Chapter I: Preface

The present Volume has been written among the rocks which it seeks to describe, during the intervals of leisure of a field-geologist. Its composition has been carried on by snatches, often short and far apart, some of the descriptions having been jotted down on the spot by streamlet and hill-side, or in the quiet of old quarries; others, again, in railway-carriage or stage-coach. By much the larger portion, however, has been written by the village fireside, after the field-work of the day was over--a season not the most favourable to any mental exercise, for weariness of body is apt to beget lassitude of mind. In short, were I to say that these Chapters have been as often thrown aside and resumed again as they contain paragraphs, the statement would probably not exceed the truth. But the erratic life of an itinerant student of science is attended with yet greater disadvantages. It entails an absence from all libraries, more especially scientific ones, and the number of works of reference admissible into his _parva supellex_ must ever be few indeed. With these hindrances, can the writer venture to hope that what has thus been so disjointed and unconnected to him, will not seem equally so to his readers? Yet if his descriptions, written, as it were, face to face with Nature, are found to have caught some tinge of Nature's freshness, and please the reader well enough to set him in the way of becoming a geologist, he shall have accomplished all his design.

It cannot be too widely known, or too often pressed on the attention, especially of the young, that a true acquaintance with science, so delightful to its possessors, is not to be acquired at second-hand. Text-books and manuals are valuable only so far as they supplement and direct our own observations. A man whose knowledge of Nature is derived solely from these sources, differs about as much from one who betakes himself to Nature herself, as a dusty, desiccated mummy does from a living man. You have the same bones and sinews in both; but in the one they are hard and dry, wholly incapable of action; in the other they are instinct with freshness and life. He who would know what physical science really is, must go out into the fields and learn it for himself: and whatever branch he may choose, he will not be long in discovering that a forenoon intelligently spent there must be deemed of far more worth than days and weeks passed among books. He sees the objects of his study with his own eyes, and not through "the spectacles of books;" facts come home to him with a vividness and reality they never can possess in the closet; the free buoyant air brightens his spirits and invigorates his mind, and he returns again to his desk or his workshop with a store of new health and pleasure and knowledge. Geology is peculiarly rich in these advantages, and lies in a manner open to all. No matter what may be the season of the year, it offers always some material for observation. In the depth of winter we have the effects of ice and frost to fall back upon, though the country should lie buried in snow; and then when the longer and brighter days of spring and summer come round, how easily may the hammer be buckled round the waist, and the student emerge from the dust of town into the joyous air of the country, for a few delightful hours among the rocks; or when autumn returns with its long anticipated holidays, and preparations are made for a scamper in some distant locality, hammer and note-book will not occupy much room in the portmanteau, and will certainly be found most entertaining company. The following pages--forming a digest of the Carboniferous rocks--may, perhaps, in some measure, guide the explorations of the observer, by indicating to him the scope of geological research, the principles on which the science rests, and the mode in which it is pursued. But I repeat, no book, no lecture-room, no museum, will make a geologist of him. He must away to the fields and study for himself, and the more he can learn there he will become the better geologist.

He need not burden himself with accoutrements. A hammer, pretty stout in its dimensions, with a round blunt face and a flat sharp tail; a note-book and a good pocket-lens, are all he needs to begin with. Having these, let him seek to learn the general characters' of the more common rocks, aiding himself, where he can, by a comparison with the specimens of a museum, or, failing that, with the descriptions of a text-book. Let him then endeavour to become acquainted with some of the more characteristic fossils of the district in which he resides, so as to be able to recognise them wherever they occur. Private collections and local museums are now becoming comparatively common, and these, where accessible, will aid him vastly in his studies. Having at length mastered the more abundant rocks and organic remains of his neighbourhood, let him try to trace out the connexion of the different strata across the country, so as to understand its structure. For this purpose it will be necessary to examine every ravine and natural exposure of the rocks, along with quarries, ditches, railway-cuttings, and, in short, the whole surface of the district. A general notion of the geology of the place will, not perhaps be of very difficult attainment; and this done, the observer should attempt to put down the connexion of the rocks on paper, for till this is accomplished he will have at the best but an imperfect, and perhaps incorrect notion of the subject. The best map of the district should be obtained, also a clinometer, or instrument for ascertaining the angle at which rocks _dip_ with the horizon, and a pocket-compass with which to mark the direction of the _dip_ and _strike_ of strata, that is, the _outcrop_, or line which they form when they come to the surface. Thus armed, he may commence a geological survey of his neighbourhood. Wherever he sees a bed of rock exposed, it should be marked down on his map with an arrow pointing to the direction in which the stratum is dipping, the angle of dip, ascertained by the clinometer, being put alongside. The nature of the rock, whether sandstone, shale, limestone, or greenstone, must be set down at the same place, and, to save room, a system of marks for the different rocks may be conveniently used. When a sufficient area of ground has been thus traversed, the student may find, say a row of arrows on his map all pointing due west, and indicating a set of quarries about a quarter of a mile distant from one another, the rock in each of them dipping to the west. If there be at the one end a limestone containing certain fossils, and at the other end a stratum exactly similar, containing the same fossils, while the quarries between display the same rock, he will infer, of course, that the whole is one limestone, and will accordingly draw a line from the last quarry on the north to the last on the south, connecting them all together. If the bed dips steeply down, the line will be narrower,--if but slightly inclined, it will be broader; the breadth of such a line (which may be coloured to taste) always varying with the thickness of the stratum and the angle which it makes with the horizon. In a district where faults and curvatures along with trap-rocks abound, the mapping becomes more complex, but the principle remains the same--a curved stratum on the ground making a similarly curved band on the map, and a fault or dislocation of a set of beds producing, in the same way, a corresponding break in the lines traced. In short, a geological map should be as far as possible a transcript of the surface rocks of a country. The beginner should avoid, however, attempting too much; it will be enough for him at first to have mastered the leading features of the geology of his district; the details cannot be shown save on a map of a large scale, and are better transferred to his note-book. The use of such mapping is to enable us to gain a correct knowledge of the geological structure of a country, and of the relation of rocks to each other as regards age, origin, &c. Bacon tells us that "writing makes an exact man;" we may say with equal truth that mapping makes an exact geologist. It is sometimes easy enough to obtain a notion of the general character of a district by taking a few rambles across it; but we can never know it thoroughly until we have mapped it. And this is done not as mere dry routine, or by a series of hard uninteresting rules. In reading off the geological structure of a country, we ascertain its history during many thousand ages long prior to that of man. We become, as it were, interpreters of hieroglyphics, and historians of long-perished dynasties.

Those who have had experience of field-geology, know how vain it is to attempt to compress into a page or two the results of years, and that a few vague general directions are about the utmost that can be attempted. The practice of the science cannot be taught in books, far less in prefaces, neither can it be learned from them. And so I once more repeat the advice: Get away to the fields. Seek to decipher the geological records for yourself, and look with your own eyes into the long series of ages whose annals lie inscribed among the rocks. If you can secure the co-operation of a few companions, so much the better. Half-a-dozen hammers zealously at work in a richly fossiliferous stratum will soon pile up a tolerable collection of its treasures. But whether singly or in company, use your eyes and your hammer, and even though in the end you should never become a geologist, you will in the meantime gain health and vigour, and a clearness of observation, that will stand you in good stead through life.

CONTENTS.

CHAPTER I.

PAGE

Scene near Colinton in midsummer--A grey travelled Boulder--Its
aspect and contents--Its story of the past,

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CHAPTER II.

Exterior of the boulder--Travelled stones a difficult problem--Once
referred to the Deluge--Other theories--Novelty of the true
solution--Icebergs formed in three ways--Progress and scenery
of an iceberg--Its effects--Size of icebergs--Boulder clay
had a glacial origin--This explanation confirmed by fossil
shells--Laws of the distribution of life--Deductions,

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CHAPTER III.

How the boulder came to be one--"Crag and tail"--Scenery of
central Scotland: Edinburgh--"Crag and tail" formerly
associated in its origin with the boulder-clay--This
explanation erroneous--Denudation an old process--Its
results--Illustration from the Mid-Lothian coal-field--The
three Ross-shire hills--The Hebrides relics of an
ancient land--Scenery of the western coast--Effects of
the breakers--Denudation of the Secondary strata of the
Hebrides--Preservative influence of trap-rocks--Lost
species of the Hebrides--Illustration--Origin of the
general denudation of the country--Illustrative action
of streams--Denudation a very slow process--Many old
land-surfaces may have been effaced--Varied aspect of the
British Islands during a period of submergence--Illustration,

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CHAPTER IV.

Interior of the boulder--Wide intervals of
Geology--Illustration--Long interval between the
formation of the boulder as part of a sand-bed,
and its striation by glacial action--Sketch of the
intervening ages--The boulder a Lower Carboniferous
rock--Cycles of the astronomer and the geologist
contrasted--Illustration--Plants shown by the boulder once
grew green on land--Traces of that ancient land Its seas,
shores, forests, and lakes, all productive of material
aids to our comfort and power--Plants of the Carboniferous
era--Ferns--Tree-ferns--Calamites--Asterophyllites--
Lepidodendron--Lepidostrobus--Stigmaria--Scene in a ruined
palace--Sigillaria--Coniferæ, Cycadeæ--Antholites, the oldest
known flower--Grade of the Carboniferous flora--Its resemblance
to that of New Zealand,

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CHAPTER V.

Scenery of the carboniferous forests--Contrast in the
appearance of coal districts at the present day--Abundance
of animal life in the Carboniferous era--Advantages
of palæontology over fossil-botany--Carboniferous
fauna--Actiniæ--Cup-corals--Architecture of the present
day might be improved by study of the architecture of the
Carboniferous period--Mode of propagation of corals--A
forenoon on the beach--Various stages in the decomposition of
shells--Sea-mat--Bryozoa--Fenestella--Retepora--Stone-lilies--
Popular superstitions--Structure of the stone-lilies--Aspect
of the sea-bottom on which the stone-lilies
flourished--Sea-urchins--Crustacea, their high
antiquity--Cyprides--Architecture of the Crustacea and
mollusca contrasted--King-crabs,

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CHAPTER VI.

Carboniferous fauna continued--George Herbert's ode on
"Man"--His idea of creation--What nature teaches on
this subject--Molluscous animals--Range of species in
time proportionate to their distribution in space--Two
principles of renovation and decay exhibited alike in the
physical world and the world of life--Their effects--The
mollusca--Abundantly represented in the carboniferous
rocks--Pteropods--Brachiopods--Productus--Its alliance with
Spirifer--Spirifer--Terebratula--Lamellibranchs--Gastropods--
Land-snail of Nova Scotia--Cephalopods--Structure of
orthoceras--Habits of living nautilus,

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