The Student's Manual of Geology

Front matter

STUDENT'S MANUAL OF GEOLOGY. Megaceros Hibernict-s. (The Iris,], Bighorn.) — Se. p. HS5. Tliis rut and the one on the title-page are borrowed from Owen's Palæontology THE STUDENT'S MANUAL OF GEOLOGY BI J. BEETE JUKES, M.A., F.R.S. LOCAL DIR*)ECTOR OF THE GEOLOGICAL SURVET OF IRELAND, AND LECTURER ON GEOLOGY TO THE MUSEUM OF IRISH INDUSTRY. A NEW EDITION, PARTIALLY RECAST, AND SUPPLIED AVITH LISTS AND FIGURES OF CHARACTERISTIC 'FOSSILS. UPPER MOLAR OF MASTODON ARVERNENSIS. EDINBUEGH: ADAM AND CHARLES BLACK. 1862. PRINTED BY R. AND R. CLARK, EDINBURG

Preface

TO SECOND EDITION. I have endeavoured in this Second Edition of the Student's Manual to come a little closer to my original conception than I was able to do in the first. I have to renew my acknowledgments to my colleague Dr. W. K. Sullivan for assistance in the part devoted to Chemistry and Mineralogy. Since that part was printed off, the Glossary of Mineralogy by another old colleague, Mr. W. H. Bristow, has been published, a little work Avhich the student will find most useful to him. Its late appearance prevented me from availing myself of it except in the compila tion of the index. In the other portions of the part which is entitled Geognosy I have tried to improve the arrangement in some places, and in others have introduced some new matter, such as the chapter on Orography. The part relating to mineral veins and mining has been kindly VI PEEFACE. looked over by my old colleague Mr. Warington W. Smyth, An interesting and instructive work on the lead mines of the Alston Moor district, entitled, " The Laws which regulate the deposition of Lead Ore," has since been published by Mr. W. Wallace, which the student will find an important contribution to our knowledge of this subject, and one directing his attention into what I believe to be the right direction.

My colleague Professor Huxley has again afforded me his valuable help in the classification of the Animal Kingdom, and I am also indebted to the books and the advice of Professor Reay Greene on this part of the subject. By the liberality of the pubbshers I have been enabled to take advantage of the presence of Mr. W. H. Baily in Dublin, who compiled for me bsts of characteristic fossils, which, with some modifications, are those given in the third part of the work. Mr. Baily also drew on the wood the figures which make the fifty "fossil groups" by which that part is illus trated. To the names of the fossils which are not figured in them, I have appended references to figures in other works, choosing, where I could, the most popular books, such as LyeU's and Phillips 's Manuals, and the Tabular View of Characteristic British Fossils pub-

PREFACE.

. VII lished by the Christian Knowledge Society ; but where no figures exist in such works, I have referred to more recondite sources, such as the publications of the Palæontographical Society, Sowerby 's Mineral Con chology, Sir R. I. Murchison's Siluria, and others. Morris's Catalogue of British Fossils has necessarily been my chief guide in selecting these references with respect to all Post -Silurian fossils, the catalogue by Morris and Salter in the last edition of " Siluria " taking its place for those of the previous periods. I am indebted to my colleague Mr. G. V. Du Noyer for some sketches, and for the drawing of some of the diagrams, but most of the latter were drawn by myself, which will in great measure account for the roughness of their execution. This rough ness, however, is not altogether undesigned, since I wished to make them just such figures as a lecturer would draw on his black board, and not to lead the student to believe from any care discernible in the drawings, that they were intended for actual representations of existing objects.

A diagram is merely a condensed explanation addressed to the mind through the eye, instead of through the ear. If it is in telligible, and assists the verbal description, it answers its purpose ; it is a mistake to endeavour to convert it into a picture, and it is better to avoid anything

PREFACE.

. calculated to mislead the mind into the supposition that it would have been one if the draughtsman could have made it one. In drawing up the Index I have followed the example of Professor Owen in the index to the second edition of his Palæontology, and given the explanation of words derived from the Latin and Greek. I have also marked the pronunciation of such words as could possibly require it, by means of the long (-) and short (J) marks commonly used to denote the quantity of vowels. In a science of pure observation like Geology, in which the facts to be observed are of so many dif ferent kinds, and where so many observers are at work all over the world, constant progress must necessarily be made, as well as continual correction and improvement Any one, therefore, who endeavours to give even so slight and general a sketch of it as is contained in this Manual, will not only find that "much change has taken place in it in the interval between the renewal of his attempts, but that some, perhaps important, alterations are going on while he is in the very act of writing. The student, however, will find, I hope, no im portant part of the science entirely neglected in the

PREFACE.

. IX work now placed before him, and something in each part that may serve to lay the foundation of his future studies. I beg leave to add that any criticisms which serve to correct errors will always be taken as favours, whether publicly or privately made. I have dis covered some mistakes myself while going over the work for the purpose of compiling the index, and pointed them out in the " errata." Others probably exist which have escaped my eye, independently of those arising from imperfect knowledge, or from in correct views. J. BEETE JUKES. CONTENTS. PAfiE Introduction ........ 1

Chapter I

— Chemistry aud Mineralogy . . . 11 ] . Laws of Composition. — A. Simple bodies ; Table of Simple Bodies. B. Compound Substances ; B 1 . Primary Compounds ; Acids and Bases ; B 2. Secondary compounds or Salts. Salt radicle Theory ; Relation of Oxygen in Base to that in Acid ; Formation of Silicates. — 2. Laws of Form ; Axes of Crystals ; Systems of Crystals ; Isomorphism, Dimorphism, and Allotropism.

Chapter II

— Rock-forming Minerals . . . . 29 Table of simple substances which enter into their composition ; Table of Primary compounds which enter into their composition ; Minerals formed of simple substances ; Minerals formed of Primary compounds ; Minerals formed of Secondary compounds, or Salts, Carbonates, Sulphates, Silicates ; Summary of Silicated Minerals.

Chapter III

— Origin, Classification, and Determination of Rocks . 50 Rock defined. — Crystallization ; Chemical Rocks ; Paragenesis of Minerals ; Mechanical Rocks ; Organic Rocks ; Mixtures ; Stratified Rocks ; Unstratified, Eruptive, and Intrusive Rocks ; Metamorphic Rocks ; Four great classes of rocks. — Determination of rocks ; of Compact Rocks ; of Granular Rocks ; of Crystalline Rocks ; of Platy Rocks ; of Metamorphic Rocks. CONTENTS. XII Pace 98

Chapter IV

— Igneous Rocks 57 Classification according to Composition ; Classification according to circumstances of formation. Varieties — Amygdaloid ; Porphyry. Volcanic Rocks or Lavas— Trachytic and Doleritic'; Ashes. Trappean Rocks — Felstones and Greenstones; Ashes. Granitic Rocks. Traps and Granites the roots of Volcanoes; Granite passing into Trap ; Sorby 's Observations on Crystals ; Contraction of Igneous Rocks on cooling.

Chapter V

— Aqueous Rocks Mechanically Formed Preliminary remarks on their origin ; — The Sea ; All Cliffs, &c, formed by Erosive Action ; Rain ; Landslips ; Ice and Snow ; Glaciers ; Icebergs ; River Valleys ; Action of Rivers ; Difference between Action of Rivers and that of Sea ; Motive powers of Water ; Amount of matter transported by rivers ; Formation of Deltas ; Transport of Matter by Ocean ; Results. Description of mechanically formed Rocks ; Conglomerates ; Sandstones ; Clays.

Chapter VI

— Aqueous Rocks Chemically and Organically Formed . . . . . . . .124 Preliminary observations on their origin ; — Carbonate of Lime ; Carbonic Acid Gas in water ; Carbonate of Lime in fresh water — in sea ; Formation of Limestone in fresh water — in sea ; Sea bottoms ; Coral reefs ; Formation of Silica in sea ; Carbonate of Magnesia ; Sulphate of Lime and Rock Salt in sea ; Composition of sea water ; Carbon ; Composition of Carbonaceous Substances ; Transformation of Vegetable Matter into Coal. Description of chemically and organically formed Aqueous Rocks ; Limestones ; Flint and Chert ; Magnesian Limestone ; Gypsum ; Rock Salt ; Coals.

Chapter VII

— Aerial Rocks .154 Sand Dunes ; Calcareous blown sand ; Sands of Deserts ; Tuffs of Terrestrial Ashes ; Soils. CHAPTER Vin.— Metamorphic Rocks . . . .156 Preliminary observations ; — Concretions ; Ironstone Balls and Septaria ; Nodules; Metamorphic actions; Pressure; Heat; Heat CONTENTS. Page 207 and Water ; Weathering of Rocks ; Formation of Pseudomorphs ; Petrifaction; Method of Pseudomorphic Action ; Metamorphosis by water at ordinary Temperatures ; Metamorphosis by Hot Water or Steam ; Metamorphosis by Dry Heat, and by Heat whether with or without Water ; Frequent appearance of Mica. Descrip tion of the Metamorphic Rocks ; Altered Sandstone, Clay and Limestone ; Mica Schist ; Gneiss. Passage of Metamorphic into Igneous Rock ; Metamorphic Igneous Rocks. Tabular Classification of Rocks.

SECTION IL

— PETROLOGY.

Chapter IX

— Formation of Rock Beds . . . .177 Lamination and Stratification ; Extent and Termination of Beds ; Relation between the extent and composition of a Bed; Irregular and oblique Lamination and Stratification ; Current mark or ripple ; Contemporaneous Erosion and filling up ; Contemporaneity of Beds on same horizon ; Interstratification ; Association and alternation of Beds ; Included groups of beds (Inlier) ; Lateral changes in the lithological characters of beds ; Nomenclature of groups of beds ; The lateral and vertical changes in groups of beds are the natural result of their mode of formation.

Chapter X

— Joints, Formation of Rock Blocks Cuboidal or Quadrangular Joints; — Joints in Limestone; Joints in Granite ; Master Joints ; Open and Close Joints ; Successive for mation of Joints ; Joints in Burren, County Clare ; Face, Slyne, or Cleat in Coal ; Art of Quarrying. — Prismatic Joints ; Articulated columns in Basalt and other Igneous Rocks. Cause of Joint Structure ; Surface exhibition of Joints ; Natural erosion of rocks in consequence of Joints.

Chapter XI

— Movements of Disturbance in the Earth's Crust ..*... ... 221 Form of the Earth ; Stability of the Earth's Axis ; Internal temperature of the Earth ; Question as to fluidify of central part of globe ; Exciting causes of disturbing action on Earth's Crust ; To produce a permanent change of relative level between the surface of CONTENTS. XIV Pace land and sea, the solid part of the Earth's Crust must move first ; Motion in rocks proved by inclination of Beds ; Motion of Earth's Crust during recent times ; Depression proved by Coral Reefs ; Two modes of Action in forces of Disturbance. CHAPTER Xsi. — Inclination of Beds ... • 233 Dip and Strike of Beds ; Geological Section and Map ; Contortions ; Anticlinal and Synclinal Curves ; Uniclinal Curves ; Inversion of beds ; Artesian Wells.

Chapter XIII

— Faults or Dislocations . . . .245 Throw of a Fault; Varieties of Faults; Variation in Faults from nature of rocks traversed ; Variation of Faults in effect according to inclination of Beds traversed ; Single and Compound Faults ; Relation between the inclination of a Fault and the direction of its Throw ; Trough Faults ; Lateral Pressure ; Connection be tween Faults and Contortions ; Vertical extension of Faults ; Connection between Intrusion of Igneous Rocks and Produc tion of Faults.

Chapter XIV

— Cleavage and Foliation . . . 265 Slaty Cleavage ; Direction of Cleavage Planes ; Origin of Cleavage ; Time of production of Cleavage ; Surface disturbance of Cleav age. — Foliation ; Mr. Darwin's observations on Foliation in South America ; Difference between Cleavage and Foliation ; Cleaved and Foliated Rocks of the Leinster district ; Relations between Gneiss and Granite.

Chapter XV

— Denudation 278 Denudation already tacitly assumed ; Amount of Erosion must be at least as great as that of Deposition ; Denudation is the production of successive New Surfaces ; Two kinds of Hills ; Hills of simple circumdenudation ; Hills of Uptiiting ; Valleys, Glens, and Ravines always caused by Denudation ; Action of Denudation proved by outcrop of beds, by escarpments, and by oultiers ; Instances of Denudation in the South of Ireland ; The Slievnamuck Fault ; General structure of the South of Ireland ; Plains caused by CONTENTS. XV Page 293 307 Denudation ; Inconceivable time required for action of denuding forces ; Atmospheric Denudation, as shewn in the valley of the Moselle and other rivers ; Different periods of denuding action.

CHAPTER XVL

— Unconformability and Overlap Unconformability arises from a surface of Denudation having been formed on one set of beds before the deposition of another set ; When the base of one set of beds rests in different places on different parts of another set of beds, the two sets are unconformable to each other ; Successive unconformabilities in South of Ireland ; Denudation involves existence of dry land, Unconformability that of subsequent depression ; Practical importance of the subject. Overlap ; The Geological Structure of the County of Dublin ex plained as an example of these structures.

Chapter XVII

— The Granitic or Hypogenous Rocks Fundamental Granite ; Primæval Granite or Primitive Rocks not known anywhere to exist ; Position and form of Granite ; Granite more likely to be associated with older than newer rocks, from its source being in interior of earth ; Relative age of granite masses, as proved by that of their Denudation ; Granite Veins ; Apparent interstratification of Granite and Mica Schist ; Original irregularities in surface of deep-seated mass of Granite, and varied appearances shewn by varied denudation.

Chapter XVIII

— Trappean Rocks 320 Form and mode of occurrence of Trap Rocks ; Distinction between Contemporaneous and Intrusive Trap ; the Traps and Ashes of the Lower Silurian Rocks of North Wales ; the Trap district of the Limerick Basin ; Association of Felstone and Greenstone ; Trap Dykes and Veins ; Plateaux of Basalt.

CHAPTER XLX

— Volcanic Rocks 332 Form and mode of occurrence of Volcanic Rocks ; supposed Craters of Elevation ; Peak of Teneriffe ; Island of St. Paul ; Crater of the Bromo ; Dykes and Veins of Lava ; Association of Trachytes and Dolerites ; Exciting causes of Volcanic Eruptions. CONTENTS. Page 344

Chapter XX

— Orography ; or, the Structure and Origin of Mountains ....-•• Relations between the intrusion of Igneous Rock and the elevation of Stratified Rocks ; Steep inclinations never communicated to Beds by disturbance acting near the surface ; Mountains are of three kinds — of Circumdenudation, of Uptiiting, and of Ejection; Valleys are of one kind only ; Intercolline spaces ; M. E. de Beaumont's Theory of the Parallelism of Mountain Chains.

Chapter XXI

— Mineral Veins 356 Metallic Ores in Beds ; Pipe Veins ; True Lodes or Mineral Veins ; Mode of Deposition of Minerals in Veins ; Occurrence of Gold ; Association of Minerals in Veins ; Relations between contents of Vein and nature of surrounding Rock ; Fallacious appearance of connection between age of Rock, or igneous origin of Rock and occurrence of Mineral Veins; North of England a better district for study of Mineral Veins than Cornwall.

Chapter XXII

— The Art of Mining . . . . . 367 Bed Mining ; Vein Mining ; Explanation of some Mining Terms. PAET II. PALÆONTOLOGY.

Chapter XXIII

— Zoology and Botany . . . . 373 Definition ; Petrifaction ; Classification of the Animal and Vegetable Kingdoms ; Distribution of Animals and Plants ; Land and Ocean Climates ; Various degrees of Climate influence ; Food to be included in Climate ; Destruction, partial or entire, of species of Plants and Animals ; Sporadic origin of Species ; Examples of the geographical limitation of Animal Species, as proving their sporadic origin ; Generic centres and districts ; Breaking up of specific and generic Areas by "geological changes.

Chapter XXIV

— The Laws and Generalizations of Palæontology ........ 400 The kinds of Animals and Plants most likely to occur Fossil ; Number of British Fossil Animals and Plants compared with existing CONTENTS. XVII Page 441 British species ; The modes of occurrence of Fossils ; The geographical distribution of Species in past time ; Difficulty in deter mining the contemporaneity of distant formations ; Barrande's Colonies ; Necessity for settling the chronological classification of each large Area separately, before forming one for the whole Earth ; Classification of groups of Beds by means of their Fossil contents ; Law of approximation to living forms ; Duration of Species proportionate to their place in the scale of existence ; Forms once extinct never reappear.

Chapter XXV

— Subject Continued . . . . 414 Supposed sudden destruction and sudden introduction of assemblages of Species a mistake ; Untrustworthiness of negative evidence in Palæontological speculations ; On the Origin of Species ; Changes of Climate ; Practical importance of Fossils.

Chapter XXVI

— Palæozoic Epoch — Præ-Cambrian and Cambrian Periods 425 Chronological Nomenclature ; Table of Geological Time. — Primary or Palæozoic Epoch. — Præ-Cambrian Periods. — Cambrian Period ; Typical Rocks and Characteristic Fossils of British Islands ; Foreign do. ; Life ofthe Period.

— Carboniferous Period . . . 506 Typical Rock Groups of Ireland ; Do. of Great Britain ; Igneous Rocks associated with them ; Characteristic Carboniferous Fossils ; Foreign Carboniferous Rocks. Life of the Period.

Chapter XXXI

— Permian Period 541 Typical Rocks of Russia and Germany; of Durham, and characteristic Fossils ; of Midland Counties of England ; of Ireland and Scotland. Life of the Period. Gaps in the Palæozoic Series. CHAPTER XXXH. — Secondary or Mesozoic Epoch — Triassic, or New Red Sandstone Period . . . 549 Typical Rocks and characteristic Fossils of Germany, etc. ; of Great Britain ; Rhætic Beds ; Lie and position of the New Red Sandstone ofthe British Islands. Life ofthe Period.

Chapter XXXIII

— Oolitic or Jurassic Period . . 562 Typical Groups of Rock and their characteristic Fossils ; Lias and Lower Oolites of South of England ; Lower Oolites of Yorkshire ; Oxford, or Middle Oolites ; Portland, or Upper Oolites. Oolitic Rocks of Scotland and Ireland ; of the Jura mountains ; of other parts ofthe world. Life of the Period.

Chapter XXXIV

— Cretaceous Period .... 602 Typical Rocks and characteristic Fossils ofthe British Area ; Maestricht and Pisolitic Chalk ; Outlying English deposits ; Lie and position of the Cretaceous Rocks in England ; The Cretaceous Rocks of Ireland ; of Switzerland ; of North America ; of South America ; of India. Life ofthe Period.

Chapter XXXV

— Tertiary, or Cainozoic Epoch — Eocæne Period ...... 633 Preliminary observations on Nomenclature. British Eocæne Rocks * Lower Eocæne, and characteristic Fossils ; Middle Eocænes and characteristic Fossils ; Upper Eocænes, and characteristic Fossils ■ Eocænes of France and Belgium ; of the Alps, Mediterranean India, and North America. Life of the Period. CONTENTS. Page

Chapter XXXVI

— Meiocæne Period . . . . 658 Basaltic formations of the Hebrides and Antrim ; Meiocæne Beds and Characteristic Fossils of France and Belgium, of Germany and Switzerland, of Italy, North America, and India. Life of the Period.

Chapter XXXVII

— Pleiocæne Period . . . . 667 Typical Groups of Rock, and Characteristic Fossils in England ; of Antwerp ; of Normandy ; of Italy ; of South Russia.

Chapter Xxxviii

— Pleistocene Period . . . 672 Typical Groups of Rock ; Norwich Crag ; High Level Gravels ; Glacial Deposits ; Boulder Clay of Britain ; Limestone Gravel, and erratic blocks of Ireland ; Glacier markings in Ireland ; Pleistocæne denudation not great ; Eskers of Ireland * ; Subsequent elevation and widely spread plain ; Cave Deposits ; Raised Beaches ; Low Level Gravels ; Submarine Forests and Peat Bogs ; Characteristic Fossils of the Pleistocæne Deposits ; Erratic Blocks of North Europe, of the Alps, of India ; Loess and Lehm of the Rhine Valley ; Pleistocæne Deposits of North America; Sicilian Beds.

Chapter XXXIX

— Pleiocæne and Pleistocæne — Life of the Periods . . . . . . . . 691 Animals ofthe British and European areas ; Newer Tertiary Fauna of America, Australia, etc. ; Extinct Animals of New Zealand, Madagascar, etc. ; Flint implements in the Drift of the north-west of France and the south-east of England; Man contemporary with the Mammoth and other extinct animals.

Chapter XL

— The Recent Period .... 704 Geological action continuous ; Antiquity of Coral Reefs ; Distribution of Volcanoes ; The antiquity of Volcanoes ; Earthquakes ; Conclusion. Addenda et Corrigenda * 710 Appendix on Geological Surveying . . . . . . _ 711 * I unfortunately omitted to mention the occurrence of these gravel ridges in Scotland, where they are called " Kames," according to Mr. R. Chambers. One was described by Mr. Milne Home at the meeting of the British Association in Manchester in the year 1861. EEEATA. Page 394. Line last, for Æpyronis, read Æpyornis. 478 and 479, for Palæochoma, read Palæocoma. 501. Line first, for perosa, read porosa. 504. Line 11 from bottom, for Proteus, read Proetus. 530 and 536. For Bellinurus, read Belinurus. 535. For Næggerathia, read Nœggerathia. 536. For Littorina, read Litorina. 536 and elsewhere.

For Cœlacanthus, read Cœlacanthus. 543. For Polycælia, read Polycœlia. 550. Line 7, for Lilliiformis, read Liliiformis. 560. Line 12, for Lilly, read Lily. 578. Line 21, for Corraline, read Coralline. 584. Line 4, for argustus, read angustus. 594. Line 13 from bottom, for Astrocænia, read Astrocœnia. 594. Line 12 from bottom, for Enallohælia, read Enallhelia. 594. Line 9 from bottom, for Placosphyllia, read Placophyllia. 594. Line ib. from bottom, for Pleurocænia, read Pleurocœnia. 595 Line 13, dele Galeropygus. 595. Line 4 from bottom, for Tetrosternon, read Tretosternon. 599. Line 28, for Copolites, read Coprolites. 611. Line 7, for intermedius, read attenuatus. 630 and elsewhere. For termination cænia, read cœnia, as it apparently refers to the common body, or koivov. 631 . Line 10 from bottom, for Decretis, read Dercetis. 646 and 649.

For Lymnæa, read Limnæa. 653. Line 26, for Ætobatis, read A.tobatis. 668. Among the Polyzoa insert Fascicularia aurantium .... Ly. Man., fio*. 154. 669. From the Actinozoa remove Echinocyamus and place it on next page under Echinodermata. INTEODUCTION. It is not easy to give an accurate and comprehensive definition of the science of Geology ; for its nature is so complex and various, that it is diflicult, in a few words, either to specify its object or to assign its limits. It is, indeed, not so much one science, as the application of all the physical sciences to the examination and description of the structure of the earth, the investigation of the processes concerned in the production of that structure, and the history of their action. "We might, perhaps, without impropriety, classify all the phy sical sciences under two great heads, namely, Astronomy and Geology.

The one would comprehend all those sciences which teach us the constitution, the motions, the relative places, and the mutual action of the Astra, or heavenly bodies ; while the other singled out for study the one Astrum on which we Uve, namely, the Earth. Giving this wide meaning to Geology, it would include all the sciences which treat of the nature and the distribution of the inorganic matter of our globe, as well as those which describe to us the living beings that inhabit it. These sciences are — first, that of Chemistry and Mineralogy (which may be called one), which teaches us what are the elements of which terrestrial matter is com posed, and what are the laws which govern the combinations of those elements into all the variety of known substances, solid, fluid, or gaseous, and the forms, properties, and qualities of those sub stances ; secondly, the science of Meteorology and Physical Geo graphy (which may also be looked on as one), which describes to AA

Introduction

. us the form and disposition of land, and water, and air, and the distribution of the temperatures and motions that affect them ; and thirdly, that of Natural History (or Biology, the science of lite), including botany and zoology in their widest signification. The sciences commonly included under the head of Physics, those which teach us the nature and laws of magnetism, electricity, light, heat, force, and motion, would be common ground to Geology and Astronomy, serving to bind together all human knowledge of matter and its laws into one great whole. In giving this high place to Geology, I have no desire unduly to exalt it at the expense of the other sciences. My object is to shew that this large view of Geology is not only a true, but a necessary one, and that if we do not sometimes look at it from this aspect, we cannot rightly understand nor fully appreciate what Geology is.

That it is true, is shewn by the very fact of the late appearance of geology in the world of science. It was not till some very con siderable advances had been made in all the physical sciences which relate directly to the earth, that geology could begin to exist in any worthy form. It was not till the Chemist was able to explain to us the true nature of the mineral substances of which rocks are composed ; nor till the Geographer and the Meteorologist had explored the surface of the earth, and taught us the extent and the form of land and water, and the powers of winds, currents, rains, glaciers, earthquakes, and volcanoes ; nor till the Biologist (natura list) had classified, and named, and accurately described the greater part of existing animals and plants, and explained to us their phy siological and anatomical structure, and the laws of their distribution in space ; — that the Geologist could, with any chance of arriving at sure and definite results, commence his researches into the structure and composition of rocks, and the causes that produced them, or utilise his discoveries of the remains of animals and plants that are enclosed in them.

He could not till then discriminate with certainty between igneous and aqueous rocks, or between livinn* and extinct animals, and was therefore unable to lay down any one of the foundations on which his own science was to rest.

INTRODUCTION.

. Neither would it be satisfactory if we were to limit the science of Geology to any period of the earth's history ; to assign to it, for instance, all time previous to the existence of the human race, and were to unite all the natural sciences under it up to that time, but then consider it to be brought to an end, or to split up and diverge into the many independent sciences that concern our cotemporary existences, whether organic or inorganic. For not only is there no trace of any hard boundary line between the human and the pre human period of the earth's natural history * but there appears in each one of the separate natural sciences a perfect blending anil continuity from the remotest geological era to the present time. The present is but a part of the past. The inorganic objects we see around us are the result of processes going on in past time, such as are still at work producing the same results ; the Uving beings around us are either the dhect descendants of those that lived formerly, or their substitutes and representatives, the living and the extinct forming parts of one great connected series and chain of species, genera, and orders, each of which parts would be incomplete without the other.

There is, therefore, no possibility of making any division in geology such as we are now considering it, or assigning any limit to its range from the earliest period of the earth's ascertainable history to the present moment. Moreover, as there is no natural science to which the geologist has not to appeal for information upon some point or other in his researches, so there is none which can be fully and completely studied without the help of the geologist, or without including facts or theories which are commonly and rightly reckoned parts of his peculiar inteUectual domain. If he has to call upon the pro fessors of each one of the physical sciences in turn, for assistance in his own investigations, he is sure, sooner or later, to repay the obligation, by the discovery of a number of facts that enlarge the boundaries of the science he has appUed to, or by the statement of many problems whose solution throws light upon parts of it that have been hitherto imperfect and obscure. The reader must not infer from what has been said, that in

INTRODUCTION.

. order to be a geologist, he must be thoroughly acquainted with the whole circle of the physical and natural sciences. Such universal acquirement few meu have the power to attain to, and of these stiU fewer retain the ability and the wiU to make original advances in any particular branch. No man, however, can be a thorough geologist without being acquainted, to some extent, with the general results of other sciences, and being able both to understand them when stated in plain un technical language, and to appreciate their application to his own researches. Such a general acquaintance involves neither profound study, nor requires any great power of mind above the average of human intellect. It is, indeed, what every well-educated man ought to possess. The necessary preliminary to the science of Geology is not the possession of great and accurate knowledge of the whole circle of the natural sciences by any individual persons, but that this know ledge must exist somewhere.