. Thanetbeds. .f Cretaceous Formations. White chalk with flints. White chalk without flints. Chalk marl. Upper greensand. Gault. f Lower greensand or neocomian. \ Speeton clay. Wealden beds, weald clay, and Hastings sand. Oolitic or Jurassic Formations. Purbeck beds. Portland beds. Kimeridge clay. Coral rag. Oxford clay. Cornbrash. Forest marble and Great or Bath oolite. Fullers' earth. Inferior oolite. Upper lias sand and clay. Marlstone or middle lias. Lower lias clay and limestone. Triassic Formations. Penarth or Rhsetic beds. Dolomitic conglomerate. Red marls -with rock-salt and gypsum. White and brown sandstones (waterstones) . Red and mottled sandstones, pebble-beds of conglomerate. GERMANY. Aralo-Caspian deposits. Molasse formation of the Alps Tegel, near Vienna. Browncoal formation in North Germany. Nummuliten formation. Flysch formation. Maestricht beds. Turonien, quadersand, planer. Cenomanien. Albien, aptien. Hils-formation. Deister formation. White Jura. Lithographic slate of Solen- hofen. Brown Jura. Black Jura. Keuper. Koessen or Upper St. Cassian beds. Muschelkalk (absent in Eng- land. Buntsandstein. 262 SEDIMENTARY JIOCKS. ENGLAND. Dyas or Permian Formations. Red marls and magnesian limestone. Lower sandstone. Carboniferous Formations. Coal-measures. Millstone grit. Carboniferous limestone Lower limestone shale. GERMANY. Zechstein formation. Kupferschiefer. Rothliegendes. Steinkohlen formation. Flotzleerer sandstein. Kohlenkalkstein. Kohlen formation of Hai- nichen, or kulm. Devonian Formations {Old Red Sandstone). Dartmouth slate group. Plymouth group. Liskeard or Ashburton group. Old red sandstone. Cypridinenschiefer, or Kramenzelstein. Str5ngocephalen-Kalk. Calceolaschiefer. Spiriferen-Sandstein and Schiefer. Silurian Formations. Ludlow group "j Wenlock group > May hill group J Lower Llandovery beds 1 Caradoc sandstone and Bala beds I Llandeilo flags Lingula flags Cambrian Formations. Gritstone, sandstone, and slate, with few or no organic remains. Laurentian rocks of Canada and the north-west of Scotland. Below the sedimentary rocks are usually found the crystalline schists. The entire series of formations is, however, never to be found in any one locality. The mere geological age of deposit does not inform us of the nature of the rock, nor can we, on the other hand, from the petrographic character arrive at its geological age. Both attributes are to a certain extent independent of each other. No kind of rock is restricted to any particular period, and although there exist some very general differ- ences between the rocks of recent and ancient deposit, yet even these do not prevail universally. ARGILLACEOUS GROUP. 263 ARGILLACEOUS GROUP. The argillaceous rocks were originally nothing but sediments of clayey mud, with some admixture of fine quartz-sand, flakes of mica, hydrated oxide of iron, and organic remains. These materials, by a slow process of transmutation and mechanical consolidation, have ulti- mately become solid rocks, some of them carboniferous or bituminous. The principal rocks of this group are clay-slate, argilla- ceous shale, claystone, clay, and mud or silt (loess), with their several varieties. To these we must also add the marl rocks. To arrange these rocks according to the order of their origin and development, we should begin with the clay and loess, from which (perhaps by the simple agency of pressure) claystone, argillaceous shale, and clay-slate have been successively formed ; the several varieties of these rocks being occasioned by the accessory admixtures con- tained in the original compound. In the present treatise the order is inverted, and the metamorphic rocks having been already described, we most naturally pass first to those of the sedimentary rocks which are nearest to them, i. e., the most changed, taking the newer formations last. We cannot draw a sharp distinction between argilla- ceous mica-schist, clay-slate, and argillaceous shale, but the extreme or ideal development of each of these stages of transmutation has a marked character, distinct from the others. Characteristic argillaceous mica-schist is still somewhat crystalline ; clay-slate is not crystalline, and in fracture it is dull, but yet firm, and has a perfect slaty cleavage ; characteristic argillaceous shale, on the other hand, is soft or flexible, separates along the lamination instead of by slaty cleavage, and is more obviously an earthy aggregate. Argillaceous mica-schist frequently contains various crystalline accessory minerals, but genuine clay-slate much more rarely, and of fewer kinds ; argil- laceous shale at the most only occasionally contains some pyrites. 30. CLAY-SLATE. THONSCHIEFER. (Germ.} SCHISTE ARGILEUX, SCHISTE ARDOISIER. 264 SEDIMENTARY ROCKS. A compact fissile rock of a dull blue-grey ', bright red, purple, green, or black colour ; consists chiefly of clay ; sometimes with accessory admixtures of quartz, mica, and other minerals. The slaty cleavage is usually very perfect, and only occasionally coincides with the original lamination of the rock. Spec. grav. . '.'".' . ... . 2-52-8 Contains silica . . .- .. v . 40 75 The characteristic feature of clay-slate as distinguished .from other rocks of the argillaceous group is that its slaty cleavage, frequently very perfect, is altogether inde- pendent of its original bedding, although in some instances (which we may regard as accidental) it coincides with the original lamination. Whether this slaty cleavage is due to pressure, or to some agency resembling the crystallising force which has acted on smaller mineral masses, has been a subject of debate since the time of Sedgwick, who first called attention to this important phenomenon. It is a question which is still unsettled, and which must probably so remain for some time longer. Varieties in Texture. (a) COMMON CLAY-SLATE. ) With perfect or imperfect GEMEIXER THONSCHIEFER. (Germ.) L cleavage, very variously CO- SCHISTE ARGILEUX OOIUK. (Fr.) J loure( ^ ^ ^ ^ &c _ cessory minerals. It contains, e. g., quartz, in irregular masses (or swellings), or lenticular masses, or in veins ; pyrites, in crystals or nodules, &c. Sometimes its slaty cleavage is much distorted. It is very frequent in all districts of the transition period (greywacke) in Germany. (&) ROOFING SLATE. \ The name given to the purest DACHSCHIEFER und TAFEL- |_ varieties of clay-slate, whose cleav- SCHIEFER. ((rerm.) t* i t ,1 SCHISTE ARDOISIER, (Fr.) a g e is very perfect and smooth, ' allowing of their being split into very thin plates, which nevertheless retain a high degree of firmness and solidity. A dark- coloured variety, containing an admixture of carbon, is termed in Germany Tafelschiefer. Roofing slate, with a view to its fitness for the purpose its name indicates, should be free from accessory crystallised in- gredients. North Wales, Lehsten in the Thuringian Forest, &c. (c) PENCIL-SLATE, PINSILL \ A clay-slate of pure composition, or PENCIL. f soft, but withal firm; separated or * se P ara ^ le into pencils (the slaty clea- vage crossing the planes of lamina- tion), and used for writing on slate. Found in North Wales, Sonnerberg in the Thuringian Forest, and other slate districts. ARGILLACEOUS GROUP. 265 Varieties in Composition. (d) WHETSLATE, WHETSTONE, HONE/ OILSTONE, NOVACULITE. WETZSCHIEFER. Germ. SCHISTB 8IUCEUX (NOVACULAIRE), De Charpentier. (Fr.) This is a very highly sili- ceous clay-slate, perfectly compact and homogeneous. Usually only indistinctly of slaty cleavage, and its fracture often conchoidal and even splintery. Used for sharpen- ing knives and other instruments. E. g. Wales, Devonshire, Katzhiitte in the Thuringian Forest. 0) CARBONACEOUS CLAY-SLATE. ) Passes into alum-schist and Kon ( r SJ? ) CHER T 110 * 8011 11 - [ black chalk (Zeichnenschiefer), SCHISTE HOUILLER. (Fr.) ' see p. 257, ante. (/) ARENACEOUS CLAY-SLATE. ] Passes into argillaceous sand- SAXUIGER THOXSCHIEFER (GRAU- \ stone. Bv the Germans it WACKENSCHIETER). (Germ.) I j g frequ / ntly termed ^^ wacke-slate, from its occurrence in the transition or greywacke* formations. (g) MICACEOUS CLAY-SLATE. ) Differing from clay- <-,UMMERREICHER THoxscHUFER. (Germ.) \ mica-schist, in that the 8CHI8TE MICACE (PAILLKTE). (Fr.) dently only mechanically dispersed. This variety also passes in Germany under the name of greywacke"-slate. (A) CALCAREOUS CLAY-SLATE. ) Containing numerous lenti- KALKKXOTIGER THONSCHIEFER (KRA- L cular or irregular nodules j of limestone (which fre- quently owe their origin to fossils) j passes over into nodular limestone. The varieties which we have already described under the head of argillaceous mica-schist we find repeated in the clay-slate, and accordingly we have : chlorite-slate, talc-slate, sericite-slate, ottrelite-slate, chiastolite-slate, nodular and spotted or mottled slate, alum-slate, and carbonaceous slate. Clay-slates are usually very distinctly stratified, although their slaty cleavage does not in general correspond with the planes of their stratification. Clay-slates ar not confined to one geological period of formation ; the genuine clay-slates, however, usually only occur in the older formations, viz. the transition or grey- wacke. In the newer formations shales are usually found. Nevertheless there are exceptions to this rule; in the Alps there occur genuine roofing slates, also com- mon arenaceous and micaceous clay-slates (Grauwacken- schiefer) belonging to the Chalk and even to the Tertiary periods. 266 SEDIMENTARY ROCKS. Geological Varieties. (1) GLAEUS SLATE. \ A genuine clay-slate, in part a MATTERERSCHTEFEK, Heer. [ roofing-slate, occurring in Switzer- Scm^^iNE ( LUIS A* T ). l *> ^longing to e of tte ^ (Fr.) i tiary penods. (2) CYPRIS SLATE. ) A clay-slate with ftmefiJMe, the CYPRIDINERSCHIEFER. (Germ.) \ upper member of the Devonian SCHIKTE A CYPRIDINE. (/y-.) J formation at the Rhine and Hartz. (3) WISSENBACH SLATE. ] A c i ay . s i at e of the Devonian WlSSENBACHERSCHIEFER. (Germ.) f f , 4.1 TT SCHISTE DE WISSBNBACH. (Fr.) ) aUttUOUn at the Hartz. (4) CALCEOLA SLATE. ) A Mack and sometimes calcareous CALCEOLASCHIEFER. (Germ.) [ clay-slate of the Devonian forma- SCHISTE 1 CALCEOLES. (Fr.) ) tion at the Hartz. (5) GREYWACKE-SLATE. ) An arenaceous and usually mi- GRAUWACKEXSCHIEFER. (Germ.) \ caceous clay-slate of the transi- GRAUWACKE SCHISTEUSE. (Fr.) > t ion periods. (6) GBAPTOLITE SLATE. ^ ,4 clay-slate or sometimes a si- GRAPTOLITENSCHXEFER. (Germ.) I liceous slate (lydian-stone) With SCHISTE 1 GRAPTOLTTES. (Fr.) ) Graptolites, belonging to the Si- lurian formation. 31. AKGILLACEOUS SHALE, SHALE. SCHIEFEETHON. (Germ.) AEGILE SCHISTEUSE. (Fr.) A laminated clay-rock ivhose fissile texture is due to its original stratification and not to slaty cleavage. In other respects, similar to clay-slate. Shale and clay- slate pass into each other, and many shales show a tendency more or less decided towards a slaty cleav- age. Shales are usually more recent, geologically speaking, than the genuine clay-slates. Varieties in Texture. (a) COMMON ARGILLACEOUS SHALE. \ Is only a softer, less firm, GEMEINER SCHIEFERTHON. (Germ.) I and more earthy variety of ARGILE SCHISTEUSE COMMUNE. (Fr.) j clay . slate w ' lih ^t its cleav- age, but laminated according to the plane of its original deposition. It is often mixed with quartz grains and with flakes of mica. (&) SCHIEFERLETTEN (of German geologists) is a modification of the usual argillaceous shale in which the clay is still some- what moist, and the rock therefore is somewhat plastic and greasy^ ARGILLACEOUS GROUP. 267 Varieties in Composition. (c) BITUMINOUS SHALE. ) Of dark-brown colour, pass- BITUMINOSER SCHIEFERTHON. (Germ.) r ing into Brandschiefer. SCHISTS BITUMINEUX. (Fr.) ' (d) CARBONACEOUS SHALE, CARBONIFEROUS] Dark-grey to black, SHALE (BATT or BASS, KELVE). I from admixture of KOHLENSCHIEFER. (Germ.) r carbonaceous matter ; SCHISTE HOUIIXER. (Fr.) ) frequentlyarenaceou ; or micaceous. When many fossil plants occur in the rock, it is sometimes called in Germany Krauterschiefer. This rock es- pecially belongs to the Coal formation. (e) VARIEGATED SHALE. ] Yellow, red, violet, or green, BUNTER ^^ 1 ON ^^ [ according to the different degrees rm '') of oxidation of the iron which it contains. (/) ARENACEOUS SHALE. 1 Passing into argillaceous sand- SANIUGER SCHIEFERTHON. (Germ.) \ stone SCHMTTE 8ABLEUX. (Fr.) (ff) MICACEOUS SHALE. ) Corresponding with mi- GLIMMERREICHER SCHIEFERTHON. (Germ.) \ caceous clay-slate. SCHISTE MICAC6. (Fr.) J (A) CALCAREOUS SHALE. ) Slightly effervescing with MBRGELIGER SCHIEFERTHON. (Germ.) f ac id . passing into calca- IMARNBUX ' *** ] reous slate*" Geological Varieties. (1) FLYSCH, an arenaceous and micaceous shale, sometimes approach- ing the state of a clay-slate. Eocene in the Alps. (2) FUCOIDAL SHALE ) With remains of Fucoids. Eocene FUCOIDENSCHIEFER. (Germ.) \ and older in the Alns and Can>a- SCHI8TE X FUCOlDES. (Fr.) I tjjjjjjjg (3) ROETH, a term employed by the German geologists for a varie- gated arenaceous shale, which occurs imbedded between the Sluschelkalk and variegated sandstone (Thuringia) . * 'The colliers' and quanymen's terms for shale are bind, blue- bind, metal, plate, &c. ; when very fine and containing a large pro- portion of carbonaceous matter, the collier calls it batt or bass, the geologist carbonaceous (or bituminous) shale, and the coal merchant often slate. In Scotland the collier's term for shale appears to be blaes or blues, the shale being often bluish-grey ; when lumpy they are called lipev blaes. Black argillaceous shales or " batts " are called " dauks. Fekes or grey fekes seem to be sandy shales such as would be called rockbinds in South Staffordshire (see Williams' " Mineral Kingdom.") In the South of Ireland, carbonaceous shale is called kilve, and indurated slaty shale is termed '' pinsill " or "pencil," as it is often used for slate pencils.' Jukes. 268 SEDIMENTARY KOCKS. (4) WERFNER SCHIEFER, a shale, usually arenaceous and micaceous, occurs in the Alps in strata, which there represent the varie- gated sandstone formation. (5) CARBONIFEROUS SHALE or SLATE. ] This is a geological KOHLENSCHIEFER (KRAUTExscHiEFEB). (Germ.) \ designation applied j to all shales of the Coal formation, whether or not they actually contain carbon (see ante, e). (6) POSIDONOMYA SHALE. ~\ A dark-coloured shale of the POSIDONOMYENSCHIEFER. (Germ.) I Carboniferous formation (that SCHISTEXPOSIDONOMYES. (FT* J of the Lias formation is a bitu- minous marl- slate). (7) WENLOCK SHALE. Silurian formation, England. The following relate chiefly to chemical analysis of clay- slates and argillaceous shales. References. O. L. Erdmann, Thonschiefer in Thiiringen, Joum. f. techn. Chem. 1832, vol. xiii. p. 114. Frick, Thonsch. in Thiir. am Harz in Westphalen, Poggend. Ann. 1835, vol. xxxv. p. 193. Pteischly Thonsch. in Bohmen, Journal f. prakt. Chemie, 1844, vol. xxxi. p. 45. Delesse, Thonsch. in den Vogesen, Ann. des Mines, 1847, [4] vol. xii. p. 303 ; 1853, [5] vol. iii. p. 747 j and Bullet, de la Soc. ge"ol., [2] vol. x. p. 562. Forchhammer, Thonsch. v. Christiania, Oversigt over det K. Danske Vidensk Silesk Forhandlinger, 1844, p. 91. Journ. f. prakt. Chem. 1845, vol. xxxvi. p. 394 ; and on Bornholm, Berzelius, Jahresber. 1844, [25] p. 405. Dahl, Thonsch. bei Christiania, Nyt. Mag. f. Naturv. 1848, [5] p. 317. Kjerulf, Thonsch. bei Christiania, in Christianias Silurb. 1855, p. 34. Jwanhow. Thonsch. bei Christiania, Mem. Acad. de St. Petersb. 1859, [6] p. 325. Wilson, Thonsch. in Schweden, Phil. Mag. 1855, [4] p. 114 ; p. 417. K. v. Hauer, Thonsch. in Steiermark, Jahrb. d. geol. Eeichs- anst. 1854, pp. 362 and 869. J^r/ew^'&,Weriher Schiefer, Jahrb. d. geol. Reichs. 1855, p. 852. Sauvaqe, Ardennenschiefer, Ann. des Mines, 1845, [4] vol. vii. p. 420. List, Tannusschiefer, Ann. d. Chem. u. Pharm. 1852, vol. Ixxxi. pp. 192 to 260. Kayser, Thonsch. von Clausthal, v. L. u. Br. Jahrbuch, 1850, p. 682. Schnabel, Amelung and v. d. Mark, in den Verhandl. d. naturh. Ver. d. pr. Rheinlande, 1851, pp. 10, 56, and 127 j 1853, p. 127; and 1855, p. 122. Rissc, Geol. Beschr. d. Gegend von Baden, 1861, p. 47. ARGILLACEOUS GROUP. 269 32. CLAY and LOAM. THON und LEHM. (Germ.) ARGILE. (Fr.) These are earthy deposits chiefly consisting of clay, and when moist are more or less plastic. Loam or lehm is a word of German origin ; between it and clay there is no sharp distinction. The purest and therefore the most plastic varieties are called clay (also potter's clay or pipe-clay). They are usually white or greyish-blue, but sometimes yellow, red, or greenish, or (if containing carbon) even black. Those varieties which contain much fine sand and hydrated oxide of iron are called loam (in Germany, Lehm), and the iron usually gives them a yellow or brownish colour. Varieties in Composition. (a) CLAY. ) The purest varieties are white or light-bluish THON. (Germ.) j. grey, and are very plastic. These are called " ) potter's clay or pipe-clay. Those containing much silica or fine sand are called fire-clay ; those containing bitumen, bituminous clay; some are variously coloured by different oxides of iron, and are then termed variegated clay. (6) LOAM. ) Contains more or less sand, flakes of mica, and LEHM. (Germ.) j guc h like admixtures ; is coloured by hydrated oxide of iron, and is therefore less plastic than clay, almost earthy and yellow or brown in colour. It sometimes even con- tains small crystals of felspar (Glasurlehm of the Germans) ; or it contains particles of lime, marly loam (Mergellehm) j or nodules of marl (Losskindeln) ; nodules of pyrites (Kiesknollen) ; microscopic shells, &c. If it contains a very large proportion of hydrated oxide of iron, then it passes over into yellow ochre (Gelberde), which is used as a colouring matter, (c) SALIFEROUS CLAY. j A clav containing chloride of sodium, SALZTHON. (Germ.) L sometimes with distinct grains or crys- ARGILK BALiFfcRE. (fr.)J ^ of this salt ; usually occurs together with rock-salt. The following are the geological terms of certain clays : (1) LOESS, or DILUVIAL LOAM. \ Frequently somewhat calcareous L^L^ILUVIKN. (Fr.) J ^th marly nodules (Losskindeln). (2) TILE OR BRICK EARTH. A Miocene or Neogene deposit of clay TKOBL. (Germ.) i i n the Vienna basin. (3) BROWNCOAL CLAY. > Usually white. Miocene in North- BRAUNKOIILENTHON. (Germ.) j ern Germany. 270 SEDIMENTARY BOOKS. (4) SEPTARIAN CLAY. > Containing septaria of lime, in North- SEPTARIENTHON. (Germ.)} ern Germany Miocene (or Eocene). (5) BARTON CLAY. Hampshire, Eocene. (6) BOGNOR CLAY. Eocene of the Hampshire basin. 7 LONDON CLAY. Eocene in the London basin. (*.,} Eocene in the Paris basin. (9) HILS CLAY. \ In the Hils formation (Wealden) of West- HILSTHON. (Germ.) J phalia. (10) SPEETON CLAY, in the Lower Greensand formation of England. (11) WEALD CLAY. ) In the Wealden formation of Sussex. ARGILE WEALDIENNE. (Fr.) ) (12) ORNATEN-THON. (Germ.) With Ammonites ornatus in the Jura formation of Swabia. (13) OPALINUS-THON. (Germ.) With Ammonites opalinus in the Brown Jura of Swabia. (14) KIMERIDGE CLAY. \ In the Jura f ormat ion of England. ARGILE KIMMERIDIENNE. (Fr.) > (16) AMALTHEEN-THON. (Germ.) With Ammonites amaltheus, in the Lias formation of Swabia. (17) TURNERI-THON. (Germ.) In the Lias formation of Swabia. (18) MIACYTEN-THON. (Germ.) Containing Myacites, and frequently also remains of plants, the lowest branch of the Keuper forma- tion in Thuringia. As clay loses its plasticity when subjected to a strong pressure, especially if accompanied by high temperature, the plastic clays are chiefly confined to the recent forma- tions : the older clays have doubtless been converted into argillaceous shale, clay-slate, or claystone. There can be no doubt that all these rocks originally were mud deposits. Literary references on the subject of clay and loam appear unnecessary. 33. CLAYSTONE and HARDENED CLAY. THONSTEIN, oder VERHARTETER THON. (Germ.) A compact and tolerably solid mass, chiefly consisting of clay, not slaty ; its fracture earthy ; very variously coloured. The rock designated by this name is not always an actual sediment, but sometimes a product of the disintegra- tion of felsitic rock. The nature of its origin is generally only to be determined by its geological position and sur- MARL GROUP. 271 roundings. The sedimentary claystones are always stra- tified sometimes in very thin layers, white, yellowish grey, red-brown, greenish, or brownish, sometimes with variegated stripes or spotted. They sometimes contain nodules of pyrites, flakes of mica, impressions of plants, or petrified parts of plants. We have already said that the distinction between the sedimentary claystones and certain weathered felsitic rocks is sometimes difficult. In like manner it is fre- quently difficult to distinguish the former from certain tuff rocks, e. g. from porphyry-tuff, which indeed is very often called claystone, especially in England; but the genuine sedimentary clay rock seems to have at least as good a title to the name. MARLS. These are closely allied to the clays, standing between them and the limestones. They are in fact compounds of clay and carbonate of lime, and also sometimes contain carbonate of magnesia ; they likewise frequently contain fine particles of quartz, flakes of mica, oxide of iron, bitumen, or carbon. According to their state or texture, they may be divided into the slaty, the compact, and the earthy varieties ; according to the predominance of one or other of their ingredients, they may be further divided into the calcareous, dolomitic, arenaceous, micaceous, fer- ruginous, and bituminous. Of carbon they only contain very subordinate quantities, serving as a dark colouring matter. The original state of these rocks, like that of the clays, was a muddy sediment somewhat more various in its character than in the case of those rocks. The same process of pressure has consolidated them into firm, rocky, slaty, or sometimes bituminous masses. The processes of animal and vegetable life have even participated in the formation of some of these rocks to the extent of contributing their calcareous and bituminous ingredients. The calcareous ingredients often show traces with the microscope of organic remains. Marls as well as clays occur in the deposits of almost every geological period; and as to the di Terence between those of different 272 SEDIMENTARY ROCKS. periods, we can only in general terms say that the older varieties are usually slaty or fissile, whereas in the more recent deposits earthy varieties more frequently occur, but this is by no means a rule without exception. 34. MAKL. MERGEL. (Germ.) MARNE. (Fr.) A compound of clay and lime, earthy, compact, or fissile, usually soft; crumbles on exposure to air, effervesces with acid. Marl is a compound of clay and lime or dolomite, but its ingredients are blended together and cannot be dis- tinguished except by chemical agents. The proportion of lime or dolomite varies from 10 to about 50 per cent. Outside of these limits the rock ceases to be marl, and does not crumble on exposure to the air. It will then either be a clay or a limestone. The most frequent colour is grey, but marl is sometimes yellow, brown, red, violet, bluish, or greenish. Varieties in Texture. (a) MARL-SHALE. ] In fresh state very similar to argil- MERGELSCHIEFER. (Germ.) laceous shale, but crumbles on ex- MAKNEUX. (Fr.) tains much quartz, sand, mica, or bitumen. (b) COMPACT MARL, or MAKLSTONE. ] Without distinct fissile DICHTER MERGEL, VERHARTETER MERGEL, [ s l at y structure, similar to STEIKMERGEL, Oder MERGELSTEIN. ^^ ^ f^ fo MARNE COMPACTS. (Fr.) > pieces on exposure to the air. Admixtures of quartz and mica or bitumen similar to marl-shale. A modification of compact marl, separates into small conical concretions (cone in cone). Germ. Tuten- Merc/el. (c) EARTHY MARL. ) In its dry state resembles clay, but ERDIGER MERGEL. (Germ.) > is not plastic when wet. Its ingre- dients are the same as those of the other marls. Varieties in Composition. (d) CALCAREOTTS MARL. ) with much carbonate of lime in its KSfSSiB^P composition. (e) DOLOMITIC MARL. ) With dolomite, and usually also DOLOMITMERGEL. (Germ.) r with carbonate of lime. The dif- MARNE MAGXESIEK.NE. (Fr.) > f erenceg be tween (d) and (e) can only be determined by chemical analysis. MARL GROUP. 273 (/) ARGILLACEOUS MARL. ) With little carbonate of lime or dolo- THOXMEKOKL. (Germ.) \ mite : forms transitions into clay, clay- MAIIXK AHGILEUSE. (Fr.) J 8t()ne) or ^^0^ shale. O) ARENACEOUS MARL. ^ SAM.MKHGEL. (Germ.) \ With much sand. MAKNE SABLEUSE. (Fr.) ) (A) MICACEOUS MARL. % . GLIMMERMERGEL. (Germ.) \ Contains mucn mica. MARXE MICACEE. (Fr.) ) (t) BITUMINOUS MARL. ) Usually in the form of shale, al- BiTUMiNosr.u MKIUJEL. (Germ.) j ways dark-coloured by reason MARXK r.m M.NK, SK. (Fr.) > of ^ bitumen> sometimes even black. To this belong the so-called Oelschiefer (oil-slate) and Kupferschiefer (cupiferous slate) of the Germans ; the latter is distinguished by the quantity of copper which it contains. (A') GLAUCONITE MARL. } With much glauconite in its compo- GLAUKOXITMERGEL. (Germ.) L 8 ition, and by it coloured green. The MAKXK GU.UCOXIEUSE. (Fr.) | ^^'^^ when examined under the microscope, appear mostly to proceed from the shells of microscopic Foraminiferae. (0 GYPSEOUS MARL. , A marl penetrated by stringy veins of *!??&. J gyP^m, or thin laminae of the same. Besides the above-mentioned varieties of composition, some marls have been named according to their geological position ; e. g. : (1) SUB-APENNINE MARL. ) SUBAI-KXNINKX-MEROBL. (Germ.) \ Pliocene in Upper Italy. NE SUBAPEXXIXE. Fr. ' MABNE SUBAPEXXIXE. (Fr.) (2) CYRENIAN MARL. ) With many Gyrenes : Miocene, in ) ( ^- } I the Mayence basin. (3) CHALK MARL. ) i n the Chalk formations of England Ki;KinKMEHQEU (Germ.) . TTVoct^linlifl. CRAIE MARNEUSE. (Fr.) ) and Westphalia. (4) PLAXER MARL. \ In the Quadersandstone formations of PLAXEIIMEIIOEL. (Germ.) > Saxony and Bohemia. (5) FOLKESTONE MARL. I j n the Gault formation of England. MARXE DC GAULT. (Fr.) > (6) SPEETON MARL, belonging to the Lower Greensand formation of England. (7) FOREST MARL. | j n t h e Lias formation of England. CALCAIRE MARNEUX. (Fr.) > (8) LIAS SLATE. ) A bituminous marl-slate of the Lias LIASSCHIEFER. (Germ.) I formation, sometimes called Oel- 8CHIOTE L1A8IQUE. (Fr.) (9) JURENSIS MARL. ) With Ammonites jurensis, in the JIKEXSIS-MEROEL. (Germ.) } Lias formation of Swabia. (10) POSIDONOMYA SLATE. ) A dark bituminous marl-elate PosiDoxoMTEN-ScraEFER. (Germ.) i- of the Lias formation of Swa- J bia, with many Posidonomya. T 274 SEDIMENTARY ROCKS. (11) NTJMMISMALIA MARL. \ With Terebratula mtmnwmalis, NUMMISMALIS-MERGEL. (Germ.) I in the Lias formation of Swabia. (12) BELEMNITE MAEL. ) A dark bituminous marl -slate in BELEMNITENSCHIEFER. (Germ.) [ the Lias formation of Swabia, MARNE A BELEMNITES. (Fr.) J with many ^ tefc (13) SPOTTED MARL, or ALGAU SLATE. \ In the formation FLECKENMERGEL, oder ALGAUSCHIEFER. (Germ.) ]" Q the Northern Alps answering to the uppermost Lias. (14) KETJPER MARL. ) Chiefly variegated in colour, fre- f7 quently withypsun, (15) PARTNACH SLATE, or BACTRILLIAN SLATE. ) A marl formation PARTNACHSCHIEFER oder BACTRILLIENSCHLEFER. L -with thick slaty J cleavage, which in the Northern Alps is found in part answering to the Keuper formation. (16) BITUMINOUS MARL-SLATE. ) Of the Zechstein forma- BITUMINOSER MERGELSCHTEFER. (Germ.) j tion of Thuringia. (17) COPPER SLATE. \ Is a bituminous marl-slate of the KUPFERSCHIEFER. (Germ.) j Zechstein formation of Thuringia, in which various sulphurous compounds of metals are contained. These sulphur compounds, besides their copper, contain iron, silver, lead, cobalt, nickel, &c. It will hardly be necessary to add anything respecting the occurrence of marl in nature, nor to refer to literature on the subject. LIMESTONE GKOTJP. (Limestone, Dolomite, Gypsum, Anhydrite.) Pure limestone is an aggregate of particles of calcspar : it therefore consists of carbonate of lime. Pure dolomite or magnesian limestone is an aggregate of particles of the mineral dolomite or bitter-spar : it is therefore a car- bonate of lime and of magnesia. Gypsum is a sulphate of lime combined with water ; anhydrite is gypsum with- out water. Rocks consisting of pure limestone or dolomite rarely occur in nature. What we chiefly find are rocks of in- termediate character, which we may regard as transitions between the two extremes ; in other words, all limestones are more or less magnesian, probably consisting of an intimate compound of the two minerals, calcspar and bitterspar. These rocks likewise usually contain other admixtures in small quantities ; e. g. clay, silica, oxides of iron, or bitumen. The presence of such minerals occasions many LIMESTONE GROUP. 275 varieties in colour as well as composition ; there are also many modifications in texture, so that the limestones present us with many very dissimilar rocks. It is not always easy or possible without analysis to dis- tinguish limestone from dolomite, even if pure, still less to determine the various rocks of intermediate character. Many rocks have been long held to be limestone which later chemical analysis has shown to be dolomite. Never- theless, the distinction is important enough to be pre- served, although it may be difficult always to apply it.* We are compelled to create an arbitrary boundary by determining how great a percentage of magnesia should entitle a rock to be called a dolomite. The mineral dolo- mite contains about 45*7 per cent, carbonate of magnesia to 54-3 per cent, carbonate of lime. We may therefore halve the 45*7 per cent., and say that all rocks contain- ing more than 23 per cent, carbonate of magnesia should be called dolomites, and those containing less than that amount retain the name of limestones. Some such divi- sion must be agreed on for purposes of classification, although otherwise of little scientific value. The general difference between characteristic forms of the two rocks may be briefly stated as follows : LIMESTONE. DOLOMITE. Hardness . . 3' Hardness .... 3-5 Spec, jrrav. . 2'6 2-8 Spec. grav. . . . . 2*8 2*9 Crystalline-granular lime- The crystalline-granular and sac- stone seldom occurs except charoid varieties of dolomite occur in between strata of crystalline sedimentary formations, as well as schists. between strata of crystalline schists. Many beds of limestone of Sometimes these varieties pulverise Silurian and carboniferous age to a crystalline sand, are coarsely crystalline ; as are, also, the limestone of some coral (reefs and some stalagmites. Very often compact. Seldom quite compact. Frequently oolitic. Probably never oolitic. Lustre, when crystalline, Lustre, when crystalline, vitreous vitreous. to pearly. * The quicksilver mines of Idria are in dolomite rock, which adjoins and is intersected by limestone in many places; and the difference between the two rocks is there very important, as the ore is confined to the dolomite, none being ever found in the limestone. TRANSLATOR. T 2 276 SEDIMENTARY ROCKS. LIMESTONE. DOLOMITE. Effervesces strongly with Solid portions of the rock do not acid. effervesce with acid. The powder effervesces, especially if heated. Its powder, when heated When its powder is heated on before the blowpipe on pla- platinum foil, before the blowpipe, it tinum foil, adheres together. tumefies and does not gelatinise. The circumstances under which these two rocks occur in nature are very similar. They both occur in a crys- talline-granular state, imbedded between strata of meta- morphic schists ; they both form strata in formations of various geological periods ; but in the sedimentary forma- tions the dolomites are frequently also found in a crys- talline-granular state, whereas the limestones, though often crystalline, are almost always compact, earthy, or oolitic. Deposits of genuine dolomites are never formed by springs, but limestones frequently. Limestones, again, are more frequently fossiliferous, and they are also more usually distinctly stratified than dolomites. Gypsum and anhydrite are not so extensively developed as limestone and dolomite; they are prevalent only in distinctly sedimentary formations, and are usually crystal- line, seldom distinctly stratified, seldom fossiliferous. They are often accompanied by rock-salt. In general they are much more free from foreign ingredients than either lime- stone or dolomite. 35. LIMESTONE. KALKSTEIN. (Germ.') CALCAIRE. (.Fr.) A crystalline-granular, compact, earthy, or oolitic ag- gregate of calcspar ; effervesces strongly icith acid; easily scratched with the knife. Spec, grav 2-62-8. Pure limestone consists of 56 per cent, lime and 44 per cent, carbonic acid. It seldom occurs so pure in nature, but is usually more or less intimately combined with dolomite, alumina, silica, peroxide and protoxide of iron, bitumen, or carbon. By these ingredients its pro- perties undergo alteration, and there arise distinct varie- ties in composition when their quantity is considerable. The texture of the limestone rocks is likewise various, and gives rise to other varieties, to many of which sepa- LIMESTONE GROUP. 277 rate names attach. Many limestones consist entirely, and others partially, of the calcareous shells of animals ; and it is very possible that this is the case with several whose original structure is no longer apparent. There are other limestones which are undoubtedly the product of chemical precipitate of carbonate of lime from aqueous solutions ; and some that are the result of consolidation of calcareous mud proceeding from the mechanical disintegration of older limestones. In appearance, many limestones and dolomites much resemble some siliceous rocks, or compact felsitic rocks, or gypsum. But from these they may easily be distin- guished by the difference of their hardness, and by their effervescence with acids. Varieties in Texture. (a) GRANULAR LIMESTONE. ] Including marble. A granular KORXIGER KALKSTEIX. (Germ.) I aggregate of distinct individual CALCAIRE SACCHAROSE. (Fr.) f ^J^ ^^ of calcspar . The grains vary in size from the almost invisibly small (fine- grained compact varieties) to the size of a nut (coarse- grained). Most usually the colour is white, but sometimes yellowish-grey, reddish, greenish, bluish, and even black. By admixture of dolomite it passes into magnesian limestone and dolomite. Granular limestone also contains other ad- mixtures, especially in its crystalline state, and these are then porphyritically disposed, as, for instance, mica, chlorite, talc, hornblende, pyroxene, garnet, vesuvian, felspar, chondrodite, couzeranite, chiastolite, epidote, zircon, titanite, spinel, corun- dum, quartz, fluor-spar, apatite, magnetic iron-ore, iron pyrites, zinc-blende, galena, copper pyrites, anthracite, and graphite. The rock also contains geodes, nests, or veins, with fully developed crystals of calcspar, aragonite, bitter-spar (dolomite), asbestus, serpentine, &c. The following special varieties of granular limestone are occasioned by the occurrence of some of the above minerals in considerable quantity and characteristic form. (), and () are probably always contact formations. () HISLOPITE. ) The name given by Samuel Haugh- HISLOPIT. (Germ.) ] ton to a granular limestone occur- ring at Takli in the East Indies. Granular limestone is of irregular massive structure ; it like- wise usually shows distinct traces of stratification, sometimes also a fissile texture j it most usually occurs in subordinate beds between strata of crystalline schists, and is frequently itself the product of metamorphosis from compact sedimentary deposits of limestone. The form of its beds is sometimes very irregular, they assume a swollen shape, or resemble the dykes or veins of igneous rocks. It would seem as if the limestone, in the pro- cess of transmutation, had become softer than the surrounding schist, and that its mass had consequently been squeezed into the breaches and clefts of the latter. This appearance may be observed at Miltitz near Meissen, and at Auerbach near Heidelberg. In England and Ireland beds of crystalline limestone occur variously interstratified with the compact limestones of the carboniferous limestone series through a thickness of from 2,000 to 3,000 feet. Granular limestone is also found at the margin of those igneous rocks which have broken through the compact or earthy limestones. Such may be observed at the Kaiserstuhl in Breisgau, in County Antrim and Island of Rathlin, Ireland. (6) COMPACT LIMESTONE. ) The particles of calcspar are in- DICHTER KALKSTEIN. (Germ.) \ visibly small, and the mass there- CAI^AIKE COMPACTE. (Fr.) I fore to be compact> Its fracture is conch oidal, or splintery, or dull. Its prevailing colour is grey or yellowish ; it varies, however, to white, blue, green, red, brown, and even black. Some varieties are variegated, spotted, or veined, like marble. The following ac- cessory ingredients are usually intimately blended with the general mass, viz., dolomite, clay, silica, oxide of iron, bitu- men, or carbon. If these only occur in small quantity, they can hardly be recognised, but if their quantity be consider- able, then distinct varieties of the rock are occasioned, such as the folio wing: LIMESTONE GROUP. 279 (rr) DOLOMITIC. DOLOMITISCHER DICHTER KALKSTKIN. (Germ.) MAGNESIEN. (Fr.) 63) BITUMINOUS. ) Fetid limestone, swine- STINKSTELV, STINKKALK, (Germ.) [ stones, always dark- CAIX.AIRE BITUMINEUX. (Fr.) J co i ouredj and emitting a bituminous smell when rubbed. (:/) ARGILLACEOUS or MARLY LIMESTONE. ) With consider- MERGELKALKSTEIX. (Germ.) [ CAIX^RE ARGI^UX ou MARKED. (Fr.) J grey, and in fracture dull, almost earthy. (<>) FERRUGINOUS LIMESTONE. ) Very rich in hydrated EISENKALKOTEIN. (Germ.) I ox j(fe of iron, which im- CAXCAIRE FEBKUGINEUX. (Fr.) -, ) parts a brown colour to the rock. (*) CHERTT LIMESTONE, or SILICEOUS "I Combined with si- LIMESTONE. I lica, and therefore SSSJSSfeM I harder * t ordi - 1 nary limestone, Very frequently traversed by veins of chert or hornstone. In all the varieties of these compact limestones there occur, occasionally, veins, seams, nodules, or nests of calcspar, horn- stoie (chert), or flint. Jukes remarks, l Almost all large masses of limestone have ther Hints or siliceous concretions. These are frequently called cheft, as in the carboniferous limestone (see post, p. 351), where the lodules and layers of chert exactly resemble the flints in chall. Even the tertiary limestones round Paris have their flints the menilite of that locality being nothing but a siliceous concrtion (see post, p. 349), found in the calcaire St. Ouen, and possity other places. Pure siliceous concretions occur even in the freshwater limestones and gypsum beds of Montmartre. This invariable, or nearly invariable, accompaniment of lime- stone jid siliceous deposits, those siliceous parts having a chemial and not a mechanical formation, strengthens the hypo- thesis f the organic origin of both, as previously described. The silca diffused through the calcareous mud, of which the limestoie was composed, has sometimes remained so diffused instead -f separating as nodules or layers, producing a cherty or siliceouslirnestone.' Page ,ays, ' To the percolation of water charged with car- bonic aci, we owe the production of rottenstone from beds of siliceas limestone, the carbonated waters dissolving the limy porion, and leaving the light porous siliceous residuum which fonis the rottenstone of commerce.' The ccnpact limestones are usually distinctly stratified, and are founc associated with other sedimentary rocks of almost every age (e) EARTHY LMESTONES. ) Chalk (in part). Rough to the ERDIGER KLKOTEIN. (Germ.) I f ee l ; friable ; the white chalk CAHAIM .UYEUX. (Fr.) J ^^ fapjfa fa ^^ fr my body agabst which it is rubbed. In chalk the particles consist 280 SEDIMENTARY ROCKS. of very minute shells of Foraminifera, Polythalamiae, &c., which may "be recognised under the microscope. These minute shells constitute a fine earthy mass, in which larger fossils are likewise found, as well as nodules and layers of flint or chert, grains of glauconite, or of sand and other mine- ral substances. The following sub varieties may be named: () WHITE CHALK. WEISSE KREIDE. (Germ.) CRAIE BLANCHE. (Fr.) (/3) GLAUCONITIC CHALK. GLAUKOxmscHE KREIDE. (Germ.) CRAIE GLAUCONIEUSE. (Fr.) (y) ARENACEOUS SANDSTONE. \ Consisting of remains of SANDIGER KALKSTEIN. (Germ.) L shells. These earthy and CALCAIRE ARENACE. {Fr.) J distiuc tly ZOO genic rocks are more frequent in recent than in old formations. We may presume that in the older formations they have been metamorphosed into compact limestone. (d) OOLITIC LIMESTONE, OOLITE, ROESTONE,^ This variety is en- PEASTONE, or PISOLITE. tirely composed of OOLTTHISCHER KALKSTEIX, OOLITH, ROGENSTEIN, f Sma ll anc [ alniOSt EBBSKSsmif, oder PISOLITE. (Germ.) ""(, . f "- t f CALCAIRE OOLITHIQUE, CALCAIRE PISOLITHIQUE. J spneneal grams, Irom ( Fr <) the size of a millet- seed to that of a pea or larger. This granular texture is very different from the crystalline granular. The single round grains usually lie close together, but this is not always the case; they are sometimes wide apart, connected by a com- pact matrix indeed they are always held together by a matrix. The individual grains are often of compact structure, more usually, however, of radial texture; sometimes both radial and concentric in alternate coats, with a nucleus of foreign substance, such as a grain of sand; sometimes they are nothing but fossils. The geological position of these oolites is identical with that of the compact limestones. The genuine peastone is, however, an exception. It is (e. g. Carlsbad) evidently a formation from a spring of water holding in solution carbonate of lime (see p. 94), and it moreover consists of aragonite and not calcspar. Jukes remarks, 'Its peculiar struc- ture gives to oolite the character of a freestone, working easily in any direction, whence its value as a building stone. Bath stone, Portland stone, Caen stone are well-known examples of oolitic limestone.' The pea-grit of Cheltenham is a marine formation, one of the oolites, only the spherical nodules are somewhat irregular and elliptical in shape. (e) NODULAR LIMESTONE. ] This variety consists entirely of KNOTENKALKSTEIX. (Germ.) I sma ll compact nodules or irregular CALCAIRE XODULEUX. (Fr.) 11 . r ., -, -, -, ' J swellings, united and bound to- gether by a compact limestone mass, or by a matrix of marl or clay-slate. Its composition, as well as its texture, there- fore, presents varieties : (a) NODULES OF LIMESTONE IN LIME-) STONE or MARL MATRIX. I At Partenkirchen KALKKXOTEX ix KALK oder MERGEL. f in Bavaria. (Germ.) LIMESTONE GROUP. 281 (/3) KRAMEXZELSTEDT. I Nodules of lime in a matrix KRAMEXZELSTEIN. (Germ.) > O f clay-slate, hence the rock itself is somewhat slaty. These nodules sometimes are nothing else than indistinct fossils. Polwand, near Saalfeld. (/) SLATY LIMESTONE. ) This is, however, usually not SCHIEFRIGER KALKOTEIN. (Germ.) I o f genuine slaty texture or J cleavage, but only a thin strati- fication (lamination) presenting a slaty appearance ; thus, e. g., at Solenhofen in Bavaria, where a finely laminated limestone is even used for roof-slating. (g) POROUS LIMESTONE. ) -IT, POROSER KALKOTEIX. (Germ.) \ We here distinguish between CALCAIHE CAVEUXEUX. (Fr.) ' () SPONGY LIMESTONE, APHRITE.) Very extensively de- SCIIAUMKALK Oder MEHLBATZEX. L veloped in the Mu- j schelkalk formation of Thuringia, and (/5) LIMESTONE TUFF, GALCA-) A deposit from springs, REOUS TUFF. I usually porous by reason of KALKTUFF. (Germ.) \ j^s orioin as an incrustation TUF CALCAIRE. (Fr.) (A) GEODIC LIMESTONE. ] With numerous sparry ca- DRUSIGER KALKSTEIN. (Germ.) I ^ties of crystallised calcspar, j brownspar, and the like. (*) CELLULAR LIMESTONE, or ROUGH j With numerous angular LIMESTONE. I cells or holes. These latter ZELLEXKALK oder RAUHKALK. (Germ.) I are sometimes occasioned CALCAIRE CELLULEUX. (Fr.) ) ^ ^ decfty Qr ^^e^ of fragments enclosed in the rocks, in which case the porosity of the rock is only at the surface. (&) BRECCIA-LIMESTONE, or LIMESTONES Fragments of limestone BRECCIA. I cemented together by BUIX CIKXKALK oder KALKBREcciE ; TnttM- r limestone. The partial MER und RUIXEX-MAIOIOR. (Germ.) I i j n ' -t BRECHE CAWAIRK. (Fr.) ) weakening or decay of these fragments some- times causes a cellular tissue on the surface of the rock. (/) STYLOLITE LIMESTONE. ) Names given by Ger- STYLOLITHEXKALK und NAOELKALK. (Germ.) [ man geologists to cer- CAIXAIBE A STYLOLITES. (Fr.) j tftin c J t Umestones which show peculiar striped jointings, so-called stylolites, or are made up of small conical or wedge-shaped pieces. (m) FIBROUS LIMESTONE ] To this variety we may reckon FASERIGER KALKSTEIN, FASER- I the calc-sinter and aragonite- CAIQUE r^Sci (Fr.) I sinter, formed by the dripping of ' water contaimng lime m solution, e. g. at Carlsbad in Bohemia. There also occur seams or layers of fibrous limestone between beds of marl, which have clearly some other origin. Stalactitic calc-sinter is frequently sparry and not fibrous, but as it is a subordinate formation we include it here because of its origin. Over and above the varieties in texture and composi- 2S2 SEDIMENTARY ROCKS. tion which we have enumerated, limestone is very various in its geological character, and especially in the nature of the fossils which it contains. The geological varieties are not of distinct lithological character, but they never- theless deserve a brief enumeration, as they sometimes acquire local importance. They are only to be distin- guished with certainty by means of their fossils ; we will arrange them as nearly as possible according to their respective ages. Geological Varieties. (1) LIMESTONE TUFF, CAL- \ Usually a porous friable deposit from CAREOUS TUFF. I springs, and containing many remains KALKTUFF. (Germ.) rf rdirnta imd imriid TUP CALCAIRE. (Fr.) ' OI P lants ana animals. (2) TRAVERTINE. \ A formation in Italy similar to calc-tuff, TRAVERTIN. (Germ.) I pri - f j )1 - f} CALCAIRE A CERITES. (Fr.) > (9) CALCAIRE GROSSIER (Grobkalk), sandy, and full of fossil shells. Eocene in the Paris basin. (10) NUMMTJLITIC LIMESTONE. \ Consisting almost exclusively NUMMULITENKALK. (Germ.) \ of Nmnmulites. Eocene; very CALCAIKE A NUMMULITES. (Fr.) j extensively deve loped in the South of Europe. ' The nummulitic formation, with its characteristic fossils, plays a far more conspicuous part than any other tertiary group in the solid framework of the earthy crust, whether in Europe, Asia, or Africa. It often attains a thickness of many thousand feet, and extends from the Alps to the Carpathians, and is in full force in the North of Africa, as, for example, in Algeria LIMESTONE GKOUP. 283 and Morocco. It has also been traced from Egypt, where it was larjjrelv quarried of old for the building of the Pyramids, into Asia Minor, and across Persia, by Bagdad, to the mouths of the Indus. It occurs not only in Cutch, but in the mountain ranges which separate Scinde from Persia, and which form the principal passes to Cabul ; and it has been followed still farther east- ward into India, as far as Eastern Bengal and the frontiers of China.' Page. (11) ORBITOIPAL LIMESTONE. ) 'As the nummulitic limestone CALCAIHE X ORBITOLITES. (Fr.) } seems characteristic of the old world, so the orbitoidal limestone seems characteristic of the new, mountain masses full 300 feet in thickness, and almost wholly made up of Orbitoides, occurring near Suggsville, in North America, and apparently in the same, or nearly the same, geological horizon.' Page. (12) MAJOLICA, a white compact limestone. ( 13) SCAGLIA, a red limestone, in the Alps. (14) OSTRJSA LIMESTONE. \ ? u \\ O f Qstraa. Eocene ; occurs cSSS^SSi (Fr.) I to the north of Kusstein, in Tyrol. (15) UPPER AND LOWER CHALK. \ Nearly white. The upper and KKEIDEKALK, KREIDE. (Germ.) f principal branch of the Chalk formation in England, containing many flints. ' Chalk flints occur as rounded nodular masses of very irre- gular and sometimes fantastic shape, and of all sizes, up to a foot in diameter. They are commonly white outside, but internally are of various shades of black or brown, sometimes passing into white. They have sometimes concentric bands of black and white colours internally, and exhibit markings derived from organic bodies, round which they have often been formed. Flint occurs in chalk, not only in nodules, but also in seams or layers, sometimes short and irregular, sometimes regular over a distance of several yards. These seams vary from half an inch to two inches in thickness, and are commonly black in colour.' Jukes. (16) HIPPURITIDEA, or HIPPTJRITE x Full of Ilippuritidea ; equiva- LIMESTONE. lent to the Lower Chalk for- SESTlSJS^CIh) J tion in Europe, Northern Afnca, and America. (17) RUDISTENKALK, oderHiEROGLYPHEN-<| Equivalent to the Lower KALK. (Germ.} \ Chalk formations. CRAIE X RUDISTES. (Fr.) (18) SPATANGUS LIMESTONE. ] Containing many Spatangida ; SPAT.\N.;KNK.\I.K. (Germ.) [ belonging to the Chalk group in CAIXUIRE X SPATANGUB*. (Fr.)\ ^ JJ (19) APTYCHUS LIMESTONE. ") Containing many Aptyclii-, there AITYCHKXKALK. (Germ.) I are two species of this fossil, one CALCAIRE X APTYCHUS. (Fr.) J ^^g^f^ t he Chalk, and the other to the Jura formation. (20) PLANER LIMESTONE. Thinly stratified, usually somewhat PLAKEUKALK. (Germ.) j marly, occurs with the Quadersandstein in Saxony. 284 SEDIMENTARY ROCKS. (21) SERPTTLITE LIMESTONE. ) Full of fossil Serpulae ; oftheDeister SERPULTT. (Germ.) \ or Wealden tormation ot West- CALCAIRE A SERPULES. (Fr.) j phalia. (22) PORTLAND STONE AND OOLITE.) A limestone belonging to the PORTLAND-OOLITH. (Germ.) \ upper Jura of England, fre- CALCAIRE PORTLANDIEN. (Fr.) ) quently Oolitic. 1 A well-known group of the upper Oolite as developed in the South of England. It consists of shelly freestones of variable texture underlaid by thick beds of sand, and derives its name from the Isle of Portland in Dorsetshire, where certain of the freestones have for centuries been largely quarried for architectural purposes. The Portland beds abound in fossil shells, bones of saurians, and drift coniferous wood.' (23) ASTARTE LIMESTONE. ] Containing many Astartida be- ASTARTENKALK. (Germ.) [ longing to the upper Jura forma- CALCAIRE 1 ASTARTES. (Fr.) j ^ Q (24) DICERAS LIMESTONE. ) Containing Dicers, and belonging (Fr, ) to the upper Jura formation. (25) CORAL RAG. \ Frequent in the Jura forma- KORALLENKALK, PoLYPENKALK, oder L tion, the upper member of CA^rS. ( 5ET ) ) the Middle Oolite in England. (26) NERINEA LIMESTONE. ) F U H O f Nerinece of the Jura for- NERINEENKALK. (Germ.) f ^t^ CALCAIRE 1 NERINEES. (Fr.) > x (27) AMMONITE LIMESTONE. ) F U H of Ammonites of the Jura or AMMONITENKALK. (Germ.) I T ia fnrnifltirm CALCAIRE AMMONITIFERE. (Fr.) > LMB IO^ m atlon. (28) JURA LIMESTONE. ) . JURAKALK. (Germ.) \ Usually white, yellowish, or grey. CALCAIRE JURASSIQUE. (Fr.) ' (29) OXFORD OOLITE. ) Belonging to the Jura or Oolite for- OXFORD-OOLITH. (Germ.) f . f -p no .l fln ^ OOLITHE D'OXFORD. (Fr.) > ma on 01 Jj^ngiana. (30) CORNBRASH. ) PLASSENKALK. (Germ.) f The same formation. CORNBRASH. (Fr.) > (31) BATH OOLITE. ) GRAND OOLITHE, OOLITHE f Ine 11K6. DE BATH. (Fr.) > (32) INFERIOR OOLITE. ) VII^ER KALIC. (Germ.) f I he like. OOLITHE INFERIEUR. (Fr.) ' (33) LIAS LIMESTONE. ) __ -,-,-,.,. LEIAS-KALK. (Germ.) \ Usually dark-coloured and bituminous. CALCAIRE LIASIQUE. (Fr.) ' (34) GRYPHITE LIMESTONE. | Containing numerous Grypha, the GRYPHITENKALK. (Germ.) L former designation for the Lias CALCAIRE A GRYPHITES. (Fr.) J limestone< (35) BELEMNITE LIMESTONE. } Containing numerous Belemnites, BELEMNITENKALK. (Germ.) and belonging to the Lias for- CALCAIRE A BELEMNITES. (Fr.) (36) DACHSTEINKALK (Germ.), a limestone of the Northern Alps, corresponding with the Lias formation in other parts of Europe. (37) KLIPPENKALK (Germ.), a limestone occurring in the Carpathians, its age not to be determined with certainty. (38) HALLSTATTER LIMESTONE. ) A limestone of the Alps correspond- HALLSTATTERKALK. (Germ.) > ing with the Keuper of Germany. LIMESTONE GROUP. . 285 (39) MUSCHELKALK (SHELL \ The middle member of the Trias LIMESTONE). L j n Germany, usually grey, and very MUSCHELKALK. (Germ.) OY fpnaivplv lime- KOHLEXKALK, oder BEROKALK. (Germ.) f stone formation in CALCAIRE CARBOXIFERE. (Fr.) ) England ; when it con- tains metal, it is called metalliferous limestone ; when it con- tains much hornstone or chert, it is called chert-limestone. (47) SCAR LIMESTONE, a lower member of the Carboniferous lime- stone in Westmoreland and Cumberland. (48) TRANSITION or GREYWACKE LIMESTONE. ) A limestone of G-RAUWACKENKALK, Oder UEBERGANOSKALK. (Germ.) f the transition p6- GIIAUWACKE CALCAIRE. (Fr.) ) jjod, usually com- pact, solid, and grey. (49) STRINGOCEPHALUS LIMESTONE. > Containing many StrinyocepJiahis STRINGOCKPHALENKALK. (Germ.) > Burt'mi in the Devonian forma- tion of Germany. 286 SEDIMENTAEY KOCKS. (50) ELFEL LIMESTONE. \ Lying immediately under the pre- EIFLER KALK. (Germ.) } ceding. (51) ORTHOCERAS LIMESTONE. ] Full of remains of Orthocera- ORTHOCERATITENKALK. (Germ.) I tites belonging to the Silurian CALCAXKEAORTHOCEKES. (Fr.) ^ J formatioil) D e .^ in Scandinavia. (52) URKALK (aboriginal or primitive limestone) is a general name, formerly very frequently applied in Germany to denote all granular limestones, especially those associated with the crys- talline schists. Limestones, as we have already remarked, are of various origin. A few only are direct chemical precipitates from aqueous solutions; the greater part are probably the product of certain animals. Some have been occasioned by the washing together of lime mud. The crystalline lime- stones owe their state chiefly to a plutonic process of transmutation. As to their bedding in relation to that of other rocks, we have nothing to add to what has previously been stated. We only adduce a few leading references on the sub- ject of limestones. It would serve no useful purposes to cite all treatises respecting their local occurrence. {References.* Ehreriberg, on the Animal Origin of many Limestones, Die fossilen Infusorien, 1837, Mikrogeologie, and v. L. u. Br. Jahrb. 1861, p. 785. Darwin, on the Formation of Coral Limestones in his ' Coral Islands.' G. Rose, on the heteromorphic State of Carbonate of Lime in the Abhandl. d. k. Akad. d. Wissenschaft zu Berlin, 1856-1858. HaugMon, on Hislopite in the Philos. Mag. 1859, [17] p. 66. Deksse, on Hislopite in the Ann. des Mines, 1861, vol. xx. p. 435. L. Cordier gives his views on the formation of limestones in an article published in the Compt. rend. 1862, vol. Ixiv. p. 293. He takes them to be principally chemical precipitates from the sea, which formerly held much greater quantities of salts of lime and magnesia in solution than at present. Leymerie expounded similar views in his Elements de Mine- ralogie et de Geologic, 1861, p. 358. Chemical analyses of limestone exist in great va- riety ; but they are only of local importance, serving to decide the character of any given rock : for instance, whether it be a limestone or a dolomite, or whether it be fitted for building or other practical use. As to the formation of oolite, see pp. 94-5, ante. LIMESTONE GROUP. 287 36. DOLOMITE, MAGNESIAN LIMESTONE. DOLOMIT. (Germ.) DOLOMIE. (Fr.) A granular, compact, or earthy aggregate of bitter-spar (dolomite), usually combined with some calcspar ; does not effervesce, or only slightly effervesces with acid ; is easily scratched with the knife. Spec. grav. 4 -* * . 2-82-9. Pure dolomite, or bitter-spar, is a mineral, which we have already described as such in the earlier part of this work; chemically it consists of 54 carbonate of lime to 46 carbonate of magnesia. It is very seldom that the rock occurs in this pure state ; it usually contains a much larger proportion of carbonate of lime, and most probably in such case consists of an intimate compound of bitter- spar and calcspar. It usually also contains small quan- tities of several other substances, such as clay, silica, oxides of iron, bitumen, and the like. The chief differ- ences between limestone and dolomite, and the mode of distinguishing the two rocks, have been explained (p. 275, ante). In general terms, we may say that the dolomites closely resemble the limestones as regards their bedding and their other attributes, except that they are more frequently crystalline than the limestones, and sometimes even are entirely made up of small rhombohedrons. It was long supposed that all dolomites had been formed by process of transmutation from limestone. It is, however, much more probable that dolomites and magnesian limestones were for the most part formed by sedimentary deposit, in the same manner as the limestones proper. Many coralline structures, and probably many marine shells, contain some magnesia, and therefore may likewise yield magnesian limestones ; some dolomites again have very probably resulted from chemical pre- cipitate from aqueous solutions. Nevertheless the origin of many dolomites still remains very problematical, and it is by no means impossible that transmutations of lime- stone into dolomite may have taken place and may still take place in the interior of the earth. We know that magnesia plays an important part in the transmutation of 288 SEDIMENTARY KOCKS. several rocks, in proof of which we need only instance chlorite-schist, talc-schist, serpentine, steatite, &c. The magnesia would appear in such cases to have penetrated in a state of solution into the pores of the rocks, whose character it has changed, displacing other substances. Haidinger has suggested that sulphate of magnesia might in very high temperature, and under great pressure, de- compose carbonate of lime, converting it into dolomite and gypsum ; and Von Morlot has in some measure confirmed this suggestion by. experiment. Dolomite, like limestone, has many varieties, most of which are analogous to those of limestone, and resemble them also in their geological relations ; we may therefore treat them briefly. ( See Sterry Hunt, in Report of Brit. Association for 1860.) Varieties in Texture. (a) GRANULAR DOLOMITE. ) Closely resembles granular lime- KORNIGER DOLOMIT. (Germ.) \- stones, sometimes however sac- DOLOMIE SACCHAROIDE. (Fr.) J c haroid, consisting of small rhom- bohedrons, sometimes crumbling into dolomite sand ; usually more porous than limestone. Frequently penetrated by geodes and cavities. Its accessory ingredients are similar to those of limestone, perhaps more abundant and multifarious. Granular dolomites are more frequently associated with dis- tinctly sedimentary rocks than are the granular limestones. (6) COMPACT DOLOMITE. } Difficult to distinguish from com- DICHTER DOLOMIT. (Germ.) L pact limestone, perhaps more rare. DOLOMIE COMPACTE. (Fr.) J ^ ccessory admixtures and varieties of composition are probably the same. (c) EARTHY DOLOMITE. j Usually rougher to the feel than ERDIGER DOLOMIT. (Germ.) I earthy limestone, probably owing DOLOMIE GROSSIERE. (Fr.) J to ^ m i croscopic J lv sma ll rhom _ bohedral crystals. If it be grey, which is sometimes the case, by reason of its accessory ingredients, then it is sometimes called dolomitic sand. (d) POROUS DOLOMITE. POROSER DOLOMIT. (Germ.) (e) CELLULAR DOLOMITE. ) ZELLIGER DOLOMIT (RAUHWACKE). (Germ.) \ Wltn angular Cavities. CARGNEULE. (Fr.) (/) BRECCIAN DOLOMITE, or \ DOLOMITE BRECCIA. I Corresponds with limestone breccia DOLOMITBRECCIE. (Germ.) | (? "81, ante). BRECHE DOLOMITIQUE. (Fr.)' (g) CONCRETIONARY DOLOMITE. I Consisting of a number of balls DOLOMIE CONCRETIONXEE. (Fr.) > touching each other either like bunches of grapes (when it is called botryoidal), or like musket-balls, or great piles of cannonshot. Many of these balls when broken open are found to have a radiated structure. But LIMESTONE GROUP. % 289 they have been produced subsequently to the deposition of the mass, as is shown by the fact of the lines of stratification proceeding through them regularly. (Jukes.) Dolomite is seldom oolitic, slaty, fibrous, or stylolotic, or at all events, such varieties are much more rare than in lime- stone. The calcareous dolomite is very similar to the dolomitic limestone. The two may be said to meet half way. The argillaceous, bituminous, micaceous, siliceous, arenaceous, ferru- ginous, and carbonaceous varieties, correspond with the similar varieties of limestone. Three crystalline varieties of dolomite must, however, be mentioned. Varieties in Composition. ( K) CHROMIC DOLOMITE. ) Is the name given by Breithaupt to a CHROM DOLOMIT. (Germ.) I compound of dolomite, chromite, and oxide of chromium, occurring at Nischne-Tagilk in the Ural, and valued as a marble on account of its beautiful green colour. The chromite appears in the form of delicate grains or crystals, the green oxide of chromium appears to form thin laminae. This beautiful rock also contains some iron pyrites and native gold, and appears to be penetrated by manifold veins of quartz. (t) DOLOMITE OF THE BINNEN THAL (ALPS). This dolomite occurs with very rich combination of various minerals. According to Hugard, it is somewhat phosphorescent in the dark. It con- tains the following minerals pyrites, quartz, much mica, or- thoclase, tourmaline, tremolite,chiastolite, garnet, ruby, realgar, orpiment, blende, antimony-glance, dufre*nite, binnite, celestine, barytes, and calcspar. (Compt. rend. 1858, vol. xlvi. p. 1261 ; v. L. u. Br. Jahrb. 1858, p. 591.) (A;) PREDAZZITE (from Predazzo, \ Is the name given by Petzold in Tyrol). I to a dolomite occurring at Pre- PREDAZZTT. (Germ.) f dazzo, in South Tyrol. It ad- J joins syenite-granite, of which it is a metamorphic product. It is white and crystalline- granular, resembling the most beautiful marble. Besides car- bonate of lime and magnesia, it contains some siliceous clay and some water. Hence Petzold called it a special mineral : probably it is a compound of dolomite and brucite. (v. L. u. Br. Jahrb. 1848, p. 583.) Geological Varieties. (1) CORALLINE DOLOMITE. ) Jura formation in England and KORALLEJJDOLOMIT. (Germ.) f Germany. DOLOMIE CORALLIENNE. (/V.) ' J (2) ALPINE DOLOMITE. \ Chief dolomite of the North- DOLOMDJ ALPINE (cARGNEULEs). (Fr.) j era Alps, corresponding with the lower part of the Lias formation. (3) KEUPER DOLOMITE. I in the Keuper of Germany. KEUPERDOLOMTT. (Germ.) ' (4) Fl 2SSS I Si~, } In the Keuper of Swabia. DOLOM1E ROUGE. (Fr.) ' U 290 SEDIMENTARY EOCKS. (5) MYOPHORIA DOLOMITE. I In the lower division of the MYOPHORIEN-DOLOMIT. (Germ.) > Keuper formation. (6) MALBSTEIN or NAGELFELS (Germ.}. A dolomite of the upper division of the Muschelkalk, in Swabia. (7) WELLENDOLOMIT (wavy dolomite), belonging to the lower divi- sion of the Muschelkalk, in Germany. (8) MAGNESIAN LIMESTONE. > A dolomite limestone of the Per- CALCAIRE MAGNESIEN. (Fr.) } m i an formation in England. (9) ZECHSTEIN DOLOMITE. \ In Thuringia and ZECHSTEIN-DOLOMIT, RAUHWACKE. (Germ). ) Franken G0) D C Hr} ^ the Zechstein of Thuringia. Many different varieties of dolomite are known in the Car- boniferous system, or occur in the Cambrian, Silurian, De- vonian, and Permian formations. The dolomite of Derbyshire, Durham, and Yorkshire in the latter formation furnishes the well-known building-stone of which the Houses of Parliament are built. In the more recent formations, dolomite would appear to be less frequent, unless it be that many compact dolo- mites are still mistaken for limestones. Much has been written on the formation of dolomites since the first celebrated treatise on that subject of L. v. Buch, in Leonhard's Almanack, 1824. Of the various arguments in favour of the transmutation of limestone into dolomite, perhaps the most deserving attention is the hypothesis developed by Haidinger and v. Morlot, according to which the conversion was effected by means of solutions of sulphate of magnesia (Epsom salt), and gypsum was produced at the same time. In many cases this is very probable. (Haidinger's Naturw. Abhandl. vol. i.) To us it appears very probable that many dolomites have been formed by crystallisation of coral-reefs, as v, Eichthofen has ably proved in the case of some of the dolomites of Southern Tyrol. Vide MM. Seemann and Guyerdot, Bullet, de la Soc. geol. de France, (n. s.) vol. xix. p. 995,1862. GYPSUM AND ANHYDRITE. Gypsum is a combination of sulphate of lime with water. Anhydrite is sulphate of lime without water. Gypsum as a rock is much more frequent than anhy- drite at least ,we seldom find anhydrite on the surface of the earth a circumstance which is explained by its readiness to absorb water, and consequent conversion into gypsum. For the rest, the geological position of the two is very similar. 37. GYPSUM. GYPS. (Germ.) GYPSE. (Fr.) An aggregate of sulphate of lime, usually crystalline, sometimes compact or fibrous - 3 soft, and usually white. Spec. grav. ...'... ',.- 2-3. LIMESTONE GROUP. 291 Pure gypsum consists of 46*5 per cent, sulphuric acid, #2 '5 lime, and 21 water. It is so soft that it may be scratched with the nail, and only gives a dead sound when struck with the hammer. By these properties it may be most easily distinguished from white granular limestone, to which it bears great resemblance. Its texture is most usually fine-grained (alabaster), sometimes also porphy- ritic, containing large shining crystals of selenite. It is only rarely quite compact; in thin layers or narrow veins it is frequently fibrous or sparry. Its original snow- white colour is sometimes tinged grey by admixture of bitumen or clay, or red by oxide of iron. The mass sometimes (though rarely) contains as accessories some mica, talc, quartz, boracite, pyrites, copper pyrites, grey copper, zincblende, and sulphur. Moreover, in gypsum rock are sometimes found nests or veins of aphrite, anhydrite, rock-salt, sulphur, and chert. The weathered surfaces of gypsum (owing to its solu- bility in water) are usually much worn or eaten into. Varieties in Texture. (a) GRANULAR GYPSUM or ALABASTER. } Almost always white somewhat translucent. ' (6) PORPHYRITIC GYPSUM. ) With crystals of gypsum in a fine- POR (SJ,. 1 T IOEH GYP8 ' I g 111 ^ gJP sum matrix. (c) COMPACT GYPSUM. ) 5 are > usually mixed with clay or DICHTER GYPS. (Germ.) bitumen, which impart a grey colour GYPSE COMPACTK. (Fr.) ) to the rock. (rf) FIBROUS GYPSUM. ) Usually only in the form of thin veins FASERGYPS. (Germ.) \ or seams occurring in other gypsum, GYPSE FIBRETJX. (Fr.) ) or j n argillaceous shale or marl. (e) SPATHIC or SPARRY GYPSUM, or SELENITE. \ Occurs in similar SPATHIGER GYPS oder BLATTERGYPS. (Germ.). I manner to the J fibrous variety. (/) TRIPESTONE. \ Is a variety both of texture and com- GEKROSESTEIN. (Germ.) I position. It is formed of thin lavers PIERRE DE TRIPES. (/T.)J g pure white gvpsum) alternating with grev argillaceous gypsum, the whole twisted or crumpled to resemble a ruff, whence the German name. Varieties in Composition. ARGILLACEOUS GYPSUM. THONGYPS. (Germ.) MARXE GYPSEUSK. (Fr.) u 2 \ Grey, spotted, or striped, by reason \ o f an admixture of clav. > 292 SEDIMENTARY ROCKS. (A) BITUMINOUS GYPSUM. \ Difficult to distinguish, from the BrruMiNbsER GYPS. (Germ.) v last-named variety. GYPSE BITUMINEUX. (Fr.) ) (t) MICACEOUS GYPSUM. \ Mixed with mica or talc j analogous to GIJMMERGYPS. (Germ.) ! micaceous limestone ; of rare occur- GYPSE NIVIFOKME. (Fr.) J ^^ ^ ^ {a ^^ Q crygtalline schists, as (e.g.) on the south slope of the St. Gotthard. Gypsum is rarely distinctly stratified or fossiliferous ; both facts are in all probability connected with the mode of its original formation, pointing to a chemical rather than mechanical origin. It is contained in deposits of the most different periods, and exceptionally in the crystalline schist formations. It seldom forms extensive beds parallel to the other strata, but rather flat lenticular or irregular masses or accumulations in connection with anhydrite, rock-salt, and clay, or sometimes with dolomite. Some- times it even occurs in abnormal bedding between other sedimentary rocks. From the circumstances under which it is found to occur, it has been inferred that gypsum must be a product of the local conversion of limestone. Chemically, no doubt, this would be possible, if the requisite sulphuric acid were present, but such origin on a large scale is not capable of demonstration from any known facts. Some gypsum rocks may be actually shown to have been formed by deposit from aqueous solution of sulphate of lime ; others by the decomposition of pyrites in the immediate neighbourhood of calcspar ; others, again, by the absorption of water into anhydrite. Hai- dinger and Von Morlot have also shown that gypsum and dolomite may together be formed by the operation of solutions of sulphate of magnesia (Epsom salt) on lime- stone ; nevertheless all these different facts or theories of possible formation hardly suffice to account satisfactorily for the origin of the great masses of gypsum (frequently combined with rock-salt and anhydrite) which occur in the flotz or secondary series. The supposed origin of gypsum from anhydrite leaves the greater difficulty un- solved of the original deposit of anhydrous sulphate of lime. The exceptional nature of the bedding of gypsum rocks, as well as the frequent disturbances which appear in the adjoining strata, are best explained by the action of water in partially washing away the original deposit of gypsum, LIMESTONE GROUP. 293 and also the rock-salt with which it is usually accompanied. The first consequences of such process would be to form great cavities ; after a time the roofs of these cavities would break down and cause disruption in the super- incumbent rocks. This is to us the most probable mode of accounting for the existing phenomena. Certain it is that these disturbances of the neighbouring strata are not of a nature to authorise us to infer an eruptive origin of the gypsum rock. The gypsum beds of different geological periods have not received different names, as they are not petrographi- cally to be distinguished from each other. It may never- theless be of interest to compare the different places of their occurrence in the European geological series. These are chiefly as follows : (1) In Miocene deposits, with remains of plants at Paria, in Italy with sulphur and rock-salt in Sicily. i2) In Eocene deposits, with bones of animals, in the Paris basin. 3) In the Triassic formations of the French and Swiss Alps with rock-salt and cargneule (Lory, Favre, &c.) (4) In the Keuper of Germany, sometimes with rock-salt, but with- out fossils. (5) In the Muschelkalk of Germany, with anhydrite and rock-salt, without fossils. (6) In the Upper Variegated Sandstone of Germany and the Alps, with rock-salt and anhydrite, without fossils. (7) In the New Red Sandstone of England, with rock-salt, without fossils. (8) In the Zechstein of Germany, with rock-salt and anhydrite, without fossils. (9) In the Permian formations of Russia, with rock-salt. (10) In the clay-mica-schist of Herren-Grund, in Hungary (of un- doubted antiquity), with fahlerz and copper pyrites. (11) In the crystalline schists of the Alps at St. Gotthard, with mica ; at Bugg, in Switzerland, with mica and talc. References. Hausmann, Bemerkungen iiber Gyps und Karstenit, 1847. Karsten, iiber Gyps und Karstenit 'in his Archiv, 1848, vol. xxii. pp. 545 and 578. 38. ANHYDRITE, MURIACITE, KARSTENITE. AMIYDRIT, MURIACIT, KARSTENIT. (Germ.) ANHYDRITE. (J?r.) A granular or compact aggregate of anhydrous sulphate of lime ; harder than gypsum ; white, grey, or blue. Spec, gray 2-82-9. 294 SEDIMENTARY ROCKS. Pure anhydrite is white, and may easily be mistaken for gypsum or dolomite. It may, however, be easily dis- tinguished from dolomite by its not effervescing with acid even when pulverised and heated ; and it is much harder than gypsum. The colour of the grey or blue varieties is caused by the admixture of clay or bitumen in small quantities. There are scarcely any distinct varieties of texture. It occurs in nature under similar relations to gypsum, except that it is scarcely ever met with on the surface of the ground, because there, by the absorption of water, it is converted into gypsum. For literary references refer to those under the head of gypsum. FRAGMENTAL ROCKS. These rocks are composed of the fragments of older rocks, which have been broken up by mechanical forces, , and their parts deposited and reunited or cemented to- gether into a solid mass ; they are therefore termed frag- mental rocks. A somewhat similar origin may no doubt be ascribed to the argillaceous rocks, marls, and some limestones, but in this case the parent rocks have undergone chemical decom- position, as well as mechanical disintegration, and the dis- integrated parts have been resolved into very fine mud before the work of reconstruction commenced, so that the connection of the new rocks thus formed with those from which they spring is not so evident or easily traceable as in the fragmental rocks proper. SANDSTONES consist of grains of some mineral (usually quartz) compacted together ; CONGLOMERATES of rounded stones or pebbles cemented together ; BRECCIAS of angular fragments likewise bound, Uncompacted SAND, GRAVEL, SHINGLE, and HEAPS OF RUBBISH belong to this division of the materials of which the earth's crust is composed. TUFA rocks are conglomerates, more or less firmly united, of fragments thrown from volcanoes of the pre- sent or an earlier time. FRAGMEXTAL GROUP. 295 39. SANDSTONE and GRITSTONE. SANDSTEIN, PSAMMIT. (Germ.) ORES. (Fr.) Small grains of some mineral, usually of quartz, are cemented together by some mineral substance. The process of the original formation of all sandstones has consisted jn the washing together of small grains of some solid mineral, usually quartz, and these were after- wards bound together into a solid rock by some cementing medium, or perhaps by simple pressure. In other words, these rocks were formed from sand, into which they may be resolved again. The grains are usually rounded off, and only exceptionally exhibit faces and edges of crystals. Quartz being the most abundant mineral of the earth, and at the same time very hard and difficult of decompo- sition, furnishes the material for the most sandstones ; these, however, also contain particles of felspar, flakes of mica, fragments of shells, and grains of glauconite. The binding medium of these grains usually consists of clay, marl, or hydrated oxide of iron ; less usually of silica, carbonate of lime, kaolin, talc, or asphalte. Sandstones often contain as accessories concretions of hydrated oxide of iron, frequently in the form of balls (eagle stones*) or irregular masses, nodules of pyrites, rounded pieces of amber, coal, and the like. As all sandstones are mechanical aqueous deposits, they are always stratified. They frequently are interstratified with other rocks in alternate beds, such, for instance, as clay-slate, argillaceous shale, marl, &c. They belong to no exclusive geological period, but are found in those of most various age. Varieties in Texture. (a) COMMON SANDSTONE. ) With grains about the size of a SANDSTEIN. (Germ.) j mustard-seed. * ' " Eagle stone," the ^Elites lapis of the ancients, fabled to have been laid in the nest of the eagle. A variety of nodular argilla- ceous iron-ore, having a concentric structure and occasionally so de- composed within as to have a loose kernel which rattles on being shaken. This kernel was known by the name of Callimus, and was supposed to be the young in the womb of the parent nodule ; hence the fable of the aetites bringing forth young. When there is no in- ternal kernel the nodule becomes a geode.' Page. 296 SEDIMENTARY ROCKS. (6) COARSE-GRAINED SANDSTONE. ) GROBKORNIGER SANDSTEIN. (Germ.) h -Passing into conglomerate. GRES A GROS GRAINS. (Fr.) (c) FINE-GRAINED SANDSTONE. ) ~ _ , . . , FEINKORNIGER SANDSTE^ oder L Or fine sandstone, passing into an FEINSANDSTEIN. (Germ.) apparently compact state. GRES A GRAINS FINS. (Fr.) J (d) CRYSTALLISED SANDSTONE. ( With grains of quartz-crystals KRYSTALLSANDSTEIN. (Germ.) \ n wni ch the crystalline faces may GRES CRISTALLIN. (Fr.) ) be recognised. In all these sandstones the texture varies not only in respect of the size of the grains, but in respect of their quantity or abundance compared with that of the cement- ing medium. Some sandstones, owing to the predomi- nance of the latter, pass into rocks of a totally dif- ferent character, such as marl, claystone, &c. (e) FISSILE SANDSTONE. ^ Flagstone in part j usually owes SCHIEFRIGER SANDSTEtN oder L jt s texture to a plentiful ad- GRES^S"" ( ^ I mixture of mica. (/) GLOBULAR SANDSTONE. ] With ball-shaped concretions of com- KTTGELSANDSTEIN. (Germ.) L pac t or firm sandstone in a matrix of GRES NODULEUX. (Fr.) J ^ ^^ stmcture< In Transy l_ yania very extensively developed. According to differences in the nature of the cementing material, we have the following varieties : (ff) ARGILLACEOUS SANDSTONE. ) The most frequent variety. ' GRES ARGILEUX. (Fr ' passes into arenaceous clay, ar- gillaceous shale, or clay-shale. (A) MARLY SANDSTONE. \ The next most frequent va- MERGEIJGER SANDSTEIN oder L ^ety. If the marl predomi- MERGELSANDSTEIN. (Germ.) , J ,-, ., GRES MARNEUX. (Fr.) ' nat es, then it passes into are- naceous marl or marl-shale. (t) CALCAREOUS SANDSTONE. "j With a calcareous cementing KALKIGER SANDSTEIN oder KALK- L medium ; somewhat rare ; G^fcS^KE* rT (Fr.) ) Passes into arenaceous lime- stone. (k) SILICEOUS SANDSTONE, -j With a very solid hornstone-like KEESELSANDSTEIN. (Germ.) \ cementino: material, in which the in- GR6s SILICEUX - (Fr '> } dividual grains of quartz are finely imbedded and are frequently not to be distinctly recognised. When these grains are intimately blended with the matrix, then this variety of sandstone passes into quartzite, quartz- rock, or a kind of hornstone. (7) FERRUGINOUS SANDSTONE. \ A sandstone with hydrated EISENSANDSTEIN oder EisENscHiissiGER [ oxide of iron, or peroxide GREs A F E N iNESn^.) J of iron, as its cementing material, which always gives the rock a red or brown colour. Sometimes it is spotted or FKAGMENTAL GROUP. '297 striped from the unequal distribution of the iron (Tiger Sand- stein, Germ. ; Tiger sandstone, Engl}. If the hydrated oxide of iron should become predominant, as is sometimes the case, then we even find transitions into brown haematite. (m) KAOLIN SANDSTONE. \ With kaolin as cementing medium ; KAOLINSANDSTEIX. (Germ.) ) almost always white. Occurs, e. g., at Wissenfels in Thuringia. If sandstones of this description contain only quartz and kaolin, they form very fine fire-proof stones, and may be used for lining furnaces j e. g. Steinhaide, in the Thuringian Forest. (n) TALCOSE SANDSTONE. ) With a talcose cementing medium. TALKSANDSTEIN. (Germ.) | This varietv approaches in character GRES TAIAJUEUX. (Fr.) > io itacolumite, which, as we have already seen, is a kind of sandstone (vide p. 247, ante). (o) ASPHALTIC SANDSTONE. \ With asphalte as cementing me- ASPHAI.TSAM.STKIV. (Germ.) [ dium, a variety only of exceptional Ctete BITUMINEUX. (Fr.) J NOTE. It is frequently very difficult to determine the exact nature of the cementing medium, especially as two or more kinds often occur together in the same rock. According to differences in the nature and substance of which the grains themselves are composed, we have the following varieties : (;>) QUARTZ-SANDSTONE. QUARTZ-^ (The quartz-psammit of Nau- PSAMMIT. QUARTZ-GRIT. mann.) \Vith grains of quartz. QuARzsANDsrrEiN. (Germ.) I his is the most frequent of GIIES QUARTZEUX. (Fr.) ' all sandstones. (The mico-psammit (?) MICACEOUS SANDSTONE. MICACEOUS GRIT. \ ofNaumann) Con- GLIMMERSANDSTEIN. Mico-P8AM M rr, Naumann. f (Germ.) \ taming flakes of PSAMMITE (GRES MicACE), Brongniart. (Fr.) ) mica with the grains of quartz. (r) ARKOSE or FELSPATHIC SANDSTONE.) with g 1 of felspar as . ARKOSK. (Germ.) f well as quartz, combined ARKOSK. (Fr.) ) i n 8Om e cases with flakes of mica. This rock thus resembles granite in its composition, and is therefore sometimes called Regenerated granite. () GREEN SANDSTONE (GREENSAND).) Containing grains of glauco- GRtfxsANDSTEiN. (Germ.) I nite with uartz, imarti (Germ.) nite with quartz, imparting VKRT. (Fr.) J l the whole rock, sometimes even a dark-green colour. Ac- cording to Ehrenberg's microscopic analysis, these glauconite grains usually consist of the fossils of very minute Testacea. (0 SHELL-SANDSTONE. x Coral sandstone : the grains are fragments IU9 ^T DSmN ' f . f shells or coral '. the cementing mate- GRES COQUILLIER. (Fr.)) rial carbonate of lime. Rare. The difference between sandstone and gritstone is a vague and undeterminable one, as must necessarily 298 SEDIMENTARY ROCKS. be the case where the things themselves are so various and capricious in composition and texture. The term gritstone is, perhaps, most applicable to the harder sand- stones, which consist most entirely of grains of quartz, most firmly compacted together by the most purely sili- ceous cement. The angularity of the particles cannot be taken as a character, since the rock commonly called 4 millstone grit ' is generally composed of perfectly round grains, sometimes as large as peas and even larger : the stone then commencing to pass into a conglomerate.' Jukes. Jukes gives the following local terms for sandstone : Rock, used generally in South Staffordshire to denote any hard sandstone. Rotclie or Roche, generally used for a softer and more friable stone. Rubble means either loose angular gravel, or a slightly compacted brecciated sandstone. Hazel is a North of England term for a hard grit. Post is a similar term for any bed of firm rock, and is usually applied to sandstone. Peldon is a South Staffordshire term for a hard, smooth, flinty grit. Calliard or Galliard is a northern term for a similar rock. Freestone is a term in general use which is often applied to sandstones, but sometimes to limestones and even to granite, as in the counties of Dublin and Wicklow. It means any stone which works equally freely in any direction, or has no tendency to split in one direction more than another. Flagstone (see ante, p. 296), on the contrary, means a stone which splits more freely in one direction than any other, that direction being along the lines of the original deposition of the rock. These stones are ordinarily sandstones, though often very argillaceous, and some flagstones are perhaps rather in- durated clay in their beds than sandstone. Thin-bedded limestones may also be flagstones. Independently of the different petrographic varieties of sandstone, we have numerous geological varieties. These must always be determined by their bedding or by their fossils ; and they are frequently only local in their cha- racter. (1) THE MOST RECENT MARINE \ mich on some coasts is still SANDSTONE. in process O f formation. NEUESTER MEERESSANDSTEIN. (Germ.)) r FRAGMENTAL GROUP. 299 (2) BLATTERS ANDSTEIN (Germ.), containing impressions of leaves of trees ; occurs in the Mayence Tertiary basin. (3) MOLASSE SANDSTONE. \ A sandstone of the Molasse forma- MOLASSESANDSTEIN. (Germ.) I tion on the northern margin of the MOLASSE. (Fr.) I Alpg . ugually (4) BROWNCOAL SANDSTONE. \ Sandstone of the Browncoal BRA0NKOHLEN8AXD8TE1N. (Germ.) j formation in Bohemia and Northern Germany. Miocene, Frequently siliceous sandstone. (5) BAGSHOT ^AND, in 'England. Eocene. (6) THANET SAND, in England. Eocene. (7) V ^K^ *.,} P^ Eocene, partly older. (8) C ^^^grS~.) } *** Eocene, partly older. (9) FUCOIDAL SANDSTONE. ) FUCOIDBNSANDOTEIN. (Germ.) \ With remams of Fucoids. - CfefeB 1 FUCOtDES. (Fr.) J (10) NUMMULITIC SANDSTONE. \ Containing remains of Num- NUMMUUTENSANDOTEIN. (Germ.) } m ,,)\+ oa GRES JfUMMULITHIQtJE. (Fr.) ) l XS ' (11) RALLIGSANDSTEIN (Germ.). A sandstone of Switzerland. Eocene. (12) TAVIGLIANAZ SANDSTONE. . T , 1-1 -p^^n, TAVioLiANAZ-SANDerEiN. (Germ.) f (13) MACIGNO. \ _ MACIGNO. (Germ.) I In North Italy. Eocene, or older. MACIGNO. (Fr.) ) (14) QUADER SANDSTONE. ) So called on account of its rectan- QUADERSANDSTEIN. (Germ.)} gular jointings. In conjunction with the planer limestone, with which it is associated and inter- stratified, it forms a part of the Chalk group in Saxony and Bohemia. (15) GREENSAND (UPPER AND LOWER). ] These constitute two di- GRUNSAND. (Germ.) \ visions of the cretaceous GRES^VERT (SUPERIEUB ET INFERIEUR). J grQup ^ England- (16) HILS SANDSTONE. \ The lowest member of the Chalk group HILSSANDOTEIN. (Qerm.) ) in Westphalia. (17) TASE^O^ ^^ | A 8an( istone of the Chalk period in Istria. (18) DEISTER SANDSTONE. i Westphalia, belonging to the Weal- DEISTERSANDSTEIN. (Germ.) j den formation. (10) HASTINGS SAND, England. Wealden formation. (20) PORTLAND SAND. Upper Oolite formation of England. (21) DOGGER (Germ.). A coarse-grained sandstone, brown, some- times very argillaceous. Whitby, Yorkshire. W T estphalia. Jura formation. (22) LIAS SANDSTONE AND SAND. I Usually light-yellow and fine- LHASSANDSTEIN. (Germ.) I grained. A lower member of J the Lias, at Gotha. An upper member of the Lias of England. (23) CARDINIA SANDSTONE. ) Containing many Thalassites THALASSTTKN-SANDSTEIN. [(Germ.)} (Cardmia). (24) (25) SCHILF SANDSTONE. I A member of the Upper Keuper in SCHILFSANDSTEIN. (Germ.) > Swabia. 300 SEDIMENTARY ROCKS. (26) VARIEGATED SANDSTONE. ) So called on account of its being BUNTSANDSTEIN. (Germ.) \ frequently particoloured. It is, GRES BIGARRE. (Fr.) ) however," sometimes of one uniform colour (white, yellow, or red). It constitutes the chief mem- ber of the Buntsandstein formation of Germany. (27) VOSGES SANDSTONE. | Lower division of the Sandstone VOGESENSANDSTEIN. (Germ.) f formation of the Vosges Mountains. (rRES VOSGIEN. (/*/*.) (28) RED SANDSTONE OF THE ALPS] Corresponds with the Varie- (VERRUCANO). I gated Sandstone of Germany ROTHER ALPENSANDSTEIN. (Germ.) [ and the New Red Sandstone GRES ROUGE DES ALPES. (Fr.) J o f En?lancL (29) NEW RED SANDSTONE. Name applied in England to the whole series of strata lying between the Lias and the Permian rocks. (30) NEWENT SANDSTONE. A member of the Keuper series of Gloucestershire. (31) WEISS- oder GRAULIEGENDES. (Germ.} A White or Grey Sandstone (frequently conglomeratic), forming the lowest mem- ber of the Zechstein in Thuringia, and sometimes containing copper-ore (Sanderz). (32) CUPRIFEROUS SANDSTONE. \ A member of the Permian forma- KUPFERSANDCTEIN. (Germ.) I tion in Russia. Old Red Sand- GRES CUPRZFERE. (Fr.) J gtone of gout k of Irelan(L (33) ROTHER SANDSTEIN. (Germ.) Former designation for the Roth- liegende formation, containing arkose and other sandstones, usually of red colour. (34) CARBONIFEROUS SANDSTONE. \ White, brown, yellow, grey, KOHLENSANDSTEIN. (Germ.) I or almost black, in which case ) it contains carbon. Frequent in the Carboniferous strata of old countries. (35) MILLSTONE GRIT. } Lowest member of the Coal formation sometimes. (36) GREYWACKE SANDSTONE. \ Usually very firm, with ar- GRAUWACKEN-SANDSTEIN, oder KOR- I orillaceous cementing medium. wJKfiSSTillS"* ^hen very fine-grained or ; almost thick, it has been called grauwacke or quartzite ; sometimes it is very coarse- grained, even conglomeratic. If the clay medium should become slaty, then it goes over into greywacke-schist. It is frequent in Devonian formations. Delesse, however, appears to have understood something different in the Vosges under the term of greywacke, since he says that it consists almost entirely of albite, forming a felspathic matrix, containing quartz, hornblende, several kinds of mica, chlorite, and occa- sionally some carbonates. Ann. des Mines, vol. iii. p. 747 ; v. L. u. Br. Jahrb. 1856, p. 359. 37) BAGGY POINT SANDSTONE (Page}. Upper Devonian. '38) DURA-DEN SANDSTONES, Fifeshire (Page), with Hdoptychn and Pterichthys. Upper Devonian. (39) DUNSE SANDSTONES, Scotland (Page). Red and white. Upper Devonian. (40) FLAGSTONES OF FORFAR, with Cephalaspis, Cheiracanthus, and Pt,erygotus. Lower Devonian. FRAGMEXTAL GROUP. 301 (41) LTIDLOW SANDSTONE, micaceous, prey. Upper Silurian. (42) WENLOCK SANDSTONE, Upper Llandovery; gritty. Upper Silurian. (43) CARADOC SANDSTONE, frequently quartzite. Lower Silurian. (44) LLANDEILO and LINGULA FLAGS, laminated sandstone, rich in mica. Lower Silurian. (45) STJPER STONES, Shropshire j siliceous sandstones, passing into quartz rock. Cambrian. We will cite a few treatises only as to sandstone, re- lating to special varieties. References. Gerhard draws attention to the fact that the grains of quartz are angular and transparent in many sandstones. Abhandl. d. berl. Akad. 1810-17, p. 13. Schafthatctl found grains of amorphous silica in sandstone, v. Leonhard's Jahrb. 1846, p. 648. Zeuschncr, SchMERAT ALPIN. (Fr.). ) o f the Alps, the pebbles chiefly con- sisting of Alpine limestone, but partly of quartz, lydite, granite, gneiss, &c. (2) PLANERCONGLOMERAT (Germ.) in Saxony belongs to the Quader- sandstone, with pebbles of granite, syenite, or quartz-porphyry bound together by sandstone cement. (3) HILSCONGLOMERAT (Germ.), with limestone and ironstone peb- bles, and likewise many remains of shells, occurring in the lower division of the Hils formation of Westphalia. (4) VOSGES CONGLOMERATE. 1 Lower division of the variegated CONGLOMERAT vosoiEN. (Fr.) > sandstone of the Vosges, with many pebbles of quartz and lydite. (5) CONGLOMERATE OF THE WEISSLIEGENDE. I In Thuringia, the CONGIX>MERAT DBS WEI3SUEGENDEX. (Germ.), ' lowest member of the Zechstein formation, with numerous pebbles of quartz, lydite, and clay-slate. (6) CONGLOMERATE OF THE ROTHLIEGENDE. I In Germany, with CONGLOMERAT DBS ROTHUEGENDEN. .(Germ.) > pebbleS of " quartz, lydite, granite, gneiss, mica-schist, and quartz-porphyry, and a cementing medium of ferruginous sand. (7) GREY CONGLOMERATE. 1 Lowest member of the Rothlie- GRAUES CONGLOMERAT. (Germ.) > gende, in Saxony. (8) CONGLOMERATE OF HAINICHEN. I In Saxony, answering to CONGLOMERAT VON HAINICHEN. (Germ.) > the Carboniferous Lime- stone formation j containing clay-slate, mica-schist, gneiss, 304 SEDIMENTARY ROCKS. granulite, granite, and greenstone j binding medium arenaceous and of brown colour. (9) GRETWACKE CONGLOMERATE. j At the Hartz, in Thuringia, GRAUWACKEN-CONGLOMERAT. (Germ.) \ in Bohemia, and other places, ^ partly Devonian, partly Si- lurian, with pebbles of quartz, lydite, clay-slate, granite, &c. Binding medium argillaceous, or arenaceous, and of grey colour. We should state that there are some so-called pudding- stones which have altogether the appearance of conglo- merates, but, in fact, are not such, as they do not consist of pebbles cemented together, but they contain rounded concretions of some siliceous or calcareous substance. We shall confine our references to some treatises con- taining mention of special phenomena. References. Haidinger, on the Lauretta Conglomerate, in Ber. d. k. k. Akad. d. Wissensch. zu Wien, 1856, July 15. Lartet, on Pebbles showing Indentations, in v. L. u. Br. Jahrb. 1836, p. 196. Blum, on the same, ibid. 1840, p. 525. Daithree, on the same, in Compt. rend. vol. xliv. p. 823. Cotta, on the same, Geol. Fragen, 1858, p. 204, and on Ver- worfene Geschiebe in the same account, p. 212. Wiirtetiberger, on the same subject, in v. L. u. Br. Jahrb. 1859, p. 153. Deicke, on the same subject, ibid. 1860, p. 219. GttrU, on the same subject, ibid. 1861, p. 225. Appendix. BOULDERS and PEBBLES. GESCHIEBE und GEROLLE. (Germ.) These may consist of very various materials ; and when united by a cementing medium, they form a conglomerate rock. Erratic Slocks and Boulders are of especial geological im- portance ; they are sometimes only partially rounded, and they are dispersed over the earth's surface, far from their parent rocks. They consist of very different kinds of rock, and have for the most part been transported to their present position by means of glaciers or of drift-ice. 41. BRECCIA. BRECCIE. (Germ.) BRECHE, BRECCIOLA, Brongniart. (Fr.) A rock composed of angular fragments of minerals or solid rocks cemented or bound together by some matrix or binding medium. [BKECCIOLA when the frag- ments are small.] FRAGMEXTAL GROUP. 305 Breccias, like conglomerates, may consist of the most various substances, both in their fragmental ingredients and their connecting medium, whence a similar richness in the number of varieties, which are too numerous and manifold to admit of classification. They must in each case be named according to the character of their in- gredients thus, quartz-breccia, gneiss-breccia, limestone- breccia, &c. or according to the nature of their matrix, as in the case of conglomerates. Breccias are geologically important, because in every case the fragmental parts must be of greater age than that of the rock itself; also because they indicate violent disruption of the rocks in their immediate neighbourhood, and from the circumstance that very angular fragments can never have travelled very far from the place of their original bedding. The following kinds of breccia are noteworthy on geo- logical grounds. Geological Varieties. (1) FRICTION BRECCIAS. ] These are breccias formed REIBUNOSBRECCIEN. (Germ.) I at the maroin of eruptive BKfcCHES DK FIU,N (DK FROTTEMHNT). ^ . ^ Jg ftt t he time pf J their eruption ; the matrix of the breccia consisting of the substance of the igneous rock, and the enclosed fragments being pieces of the rocks broken through. These breccias are very frequently found at the margin of porphyries, greenstones, basalts, trachytes, &c., and 1 may be designated accordingly. Simler has given the name of Metamixite to these contact formations. (Ueber Petrogenese, 1862.) (2) QUARTZ-BRECCIA. \ Consisting of fragments of quartz QUARZBROCKENFBLS. (Germ.) \ bound together by quartz or by BRfccHE 8IUCEIT8B. to compact texture, sometimes containing sanidine, hornblende, augite, &c. It is found, e.g., in Hogau and at the southern foot of the Erzgebirge. (B) TUFF FORMATIONS OF PLUTONIC ROCKS. (&) PORPHYRY-TUFF, or FELSITE-TUFF \ Sometimes called clay- (FELSPATHIC ASH), Jukes. [ stone; a compact ag- PORPHYRTUFF oder FELSTITUFF. (Germ.) [ cn-egate of felsitic parts, TUF PORPHYRIQUE OU FEUSPATHIQUE. (Fr.) J ^^^ deC ompOSed, fracture earthy, often variegated in colour, seldom distinctly stratified, but sometimes containing fossil plants, especially trunks of trees. At Chemnitz, in Saxony, where this tufa occurs as the lowest member of the Rothliegende, it is supposed to belong to the quartz-porphyries of that district- It is, how- ever, very diificult to distinguish these rocks in themselves from ordinary claystones, or Jrom certain products of decom- position of compact or porphyritic felsitic rocks. 310 SEDIMENTARY ROCKS. Porphyry-tuff sometimes encloses fragments and pebbles of quartz-porphyry, and thereby passes over into a kind of por- phyry-breccia or conglomerate. At Fidha, in Saxony, there occurs a porphyry-breccia of this description, the matrix con- sisting of crystalline particles of felspar. (T) GREENSTONE-TUFF, and GREENSTONE-CONGLO-] A compact ag- MERATE (GREENSTONE-ASH). ( gregate of pul- GRUNSTEINTUFF und GRUNSTEINCONGLOMERAT. (Germ.) [ verised or sand- TUF DIOBITIQUE et CONGLOMERAT DIORITIQUE. (Fr.) J -i-i ,- -i P greenstone j fracture earthy ; colour grey or brownish-green, sometimes enclosing fragments or pebbles of greenstone, and frequently organic remains. At Planschwitz, in Saxony, greenstone-tufa is imbedded between strata of greywacke slate, and contains many fossils of the Devonian formation. Probably much of what in Nassau has been called schalstein belongs to greenstone-tufa. On account of the indistinct character attached to the name schal- stein, we have preferred to treat it separately. In Southern Tyrol, in theFassa district, Von Richthofen has lately made distinctions between eruptive tufas, sedi- mentary tuffs, and regenerated tuffs, but they all belong to augite rocks, and take their geological rank amongst the deposits of more recent Trias formations. References. Natimann, on Porphyry-tufa, in the Erlauter. z. geogn. Karte v. Sachsen, 1838, No. 2, p. 434 Gruner, Porphyry-tufa with Mica Crystals in the Dep. of the Loire, Ann. des Mines, 1841, [3] vol. xix. pp. 98 and 122. Beudant, Voyage min. et geol. en Hong-rie, vol. ii. p. 416. v. Oeynhausen, on Trass, in the Erlauter. z. geogn. Karte des Laachner Sees, 1847. Brongniart has given the name of Brecciole to certain basalt- tufas of an arenaceous texture, in the Mem. sur les terr. des sedim. sup. du Vincentin. Paris, 1823. Sartorim v. Wattershamen, on Palagonittuff : Die submarinen Ausbr. des Val di Noto, 1846, p. . 34 ; Skizze von Island, 1847, p. 76; Vulk. Gest. in Sicilien und Island, 1853, pp. 179 and 215. Danvin, Palagonittuff on Chatham Island, in Geol. obs. on the vole, islands, 1844, p. 98. SandbergeT) Palagonittuff at Limburg in Nassau, in Geol. Verh. d. Herzgoth. Nassau, 1847, p. 81. Girard, Palagouittuff near Montpellier, in v. L. u. Br. Jahrb. 1853, p. 568. v. Richthofen, Geogn. Beschr. v. Siid-Tyrol, 1861. W. Evas, Felsittutf von Chemnitz Analyse, v. Leonh. u. Br. Jahrb. 1861, p. 643. Mitscherlich iiber den Alaunstein, Zeitschr. der geol. Ges. 1862, p. 253. FKAGMENTAL GKOUP. 31 L Appendix. Some part at least of what has been called schalstein belongs to the tufa formations ; we therefore propose here to treat of all the rocks to which this name has been applied, and we shall subjoin a few observations on the so-called laterite. 43. SCHALSTEIN. SCHALSTEIN. (Germ.} So many rocks have been described under this name, that we can only say in general that by it is understood a laminated rock interspersed with small particles of calc- spar. "We must distinguish them according to their localities and the authors who have described them. (A) SCHALSTEIN, or BLATTERSTEIN-SHALE. ) In Nassau. This SCHALSTTEIN oder BLATTERSTEINSCHIEFER. (Germ.) } rock was certainly first to receive the name, but it varies greatly in its character. The base or matrix appears here to be a very fine somewhat laminated greenstone-tufa, which contains calcspar in grains or thin layers of green, grey, or variegated spotted colour. In some places, however, this rock partakes of the character of breccia, or is porphyritic by reason of crystals of labradorite, or it is amygdaloidal, or is even penetrated by clay-slate and chlorite-schist. In the Rhenish grauwacke district it usually occurs in company with greenstone (diabase) a circumstance which confirms its origin as a tufa formation. Sandberger distinguishes the following varieties of schalstein in Nassau: ) NORMAL SCHALSTEIN. CALCAREOUS SCHALSTEIN, with much calcspar. SCHALSTEIN-BRECCIA, with calcspar as the cementing medium. SCHALSTEIN-CONGLOMERATE. e) SCHALSTEIN-AMYGDALOID. (/) PORPHYRITIC SCHALSTEIN, with crystals of labradorite. These are therefore varieties consisting of what under other circumstances we should perhaps consider quite dissimilar rocks, and which here are only classed together because of their occurring together or under similar cir- cumstances in the Devonian formation. (B) SCHALSTEIN, or CALC-TRAP, which is a somewhat slaty diabase or aphanite, containing grains of calcspar, and therefore may be classed among those greenstones (see pp. 148, 159). (C) SCHALSTEIN OF ZELLE, NEAR NOSSEN. ) Is only a variety of SCHALSTKIN VON ZELLE BET NOSSEN, oder ScHAi> I clay-slate containing 1 HTEINAHNLICHBK THON8CHIEFEB. (Germ.) j loids of calcareous spar. 312 SEDIMENTARY EOCKS. The name of schalstein has been used, or abused, for many other kinds of rock, and hence we find a tolerably rich literature on the subject. References. Stift, in v. Leonhard's Zeitschr. f. Min. 1825, vol. i. pp. 147 and *236 ; also in Geogn. Beschr. d. Herzogth. Nassau, 1831, p. 468. Oppermann, Dissert, iiber den Schalstein und Kalktrapp, 1836. Dollfus and Neubauer, Analyses of Schalstein in the Journ. f. Prakt. Chemie, 1855, vol/lxv. p. 199. Eglinger, Analyses, in the Jahrbuch des Ver. f. Naturk. in Nassau, 1856, No. 11, p. 205. Murchism and Sandberger, Transact, of the Geol. Soc., second series, vol. vi. p. 249. v. Dechen, in Nb'ggerath's Rheinland Westphalen, 1822, vol. ii. p. 71 5 and in Archiv f. Miner. Geogn. &c., vol. xix. p. 516. Hausmann, on the Formation of the Harz Mountains, 1842, p. 23. Sandberger, Ubers. der geol. Verh. des Herzogth. Nassau, 1847, p. 33. Gumprecht, in v. L. u. Br. Jahrb. 1842, p. 825. Naumann, Erlauter. d. geogn. Karte v. Sachsen, 1836, No. 1, p. 60. Appendix. We shall here append a rock of somewhat doubtful character. LATEEITB. This is the name given by English geologists to certain rocks of East India, which in part are red traps, very much resembling brick, but others are the products of the decomposition of crystalline schists. Upon such uncertain data, of course, no definite character can be established for a rock. References. GumprecMs Zeitschr. f. Erdkunde, vol. v. p. 160. According to v. Richthofen, the laterite of Ceylon is decom- posed calcareous gneiss : v. Leonhard's Jahrb. 1862, p. 739. 313 CHAPTER IV. ROCKS OF SPECIAL CHARACTER OR BEDDING. WE propose under this general head to gather together several formations of very various character, but subor- dinate extent in point of comparative bulk hardly im- portant enough to be considered altogether essential ingredients of the earth's crust. Several of the rocks we have classed under previous heads are likewise compara- tively insignificant in point of their extent, but they form part of larger connected groups, and so enter into the family of the great rock formations of the globe. In this chapter we have to deal with more separate and discon- nected formations, frequently of local character only, and which we rather force into groups for the sake of conve- nience than in conformity with the nature of their origin, which is very various and in many cases doubtful. Some are of igneous, some of sedimentary or metamorphic origin, but others, in their bedding and composition, differ so much from the greater part of the rocks of each of those three classes, that we are compelled to regard them, for the present at least, as problematical formations, al- though we may account for several by supposing a con- currence of extraordinary and exceptional circumstances at their first origin or during their mutations. We have not, therefore, attempted to classify these special rocks according to origin ; but have arranged them somewhat arbitrarily in groups in the following order : 1. Serpentine rocks. 2. Garnet rocks. 3. Greisen and schorl rocks. 4. Coal and carbonaceous rocks. 5. Ironstone rocks. 6. Various minerals as rocks. 314 MISCELLANEOUS DIVISION. SERPENTINE GROUP. These are rocks, probably, of very various original character, but which have all undergone the same special transmutation. This process has not been one of increase of crystallisation, nor of actual decomposition : it seems to have simply consisted in the absorption of magnesia, just as we know has happened in the case of many and various minerals. These have been converted from their original state into serpentine, steatite, or other magnesian com- pounds, and are pseudomorphs retaining the form of their original crystallisation. 44. SERPENTINE, OPHIOLITE. SERPENTIN, OPHIOLITH. (Germ.} SERPENTINE. (Fr.) A compact rock } dull in fresh fracture, soft, with greasy feel, usually dark-green or brown. Spec, grav ; '''' .' . 2-5 2-7. It may be doubted whether serpentine exists as an original and independent mineral ; for the crystals with amorphous fracture, which some mineralogists call ser- pentine, according to others are nothing more than pseudomorphs of chrysolite or some other mineral. If, however, the existence of serpentine as an independent mineral were established, the question still remains whether the rock which we term serpentine is to be re- garded as consisting of such mineral, because, although its composition is similar, in many cases it may be dis- tinctly shown that the rock has been derived by trans- mutation from other rocks. We know of undoubted pseudomorphs of hornblende, felspar, augite, &c., con- sisting of a substance bearing at least a very close resem- blance to serpentine, and actually so called. We will not pursue this mineralogical question further, but proceed to the description of the rock. Serpentine rock consists of two-thirds silicate of mag- nesia combined with 12 21 per cent, of water. It also contains some protoxide of iron, and this, as well as the water, enters into combination with the silica, supplanting a part of the magnesia : the proportion of silica varies from 38 to 43 per cent. ; the magnesia from 34 to 44 ; lime, clay, manganese, bitumen, and carbon are only SERPENTINE GROUP. 315 present in small quantity. The mass is so soft and trac- table, and yet so tough, that it admits of being cut into various shapes or turned with the lathe. Its unctuous feel is a very characteristic property of serpentine, and is caused by the great quantity of magnesia which it con- tains. Probably the numerous friction surfaces which often divide the rock in all directions are also owing to the presence of magnesia. These surfaces have a resinous lustre and are sometimes striped. The rock is usually of a dark-green colour, but some varieties are light-green, grey-green, brown, reddish-brown, or almost black, and the rock sometimes presents rapid alternation of colour, causing spots, flames, or vein-like markings. The principal mass of serpentine often porphyritically encloses many minerals of various kinds. The most fre- quent are pyrope, or magnesia-garnet, sometimes accom- panied by talc, less frequently bronzite, schiller-spar, chlorite, mica, magnetic iron-ore, pyrites, mispickel, chromic iron-ore, and very rarely (in the Ural) native platinum. The quantity of magnetic iron-ore is ex- ceptionally so considerable, as to influence the magnetic needle ; for instance, in the Fichtelgebirge, where, how- ever, the rock is not a very characteristic serpentine. The mass of serpentine rock is frequently penetrated by veins consisting of fibrous serpentine (asbestus), chrysotile, chlorite, or picrolite. Somewhat more rarely there occur veins or nests of calcspar, calcareous magnesian spar, magnesite, saponite, pyknotrope, dermatine, talc, brucite, volknerite, horn- blende, strahlstein, quartz, chalcedony, jasper, chrysoprase* opal, pyrites, chalcopyrite, chromic iron-ore, magnetic iron-ore, and native copper. Varieties in Texture. (a) COMMON COMPACT SERPENTINE. IMI-IITER SERPENTIN. (Germ.) i-KUPENTINE COMPACTS. (Ft'.) (6) PORPHYRITIC SERPENTINE. ) Often with crystals of py- PORPHYRARTK5KR SERPENTIN. (Germ.) \ TOPC. SERPENTINE PORPHYROU>E. (Fr.) ' (c) SLATY SERPENTINE. \ . SCHIKFRIGER SERPENTIN. (Germ.) \ Of imperfect thick cleavage. SERPENTINE SCHISTEUSE. (Fr.) ) (d) VEINED SKKI-KNTINE. GBADERTER SERPENTIN. (Germ.) SEKPKXTLNE BBECUIVORKE, OPHIOUTHB, Drongniart. (Fr.) 316 MISCELLANEOUS DIVISION. Inasmuch as all serpentine is probably the product of the metamorphosis of some other rock, it need hardly be said that transition states of this metamorphosis are found which differ not only from the extreme result of the pro- cess of change the genuine serpentine but from each other. If, however, this theory of the origin of serpen- tine be well founded, we cannot always succeed in deter- mining with certainty the character of the original rock ; perhaps in these cases the whole of the rock's mass has undergone change, and if bordered by other rocks of a different character, no trace is left of its original com- position. Several of the transition states of serpentine have received specific names. (e) FORELLENSTEIN (Germ.) or TROUT-STONE, at Neurode, in Silesia. A compact labradorite mass, speckled with spots of serpentine, which are frequently of angular form, and which Von Rath believes to have formerly been crystals of labradorite now converted into serpentine. (/) RENSLAERITE is the name given by Emmons, in his American Geology, 1855, to a serpentine-like rock, somewhat more crys- talline than ordinary serpentine. Its colour ranges from greyish white to green or black. Specific gravity, 2 - 87 ; composition, 59'2 silica, 32*9 magnesia, 3'4 protoxide of iron, 1 lime, and. only 2-8 water. (g) SCHILLER ROCK. \ The name given to a compound of SCHILLERFELS. (Germ.) L schillerspar and serpentine, which goes j over into ordinary serpentine. It oc- curs at the Baste in the Hartz Mountains. It has a serpentine matrix enclosing crystals of schillerspar of considerable size. It also contains labradorite, augite, mica, chlorite, and pyrites. Cocchi proposes that serpentine rocks should be designated according to the particular rocks from which they sprang ; e.g. diallage-serpentine, diorite-serpentine, granite-serpentine, &c. This may be very advisable where it is possible. Serpentine for the most part is jointed into irregular, massive, or gnarled masses. Exceptionally it is of co- lumnar structure, but not unfrequently it shows a kind of stratification or tabular jointing. This latter may have been occasioned by actual stratification, since ser- pentine may well have arisen from stratified rocks. It is most frequently found in irregular and subordinate beds between strata of crystalline schist, but it also occurs in SERPENTINE GROUP. 317 uncrystalline rocks both in the massive form and in veins. The surface of the little round-topped hills which it often forms usually shows a very scanty vegetation. In some places, as already said, its transmutation from other rocks is very evident, as, for instance, from gabbro at Siebenlehn, near Freiberg ; from dykes of granite tra- versing serpentine rocks near Bohrigen and Waldheim in Saxony, where the main serpentine rock itself is not improbably a transmuted granulite ; from chlorite-schist at Zell, in the Fichtelgebirge, where the change does not appear to be yet complete ; and from gneiss (probably), or an eklogite rock in the gneiss, at Zoblitz, in the Erz- gebirge. The processes and causes of the metamorphosis of serpentine are doubtless very different to those of the crystalline schists. When serpentine occurs in strata of crystalline schist, it is usually of later origin than those> and its conversion may have been occasioned by the con- tinued infiltration of water, holding magnesia in solution, during long periods of time. We are therefore unable to class this rock with the crystalline schists any more than we can with the igneous or sedimentary rocks. Ac- cording to Jukes, many serpentines are metamorphosed magnesian limestone. In the Engadine, a serpentine rock has been lately found to contain a considerable proportion of phosphate, so that it is proposed to use it as manure. Serpentine has been recently discovered by Sir Wil- liam Logan in the Laurentian limestones of Canada, replacing the remains of the foraminiferal organism, Eozoon Canadense. References. Scheerer, Mineral Serpentine, Poggend. Ann. 1854, vol. xcii. p. 287. Hauf/ht&n, Philos. Mag. 1855, vol. x. p. 253. Websky, Krystallstructur des Serpentine, Zeitschr. d. d. geol. Ges. 1858, p. 277. T. Sterry Hunt, on the Serpentines of Canada and their asso- ciated Rocks, Lond. Edin. and Duhl. Phil. Mag. vol. xiv. p. 388, 1857. Quart. Jour. Geol. Soc. vol. xxi. p. 67. v. Rath, Forellenstein, Poggend. Ann. vol. xcv. p. 652. Cocchi, in v. L. u. Br. Jahrb. 1857, p. 600. Emmon*, in Americ. Journ. of Sc. 1843, vol. xlv. p. 122. A. Streng, Serpentin in Gabbro von Neurode, v. Leonh. u. Br. Jahrb. 1864, p. 257. C. W. Fuchs, Schillerfels bei Schriestheim, v. Leonh. u. Br. Jahrb. 1864, p. 326. 318 MISCELLANEOUS DIVISION. GARNET GROUP. The one property which these rocks possess in com- mon is, that they all contain garnet as an essential, some- times a predominant, constituent. The minerals with which the garnet is combined are various, such as am- phibole, pyroxene, felspar, mica, dichroite, &c. Garnet rocks frequently occur in subordinate masses, often of irregular shape and doubtful origin, in strata of crystal- line schists, or in granitic rocks. We include in this group the following rocks : Eklogite, Disthene rock, Eulisite, Garnet rock, Kinzigite, and Dichroite rock. 45. EKLOGITE, OMPHACITE ROCK, SMA- RAGDITE KOCK, DISTHENE ROCK. EKLOGIT, OMPHACITFELS, SMARAGDITFELS, DISTHENFELS. (Germ.} ECLOGITE, OMPHAZITE, Hauy. (Fr.) A compound of green smaragdite and red garnet. The smaragdite forms a finely crystallised matrix., usually somewhat slaty or fibrous, in which the crystals of garnet are porphyritically enclosed. This rock, to which Haiiy gave the name of eklogite, is usually very firm and coherent, difficult to break with the hammer. Its fresh fracture presents a peculiarly beautiful appearance, from the red garnets sparkling in a light-green matrix. Its accessory ingredients cause it to vary somewhat in different localities. The beautiful eklogites of the district of Miinchberg, in the Fichtel- gebirge, sometimes contain mica ; more rarely they con- tain zoisite or some other variety of epidote, quartz, pyrites, and magnetic iron-ore. In the eklogite of the Sau-Alp mountain in Styria, zoisite and actinolite are almost its predominant constituents, and it contains in addition to the crystals of garnet some quartz, corinthine, and disthene. On the island of Syra, the common eklo- gite is found in layers or strata, alternating with a rock consisting of a compound of disthene-garnet and mica of a silvery white colour : this latter rock has been termed by Virlet disthene rock ; we might, however, with equal propriety, call it a variety of eklogite. A rock occurring at HaslaUj near Eger, which has been sometimes called GARNET GROUP. 319 eklogite, consists principally or in great part of idocrase (so-called Egeran). Eklogite most frequently occurs irregularly imbedded in strata of crystalline schist, as, for instance, at Miinch- berg, in the gneiss district of that locality. The direction of its slaty texture there is in conformity with that of the prevailing foliation of the schist, and we may therefore doubt whether it should be regarded as a contempora- neous formation with the gneiss, or as having forced its way into the latter at a subsequent period. Owing to its greater power of resistance to the decomposing influences of the atmosphere, this rock usually forms prominent knolls or rocks. Virkt, in the Bullet, de la Soc. geol. 1833, vol. iii. p. 201. 46. EULISITE. EULISIT. (Germ.) EULISITE. (Fr.) A compound composed of protoxide of iron, resembling olivine, green pyroxene, and brownish-red garnet. This name was given by A. Erdmann to a rock which forms a bed of great thickness in the gneiss at Tunaberg, in Sweden. Erdmann, Forsok till en geogn. mineral Beskrifing ofver Tunabergs Socken, 1849, p. 11. 47. GARNET ROCK. GRANATFELS. (Germ.) GRENATITE, Cordier. (Fr.) A crystalline granular compound of garnet and horn- blende, usually with some magnetic iron-ore. Sometimes the brown or yellowish garnet (aplome) predominates, so that the mass almost entirely consists of a granular aggregate of that mineral ; sometimes, again, the rock contains many other minerals besides the horn- blende and magnetic iron. This rock only occurs in subordinate matter ; e. g. in the mica-schist on the Teufelsstein and Klobenstein, near Schwarzenberg, in Saxony, where it forms small pro- jecting rocks. Cotta, Erlauter. z. geogn. Karte von Sachsen. No. 2. p. 225 ; v. L. u. Br. Jahrb. 1844, p. 413. 320 MISCELLANEOUS DIVISION". 48. KINZIGITE. KINZIGIT. (Germ.) KINZIGITE. (Fr.) A crystalline compound of black mica, garnet, oligoclase, sometimes passing over into the compact state. This is a rock which was discovered at Wittichen, at the Kinzig in the Black Forest. It was formerly con- sidered to be a garnet rock and so designated, but H. Fischer pointed out its individual properties, and gave it a separate name. He afterwards found the same rock at Gadernheim and Auerbach, in the Odenwald, and certain rocks occurring at Bodenmais in Bavaria and at Cabo de Gata in Spain are considered by him to be closely allied to it. In some of the above-named rocks, cordierite, fibro- lite, and mikrocline occur, the last as a substitute for oligoclase. Fischer, in v. L. u. Br. Jahrbuch, 1860, p. 796 ; and 1861, p. 641. 49. DICHKOITE ROCK. DICHROITFELS. (Germ.) An irregular compound of felspar, dichroite, garnet, and mica (the latter in small quantity) ; firm, dark- coloured. This rock is allied to dichroite-gneiss. It is found (e.g.) forming a dyke in the granite of the Erlbachgrund, near Kriebstein, in Saxony. Naumann, Erlauter. d. geogn. Karte v. Sachsen, No. 2, p. 13. GKEISEN AND SCHOKL GROUP. The rocks of this little group are distinguished by their consisting principally of quartz, frequently impregnated with fine particles of tin-ore, or else associated with beds or veins containing tin-ore. In addition to the quartz, there occur in these rocks white mica, chlorite, or schorl as essential ingredients, and wolfram, specular iron, and topaz as accessories. The following are the rocks included in this group : 1. Greisen, a compound of quartz and mica. GREISEN AND SCHORL GROUP. 321 2. Z witter rock, consisting of quartz, chlorite, specular iron- and tin-ore. 3. Schorl rock, a compound of quartz and schorl. 4. Topaz rock, a breccian variety of schorl rock, with topaz. 50. GKEISEN. GREISEN. (Germ.} HYALOMICTE, Brongniart. (-F/-.) A crystalline granular compound of quartz and mica. This, therefore, is granite without felspar, or we may- say it is the substance of mica-schist, without its foliated texture and conformation. It is of somewhat rare occur- rence. It actually passes into granite; that is to say, some felspar, or at least kaolin, occasionally enters into its composition. But no transitions into mica-schist are known ; in other words, it shows no disposition to a fissile texture ; it is always distinctly granular (coarse or fine^ grained). The mica of greisen is chiefly lithia-mica. Some tin- L ore likewise occurs as an accessory ingredient, and the rock is frequently penetrated with or associated with veins of tin-ore, as at Zinnwald, in the Erzgebirge, where this rock occurs very characteristically. Less character- istically it also occurs near Ober-Pobel, to the west of Altenberg. Greisen is of massive structure, without a trace of stratification. Its constant association with beds and veins of tin-ore, in the granite districts of Schlaggenwald, Corn- wall, &c., and its resemblance to the zwitter, lead us to the conclusion that special circumstances have led to its formation from granite by decomposition of its felspar, although in the coarse varieties it is difficult to conceive how and by what substance the felspar has been replaced. In this view we might regard greisen but as a variety of granite. We have separately classed it and the other tin-bearing rocks in a distinct group, because they pro- bably all owe their peculiar properties to special and analogous causes,' although these have not yet been satis- factorily ascertained. 322 MISCELLANEOUS DIVISION. 51. ZWITTEK ROCK. ZWITTERGESTEIN, SlOCZWERKSPORPHYR. (Germ.) A dark-grey aggregate, rich in quartz, texture fine- grained to compact ; its other ingredients are not to be distinguished by the naked eye. By help of the lens, we may recognise in the fine- grained mass of this rock subordinate quantities of chlo- rite, tin-ore, arsenical pyrites, and also some micaceous iron combined with the quartz. To these the dark colour of the rock is probably owing. The tin-ore in Altenberg (the only locality where the rock is known to occur characteristically) is called zwitter, and the rock therefore was called Zwitter rock by the miners there. The unsuitable name of Stock- werksporphyr is another miners' term, given under the erroneous belief that greisen belonged to the porphyries, although it has no trace of porphyritic texture. The celebrated f pinge ' of Altenberg is a large crater- like hollow, formed by the falling in of extensive mining works in this rock, which is worked for its tin-ore. At the margin of this pinge may be observed the gradual transition from fine-grained granite into zwitter rock. The granite is first found to be penetrated by numerous and very irregular cracks or fissures filled with quartz, and on each side of the quartz there is usually a dark stripe of from one quarter to one inch thick and upwards. These stripes, on closer investigation, are found to be zwitter rock, containing no felspar, although they merge gra- dually into the surrounding granite, which is of the com- mon kind. The stripes are evidently the result of influences proceeding from the fissures, and towards the principal mine they become broader and broader, so that very little unconverted granite is left between the numerous clefts. At length the last remnant of the granite disappears, the whole mass having been converted into zwitter rock, in which, however, the quartz veins still remain distinctly perceptible. It would appear that the transmutation must have been caused by some solution or vapour impregnated with tin penetrating the granite through its many fissures. Dr. Rube has carefully analysed several specimens of the unchanged granite, of the dark stripes near the quartz, and of the entirely converted zwitter rock. From these GREISEN AND SCHORL GROUP. 323 analyses it has appeared that the composition of the dark stripes and of the genuine zwitter rock were identical. They each contain 3 p. c. silica and 2 p. c. potash less than the granite. On the other hand, they contain 4 p. c. protoxide of iron, 2 p. c. alumina, 0'6 oxide of tin, and 0*5 I/O lime more than the granite. It follows, there- fore, that in addition to the ingredients which we have above mentioned as being recognisable in the zwitter rock it must also contain a silicate of alumina. The pene- trating solution appears to have decomposed the felspar and mica, and in their stead to have formed micaceous iron-ore, chlorite, tin-ore, a silicate of alumina, and also to have left a deposit of lime. The potash must have been carried away in solution ; the silica was probably concen- trated, at least in part, in the cleft of the rock, forming the veins of quartz which we now see. Cotta, in Berg- u. Huttenm. Zeitung, 1860, No. 1, and 1862, p. 74. 52. SCHORLACEOUS SCHIST and SCHORL ROCK. SCHORLSCHIEFER und ScHORLFELS. (Germ.) HYALOTOURMALITHE, Daubrte. (Fr.) A crystalline compound of schorl and quartz, foliated or granular to compact. The schistose varieties are most prevalent, and we have therefore placed them foremost ; the compact varieties are rare, and in the absence of transition states they are dif- ficult of recognition. As accessory ingredients, this rock contains mica, chlorite, felspar, tin-ore, arsenical pyrites, and exceptionally, in some places, topaz. These schorl rocks are (like griesen) almost always accompanied by or associated with beds containing tin-ore. The proportion of silica which they contain is very unequal, and depends on the prevalence of their quartz. Varieties in Texture. (a) SCHORLACEOUS SCHIST. Its somewhat indistinct foliated texture is owing to the parallel disposition or distribution of the acicular particles of schorl. The quartz sometimes forms itself into contorted layers quite independent of the schistose texture. This rock occurs (e.g.) in subordinate beds, alternating with mica-schist at Eibenstock, in Saxony, where it is traversed by veins of tin-ore. T 2 324 MISCELLANEOUS DIVISION. (b) GRANULAR SCHORL ROCK. This is either a tolerably uniform compound (fine or coarse-grained) of schorl and quartz ; or it consists principally of quartz, with small separate columnar particles of schorl, which are frequently broken. (c) COMPACT SCHORL ROCK. A blackish-grey mass, in which the in- gredients are too intimately blended to be distinguished, as, for instance, in the tin mining district of Cornwall. Varieties in Composition. (d) TOPAZ ROCK. \ Hitherto only known at the Schneck- SS^^faT f stein > f t he Voigtland where it (/y.) ) forms a dyke of considerable thick- ness in the mica-schist. The composition of the rock is sin- gular ; large fragments of schorl-schist (containing topaz), with quartz, lithomarge, and geodes of topaz, are cemented together to a kind of geodic breccia. The rock likewise contains tin- ore, apatite, malachite, and azurite as accessories. Von Eschwege has given the name of Carvoeira to a quartz rock containing schorl, found in the Brazils. References. Freiesleben, Geogn. Arbeiten, vol. iv. p. 1. Breithaupt, Paragenesis, in v. Leonhard's Jahrb. 1854, p. 787. oase, Transact, of the Geol. Soc. of Cornwall, 1832, vol. iv. pp. 240 and 373. Naumann, Erlauter. d. geogn. Karte v. Sachsen, No. 2, p. 201. Daubree (Hyalotourmalite), Ann. des Mines, 1841, 3 e ser. vol. xx. p. 84. CARBONACEOUS GROUP. In these rocks carbon is the principal ingredient. They are always of dark colour, varying between brown and black. They are usually, but not always, combustible. They are all of organic origin, and for the most part pro- ducts of vegetable accumulation ; some (exceptionally) perhaps are the result of the accumulation of animal matter. The differences now exhibited are doubtless chiefly owing to the degree of metamorphosis of the original organic substance. If we start with this assumption, we may class these rocks as follows, beginning with those whose state is the least changed, and proceeding up to those which are most completely metamorphosed : 1. Peat. The vegetable substance has undergone little change. We are not authorised to conclude that all coal has been formed from peat-mosses. On the contrary, we know of much coal which is the undoubted product of trunks and leaves of trees, and various other vegetable substances. CARBONACEOUS GROUP. 325 2. Browncoal or Lignite, containing much bitumen. 3. Common coal (German, Schwarzkohle), containing much less bitumen. 4. Anthracite, containing very little bitumen. 5. Graphite, without any bitumen, and not combustible. Some other differences result from foreign admixtures. We observe from the above series that the first process of change (from the peat to the browncoal) was accom- panied by a development of bitumen, which in the subse- quent stages of metamorphosis has again gradually disap- peared, and become lost in all probability by evaporation. The relative geological ages of the different coals in general correspond with and confirm this view ; and the only exceptions of which we are aware are capable of explanation from special local causes. We may therefore say that the varying proportion of bitumen contained in the carbonaceous rocks furnishes us with a series which at the same time is expressive of their geological age. In addition to the above, and in some measure the com- plement of the series, we have 6. Mineral pitch (including asphalte, elastic bitumen, and mineral oil) consisting of the bitumen which has been volatilised or distilled from bituminous coal. It is some- times found separately bedded as a distinct rock, some- times as an impregnation of other rocks, such as lime- stone, shale, &c. The following rocks we add by way of appendix to the coal group, as bearing an affinity with it in respect of their origin, or otherwise. 7. Bituminous shale (Brandschiefer), an argillaceous shale containing very much bitumen, and frequently car- bon. Also, 8. Kohlenbrandyesteine (burnt clay rocks), which are not carbonaceous, but are the result of burning coal upon clay rocks. 9. Guano and coprolite beds. The product of local accumulations of animal excrement. We have already stated that the usual and normal bed- ding of the different kinds of coal entirely corresponds with the theory of their origin and of the causes of their different composition and structure. The individual ex- ceptions only serve to prove the rule ; they may all be 326 MISCELLANEOUS DIVISION. explained by special circumstances, and when so explained are in fact necessary consequences of our assumed theory. The following review of the most important coal forma- tions will best explain our meaning : Age. Post Terti- ary. Tertiary. Usual Coal-beds. Peat-mosses and beds turf in many places. of Chalk pe- riod. Oolite or Jura pe- riod. Trias pe- riod. Coal pe- riod. Browncoal in North Ger- many, Bohemia. Hessen, &c. Browncoal containing little bitumen near Haring, in Tyrol (Eocene). Browncoal poor in bitumen of the Gosau formation in the Alps. Bituminous shale and coal of the Jura and Lias for- mations in Germany and England. Lettenkohle, an impure browncoal, containing little bitumen, belonging to the Keuper formation in Germany. Common black coal of the Coal and Culm forma- tions in England, Ger- many, and France. Transition Anthracite in Scotland and or Grey- in Ireland, wack e period. Still older. Graphite in the crystalline schists at Passau in Ba- varia, &c. Exceptional Coal-beds. Anthracite (with basalt) at the Meissner, in Hessen. Ordinary pit-coal or ( black coal ' at Silthal, in Tran- sylvania. Ordinary black coal at Ruszkberg, in the Banat. Ordinary black coal at Fiinfkirchen in Hun- gary, and at Steierdorf in the Banat. Anthracite at Schonfeld, Zaunhaus and Brandau, in the Erzgebirge, in the State of Ohio, adjoining the porphyry at Walden- berg, &c. We see from the foregoing that in every geological period in which any sedimentary deposits have taken place, there have been accumulations of vegetable matter, and that these have (occasionally at least) formed beds, CARBONACEOUS GROUP. 327 and have afterwards become coal. But it is very remark- able that as far as those countries which have hitherto been geologically explored extend, the principal coal formations are confined to two of the great geological periods, viz., the Tertiary, to which the browncoals be- long, and the Carboniferous, This would be a fact very difficult to explain, if it were proved to be true for the whole globe ; but as only about one-twelfth part of the surface of the earth has been hitherto explored, we may be permitted to doubt whether coal may not yet be found in large quantity in other formations than those at present known. In the interior of Africa, Asia, and Australia, and South America, as well as under the ocean, very extensive beds of coal may exist, which, together with those we already know of the Chalk, Oolite, Trias, and transition periods, would fill up all the apparent gaps, and furnish as uniform a result with reference to the deposit in all ages of material for coal-beds, as of that for any other rock. According to our present experience, we are authorised to believe that the deposit of material for coal formation lias taken place in a similar manner and under like con- ditions in every period. We accordingly find a certain petrographic uniformity or mutual relationship in the coals of all ages. The coal-beds are almost universally found interstratified and alternating with beds of argillaceous rocks and sandstones, usually of grey colour (never red), frequently with spherosiderite, or so-called clay-iron- stone (Blackband) very seldom with limestone. The state of these argillaceous and arenaceous rocks has undergone a change corresponding to that of the coal. Their greater compactness, solidity, and their laminated texture, almost always correspond with the degree in which the bitumen has been expelled from the coal, or, in other words, with the geological age of the latter. 53. PEAT, TURF, BOG. TORF, DARG. (Germ.) TOTJRBE. (Fr.) An aggregate of vegetable growth, interwoven and more or less compressed and decomposed, of yellow, brown, or black colour. 328 MISCELLANEOUS DIVISION. The plants whose remains are usually found in peat are of marshy origin, and in Germany usually spring from Sphagnum. The moss is more or less compacted, felt-like, or almost compact. Sometimes there are found imbedded in it trunks of trees, or their branches, roots, leaves, hard fruits, and the like ; some of which have undergone little or no change. Besides these vegetable ingredients, peat frequently contains earthy admixtures, also red ochre, nodules of ' kieselguhr ' (an aggregate of fossil infusoria), crystallised gypsum and pyrites, or earthy particles of vivianite. The following varieties are sometimes distinguished, though they cannot be definitely characterised and sepa- rated: () PEAT-MOSS. \ FILZ- oder MOOSTORF. (Germ.) \ Loose and felt-like. TOURBE FIBREUSE. (Fr.) J (6) HEATH-TURF. HAJDETORF. (Germ.) (c) GRASS-TURF. RASENTORF. (Germ.) (d) LEAF-TURF. PAPIERTORF oder BLATTERTORF. (Germ.) (C) Mt . *, } Very wet, and thereby mud-like. (/) PITCH-TURF. } Very compact and solid, the vege- PECHTORF. (Germ.) I table matter having been much com- '. vol. xii. p. 161. Herter, Graphitschiefer mit Pflanzenresten, Zeitsch. d. deut. geol. Ges. vol. xv. p. 459. Respecting the localities of the occurrence of Graphite, refer to v. L. u. Br. Jahrb. 1833, p. 552 ; 1836, p. 595; 1838, p. 427; 1839, p. 448; Journ. d. Phys. vol. xliv. p. 301 ; Cor- respondenzbl. des zool. mineral. Vereins zu Regensburg, 1827. p. 29, and 1848, p. 158. 58. BITUMEN and MINEKAL PITCH. BITUMEN und ERDPECH, ASPHALT. (Germ.} BITUMJE, MALTHE, ASPHALTE. A pitch-like mass, colour varying from dark-brown to black) softens with heat. Spec. grav. bitumen ..... 0-7 0*9 Mineral pitch ...... 1-1 1-2 This bituminous mass consists of 80*82 carbon, 910 hydrogen, and 8*9 oxygen and nitrogen. Bitumen is very seldom found in mass in the interior of the earth, but frequently as an accessory admixture in calcareous, marly, or argillaceous rocks. On the surface of the earth it occasionally forms small pitch lakes, as at the Dead Sea, and in the island of Trinidad. To this class belongs the petroleum, or rock-oil, which in North America has been recently found streaming in great abundance from the earth. The origin of bitumen may be, and probably is, two- fold. Bitumen or the gaseous elements of bitumen must of necessity be disengaged where bituminous coals un- dergo transmutation into coals of a less bituminous cha- racter, or into anthracite. This bitumen may either permeate the neighbouring rocks and make them bitu- minous, or it may rise to the surface of the earth and become a separate deposit of a fluid or semi-fluid sub- stance. Again, bitumen will be formed wherever animal remains gasteropods, fishes, and the like have been enclosed by stratified beds of rock, and have become transmuted. And thus some limestones, marls, or clay- rocks may have become bituminous (being converted into oil-slate, stinkstein, &c.). Or the bitumen contained in z 338 MISCELLANEOUS DIVISION. such rocks may, under the influence of heat or other causes, again escape and become deposited elsewhere. The occurrence of bitumen in nature, taken in con- nection with the animal and vegetable fossils found in coal, completes the evidence in support of the established view of the origin of coal. Mayer's Asphalt des Val de Travers, 1839, is the only sepa- rate treatise on bitumen known to us. On rock-oil springs in North America, Tide Petermann's Mittheilungen, 1861, vol. iv. p. 151 : and Kane's Zeitschrift d. Erdkunde. 1862, vol. xii. p. 279. 59. PYROSCHIST(#ww), BITUMINOUS SHALE. BRANDSCHIEFER. (Germ.) SCHISTE BITFMINEUX, MARNOLITE, Cordier. (Fr.) Is the name given to very bituminous and thereby dark- brown or black-coloured argillaceous shale, which, although, it burns in five, yet, owing to its containing so much clay, cannot itself be used as fuel. These are best classed with the carbonaceous rocks, together with which they frequently appear, and for which they have sometimes even been mistaken. Their streak is of resinous lustre ; they often contain distinct remains of plants or fishes ; sometimes bitumen may be extracted from them, and they are then sometimes called oil-slate ( Oelschiefer, Germ.; Schiste oleifere, Fr.). Bituminous shales of this class are found in Germany, especially in the lower Rothliegende, e.g. at Oschatz, in the Lias of Wiirtemburg, and in the chain of the Weser, and in the Brown-coal formation at many places. Sterry Hunt, Bitumen and Brandschiefer (Pyroschist), Silliman and Dana's American Journal, vol. xxxv. p. 157. Appendix. We may here add the burnt clays and the beds of guano or coprolites. The first because they have ori- ginated from the burning of coal-beds, the latter as accu- mulations of organic matter. 60. BUENT CLAYS. GEBRANNTE THONE, KOHLEISTBRANDGESTEIKE, ERDSCHLACKEU und PORZELLANJASPIS. (Germ.) THERMANTIDE, Cordier. (Fr.) CARBONACEOUS GROUP. 339 These are local products of transmutation from clay rocks produced by burning coal-beds. They are too un- like in character to admit of a common definition. We, therefore, separately describe a few principal varieties. (a) BURNT ARGILLACEOUS SHALE. ) Hard, and resembling GEBRAN-NTER SCHIEFEHTHON. (Germ.) I buck-colour, yellow, AK.IILK acmonusE MfcTAMORPHiQUE. (Fr.) nevertheless, still exhibiting the original laminated texture, and impressions of plants of the slate-clay. At Planitz, near Zwickau, in the Coal formation, and at Zittau in Saxony, in the Browncoal formation. (&) ROCKSLAG. \ By reason of greater heat the lami- ERDSCHLACKE, KOHLEXBRAND- I n ated texture has been destroyed. OLA SE BJ gSj ( (i) AN ARGILLACEOUS VARIETY (BROWN OR YELLOW CLAY-IRON- STONE). THONREICHER BRAUNEISENSTEIX, THOXEISENSTEIX. (Germ.) (k) A SILICEOUS VARIETY, PASSING INTO BROWN FERRUGINOUS QUARTZ. KlESELREICHER BRAUNEISEXSTEIN. (Germ.) HEMATITE BRXJNE SIUCEUSE (JASPOIDE). (Fr.) All these different varieties (with the exception of bog- ore, which only occurs on the surface of the ground) fre- quently form subordinate beds or veins filling up clefts in other rocks. Sometimes, but more rarely, they form local massive and irregular accumulations especially at the con- tact of two different rocks (contact formations). Bog-ore is formed at the present day as a chemical precipitate from water holding salts of iron in solution ; this process is occasioned or accompanied by decomposition of organic substances. If we suppose similar deposits of brown hematite to have taken place in former periods, and then to have been covered by other sedimentary formations, we may easily conceive how in process of time the thin compact layers of iron-ore which we find imbedded in other strata would have arisen. Sometimes brown hematite is evidently a product of transmutation from spathic iron, or even magnetic iron-ore. 63. EED HEMATITE. ROTHEISENSTEIN. (Germ.) HEMATITE ROUGE. (Fr.) A compact, earthy., or fibrous, or sometimes crystalline, slaty, aggregate of red iron-ore ; colour red to black ; streak red. Spec. grav. 4 5. Red hematite consists entirely or essentially of peroxide IRONSTONE GROUP. 343 of iron (70 p. c. iron + 30 p. c. oxygen), sometimes inti- mately combined with oxide of manganese, silica, or clay. Its crystalline state is termed specular iron (Eisenglanz), or micaceous iron (Eisenglimmer). Varieties in Texture. (a) COMMON RED HEMATITE. \ GEMEINER DICHTER ROTHEISENSTEIN. I ComDact (Germ.) HEMATITE ROUGE COMPACTS. (Fr.) > (b) EARTHY HEMATITE, or RED IRON-MOULD. ERDIGER ROTHEISENSTEIN, oder ROTHER EISENMULM. (Germ.) (c) FIBROUS HEMATITE, REDDLE. FASRIGER ROTHEISENSTEIN, ROTHEL oder ROTHER GLASKOPF. (Germ.) HEMATITE ROUGE FIBREUSE. (Fr.) (d) OOLITIC HEMATITE, or FERRUGINOUS OOLITE. OOLTTHISCHER ROTHEISENSTEIN, Oder ElSENOOLTTH. (Germ.) HEMATITE ROUGE OOLITHIQUE. (Fr.) (e) MICACEOUS IRON-SCHIST. 1 Consisting of a schis- EISENGLIMMERSCHIEFKU. (Germ.) I tosc acTgregate of mica- 1 Kit OUGISTE ECAILLEUX OU MICACE. (Fr.) I ceous ij. on e g QU the Gorgeleu in Marmaros, in Hungary, where it is imbedded between strata of chlorite-schist and "limestone. (f) SPECULAR IRON. 'j As rock, an aggregate of specular i:isKxuLA>-zoEOTEix. (Germ.) I i r() n (iron-glance), usually combined PER SPECULAIRE. (Fr.) J ^ ^ f^ Qf J^ ^^ rence as a rock ; e.g. on the Island of Elba, and at Picton-nob, r in North America. Varieties in Composition. 0) A VARIETY RICH IN MANGANESE r Whence its black (BLACK HEMATITE). J colour ; sometimes MANGANHEICHER ROTHEISENSTEIN (SCHWARZ- 1 called black hematite UiiMATITK MANCrAVKSIF^RE (Fr} V OCll\VflJ*ZGlSCllSLClD ) (A) RED CLAY-IRONSTONE, RED OCHRE. THONREICHER ROTHEISENSTEIN (THON- L An arefillaceous vanety. (Germ.) J OCRE ROUGE. (Fr.) (i) SILICEOUS HEMATITE. \ KlESELREICIIER ROTHEISEN- I T j. J f RBV. (Germ.) f Passing into red ferruginous quartz. HEMATITE ROUGE SHJCEUSE (JASPOtoE). (Fr.) I (K) ITABIRITE. \ A compound of specular iron, micaceous ITABIRIT. (Germ.) I iron, magnetic iron-ore, and some quartz ; ' .) granular, schistose, or compact. As acces- sories, it contains talc, chlorite, actinolite, and native gold. Found at Itabira, in Brazil (v. Eschwege, ' Brasilien '). (7) TOPANHOACANGA (MooRSHEAD ROCK). This rock consists of angular or somewhat rounded fragments of specular iron, mi- caceous iron, and magnetic iron-ore, cemented together by a ferruginous compound. Sometimes it also contains fragments of quartz, itacolumite, clay-slate, &c., rarely also, grains of native gold. At Itabira. Villa Rica, and Marianna, in Brazil, it forms a crust on the surface of the ground of from four to twelve feet thick. 344 MISCELLANEOUS DIVISION. Most of the above-mentioned varieties of red hematite occur in stratifications or veins, like the brown hematite ; and they are also (though more rarely) found irregularly massed between other rocks, usually of the transition or crystalline schist formations never those of very recent origin. We may, perhaps, be justified in regarding the red hematites as products of catogenic transmutation from brown hematite ; yet it would appear that they have some- times been formed from spathic iron under special circum- stances. Certain it is from their anhydrous state we may safely say that they are never original deposits from aqueous solution, although they sometimes contain dis- tinct fossils. Specular iron, or iron-glance (as a mineral), is some- times found in the clefts or fissures of volcanoes, where it is a product of sublimation. 64. MAGNETIC IRONSTONE, MAGNETITE. MAGNETEISENSTEIN. (Germ.} MAGNETITE, FEE OXYDFLE, Hauy and Dufrenoy. (-FV.) A granular or compact aggregate of magnetic iron-ore ; black ; streak black ; metallic lustre ; influences the magnetic needle. Spec, grav 4-5 5-2. Pure magnetic iron-ore consists of 69 to 75 per cent, peroxide of iron, and 31 to 25 per cent, protoxide of iron (therefore it contains about 72 per cent. iron). As a rock it occurs mixed with specular iron, chlorite, chromic iron- ore, titanic iron-ore, pyrites, chalcopyrite, quartz, horn- blende, augite, garnet, or felspar, &c. Varieties in Texture. (a) GRANULAR. (6) COMPACT. (c) SCHISTOSE. The foliation is occasioned by admixture of foreign minerals. Varieties in Composition. (d) PUKE MAGNETIC IRON-ORE. (e) CHLORITIC MAGNETIC IRONSTONE. (/) CHROMIC IRONSTONE, in which chromic iron predominates or forms the only ingredient. (g) GARNETIFEROUS IRONSTONE ; passing over into garnet rock. IEONSTOXE GROUP. 345 (h) PYRITO-MAGNETIC IRONSTONE. (i) CATAWBIRTTB is the name given by 0. Lieber to a rock found by him in South Carolina, occurring there in great abundance. It consists of a compound of talc and magnetic iron, intimately blended together. Magnetic ironstone forms subordinate beds or veins in the crystalline schists. It is very extensively developed at Schmiedefeld, in the Thuringian Forest, at Arendal in Norway, at Danemora in Sweden, as a stratum in the clay-slate at Berggieshiibel in Saxony. Chromic iron- stone is usually associated with serpentine. 65. SPATHIC IRON; SIDERITE. SPATHEISENSTEIN. (Germ.) FER CARBONATE, Haily ; SIDEROSE, Seudant. (Fr.) A granular or compact aggregate of spathic iron ; yel- lowish-white, grey, or yellowish-brown; streak white; effervesces with acid. Spec. grav. . * . - . . f 37 3-9. Spathic iron is carbonate of protoxide of iron (62 per cent. protoxide of iron, and 38 carbonic acid) ; where it occurs as a rock it is sometimes mixed with ankerite, calc-spar, clay, specular iron, copper pyrites, &c., in small quantities. Varieties in Texture. (a) GRANULAR. (b) VERY FINE-GRAINED. (c) COMPACT SPHEROSIDERITE (CLAY- \ So called from its oc- IRONSTONE). I curring in the form of DICHTER SPATHEISENSTEIN, SPHAROSIDERIT. j spheroidal concretions <<*-> J orsentaria SIDEROSE COMPACTS. (Fr.) U1 8e p l ' ttilt| " (d) A SHALY VARIETY OF SPHEROSIDERITE, Or CARBONIFEROUS IRONSTONE (BLACKBAND). SCHIEFRIQER SPHAROSIDERIT, Oder KOHLENEI8ENSTEIN. (Germ.) Varieties in Composition. (e) ROHWAND (Germ.). A granular spathic ironstone, mixed with much ankerite or calcspar. (f) ARGILLACEOUS SPHEROSIDERITE, \ or CLAY IRONSTONE. I Also called clay carbonate THONREICHER SPHAROSIDERIT, oder J O f i ron< SEPTARIA AROILEUX. (Fr.) ' (g) CARBONIFEROUS IRONSTONE, BLACKBAND. \ Dark-coloured by KHHLENEISKNOTEIN. (Germ.) v reason of admixture J of coal j usually a slaty spherosiderite or clay ironstone (d). 346 MISCELLANEOUS DIVISION. This is the black "band of Scotland. < This natural admixture of coaly matter confers on these rocks their special value, the raw stone being readily calcined, in fact igniting and slagging itself without the expensive admixture of coal, as is the case with the ordinary clay ironstones and hematites.' Page. Mushet makes a distinction between Blackband and Clayband, Berg- u. Huttenm. Zeit. 1863, p. 295. The crystalline varieties occur as subordinate strata, veins or regular masses, in the crystalline schists or the older sedimentary formations. The compact spherosi- derites are most usually found with beds of coal. The origin of these stratified beds and irregular masses of spathic iron has not hitherto been satisfactorily explained, since a carbonate of protoxide of iron could not be de- posited under atmospheric influences. Probably the car- bonic acid may have supervened at a later period. On the other hand, the influence of the air will quickly change spathic iron into brown hematite, and hence it is that we find the surface of spherosiderite usually coated with a brown crust, and many entire beds of brown hematite appear to have been formed in this manner. A different process of mutation may, perhaps, in some cases, have produced red hematite and magnetic iron-ore. Appendix. 66. DISILICATE OF PROTOXIDE OF IRON. HALBKIESELSATJRES EISENOXYDTJL. {Germ.} CHAMOISITE (Chamoison, Valais). (Fr.} This compound sometimes occurs in the form of pea-iron-ore contained in ferruginous clay, together with nodules of jasper, as, for instance, at Kandern, on the western margin of the Schwarzwald in Germany. Deffner, zur Erklarung der Bohnerzgebilde, Stuttgart, 1859. 67. SILICEOUS SPHEROSIDERITE. KIESELIGER SPHAROSIDERIT. (Germ.) CARBONATE DE FER SILICETJX. (Fr.~) This is a rock, described by Naumann, of a peculiar and fine arenaceous character, consisting essentially of spherosiderite (containing manganese) and siliceous earth or quartz-sand. It forms a stratum (very rich in fossils) in the Nummulite forma- tion of the Bavarian Alps between Traunstein and Sonthofen. Schafthautl, in v. L. u. Br. Jahrbuch, 1846, p. 664. 347 CHAPTER V. MINERALS AS ROCKS. WE have in the first three chapters treated of those rocks which, by reason of their great extent and volume, may be regarded as the principal ingredients of the earth's crust. We have seen that they are mostly of compound character, although some few are essentially simple mine- ral substances. In this place we propose to enumerate those simple minerals which appear as local accumulations in different parts of the globe, forming essential members of particu- lar formations, sometimes as stratified beds, sometimes as veins or dykes, or irregular masses ; their volume being just sufficient to entitle them to be considered* as members of the rock family, taking an independent part in the structure of the solid crust of the earth, although in comparison with the other rock-formations which we have hitherto treated, their bulk is for the most part very inconsiderable. A description of the formation, texture, &c., of these mineral rocks will, in most cases, be unnecessary, as they must be mineralogically determined and recognised. We shall, therefore, in each case only give the name of the mineral, adding some short remarks as to its exceptional lithological character. 68. ICE. Eis. (Germ.} GLACE. (Fr.) Sometimes compact, sometimes granular , fibrous or lami- nated. We need not here describe the properties of ice, but it is not unimportant to consider the conditions under which perpetual ice occurring in large masses forms part of the solid crust of the earth. The snow which falls in the polar regions, and in 348 MINERALS AS EOCKS. mountain districts above the snow-line, only partially thaws in summer ; the remainder accumulates year by year. The successive falls of snow form a series of super- jacent strata, the fleecy mass becomes consolidated by pressure, and grains of ice are formed which unite into a stratified granular ice ; this in the Alps is called firn or neve. The masses of neve thus formed glide gradually down over the mountain slopes and precipices into the ravines and valleys. In the course of their downward movement their stratification becomes much contorted and otherwise disturbed ; they are, moreover, transformed from distinctly granular neve into indistinctly granular ice, or so-called glaciers. The glacier continues to glide with a slow movement down the valley. Its lower extremity, thus arrived in warmer regions, thaws more rapidly and equalises the accumulation of snow pressing down in fresh masses from above. Hence the general extent and size of the glacier usually remains much the same, although the individual parts are constantly changing their position. By the mo- tion of the glacier the traces of original stratification be- come more and more contorted and effaced. The glacier, moreover, becomes rent with frequent fissures (crevasses), and in these the water arising from occasional thawing accumulates and freezes during night or winter into new ice, which may be distinguished from the genuine glacier ice by its more compact structure. All these phenomena are very instructive, and afford many analogies to other rock formations and transfor- mations. From loose accumulations, by means of pressure and consolidation, masses are formed which become firmer and more solid, and at last tolerably compact. Strata are bent, pushed out of place, and overturned. The mass is torn by cracks and fissures, which are filled by water rendered fluid by heat. This freezes and constructs ice veins in ice, somewhat like granite veins in granite, only that these latter were probably filled from below, and under a much higher temperature. By a kind of weather- ing process even the compact venous ice in its turn be- comes granular or separates into thin columnar parts, and all these changes take place before our eyes in compara- tively short spaces of time. MINERALS AS ROCKS. 349 Very similar phenomena occur on a much larger scale in the polar regions ; only they are less accessible, and therefore more difficult of observation. Besides these permanent masses of ice lying on the surface of the earth, there occur in the northern plains of Siberia extensive underground ice strata of great thick- ness, sometimes interstratified with beds of sand, or they contain sand mixed with the ice, and occasionally these strata are covered with a surface layer of soil, which during the short summer of Siberia supports vegetation. 69. OPAL. OPAL. (Germ.) OPALE. (Fr.) As a rock, usually only forms very subordinate masses, e.g. the so-called vitrite, which occurs at Meronitz, in Bohemia, and contains numerous py ropes. If, however, we reckon under the name of opal all the various amorphous silicates enumerated by Naumann, we find amongst them several very important rocks : Varieties. (a) SiLiCEOU8 SINTER, or SILICEOUS TUFF. "| Stratified incrustations KIESKUSINTER Oder KiESELxcFF. (Germ.) i- and porous masses ; J found as a deposit of hot springs in Iceland and Kamtschatka, and, according to Hoch- stetter, still more frequently in New Zealand. (Novarareise, 1862, vol. iii. p. 165.) (6) SEMI-OPAL. \ Forms independent deposits, e. g. at Bilin, HALBOPAL. (Germ.) I in Bohemia ; also irregular fillings of clefts MB-OPALK. (Fr.) ) ^ ^^c rocks, e. g. at Hanau on the Maine, in the dolerite. (c) MENILITE. t Menilite occurs in the Paris basin in clumps HEXTUT. (Germ.) 1 and beds. It is found there in gypsuin and rat (Fr.) { in marl ( Eocene ) . in Auvergne, in fresh- water marl (Miocene). (d) POLISHING SLATE, TRIPOLI. ] Consists of small shell-shaped POLIRSCHIEFER, SAUGscHiEFER, KLEB- [ particles of silica of a peculiar Tmp^ F ??;J Rn>PEU (<7m "' ) I form, only to be distinguished ' with the aid of the micro- scope, so-called siliceous armour of Diatomacece or Infusoria ; Nuiiinann therefore calls it Diatomeenpelit. Ehrenberg reckoned that the polishing slate of Bilin m Bohemia contained in a cubic inch 41,000 millions siliceous shells of Gattlonella. Each individual is invisible to the naked eye, so that when used for polishing metallic surfaces it produces only fine in- visible scratches. Distinction is made in Bohemia between 350 MIXEKALS AS KOCKS. tlie polirscliiefer (soft, friable, not adhering to the tongue) and sangschiefer (adhering to the tongue and more solid, probably because it is impregnated with opal substance). Both are only known in very recent deposits; the older ones have probably been transmuted into hornstein or lydian stone. (Ehrenberg, Fossil Infusoria, Berlin, 1837, and Mikrogeologie.) (e) KIESELGUHR. '| The same substance as polishing slate, EJESELGUHR. (Germ.) [ b u t more dust-like, earthy, generally ^^^551 white or yellow. Found in beds many * feet thick in the turf deposits at Soos, near Franzensbad, Bohemia. The rock called RANDANITE by Salvetat belongs to this species ; it consists of a white powder. (v. L. u. Br. Jahrb. 1848, p. 124.) 70. QUARTZ. QUARZ. (Germ.} QUARTZ. (Fr.) Occurs as an essential ingredient in many rocks, but it also occurs as an independent rock in many varieties, some of which are of considerable extent. We repeat the mention in this place of several quartz rocks which we have already noticed and included in other groups. Varieties. (a) ROCK CRYSTAL and AMETHYST. \ Sometimes the essential BERGKRYSTALL und AMETHYST. (Germ.) I ingredient of veins and CRYSTAL DE ROCHE et AMETHYSTE. (Fr.) I J^Lgg (b) COMMON QUARTZ. ) Forms independent bed-veins or irre- QUARTZ COMMUN. (Fr.) ) gular masses. Quartz -schist, see p. 246, ante ; Quartz -breccia, p. 305 ; Quartz-sandstones (siliceous sandstone), p. 296. Millstone-quartz, freshwater-quartz, or lemon-quartz, are porous varieties resembling chert, which, . according to the fossils occasionally found in them, have been deposited by fresh water, as, e. g., the celebrated millstones of the Paris basin (Quartz meulier). (c) FERRUGINOUS QUARTZ. j Yellow, red-brown, or black : forms EISENKIESEL. (Germ.) [ transition states into iasper. Its QUARTZ FERRUCHNEUX. (Fr.)) mode o f occurrence in nature is the same as that of ordinary quartz. (d) HORNSTONE, CHERT. ") Compact, forms independent beds, HORNSTEIN; HORNFELS. (Germ.) [ veins, and masses. In Germanv J thenameofHornfelsispivento certain rocks, the product of transmutation of argillaceous deposits, and found adjoining to plutonic rocks, to which they probably owe the change they have undergone. (e) LYDIAN STONE, or LYDITE, BLACK j Contains carbon which CHERT. I gives it a greyish colour KIESELSCHIEFER oder LYDIT. (Germ.) inclining to black QUARTZ LYDIEN. (Fr.) ) ^ gtratified in thin laminse, and hence of a laminated texture ; generally pene- trated by numerous white veins of quartz j much rent by MINERALS AS ROCKS. 351 angular fissures, sometimes containing lenticular concretions, and also sometimes containing laminae of clay-slate. In fissures it contains wavellite, calaite, variscite. It occurs with tolerable frequency as a subordinate stratum in clay-slate, slate-clay, or even mica-schist. (/) JASPER. \ Compact, variegated, frequently striped or JASPIS. (Germ.) I flamed (riband -i asper, agate-jasper). Much JASPE. ( r.) j ^^ ^ een ca |i e( j jasper which properly belongs to the feLsitic rocks, even to the felsitic tufis. It forms subordi- nate layers imbedded in other rocks, and nodular concretions. Jasper may be readily distinguished from petrosilex (which it otherwise sometimes resembles) by the fusibility of the latter. (g) AGATE. j The name given to certain combinations of ACHAT. (Germ.) L chalcedony, carnelian, amethyst, and quartz. AGATE. (Fr.) j There ^ mftny varieties : _i,anded agate, fortification-agate, coral-agate, &c. It frequently forms veins or fills cavities in other rocks. (h) FLINT. \ Very similar to hornstone, but half amor- FEUEROTETS. (Germ.) L phous, chiefly yellow, brown, grey, or J black. Forms nodules, and then are fre- quently disposed in layers ; very frequent, e. g. in chalk. 71. CORUNDUM. KORUND oder SCHMIRGEL. (Germ.) CORINDON. (Fr.) Forms fine-grained subordinate layers imbedded in crystalline schists, frequently accompanied by magnetic iron-ore. Ochsenkopff, in the Erzgebirge ; Gumuchdagh, in Asia Minor ; Naxos ; Chester, Massachusetts. 72. FLUOR-SPAR. FLUSSSPATH. (Germ.') FLUORINE, SPATHFLTJOR. (Fr.) Frequently an essential ingredient in metalliferous veins. A compact aggregate of fluor-spar forms a rock at Rottleberode and Strassberg in the Hartz Mountains. 73. ROCK-SALT. STEINSALZ. (Gtrm.) SEL GEMME. (Fr.) Chloride of sodium occurring as a rock is usually crys- talline-granular, white, translucent or transparent, easily soluble in water, and possesses a saline taste. Spec, grav 2-12-2. Pure chloride of sodium consists of 60 per cent, chlorine to 40 per cent, sodium. In nature, however, it almost always contains sulphate of lime, chloride of calcium, 352 MINERALS AS HOCKS. chloride of magnesium, and other salts ; frequently ad- mixtures of bitumen, clay, or boracite. Salt itself some- times only forms an ingredient of some clays (Salzthon, saliferous clay). The colour of rock-salt is variable ; it is sometimes yellow, red, bluish, or greenish, by reason of small ad- mixtures of oxide of iron. Varieties. (a) GRANULAR ROCK-SALT. KORNIGES STEINSALZ. (Germ.) SEL GEMME GRANULAIRE. (Fr.) (b) SPARRY ROCK-SALT. BLATTRIGES STEINSALZ. (Germ.) SEL GEMME LAMrNTAIRE (SPATHIQUE). (Fr.) (c) FIBROUS ROCK-SALT. FASRIGES STEINSALZ. (Germ.) SEL GEMME FIBREUX. (Fr.) (d) KNISTERSALZ. (Germ.) (e) GRUNSALZ, SPIZASALZ, SZYBIKER SALZ. (Germ.') Reference. The origin of the rock-salt of Strassfurt, near Magdeburg, has been lately treated in a masterly manner by F. Bischof, Die Steinsalzwerke zu Strassfurt, 1864. 74. TKONA. TRONA. (Germ.) SESQUI-CARBOKTATE DE SOUDE. (Fr.) Occurs in Fezzan, in North Africa, forming a rock which is even used for building purposes. 75. ALUNITE, or ALUM STONE. ALTJNIT, oder ALAUNSTEIN. (Germ.) ALTJNITE. Forms a rock in the neighbourhood of Tolfa, near Civita Vecchia. (See p. 185.) 76. BARYTES, or HEAVY SPAR. BARYT, oder SCHWERSPATH. (Germ.) BARYTINE, ou SPATH PESANT. (Fr.) This mineral, which forms an essential part of many metalliferous veins, was discovered by Yon Dechen, as constituting a compact rock forming a bed some ten feet in thickness, in the clay-slate of Meggen in the Lenne- thal. Its colour was dark-grey. MINERALS AS ROCKS. 353 Karsten's Archiv, 1845, vol. xix. p. 748 ; see also v. Hoinm- gen, Verb, der naturh. Ver. d. pr. Rheinl. 1856, vol. xiii. p. 300 ; Sandberyer, geol. Verb. d. H. Nassau, p. 11 j and Zim- mermann, Harzgebirge, 1834, voL i. p. 151. 77. BORACITE, or STASSFURTITE. BORACIT, STASSFURTIT. (Germ.) BORACITE, STASSFURTITE. (Fr.) Forms irregular layers imbedded in the rock-salt of Stasfurt. Zeitschr. d. d. geol. Ges. 1856, voL viii. p. 156. 78. PHOSPHORITE. PHOSPHORIT. (Germ.) CHAUX PHOSPHATEE, APATITE. (Fr.) Sometimes forms compact spheroidal masses, or sub- ordinate layers, and even dykes or veins. Krageroe in Norway. 79. CRYOLITE. KRYOLITH. (Germ.) CRYOLITE. (Fr.) Forms considerable veins in the granitic gneiss at Evigtok, in Greenland. (Journ. of Geol. Soc.) 80. ARAGONITE. ARAGONIT. (Germ.) ARAGONITE. (Fr.) Many so-called calcareous sinters and peastones consist, properly speaking, not of calcspar, but aragonite. (See p. 281.) 81. ANKERITE. ANKERIT. (Germ.) ANKERITE. (Fr.) This is most frequently found mixed in subordinate quantities with spathic iron (vide p. 345, ante) ; and is sometimes found separately as an independent rock. 82. MAGNESITE. MAGNESIT. (Germ.) MAGNKSIE CARBONATEE. (Fr.) Frequently forms compact masses, but of subordinate size and extent. A A 3o4 MINERALS AS ROCKS. 83. DIALLOGITE, CARBONATE OF MANGA- NESE. MANGANSPATH. (Germ.') DIALLOGITE. (Fr) Frequently forms the principal constituent of metal- liferous veins, e.g. at Kapnik, in Hungary. 84. MALACHITE. MALACHIT. (Germ.) MALACHITE. (Fr.) Sometimes forms great clumps or masses in beds of copper-ore in Russia. 85. TALC, or STEATITE. TALK oder SPECKSTEIN. (Germ.) TALC ou STEATITE. (Fr.) Forms independent compact beds, e.g. at Gopfers-Griin, in the Fichtelgebirge, where it forms a rock which can- not be classed as a talc-schist. 86. MEERSCHAUM. MEERSCHAUM. (Germ) ECUME DE MEK, MAGNESITE. (Fr.) Forms separate beds in Natolia, Negroponte, Crimea, &c. 87. AGALMATOLITE, or FIGURE-STONE. AGALMATOLITH oder BILDSTEIN. (Germ.) AGALMATOLITHE. (Fr.) The principal member of a dyke or vein at Dilln, near Schemnitz. Also in China. 88. KAOLIN, or PORCELAIN CLAY. KAOLIN oder POKZELLANERDE. (Germ.) KAOLIN. (Fr.) This is probably everywhere merely a product of the decomposition of rocks very rich in felspar. Aue, in Saxony, where it is a decomposed granite. In some places a slight change has converted it into clay. MINERALS AS ROCKS. 355 89. LITHOMARGE. STEIN MARK. (Germ.) LITHOMARGE. (Fr.) Is found in very subordinate quantity between other rocks. 90. ORTHOCLASE. ORTHOKLAS. (Germ.) ORTHOSE. Sometimes forms independent dykes and accumulations, e. g. in the granite at Carlsbad. 91. PYCNITE. PYKNIT. (Germ.) PYCNITE. (Fr.) Forms concretions and dykes in the Zwitter rock, at Altenberg, in Saxony. 92. EPIDOSITE, or PISTACITE ROCK. EPIDOSIT oder PISTAZITFELS. (Germ.) EPIDOSITE. (Fr.) Epidote usually combined with some quartz. A sub- ordinate formation in the Island of Elba. 93. LEPIDOLITE, or LITHIA-MICA. LEPIDOLITH oder LITHIONGLIMMER. (Germ.) LEPIDOLITE (MiCA A LITHINE). (Fr.) Forms an independent rock of fine-grained and foliated texture, e. g. at Rozena, in Moravia. 94. ROCK SOAP. BERGSEIFE. (Germ.) PIERRE DE SAVON. (Fr.) Occurs in masses of subordinate extent, e. g. at Bilin, in Bohemia. 95. BOLE. BOL. (Germ.) BOLE. (Fr.) Occurs in masses of subordinate size in many limestone rocks. 96. FULLERS' EARTH. WALKERDE. (Germ.) TERRE A FOTTLON. ^(Fr.) AA 2 356 MINERALS AS ROCKS. A substance resembling clay, somewhat greasy, but not in the smallest degree plastic, but falling to pieces in water, usually of yellowish green colour; is probably a product of the decomposition of basic igneous rocks. Cilli in Styria ; Nutfield, near Reigate. 97. FERREO-LITHOMARGE. EISENSTEINMARK. (Germ.) TERATOLITE. (Fr.) Occurs in subordinate masses at Zwickau, in Saxony. 98. YELLOW EARTH, or MELINITE. GELBERDE. (Germ.} Occurs in small accumulations at Amberg, and other places. 99. GALMEY, CARBONATE OF ZINC (in part). GALMEI. (Germ.} CALAMINE. (Fr.} This name is indifferently applied to both the principal zinc-ores : the silicate of zinc and the carbonate of zinc. They occur together, and they form aggregates of con- siderable size in the dolomite limestones of Tarnowitz, Iserlohn, Aix-la-Chapelle, &c. 100. RHODONITE (in part), MANGANESE SPAR (Bisilicate of Manganese). KIESELMANGAN oder MANGANKIESEL. (Germ.} RHODONITE (MANGANESE SILICATE). (Fr.} Occurs (e. g.) in subordinate beds at Rosenau, in Hungary; Cummington, Massachusetts, U.S. 101. LIEVRITE, or ILVAITE. LIEVRIT. (Germ.} ILVAITE. (Fr.} Occurs (e.g.) in subordinate beds in the mica-schist of the Island of Elba. 102. MANGANESE-ORES. MANGANERZE. (Germ.} MINERAIS DE MANGANESE. (Fr.} MINERALS AS ROCKS. 357 One or more of these form veins of considerable thick- ness, or beds of irregular shape, at Ilmenau, Ilfeld, Kleinlinden, Warwickshire, &c. 103. RED ZINC-ORE. ROTHZINKERZ. (Germ.) MlNERAI ROUGE DE ZlNC (FRANKLnrTTE) . (Fr.) Combined with Franklinite forms a bed of very con- siderable thickness at Franklin, in New Jersey. 104. GALENA. BLEIGLAKZ. (Germ.) GALENE. (Fr.) Usually associated with blende and sulphurets ; forms veins of considerable extent and thickness, and occurs otherwise in separate beds.. 105. ANTIMONY-GLANCE. ANTIMONGLANZ. (Germ.) ANTIMOINE. (Fr.) Forms veins of considerable thickness, e.g. at Magurka, in Hungary. 106. ARSENICAL PYRITES. ARSENKIES. (Germ.) PYRITES ARSENICALES. (Fr.) Usually associated with other sulphurets ; occurs in separate formations of considerable thickness. 107. MARCASITE, or HYDROUS PYRITES. MARKASIT oder WASSERKIES. (Germ.) MARCASSITE. (Fr.) Forms subordinate layers imbedded in other rocks, e. g. in the Browncoal formation at Littmitz, in Bohemia. 108. PYRITES. ScnWEFELKIES PYRITES. (Fr Usually associated with some chalcopyrite ; forms beds, ScnWEFELKIES, PYRIT. (Germ.) PYRITES. (Fr.) 358 MINERALS AS ROCKS. veins, or irregular masses of considerable size, e.g. at Domokos in Transylvania, Rio Tinto in Spain, Schmoll- nitz in Hungary, Groslar at the Hartz, Fahlun in Sweden, Agordo in the Alps. 109. CINNABAR. ZINNOBER. (Germ.} CINABRE. Occurs but rarely in beds of considerable size or thick- ness, e.g. at Almaden in Spain, Idria, California. 110. SULPHUR. SCHWEFEL. (Germ.') SOTTERE. Forms rounded concretions and layers, in marl forma- tions, e.g. at Radoboj in Croatia, Sicily, Perticara in Umbria. 359 PART III. OBSEEVATIONS ON THE PROCESSES OF ROCK FORMATION IN NATURE. THE NATURAL PROCESSES by which rocks have been formed and are still in course of formation are partly in- dicated in the foregoing pages. The following are those known to us from actual observation : 1. CONSOLIDATION OF SUBSTANCES FROM A STATE OF IGNEOUS FUSION BY PROCESS OF COOLING. This is the process which all lavas undergo, and by which, pro- bably, all igneous rocks have been formed. We must assume that a first crust of the earth was likewise so formed, but we cannot with certainty point to any of the rocks remaining to us at the present day as representing this primeval formation. 2. DEPOSIT OF SUBSTANCES FROM A STATE OF SUS- PENSION IN WATER, AND OF SUBSTANCES FALLEN THROUGH THE AIR. Thus are formed the sedimentary rocks, under which general designation every kind of de- posit is included. They may be divided as follows : (a) Mechanical deposits (actual sediments). To this class belong deposits of mud, sand, and pebbles of every kind, which by process of condensation and cementa- tion produce argillaceous shale, clay-slate, limestone, sandstone, conglomerate, and other similar rocks. From the atmosphere are deposited particles of dust and sand. These are frequently held in a state of suspension for a considerable time, and transported by the wind to great distances. Volcanoes vomit detached 360 PEOCESSES OF ROCK FORMATION: substances or fine particles of dust, which with the aid of water form volcanic tufas of various kinds. (b) Chemical precipitates from aqueous solutions. By chemical agency many kinds of deposit are formed. For instance, calc-tuff, siliceous tuff, bog iron-ore, in- crustations of salt, and many mineral formations in clefts and cavities of rocks. The crystalline particles of ice which fall from the air in the form of snow may be considered as a chemical precipitate. Snow, as we have seen, forms the neve and glaciers of high mountain regions. (c) Zoogenic deposits are products of animal agency. Their massive accumulation is partly a mechanical pro- cess. Thus we have rocks formed entirely of siliceous infusoria, also the chalks, banks of shells, coral-reefs, guano and coprolite beds, &c. From the condensation of these rocks, hornstone, lydian-stone, limestone, &c., may have resulted. (d) Phytogenic deposits are such as consist chiefly of vegetable substances ; these have either grown in situ, or have been washed together. From these deposits, by process of consolidation and subsequent conversion, the different coal formations have resulted. The above-mentioned processes of rock-formation are those which admit of direct observation. There are others at whose nature we only arrive by reasoning from the results. Such are : 3. METAMORPHOSIS, OR TRANSMUTATION or PRE- VIOUSLY EXISTING ROCKS. This is a process constantly at work it has even begun to affect most of the dis- tinctly sedimentary rocks. Few of these but have under- gone some change. Thus the changes from argillaceous mud to shale and then to clay-slate, from sand to sand- stone, from loose stones to conglomerate, from calcareous silt to limestone, from peat-moss to browncoal, or ordinary black coal, &c., are, properly speaking, all cases of meta- morphosis, although the rocks we have just named are not usually termed metamorphic. That term is reserved for the further stages of transmutation, where the change is so complete that the first state of the rock can no longer be easily or with certainty recognised by mere observa- IGXEOUS ROCKS. 361 tion. The genuine metamorphic rocks are mica-schist, gneiss, and the other crystalline schists, whose identity with their originals can only be proved by deduction from a variety of collateral circumstances. The foregoing, are the only processes of rock-formation known to us by observation, or which can be ascertained by deduction from known facts. These processes are, however, undoubted and indisputable, and our chief diffi- culty consists in determining in each instance to which mode of formation a rock owes its origin. Here many difficulties and justifiable doubts present themselves. Let us therefore attempt the application of these experiences and their consequences to the several groups of rocks which we have described in the preceding pages. IGXEOUS EOCKS. ' (Eruptiv-Gesteine.) No unprejudiced observer of geological phenomena can doubt that those which we have classed and named as igneous rocks were once in a fluid or viscous state, and that whilst in that state they broke through pre-existing rocks, overflowed them, and afterwards consolidated. Ample proofs of these operations of nature are found in the relation of the bedding of the igneous to those of their surrounding rocks, the disturbances which they have fre- quently (but not invariably) caused in the rocks broken through, the fragments of the latter which they enclose, and the veins or branches which they have thrust into those adjoining. These general conditions established, there still remain many special phenomena of formation to be explained and accounted for, which we propose briefly to consider in this place. The great mutual resemblance of all igneous rocks both chemically and mineralogically bespeaks a like pro- cess of formation for all, i.e. they were all forced upwards from the interior towards the surface of the earth in a 362 PKOCESSES OF EOCK FOKMATIOX : molten state, like the lavas (which are evidently igneous products) from the active volcanoes of the present ^day. But although the composition and mode of occurrence of all these rocks is, generally speaking, of a very uniform cha- racter, yet special differences show that a great part of those which are now exposed to our view did not originally reach the surface and overflow at the time of their up- heaval in the manner of genuine lavas, but became solid at a considerable depth underground, where they still were covered by or imbedded between other rocks ; and we must assume that their present appearance on the face of the earth is owing to subsequent destruction and wash- ing away of the superincumbent rocks. Hence we dis- tinguish between volcanic and plutonic rocks. The vol- canic (as we have seen) are those which are known, or supposed, to have consolidated at or near the surface ; and the plutonic those which are presumed to have solidified at a considerable depth in the interior of the earth. There is no definite depth of measurement which we can fix as a boundary between these two kinds of formation ; the question of such depth must remain a subject for entirely speculative estimate. Nor is the division of rocks into volcanic and plutonic dependent on their mere age, although in most cases it corresponds to a certain extent in fact with their relative antiquity, because most of the older volcanic formations have decayed away and disappeared, whilst the newer plutonic formations have not yet been laid bare, and are therefore inaccessible to our view. The deeper in the earth that any rock was formed, the longer would be (cceteris paribus) the time necessary for its denudation ; and therefore the older will it be when we meet with it at the surface. Recent chemical analysis (as we have already had oc- casion to remark) shows a great uniformity of elementary composition in all classes of igneous rocks. We have seen that they all consist of silica, alumina, peroxide or protoxide of iron, lime, magnesia, potash, and soda, and frequently some water. Their other ingredients are but subordinate in quantity, and can only be re- garded as accessory ; such are protoxide of manganese, titanic acid, carbonic acid, phosphoric acid, sulphuric IGNEOUS KOCKS. 363 acid, oxide of chromium, oxide of copper, baryta, lithia, sulphur, &c. The quantitative proportions of the essential elements vary considerably in different rocks, but this variation is almost as great between different kinds of the same rock as between the different rocks themselves ; and no igneous rock is of so invariable or marked a chemical character as to be distinguishable from the rest by it alone. Taking the whole range of the igneous rocks, the average values of their chemical constituents may be stated somewhat as follows : Extreme actual values. Ideal average. 45 15 10 6 5 4 4 2 Where the extreme values, as above given, are found to be exceeded on the one side or the other, the excess or deficiency appears invariably to have been the result of change, decomposition, or some similar process subsequent to the formation of the rock, which, therefore, is no longer in its original state. We have already indicated the division of the igneous rocks, in respect of their chemical composition, into two principal groups. 1. Poor in silica, or basic. 2. Rich in silica, or acidic igneous rocks. The distinction between these two groups is deserving of considerable attention, for they also differ to some extent both mineralogically and geologically, although they cannot be very rigidly separated from each other ; and certain rocks of each group vary so greatly in their composition as actually to graduate into the opposite group. The following proportions may be stated as an approxi- mate average of the analysis for the two groups : Silica Alumina Peroxide a Liine Magnesia Potash Soda Water mdP rotox de oi Iron 5080 1025 125 015 012 010 7 5 364 PROCESSES OF ROCK FORMATION : Basic. Acidic Silica . . * '" ~. 4560 55-80 Alumina 1025 1015 Iron (Peroxide or Protoxide) . 1 25 1 15 Lime J , .'. ! . . . ' , . 115 08 Magnesia 112 4 Potash 19 111 Soda 17 28 Water 04 06 These two groups nearly correspond with the pyroxenic and trachytic groups of Bunsen, for which he calculated certain ideal or normal average values of their elementary constituents.* (See Poggend. Ann. 1851, vol. Ixxxiii.) Without, therefore," being able to fix any very precise standard, the distinguishing feature of the basic rocks is, that they contain less silica, more alumina, iron, lime, and magnesia, and less alkali than the acidic rocks. Within the limits of each group we find no constant differences of chemical composition between the several species. These only differ in their mineral development, their texture, or the mode and accidents of their occurrence in nature. We may, therefore, say in general terms that all igneous rocks consist of one or other of two compounds normally differing in the proportions of their elementary constituents, but that several intermediate gradations exist between the two extremes. Each of these two compounds has produced many different species and mo- difications of rock which have received different names. The differences are partly those of texture, partly of mineral composition. The first may in most cases be very simply accounted for by the particular circumstances of * Bunsen's values of the different elements were as follows : Pyroxenic. Trachytic. Silica 48-47 76-67 Alumina and Protoxide of Iron 30-16 14-23 Lime ; . . . . 11-87 1-44 Magnesia 6-89 0-28 Soda ... . . . 1-96 3-20 Potash 0-65 4-18 100-00 100-00 IGNEOUS ROCKS. 365 cooling. The quicker the cooling process, the more com- pact or even vitreous the product would be; and the slower the process, the more crystalline and coarse- grained would the rock become. Inequality in the crys- tallising power of the different ingredients would give a porphyritic texture ; parallel arrangement of certain of the ingredients would give a slaty or schistose texture ; development of gases during the cooling would give a vesicular or slag-like texture. The differences of mineral composition are not great. In most cases the elementary substances are the same ; and the differences of proportion in which they are com- bined are so small as to appear unimportant. We are unable satisfactorily to explain in any particular case why, with differences of composition so trifling, one particular species of felspar, of hornblende or pyroxene, or of mica was produced rather than another, or why, under ap- parently similar conditions in another rock, other mi- nerals, such as nepheline, leucite, talc, chlorite, &c., were formed in their stead. A part only of these differences can be traced to have any distinct relation to the quan- titative proportions of the chemical composition of the whole rock. Other differences consist in the presence of various accessory minerals. These we may presume to represent a surplus or residuum of certain elementary substances remaining uncombined after the crystallisation of the essential mineral ingredients. Many accessory minerals are, however, evidently the result of later pro- cesses of transmutation. If we disregard the specific but minor differences be- tween those similar minerals, which, to a certain extent, occur as substitutes for each other in rocks, we find a certain correspondence in the mineralogical with the che- mical phenomena, and that, speaking generally, there are two principal kinds of rock essentially differing from each other in the aggregate of their mineral composition, if only in their normal states of development one a basic, and the other an acidic compound. These are again subdivided, according to their texture and recognisable mineral differences, into rocks of several species, as indi- cated in the following tabular statement. PROCESSES OF KOCK FORMATION: Granular Porphyritic Compact Vitreous, vesicu- lar, or amygda- loidal Slaty-schistose (chiefly meta- morphic) ^ /Granite "1$ Syenitic- ^ j granite .0 ] Protogine ^ Trachyte ^ V(Greisen) Granitic- porphyry Quartz- porphyry Trachyte- porphyry Felsite rock Petrosilex Pitchstone Pearlstone Obsidian Pumice-stone Granulite Gneiss Protogine- gneiss Felsite-schist (Mica-schist) 4 f. ^Syenite Diorite Diabase Timacite Dolerite Nepheline- dolerite Gabbro Miascite ^Mica-trap Hornblende- porphyry Mica-por- phyry Porphyrite Aphanite- porphyry Melaphyre Melaphyre Aphanite Basalt Vesicular rocks and amygdaloids Hornblende- schists Chlorite-schist Talcose schist As already stated, the mineral differences in the ig- neous rocks do not appear to have been all original, but to have been partly produced at a later period by process of transmutation. In individual cases this has been very well shown to be the fact by Bischof and Rose, although both of those distinguished men may, per- haps, have gone too far in their hypotheses on this sub- ject. The extent to which such transmutations have taken place is not yet established by proof, and we may say generally that it is impossible to be too cau- tious in admitting the process of transmutation as a suffi- cient explanation of differences between rocks, unless we are willing to be content with mere convenient hypo- theses. We have already observed that the causes are not yet satisfactorily ascertained why, from compounds chemically very similar, in one rock orthoclase has resulted, in others sanidine, oligoclase, labradorite, anorthite, &c. ; in one rock a hornblende, in another a pyroxene. The exact causes of these phenomena can never be ascertained with certainty. One cause, however, of dif- ferent forms of mineral development may be well con- ceived, viz. the different depths at which cooling and solidification have taken place in rock masses. It cannot IGXEOUS ROCKS. 367 be doubted that the conditions under which substances have combined to form minerals were very different at a depth of 10,000 feet from those which prevailed at a depth of 10 or 100 feet only from the surface. In the former case the masses have been subjected to far higher pressure were shut out from the atmosphere they were probably exposed in some degree to the action of water, but their cooling must, in masses of equal bulk, have been on the average a much slower process than would have obtained near the surface. Again, not only the depth of the formation, but the geological period of the earth's development may have had considerable influence in determining the character of minerals. For if the theory is correct that the earth has cooled into a solid from a previous molten state, its average temperature in former periods, even at the surface, must have been higher, and the atmosphere more dense and heavy than at present. Each cooling process under such circum- stances would be slower, and would take place under a different degree of pressure than now. Thus we have one recognised general cause for the differences we ob- serve ; but the definite proof of what its precise effects have been under different circumstances is wanting. The cause for a division of the igneous rocks into those poor in silica and rich in silica remains a great problem for solution. A priori we should expect to find all igneous rocks of the same composition. Bunsen's theory of the existence of two separate volcanic furnaces in the interior of the earth is a mere hypothesis, which, no doubt, might, if it were true, suffice to explain the exist- ing differences, but which in itself is very improbable. Such furnaces, if they existed at all, must have been in existence through all geological time ; in almost every part of the globe they must have been placed side by side or one above the other, and yet have remained dis- tinct and unmixed. No circumstance, unless it be the very difference which we are endeavouring to explain, speaks for such an assumption. Even if the cooling and solidifying of the fluid mass of the globe should have pro- ceeded contemporaneously equally from the centre and surface towards a middle plane, as Bunsen supposes, so that at last only an intermediate stratum of fluid matter 368 PROCESSES OF ROCK FORMATION : will remain between the two, the existence of separate basic and acidic basins of lava will not by this assume greater probability. For the present we must confess that the cause of the differences between these two chief groups of igneous rocks has not yet been satisfactorily explained. It has been very ingeniously suggested that a cause might be sought in the different specific gravity of the several rock masses, starting with the assumption that in the former molten state of the earth the ingredients must have arranged themselves in some measure according to their specific gravity ; so that the heaviest substances would be accumulated towards the centre, and the lighter towards the surface. If the cooling process began with the outside of the globe proceeding inwards, then it follows that the specifically lighter bodies would first attain the solid state, and these we actually find to be richest in silica ; and that the heavier bodies, which are at the same time the most basic, would only cool at a later period. This law, it was considered, must prevail alike in an incrustation formed under quiet circum- stances, as in the case of eruptive rocks necessarily emer- ging from a great and ever increasing depth ; so that the oldest would be the lightest and most acidic ; the recent the heaviest and most basic. This theory, which Petz- bold (in his Geologie, 1840) pushed to the utmost ex- treme, i. e. to the formation of mineral veins, has been lately attempted to be applied in a narrower sense by Von Eichthofen (Greol. Beschreib. von Sud-Tyrol, 1861, p. 308). It evidently has a great appearance of theo- retical probability in its favour. But when we come to test this theory by comparison with ascertained facts, we at once find it untenable, at least in part, and undoubtedly altogether insufficient satisfactorily to explain those facts. Every geological age has produced acidic as well as basic, specifically light and specifically heavy, igneous rocks. Where syenite and granite occur together, it is even most usually the case that the basic syenite is older than the acidic granite. The basic porphyries in the Thuringian Forest and the Erzgebirge are on the average older than the acidic quartz-porphyries which belong to the same great period. The trachyte-por- IGNEOUS ROCKS. 369 phyries belong to the most acidic and yet frequently to the most recent eruptive rocks. According to von Richthofen's own investigations, they are, on an average, of more recent formation than the trachytes, which con- tain less silica and are also somewhat heavier. Therefore, von Richthofen himself, to support his theory, was com- pelled to have recourse to various hypotheses, such as a second fusion and new eruption of old igneous rocks, &c., which in themselves are neither probable nor sufficient to solve all the difficulties of the case. We have yet to seek the true solution of many important problems relating to this subject. Nevertheless, we are not of opinion that the theory of an arrangement of substances according to their specific gravity should be disregarded as entirely un- worthy of serious attention. Specific gravity may, and probably has had, a certain influence in the first arrange- ment of rock masses ; and if we are unable now to trace a consistent arrangement deducible from the laws of specific gravity, it may be only because those traces have to a great extent been subsequently effaced by other cir- cumstances which we have not yet discovered. A primary crust formed by cooling and the first sedimentary deposits, resulting from the decay of that first crust, may well have been pre-eminently rich in silica ; more especially if at the time of those sedimentary deposits animal life had not begun to act on the calcareous waters, and so cause a redeposit of the dissolved lime in large masses. If this primary portion of the earth's crust should at a later date have been subjected to a second process of fusion under high pressure, at a considerable depth, it may have become partially eruptive, and have produced recent rocks very rich in silica and of very uniform chemical composition. We may, in fact, reasoning from analogy to the meteoric stones, which represent to us the small planetary bodies of our solar system, believe the aggre- gate of the earth's mass to be far more strongly basic than that part of it which is open to our observation. Taking into account composition, on the one hand, and geological character, on the other, we come to distinguish four great groups of igneous rocks, which groups are, however, not divided from each other by exact bounda- ries. Each may be characterised by some typical rock ; B B 370 PKOCESSES OF ROCK FORMATION : and each may be also connected with the other groups by means of other rocks of intermediate character. We may represent these groups somewhat as follows : BASIC -f ^ mmc : Basalt ") Diabase, Porphyrite, ' \ Plutonic : Diorite J Melaphyre or : ACIDIC [ ^kamc : Trachyte 1 Trachyte-porphyry ' I Plutonic : Granite J Quartz-porphyry Vn , .,. {Basic : Basalt \Trachydolerite. Andesite, C ' \ Acidic : Trachyte JPorphyrite -r^ {Basic : Diorite | ., PLUTONIC . . Senite A ^. Q . Granite | ., j Syenit We must not omit to remark that some considerations entitled to attention have been started against the igneous character of certain of the rocks so named, and chiefly those which contain quartz. Granite is the principal representative of these rocks. In the case of this rock, so universally spread over the surface of the globe, it has been objected that, look- ing to the mode in which its essential ingredients, fel- spar, quartz, and mica are joined together, and fitted one into the other, those minerals could not have been formed in the order of their respective degrees of rapidity of solidification from a state of fusion, i. e. first the quartz, then the felspar, and last the mica ; but, on the contrary, that it very often appears distinctly that the quartz, which is the most difficult of fusion, has been formed the last. It has been further objected that in granite, as well as in many other, even in certain basic igneous rocks, there sometimes occur accessory minerals whose formation by igneous means can scarcely be con- ceived as possible, or at least is contradicted by all experience. For instance, pyrites, apatite, pyrochlore, carbonate of lime, carbonate of magnesia, protocarbonate of iron, &c. These are found side by side with silicates, and yet without forming chemical combinations with the latter. Finally, it has been objected that many so-called igneous rocks contain some water, and according to the analyses of Delesse, even small quantities of nitrogen. (Ann. des. Mines, 1860, vol. xviii.) Now, as regards the first objection the solidification of IGNEOUS ROCKS. 371 the quartz subsequently to the felspar Durocher has long since shown (Gompt. rend. 1845, p. 1275), that in fusing the compact rock petrosilex, whose composition is often precisely the same as that of granite, the quartz which it contains being associated with the other ingredients of the rock, is quite as readily fusible as felspar alone ; and hence we may conclude that upon the cooling of such a mass the quartz would not necessarily separate itself from the rest of the compound by solidifying sooner than the felspar. If this be so, in the case of a granitic mass it might depend on some circumstance, which for want of a better term we may call accident, whether the quartz or the felspar should first happen to complete the pro- cess of its crystallisation, and whichever of those two minerals first crystallised would necessarily determine the form of the other. Now the felspar in granite ap- pears to have been the first to crystallise, and has deter- mined the form of the quartz in many cases. Bunsen has lately thrown much light on this question (vide Zeitsch. d. geol. Ges. 1861, p. 61); he has shown that the melting and solidifying points of a mineral, when taken singly, by no means determine those of an intimate compound or alloy of such mineral with other mineral or minerals. In a letter to Streng, which appeared in the Berggeist (1862, p. 1), Bunsen, in illustration of the same law, adduces instances of aqueous solutions, where heat is ne- cessary to the solution. The so-called PattinsorCs pro- cess is the result of a similar experience. It is found that pure lead crystallises sooner than lead containing a pro- portion of silver ; and accordingly when the liquid mass of mixed lead and silver is subjected to a process of slow cooling, the pure lead congeals first, leaving the richer metal still in a fluid state (termed ( mother water'). More- over, high pressure and water (chemically combined) may have exercised many important modifying influences upon the process of the formation of the granitic rocks. The second suggestion referring to the presence of cer- tain minerals as accessory ingredients in so-called igneous rocks which appear incompatible with their igneous origin, loses much of its force from our likewise finding some of the same minerals in genuine lavas, whose origin is un- doubted. Moreover, those minerals or substances may BB 2 372 PEOCESSES OF ROCK FORMATION : not have been actually present in the rocks in question at the period of their first formation, but have originated in them at a later date. As to the water contained in rocks, Scheerer has clearly proved that water forms a basic in- gredient of many minerals (e.g. many kinds of mica), entering into combination with silica and other acids in precisely the same way as any other basic oxide. Dau- bree has established the same fact synthetically, showing that under great pressure at a high degree of temperature, water may be made chemically to combine with mineral matter. Whether the very small quantity of nitrogen contained in many igneous rocks was there originally, or whether it only insinuated itself into them at a later period, may, for the present, remain an open question ; all minor difficulties like this will probably find a satis- factory solution in time. On the other hand, as regards the carbonates of lime, magnesia, and iron contained in igneous rocks, they appear to be invariably the result of change or transmutation subsequent to the formation of the rock. Hence we never find them in very recent lavas, but only in those igneous rocks which have been long and continuously exposed to the action of chemical in- fluences, calculated to bring forth those minerals, and therefore we find them more frequently in the plutonic than the volcanic rocks. Pyrites, magnetic pyrites, chlo- rite, and talc, all likewise appear to have been the result of such transmutations, even if we cannot as yet satis- factorily so explain every single case of the occurrence of a particular mineral. These considerations prevent us from attaching much weight to the objections raised to the igneous origin of granite an origin which on other grounds appears so conclusively established. The differences between the volanic and plutonic rocks of both principal groups, the basic and acidic (although smaller and more filled up by transition states than those between the two groups themselves), deserve a full share of our attention, and require some explana- tion. We have already more than once adverted to one general cause of difference, namely, the unequal condi- tions, under which the cooling and solidification first took place, whether under simple or multiplied atmospheric pressure ; and whether on the surface of the globe, or in a closed space, where water probably had access. IGNEOUS ROCKS. 373 Besides these original causes of difference, there are also the many changes which appear to have taken place in the state as well as composition of all rocks, subsequently to their first formation, chiefly no doubt under the in- fluence of water and gas penetrating and permeating them. In the present state of science it is impossible every- where separately to specify and define the results of all these different causes, yet we will attempt by contrasting the characteristic attributes of the two principal groups to present some general views applicable to the subject. The original differences may shortly be stated as fol- lows : In Volcanic Rocks. Prevalent compact, porphy- ritic, vesicular, or vitreous states. Seldom or never slaty or schistose texture. Small content of water. Seldom crystallised quartz. Frequent tufa formations. In Plutonic Hocks. Prevalent crystalline -granular and porphyritic, sometimes also schistose or slaty texture; seldom vitreous or vesicular. Greater content of water. More frequently crystals of quartz. Seldom tufa formations. The differences occasioned by gradual metamorphosis are as follows : In Volcanic Rocks. In Plutonic Rocks. There is little or no change. The formation of amygdaloids, by the filling up of previously existing vesicular cavities with newly-formed minerals. The new formation or transforma- tion of certain minerals in the in- terior of the mass, e.g. pyrites, car- bonates, zeolites, apatite, chlorite, talc, serpentine, &c. The absorption of more water. Decomposed wacke- nitic states; possibly even many formations of quartz. To sum up these observations : It appears that in the present state of science we cannot but regard all the so- called igneous rocks as parts of the earth's interior mass, thrust out whilst in a state of fusion, without being able as yet satisfactorily to explain their division into the two 374 PROCESSES OF KOCK FORMATION : principal groups of acidic and basic composition respec- tively, the minor differences inside of these groups being capable of explanation by the different circumstances under which the several rocks attained the solid state or by subsequent process of their transmutation. In addition to the works cited in the text we will here only notice the following : Deksse, on the origin of igneous rocks, in Compt. rend. 1859, vol. xlviii. p. 955 ; v. L. u. Br. Jahrb. 1859, p. 459 ; and Ann. des Mines, 1858, vol. xv. p. 459. Delesse distinguishes between Igneous rocks (trachyte, dolerite), Pseudo-Igneous rocks (trap), and Non-Igneous rocks (granite, diorite, &c.). If we wish for extreme precision of nomenclature, the term Igneous is altogether inappropriate, even for the volcanic rocks, which have but consolidated from a state of liquid fusion, without any fire or burning in the ordinary accepta- tion of the word fire. Hence in Germany the Igneous rocks are termed Eruptive rocks. One name is as good as another for practical purposes, if we do not seek to attach theory too closely to nomenclature. Daubree, Sur le Metamorphisme et sur la Formation des Roches Cristallines, 1860. Scheerer, iiber den Astrophyllit und sein Verhaltniss zu Augit und Glimmer und Zirconsyenit nebst Bemerkungen iiber die plutonische Entstehung solcher Gebilde, 1864. See also Cotta's Geologische Fragen, 1858. The argument against the igneous origin of granite which has been built on the score of the specific gravity of the quartz falls to the ground if we believe that it became solid under high pressure. SEDIMENTARY ROCKS. The general character of the processes by which these rocks were formed is well known and evident. They are deposits of fallen substances, chiefly precipitated from water a small part from the atmosphere. This, their origin, is proved in a variety of ways, by their composi- tion, their stratification and bedding, and the fossils which they enclose. A few words as to their composition may not be out of place here. If the views now prevalent respecting the earth's history- are correct, the igneous rocks must be regarded as the SEDIMENTARY ROCKS. 375 most original, or rather the only original formations. Should it appear that any part of the first crust produced by the original cooling of the earth's surface remains un- disturbed at the present day, it will properly belong to the igneous rocks, although not like the other igneous rocks, eruptive. If we take all the igneous rocks together, we have products of the eruptions of all geological pe- riods. To these products we must, therefore, chiefly look for information as to the nature of the substances con- tained in the interior earth's mass. They may represent a part only of that mass, but they constitute our only evidence on the subject. The nucleus of the earth may possibly be differently composed, but we possess no means of investigating it. In the aggregate composition of the sedimentary rocks, which we assume to be but the product of decomposition, re-deposition, and transmutation of the original and first consolidated igneous rocks, we should expect to find the same ingredients as in the igneous rocks, and in somewhat similar proportions. Therefore we should look for silica as the predominant ingredient, and alumina, oxides of iron, lime, magnesia, potash, and soda in smaller quanti- ties. We do, indeed, find these to constitute the sub- stance of the stratified rocks (although not grouped in the same manner as in the igneous rocks). We likewise find other ingredients such as compounds of carbon, sul- phur, and chlorine ; but these we infer have been derived from the atmosphere or from water. It is doubtless very difficult to form a sound opinion, whether in point of fact, the quantitative proportions of the ingredients we have first named are in the aggregate about the same in the sedimentary as in the igneous rocks, since the combina- tions are for the most part very different in the two classes. In the sedimentary rocks the lime and magnesia have vmited with carbonic acid to form the limestones and dolomites, or with sulphuric acid to form gypsum and anhydrite ; silica has produced quartzite rocks and the sandstones ; alumina has combined with silica to form the argillaceous rocks; oxides of iron, the ironstones (iron is also much disseminated in other rocks); potash and soda have become very much distributed amongst many kinds of sedimentary rock ; soda, again, has united 376 PKOCESSES OF EOCK FORMATION : with muriatic acid to form rock-salt ; carbon (concentrated by process of vegetation) has formed coal-beds. At a cursory glance it might appear as if the sedi- mentary rocks in the aggregate contained more lime and less potash than the igneous. We must, however, re- member that some lime is contained in almost all igneous rocks (especially the basic rocks), but by no means in all sedimentary rocks ; again, that the sulphuric acid and water make up a very considerable part of the bulk of the limestones, dolomites, and gypsums ; which bulk we may moreover easily be led to overrate as they are apt to stand out very conspicuously and prominently amongst the other sedimentary rocks in separate and excep- tionally compact masses. Taking all these circumstances into account we should probably find that the proportion of lime in the aggregate of the stratified rocks does not essentially differ from that in the aggregate of the igneous rocks. As regards the potash we must recollect that its quantity in the igneous rocks only reaches about 4 per cent, as an approximate average, that the greater part of the sedimentary rocks contain some potash, and several a very considerable quantity. Great quantities of soda have been converted into rock-salt. We have, therefore, no sufficient reason to doubt that the aggregate ingre- dients of the igneous and the sedimentary rocks are equally balanced. In the case of all sandstones, stratified conglomerates, tuff formations, compact and slaty argillaceous rocks, as well as the greater part of the marls, limestones, dolo- mites, and coals, their sedimentary origin is so appa- rent that nobody will doubt it. The matter is less clear in the case of many granular limestones and dolomites, also in that of the massive accumulations of rock-salt and gypsum, although the sedimentary origin of these latter is now generally admitted. It is most difficult to dis- tinguish the sedimentary from the igneous rocks in those cases where the two are found interlying each other in parallel beds as sometimes happens, the igneous perhaps indistinctly composite or even somewhat decomposed. Whilst we thus find no difficulty in pronouncing on the origin of the sedimentary rocks in general, it is somewhat difficult to determine what rocks we should reckon as SEDIMENTARY ROCKS. 377 sedimentary, and in what cases we should apply the terra * metamorphic.' The expression ' metamorphic ' will best serve a useful purpose of distinction if it be reserved for cases where a rock originally sedimentary (according to our previous definition) is so essentially changed in its mineral cha- racter as not to be capable of recognition without the evidence of collateral circumstances to identify it with the original formation. From the nature of the case, how- ever, no distinct division between the sedimentary and the metamorphic rocks is possible ; on the contrary, gradual transitions take place from one to the other, and the ex- tremes alone are distinctly different in their character. There remains much for investigation as to the parti- cular circumstances under which the several kinds of sedi- mentary rock came to be deposited. \Ve cannot lay down any general law applicable to all sedimentary rocks as to the conditions under which their first deposit took place. The case of each rock has to be separately considered with reference to its bedding, and the organic remains which it contains. The most that we can say as a general proposition is, that many of these rocks have been deposited by the sea some on the coasts, some at a great distance from the shore ; others have been deposited in freshwater lakes by means of rivers or springs. The greater part consist of matter washed together by floods ; some consist of the ejectamenta of volcanoes ; some are crystalline precipitates, and some are the result of processes of animal and vegetable life. Nor can we in general terms describe the mechanical forces which have acted on the materials of the sedi- mentary rocks to fit them for union, the mode of that union, the separation or combination of the chemical ingredients, the nature of the substances which have been introduced or become changed subsequently to the first deposit, the alterations of level which have taken place in the beds of those rocks by depression or upheaval, &c. All these are of great moment to be determined, but they can only be subjects of separate consideration in each individual case. The oldest rocks which are capable of being recognised at the present day as distinctly sedimentary, are those of 378 PROCESSES OF ROCK FORMATION I the transition period. Now as these rocks still contain a considerable number and variety of organic remains, it is reasonable to conclude that there have been many of yet more ancient date, for, according to the igneous theory of the earth's structure there must necessarily have existed a long period of time in which deposits took place before any organic remains existed. These oldest deposits would be the lowest sedimentary formations, and would contain few or no fossil remains. It is probable that they have been changed into, and now form the principal bulk of the metamorphic schists. If we would speculate on their former probable structure, we should expect their compo- sition to have been very uniform, because at the time of their deposit there were fewer causes for difference in rock formation than in later periods ; many of such causes having arisen subsequently, such for instance as organic life, the origin of many calcareous, and all the carboniferous strata. Reasoning backwards, if we believe the crystalline schists to have chiefly sprung from the oldest sedimentary rocks, we may thus account for their very rarely enclosing calcareous or carboniferous beds (limestone and graphite). That the composition of these crystalline schists should much resemble that of the first igneous rocks, would seem to be but a natural consequence of their transmutation from the earliest sedimentary rocks, which themselves were the products of the disintegration of those first igneous rocks. But these speculations should be indulged in with caution, as they may easily lead us too far into the regions of unfounded hypothesis. METAMORPHIC CRYSTALLINE SCHISTS. Notwithstanding what we have had occasion to remark in describing the sedimentary rocks, the true interpreta- tion of the crystalline schists remains one of the most difficult problems for the geologist, since the process of their formation can only be subject of theory, and not of direct observation. Various theories as to the nature of their origin have been advanced. They have .been taken for the original deposits of a so-called antediluvian age ; for the first cooled igneous products of the earth ; a part for rocks of eruptive METAMORPHIC SCHISTS. 379 character ; and finally for sedimentary rocks very greatly changed or transmuted. These different views have been put forward at different times, have been more or less accepted, but all except the last have been very generally abandoned. Nobody now holds that the crystalline schists were deposited in their present state and condition. A few at most may have been formed by the first cooling of the earth's crust perhaps some gneiss districts, if any such can be found entirely free from subordinate interlying beds. It is improbable that such origin can ever be satis- factorily proved, and it remains for the present at best an hypothesis which is possible for certain cases. Some gneiss certainly appears to be of igneous (eruptive) origin, but a very large proportion of the known gneiss forma- tions admit of no such explanation, nor is it applicable to any of the other crystalline schists. From a geological point of view we shall therefore do well to consider the eruptive gneiss as a schistose variety of granite, and every other (for the present at least) as metamorphic. Hence, according to the present state of our scientific knowledge, the only explanation left for by far the greater part of the crystalline slates is that of transmutation from sedimentary formations. The following are some of the principal reasons which appear clearly to speak for such transmutation, without, however, giving us certain information as to the manner of the process : 1. Those rocks the traces of whose sedimentary origin are evident and distinct, present us with numerous series of transitions tending towards or rendering possible further transitions into crystalline schist, or corresponding with the subordinate beds which are found interlying those schists. We will give a few instances of such series of transmutation : (a) Clay -mud successively passes into (or becomes) argillaceous shale, clay-slate, argillaceous mica-schist, and mica-schist. If this be so we should expect in the final products of this series of transmutations to find indications of the special composition of the dif- ferent original clays influencing the character of each rock, which accordingly should vary with the varying 380 PROCESSES OF ROCK FORMATION: quantities of sand, lime, magnesia, potash, or soda con- tained in the original clay. And to such differences of original composition we do in fact attribute the different varieties of mica-schist, or the formation in its stead of gneiss, hornblende-schist, chlorite-schist, or talc-schist (although the special character of the two latter is pro- bably in some measure owing to the later accession of solutions of magnesia). (#) Sand passes into (or becomes) sandstone, quartz- ite, quartz-schist, or itacolumite, according to the character of the substances originally mixed with the sand, or which have subsequently come to it. A mica- schist rich in quartz, or a gneiss, might also result from the transmutation of a sandstone having a copious com- bining medium. (c) Calcareous mud, consisting of microscopically small shells, passes into (or has actually become) chalk ; chalk (probably by means of pressure) has turned to compact limestone. Chalk or compact limestone under pressure, by means of a high degree of tem- perature, may have been transmuted into granular lime- stone, beds of which frequently occur in subordinate layers between the strata of crystalline schists. (c?) Browncoal, coal, anthracite, and graphite have without doubt resulted from peat or other vegetable accumulations. Anthracite and graphite we again find as subordinate formations imbedded between strata of crystalline schists. (e) Hydrated oxide of iron forms a deposit in the form of bog-ore or brown hematite, and these under the pressure of thickly overlying masses appear to have parted with their water, and become converted into red iron-ore, or red hematite. Further, by the absorption of one part of oxygen, red iron-ore is converted into magnetic iron-ore. The latter is found in subordinate layers between beds of crystalline schists. But in each of these cases the transmutations are sometimes found to have been reversed, and other processes have taken place which have somewhat complicated the actual phenomena. 2. The several kinds of crystalline schist and their different varieties are found imbedded in manifold parallel METAMORPHIC SCHISTS. 381 alternating layers or strata. Between these lie subordi- nate layers of granular limestone, dolomite, quartzite, ironstone, graphite, &c., and the whole series are found stratified in a parallel direction. This alternate bedding and imbedding correspond exactly with that of the sedi- mentary rocks their state only is changed, being usually crystalline. The bedding and stratification of the crys- talline schists therefore furnishes a second and most im- portant argument for their metamorphic origin ; in no other way can the existing phenomena be accounted for. 3. The usual or normal bedding of the crystalline schists is lower than that of all sedimentary rocks, and complete gradual transitions between the two are fre- quently to be observed. These outward indicia alone are strong evidences of metamorphic origin. 4. Finally, we may bring certain more rare or ex- ceptional phenomena in proof of the theory of transmu- tation, e.g. the occurrence in strata of crystalline schist of beds containing certain still recognisable fossils ; as for instance the limestone-slate with remains of belemnites between the mica-schist and gneiss of the Alps, at the Furca and Pass of Nufenen. At the last-named locality more recent formations are also found exceptionally very much changed, but not entirely transmuted. Taking all these facts together they appear to us to furnish as complete a chain of indirect evidence in favour of the transmutation of a very large proportion of the crystalline schists as we could well expect to find where from the nature of the case direct observation is un- attainable. The causes and manner of the transmutation, however, constitute a different question. The first theory of geologists upon this matter was that the crystalline schists had been formed out of the sedi- mentary by the operation of great eruptive masses of igneous rocks thrusting themselves through, over, and by the side of the sedimentary rocks therefore by the effect of contact ; and it was also supposed that the felspar of the gneiss was only forced into it from granitic compounds. The frequent occurrence of granite in the immediate neighbourhood of gneiss, the fact that granite districts are frequently entirely surrounded by gneiss, which latter 382 PROCESSES OF ROCK FORMATION : gradually merges into mica-schist towards its external boundary (as for instance, in many parts of the Erzge- birge) ; all these and like phenomena might no doubt be cited in favour of such an hypothesis. But on the other hand, no possible explanation could be afforded on this assumption for the uniform distribution of the felspar in the gneiss, nor for the extent of the supposed effect of the contact without a regular diminution of force cor- responding with the distance from the transforming cause. Very frequently the observable mass of eruptive rock (which according to the theory should be the cause of the transmutation) bears no adequate proportion to the extent of the crystalline schist (which has become trans- muted). Many large districts of crystalline schist are, moreover, entirely free from granitic or other eruptive intrusions ; and it would, to say the least, be hazardous in such cases always to presume the existence of a substratum of granite which had failed to penetrate to the surface. Again, many considerable granite districts are not sur- rounded by gneiss or other crystalline schists, but on the contrary are immediately in contact with distinctly sedi- mentary rocks, which latter have remained almost entirely unchanged by the contact, or at all events are not changed into crystalline schists, although their bedding shows clearly enough that they have been actually broken through by the granite. The Hartz and Saxon Yoigt- land afford remarkable instances of this kind. Thus we find clay-slate formations of different ages broken through by great masses of granite ; at the margin of the granite, however, we find no trace of gneiss or mica-schist forma- tions, but only the ordinary clay-slate changed for a relatively small distance into horns tone, nodular schist (Knotenschiefer), or chiastolite-schist changes which no doubt have been caused by contact with the granite, but which bear no resemblance to gneiss-formations, and are probably the consequence more of a hydroplutonic operation than of the high temperature of the granite alone. We are aware that Credner (in v. L. u. Br. Jahrb. 1849, p. 8) has described an occurrence at Glasbach on the Schwarza, in the Thuringian Forest, where it really appears as if the clay-slate, broken through by a very METAMORPHIC SCHISTS. 383 considerable dyke of granite, has been transmuted into gneiss for some short distance from the granite. Under special circumstances, and if we find the clay-slate to contain the same elements as the gneiss, we may well admit the possibility of such an effect of the contact of granite without our being authorised therefore to con- clude that all gneiss has arisen from the same or similar transmuting causes. We should rather regard such an instance as proving that in particular cases special causes have been competent to supply those more universal con- ditions and processes of transmutation by which the greater part of gneiss rocks have been formed ; just as in the neighbourhood of basaltic rocks and porphyries ex- ceptional formations of anthracite have taken place. From all these considerations we gather that no effect which could be produced by the contact of eruptive igneous rocks would be sufficient to have caused the formation of the great mass of the crystalline schists, but that we should rather look for causes much more general in their operation. These are most probably no other than pressure and heat. We accordingly hold that not only the crystalline schists but also the subordinate masses imbedded in them are nothing more than the latest result of that very general process of transmutation which all sedimentary deposits have undergone and are still under- going from the moment that they begin to be covered more or less thickly with other more recent deposits. Now a very thick covering with recent deposits can only be the consequence of a previous depression. But by the combined effect of depression and the weight of fresh deposits the underlying strata are subjected not only to an increased pressure but also an increased temperature. In the earliest periods of the earth's development, there probably was also an increased pressure from a denser and more heavily laden atmosphere, and besides the increase of heat with the depth from the surface, there was doubtless a generally higher temperature of the whole globe, so that the difference which now exists between older and more recent igneous rocks, and be- tween volcanic and plutonic rocks, would at that time be much smaller, all volcanic formations partaking more or less of the nature of the plutonic. 384 PROCESSES OF ROCK FORMATION: Therefore, pressure and heat, with the addition, per- haps, of water (which has either penetrated the earth to a considerable depth or which chemically formed a part of its original composition), appear to have worked together through great periods of time to produce the final result of the transmutation into crystalline schist; and those crystalline schists which are now to be seen on the earth's surface must also have been lifted and partially deprived of their superincumbent masses. But as each process of covering, of transmutation, of raising and re-exposure, must have occupied extensive periods of time, it follows that all crystalline slates which are now accessible to ob- servation are of very ancient formation. In general lan- guage, they may be said to represent the oldest deposits in a metamorphosed state. Exceptions to this character can only be attributed to special circumstances. In the Alps, such exceptions do appear to have taken place. The deposits of the Jurassic, the Chalk, and the Tertiary periods exhibit there an extraordinary thickness of development, and, consequently, belemnitic strata (of the oldest deposits of the Jurassic period) appear in certain places to have been so thickly covered as to have been changed into crys- talline schist ; and very energetic upliftings have also at a later period exposed them. In general we may say of the Alps, that the process of metamorphosis has been there pushed up higher in the scale of the earth's history than elsewhere is usual. The Eocene deposits contain firm clay-slate, which is used for roofing purposes ; the Miocene browncoals of the Mo- lasse formation appear already to have almost become ordinary black coal, &c. On the other hand, we find the converse of this state of things in the low lands of Russia, where the oldest Silurian formations are still partially in the state of plastic clay and friable sandstone, probably because they have never been thickly covered. The temperature to which the lowest deposits have been subjected, under very great pressure of thicklying super- incumbent masses, may even have reached so great a degree that some or all of the rocks composing such strata have been softened or perhaps partially fused. In this way, for instance, we may explain the otherwise singular pheno- menon of layers of granular limestone which sometimes METAMORPHIC SCHISTS. 385 lie between beds of crystalline schist; yea, even sili- ceous rocks may have been softened by this means, en- tirely losing their slaty texture and stratification. No doubt, we may be easily led by such speculations into regions of unfounded hypothesis, but the causes to which we have referred afford a possible explanation of many bedding relations between granulite and gneiss, which cannot be accounted for by simple transmutation from a sedimentary formation. Now, granted that we are able to explain the special state of the crystalline schists by such general plutonic influences as pressure and heat, there yet remains the im- portant question whether their chemical composition also corresponds with this theory of their transmutation; in other words, whether the sedimentary rocks originally contained, or could have subsequently absorbed, those in- gredients which were necessary to the formation of the crystalline schists. In many of the sedimentary rocks this is most certainly the case. We need only compare the ingredients of the crystalline schists with those of the as yet uncrystalline slates as given in the tables, p. 86, ante, in order to perceive that, even without the accession of new ingredients or parting with any which they now contain, many a clay-slate might be changed into a mica* schist, and others into a gneiss, if their ingredients could be so disposed as to combine into crystalline mineral ag- gregates. The elements are there; the opportunity of assuming a new shape is the only thing wanting. The composition of different clay-slates, several of which also contain some lime and magnesia, corresponds with that of many different varieties of gneiss, mica-schist, and hornblende-schist. Doubtless an additional quantity of magnesia would be necessary to the formation of the chlorite and talcose schists, but the possibility of the ac- cession of solutions of magnesia is proved beyond doubt Ity llie existence of numerous pseudomorphs of certain well-known minerals. With reference to the formation of these magnesian rocks (to which serpentine also belongs), certain special conditions would appear to have been ne- cessary in their case in addition to the general causes which contributed to the formation of the great mass of the other crystalline schists. c c 386 PKOCESSES OF KOCK FORMATION : Our hypothesis (to which, however, we lay no personal claim) by no means excludes the possibility of water as an auxiliary agent in such transmutations as we have de- scribed. The comparatively recent experiments of Daubree have established that water will remain in combination with other substances, such as silicates, under high atmo- spheric pressure, even at a white heat ; and that in such cases it even materially affects the fusing point of sub- stances ; and Scheerer has proved that the water con- tained in the mica of gneiss was a part of its original com- position. This water may have caused many phenomena in the interior of the earth, which as yet we are not able accurately to explain or prove. What thickness of superlying strata should be assumed as sufficient to produce the transmutation which has re- sulted, we are unable to say ; and we have fewer data for any computation, as, according to the igneous theory of the earth's formation, the average temperature of the whole globe, including the surface, must formerly have been much higher, and the atmosphere more compact and dense, therefore the pressure much greater, than at the present day. Moreover, in all geological phenomena the duration of a particular influence will to some ex- tent supply any deficiency in its energy ; and, as we have no standard by which to measure the time of geological processes, we have free scope to assume any duration of time that appears necessary to explain their operation. The crystalline schists, if we take their principal repre- sentatives, gneiss and mica-schist, are more closely allied to the acidic than the basic igneous rocks. The cause of this is easily explained. In the igneous rocks, the two principal bases, whose greater or less proportion chiefly creates the distinction between the acidic and basic groups, are lime and magnesia. Now, on the decomposition or disintegration of the igneous rocks, their lime and mag- nesia having first been taken up in solution (for the most part in combination with carbonic acid), have then been separately deposited in the form of independent beds of limestone and dolomite. The aluminous and quartzose ingredients of the igneous rocks have formed the more mechanical deposits of clay and sand, free from lime, and appear to have produced the greater part of the crystal- METAMORPHIC SCHISTS. 387 line schists ; and as the calcareous and magnesian deposits were originally formed between the strata of clay and sand, so we again meet with limestone and dolomite rocks imbedded between the acidic crystalline schists ; and we may assume that they represent the collective amount of lime and magnesia in which the average of the crystal- line schists is deficient as compared with the average of the igneous rocks. This separate development of the lime and magnesia may likewise be the reason why com- binations of hornblende, pyroxene, and labradorite are, generally speaking, far less frequent in the crystalline schists than in the igneous rocks. The crystalline schists, according to our theory, must represent the most ancient or undermost deposits of the world's history. They are the oldest rocks of which we have knowledge, since we find them overlaid by all the sedimentary rocks, and broken through by every kind of igneous rock. But the question arises, upon what foun- dation can these deposits have first rested, if no other rocks were previously in existence? Doubtless there must have previously existed a firm foundation or floor of deposit separating the fused mass of the interior from the covering of water and air, by whose means alone deposits could be formed. If, therefore, we acknowledge the fused state of the whole earth as its most ancient geological condition, we are necessarily led to assume the existence of a very thick first crust, caused by the cooling of the surface of this molten matter before it would be possible for any sedimentary or eruptive rocks to form. Now what has become of this first crust, unless it be repre- sented by the crystalline schists ? It is certainly difficult categorically to answer a question of this nature, refer- ring to ages and circumstances long since passed; but one thing is certain, viz. that such gneiss, mica-schist, or argillaceous mica-schist, as contain parallel subordinate in- terlying beds of limestone, dolomite, hornblende-schist, quartz-schist, ironstone, or graphite, and the like, can- not have been formed by the first cooling of the earth's mass. No doubt where such interlying beds are entirely absent, as, for instance, in some gneiss, it is possible that such districts may be the remains of a first crust of the earth. Further, it is not certain that all granite is of c c 2 388 PROCESSES OF EOCK FORMATION: eruptive origin ; indeed, there are many circumstances that point to a contrary assumption in certain districts. Here, therefore, we have something which may possibly date from the first cooling of the earth's surface. But uniform districts of gneiss containing no foreign subordi- nate beds, and granite districts without recognisable traces of eruptive origin, are phenomena so rare to our present geological experience, that they evidently do not suffice to represent a great primeval crust of the earth. Under these circumstances, there seems nothing left for us in the present state of our knowledge but to assume that the greater part of the first crust, having become very thickly covered with deposits, has been gradually remelted and become eruptive, perhaps in the form of granite. There is, indeed, no reason why the same fate should not have been shared by the oldest rocks of de- posit ; and thus it may be that the chronological starting- point of geological development has frequently been effaced, and become altogether uncertain. In what we have said above, we have endeavoured to develope the plutonic theory of the origin of crystalline schists. Recently, however, other explanations of the origin of those rocks have been started, not so much by geologists as by chemists, who also assume their origin by transmutation from sedimentary rocks, and differ from the geologist chiefly in denying all plutonic agency, only acknowledging the efficacy of such chemical processes as might have taken place under the conditions existing at the surface of the globe. We have already more than once shown, in the course of this work, that plutonic processes do not exclude the combined action of water as an auxiliary agent ; and thus may deserve the name of HTDROPLUTONIC; but, according to the more recent views of some chemists, water alone is said to suffice, under circumstances of ordinary pressure and temperature, to have brought about these transmu- tations in the course of time. We do not venture to pronounce upon such theories from a chemical, but only from a geological point of view, and in this respect they do not satisfy our mind, chiefly because they disregard the effect and influence of very thick overlying strata, therefore of high pressure and METAMORPIIIC SCHISTS. 389 increased temperature ; because they do not explain why, for instance, in the Alps, very recent deposits are greatly altered in character, whereas in other countries very old deposits where they have remained uncovered are scarcely changed at all (as, for instance, in Northern Russia); and finally, because they leave the phenomena of con- temporaneous mechanical changes, such as condensation, slaty structure, &c., entirely unexplained. Assuming it to be the fact that by the agency of water alone, under circumstances of ordinary pressure and temperature, mica- schist or gneiss, hornblende-schist, &c., might be produced from clay (argillaceous shale or clay-slate), it would still be difficult to believe that by such agency proceeding from the surface, whole complicated systems of strata should not have been more locally influenced, and very differently affected at different depths, instead of having been almost everywhere equally and uniformly influenced by the trans- forming cause. Again, if all these important changes and transmutations were entirely or chiefly due to water, it would be very extraordinary if we did not find that they had been occasionally modified by the increase of temperature and of pressure to which they must have been subjected, since we cannot shut our eyes to the existence of such influences in the interior of the earth, and numerous geological facts sufficiently prove that many rocks which once were very thickly covered have been subsequently laid bare by processes of uplifting and denudation. If we adopt the pure chemical hypothesis, then we must abandon the idea of that relationship existing between bedding and transmutation which, according to the plutonic theory, is an invariable law. It is indeed somewhat sus- picious that the supporters of the chemical theory, in order to make the plutonic appear improbable, almost entirely dispute as a fact the operation of pressure and in- creased temperature in the interior of the earth, whereas every unprejudiced person acquainted with the rudiments of physics must admit these forces to exist inevitably under the given circumstances. The same persons are even in the habit of disputing the eruptive character of the greater number of igneous rocks, from which we infer that they are deficiently acquainted with geological facts from personal observation. We purposely use the 390 PROCESSES OF ROCK FORMATION: word eruptive (not igneous) because the eruptive cha- racter of the rock is unmistakably proved by the form of its mass, even if occasional doubts should arise as to the actual state of some few rocks at the time of their in- trusion. In other words, we do not regard those chemists very competent guides in pure geological questions, who fail adequately to regard the external phenomena of form and bedding no less than the elementary composition of rocks. We would not be understood to depreciate the careful experiments and researches which we owe to Gr. Bischof and others on the effect of water in the processes of for- mation and transmutation of minerals. These are highly instructive, and they are more especially valuable as clearing up and explaining very scientifically what was previously only matter of surmise respecting the nature of the process of formation of mineral deposits in vesicular cavities and fissures of some rocks, and respecting the special formation and transmutation of minerals in the interior of other rocks, by which latter process, for in- stance, serpentine, chlorite-schist, talcose schist, &c., may in many instances have resulted. In the course of these observations mention has been made of transmutation by means of contact ; i. e. of such transmutations as are found at the margin or in the neighbourhood of eruptive igneous rocks which have broken through sedimentary rocks. That such exist cannot be doubted ; as a rule, however, they extend to only a very limited distance from the eruptive rock. They may be divided into such as are purely plutonic or hydroplutonic, and such as are volcanic processes. To the plutonic processes belong the formations of hornstone, nodular schist (Knotenschiefer), and chiastolite-slate on the contact-margins of granite or greenstone. To the volcanic processes belong special induration, slacking, vitrefaction, coking and columnar jointing of argilla- ceous sandy or carboniferous rocks on the margins of basalt, trachyte, or porphyry. These latter cases appear to be simply the result of greatly increased temperature and subsequent rapid cooling without water. The plu- tonic processes, on the other hand, admit of the combined agency of water and heat. METAMORPHIC SCHISTS. 391 Transmutations occasioned by the burning of beds of coal (as the burnt clays, described p. 338, ante) are pro- cesses of entirely local character, and there may be many other such which it is unnecessary further to describe for our present purpose. The transmutations of which we have hitherto spoken are chiefly such as have taken place in the interior of the earth with exclusion of atmospheric air. For these Haidinger has proposed the term catogenic in contradistinction to the anogenic transmutations which proceed from the ex- terior towards the interior, under the influences of air and water. These latter correspond in part with the very general process of weathering the rocks ; they do not, however, always consist in the decomposition or disin- tegration of the masses affected, but sometimes rather in the formation of hydrates. To this belong the coalescing of the felspathic rocks, the formation of wackes by means of compounds containing augite or hornblende, the for- mation of gypsum from anhydrite, &c. These anogenic transmutations likewise play an important part in the chain, of processes by which in nature matter circulates through its various forms. The most striking of the contrasts between the cato genie and anogenic transmutations may be stated some- what in the following manner : Catogenic. Anogenic. Condensation and induration. Disintegration. Crystallisation. Frequent destruction of the crys- talline state. Deoxidation. Oxidation. Loss of water (to a certain Formation of hydrates. extent). Formation of slaty schistose or texture. The following recent works may be here cited as espe- cially noteworthy upon the metamorphosis of rocks : St. Claire Deville, the Operation of Chlorides and Sulphates upon the Metamorphism of the Sedimentary Rocks, Compt. rend. 1858, vol. xlvii. p. 89. A. Gages, on the Study of some Metamorphic Rocks, Philos. Mag. 1859, March, p. 169. O. Lieber, Critique on the Views of Bischof and Naumann on the Subject of Metamorphism. in Mining Mag. vol. i. Decem- ber 1859. 392 PROCESSES OF ROCK FORMATION. Delesse, Etudes sur le Metamorphisme des Roches, Paris, 1861 : v. L. u. Br. Jahrb. 1858, pp. 335 and 727, 1859, pp. 222 and 223 ; 1'Institut, 1861, p. 276. Daubree, Etudes sur le Metamorphisme et sur la Formation des Koches Cristallines, Paris, 1860. MINERAL VEINS AND VEINS OF ORE. These almost form a special group of rocks, and would be entitled to an equal place by the side of the three other groups, if the extent of space which they occupy in nature were not so small. They but fill up narrow fis- sures in other rocks. Their origin appears, almost with- out exception, to have been hydroplutonic. They are, for the most part, chemical precipitates from aqueous solu- tions formed in the interior of the earth under very dif- ferent circumstances of pressure and heat than those which prevail upon the surface. Having treated these formations, which occupy so sub- ordinate a space in the composition of the earth's crust, at length in our book on ' Erzlagerstatten,' we shall not devote further space to them here. CONCLUSION. BEARING in mind the facts and considerations above stated, if we take a general review of the various forma- tions and transformations of rocks, we shall discover in them a perpetual process of circulation or rotation of substances, and of their different states. The substances remain, but the forms in which they appear and the mode of their combinations vary. Disregarding for the moment the first solid products of cooling on the earth's surface, as not being capable of identification at the present day, we may most conve- niently enter the circle of transmutations with the erup- tive igneous rocks, as approaching most nearly to original formations. These then are constantly attacked and de- composed by chemical and mechanical forces acting from their surface inwards, and from their cracks and fissures outwards. The products of this decay are deposited either in the form of chemical precipitates or mechanical aggregates. By chemical process of precipitation cavities and fissures in rocks become filled up (amygdaloids and veins), depo- sits are made at the mouths of springs of limestone-tuff, siliceous tuff, bog-ore, &c. ; or else, other crystalline rocks are formed, such as gypsum or rock-salt. By mechanical agency, on the other hand (partly aided by organic pro- cesses), there arise the much more important and exten- sive deposits of clay, sand, pebbles, marl, limestone, and dolomite ; and during the process of deposit, carbon (in the form of carbonic acid from the atmosphere), water, chlorine, and some other substances are added to the pre- viously existing materials. But, like the eruptive masses, all these deposited masses in their turn are partly decomposed and washed away by external forces, and in other part they become greatly changed internally by pressure and the action of heat. 394 PROCESSES OP EOCK FORMATION. By means of heat and pressure acting during long periods, parts which thus in the first instance were only mecha- nically bound together, enter into new chemical com- binations with each other, and assume a crystalline state more or less analogous to that of the crystalline mineral aggregates of the eruptive rocks. It is even pro- bable in many cases that the substance of these deriva- tive rocks has been fused and become eruptive a second time. Thus the process of destruction and new formation of rocks, be it ever so slow, and therefore difficult of ob- servation, has never, at any time of the earth's history, been interrupted, but continues at the present day ; and not only is this true of the original formations, but the new products of consolidation, of deposit, and of transmu- tation have always been equally subjected, and are still subject, to the same processes. This is the perpetual circulation of matter in the world of rocks. In the course of such various and renewed working up and transformation of the same substances, with the addi- tion of those others furnished by the air and water, it cannot be matter of wonder that the variety of their groups has been always somewhat on the increase ; for, if certain processes in this rotation are altogether universal in their character, recurring in the same way, everywhere and in every age, yet in consequence of the general mul- tiplication of conditions and circumstances, and the in- creasing aggregate of their results, special combinations of the same processes have constantly arisen in later times and brought about special formations of rocks which were not previously in existence, or which do not belong to the normal phenomena of nature. This increase in variety of the products of later times is not confined to geological and mineral substances ; a greater and more rapid increase has taken place in the organic world, where the forms of life have multiplied in an ever ascending ratio (partly in consequence of the change and increase of the conditions of existence from geological causes). The processes of change, to which the outward con- formation of the globe's surface is subject, likewise mul- CONCLUSION. D95 tiply more rapidly than mere strictly geological pheno- mena. Reasoning, therefore, from the past and from analogy with other kingdoms, we must expect the species of rocks and kinds of rock-formation to go on increasing inde- finitely for the future, as they have been increasing con- tinually ever since the first solidification of our earth's crust. INDEX OF LOCALITIES. AAC * ACFIEN, smithsonite of, 34 ** Aberdeenshire. andalusite of, 35 Adamello Mountains, in Southern Tyrol, tonalite of, 207 Adam's Peak, Ceylon, oligoclase-gneiss of, 239 jEcrjna, trachyte of, 186 .f, 320 Kirkcudbright, zircon of, 41 Kleinlinden, manganese-ores of, 357 Klobenstein, in Saxony, garnet rock of the, 319 Klumpsen Mountain, in Oberlausitz, diorite of the, 155 Kongbberg, in Norway, analcime of, 30 axinite of, 44 mispickel of, 74 Koi bach, in the Fichtelgebirge, mica- schist near, 243 Korgon, in the Altai Mountains, porphy- rite of, 170 Kozelniker Valley, near Schemnitz, tra- chyte of the, 186 Krageroe, in Norway, phosphorite of, 353 Kremnitz, in Hungary, trachyte of, 184 Kriebstein, dichroite rock near, 320 Kronberg, near Erbendorf, porphyry of, 218 Krummau, in Bohemia, granulite of, 231 Kiinlsbrunnen, in the Siebengebirge, tra- chyte of, 191 Kusstein, in Tyrol, ostraea limestone of the, 283 T AACHERSEE, titanite of, 47 L* Lagoda Lake, wernerite of the, 222 Liilni, melaphyre of, 166 Landshut, in Silesia, melaphyre of, 166 Langenstriegis, near Freiberg, wavellite of, 55 Lauenstein, in the Erzgebirge, gneiss of, 239 Lanrvig, in Norway, zircon-syenite of, 181 LYO Lauterbach.near Marienberg, granulite- gneiss of, 239 Lehnau, near Kemnath, porphyry of, 218 Lehsten, in the Thnringian Forest, roof- ing slate of, 264 Leitha Mountains, conglomerate of the, 303 limestone of the, 282 Lemberg, amber of, 76 Lengefeld, gneiss of, 238 Lenne-Gebiet, in Westphalia, porphyrite of, 170 Leschtina, Bohemia, basalt of, 141 Leukersdorf, in Saxony, porphyry of, 217 Lherz, Lake, in the Pyrenees, augite rock of the, 149 Liebenstein, in the Thuringian Forest, granite- porphyry of, 213 Limoges, kaolin of, 13 Linares, galena of, 70 Liorant, in Cantal, trachyte of, 186 Lipari Islands, perlite of the, 184, 196 obsidian and pumice-stone of the, 197 Lippersdorf. gneiss of, 238 Liscanera, Lsland of, trachydolerite of, 192 Littnitz, in Bohemia, marcasite of, 357 Lizard's Point, Cornwall, saponite of, 26 Llandeilo, flags of, 301 Llandovery, handstone of, 301 Lobau, in Saxony, apatite of, 53 Lobejiin, coal of, 333 Lochwinnock, in Renfrewshire, thorn- son ite of, 31 Lombardy, trachyte of, 184 trachyte- porphyry of, 195 London, clay of, 270 Lowenherg, melaphyre of, 166 Lb'wenburg, in the Siebengebirge, trachy- dolerite of the rock of the, 192 Lozere, fraidonite of the, 175 Ludwigstadt, in the Thuringian Forest, carbonaceous schist of, 258 Ludlow, sandstone of, 301 Lugano, porphyrite near, 170 Luneburg, Hanover, boracite of, 52 Luneville, in France, boracite of, 52 Luschitz, in Bohemia, mellite of, 77 Luxembourg, ottrelite of, 27 Lyons, granite near, 206 malachite near, 60 406 INDEX OP LOCALITIES. MAG MAGDEBURG, boracite of, 52 rock-salt near, 352 Magurka, in Hungary, antimony-glance of, 357 Manebach, in the Thuringian Forest, porphyry of, 218, 219 Maracaibo, in Peru, trona of, 59 Marebach, aphanite of, 159 Margola, rock of the summit of the, 164 Marianna, in Brazil, moorshead rock of, 343 Marienburg, in Bohemia, granulite- gneiss of, 239 phonolite of, 200 Marienberg, in Saxony, porphyrite- wacke of, 171 Markersdorff, in Bohemia, bituminous substances of, 77 Marmaros, in Hungary, red hematite of, 343 Massachusetts, chabasite of, 31 columbite of, 46 rutile of, 66 titanite of, 47 Matlock, in Derbyshire, smithsonite of, 34 Mautern, near Mblk, granulite-gneiss of, 239 Mayence basin, limestone of the, 282 marl of the, 273 sandstone of the, 299 Megeen, in the Sennethal, barytes of, 352 Meissen, in Saxony, granite of, 207 granular limestone near, 278 hornblende-schist near, 253 mica-porphyrite of, 173 pitchstone of, 225 quartz-porphyry of, 217 M?lfi, haiiynophyry of, 141 leucite of, 186 Menaccan, in Cornwall, titaniferous iron of, 64 Mendip Hills, smithsonite of, 34 Menil Montant, Paris, menilite found at, 8 Meronitz, in Bavaria, opal of, 349 Meissner, in Hesse, browncoal of, 330 Messner Mountain, in Hessen, dolerite of, 135 Mexico, obsidian and pumice-stone of, 197 perlite of, 196 trachyte of, 186 Miask, pyrochlore of, 45 titaniferous iron near, 63 NAS Miesbach, Molasse coal of, 330 Mileschauer, in Bohemia, phonolite of, 200 Milo Isles, alunogen of, 50 Milsburg, on the Rhon Mountain, pho- nolite of, 200 Miltitz, near Meissen, granular limestone of, 278 hornblende-schist of, 253 Mittelgebirge, in Bohemia, basalt of the, 142 phonolite of the, 187, 200 titanite of the, 47 Mittweida, in Saxony, granulite of, 231, 232 Mohorn, near Freiberg, pitchstone-por- phyry of, 225 porphyry of. 217 Molina, in Aragon, aragonite of, 58 Molk, granulite-gneiss near, 239 Mondhalde, at the Kaiserstuhl, trachyte of, 190 Monfina, Rocca, leucite of, 186 trachyte doJerite of, 192 Montabaur, in Nassau, trachyte of, 186 Montdore, Auvergne, alunite of, 52 Monte Rosa, granite of, 207 Montmartre, Paris, siliceous concretions of, 279 Monzoni, pleonaste of, 61 Moravia, lepidolite of, 355 Moritzburg, in Saxony, granite of, 207 granite-gneiss near, 238 Morocco, nummulitic limestone of, 283 Mourne Mountains, Ireland, beryl of, 39 common felspar of, 10 fayalite of, 38 topaz of, 35 Miihlhausen, in Thuringia, peat-beds of, 328 Mulatto, porphyritic rocks of, 170 Miinchberjr, in the Fichtelgebirge, eklo- gites of the, 318, 319 granulite-gneiss near, 239 hornblende-schist of, 253 Mursinsk, in Siberia, topaz of, 35 Mussa Alp, Piedmont, idocrase of, 41 Muzay, Hungary, alunite of, 52 Muzo, in Columbia, beryl of, 39 NAGYAG, in Transylvania, trachyte of, 186 Nassau, palagonite of, 19 schal stein of, 310, 311 trachyte of, 186 INDEX OF LOCALITIES. 407 NAT Natolia, meerschaum of, 354 Naxos, corundum of, 351 emery of, 8 Negroponte, meerschaum of, 354 Neurode, in Silesia, hypersthenite of, 152 troutstone of, 316 Neusohl, trachyte-porphyry of the Schlossberg ot, 195 Newcastle, coal of, 332 Niedermendiir, on the Rhine, basaltic lava of, 141 corundum of, 8 haUyneof, 15 Niederschona, near Freiberg, granite- porphyry of, 213 Nile, jasper in the sand of the, 6 Nischne-Tagilk, in the Ural, dolomite of, 289 Norway, axinite of, 44 gadolinite of, 43 magnetic ironstone of, 345 mispickel of, 74 norite of, 156 , orthite of, 43 phosphorite of, 353 porphyrite of, 1 70 potstone of, 251 pyrochlore of, 45 wohlerite of, 46 zircon of, 41 zircon-syenite of, 181 Nossen, sclialstein near, 311 Nuovo, Monte, leucite of, 185 trachyte of, 190 OBERHASLI, in the Alps, gneiss of, 239 Oberhohndorf, coals of, 333 Oberlausitz, in Bohemia, aphanite of, 161 diorite of, 155 phonolite of, 200 Oberpfalz of Bavaria, apatite of the, 53 Ober-Pobel, near Alteuberg, greisen of, 321 Oberstein, harmotome of, 32 characteristics of amygdaloid of, 166 melapliyre near, 164 Oberweishenthal, in the Erzgebirge, actinolite-schist of, 254 Ochuenkopf, in the Erzgebirge, corun- dum of, 351 granite of, 205 talc-schist of, 252 PER Odenwald, granite of, 207 kinzigite of the, 320 porphyry of the, 2 1 7 Oederan, in Saxony, minette of, 174 porphyry of, 218 Oehrenatock, near llmenau, braunite of, 64 manganite of, 66 Ofen, in Hungary, perlite of, 184 Oisans, St. Gotthard, axinite of, 44 Olibano, Monte, near Pozzuoli, trachyte of, 190 Orizaba, Mount, in Mexico, trachyte of, 186 Oschatz, bituminous shale of, 338 Osnabruck, anthracite of, 336 PALAGONIA, in Sicily, tufa of, 308 * Pargas, apatite of, 53 crystals of hornblende and pyroxene disseminated in limestone rocks in the, 21 Paria, in Italy, gypsum of, 293 Paris, glauconite of, 27 gypsum of, 293 inenilite. 8, 279,349 milistofts of the Paris basin, 350 Paris basin, calcaire grossier of the, 282 plastic clay of the, 270 Partenkirchen, in Bavaria, nodular lime- stone of, 280 Passau, on the Danube, gneiss of, 239 granite of, 207 graphite of, 336 kaolin of, 14 Pasto, volcano of, alunogen of, 50 trachyte of, 186 Paterno, Monte, near Bologna, barytes of, 48 Pausilippo tufa, 309 Pelegrin, in Tyrol, porphyry of, 218 Pennig, in Saxony, granulite of, 231 hypersthene of, 19 Pennsylvania, naplitha of, 77 Pentland Hills, near Edinburgh, por- phyry of the, 170 Perlenhardt, in the Siebengebirge, tra- chyte of, 185 Persia, naphtha of, 77 nummulitic limestone of, 283 turquoise of, 54 Pern, glauberite of, 49 troiia of, 59 408 INDEX OP LOCALITIES. PET Peterhead, spodumene of, 22 Phelegrai, Campi, trachytic rocks of the, 185 Pic Blanc, Monte Rosa chain, granite of the, 207 Picota Mountain, in Portugal, foyaite of, 181 Picton-nob, in North America, specular iron of, 343 Piedmont, idocrase of, 41 Pike's Peak, in Kansas, nacrite of, 244 Pinchincha, andesite of, 192 Planitz, in Saxony, burnt shale of, 339 felsite-balls of; 224, 225 Planschwitz, in Saxony, greenstone-tufa of, 310 Flatten, in Bohemia, polianite of, 65 Plauenschen-Grund, near Dresden, horn- blende-porphyrite of the, 172 syenite of the, 176, 178, 179 Plombieres, apophyllite of, 30 fluor-spar of, 69 Polwand, near Saalfeld, nodular lime- stone of, 281 Pontellaria, fibrous trachyte of the, 184 Pont Jean, in the VosgesliMountains, dioriteof, 156 Ponza Islands, trachyte-porphyry of the, 184, 195 Popayan, trachyte near, 186 Popocatapetl, Mount, trachyte of, 186 Poppenrent, near Miinchberg, granulite- gneiss of, 239 Potschappel, near Dresden, hornblende- porphyrite of, 171 Portland, sand of, 299 stone of, 280, 284 Portugal, foyaite of, 181 itacolumite of, 249 Pozzuoli, trachyte near, 1 90 Predazzo, in the Tyrol, chalcopyrite of, 74 granite of, 207 lievrite of, 37 uralite of, 18 Prese, La, in Upper Italy, gabbro of, 151 Prussia, Rhenish, zircon of, 41 Purace, near Popayan, trachyte of, 186 Pusu, Island of, in the Ladoga Lake, wernerite of, 222 Puy de Chaumont, near Clermont, tra- chyte of, 186 ROS Puy de Dome, domite of the, 184, 188 oligoclase of, 186 trachyte of the, 191 Pyrenees, augite rock of the, 149 QUIMPER, in Brittany, kersanton of, 175 Quito, mud-streams of, 307 RABEN KLIPPEN, in the Hartz, melaphyre of, 166 Rabenau, in Saxony, gneiss of, 239 Rabertshausen, in Hessen, trachyte of, 190 Radeberg, near Dresden, gneiss of, 238 Radegrube, near Freiberg, gneiss of, 238 Radoboj, in Croatia, sulphur of, 358 Raibl, in Carinthia, smithsonite of, 34 Rathlin, Island of, in Ireland, granular limestone of, 278 Raubschlb'sschen, near Weinheim, por- phyry of, 219 Redwitz, in the Fichtelgebirge, gneiss of, 238 granite near, 205 Regenberg, in the Thuringian Forest, porphyry of, 217, 218 Reiohenbach, in Voigtland, alum-schist of, 257 Rhine, basaltic lava of the, 141 corundum of the, 8 cypris-slate of the, 266 hauyne of the. 15 itacolumite of the, 249 titanite of the, 47 Rhb'n Mountain, phonolite of, 200 Riccamonfina, in the Albanian Moun- tains, leucite rock of, 143 Richenstein, in Silesia, leucopyrite of, 73 Rieden, leucite rock of, 143 Riesengebirge, granitite of the, 207 malakolite of the, 149 Rio Tinto, in Spain, pyrites of, 358 Rocklitz,in the Riesengebirge, malakolite of, 149 Rome, alunite near, 52 mellilite of, 42 phillipsite near, 32 Rosenau, in Hungary, rhodonite of, 356 Rosswein, in Saxony, gahbro of, 151 granulite of, 231 INDEX OF LOCALITIES. 409 ROT Rottleberode, in the Hartz, fluor-spar of, 351 Rovigo, near Lugano, porphyrite of, 170 Kozena, in Moravia, lepidolite of, 355 Rumburg, in Bohemia, granite of, 202, 207 Russia, black earth of Southern, 340 cupriferous sandstone of, 300 gypsum of, 293 malachite of, 354 steppe-limestone of, 282 volborthite of, 47 Ruszkberg, in the Banat, coal of, 334 SAAFELD, nodular limestone near, 281 Saalburg, diabase of, 147 Saarbrucken, Bohemia, alum of, 50 Sageritz, near Grossenhain, granite- gneiss of, 238 Saidhdiutz, in Bohemia, epsomite of, 51 Sainte Marie, in the Vosges, kersanite of, 176 Salzburg, beryl of, 39 Sau-Alp, in Styria, eklogite of the, 318 SiUtina, diorite of, 155 S ivoy, aphanite of, 159 Saxony, alunogen of, 50 apatite of, 53 basalt of, 140 burnt shale of, 339 chlorite of, 25 coals of, 333 conglomerate of, 303 cordierite of, 44 dichroite-rock of, 320 felsite-balls of, 224 felstone of, 222 ferreo-liihomarge of, 356 jiabbro of, 151 garnet-rock of, 319 gneiss of, 238, 239 granite of, 206, 207 granular limestone of, 277 granulite of, 231 green porphyry of, 214 greenstone-tufa, 310 hornblende-porphynte of, 171, 172 liy}>ersthene of, 19 hypersthenite of, 152 idocrase of, 42 kaolin of, 354 pycnite of, 354 limestone of, 283 magnetic ironstone of, 345 SCH Saxony continued marcasite of, 73 "marl of, 273 mica-schist of, 244 mica-porphyrite of, 173 minette of, 174 nodular or spotted schist of, 257 occurrence of emery in, 8 orthite of, 43 polianite of, 65 porphyrite-wacke' of, 171 porphyry of, 217 porphyry-tuff of, 309, 310 pyrope of, 4 1 quartz- porphyry of, 217 sandstone of, 299 schorlaceous schist of, 323 serpentine of, 317 syenite of, 176, 178, 179 topaz of, 35, 36 Scandinavia, limestone of, 286 Schaumberg, tboleite of the, 138 Schellerhau, in the Erzgebirge, granite- porphyry of, 213 Schemnitz, in Hungary, agalmatolite near, 354 diorite dL 155 granithffrachyte of, 184 perlit*of, 184, 196 timazifes of, 161 trachyte of, 184, 186 trachyte-porphyry of, 195 Schivelutsch, in Kamtechatka, trachy- dolerite of the, 192 Schlaggenwald, greisen of the, 321 Schleusenthal, in the Thuringian Forest, melaphyre of, 1 64 Schlossberg, Saxony, basalt of, 140 Schloitzbachthal, in Saxony, granite of, 206 Schmiedefeld, in the Thuringian Forest, granite porphyry of, 213 magnetic ironstone of, 345 melaphyre near, 167 Schmollnitz, in Hungary, pyrites of, 358 Schneckenstein, in the Voigtland, topaz rock of the, 324 Schneeberg, in the Erzgebirge, granite of, 206 Schneeberg, in the Fichtelgebirge, gra- nulite-gneiss of the, 239 Schneekopf, in the Thuringian Forest, porphyry of, 218 Schneidemiillersberg, near Ilmenau, me- laphyre of, 164 410 INDEX OF LOCALITIES. SCH Schonfeld, in the Erzgebirge, anthracite of, 336 Schwarzbach, in the Fichtelgebirge, chlorite-schist of, 250 Schwarzenbach, in the Fichtelgebirge, mica-schist of, 242 Schwarzenberg, in Saxony, garnet-rock near, 319 Sehwartzenberg, in the Erzgebirge, gneiss of, 238 talc-schist of, 252 Schwarzenfels, in the Erzgebirge, quartz- breccia of, 305 Schwarzwald, common quartz in the sandstone of, 6 disilicate of protoxide of iron of the, 346 Scotland, analcime of, 39 basalt of, 142 cannel or parrot-coal of, 332 carboniferous ironstone, or blacfcband of, 346 hypersthenite of, 152 laumontite of, 32 natrolite of, 32 phonolite of, 201 porphyry of, 170 prehnite of, 31 sandstone of, 300 thomsonite of, 31 titanite of, 47 Seegeberg, in Holstein, boracite of, 52 Seerenbach, near Tharand, gneiss of, 239 Seisser Alp, analcime of the, 30 inelaphyre of, 163 Servia, timazite of, 156 Shelburne, in Massachusetts, rutile of, 66 Shropshire, stiper stones of, 301 Siberia, epsomite of, 51 malachite of, 60 topaz of, 35 Sicily, analcime of, 30 gypsum of, 293 palagonite of, 19 tufa of, 308, 309 Siebengebirge, trachyte of the, 186, 188, 191 trachydolerite of the, 192 Siebei'.helm,near Freiberg, serpentine of, 317 gabbro of, 151 Siegburg, dolerite of, 135 Siegen, polianite of, 65 Silesia, corundum in the granite of, 8 galena of, 70 hypersthenite of, 152 STE Silesia continued leucopyrite of, 73 melaphyre of, 164, 166 native coke or anthracite of, 334 pebbles of, 103 porphyry of, 219 smithsonite of, 34 Silthal in Transylvania, coal of, 334 Skiddaw, in Cumberland, chiastolite- schist of, 257 Skutsch, in Bohemia, amber of, 76 Skye, Isle of, heulandite of, 33 hypersthene of, 19 hypersthenite of, 152 labradorite of the, 1 1 Slatoust, in the Ural, perofskite of, 45 Solenhofen, in Bavaria, slaty limestone of, 281 Somma, Monte, anorthite in the lavas of, 12 leucite rock of, 143, 186 meionite of, 42 spinel of, 61 Sonnenberg, in Bohemia, gneiss of, 238 Sonnerberg, in the Thuringian Forest, pencil-slate of, 264 Soos, in Bohemia, polishing slate of, 350 Spain, aragouite of. 58 cinnabar of, 358 galena of, 70 glauberite of, 49 glaubersalt of, 51 itac.lumite of. 249 kinzigite of, 320 nitre of, 55 pyrites of, 358 Spechtshausen, in Saxony, felsite-balls of, 224 pitchstone-porphyry of, 225 Staffa, basalt of, 142 scolecite of, 33 Staffordshire, coals of, 332 peldon of, 298 St. Agnes, Cornwall, vivianite of, 54 Staniren Alf, in Styria, anthracite of, 336 Stassfurt, near Magdeburg, boracite of, 52 St. Austell, Cornwall, common quartz of, 5 Steindoif, in the Banat, coal of, 334 Steingrun, near Eger, gneiss of, 239 Steinhaide, in the Thuringian Forest, sandstone of, 297 Stemzelberg, in the Siebengebirge, tra- chyte of,' 186, 188, 191 INDEX OF LOCALITIES. 411 ST. St. Gall, pebbles of, 102 St. Gotthard, axinite of, 44 ad ul aria at, 9 corundum of, 8 fluor-spar of, 69 gneiss of, 239 gypsum of, 292, 293 paraeonite-schist of, 244 tourmaline near, 37 St. Loretta, in the Leitha Mountains, conglomerate of, 303 Stockholm, oligoclase of, 11 Stolpen, basalt near, 140 St. Ouen, Faris, siliceous concretions of, 279 Strassberg, in the Hartz, fluor-spar of, 351 Strassfurt, near Magdeburg, rock-salt of, 352 boracite of, 353 Stromboli, dolerite of, 137 trachydolerite of, 192 Stroutian, Ar^yleshire, titanite of, 47 St. Stephen's, in Cornwall, kaolin of, 13 Styria, anthracite of, 336 eklogite of, 318 fullers' earth of, 356 graphite of, 75 paragonite of, 58 trachyte of, 190 St. Yiieix, near Limoges, kaolin of, 13 Supgsville, in North America, orbitoidal limestone of, 283 Sussex, Weald clay of, 270 Swabia, barytes of, 48 celestine of, 48 clays of, 270 dolomite of, 289, 290 marl of, 273, 274 sandstone of, 299 Swarzenbertr, Saxony, idocrase of, 42 Sweden, automolite of, 61 eulisite of, 319 felsite-schist of, 222 hsulandite of, 33 gadolinite of, 43 hypersthenite of, 152 idocrase of, 41 magnetic ironstone of, 345 mica-schist of, 242 porphyrite of, 170 pyrites of, 358 spodumene of, 22 stilbite of, 33 tantalite of, 46 THU Sweetwater River, Rocky Mountains, trona of, 59 Switzerland, common quartz in the gra- nites of, 6 glarus-slate of, 266 gypsum of, 293 sandstone of, 299 staurotide of, 36 Syra, island of, eklogite of the, 318 TABARZ, in the Thuringian Forest, aphanite of, 159 Takli, in the East Indies, hislopite of, 278 Tannebergsthal, in the Erzgebirge, por- phyry of, 217 Tarapaca, in Peru, glauberite of, 49 Tarnowitz, in Silesia, galena of, 70 galmey of, 356 smithsonite of, 34 Taunus, sericite-schist of the, 256 Telkebanya, in Hungary, perlite of, 184 perlite of, 196 Teneriffe, peak of, obsidian and pumice- stone of the, 197 trachydolerite of, 192 trachyte of the, 186, 188 tufa of, 309 Ternuay, in the Vosges, aphanite of, 160 Test-hen, variety of diabase of, 148 Tet.schen, in Bohemia, phonolite, near, 200 Teufelsstein, in Saxony, garnet- rock of the, 319 Tharand, in Saxony, felsite-balls near, 224 felstone near, 222 gneiss of, 239 granite near, 206 marcasite of, 73 quartz-porphyry of, 217 Thibet, borax of, 53 Thuringian Forest, aphanite of the, 159 carbonaceous schist of the, 257 conglomerate of the, 303, 304 diorite of the, 155 dolomite of the, 290 dolomitic sand of the, 290 granite-porphyry of the, 207, 213 hau.smannite of the, 64 kaolin-sandstone of the,297 magnetic iron-stone of the, 345 manganite of the. 66 marl of ihe, 274 412 INDEX OP LOCALITIES. THU Thuringiah Forest continued melaphyre of the, 163, 164 mellite of the, 77 miacytan clay of the, 270 mica-porphyrite of the, 173 oilstone of the, 265 peat-beds of the, 328 pencil-slate of the, 264 porous limestone of the, 281 porphyries of the, 217, 218, 219 quartz-porphyry of the, 217 quartz-porphyries and mica-porphy- ries of the, 187 roofing-slate of the, 264 shale of the, 267 white or grey sandstone of the, 300 Tokay, in Hungary, perlite of, 196 trachyte of, 184 Tolfa, La, Italy, alum-stone of, 309, 352 trachyte of, 184 trachytic rocks of, 185 Tolima, in South America, trachyte of, 186 Toluca, Mount, in Mexico, trachyte of, 186 Tolz, Molasse coal of, 330 Totnn Fjeld, in Norway, orthite of, 43 Transylvania, coal of, 334 porphyry of, 219 * _ pyrites of, 358 sandstone of, 296 syenite of, 179 trachyte of, 186, 191 wohlerite of, 46 Trebendorf, near Eger, granite of, 205 Treyalgan, Cornwall, tourmaline of, 38 Triebisch Thai, near Meissen, pitch- stone of the, 225 Trinidad, asphalte of, 77 bitumen of, 337 Trostburg, in Tyrol, porphyry of, 218 Tumilla, apatite of, 53 Tunaberg, in Sweden, eulisite of, 319 Tunguragua, in South America, tra- chyte of, 186 Turkey, nephrite and jade of, 18 Tuscany, trachyte of, 184 Tyrol, amphilogite-schist of the, 244 chalcopyrite of the, 74 crystals of hornblende and pyroxene disseminated in the limestone rocks in the, 21 eocene coals of the, 330 granite of the, 207 VIT Tyrol continued granitite of the, 207 hypersthene in the, 19 lievrite of the, 37 melaphyre of the, 164 oligoclase of the, 11 ostrsea limestone of the, 283 porphyrites of the, 1 69 porphyritic rocks of the, 170 porphyritic syenite of the, 178 porphyry of the, 218 predazzite of the, 289 staurotide of the, 36 tonalite of the, 207 tufas of the, 310 TTNITED STATES,alunogenof the, 50 U Unst, Island of, chromic iron-ore of the, 62 Ural Mountains, beresite of the, 207 dolomite of the, 289 itacolumite of the, 249 miascite of the, 180 oligoclase- porphyry of the, 160 perofskite of the, 45 talc-schist of the, 252 zircon of the, 41 Uto, in Sweden, apophyllite of, 30 spodumene of, 22 yALENCIA, in Aragon, aragonite of, Velay, trachyte of, 184 Vesuvius, garnet in the lavas of, 40 hematite of, 63 idocrase in old lavas of^ 41 leucite of, 186 leucite rock of, 143 magnetic pyrites in the lavas of, 72 natron of, 59 thomsonite in the lavas of, 31 Vienna basin, tile- or brick-earth of the, 269 Vienna-sand, 299 Viesembach, in the Vosges Mountains, kersanite of, 176 Villa Rica, itacolumite of, 248 moorshead rock of, 343 Villa Rubia, in Spain, glauberite of, 49 Visena Valley, in Tyrol, porphyritic syenite of the, 178 Viterbo, trachyte of, 184 INDEX OF LOCALITIES. 413 VOI Voigtland, chiastolite-schist of, 257 alum-schist of. 257 diabase of, 1 49 granite-gneiss of, 238 topaz rock of. 324 Volturara, near Melfi, haiiyne, of, 15 Vosges, andesine of the, 1 1 apatite of the, 1 60 conglomerate of the, 303 diorite of the, 156 mica-diorite of the, 179 niinette of the, 173 kereanite of the, 176 sandstone of the, 300 Vulture, near Melfi, haiiynopbyry of, 141 extinct volcano of, leucite of the, 186 WACHENBERG, in the Odenwald, porphyry of, 217 Waldenberg, in Silesia, porphyry of, 219 native coke or anthracite of, 334 pebbles of, 103 Waldheim, in Saxony, serpentine of, 317 Waldshut, fluor-spar of, 69 Wales, oilstone of, 265 roofing and pencil-slate of, 264 Walkberg, in Bohemia, basalt of, 141 Walpenruth, in the Fichtelgebirge, mica- schist near, 243 Warwick, in America, rntile of, 66 Wechselburg, in Saxony, gneiss of, 239 nodular or spotted schist of, 257 Weigmannsdorf, in Saxony, gneiss of, 238 Weinheim, porphyry near, 219 Weisig, near Dresden, hornblende-por- phjrite of, 172 Weissenborn, gneiss of, 238 Weissenfels, in Thuringia, kaolin-sand- stone of, 297 Weissritzthal, in Saxony, minette of the, 174 Wenlock, sandstone of, 301 Weser Mountains, bituminous shale of the, 338 Weslau, near Redwitz, granite of, 205 Westmoreland, limestone of, 285 Westphalia, conelomerate of, 303 Hils clay of, 270 Hils sandstone of, 299 marl if, 273 porphyrite of, 170 serpulite limestone of, 284 ZOB Wettin, coals of, 333 Weiford, garnet of, 40 Whitby, dogger sandstone of, 299 Wicklow, freestone of, 298 Wiegersdorff, black melaphyre of, 166 Wiener Neustadt, granulite of the Glocknitzer Schossberg at, 231 Wiersberg, in the Fichtelgebirge, chlo- rite-schist of. 250 Wight, I.sle of, glauconite of the, 27 Wilsdruff, in Saxony, hornblende-por- phyriteof, 171 Winterstein, in the Tlmringian Forest, quartz-porphyry of, 217 Wittichen, in the Black Forest, kinzigite of, 320 Wolkenburg, in the Siebengebirge, tra- chyte of, 186. 188, 191 Wiirtemburg, bituminous shale of, 338 Wurzen, in Saxony, green porphyry of, 214 yORK, New, rutile of, 66 -*- Yorkshire, amber on the coast of, 76 dogger sandstone of, 299 dolomite of, 299 7AWHAUS, in Saxony, anthracite of, fl 336 granular limestone of, 277 in the Erzgebirge, mica-schist near, 244 Zbirow, in Bohemia, wavellite of, 55 Zealand, New, nephrite and jade of, 18 olivine of, 39 siliceous tuff of, 349 Zebernick, in Hungary, talc-schist of, 252 Zell, in the Fichtelgebirge, serpentine of, 317 Zelle, near Nossen, schalstein of, 311 Zermatt, perofskite of, 45 Ziegenrucken, near Hohenelbe, porphy- rite of, 170 Zillerthal, in the Tyrol, amphilogite- schist of 244 apatite of. 53 Zimpan, in Mexico, perlite of, 196 Zinnwald, in the Erzgebirge, greisen of the, 321 Zittau, in Saxony, burnt shale of, 339 Zoblitz, in the Erzgebirge, serpentine of, 317 414 INDEX OF LOCALITIES. zsc Zschopau, the, in Saxony, granulite of, 231 Zweibrucken, harmotome of, 32 Zwickau, in Saxony, burnt shale of, 339 coals of, 333 ZWI Zwickau continued felsite balls of, 224, 225 ferreo-lithomarge of, 356 mica-porphyrite of, 173 porphyry of, 218 pycnite of, 354 GENERAL INDEX. ACI 4CIDIC rocks, 128 ft- Actinolite, characteristics and oc- currence of, 17 classy, 17 Adularia, characteristics and occurrence of, 9, 2C3, 207 Agalmatolite, or figure-stone, occurrence of, 354 Agate, characteristics and occurrence of, 6,351 Alabaster, characteristics and occurrence of, 49 Albine. See Apophyllite, 30 Albite, characteristics and occurrence of, 10 Allanite, characteristics and occurrence of. 43 Allogovite, 142 A hi iand hie. 40 Alpinite, 239 Alum, characteristics and occurrence of, 50 Aluminum, oxides of, 5 Alum-schist, 257 Alumstone, 51, 309, 352 Alunite, characteristics and occurrence of, 51, 352 Alunogen, characteristics and occurrence of, 50 Amber, characteristics and occurrence of, 76 Amethyst, colouring matter of, 6 occurrence of, 350 Amphibole. See Hornblende, 16 Amphilogite-schist, 244 Amygdaloid, the term explained, 97 of Oberstein described, 166 Analcime, characteristics and occurrence of, 29 Analcymite, 138 Auamesite, 134 Andalusite section of minerals,'34 characteristics and occurrence of, 34 Andesine, composition and occurrence of, 11 BAR Andesite, 185, 191 Anhydrite, characteristics and occur- rence of, 48, 290, 293 Ankerite, characteristics and occurrence of, 57, 355 Anorthite, characteristics and occur- rence of, 12 Anthracite, characteristics and occur- rence of, 335 Anthraconite, 277 Antimony-glance, occurrence of, 357 Apatite, characteristics and occurrence of, 53 Aphanite, characteristics and occurrence of, 157 varieties in texture of, 158 in composition of, 159 Aplite, or semi-granite, 207 Aplome garnet, 40 Apophyllite, characteristics and occur- rence of, 30 Aragonite, characteristics and occur- rence of, 58, 353 Arenaceous, the term explained, 97 Argillaceous fonnationsof rocks,! 1 5, 263 Arsenical pyrites, 357 Arseniurets, 69 Arsenopyrite, characteristics and occur- rence of, 73 Asbestus, occurrence of, 18 Asphalte, characteristics of, 76 localities of, 77 Augite section of minerals, 16 characteristics and occurrence of, 19, 148 Automolite, 60 Axinite, characteristics and occurrence of, 43 T) AGSHOT sand, 299 -D Baryt-harmotome, characteristics and occurrence of, 32 Barytes, characteristics and occurrence of 47, 352 416 GENERAL INDEX. BAS Basalt, characteristics of, 138 varieties in texture of, 140 in composition of, 141 Basaltic rocks, characteristics of, 132 Basic rocks, 128 composition of, 129 Bath-stone, 280 Bedding of rocks, 108 Beresite, 207 Beryl, characteristics and occurrence of, 39 Biotite, characteristics and occurrence of, 23 Bitter-spar, characteristics of, 57 Bitumen and mineral pitch, character- istics and occurrence of, 76, 337 Bituminous shale, 338 Blende, characteristics and occurrence of, 70 Bog, 327 Bog-ore, 342 Bole, occurrence of, 355 Bologna-spar, or Bologna-stone, 48 Boracite, characteristics and occurrence of, 52, 353 B orates, 52 Borax, characteristics and occurrence of, 52 Boulders, formation of, 102, 304 Braunite, characteristics and occurrence of, 64 Braunstein, 64 Breccia, the term explained, 97 characteristics and occurrence of, 304, 308 geological varieties of, 305 Breunnerite, characteristics of, 57 Browncoal, or lignite, characteristics and occurrence of, 329 varieties of, 329 Brown-spar, characteristics of, 57 C\ AEN stone, 280 ^ Calaite, characteristics and occur- rence of, 54 Calarnine, 58 Calamite, characteristics and occurrence of, 17 Calcareous spar, 57 Calciphyre, 278 Calcite, 57 Calcspar, characteristics and occurrence of, 57 Cannel coal, 332 Carbonaceous group, 324 CLA Carbonaceous group continued varieties of composition, 324 f review of the important coal or- mations, 326 Carbonates, 56 anhydrous, 56 hydrous, 59 Carlsbad twins, 10 Cassiterite, characteristics and occur- rence of, 65 Celestine, characteristics and occurrence of, 48 Cerine, characteristics and occurrence of, 43 Cerusite, 70 Ceylonite, characteristics and occur- rence of, 60 Chabasite, characteristics and occur- rence of, 30 Chalcedony, composition of, 6 Chalcopyrite, characteristics and occur- rence of, 74 Chalk, red, 62 black, 257 white, 280 glauconitic, 280 upper and lower, 283 Chert, characteristics of, 7, 350 formation of, 350 black, 350 Chiastolite, characteristics and occur- rence of, 34 Chiastolite-schist, 256 Chlorides, 67 Chlorite, characteristics and occurrence of, 24 Chlorite-schist, and potstone, character- istics and occurrence of, 250 varieties of, 250 Chromic iron-ore, characteristics and occurrence of, 62 Chromite, 62 Chrysolite, characteristics and occur- rence of, 38 Cinnabar, characteristics and occurrence of, 71, 358 Cipollmo, 277 Clay, characteristics and occurrence of, 269 varieties and composition, 269 geological terms for certain clays, 269 Clay-ironstone, 58 Clay-slate, characteristics and occur- rence of, 263 varieties in texture of, 264 varieties in composition of, 265 GENERAL INDEX. 417 CLA Clay -slate continued geological varieties of, 266 Clays, occurrence of, 14 burnt, characteristics and occurrence of, 338 varieties of, 339 Claystone and hardened clay, character- istics and occurrence of, 270 Clink.^tone, 198 Clinochlore, 25 Coal formations, 117 common, black coal, pit-coal, cha- racteristics and occurrence of, 331 varieties of, 332 Colophonite, 40 Columbates, 45 Coluinbite, characteristics and occur- rence of, 46 Comptonite, characteristics and occur- rence of, 31 Cone-in-cone, 99 Conglomerate, the term explained, 97 formations, 1 1 6, 302 characteristics and occurrence of, 302 Copper-ore, blue, 60 Copper-pyrites, characteristics and oc- currence of, 74 Coprolite beds, composition and occur- rence of, 340 Coral rag, 284 reefs, 282 Cordierite, 44 Cornbrash, 284 Corundum, characteristics and occur- rence of, 8, 351 Crichtonite, characteristics and occur- rence of, 63 Cryolite, characteristics and occurrence of, 69, 353 T\AMOURITE, character of, 23 Davyne, characteristics and occur- rence of, 16 Delessite, 25 Dendrites, formation of, 100 Desinine, characteristics and occurrence of, 33 Diabase, characteristics and occurrence of, 146 varieties in texture of, 147 in composition of, 148 Diallage, composition of, 19 rock, 150 Diallogite, occurrence of, 354 EUR Diamond, 336 Dichroite, characteristics and occur- rence of, 44 rock, characteristics and occurrence of, 320 Diopside, characteristics of. 18 Diorite, characteristics and occurrence of, 153 varieties in texture of, 155 Disthene, characteristics and occurrence of, 36, 318 Dolerine, 252 Dolerite, characteristics of, 134 analysis of, 135 varieties in texture of, 136 variety in composition of, 136 sub varieties ot texture of, 137 Dolomite, characteristics and compo- sition of, 57, 274, 287 varieties in texture of, 288 in composition of, 289 geological varieties of, 289 Dnnite, 39 Dyke, the term explained, 108 "pAGLE-stone, 295 *-* Earth, black, composition and oc- currence of, 340 fullers', 355 - yellow, 356 Egeran, characteristics and occurrence of, 41 Eklogite, characteristics and occurrence of, 318 Elsoolite, characteristics and occurrence of, 16 Elaterite, 77 Elements, native, 74 Elvanite, 214 Emerald, characteristics and occurrence of, 39 Emery, occurrence of, 8 Epidosite, occurrence of, 35, 355 Epidote, characteristics and occurrence of, 42 Epsom salt, 51 Epsom ite, characteristics and occurrence of, 51 Erratic blocks, 304 Esbonite, 40 Eukrite, 148 Eulisite, characteristics and occurrence of, 319 Euphotide, 151 Eurite, 220 418 GENERAL INDEX. FAH TUHLUNITE, occurrence of, 44 Felsite rock, 220 Felsite-schist, 220 Felspar, characteristics of, 8 orthoclastic, 9 varieties of colour and lustre, 9 plagioclastic, 10 some aids for distinguishing the felspar species, 12 Felspar-porphyry, 169 Felstone, characteristics and occurrence of, 220 varieties of, 222 Ferreo-lithomarge, 356 Figure-stone, 354 Flint, colouring matter of, 6 where found, 6 chalk-flints, 283 Fluor, Fluor-spar, characteristics and occurrence of, 68, 351 Fluorides, 67 Foyaite, characteristics and occurrence of, 181 Fragmental rocks, 294 Fraidronite, characteristics and occur- rence of, 174, 175 Fullers' earth, composition and occur- rence of, 355 Fyalite, 38 p ABBRO, composition of, 150 ^J varieties in composition of, 1 50 Gadolinite, characteristics and occur- rence of, 43 Gahnite, 60 Galena, characteristics and occurrence of, 69, 357 Galmey, 33, 58 composition and occurrence of, 356 Garnet section of minerals, 38 characteristics and occurrence of, 39 varieties, 40 Garnet rock, characteristics and occur- rence of, 319 Glaciers, formation of, 348 Glauberite, characteristics and occur- rence of, 49 Glaubersalt, characteristics and occur- rence of, 51 Glauconite, characteristics and occur- rence of, 27 Gneiss, characteristics and occurrence of, 232 varieties of, 234 HEM Gneiss continued varieties in texture of, 238 in composition of, 239 Gneissite, 234 Gb'thite, 67 Grammatite, characteristics and occur- rence of, 17 Granite, characteristics of, 203 varieties in texture of, 205 occurrence of, 208 proposed new division of, 209 Granitic porphyry and syenitic por- phyry, 212 characteristics and occurrence of, 2 1 2 Granitite, 207 Granitone, 150 Granulite, Leptynite, characteristics and occurrence of, 229 varieties in texture of, 231 Graphite, characteristics and occurrence of, 75, 336 Gravel, formation of, 102 Green earth, occurrence of, 19 Greenovite, 47 Greenstones, characteristics, varieties, and occurrence of, 145 Greisen, essential ingredient of, 23 as a variety of granite, 207 characteristics and occurrence of, 32 1 Gritstone, 295 Grossularite, 40 Guano, composition and occurrence of, 339 Gypsum, characteristics and occurrence of, 49, 274, 290 varieties in texture and compo- sition of, 291 TTALLEFLINTA, 220, 222. -*--* Halunogen. characteristics and oc- currence of, 50 Harmotome, characteristics and occur- rence of, 32 Hastings sand, 299 Hausmannite, characteristics and oc- currence of, 64 Haiiyne, characteristics and occurrence of, 15 Hatty nophyry, 141 Hematite, characteristics and occurrence of, 62 brown, 67, 341 varieties in texture of, 341 in composition of, 342 red, 342 GENERAL INDEX. 419 HEM Hematite continued red, varieties in texture and compo- sition, 343 Hemitrene, 278 Heulandite, characteristics and occur- rence of, 33 Hislopite, 278 Hohlspath, characteristics and occur- rence of, 34 Hone, 265 Honey-stone, 17 Hornblende, characteristics and occur- rence of, 16, 17 varieties of, 16 differences between hornblende and pyroxene, 20 Horublende-porphyrite, 171 Hornblende-schist, and Hornblende-rock, characters and occurrence of, 253 varieties in texture of, 253 variety in composition of, 254 Hornstone, characteristics of, 7, 350 occurrence of, 350 Hyacinth, characteristics and occurrence of, 41 Hyalite, colourless, where found, 8 Hypersthene, characteristics and occur- rence of, 19 Hyperstheuite, composition of, 152 TCE, as a rock, formation of, 347 -*- glaciers, 348 underground ice-strata of Siberia,349 Ichthyophthalmite, characteristics and occurrence of, 30 Idocrase, characteristics and occurrence of, 41 Igneous rocks, 127 composition of, 129 varieties of, 129 basic, 131 volcanic, 131 plutonic, 144, 201 acidic, 182 volcanic, 182 observations on the processes of igneous rock-formation, 361 Ilmenite, characteristics and occurrence of, 63 Ilvaite, characteristics and occurrence of, 36, 356 lolite, characteristics and occurrence of, 44 Iron-earth, blue, characteristics and oc- currence of, 54 LAS Iron, spathic, 57, 345 oxydulated, 61 specular, 62, 344 red, 62 fibrous, 62 scaly, 62 froth, 62 micaceous, 62 titaniferous, 63 pyrites, 72 white, 72 hydrous, 72 disilicate of protoxide of iron, 346 Iron-ore, sparry, 57 magnetic, 61, 344 red, 62 titanic, 63 brown, 67 Iron-stone group of rocks, 340 geological varieties of, 340, 341 Itabirite, 343 Itacolumite, characteristics and occur- rence of, 247 varieties of, 248 JASPER, characteristics and occur- J rence of, 6, 351 Jenite, characteristics and occurrence of, 36 Jointed structure of rocks, 103 Jointing, various kinds of, 103-105 KAOLIN, characteristics and occur- rence of, 18, 354 Karren, or Earrenfelder, 101 Karstenite, characteristics and occur- rence of, 48 Kersantite, characteristics and occur- rence of, 175 Kersanton, characteristics and occur- rence of, 175 Killinite, composition of, 22 Kinzigite, characteristics and occurrence of, 320 Kyanite, characteristics and occurrence of, 36 T ABRADORITE, characteristics and " occurrence of, 1 1 Lapis lazuli, characteristics and occur- rence of, 15 Lasionite, characteristics and occurrence of, 54 E S 2 420 GENERAL INDEX. LAS Lasurite, characteristics and occurrence of, 60 Laumontite (Laumonite), characteristics and occurrence of, 32 Lava, the term explained, 96 Lead-ore, blue, characteristics and oc- rence of, 69 Lepidolite, characteristics and occur- rence of, 23, 355 Leucite, characteristics and occurrence of, 15. 142 varieties in texture of, 143 Leucopyrite, characteristics and occur- rence of, 73 Liebnerite, occurrence of, 44 Lievrite, or Ilvaite, characteristics and occurrence of, 36, 356 Lignite, 329 Lime-mesotype, characteristics and oc- currence of, 33 Limestone formations, 116, 274 characteristics and occurrence of, 276 varieties in texture of, 277 geological varieties of, 282 Limonite, characteristics and occurrence of, 67 Listwenite, 252 Lithia-mica, characteristics and occur- rence of, 23, 355 Lithionite, characteristics and occur- rence of, 23, 355 Lithomarge, occurrence of, 355 Loam, 269 Lode, the term explained, 108 Lydian stone, Lydite, black chert, com- position and occurrence of, 350 MAGNESIA - MICA, characteristics "- and occurrence of, 23 Magnesite, characteristics and occur- rence of, 57, 355 Magnetic iron-ore, Magnetite, character- istics and occurrence of, 61, 344 varieties in texture and compo- sition of, 344 Magnetic pyrites, characteristics and occurrence of, 71 Magnetite, 61 Majolica, 283 Malachite, characteristics and occur- rence of, 59, 354 Malakolite, occurrence of, 19, 149 Manganese-ores, occurrence of, 356 Manganese-spar, occurrence of, 356 MIN Manganite, characteristics and occur- rence of, 66 Marcasite, or hydrous pyrites, character- istics and occurrence of, 72 Margarodite, characteristics of, 23 Marl formations, 116, 271 Marl, characteristics and occurrence of, 272 varieties in texture and composition of, 272 Marlstone, 272, 274 Meerschaum, characteristics and occur- rence of, 28, 354 Meionite, 42 Melanite, 40 Melaphyre, characteristics and occur- rence of, 162 Mellilite, 42, 77 Mellite, characteristics and occurrence of, 77 Melinite, occurrence of, 356 Menilite, 349 Menachine-ore, 46 Mesitine-spar, characteristics of, 57 Miarolite, 206 Miascite, characteristics and occurrence of, 180 Mica section of minerals, characteristics of, 22 binaxial mica, 22 hexagonal or uniaxial, 23 Mica-diorite, 157, 179 Mica-porphyrite, or Micaceous Porphyry, 172 Mica-schist, characteristics and occur- rence of, 241 varieties in texture and composition of, 243 Mica-schist, argillaceous, characteristics and occurrence of, 254 varieties in texture of, 255 in composition of, 256 Mica-trap rocks, 173 Mica-trap, characteristics and occur- rence of, 174 Microcline, characteristics and occur- rence of, 9 Mimetisite, 70 Minerals, 1 the principal minerals, 2 the accessory ingredients of rocks, 2 ' Paragenesis ' of minerals, 3 mode of classification adopted, 3 chemical symbols used, 4 minerals as rocks, 347 mineral veins and veins of ore, 392 GENERAL INDEX. 421 MIN Minette, characteristics and occurrence of, 174 Mirabilite, characteristics and occurrence of, 51 Mispickel, characteristics and occurrence of, 73 Mnja, 307 Moorshead rock, 343 Mountain leatlier, 18 Muriacite, characteristics and occur- rence of, 48 Muscovite. See Potash-mica VTACRITIDE, 244 -L' Naphtha, characteristics and occur- rence of, 76 Natrolite, characteristics and occurrence of, 31 Natron, characteristics and occurrence of, 59 Nepheline, characteristics and occurrence of, 1 6 Nephrite, characteristics and occurrence of, 18 NeVe, 348 Nigrine, characteristics and occurrence of, 64 Niobite, characteristics and occurrence of, 46 Nitrates, 55 Nitratine, characteristics and occurrence of, 55 Nitre, characteristics and occurrence of, 55 Xorite, characteristics of, 151, 156 Nosean, characteristics and occurrence of, 15 Nosean-melanite rock, 144 Xovaculite, 267 ABSIDIAN, pure, 185 characteristics and occurrence of, 197 varieties, according to differences of texture, 197 Ochre, yellow, 341 red, 343 Oilstone, 267 OLgoclase, characteristics and occur- rence of, 1 1 Oligoclase-dolerite, 138 Olivine, characteristics and occurrence of, 38 Omphacite rock, 318 PHA Omphazite, characteristics of, 19 Oolite, formation of, 94 varieties of oolites, 284 Oosite, occurrence of, 44 Opal, characteristics of, 7, 349 occurrences and mode of formation of, 7, 349 varieties of, 349 Ophicalcite, 278 Ophiolite, 314 Ophite, 156 Organic compounds, 76 Ortliite, characteristics and occurrence of, 43 Orthoclase, characteristics and occur- rence of, 9, 355 varieties of colour and lustre of, 9 Ottrelite, characteristics and occurrence of, 26 Ottrelite-schist, 256 Oxides of elements of the hydrogen group, 60 anhydrous, 60 hydrous, 66 Oxydulated iron, 61 Oxygen compounds, 5 TJALAGONITE, occurrence of, 19 -*- ' Paragenesis ' of minerals, 3 Paragonite-schist, 244 Parrot-coal, 332 Paulite. See Hypersthene Pea.ore, 341 Peastone, 282 Peat, characteristics and occurrence of, 324, 327 varieties of, 328 Pebbles, formation of, 102, 304 Pegmatite, 206 Pegmatolite, characters and occurrence of, 9 Peperino, 308 Pencil-slate, 264 Pennine, 25 Peridot, characteristics and occurrence of, 38 Perlites, and Pearlstone-porphyry, 184 characteristics and occurrence of, 196 varieties in texture of, 196 Perofskite, characteristics and occur- rence of, 45 Petrosilex, 220 Phacolite, characteristics and occurrence of, 30 422 GENERAL INDEX. PHE Phenakite, or Phenacite, characteristics and occurrence of, 39 Phengite. See Potash-mica Phillipsite, characteristics and occur- rence of, 32 Phlogopite, 24 Pholades, on the sea-coast, 102 Phonolite group of rocks, 198 Phonolite, Clinkstone, characteristics and occurrence of, 198 varieties in texture of, 200 Phosphates, 53 anhydrous, 53 hydrous, 54 Phosphorite, characteristics and occur- rence of, 53, 353 Finite, occurrence of, 44 Pinsill, or Pencil-slate, 264 Pistacite in hornblendic and pyroxenic rocks, 20 characteristics and occurrence of, 42, 355 Pitchstone and Pitchstone-porphyry, cha- racteristics and occurrence of, 223 varieties in texture of, 225 Pleonaste, 60 Plumbago, characteristics and occurrence of, 75, 336 Plutonic rocks, 111, 113, 114, 128 Polianite, characteristics and occurrence of, 64 Porcelain clay, 13, 354 Porphyrite, characteristics and occur- rence of, 1 68 Porphyrites, 168 Porphyry, 96 Portland-stone, 280, 284 Pot-holes, formation of, 101 Potash-mica, characteristics and occur- rence of, 22 damourite, margarodite, 23 Potstone, characteristics and occurrence of, 251 Prehnite, characteristics and occurrence of, 31 Protogine, 206 Psilomelane, characteristics and occur- rence of, 67 Puddingstone, 302, 304 Pumice-stone, and its varieties, 97, 185, 197 Puzzulana, 308 Pycnite, occurrence of, 35, 355 Pyrites, characteristics and occurrence of, 72, 357 in hornblendic and pyroxenic rocks 20 ROC Pyrites continued magnetic, 71 white, 73 hydrous, 72, 357 arsenical, 357 Pyroohlore, characteristics and occur- rence of, 45 Pyromeride, or Ball-porphyry, 218 Pyromorphite, 70 Pyrope, characteristics and occurrence of, 40 Pyroschist, 338 Pyrolusite, 65 Pyroxene, characteristics and occurrence of, 18 varieties of, 18 appendix to, 19 hydrous products of the decomposi- tion of, 19 differences between hornblende and pyroxene, 20 QUARTZ, characteristics of, 5, 350 common quartz, how found, 5, 350 amethyst, 6, 350 chalcedony, 6 agate, 6, 350 jasper, 6, 350 flint, 6, 350 chert, hornstone, 7, 350 modes of formation of quartz, 7, 350 Quartz-porphyry, Elvanite, characteris- tics and occurrence of, 215 varieties in texture of, 217 in composition of, 218 Quartz-schist, characteristics and com- position of, 246 varieties in texture of, 247 RAINDROPS, traces of, on rocks, 101 Randanite, 350 Reddle, 62 Rennsellaerite, 316 Resins, 76 Rhodonite, occurrence of, 356 Rhoetizite, characteristics and occurrence of, 36 Rbyolite, characteristics and occurrence of, 193 Ripidolite, characteristics and occurrence of, 24 Rock-salt, characteristics and occurrence of, 67, 351 formations, 117 varieties of, 352 GENERAL INDEX. 423 ROC Rock-soap, occurrence of, 355 Rocks, acidic, analyses of, 85 basic, analyses of, 86 composite, 1 igneous, 127 metamorphic, 227 plutonic, 144, 201 sedimentary, 1 1 5 analyses of, 86 volcanic, 131,182 simple, 1 accessory or non-essential, 1 analyses of, 78 microscopic, 78 magnetic, 78 chemical, 79 physical structure of, 87 texture of, 87 peculiar states of rocks, 95 concretionary structure of, 98 special forms of external structure of, 99 jointed structure of, 1 03 stratification of rocks, 105 shape and bedding of rock masses, 106 geological formations and groups of rocks, 111 volcanic, 111 the older, 112 upper plutonic, 1 1 3 lower plutonic, 114 argillaceous, 115 marl formations, 116 limestone formations, 116 sandstone formations, 116 conglomerate formations, 116 coal formations, 117 rock-salt formations, 117 crystalline schist formations, 118 great geological periods of de- posit, 119 transitions and transmutations of rocks, 120 classification of rocks, 123 rocks of special character or bedding, 313 observations on the processes of rock- formation in nature, 359 Roofing-slate, 264 Rottenstone, 279 Rounded stones, formation of, 202 Rubellan, 24 Rutile, characteristics and occurrence of, 66 S SED AL- AMMONIAC, characteristics and occurrence of, 68 Sahlite, characteristics and occurrence of, 18, 19 Salt, common, characteristics and oc- currence of, 67, 351 rock, 67 Saltpetre, characteristics and occurrence of, 55 Chili saltpetre, 55 Sand, varieties of, 299 characteristics and occurrence of f 301 Sandstone, the term explained, 97 formations, 116 characteristics and occurrence of, 295 varieties in texture, 295 in composition, 297 geological varieties of, 298 San id inc. characteristics and occurrence of, /d Saponite, characteristics and occurrence of, 25 Saussurite Qade\ characteristics of, 11 Scaglia, 283 Scapoiite, characteristics and occurrence of, 41 Schalstein, characteristics and occur- rence of, 311 varieties of, 311 Schiller-rock, 314 Schist, the term explained, 97 Schists, metamorphic crystalline, 227 composition of, 227 properties of, 228 schorlaceous schist, 323 observations on the processes of for- mation of metamorphic crystalline schists, 378 contrasts between the catogenic and anogenlc transmutations of, 391 Schorl, characteristics and occurrence of, 37, 323 varieties in texture, 323 in composition, 324 Scolecite, characteristics and occurrence of, 33 Scoria, 97 Sedimentary and fragmentary rocks, 259 characteristics of, 259 table of geological periods of, 260 observations on the processes of the formation of, 374 424 GENERAL INDEX. Selenite, characteristics and occurrence of, 49 Sericite, 23 Sericite-schist, 256 Serpentine group of rocks, 314 Serpentine, characteristics and occur- rence of, 26, 314 varieties of, 315 Shale, the term explained, 97 argillaceous, characteristics and oc- currence of, 268 varieties in texture of, 268 in composition of, 269 geological varieties of, 269 miners' terms for shale, 29 note bituminous shale, 338 Shingle, formation of, 102 Siderite, characteristics and occurrence of, 57, 345 varieties in texture and composition of, 345 Silicates, 8 felspar section, 8 augite section, ] 6 mica section, 22 hydrous magnesian silicates (talc section), 24 zeolite section, 28 andalusite section, 34 garnet section, 38 Silicon, oxides of, 5 Slag, volcanic, 67 Slate, the term, 97 polishing, tripoli, 349 Slates, varieties of, 264-266, 273 Smaragd, characteristics and occurrence of, 39 Smaragdite rock, occurrence and com- position of, 19, 318 Smithsonite. characteristics and occur- rence of, 33 Soapstone, characteristics and occurrence of, 25 Soda, carbonate of, characteristics and occurrence of, 59 Soda-mesotype, characteristics and oc- currence of, 31 Sodalite, characteristics and occurrence of, 14 Spar, heavy, characteristics and occur- rence of, 47, 352 manganese, 356 Spargelstein, characteristics and occur- rence of, 53 Sparry iron-ore, 57 TIM Spathic iron, characteristics and occur- rence of, 57, 345 varieties in texture and composition, 345 Sphserosiderite, 58, 346 Sphalerite, 70 Sphene, characteristics and occurrence of, 46 Spinel, characteristics and occurrence of, 60 Spodumene, characteristics and occur- rence of, 21 Killinite, 22 Stalactites, formation of, 99 Stalagmites, formation of, 100 Stassfurtite, occurrence of, 52, 353 Staurotide (Staurolite), characteristics and occurrence of, 36 Steatite, characteristics of, 27, 354 Stilbite, characteristics and occurrence of, 33 Stilpnosiderite, 67 Strahlstein. See Actinolite Stratification ot rocks, 105 Styolites, 99 Sulphates, 47 anhydrous. 47 hydrous, 49 Sulphur, characteristics and occurrence of, 74, 358 Sulphurets, 69 Syenite group of rocks, 176 Syenite, characteristics and occurrence of, 177 varieties in texture of, 178 TALC section of minerals, 24 -*- Talc, characteristics and occurrence of, 27, 354 varieties of, 27 Talc-schist, characteristics and occur- rence of, 251 varieties of, 252 Talc-spar, characteristics of, 57 Tantalates, or Columbates, 45 Tautalite, characteristics and occur- rence of, 45 Teschinite, 148 Tholeite, 138 Thomsonite, characteristics and occur- rence of, 31 Thumite, characteristics and occurrence of, 43 Timazite (Trachytic Greenstone), cha- racteristics and occurrence of, 156 GENERAL INDEX. 425 TIN Tin-ore, Tinstoue, characteristics and occurrence of, 65 Tinkal, characteristics and occurrence of, 52 Titanic iron-ore, 63 Titaniferous iron, characteristics and occurrence of, 63 Titanite, characteristics and occurrence of, 46 Titanites, 45 Tonalite, 207 Topanhoacanga, composition of, 343 Topaz, characteristics and occurrence of, 35 Topaz rock, 306, 324 Tourmaline, characteristics and occur- rence of, 37 Trachyte group of rocks, 183 varieties of, 184 Trachyte, characteristics and occurrence of, 189 varieties in texture, 189 in composition, 190 Trachyte-porphyry, characteristics and occurrence of, 194 varieties in texture of, 195 Travertine, 282 Tremolite, characteristics and occurrence of, 17 Tripestone, 291 Triphane, characteristics and occurrence of, 21 Tripoli, 349 Trona, characteristics and occurrence of, 59, 352 Tuff, Tufa, the terms explained, 97 characteristics and occurrence of, 306 volcanic tufas, basaltic and trachytic, 308 tuff formations of plutonic rocks, 309 siliceous, 349 Turf, 327 Turquois, characteristics and occurrence of, 54 TTLTRAMARINE, characteristics and occurrence of, 17 Uralite, characteristics and occurrence of, 18 Urao, characteristics and occurrence of, 59 ZWI yANADATES, 45 ' Vein, the term explained, 108 Veins, mineral, and veins of ore, 392 Vesuvian, characteristics and occurrence of, 41 Vivianite, characteristics and occurrence of, 54 Volcanic rocks, 111, 127, 131 Volcanic tufas, basaltic and tracbytic, 308 Volbortbite, characteristics and occur- rence of, 47 WACKE, the term explained, 96 Wad, characteristics and occurrence of, 67 Wavellite, characteristics and occurrence of, 54 Wernerite, characteristics and occur- rence of, 42, 222 Whetslate, Whetstone, 265 Wiluit, characteristics and occurrence of, 41 Wohlerite, characteristics and occurrence of, 46 Woodstone, material of, 7 ^EOLITE section of minerals, cha- " racteristics, properties, and occur- rence of, 28 monometric zeolites, 29 hexagonal, 30 t rime trie, 31 monoclinic, 32 Zinc, hydrous silicate of, 33 carbonate of, 356 Zinc-ore, red, 357 Zincblende, 70 Zinc-spar, characteristics and occur- rence of, 58 Zircon, characteristics and occurrence of, 41 Zircon-syenite, characteristics and oc- currence of, 181 Zoisite, characteristics and occurrence of. 41 Zwitter rock, characteristics and occur- rence of, 322. F F LONDON PRINTED BY SPOTTISWOODB AND CO. NEW-8TBEET SQUAEE MR. BRISTOW'S DICTIONARY OF MINERALS. In crown 8vo. with 486 Figures on Wood, price 12. cloth, A GLOSSARY OF MINERALOGY. By HENRY WILLIAM BRISTOW, F.G.S. OF THE GEOLOGICAL SURVEY OP GREAT BRITAIN. OPINIONS OF THE PKESS. ' THIS is really a handy book. A con- j else account of all known minerals is given in alphabetical order, and references are added to the cases in which specimens may be found in the British Museum and the Museum of Practical Geology. There is also a useful introduction on the cha- racters, properties, and chemical compo- sition of minerals.' MEDICAL TIMES and GAZETTE. 'WE can recommend Mr. BRISTOW'S Glossary of Mineralogy to all geologists, as well as to mining students, and the cadets of Sandhurst and Woolwich. It is a real handy book; the arrangement, being alphabetical, is suited to everyone's capacity As a work of general utility, this book is the best of its class, and the only one we should ever think of opening by way of amusement. We refer to such articles as arsenolite, amber, asbestos, asphalt, avanturine, &c., or to that on the diamond.' CRITIC. 'THE student in physical science has long desired a book combining facility of reference with a concise and familiar account of all the known minerals. This want is now fully supplied by the present work, which is not a mere glossary, as its title would imply, but is intermediate between it and a manual. The first fifty pages contain a description of the general characters of minerals, their various properties, composition, and classification ; whilst the Glossary professes to give in- formation upon every known mineral substance, and this information is as complete as the present state of our know- ledge will allow The Author's task has been ably executed, and his work will be much in request.' LANCET. ' THERE has been hitherto no work in English at all answering to this Glossary of Mr. BRISTOW. It is a Dictionary of Mineralogy of the most complete kind, and yet in the most portable form, and must become a fine qua non to every practical mineralogist. Unincumbered with any system of classification, it de- scribes every mineral species or variety alphabetically, with references to syno- nymes, English, French, and German. The description of the minerals is at once concise and yet sufficient for practical purposes. 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