RIMERS, 
 
 H 
 
 UXLEY- 
 
 R 
 
 Y 
 
 A. GEIKIE.
 
 UNIVERSITY OF CALIFORNIA 
 AT LOS ANGELES 
 
 GIFT OF 
 
 Pacific .'lectric Co,
 
 LOCKYER'S ASTRONOMY. 
 
 ELEMENTS OF ASTRONOMY: 
 
 Accompanied with numerous Illustrations, a Colored Repre- 
 sentation of the Solar, Stellar, and Nebular Spectra, 
 and Celestial Charts ot the Northern 
 and' the Southern Hemisphere. 
 
 By J. NORMAN LOCKYER. 
 
 American edition, revised and specially adapted to the Schools 
 of the United States. 
 
 Lzmo. -p.?. pages. Price, $1.50. 
 
 The volume is as practical as possible. To aid the student 
 in identifying the stars and constellations, the fine Celestial 
 Charts of Arago, which answer all the purposes of a costly Atlas 
 of the Heavens, are appended to the work this being the only 
 text-book, as far as the Publishers are aware, that possesses this 
 great advantage. Directions are given for finding the most in- 
 teresting objects in the heavens at certain hours on different 
 evenings throughout the year. Every device is used to make 
 the study interesting; and the Publishers feel assured that 
 teachers who once try this book will be unwilling to exchange 
 it for any other. 
 
 D. APPLETON & CO., PUBLISHERS, 
 
 540 & 5 ; i_ BROAD WAY. NEW YORK. 
 
 The RALPH D. REED LIBRARY 
 
 i.NT OF GEOLOGY 
 
 VERITY of CALIFORNIA 
 
 LOS ANGELES, CALIF.
 
 SCIENCE PRIMERS, edited by 
 
 PROFESSORS HUXLEY, RoscoE, and 
 BALFOUR STEWART. 
 
 V. 
 GEOLOGY. 
 
 REED 

 
 Srimte 
 
 GEOLOGY. 
 
 ARCHIBALD GEIKIE, LL.D., F.R.S., 
 
 Director of the Geological Survey of Scotland, and Murchison-Professof 
 of Geology and Mineralogy in the University oj Edinburgh. 
 
 WITH ILLUSTRATIONS. 
 
 NEW YORK: 
 D. APPLETON AND COMPANY, 
 
 549 & 551 BROADWAY. 
 18V9.
 
 CONTENTS. 
 
 ART. PAGE 
 
 INTRODJCTORY i 14 i 
 
 DIFFERENT KINDS OF STONES . . . ' . 15 31 6 
 
 WHAT STONES HAVE TO TELL us ... 3242 14 
 SEDIMENTARY ROCKS : 
 
 I. What Sediment is 43 56 19 
 
 ii. How Gravel, Sand, and Mud are 
 
 made . . . 57 76 23 
 
 in. How Gravel, Sand, and Mud be- 
 come Sedimentary Rocks ... 77 105 32 
 
 IV. How the Remains of Plants and 
 Animals come to be found in 
 Sedimentary Rocks 106117 44 
 
 v. A Quarry and its Lessons . . . . 118131 50 
 
 ORGANIC ROCKS, OR ROCKS FORMED OF 
 THE REMAINS OF PLANTS AND ANI- 
 MALS : 
 
 i. Rocks formed of the Remains of 
 
 Plants 132 152 56 
 
 ii. Rocks formed of the Remains of 
 
 Animals 153162 66 
 
 311989
 
 CONTENTS. 
 
 IGNEOUS ROCKS: 
 
 I. What Igneous Rocks are .... 163 175 74 
 
 II. Where, Igneous Rocks come from . 176 187 83 
 
 THE CRUST OF THE EARTH: 
 
 I. Proofs that parts of the Crust have 
 
 been pushed up 188 206 91 
 
 II. Proofs that parts of the Crust have 
 
 sunk down 207 217 loo 
 
 in. Proofs that the Rocks of the Earth's 
 Crust have been tilted, crumpled, 
 
 and broken 218 225 106 
 
 IV. The Origin of Mountains .... 227 242 1 1 2 
 v. How the Rocks of the Crust tell the 
 
 History of the Earth .... 243 254 120 
 
 CONCLUSION . . 255 258 127
 
 SCIENCE PRIMERS. 
 
 GEOLOGY. 
 
 INTRODUCTORY. 
 
 i. AN ordinary dwelling-house, such as those in 
 which most of us live, is built of various materials, and 
 one of these is always stone . In the walls, the hearths, 
 the chimney-pieces, and the roofs, stone is used. But 
 in each of these cases the kind of stone usually differs 
 from that employed in the rest of the building. Thus 
 the walls may be made of freestone, or limestone, or 
 brick, the hearths of flagstone, the roofs of slate or 
 tiles, the chimney-pieces of marble, while still another 
 sort of stone called coal is burnt in the fireplaces. 
 Go out into the streets and you find a still greater 
 diversity. The causeway-stones are of one kind, 
 those of the foot-pavement of another. Many dif- 
 ferent ornamental varieties are made use of in the 
 shops and buildings. So that merely by looking at 
 houses and streets you may readily perceive that 
 there are many different kinds of stone.
 
 2 SCIENCE PRIMERS. [INTRODUCTORY. 
 
 2. If you examine them a little more narrowly you 
 will see that they receive various treatment before they 
 become part of a building. The stones of the walls 
 have been chipped and dressed with chisels and 
 hammers ; the marble of the chimney-pieces has been 
 smoothed and polished ; the slates have been split 
 into thin plates. But some of these building mate- 
 rials have undergone much greater changes. The 
 bricks, for instance, were originally soft clay which 
 has been hardened by being baked in ovens. The 
 mortar by which the stones or bricks of the walls 
 are held together has been obtained by burning 
 limestone in kilns. The iron used in the house was 
 first of all in the state of a dull red or brown stone, 
 which had to be roasted and melted before the clear 
 bright metal came out of it. 
 
 3. But although these various stones differ so much 
 from each other, they agree in one point they 
 come from underneath the surface of the 
 ground. If you could trace back each of them to 
 the place from which it came you would find that the 
 freestone and limestone were taken out of quarries, 
 perhaps not very far away, that the slates were cut 
 out of the side of some hill, probably in Wales, that 
 the marble was quarried out of some distant moun- 
 tain, possibly in Italy, that the coal was dug out of 
 mines, sunk deep into the earth in some part of Bri- 
 tain, and that the bricks were made from clay dug out 
 of pits on some low ground in your neighbourhood. 
 
 4. In this country the greater part of the surface 
 has a green grassy covering even over the sides of 
 the hills cornfields, meadows, woods, and orchards 
 spread over it, concealing what lies beneath them, as a
 
 INTRODUCTORY.] GEOLOGY. 
 
 carpet conceals a floor. But this mantle of vegetation 
 with the soil on which it grows is only a thin coating. 
 You can easily dig through the grass and soil, or, better 
 still, you can watch their removal in quarries, pits, or 
 excavations of any kind. You find them to form a 
 mere outer layer only a few feet thick at the most. 
 Underneath them there always lies some kind of 
 stone. So that just as in pulling up the carpet of a 
 room you lay bare a wooden floor, so in peeling off 
 the outer skin of vegetation and soil from any part 
 of the land you expose a stone floor. 
 
 5. On this floor of stone we are walking every day 
 of our lives. It stretches all over the globe, forming 
 the bottom of the sea and the surface of the land. 
 Unlike the floors of our houses it is very uneven, as 
 you well know. In some places it spreads out into 
 wide flat plains, elsewhere it shoots up into high and 
 rugged mountains. 
 
 6. Again, this vast world-wide floor differs from our 
 little wooden floors in the wonderful variety of its 
 materials. You see only a small part of this variety 
 in the various stones we use in building. There 
 is an almost endless number of other stones. A 
 builder is content if he can get his floors made of 
 one uniform sort of wood which will last. But the 
 great stone floor on which we are living has no 
 such uniformity. Its varied materials are grouped 
 together in the most irregular and changing manner, 
 insomuch that if you made a map of them all, it 
 would be like the intricate pattern of some costly 
 carpet. 
 
 7. It is this stone floor of which I wish to speak to 
 you in the following Lessons what it is made of and
 
 4 SCIENCE PRIMERS. [INTRODUCTORY. 
 
 how its different parts were put together. At first 
 sight, perhaps, it may seem to you that there can 
 be nothing very interesting or attractive about such a 
 subject. Let me show you how it is related to you 
 by the following illustration. 
 
 8. Take a map of the British Islands and draw 
 across it two pencilled lines. Let one of these lines 
 begin at Liverpool and stretch across England, touch- 
 ing Stafford, Birmingham, and Cambridge, to the sea 
 at Harwich. Let the other run across the breadth of 
 Scotland from the island of Skye to Montrose.* 
 
 9. Suppose that two foreigners who had never been 
 in this country were to land on the west coast, and after 
 crossing the island, each along one of the lines you 
 have drawn, were afterwards to meet again on the 
 Continent and compare notes as to what they had 
 seen. The traveller who journeyed along the line 
 from Liverpool to Harwich might report in some 
 such words as these : " I am astonished at the flat- 
 ness of Britain. I went across the whole breadth of 
 the island and did not see a single undulation of 
 the ground worthy of the name of a hill. Most of 
 the land is wonderfully fertile, being in one part 
 covered with corn-fields, in another with orchards or 
 woods, while wide tracts are given up to pasture. 
 The houses are built of brick. I saw some large 
 cities crowded with people and alive with all kinds of 
 industry. I noticed, too, that in some parts of the 
 country a great deal of the wealth of the inhabitants 
 came from underground. In Cheshire they bring up 
 large quantities of salt from mines. In Staffordshire 
 
 * A similar illustration has been used by Buckland, in his 
 Bridgewater Treatise.
 
 INTRODUCTORY.] GEOLOGY. 
 
 they extract coal and iron from numerous deep pits. 
 But on the whole Britain seems to me given up 
 chiefly to the growing of corn and the feeding of 
 cattle." 
 
 10. The other traveller would have a very different 
 story to tell. " I cannot understand," he might say, 
 " how you can talk of Britain as in any sense a flat 
 country. I too crossed the island from sea to sea, 
 landing on the coast of Inverness-shire and sailing 
 from the port of Montrose. But I could see very 
 little low or level land the whole way. It is one inter- 
 minable succession of rough high mountains and 
 deep rocky valleys. I could see no towns, hardly 
 any villages, until I came to the eastern coast. The 
 people live in houses of stone ; I could not see a 
 single brick anywhere. They have no coals except 
 what are brought from a distance, and most of the 
 poorer people cut the peat on the hills and use it for 
 fuel. I saw no mines in my journey, and no manu- 
 factures of any kind. The population is but scanty, 
 and seems to be occupied chiefly with sheep-farming. 
 If I might judge of the whole of Britain from what 
 I have seen with my own eyes I would describe it as 
 a rough, mountainous, barren island, without com- 
 merce or industry, and fit only for pasture-land or 
 grouse-shooting, and here and there for tillage." 
 
 ii. Now each of these supposed travellers would 
 have given a true enough account of this country so 
 far as his own personal experience of it went. And 
 yet both of them would have been quite wrong in 
 supposing that what he had seen to be true of one 
 part of the country was true in like manner of the 
 whole.
 
 6 SCIENCE PRIMERS. [DIFFERENT 
 
 12. But why is it that there should be this great 
 difference between different portions of Britain ? 
 What makes one region mountainous, another level, 
 one fertile, another barren, one crowded with people 
 and the scene of all manner of industry, another 
 thinly peopled and given up to the rearing of sheep 
 and the shooting of game ? 
 
 13. These great differences of the surface 
 of the country depend upon differences be- 
 tween the stones or rocks. 
 
 14. Now you can easily understand that if so much 
 of the character of a country and of its inhabitants 
 depends upon the nature of the stones underneath, 
 it is very desirable that we should know something 
 about these stones, how they came to be formed, what 
 they consist of, and how it is that they should form 
 plains or low grounds in one place, and single hills 
 or lofty mountains in another. This kind of know- 
 ledge belongs to the science of Geology. 
 
 DIFFERENT KINDS OF STONES. 
 
 15. If I were to ask you how many different kinds 
 of books you have seen in the course of your lifetime, 
 you would perhaps say that it was quite impossible to 
 count them. You have seen many that were ne\v, 
 some that were old ; big books and little books ; some 
 with boards, others merely wrapped up in paper ; 
 some beautifully bound in cloth of red, green, blue, 
 or other colours, others cased in leather and covered 
 with rich gilding ; some printed in large, others in 
 small letters ; some plentifully supplied with pictures,
 
 KINDS OF STONES.] GEOLOGY. 
 
 others without any at all. In short, you might go on 
 for a long time trying to count up all these differ- 
 ences among the books which you have met with. 
 But now if you think a moment you will see that, after 
 all, these are only outside differences. The really 
 important part of the book is not the binding, or the 
 paper, or the printing, but the words which the book 
 has to make known to you. You might print these 
 words in very small type and make them up into a little 
 book, or in very large and widely spaced type and 
 make a big book ; you might put in pictures or leave 
 them out ; you might bind the book in cloth or in 
 leather, or give it no binding at all ; but still it would 
 be in reality the same book all the time. 
 
 1 6. When you pass, then, from such mere unimpor- 
 tant external resemblances or differences to what the 
 books properly are in themselves, you soon discover 
 that after all there are not so many kinds as you had 
 imagined. You can pick them out and sort them into 
 groups according to the subjects of which they treat. 
 Thus in your little libraries you find that some are 
 Books of Grammar, others Books of History, others 
 Books of Geography, with Books of Poetry, Books 
 of Travels, Books of Tales, and so on. Under each 
 of these names you could put, if you had them, hun- 
 dreds of books, resembling each other in treating 
 about the same things, whether they were old books 
 or new, large or small, bound or unbound. 
 
 17. In arranging your books in this way, not accord- 
 ing to their mere superficial accidental resemblances, 
 but according to the subjects which they treat of in 
 common, that is, their real resemblances, you would 
 follow what is called a Principle of Ciassifica- 
 
 2
 
 8 SCIENCE PRIMERS. [DIFFERENT 
 
 tion. It would not matter how many different books 
 came into your hands ; they might be written, too, 
 in English, French, German, Latin, Greek, or in any 
 language. Still, following your principle of classifica- 
 tion, you would be able to arrange them all in their 
 proper places, all the books on the same subject 
 being put together, so that at any moment you could 
 lay your hands on any particular book which might be 
 wanted. 
 
 1 8. Suppose that instead of books you are asked to 
 arrange stones according to their several kinds. You 
 think over the names of all the different stones you 
 know and try to recollect their characters. Perhaps 
 you begin by arranging them according to colour, as 
 for instance, Black Stones, such as Coal ; White Stones, 
 such as Chalk. But in a little time you find that the 
 same stone, marble for instance, is sometimes black 
 and sometimes white. Plainly, therefore, colour will 
 not do for your principle of classification among 
 stones, any more than it would do for books. Then 
 you might go on to see how a grouping into Hard 
 Stones and Soft Stones would do. But as soon as 
 you begin this kind of classification, you find that you 
 need to put side by side stones which are so utterly 
 unlike each other that you feel sure that mere hard- 
 ness or softness is one of those accidental or outside 
 characters, like the paper or printing of a book. 
 
 19. You must find out then what are the real and 
 essential characters of stones. Now how did you do 
 this in the case of books ? You examined their 
 contents and placed those together which on reading 
 them you found to be devoted to the same subject. 
 You must follow the same course with stones.
 
 KINDS OF STONES.] GEOLOGY. 
 
 20. But you may ask, " How are we to read the 
 contents of stones ? Surely this must be very difficult, 
 for is there not an infinitely greater number of kinds 
 of stones than of books ? " By no means. You will 
 soon learn that it is not so difficult as you might sup- 
 pose to read the contents of stones, and that in reality 
 the chief groups of stones are very much fewer in 
 number than the chief groups of books. Let us see. 
 
 21. Here are three pieces of stone : 
 
 1. A piece of Sandstone. 
 
 2. A piece of Granite. 
 
 3. A piece of Chalk. 
 
 2 2. You are quite familiar with each of these kinds 
 of stone. Sandstone is a common material for walls, 
 lintels, hearths, and flagstones. Granite may now be 
 
 FIG. i. Piece of Sandstone. 
 
 frequently seen in polished columns and slabs in 
 public buildings, shops, and in tombstones ; and the 
 streets in many of our large cities and towns are now 
 paved with it. Common white Chalk is well known 
 to everybody. 
 
 23. Take the piece of sandstone in your hands and
 
 io SCIENCE PRIMERS. [DIFFERENT 
 
 examine it carefully, using even a magnifying glass if 
 the grains are minute. Then write down each of the 
 characters you observe one after another. You will 
 of course pay little heed to the colour, for sandstones, 
 like books, may be red or white, green or yellow, or 
 indeed of almost any colour. Nor will you give 
 much weight to the hardness or softness as an essen- 
 tial character, for you may find even in a small piece 
 of the stone that one part is quite hard while a neigh- 
 bouring place is soft and crumbling. 
 
 24. If your piece of sandstone has been well chosen 
 for you, you will be able to write down the following 
 characters : 
 
 (i.) The stone is made up of small grains. 
 
 (2.) The grains are all more or less rounded or worn. 
 
 (3.) By scraping the surface of the stone these 
 rounded grains can be separated from the stone, and 
 when they lie in this loose state they are seen to be 
 mere grains of sand. 
 
 (4.) More careful examination of the stone shows 
 that the grains tend to lie in lines, and that these 
 lines run in a general way parallel with each other. 
 
 (5.) The grains diifer from each other in size and in 
 the material of which they are made. Most of them 
 consist of a very hard white or colourless substance like 
 glass, some are perhaps small spangles of a material 
 which glistens like silver, others are softer and of 
 various colours. They lie touching each other in 
 some sandstones ; in others they are separated by a 
 hard kind of cement which binds them all into a 
 solid stone. It is this cement which usually colours 
 the sandstone, since it is often red or yellow, and 
 sometimes green, brown, purple, and even black.
 
 KINDS OF STONES.] GEOLOGY. 
 
 25. Summing up these characters in a short defini- 
 tion, you might describe your sandstone as a stone 
 composed of worn, rounded grains of various 
 other stones arranged in layers. 
 
 26. Proceed now in the same way with the piece 
 of Granite. You find at once a very different set of 
 appearances, but after a little time you will be able to 
 make out and to write down the following : 
 
 FIG. 2. Piece of Gi 
 
 (i.) The stone contains no rounded grains. 
 
 (2.) It is composed of three different substances, 
 each of which has a peculiar crystalline form (see 
 Chemistry Primer, Art. 23). Thus, one of these, 
 called Felspar, lies in long smooth-faced, sharply 
 defined crystals of a pale flesh colour, or dull white, 
 which you can with some difficulty scratch with the 
 point of a knife. These are the long white sharp- 
 edged objects shown in the drawing (Fig 2). Another, 
 termed Mica, lies in bright glistening plates which 
 you can easily scratch and split up into thin trans- 
 parent leaves. If you compare these shining plates 
 with the little silvery spangles in the sandstone you 
 will see that they are the same material. The third, 
 named Quartz, is a very hard, clear, glassy substance
 
 12 SCIENCE PRIMERS. [DIFFERENT 
 
 on which your knife makes no impression, but which 
 you may recognize as the same material out of which 
 most of the grains of the sandstone are made. 
 
 (3.) The crystals in granite do not occur in any 
 definite order, but are scattered at random through 
 the whole of the stone. 
 
 27. Here are characters strikingly different from 
 those of the sandstone. You might make out of 
 them such a short definition as this Granite is a 
 stone composed of distinct crystals not laid 
 down in layers but irregularly interlaced with 
 each other. 
 
 28. Lastly go through the same process of examina- 
 tion with your piece of Chalk. At first sight this stone 
 seems to have no distinct characters at all. It is a 
 soft, white, crumbling substance, soils your fingers 
 when you touch it, and seems neither to have grains 
 like the sandstone nor crystals like the granite. You 
 will need to use a magnifying glass, or even perhaps a 
 microscope, to see what the real nature of chalk is. 
 Take a fine brush and nib off a little chalk into a 
 glass of clear water ; then shake the water gently and 
 let it stand for a while until you see a layer of sedi- 
 ment on the bottom. Pour off the water and place a 
 little of this sediment upon a piece of glass, and look 
 at it under the microscope or magnifying-glass. You 
 will find it to have strongly marked characters, which 
 might b set down thus : 
 
 (i.) The stone, though it seems to the eye much 
 more uniform in its texture than either sandstone or 
 granite, is made up of particles resembling each other 
 in colour and composition, but presenting a variety 
 of forms.
 
 KINDS OF STONES.] GEOLOGY. 13 
 
 (2.) It consists of minute shells, pieces of coral, 
 fragments of sponges, and white particles, which are 
 evidently the broken-down remains of shells. In 
 Fig. 3 you see some of these chalk grains as they 
 appear when you place them under a microscope which 
 
 FIG. 3. Some of the Grains of a piece of Chalk. 
 
 magnifies them fifty times. Larger and well-preserved 
 shells, sea-urchins, and remains of other sea-creatures 
 occur imbedded in the chalk. (See Fig. 23.) 
 
 29. As a brief description of chalk you might say 
 that it is a stone formed out of the remains 
 of once-living animals. 
 
 30. You should repeat this kind of examination 
 again and again until you get quite familiar with the 
 characters which have been written down here. And 
 you will see why it is important for you to do so when 
 you come afterwards to find out that these three 
 stones are examples of the three great groups into 
 which most of the rocks of the world may be ar- 
 ranged. So that when you master the composition of 
 a piece of sandstone, or chalk, or granite, and learn 
 how each stone was formed, you not only do that, but 
 lay a foundation of knowledge which will enable you 
 to understand how by far the greater part of the 
 stones of our mountains, valleys, and sea-shores came 
 into existence.
 
 14 SCIENCE PRIMERS. [WHAT STONES 
 
 31. In spite then of the apparently infinite diversity 
 of the stones of which the globe is built up, you see 
 that by a little study they may be grouped into very 
 few classes. You have to follow a simple prin- 
 ciple of classification, and each stone you may meet 
 with falls naturally into its own proper group. You 
 do not concern yourselves much with mere outer 
 shape and hue, but try to find out what the stone is 
 made of, and ask whether it should be placed in 
 the Sandstone group, or in the Granite group, or in 
 the Chalk group. 
 
 WHAT STONES HAVE TO TELL US. 
 
 32. But if you went no further than merely being 
 able to arrange stones under their proper divisions it 
 would be hardly worth your while to study them at 
 all. You would be like people who could put a 
 library into such excellent order that every volume 
 should stand on its proper shelf and compartment, 
 ready for easy reference at any moment, but who 
 should rest content with this mere systematic arrange- 
 ment and never open any of the books to make 
 themselves acquainted with the contents as well as 
 with the boards. The classification of stones, or 
 flowers, or birds, or fishes, or any other objects in 
 nature, is in itself of no more service than such an 
 arranging of a library, unless you use it in helping 
 you to understand better what is the nature of the 
 things you classify and how they are related to each 
 other.
 
 TELL us.] GEOLOGY. 15 
 
 33. This habit of classifying what we discover lies 
 at the base of all true science. Without it we could 
 not make progress ; we should always be in a maze, 
 and would never know what to make of each new 
 thing we might find out. We should be like people 
 turned into a great hall and required to educate 
 themselves there, with the floors and galleries strewed 
 all over with piles of books in all languages and on 
 every subject, but utterly and hopelessly in confu- 
 sion. 
 
 34. Let us now try what this habit can do for us 
 among the seemingly endless variety of stones with 
 which the world is stored. 
 
 35. We take again our three pieces of stone sand- 
 stone, chalk, and granite and compare other stones 
 with them. We get out of town to the nearest pit 
 or quarry or ravine, to any opening in fact, either 
 natural or artificial, which will enable us to see down 
 beneath the grass and the soil of the surface. In 
 one place we may find a clay-pit, in another a sand- 
 stone-quarry, in another a railway cutting through 
 chalk or limestone, in another a deep ravine in 
 hard rocks with a stream, flowing at its bottom. It 
 does not matter for our present purpose what the 
 nature of the opening be, provided it shows us what 
 lies beneath the soil. In all such places we meet 
 with stone of some kind, or of many different kinds. 
 By a little practice we learn that these various sorts 
 of stones may be usually arranged under one or 
 other of the three divisions of which mention 
 was made in last Lesson. For example, a large 
 number of stones will be found answering to the 
 general description which you found to be true of
 
 1 6 SCIENCE PRIMERS. [WHAT STONES 
 
 Sandstone. These will of course be placed to- 
 gether with our piece of sandstone. Another con- 
 siderable quantity of stones will be met with made 
 up wholly or almost wholly of the remains of plants 
 or of animals. These we arrange in the same 
 division with our piece of chalk. Lastly, a good 
 many stones may be met with built up of crystals of 
 different kinds, and these, for the present, we class 
 together with our piece of granite. 
 
 36. In this way you would advance from the mere 
 pieces of stone which you can hold in your hand, up to 
 the masses of stone lying under a whole parish or a 
 county or even the entire kingdom. You would 
 learn that a long range of hills, stretching completely 
 across England from the coasts of Dorsetshire to 
 those of Yorkshire, is formed of chalk, and that 
 other parts of the country lie upon kinds of stone in 
 many respects resembling chalk. You would soon 
 discover that a great part of Britain is made of stone 
 like your piece of sandstone, for example the hills 
 and dales of most of Wales, Lancashire, and the 
 south of Scotland. And if you climbed up to the 
 tops of some of our highest mountains, such as Ben 
 Nevis, you would see them to be built up of solid 
 masses of granite, quite similar to your little speci- 
 men, or of other sorts of stones belonging to the 
 same division as granite. 
 
 37. You would begin to perceive that the different 
 kinds of stone are not scattered at random over the 
 country, but have each their own places, with their 
 own kinds of hills or valleys. 
 
 38. But a little further attention to these matters 
 would bring before you a far more wonderful thing. In
 
 TELL us.] GEOLOGY. 17 
 
 questioning the stones about how they were made, 
 you would learn by degrees that each of them can 
 give you a more or less distinct answer. In fact they 
 may be compared to books each of which has a little 
 piece of history to tell. 
 
 39. You do not grudge to read books of history. 
 You find much interest in following the changes which 
 happened in old times in your country, how battles 
 were fought and laws were made, and old customs 
 gradually passed away. You have no doubt found 
 that the more you know about these events of former 
 times the better do you understand how the laws 
 and customs of the present day came to be what 
 they are. 
 
 40. Well, the solid earth under your feet has a history 
 as well as the people who have lived on its surface. 
 Take Britain for example. You will learn that once 
 a great part of this country as well as of Europe and 
 North America was buried under ice like Greenland. 
 Earlier still it had jungles of palms and other tropical 
 plants ; yet further back it lay beneath a wide deep 
 ocean; and beyond that time can be traced many 
 still more remote periods, when it was forest-covered 
 
 . land or wide marshy plains, or again buried under the 
 great sea. Step by step you may follow this strange 
 history backwards, and with as much certainty as 
 you trace the doings of Julius Caesar, or William the 
 Conqueror. 
 
 41. Now the records of all these old revolutions of 
 the earth's surface are contained in the stones beneath 
 your feet. In learning what these stones are, how 
 they were made and how they came to be as you now 
 see them, you are really unravelling a part of the
 
 1 8 SCIENCE PRIMERS. [SEDIMENTARY 
 
 history of the earth. Even the commonest bit of 
 stone has its own part of the story to tell you. If 
 you are sure that it was well worth your while to go 
 through the trouble of learning to read for the sake 
 of all the knowledge which you can gain from books, 
 you will discover, too, that you will be fully repaid 
 for any pains you take in acquiring a knowledge of 
 how to read the meaning of the stones. This earth- 
 history is written in clear and legible language which 
 with a little patience you will easily master. And 
 when you have once acquired it you will not be content 
 with what you can learn from books. It will then be 
 a constant and increasing source of delight to you to 
 get away to the quarries and brooks, and sea-shores 
 and hill-sides, to any place in short where the rocks 
 stick out to the surface, that you may question them 
 and learn what they have to tell about the ancient 
 revolutions of the earth. 
 
 42. The object of this little book is to set you in the 
 way of putting such questions to every stone and 
 rock you may meet with. We shall begin with the 
 very simplest lessons and appeal at every step to 
 things which are already familiar to you. In this way 
 you will feel how sure and steady your progress is, and 
 in the end you will be able to carry on the question- 
 ing yourselves without much help from book or friend. 
 Hy watching what takes place from day to day, as in 
 a brook or by the shore of the sea, you will understand 
 the events which have happened in long past times, 
 and be able to decipher among the rocks that won- 
 derful earth-history which it is the business of Geology 
 to study and record.
 
 ROCKS.] GEOLOGY. 19 
 
 SEDIMENTARY ROCKS. 
 
 L What Sediment is. 
 
 43. We have now advanced some way in the attempt 
 to understand what stones are. We have learned 
 that they are full of a history of old revolutions of 
 the earth, and that we may find out what this history 
 is, but that in order to make any progress we must 
 arrange into distinct groups the various stones which 
 we mean to study. We have found, too, that they 
 may be divided into three great groups or classes, 
 each having a set of well-marked characters. 
 
 44. To each of these groups names must be given. 
 We might call them the Sandstone group, the Chalk 
 group, and the Granite group. But it happens that 
 other names have been already in use, which will be 
 more convenient. Accordingly we shall refer all 
 stones having characters like those of sandstone to 
 
 the Sedimentary Rocks ; those formed of the 
 remains of plants or animals, as chalk is, to the 
 Organic Rocks ; and those having a crystalline 
 character, like our granite group, to the Igneous 
 Rocks. The meaning of these names will be seen 
 as we proceed. 
 
 45. The word " rock" is applied to any kind of 
 natural stone, whatever may be its hardness or soft- 
 ness. In this sense, sand, mud, clay, peat, and coal 
 are rocks, as much as sandstone, limestone, or granite. 
 
 46. Now it is evident at the very outset that each of 
 these groups, since it is so well defined from the others, 
 must have a history peculiar to itself, that is, its 
 various kinds of stone or rock must have been formed 
 
 3
 
 20 SCIENCE PRIMERS. [SEDIMENTARY 
 
 differently from those of the other groups, in order to 
 be so, unlike them. Let us then take up each of the 
 groups in succession, beginning with the Sedimentary 
 Rocks, that is, with those which have a more or less 
 close resemblance to sandstone. 
 
 47. But first we must understand the meaning of 
 this word, sedimentary, and why it is applied. 
 We take a glass of water and put some gravel into 
 it The gravel at once sinks to the bottom and re- 
 mains there even though we stir the water briskly. 
 We close the mouth of the glass and shake it up and 
 down so as to mix the water and gravel thoroughly 
 together ; but as soon as we cease to do so and place 
 the glass on the table again, we see that the gravel 
 has sunk and formed a layer at the bottom. This 
 layer is a sediment of gravel. 
 
 48. Instead of gravel we put sand into the water 
 and shake them up as before. We mix them so 
 completely that for a moment or two after we cease 
 the water seems quite dirty. But in a few minutes the 
 sand will have all sunk to the bottom as a layer below 
 the water. This layer is a sediment of sand. 
 
 49. We take a little mud or clay, instead of either 
 the gravel or sand, and shake it up in the water until 
 the two are thoroughly mixed. When the glass is 
 replaced on the table this time the water continues 
 quite dirty. Even after some hours it remains still 
 discoloured, but we see a layer beginning to appear 
 at the bottom. If the glass is allowed to stand long 
 enough undisturbed that layer will go on growing 
 until the water has again become clear. In this case 
 the layer is a sediment of mud. 
 
 50. Sediment, therefore, is something which after
 
 ROCKS.] GEOLOGY. 
 
 having been suspended in, or moved along by, water 
 has settled down upon the bottom. The coarser 
 and heavier the sediment the quicker will it sink, 
 while when it is very fine it may remain in suspen- 
 sion in the water for a long time. 
 
 51. Sedimentary Rocks must thus be those which 
 have been formed out of sediments. And just as 
 sediments differ from each other in coarseness or 
 fineness, so will the sedimentary rocks formed out of 
 them. 
 
 52. Here are pieces of three sedimentary rocks : 
 (i.) A piece of Conglomerate or pudding- 
 stone (Fig. 4). 
 
 (2.) The piece of Sandstone you have already 
 
 looked at (Fig. i) ; and 
 (3.) A piece of Shale (Fig. 5). 
 
 53. Examine the first of these three specimens. 
 You find it to be made of rounded little stones, 
 firmly cemented together. Were these round stones 
 
 FIG. 4. -Piece of Conglomerate or Pudding-stone. 
 
 to be separated from each other, and gathered into a 
 loose heap, you would call it a heap of gravel. The 
 stone is evidently nothing more than a hardened
 
 22 SCIENCE PRIMERS. [SEDIMENTARY 
 
 gravel, such as you might pick up on the sea-shore, 
 or in the channel of a stream. It is sometimes called 
 pudding-stone, because the stones lie together some- 
 what like the fruit in a plum-pudding. 
 
 54. Take up the piece of sandstone again, and 
 make a further examination of it. Did you ever see 
 anything like the grains of which it is made up? 
 You reply that they are mere grains of sand such as 
 might be met with anywhere. And you are quite cor- 
 rect. The sandstone consists of nothing else but sand 
 firmly held together so as to form a stone. If you 
 went down to the sea-shore, or to the bed of a brook 
 or river, you could gather sand of very much the same 
 kind, and by hardening such sand into a compact 
 mass, you might make sandstone. 
 
 55. In the third specimen you cannot so easily make 
 out what the grains of the stone are, since their size 
 is so small. But take a knife and scrape a little of 
 
 FIG. 5. Piece of Shale. 
 
 the end of the stone and work it up with some drops 
 of water. You will make a kind of paste in this 
 way. Then put this paste into a tumbler of water 
 and stir it well round. Immediately the water gets 
 dirty-looking, and remains so even for some time after- 
 wards. But put the tumbler aside for some hours and
 
 ROCKS.] GEOLOGY. 23 
 
 you will find that the water becomes clear again ; that 
 what you put in as a dirty paste has sunk to the 
 Bottom of the glass as a layer of sediment, and that 
 it is simply mud. The shale, therefore, is nothing 
 more than a stone formed of fine muddy sediment, 
 just as the conglomerate is formed out of coarse 
 gravelly sediment. 
 
 56. Thus you see that the term Sedimentary Rocks 
 is a very expressive one, for it includes stones formed 
 of all kinds of sediment whether coarse or fine. 
 
 Look again at any one of our three specimens, and 
 you will understand that we have two things to find 
 out about them. First of all, how was the sediment 
 made out of which they have been formed ? and 
 secondly, how did the sediment come to be gathered 
 and hardened into solid stone ? 
 
 II. How Gravel, Sand, and Mud are made. 
 
 57. You have taken the first step in the study of 
 the Sedimentary Rocks, you now know that they are 
 made of sediment such as gravel, sand, and mud. 
 The next step must be to find out where this sedi- 
 ment came from and how it was formed. If you can 
 settle this matter you will evidently know a good deal 
 more about the history of these rocks. And here, as 
 in all such matters, you will find it well to ask your- 
 selves at the very outset : Is there anything going on 
 now-a-days which will explain what we are in search 
 of? By starting fresh from the observation of what 
 takes place at the present time, you will be far better 
 able to understand what has been done long ago. 
 How then are gravel, sand, and mud made at the 
 present day ?
 
 24 SCIENCE PRIMERS. [SEDIMENTARY 
 
 58. A little attention will show you that the dif- 
 ference between gravel and sand is only one of degree 
 of coarseness. In gravel the stones are large, in sand 
 they are mere grains. To make this clear, place a 
 little sand under a strong magnifying glass, which will 
 make the grains appear much larger than they really 
 are, so large, indeed, as to give them the look of 
 gravel-stones rather than grains of sand. You can 
 then see that each grain is a worn, rounded stone, 
 sometimes with little chips and hollows on its 
 sides, just like those on the sides of any pebble we 
 may pick out of a heap of gravel. The longer you 
 look at the sand in this way the more sure do you 
 become that, after all, sand and gravel are just 
 different states of the same thing, the one being 
 merely coarser than the other. 
 
 59. If you were to search on the shore of the sea, 
 or on the banks of a river, you could, without much 
 difficulty, prove in another way that sand and gravel 
 only differ from each other in the size of their grains. 
 You might gather handfuls of fine sand, then of sand 
 a little coarser in the grain, and so on by degrees 
 until the material became a true gravel, with rounded 
 pieces of stone of all sizes, from mere little pebbles 
 up to blocks as big as your head. How did all 
 these fragments, whether small or large, come to be 
 broken off and ground so round and smooth, and 
 heaped up where we now find them ? 
 
 60. Let us get away up among the hills, and watch 
 what goes on where the brooks first begin to flow. 
 Where the rocks are hard and tough, they rise out of 
 the hill-sides as prominent crags and cliffs, down 
 which the little streamlets dance from ledge to ledge
 
 GEOLOGY. 25 
 
 before they unite into larger streams in the bottoms of 
 the valleys. Now look at those crags. See how they 
 are split up and wasted by the rains and frosts. You 
 have learnt already something about how this is done 
 (Physical Geography Primer, Arts. 126 142). But 
 you have now to consider some of the results of the 
 waste. 
 
 6 1. Suppose, for the sake of distinctness, that we 
 single out one special crag where the rock is of some 
 bright colour, say red, and differs in that respect from 
 the rest of the crags round about it. It rises out 
 boldly from a steep hill- side, and looks down a long 
 slope to the little stream which in the distance seems a 
 thread of silver winding through the green meadows 
 far below us. Our crag has been sorely wasted in the 
 long course of time. The rains and frosts of many 
 centuries have carved its sides into deep clefts and 
 gullies (Physical Geography Primer, Art. 142). These, 
 when wet weather sets in, become each the channel 
 of a foaming torrent, which pours headlong down the 
 slope and sweeps away every loose bit of stone or 
 earth within its reach. 
 
 62. We climb cautiously along the face of the crag 
 to look into some of these frost-splintered, torrent-swept 
 gullies, and then we descend to the base. All the slope 
 below is strewn with pieces of the crag. Some of 
 these are huge blocks, but most of the material forms 
 
 ,a kind of mere rough rubbish, which slides down the 
 slope with us as we descend with long strides to the 
 bottom. 
 
 63. Each of the deep clefts which have been scooped 
 , out of the crag has a long slope of this kind of rubbish 
 
 lying below it. You cannot for a moment doubt that
 
 26 SCIENCE PRIMERS. [SEDIMENTARY 
 
 all this broken-up material on the slope actually 
 formed at one time part of the crag itself, that in fact 
 it is simply the material which has been removed by 
 the slow wasting away of the sides and bottoms of 
 the clefts, and that if you could gather it all up again 
 so as to put it back where it formerly stood you would 
 really fill the clefts up. 
 
 64. The slope leads us down to a little brook, the 
 bed of which is strewn with pieces from our crag. Now 
 let us descend the brook and look at its channel 
 carefully as we go. The red fragments from that 
 crag will be easily distinguishable from the other dull 
 grey stones, which have been detached from the rest 
 of the crags on either side. If you look narrowly at 
 the bits of stone which are strewed about upon the 
 slope you will notice that they are all more or less 
 angular in shape, that is to say, they have sharp edges. 
 But those in the brook are not quite so rough nor so 
 sharp-edged as those on the bare hill-side above. 
 Follow the brook down the valley for some way and 
 then take another look at the stones in the bed of the 
 stream. You do not now find so many big blocks of 
 the red stone, and those you do meet with are more 
 rounded and worn than they were near the crag. 
 They have grown smooth and polished, their edges 
 have been worn off, and many of them are well 
 rounded. Once more you make a further examina- 
 tion still lower down the valley, and here and there 
 where the stream has thrown up a bank of gravel, 
 you find that the pieces of our red crag have been so 
 well ground away that they now form part of an 
 ordinary water-worn gravel. 
 
 65. In the same way by descending the stream still
 
 ROCKS.] GEOLOGY. 27 
 
 further you could trace the gravel becoming finer and 
 passing at last into sand. And if you were to place 
 some of this sand under a magnifying glass you 
 would find it partly made up of more or less rounded 
 grains of the same red stone which you detected in 
 the gravel, and which you knew to have come from 
 our crag far up in the hills. 
 
 66. Now how is it that the stones get worn down 
 in this way ? Why should lying in the bottom of a 
 stream make them smaller ? 
 
 67. If you watch the stream only in fine weather, 
 when the water is low and the current feeble, you can 
 hardly judge as to the real power of the water. 
 Come back when heavy rains have filled every gully 
 in the hills with a foaming torrent, and when every 
 streamlet rushes headlong down its valley, filling its 
 bed to the brim and even rising high on either side. 
 You cannot now see the stones on the bottom of the 
 channel, but listen and you can hear them. That 
 sharp rattle which every now and then comes out of 
 the water is caused by the stones thumping against 
 each other, as they are hurried along by the rushing 
 water. They are kept grinding against each other as 
 in a mill. Of course, they must needs have their 
 edges worn off, and their sides smoothed, while at 
 the same time they smooth and polish the rocks of 
 the channel over which they are driven. 
 
 68. When the stones first fall or are swept from the 
 hill-side into the brook, they are, as you saw, mere 
 angular chips (Fig. 6). But by the time they have 
 travelled down the brook a little way, and have suffered 
 from the grinding of a few floods, they lose their 
 sharpness. The smoothing and polishing process goes
 
 28 
 
 SCIENCE PRIMERS. [SEDIMENTARY 
 
 on till they become more or less rounded, and at last 
 appear as well-worn gravel (Fig. 7). A rounded 
 stone will travel farther and faster than an angular 
 one, but in the end gets worn down into mere sand 
 (Fig. 8). 
 
 FIG. 6. Stones detached from a cliff" by- rains, frosts, &c., and launched into 
 a brook. 
 
 69. Thus we see that as the stones grow rounder 
 they at the same time become smaller. And not only 
 do they wear away each other, they also grind out 
 the sides and bottom of the channel of the brook. 
 
 FIG. 7. Stones from same cliff after having been rolled about in the bed of 
 the brook. 
 
 A good deal of stone must be consequently rubbed 
 down (see Physical Geography Primer, Art. 175). Now 
 it is this worn material which makes gravel, sand, 
 and mud. In the bed of every stream you will never 
 fail to find plenty of this worn material, derived from 
 the rubbing away of stones by water.
 
 ROCKS.] 
 
 GEOLOGY. 
 
 29 
 
 70. The finer particles, being more easily moved, 
 travel much farther than the coarser fragments. 
 Hence, while the gravel and coarse sand are pushed 
 
 PIG. 8. A small heap of sand consisting of pieces of stone from the same 
 cliff which have been still further worn away in the bed of the brook. 
 
 along the bottom, the fine sand and mud are sus- 
 pended in the moving water and may be carried by 
 it for many miles before they slowly sink to the 
 
 FIG. 9. A glass of water taken from the same brook when in flood, to show 
 how the finer particles worn from the same stones settle down on the 
 bottom as a layer of mud. 
 
 bottom to form there a deposit of silt or clay 
 (Fig. 9)- 
 
 71. You will see from this, that while the brooks in
 
 30 SCIENCE PRIMERS. [SEDIMENTARY 
 
 the higher parts of a country may have their channels 
 encumbered with big blocks of rock, and quantities of 
 coarse, sharp, angular rock-rubbish, all this material 
 is worn down by degrees, and reaches the lowlands 
 or the sea only as fine sand and mud. As the 
 brooks are always flowing, so are they always trans- 
 porting the worn materials of the hills. But as fast 
 as they do so, the hills are crumbling down and sup- 
 plying fresh materials to the brooks. So that the 
 amount of gravel and sand ground up every year 
 even by the comparatively small streams of this 
 country must be enormously great. (See Physical 
 Geography Primer, Arts. 170 182.) 
 
 72. We can now return to our crag of red rock with 
 freshened interest. Every cleft and gully which has 
 been worn into its sides, bears witness to the general 
 crumbling which the surface of the land undergoes. 
 We may follow its ruined blocks and rubbish into the 
 brook below, watch how they are ground down there, 
 and trace them onwards until in the form of fine silt 
 and mud their remains find their way at last into 
 the far distant plains and thence to the bottom of 
 the great sea. 
 
 73. But it is not only in the beds of brooks and 
 rivers that you can watch how the hardest rocks are 
 ground away into gravel and sand. Look at any of 
 the rocky parts of the coast line of this country and 
 there mark the effects of the waves of the sea. If 
 a cliff rises from the upper edge of the beach, 
 you can at once tell which parts are exposed to, and 
 which lie beyond the reach of the waves. Over- 
 head the cliff is rough and splintered where merely 
 rain, frost, or springs have acted on it (see Physical
 
 ROCKS.] GEOLOGY. 31 
 
 Geography Primer, Arts. 137, 138). But towards its 
 base the rocks have been ground smooth and polished 
 like those in the bed of a mountain-brook.- What 
 has smoothed the bottom of the cliff and' left 
 all the higher parts rough and crumbling ? The 
 waves have done it. 
 
 74. Huge slices of the weather-roughened cliff have 
 been detached and have fallen down on the beach 
 below. Others are ready to tumble off. Examine the 
 fallen blocks and you will see that usually only those 
 lying at the base of the cliff, and which have not yet 
 been moved by the waves, have still their sharp edges. 
 A little lower down the blocks show signs of having 
 been ground 'together, while the greater part of the 
 beach is strewn with stones of all sizes, well rounded 
 and polished. 
 
 75. On a calm day when only little wavelets curl on 
 the shore you cannot easily judge what the sea really 
 does in the way of grinding down the beach and the 
 bottom of the cliffs, just as you could not form a 
 proper notion of the work of a brook merely by 
 seeing 'it lazily creeping along its bed in a season of 
 drought. But place yourselves near a cliff during a 
 storm, and you will not need any further explanation 
 as to the power of the waves to grind down even 
 the hardest rocks. Each huge breaker as it comes 
 tossing and foaming up the beach lifts- up the stones 
 lying there and dashes them against the base of the 
 cliff where it bursts into spray. As the green seething 
 water rushes back again to make way for the next 
 wave, you can hear, even perhaps miles away, the 
 harsh roar of the gravel as the stones grate and grind 
 on each other while they are dragged down the 
 
 4
 
 32 SCIENCE PRIMERS. [SEDIMENTARY 
 
 beach, only to be anew caught up and swept once 
 more towards the base of the cliff. You could not 
 conceive of a more powerful mill for pounding down 
 rocks and converting their fragments into well-worn 
 gravel and sand (Physical Geography Primer, Arts. 
 230 232). Just as in the channel of every stream 
 so along the shores of every sea you meet with the 
 fragments of the rocks of the land in all stages of 
 destruction, from the big angular block down to the 
 finest sand and mud. 
 
 76. If, therefore, I now repeat the question, "How 
 are Sand and Gravel made ? " you will at once answer 
 "Sand and Gravel are part of the material worn 
 away from the surface of the land, and ground down 
 in moving water." Materials which have been rubbed 
 smooth in this way are said to be " water-worn." 
 But you will now see that it is not the water which of 
 itself wears them away. They are in fact worn away 
 by themselves, and all that the water does is to keep 
 them moving and grinding against each other. 
 
 III. How Gravel, Sand, and Mud become 
 Sedimentary Rocks. 
 
 77. We have now got so far on our way as to under- 
 stand whence the materials of which sedimentary 
 rocks are made were derived. But the further ques- 
 tion remains, how have these materials been gathered 
 together and hardened into solid stone ? As before, 
 we must find the answer to such questions in what 
 we can see going on around us. By turning back 
 again to the brooks, rivers, and sea, we shall get this 
 next matter very clearly explained.
 
 ROCKS.] GEOLOGY. 33 
 
 78. Water flows more quickly down a steep slope 
 than over a gentle one. You know that when you 
 raise one end of a tray, water poured on it runs down 
 to the lower end, and does so the faster the steeper 
 
 'you make the inclination. 
 
 79. If you put crumbs or pebbles of different sizes 
 on the tray you will notice that they a;e swept down 
 more by the rapid than by the slower flow of water. 
 A quickly flowing current of water is more powerful 
 to move anything than one which flows slowly. 
 Hence, as you will at once see, there must be great 
 differences in the size and weight of materials which 
 different streams or different parts of the same stream 
 can move. 
 
 80. So long as a current of water is moving swiftly 
 it keeps the gravel, sand, and mud from settling down 
 on the bottom. You remember that when you put 
 some of each of these materials into glasses, and 
 kept the water in rapid motion, they continued sus- 
 pended in the water, and only sank to the bottom as 
 the water began to lose its motion, the gravel first, 
 then the sand, and last of all the mud (Arts. 47 49). 
 Now this is just what takes place in all the moving 
 waters of the globe. A rapid current will hurry 
 along, not only mud and sand, but even gravel. As 
 its rapidity flags, first the gravel will sink to the 
 bottom as a sediment, the sand will sink more slowly 
 and be carried further, while the mud will hang in the 
 water for a long time, travel a much greater distance, 
 and only fall with extreme slowness to the bottom. 
 
 8 1. You must test the truth of these statements the 
 first time you have an opportunity of looking into the 
 rocky channel of a brook as it escapes from the hills.
 
 34 SCIENCE PRIMERS. [SEDIMENTARY 
 
 Get to some part where the water, shooting swiftly 
 over ledges and rocks, has strength enough to sweep 
 even big blocks of stone along with it. A little way 
 further down you will find the channel less steep 
 and the current less strong. Now look into the 
 bottom of the stream. Is it covered with fine mud ? 
 Assuredly not. You meet only with big blocks of 
 stone and coarse gravel. These have been dropped 
 as soon as the water had its force checked by coming 
 from a steep to a more level part of its course. 
 But it still had power enough to transport the finer 
 sorts of sediment. You need to go further down 
 towards the low grounds before you see the bed of 
 the stream covered with sand, and much further yet, 
 even far into the plains, before you meet with layers 
 of mud. 
 
 82. After seeing these things with your own eyes, 
 you would be convinced that wherever you find masses 
 of gravel they tell you of strong currents of water, 
 that beds of sand point to less rapid currents, while 
 sheets of mud show where the water has had either a 
 very gentle motion or has been quite still so as to let 
 the fine sediment settle down quietly on the bottom. 
 
 83. Now see how important this knowledge becomes 
 when you begin to inquire how different stones were 
 made. If you have ascertained clearly how various 
 kinds of sediment are formed, you have got a long 
 way towards understanding how Sedimentary Rocks 
 came to be made. These rocks may be hard stone 
 now, and may be used for paving streets or building 
 houses. But you have learnt that mere hardness or 
 softness goes for little, and that it is the materials of 
 which the stone consists that you have to consider.
 
 ROCKS.] GEOLOGY. 35 
 
 When you find these materials to be water-worn 
 grains of mud, sand, or gravel, you confidently assert 
 that no matter how hard the stone may be now, 
 it was once in the state of mere loose sediment under 
 water. 
 
 84. But you can tell more than this. By seeing the 
 kind of sediment of which a rock is made up you 
 know something about the nature of the water in 
 which the materials of the rock were laid down. 
 For instance, you recognize a rock of conglomerate 
 to be only a mass of compact gravel, and you 
 are sure that like ordinary gravel now-a-days it was 
 rolled about in shallow water such as the bed of a 
 lake or river or on the shore of the sea. Again, you 
 see in a rock formed of fine mud, such as shale, proofs 
 of deeper or stiller water into which only the finer 
 particles worn away from the land were carried. 
 
 85. We have watched how the sediments are ground 
 down by brooks, rivers, and waves ; let us now follow 
 them until they are gathered into places where they 
 can accumulate without being constantly washed away. 
 
 86. Some account has already been given (Physical 
 Geography Primer, Arts. 147 and 182) of what be- 
 comes of the materials worn away from the surface of 
 the land. You have learned how they are washed 
 down by rains into brooks and rivers, how they are 
 there ground down, and how finally they are borne as 
 fine sand and mud away out to the bottom of the sea. 
 
 87. Now these deposits of sediment over the sea 
 bottom will by-and-by become hard sheets of stone, 
 like the common sedimentary rocks we have been 
 dealing with in these lessons. You cannot see what 
 goes on under the sea, but you can form some notion
 
 36 SCIENCE PRIMERS. [SEDIMENTARY 
 
 of it by watching what takes place in pools of water 
 on the land. 
 
 88. Let us suppose that we know a muddy street or 
 road which slopes down gently to a more level 
 part, and that in wet weather the rain gathers in 
 pools at the bottom of the slope. We choose a wet 
 day, and after following the course of one of the 
 gutters down the slope and noticing how the muddy 
 water sweeps along sand, gravel, bits of cork, stick, 
 paper, and whatever lies in its way, we halt at a 
 large pool which has gathered on the road, and into 
 which the current of muddy water is discharging 
 itself. So long as the water flows quickly downward 
 it sweeps away gravel and sand. But see what 
 happens when it begins to flow more slowly over the 
 flat at the bottom and enters the pool. By losing 
 speed it loses carrying power, and must needs drop 
 some of its burden of sediment. The heaviest par- 
 ticles fall to the bottom first, and tL'is takes place just 
 where the current is checked by meeting the level 
 water of the pool. Now mark the result. That part 
 of the pool where the current enters is gradually filled 
 up, except the channel which the current keeps open 
 for itself. You can see how this tongue of sediment 
 is advancing upon the water, and that it will in the 
 end, should the rain last long enough, fill the pool 
 up entirely. It is only the coarse sand which col- 
 lects there; the fine mud goes across the pool, and 
 though part of it, as you will find, settles down on the 
 bottom, much or most of it escapes at the further end 
 of the pool, because the water has not had time, in 
 its passage from the one side to the other, to drop 
 its burden of mud.
 
 ROCKS.] GEOLOGY. 37 
 
 89. Let us suppose further that when the rain has 
 ceased, no cart-wheel or other intruder comes to 
 disturb our pool, but that the water is suffered quietly 
 to soak into the ground and to evaporate, so that 
 in a day or two the hollow is laid dry. You 
 can now examine the bottom of the pool and see 
 exactly what took place when the muddy water 
 filled it. Here at the upper end is the tongue of 
 sand pushed out from the shore by the streamlet. 
 You recognize it as a true Delta (Physical Geo- 
 graphy Primer, Art. 181). The bottom of the rest o'f 
 the pool is covered with fine muddy silt or sand 
 spread out over all the space on which the water lay. 
 
 90. With a knife we carefully cut a hole or trench 
 through these deposits on the floor so as to learn what 
 they consist of from top to bottom. A cutting of 
 this kind is called a Section, and may be of any 
 size. The steep side of a brook, the wall of a ravine, 
 the side of a quarry or railway-cutting, a line of cliff, 
 are all sections of the rocks. Let us see what our 
 section has to tell. 
 
 91. In the centre of the little basin the sediment 
 brought in by the rain has accumulated to a depth, 
 let us say, of an inch, below which lies the ordinary 
 surface of the roadway. Now what feature strikes you 
 first about this deposit of sediment when you come 
 to look at the section which we have cut through it ? 
 Are the materials arranged without any order? By no 
 means. If you made a drawing of the section it 
 might be something like the following woodcut (Fig, 
 10). The materials have been deposited in layers 
 which have been laid down flat one above another. 
 Some of these layers are finer, others coarser than 
 
 'M i
 
 38 SCIENCE PRIMERS. [SEDIMENTARY 
 
 the rest. But whether coarse or fine they all show 
 the same general arrangement in level lines. 
 
 92. In looking at these layers you can follow exactly 
 how each of them was deposited. The coarse sedi- 
 ment is seen chiefly at the bottom, and marks where 
 the stronger currents carried sand and bits of stone 
 across the pool. But as the rain slackened, the 
 runnels on the roadway grew less and the currents in 
 the pool became feebler. Hence, instead of coarse 
 sand, only fine silt was deposited, so that in the 
 
 > v :< c^ a 
 
 FIG. io. Section or cutting through the sediment brought by rain into a 
 pool on a roadway, a. Surface of roadway, b. Layers of coarse sand 
 with bits of coal and ash. c. Layer containing twigs, bits of straw, leaves, 
 paper, &c. 
 
 upper half, the layers are finer than they are in the 
 lower. Together with the sand, gravel and mud, you 
 may notice chips of wood, leaves and twigs (c in Fig. 
 TO) which have been laid down among the layers of 
 sediment. 
 
 93. You may think perhaps that observations such 
 as these are too trifling, and that surely it cannot matter 
 what rain may do in a little pool on a roadway, since 
 we are not to judge of the world at large by what 
 goes on upon so small a scale. In reality, however,
 
 ROCKS.] GEOLOGY. 39 
 
 if you thoroughly understand what takes place over 
 the bottom of such a pool, insignificant though it may 
 seem, you lay a foundation from which it will be easy 
 for you to understand how sedimentary rocks are and 
 have been formed all over the world. 
 
 94. Instead of the pool imagine to yourselves a great 
 lake such as that of Geneva, and in place of the mere 
 tiny runnel on the road, formed by the sudden rain, 
 and disappearing when the rain ceases, picture a 
 great river like the Rhone, ever fed by the rains and 
 snows and springs of a huge mountain chain. And 
 yet though you make the scale on which the work 
 goes on greater, the kind of work remains the same 
 as in the pool. You look with wonderment on the 
 river rushing so swiftly past, and tossing its muddy 
 waters into wave and foam, from bank to bank. 
 You watch it enter the lake, and mark how the 
 waves one by one sink down, and how the river loses 
 itself and its tumult in the quiet silent water of the 
 deep blue lake. 
 
 95. But climb one of the mountains which rise 
 steeply from either side of the upper end of the Lake 
 of Geneva. When you get up a few hundred feet, turn 
 and look down upon the river and', lake, and see if 
 they do not strongly remind you of our runnel and 
 pool on the road. The bottom of the valley lies 
 spread out as in a map before you. The windings of 
 the river, the flat green meadows on either side run- 
 ning as a long tongue into the lake, the little cottages 
 and hamlets, and the lines of road all so dwindled 
 down in the distance that you can see at a glance how 
 they lie. That green tongue of meadows filling up 
 the upper end of the lake and stealing along each side
 
 40 SCIENCE PRIMERS. [SEDIMENTARY 
 
 of the river is the Delta. It has been formed in the 
 same kind of way as the little delta in our pool, only 
 instead of hours it has needed thousands of years for 
 its formation. About a mile and a half from the edge 
 of the lake, a little hamlet, standing among the level 
 fields, was actually at the margin of the water some 
 eighteen hundred years ago, and is still called Port 
 Vallais. The river has thus pushed out its delta and 
 filled up the lake for a mile and a half since Roman 
 times. 
 
 96. From the high ground overlooking the head of 
 the lake you can see moreover another curious fact 
 about the way in which the sediment gathers over 
 the bottom. The Rhone is very muddy, and as the 
 mud has a white colour here, the milky look which 
 it gives to the water enables you to follow the course 
 of the river into the clear blue lake. Looking down 
 upon it from the heights you can trace the pale muddy 
 current for some way out from the shore until it 
 gradually gets mixed with the lake-water and disap- 
 pears. 
 
 97. Go now to the lower end of the lake, and watch 
 where the water escapes. Do you see any mud now? 
 No, your eyes never looked on clearer, brighter, 
 bluer, water than that which comes rushing and 
 leaping between the banks and beneath the bridges 
 of Geneva. What has come of that cloud of pale 
 mud which you saw carried by the river into the 
 upper end ? It has all settled down upon the bottom. 
 Day by day, year by year, and century after century, 
 the cloud of mud is there, always sinking through 
 the water to the bottom, and always renewed by the 
 restless river.
 
 GEOLOGY. 41 
 
 98. Could you drain off all the water of the lake you 
 would find the floor covered with deposits of sedi- 
 ment stretching, not over a few square feet, as in our 
 little wayside pool, but over many square miles. The 
 coarser sediments--shing]es and gravels would be 
 met with at the upper end where the strong current 
 flowed, while the finer sediments sand and mud 
 would cover the main part of the bottom. 
 
 99. If you were to bore through these deposits, you 
 would find them in some places to be perhaps more 
 than a hundred feet thick, and digging down anywhere 
 among them you would see the same arrangement 
 into flat layers which you observed in the rain-pool. 
 Sand, mud, and gravel might follow each other from 
 top to bottom, but always in beds or layers lying one 
 above another. 
 
 100. The Lake of Geneva is many thousand times 
 larger than our little pool ; and yet it is itself only a 
 pool, and a very small one, when compared with the 
 great sea. Go to the margin of the sea where a large 
 river enters, and you will see that mere size does not 
 alter the kind of work which the river and the sea are 
 doing, and that in their case too you have the same 
 process to study which you have watched already. 
 You perceive how the river is continually carrying 
 vast quantities of sand and mud into the sea. You 
 can follow the muddy river-water to a distance from 
 the shore until, as its mud slowly sinks to the bottom, 
 it loses itself in the waters of the ocean. You know 
 that by this means the bottom of the sea for a long 
 way from the coast is constantly receiving fresh de- 
 posits of sand and mud which have been washed off 
 the land. The upper edge of these deposits is un-
 
 42 SCIENCE PRIMERS. [SEDIMENTARY 
 
 covered when the tide goes out. You can dig into 
 them where they form the beach, and when you do 
 so you recognize the same arrangement into layers 
 as you found to be the case elsewhere. 
 
 IQI. In this way you gradually would come to be 
 convinced that one grand leading feature of the sedi- 
 mentary deposits laid down under water is that they 
 
 FIG. ii. Stratification of Sedimentary Rocks, a. Conglomerate b. Sand- 
 sione. c. Shale. 
 
 are not mere random heaps of rubbish, but that they 
 are assorted and spread over each other in regular 
 layers. This kind of arrangement is called Strati- 
 fication, and the sediments so arranged are said to 
 be stratified. So characteristic is this mode of 
 arrangement among the sedimentary rocks that they 
 are often called also the Stratified Rocks. 
 
 102. The sheets of sand, gravel, or mud which 
 can be seen on the sea-shore, or at any lake or 
 pool on land, are soft or loose materials. Sand- 
 stone, conglomerate, shale, or any other sedimentary 
 rock, is usually more or less hard or compact.
 
 ROCKS.] GEOLOGY. 
 
 How is this difference to be accounted for? You 
 are quite sure that, in spite of their firmness, these 
 rocks were once mere loose sediment formed under 
 water in the same way as sediment is made every- 
 where at the present day. But what has turned 
 them into hard stone ? 
 
 103. If you take a quantity of mud, and place it 
 under a weight which will squeeze the water out of it, 
 you will find that it gets firmer. You can thus harden 
 it by pressure. Again, if you place some sand 
 under water which has been saturated with lime 
 (that is, the material of which chalk and limestone 
 are made) or with iron, or with some other mineral 
 which can be dissolved in water, you will notice that 
 as the water slowly evaporates it deposits its dissolved 
 material round the grains of sand and binds them 
 together. Were you to continue this process long 
 enough, adding more of the same kind of water as 
 evaporation went on, you would convert the loose 
 sand into a solid stone. In this case the hardening 
 of the sediment into stone would be done by the 
 process called infiltration. 
 
 104. In one or other or both of these ways most of 
 the sedimentary rocks have been hardened into the 
 state in which we now find them. AVhen sand and mud 
 are piled up over each other in wide sheets or layers, 
 to a depth of hundreds or thousands of feet, the 
 layers at the bottom, lying under such an enormous 
 weight, must be squeezed into a much firmer con- 
 dition than those at the top. But besides this, water is 
 always filtering through pores and cracks of the rocks, 
 sometimes removing, sometimes depositing, mineral 
 matter (in the way explained in the Physical Geo-
 
 44 SCIENCE PRIMERS. [SEDIMENTARY 
 
 graphy Primer, Arts. 1 1 7 125), and helping to cement 
 the grains of many rocks more firmly to each 
 other. 
 
 105. If I were now to ask you what an ordinary 
 sedimentary rock is, you would readily give me, and 
 clearly understand, such a definition as this "A 
 sedimentary rock is one formed from sediment which 
 was derived from the waste of older rocks, and de- 
 posited in water. It usually shows the stratified 
 arrangement characteristic of water-formed deposits. 
 Since its original formation it has usually been har- 
 dened into stone by pressure or infiltration." 
 
 IV. How the Remains of Plants and 
 Animals come to be found in Sedimen- 
 tary Rocks. 
 
 1 06. Although sedimentary rocks consist of such 
 materials as gravel, sand, or mud, they often contain 
 other things quite as interesting and important. For 
 example, here are two additional pieces of Shale 
 (Figs. 12 and 13), in which you will see certain objects 
 very different from the ordinary sediment of which 
 the stone is made. Let us first satisfy ourselves as to 
 what these objects are, and then as to how they came 
 to be imbedded in the stone. 
 
 107. We begin with the specimen which is drawn 
 in Fig. 12. In the stone itself you would recognize 
 merely a fragment of common shale, formed of the 
 same materials, and arranged in the same stratified 
 way as in your former specimen of that rock. 
 
 108. But what is this black object lying on the upper 
 surface of the stone ? You see at once that it has the
 
 ROCKS.] GEOLOGY. 45 
 
 form of a plant and resembles some of the fern tribe. 
 Examine it more closely, and, tracing the delicate 
 veil ling of the fronds, you cannot doubt that, although 
 no longer soft and green, it was once a living fern. 
 It has been changed into a black substance which, 
 
 FIG. 12. Piece of Shale containing portion of a fossil fern. 
 
 when you look carefully at it, proves to be a kind of 
 coal. Little fragments and layers of the same black 
 coaly substance may occur throughout the piece of 
 shale. If you scrape a little off and put it upon the 
 point of a knife, you find you can burn away the 
 black material while the grains of sand or clay 
 remain behind. These fragments and layers are 
 evidently only leaves and bits of different plants im- 
 bedded at the same time as the larger and better 
 preserved fern. Now how did plants find their way 
 into the heart of a piece of stone ? 
 
 109. To understand how this happened we must
 
 46 SCIENCE PRIMERS. [SEDIMENTARY 
 
 again go back to what nature is doing at the present 
 time. You remember that when you were watching the 
 runnel coursing down the sloping roadway (Art. 88), 
 you noticed that it sometimes swept along bits of straw, 
 wood, paper, or other loose objects which it managed 
 to reach. Some of these floated away into the nearest 
 drain and were soon lost sight of. But others sank to 
 the bottom of our little pool. Look again at the 
 section we cut open there (Fig. 10), and you will find 
 little chips of wood or straw or leaves and blades of 
 grass among the fine sand and mud left by the rain. 
 These objects lie flat between the thin layers of sedi- 
 ment. And if you think of it you will understand 
 how that should be the position they would naturally 
 take as they sank to the bottom. Rain therefore can 
 wash away leaves and other pieces of plants, and allow 
 them to drop in a pool, where they become inter- 
 stratified with the silt, that is, are deposited between 
 its layers and covered over by it. 
 
 1 10. Again : watch what takes place along the banks 
 or at the mouth of a river, and you will soon observe 
 that the leaves, branches, and other floating objects 
 carried down by the current in the end sink to 
 the bottom, there to be imbedded in and gradually 
 covered up by the growing accumulation of sand and 
 mud. If you dig into any of the deposits along the 
 banks you meet sometimes with layers of leaves and 
 twigs, grouped in the same stratified way as the 
 sediment above and below them. Such deposits of 
 drifted vegetation often form a conspicuous part 
 of the accumulations of which the delta of a river 
 consists. (Physical Geography Primer, Art. 180.) 
 
 in. But it must happen continually that before the
 
 ROCKS.] GEOLOGY. 47 
 
 leaves or branches or the trunks of trees have become 
 so saturated or water-logged as to sink to the bottom 
 they are borne onward into the sea. In such cases 
 they may float a long way from shore ere they fall to 
 the bottom and become buried in the silt and sand 
 there. Hence, whether in the beds of rivers, or at the 
 bottom of lakes or of the sea, the remains of land 
 plants must be constantly dropping among the sedi- 
 mentary deposits which are gathering there. 
 
 112. You can now see therefore how it is that pieces 
 of ferns or any other kind of land plants should be 
 found in the heart of such a solid stone as our bit of 
 shale. The stone was once merely so much sediment 
 laid down below water, and the fragmentary plants 
 were drifted away from the place where they grew 
 until at last they were buried among that sediment. 
 As the mud hardened into shale the plant became 
 more and more altered until its substance passed into 
 coal. You will find in a later lesson that coal was 
 formerly vegetation which, buried under great masses 
 of sediment, has been slowly changed into the black 
 glossy substance so familiar to us. 
 
 113. It is not only plants, however, which occur 
 imbedded in sedimentary rocks. Here for example 
 (Fig. 13) is a drawing of a piece of shale in which 
 you notice a number of shells and other animal re- 
 mains, chiefly trilobites, that is, little sea-creatures 
 belonging to the same great tribe with our common 
 crab and lobster. You do not need now to be told 
 how they came there. You have learnt that anything 
 lying at the bottom of the sea or of a lake will be 
 buried in sediment. The remains of shells, corals, 
 fishes, or any other animals which live in the water,
 
 48 SCIENCE PRIMERS. [SEDIMENTARY 
 
 must gather on the bottom when these animals die, 
 and become imbedded in the silt or other deposit 
 which is there forming. It was clearly in this way 
 
 FIG. 13. Piece of Shale with animal remains. 
 
 that the shells and corals in our piece of shale were 
 preserved. 
 
 114. Did you ever look into the little pools of sea- 
 water left upon a rocky beach when the tide has gone 
 back? How full of life they are ! Tufts of sea-weed 
 sprout up in one place, groups of brightly tinted sea- 
 anemones appear in another, periwinkles and limpets 
 cling to the sides, and down at the bottom you may 
 see tiny crabs cautiously creeping out of your sight, 
 with many other kinds of sea-creatures moving to and 
 fro of which you do not know the names. If you look 
 a little more narrowly you can observe that some of 
 the shells at the bottom are empty, the animals which 
 once lived in them having died, and that broken 
 pieces of other dead creatures lie there also. 
 
 115. You are not to suppose of course that the whole
 
 ROCKS.] GEOLOGY. 49 
 
 of the bottom of the sea is like the bottom of one 
 of these pools on the beach. The plants and animals 
 in the pools are those which live along the shore 
 or shallow parts of the sea, while the deeper parts 
 have other plants and animals peculiar to them. 
 But although these living things differ greatly in 
 different portions of the ocean floor, and though 
 here and there they may be absent from bare patches 
 of gravel, stones or sand, the floor of the great sea 
 resembles the floor of the little pool on the beach in 
 this respect that it swarms with many kinds of living 
 creatures, and with the remains of dead ones. So that 
 the deposits of sand and mud which gather upon 
 the sea-bottom must contain abundant relics of these 
 creatures. 
 
 116. If then the remains of plants and of animals 
 are very generally buried in the accumulations of sedi- 
 ment which now increase from day to day at the 
 bottom of lakes or of the sea, we may be sure that 
 the same must have been the case in past times, and 
 that sedimentary rocks, which are only so much har- 
 dened sediment of the bottom of old lakes or seas, 
 should also contain remains of plants and animals. 
 And so they do abundantly you will meet with sand- 
 stones, shales, and other sedimentary rocks, as full of 
 such remains as any part of the modern sea-bottorn 
 is now crowded with life. 
 
 117. Any relic of a plant or animal imbedded in 
 rock is called a Fossil. The fern in Fig. 12 for 
 example, and the shells and trilobites in Fig. 13 
 are fossils. Some of the questions which fossils 
 enable us to answer will be pointed out in the next 
 Lesson.
 
 SCIENCE PRIMERS. [SEDIMENTARI 
 
 V. A Quarry and its Lessons. 
 
 1 1 8. ID the foregoing lessons you have learnt what 
 sediment is, how different kinds of sediment, arranged 
 under water, have become sedimentary rocks, and how 
 they may contain the remains of plants or animals. 
 Let us now try to put some questions to these rocks, 
 and see how they tell their own story. 
 
 119. If you go into the quarries which abound in 
 many parts of this country you may learn a great 
 deal on this subject. Let us suppose ourselves to be 
 in such an one as that represented in Fig. 14. 
 
 FIG. 14. Quarry in Sedimentary R 
 
 120. In the first place what feature about the 
 quarry strikes you most forcibly when you enter? 
 You answer readily, the Stratification of the 
 rocks. They are arranged in layers or beds, one 
 above another, in that stratified arrangement which 
 you have found to be so characteristic of rocks laid 
 down as sediment under water. (Arts. 90 101.)
 
 ROCKS.] GEOLOGY. 51 
 
 121. In the second place, you observe that they do 
 not all consist of the same materials. Some are of 
 fine conglomerate (marked with little circles and dots 
 in the drawing), others of various kinds of sandstone 
 (marked with finer dots), and some of different sorts 
 of shales or clays (marked with horizontal lines). 
 These beds, or strata as they are called, alternate 
 irregularly with each other, just as gravel, sand, and 
 mud might be found alternating in the delta of a 
 river or under the sea. 
 
 122. In the third place, let me ask you to point out 
 which are the oldest of the beds. You answer without 
 hesitation that those at the bottom of the quarry must 
 be the oldest because they certainly were deposited 
 before those lying above them. The lowest bed may 
 be of exactly the same materials and thickness as one 
 or more of the others, and may so precisely resemble 
 them that you might not be able to see any difference 
 between them if you looked at them each by itself. 
 Yet their occurrence one above another would prove 
 them not to be the same bed, but to have been formed 
 at different times one after the other. In all such 
 cases the beds at the bottom are the oldest, and those 
 at the top the newest. This arrangement of one bed 
 or stratum above another is called the Order of 
 Superposition. 
 
 123. In such a quarry as that drawn in the woodcut, ' 
 this order is no doubt very simple and self evident, but 
 you will learn afterwards that it is not usually so clear, 
 for in many cases the rocks are concealed from you in 
 part by soil or otherwise, and much care and patience 
 maybe needed before their true order of superposition 
 is ascertained. But when, in spite of all difficulties,
 
 52 SCIENCE PRIMERS. [SEDIMENTARY 
 
 you succeed in showing which are the bottom rocks 
 and which the uppermost, you at the same time deter- 
 mine which are oldest and which newest. 
 
 124. In the fourth place, let us see if the rocks of 
 this quarry have preserved any Evidence as to where 
 they were deposited. We split open some of the lower 
 beds of sandstone and find that their surfaces are 
 often covered with such markings as are shown in the 
 following drawing (Fig. 15). Did you ever see anything 
 
 FIG. 15. Ripple-marks in Sandstone. 
 
 resembling these impressions elsewhere ? If you have 
 ever walked along a flat sandy beach you must have 
 noticed the ripple-marks which the shallow rippling 
 water leaves on the soft sand. They are precisely like 
 those on the sandstone. You may see them too along 
 the shelving margin of a lake, indeed wherever water 
 has been thrown by the wind into little wavelets over a 
 sandy bottom. They betoken shallow water. Hence 
 we have learnt one important fact from our quarry, as 
 to the origin of these rocks : viz. that they were not 
 deposited in a deep sea, but in shallow water.
 
 ROCKS.] GEOLOGY. 53 
 
 125. We look still further among these strata, and 
 notice at last that some of them are curiously covered 
 with little round pits, about the size of peas or less. 
 The general appearance of these pitted surfaces is 
 shown in Fig. 16. How did these markings come 
 there ? Like the ripple-marks they must of course have 
 been impressed upon the sand when it was soft, and 
 before it had been hardened into sandstone. Again, 
 you must seek for an explanation of them by watching 
 what takes place at the present time. You know 
 that when drops of rain fall upon a smooth surface 
 
 FIG. 16. Rain-prints on Sandstone. 
 
 of moist sand, such as that of a beach, they each 
 make a little dent on it. You have learnt something 
 about these rain -prints, and if you compare the 
 present drawing with the picture of the rain-prints 
 in the Physical Geography Primer, Fig. 9, you will 
 see that they are essentially the same, and that they 
 have both been made by the fall of rain-drops upon 
 soft moist sand. 
 
 126. Here then is another fact which throws still 
 more light on the history of these rocks. The ripple- 
 marks show that the water must have been shallow ; the
 
 54 SCIENCE PRIMERS. [SEDIMENTARY 
 
 rain-prints prove that it must have risen along a beach 
 liable, now and then, to be laid dry to the air and 
 rain. Now can we tell whether the water was salt 
 or fresh? in other words, was this beach the shore 
 of a lake, or of the sea ? 
 
 127. Again we turn to the rocks themselves, and 
 from some of the layers of shale we pick out a num- 
 ber of fossils, which enable us to answer the question. 
 If you were to fish in a lake, would you catch only the 
 same fish which you find in the sea? Certainly not; 
 you would soon learn that not only the fishes but the 
 other animals and the plants living in fresh water, 
 differ from those living in salt water. Star-fishes, 
 limpets, oysters, and flounders, for example, are in- 
 habitants of the sea, while your old friends the perch, 
 the minnow, and the stickleback are natives of rivers 
 
 FIG. 17. Fossils, a, Coral ; b, part of Encrinite ; c, Spirifer, 
 a marine shell. 
 
 and lakes. You can understand, therefore, that the 
 remains of animals and plants preserved in the deposits 
 of the sea-bottom must differ from those preserved 
 on the bottoms of lakes. 
 
 128. Some of the fossils which we have picked out 
 are represented in the woodcut (Fig. 17). Of these
 
 ROCKS.] GEOLOGY. 55 
 
 a is a coral ; b is part of the jointed stem of the Encri- 
 nite or stone-lily an animal related to the common 
 star-fish ; and c is a shell belonging to a family the 
 members of which are all dwellers in the sea. Now 
 these are all unmistakably marine animals, and when 
 we find them associated in this way in a bed of stone, 
 we feel certain that the materials of the stone must 
 have been laid down under the sea; they were pos- 
 sibly cast ashore on the old sea beach, as shells are 
 to this day. 
 
 129. Here, again, is a third fact about the history 
 of our rocks. The ripple-marks and rain-prints made 
 it certain that they were formed in the shallow water 
 close to shore, and along a beach ; and now the 
 fossils prove that those waters were part of the great 
 sea. 
 
 130. In this quarry then you have found clear proofs 
 that land and sea have here changed places. Though 
 the quarry may be in the very heart of the country, 
 far away from the sea, yet you cannot be more 
 sure of anything than that the sea was once upon its 
 site. But if you search among other quarries you will 
 find the same kinds of proofs of the former presence 
 of the sea. In fact, were you to start from the 
 south of England, and go north to the far end of 
 Scotland, by much the largest number of quarries 
 you would meet with would be in rocks which were 
 originally formed under the sea. In such a journey 
 you would learn that almost the whole of our country 
 is made up of such rocks. Down at the bottom of 
 deep mines, and away up at the summits of high 
 mountains, you would come upon them. Nor is 
 Great Britain singular in this respect Suppose you
 
 56 SCIENCE PRIMERS. [ORGANIC 
 
 were to cross Europe and look carefully at all the 
 rocks on your way, you would still find the sea- 
 formed ones to be the great majority. From Europe 
 into Asia, and from Asia through Africa on the one 
 hand, down the whole length of America on the 
 other, you would encounter far more rocks which 
 had been formed under the sea, than of any other 
 kind. The very highest mountains in the world con- 
 sist of sea-made rocks. 
 
 131. Now is this not a very singular fact? How is 
 it that the solid land has been chiefly made under the 
 sea? The rocks must have been raised up out of 
 the sea by some means, and since the land is so 
 uneven they would seem to have 'been raised much 
 more in some places than in others. How this 
 raising of the sea-bed has taken place, will be spoken 
 of in a later lesson. But first we must trace the 
 history of certain other rocks, many of which have 
 also been formed under the sea. 
 
 ORGANIC ROCKS, OR ROCKS FORMED OF THE 
 REMAINS OF PLANTS AND ANIMALS. 
 
 I. Rocks formed of the Remains of Plants. 
 
 132. Since the leaves, branches, and stems of plants, 
 and the shells or other remains of animals, are some- 
 times scattered so abundantly through ordinary sedi- 
 mentary rocks, it is easy to see that sometimes they 
 may occur in such quantity as to form great deposits 
 of themselves. You could hardly call such deposits 
 sedimentary, in the same sense in which common 
 shale and sandstone are so named. We may term 
 them Organic Rocks, or, Organically derived
 
 ROCKS.] GEOLOGY. 57 
 
 Rocks, because they owe their origin to the accumu- 
 lation of what are called organic remains, or fossils, 
 that is, the remains of plants or animals. A plant or 
 animal lives, moves, and grows by means of what are 
 called organs. For instance, we walk by using our 
 legs, which are OUT organs of locomotion ; we speak with 
 our mouth, which contains our organs of speech ; we see 
 by means of eyes, which are our organs of sight ; and so 
 on. Every object, therefore, which possesses organs is 
 said to be organized or to be an organism. So that 
 when you see this word organism you will remember 
 that it means either a plant or an animal, for it is only 
 plants and animals which are really organized. 
 
 133. We begin with those rocks which have been 
 formed out of the remains of plants. As an illustra- 
 tion let me ask you to examine carefully a piece of 
 coal. If you master all that it has to tell you, you 
 will not have much difficulty in tracing out the history 
 of other rocks belonging to this series. 
 
 134. You know well the general appearance of coal. 
 Did you ever notice that though brought to the fire- 
 place in rough, irregular lumps, it has nevertheless 
 an arrangement in layers like the sedimentary rocks ? 
 Try to break a big solid piece of coal, and you find 
 that it usually splits more easily in one direction than 
 in any other. This direction is that of the thin layers 
 of which the coal consists. If you want large pieces 
 of coal to burn up quickly and make a good fire, you 
 will take care so to put them in the grate that those 
 layers shall be more or less upright. In that position 
 the heat splits them up. 
 
 135. Now look at one end of a lump of coal, 
 where the edges of the layers are exposed. You
 
 58 SCIENCE PRIMERS. [ORGANIC 
 
 cannot follow them with the same ease as/ in the 
 case of a piece of shale, for they seem to blend into 
 one another. But you may notice that among the 
 layers of hard, bright, glossy substance, there occur 
 others of a soft material like charcoal. A mere general 
 look at such a piece of coal would show you that it 
 is stratified. 
 
 136. You know that coal can be burnt away so as 
 to leave only ashes behind, and that in this respect it 
 resembles wood and peat (see Art. 145). Chemists 
 have analysed coal and found that it consists of the 
 same materials as wood or peat, and that in reality 
 it is only so much vegetation which has been pressed 
 together, and gradually changed into the black sub- 
 stance now used as fuel. 
 
 137. Let us suppose ourselves at a coal-mine, with 
 the object of seeing exactly how the coal lies before it 
 is dug out of the earth and broken up into the small 
 pieces which we burn in our grates (see Fig. 37). We 
 descend in one of the cages by which the miners are 
 let down into the pit. After our eyes have got a little 
 used to the darkness at the bottom, we set out, lamp 
 in hand, along one of the roadways, and reach at last 
 a part of the pit where the miners are at work re- 
 moving the coal. Now, first of all, you see that 
 the coal occurs as a bed, having a thickness of a 
 few feet This bedded character agrees with what 
 you have already noticed as to the internal layers in 
 the stone, and confirms you in believing that coal is 
 a stratified rock. Next observe that the pavement on 
 which the coal rests, and the roof which covers it, 
 are both made of very different materials from the 
 coal itself. Were you to cut a trench or section (Art
 
 ROCKS.] GEOLOGY. 59 
 
 90) through pavement, coal, and roof, you would 
 find some such arrangement as in Fig. 18. You would 
 prove beyond any doubt that the bed of coal lies 
 among beds of common sedimentary rock. 
 
 138. But what is this layer marked <, forming the 
 floor or pavement on which the coal lies ? Examine it 
 with attention and you recognize it to be a bed of 
 dark clay, with abundance of black streaks and branch- 
 ing strings, like roots, spreading through it. You may 
 trace these root-like strings into the bottom of the very 
 
 F:G - 18 ,- Section of a Coal - seam w "h its roof and pavement, a. Sandstones, 
 bhales & c . b. Under-day forming pavement of Coal (c). d. Sandstones 
 and Shales, forming roof of Coal 
 
 coal itself. If you visited other pits you would find each 
 coal-seam to lie usually on such a bed as this. Now 
 why should the coal rest rather on a bed of clay 
 or shale than on one of sandstone or any other sort 
 of rock? If you noticed that this peculiar pavement 
 met you in every pit you visited, would you not 
 begin to feel quite sure that the constant association 
 of the coal and its under-clay could not be a mere 
 accident but must have a meaning? 
 
 139. Now look at the under-clay again. Does it 
 not remind you of a bed of soil with roots branching
 
 60 SCIENCE PRIMERS. [ORGANIC 
 
 through it ? With this idea suggested to your mind, 
 the more you examine the rock the clearer will this 
 resemblance appear, until you are driven to conclude 
 that in truth the under-day is an old soil, and 
 the bed of coal represents the vegetation 
 which grew upon it. (See Fig. 38.) 
 
 140. Each coal-seam has been in truth at one time 
 a dense mass of vegetation growing on a wide marshy 
 flat, somewhat like the swampy jungles of tropical 
 countries at the present day. These great marshy 
 plains had a bottom of muddy soil on which the 
 rank vegetation grew, and it is this very soil which 
 you still see in the under-clay. 
 
 141. Can we tell anything about the kind of plants 
 which flourished over these plains, and accumulated 
 into the thick mass which formed the coal ? Not much 
 can usually be made out from the coal itself, for the 
 vegetation has been so squeezed and altered as to 
 destroy the leaves and branches of the plants; yet 
 in many kinds of coal parts of the old plants have 
 been changed into a sort of charcoal, which soils the 
 finger, and shows traces of the vegetable fibre like 
 any ordinary charcoal. If you cut slices from coal, 
 fix these on glass, rub them down until they are 
 so thin as to be transparent, and place them under a 
 microscope, you may often find that the coal contains 
 millions of little seed-vessels, or, as they are called, 
 sporangia. These were shed by plants somewhat 
 like the club-mosses of our own moors and hills, but 
 much larger in size, and must have fallen so thickly 
 over the flat grounds as to form a kind of mould or 
 soil upon them. 
 
 142. But though the larger plants have not usually
 
 ROCKS. ] 
 
 GEOLOGY. 
 
 61 
 
 been preserved well in the coal itself, you may some- 
 times find them in great perfection and beauty in the 
 beds of rock above or below the coal. Some of the 
 common varieties are shown in Fig. 19. Now and 
 then you may see these plants lying across each other 
 
 FIG. 19. Plants out of which Coal has been formed. 
 
 and all squeezed flat, but still retaining much of their 
 original gracefulness, upon the bottom of the bed 
 of rock which forms the roof of the galleries as 
 you go through the coal-mine. 
 
 143. Each coal-seam, once a luxuriant surface of 
 vegetation, open to the sunlight, and stretching over 
 many square miles, now lies buried deep within the 
 earth, under huge masses of rock, which must be 
 bored through before the coal can be reached. How
 
 62 SCIENCE PRIMERS. [ORGANIC 
 
 this burying has taken place we shall find out in a 
 later lesson (Arts. 213 216). In the meantime you 
 should learn a little about another kind of formation, 
 where vegetation comes into play, and which you may 
 examine not in a deep mine but in the open day. 
 
 144. You have no doubt read about, you may even 
 have seen, the bogs and peat-mosses so abundant in 
 Ireland, Scotland, and some parts of England. If 
 you have not, you must imagine a wide, flat space of 
 brown moor and green marsh, in many parts so soft 
 and wet that you would sink deep into the black 
 mire if you tried to walk on its treacherous surface ; 
 in other parts having a firmer crust, which shakes 
 under your feet as you jump from one dry standing- 
 place to another. Such a flat space is called a bog 
 in Ireland, whilst in Scotland and England it is 
 known as a moss, or peat-moss. Of the whole 
 surface of Ireland nearly a seventh part is believed 
 to be occupied with bogs, and in many parts of Scot- 
 land too they occur in great numbers. 
 
 145. Visiting one of these places you notice that 
 round its edges it is usually quite firm. It may even 
 have become so dry over the very centre as to be 
 ploughed up and to furnish crops of turnips and pota- 
 toes. Wherever you can catch a sight of the substance 
 of which the moss consists, you find it to be a black 
 or dark brown sort of mould called Peat, formed 
 of the remains of plants firmly matted together. 
 Over the whole of the moss this peat extends as a 
 bed, sometimes thirty or forty feet thick. It is 
 simply a vegetable deposit, and in this and other 
 respects resembles coal. 
 
 146. Such being its composition it may of course
 
 ROCKS.] 
 
 GEOLOGY. 
 
 be readily burnt, so that at the mosses it is dug out in 
 pieces, which are dried and used for fuel. Over great 
 parts of Ireland and wide regions of Scotland the 
 peasantry have no other fuel than this peat, which 
 they cut every summer from the mosses. 
 
 147. In Fig. 20 a representation is given of one of 
 these cuttings for peat. It is in such places that the 
 mode of origin of the deposit can best be studied, 
 and as the tracing out of the formation of a peat-moss 
 
 FIG. 20. Section of a Peat moss, where the peat is cut and piled into 
 small stacks to dry for fuel. 
 
 furnishes a good example of the way in which 
 geologists try to find out the past history of the 
 earth, let me ask you to suppose yourselves looking 
 into the opening which has been made in the peat- 
 moss drawn in Fig. 20.
 
 64 SCIENCE PRIMERS. [ORGANIC 
 
 148. Below the surface of coarse grass and heather 
 lies the peat, a brown fibrous mass in the upper parts, 
 but getting more and more compact towards the 
 bottom, till it passes perhaps into a dark compact 
 substance in which no trace of any fibres may be 
 discernible. Down below the bottom of the peat 
 there sometimes lies a layer of fine clay, containing 
 the remains of shells which are only found living in 
 fresh water. Now and then, too, a rude canoe, 
 hollowed out of the trunk of an oak tree, is dug up 
 from the bottom of a peat-moss a relic of some of 
 our uncivilized ancestors. 
 
 149. Here, then, is a little bit of geological history. 
 Now put these separate facts together and make out 
 the story of the peat- moss. 
 
 150. Beginning at the bottom, the oldest formation 
 you meet with is the layer of clay just referred to. You 
 have already learnt that such a layer must have been 
 laid down under water. If it should happen to be 
 thick it will suggest to you that probably this water 
 was not a mere shallow pool or brook, but had some 
 depth and extent. But the shells indicate further that 
 the water must have been that of a lake, for they are 
 such shells as you might find still living in the lakes 
 of the neighbourhood. The first point you settle, 
 therefore, is that before a peat-moss existed here, a 
 lake occupied its site. You may even yet trace what 
 the boundaries of this lake were, for the slopes which 
 rise all round the flat peat-moss must in the same 
 way have surrounded the old sheet of water, whereon 
 our rude forefathers floated the canoes which are now 
 and then dug up from the bottom of the mosses. 
 
 151. Above the layer of clay which marks the former
 
 ROCKS, j 
 
 GEOLOGY. 
 
 lake-bottom, comes the bed of peat, made up wholly 
 of vegetable materials. Evidently it has taken the 
 place of the water. The plant-remains have filled 
 the shallow lake up, and converted it into a peat- 
 moss. In many places you may see this process 
 actually going on still. In such a peat-moss, for ex- 
 ample, as that shown in Fig. 21, it is evident that the 
 little patch of water in the centre is only a remnant 
 of the lake, which once covered the whole hollow. 
 
 FIG 21. Ground-plan or map of a Peat-moss filling up a former lake, and 
 w.th a portion of the lake still unfilled up. 
 
 At the edge of that remaining pool you find that the 
 marshy vegetation out of which the peat has been 
 formed is growing into the water on all sides. Put a 
 pole down to the bottom and you will stir up the fine 
 black or brown peat, formed out of decayed roots 
 and fibres. Here there is still some water between 
 the dead peaty matter at the bottom and the grow- 
 ing plants which form a sort of crust over the top. 
 But in the end the plants will fill up the whole of
 
 66 SCIENCE PRIMERS. [ORGANIC 
 
 this intermediate space, and then even the centre 
 will be converted into a solid bed of peat, as all the 
 outer parts of the moss have already been. 
 
 152. Peat-mosses have been formed in marshy 
 grounds or shallow lakes by the growth and decay 
 of plants, and the accumulation of their remains 
 on the place where they lived and died. Like coal- 
 seams they show how in certain circumstances the 
 growth and decay of plants may give rise to thick 
 and wide-spread deposits. 
 
 II. Rocks formed out of the Remains of 
 Animals. 
 
 153. At first when you think of it, there seems not 
 much chance of animal remains accumulating to such 
 a depth as to form any well-marked deposit. Though 
 the air may be filled with insects, though birds in 
 abundance may be seen and heard as the summer 
 slips away, though in our meadows and woodlands 
 rabbits, hares, moles, and many other creatures live 
 in great numbers, yet you nowhere see their remains 
 forming a deposit on the surface. Nay, you com- 
 paratively seldom see a dead animal at all. They 
 creep into holes and die there, and their bodies 
 gradually crumble away and disappear. But if 
 you look at the right places you will discover that 
 the- remains of animals as well as of plants, and 
 indeed much more than plants, form great accumu- 
 lations. 
 
 154. In the bed of clay under a peat-moss, as 
 described in Art. 148, the shells which are sometimes
 
 ROCKS.] GEOLOGY. 67 
 
 to be seen mouldering away belong to certain kinds 
 which live in lakes. In some parts of the country the 
 bottoms of the lakes are covered with similar shells, 
 so much so that if you were to take a boat and begin 
 to dredge up some of the soft mud from the bottom 
 of one of these sheets of 4 water, you would find it to 
 consist of a kind of white chalky substance, or marl 
 as it is called, made up of shells in all stages of decay. 
 The animals which live in these shells so abound in 
 the water that as they die their shells form a layer 
 over the floor of the lake. Now and then such a lake 
 has been either gradually filled up by being choked with 
 vegetation and silt (Art. 151), or has been drained 
 artificially so as to be converted into dry land. 
 Digging down on the site of that vanished lake 
 you would come to the fresh-water marl, forming a 
 bed or layer several feet, or even yards, in thick- 
 ness. Perhaps you would meet with the skeleton 
 of some deer, or wild ox, or other animal, which 
 had somehow been drowned in the old lake ; or 
 you might disinter the canoe or stone-hammer or 
 other relic of the early human races, which peopled 
 the country before so many of its lakes and forests 
 had disappeared. In some districts where limestone 
 is scarce, the marl of the old lakes has been dug up 
 in large quantities as a manure for the land. Hence 
 you learn that even the frail shells which are to be 
 seen on the stones and reeds along the margin of a 
 lake may afford an illustration of how rocks are formed 
 out of the remains of animals. 
 
 155. It is on the floor of the great sea, however, 
 that the most wonderful examples occur of the way in 
 which rocks are gradually built up from the remains 
 7
 
 68 SCIENCE PRIMERS. [ORGANIC 
 
 of animals to a depth of many hundreds or thousands 
 of feet, and over distances of many hundreds of 
 miles. Something has already been said on this 
 subject in the Physical Geography Primer, Arts. 236 
 and 247 ; where the use of the dredge for the ex- 
 ploration of the bottom of the ocean was referred 
 to, and allusion was made to the fine mud, formed 
 of minute organic remains, and found over most of 
 the bed of the Atlantic Ocean. Let us now consider 
 this mud a little further. 
 
 156. To the west of Britain the Atlantic soon and 
 suddenly deepens. Its floor then stretches away to 
 Newfoundland as a vast plain, the lowest part of 
 which is about 14,000 feet below the waves. It was 
 over this wide sub-marine plain that the Telegraph- 
 cables had to be laid, and hence numerous soundings 
 were made all the way across from Ireland to the 
 American coast (Physical Geography Primer, Art. 
 234). While in the shallower parts of the sea the 
 
 FIG. 22. Some of the Ooze from the Atlantic bed, magnified 25 times. 
 
 bottom was found to be covered with sand, gravel, 
 or mud, from the deeper parts there came up with 
 the sounding-lead a peculiar grey sticky substance 
 known as ooze, which must stretch over that wide
 
 ROCKS. J GEOLOGY. 69 
 
 deep-sea basin for many thousands of square miles. 
 This ooze when dried looks like a dirty kind of chalk. 
 You may purchase a minute quantity of it prepared 
 on a glass slide for the microscope. Looking at such 
 a slide with only your naked eyes, you might suppose 
 that the little specks you see are merely so many grains 
 of dust upon the glass. But place them under a strong 
 magnifying glass or microscope, and you discover that 
 they consist of minute shells called Foraminifera, some 
 of them quite entire, others broken, and all most deli- 
 cately sculptured and punctured (Fig. 22). As you look 
 at these graceful forms, reflect that they are crowded 
 together, millions upon millions, over the floor of the 
 Atlantic, that as they die their shells gather there 
 into a wide-spread deposit, and that as fresh gene- 
 rations spring up one after another this deposit is 
 continually getting deeper. After the lapse of cen- 
 turies, if the deposit were to remain undisturbed, 
 and if we could set a watch to measure its growth, 
 we should find it to have risen upward and to have 
 enclosed the remains of any star-fishes or other sea- 
 creatures which chanced to die and leave their re- 
 mains upon the bottom. Hundreds of feet of such 
 slow-formed deposit have no doubt already been 
 laid down over the bottom of the ocean between 
 Ireland and Newfoundland. Here then* is a second 
 and notable example of how a deep and far-spread 
 mass of rock may be formed out of the remains of 
 animals. 
 
 157. Now return once more to our piece of chalk 
 (Art. 28) and compare it with the ooze of the Atlantic. 
 At the first glance in many a piece of chalk you 
 can see shells, corals, sea-urchins, and other marine
 
 70 SCIENCE PRIMERS. [ORGANIC 
 
 remains, either entire or in fragments (Fig. 23). These 
 are enough to convince you that chalk must have been 
 formed under the sea. But a little further examination 
 will show that the chalk not merely contains animal 
 remains, but is altogether made up of them. If you 
 were fortunate in the piece of chalk, which you treated 
 as recommended in a former Lesson (Art. 28),you found 
 numerous little cases or shells (Fig. 3), quite like those 
 in the Atlantic ooze (Fig. 22), along with fragments 
 of larger broken shells and other remains. The whole 
 
 FIG. 23. A piece of Chalk with shell in it 
 
 of the chalk is evidently made of animal remains, some 
 quite perfect, others so broken and crumbled that you 
 cannot be sure to what kind of sea-creatures they 
 belonged. You must not be disappointed if for a 
 time none of the chalk which you brush off shows 
 you any distinct organism (Art. 132), but only shape- 
 less white grains. All these grains are only the 
 mouldered fragments of organisms, and you must 
 search among them until you find some still perfectly 
 preserved and entire specimens. When successful you 
 will meet with some such assemblage of minute organic
 
 ROCKS.] GEOLOGY. 
 
 remains as shown in Fig. 3, which represents some of 
 the chalk of Gravesend. 
 
 158. But chalk is only one of many rocks composed 
 altogether of the remains of animals. Most of the 
 limestones have been formed out of these materials. 
 Here, for instance, is a piece of limestone (Fig. 24) 
 which has been lying exposed to the air for many 
 
 FIG. 24 Fiece of Limestone, showing how the stone is made up of animal 
 
 years, and you see how its surface is crowded with 
 bits of " stone-lilies," corals, shells, and other re- 
 mains. The sight of such a piece of stone as this 
 at once sets you thinking about some old sea-floor. 
 You can picture to yourselves how all these delicately 
 sculptured little fragments once formed parts of living 
 creatures, which moved or grew beneath the clear 
 waters of the sea. The bit of limestone becomes to
 
 72 SCIENCE PRIMERS. [ORGANIC 
 
 you a kind of model of what a sea-floor must be, and 
 reminds you of what you may even have seen with 
 your own eyes at the bottoms of some of the rocky 
 pools upon the beach. (Art. 114.) 
 
 159. If a little fragment of limestone might suggest 
 these thoughts to you, what would you think if you 
 were taken to places where all the hills are made up 
 of such limestone vast piles of rock two or three 
 thousand feet thick, and stretching over the land for 
 hundreds of square miles ? And yet you may meet with 
 such wonderful masses of limestone crowded with the 
 remains of old sea-creatures, in almost every country of 
 the world. In Britain, for example, the hills and dales 
 of a great part of Derbyshire and Yorkshire are built 
 up of limestone. Looking up one of these wonderful 
 valleys you see the beds of limestone winding along 
 either side and rising in broad terraces, one above 
 the other as far as the eye can reach. In walking 
 along the surface of one of these high hill-terraces, 
 you are really walking on the bottom of an old sea, 
 and if you stop anywhere to look at the rock under 
 your feet, you will see that it is only a mass of the 
 crowded remains of the little animals which peopled 
 the waters of that sea. Somehow the sea-bed has 
 become dry land, and the thick animal deposits of its 
 bottom have hardened into limestone, out of which 
 high hills and wide valleys have been formed. 
 
 1 60. Still thicker masses of similar limestone occur 
 in Ireland. Some of the giant mountain chains of the 
 world consist in great measure of limestone. Among 
 the lofty crests of the Alps, for example, and in the 
 chain of the Himalaya, limestone, made up of the 
 remains of marine animals, is found to constitute great
 
 ROCKS.] GEOLOGY. 73 
 
 ranges of the high ground on which the eternal snows 
 rest and from which the glaciers descend into the 
 valleys. 
 
 161. Summary. Before advancing further you 
 may now look back upon what you have learnt, and see 
 exactly the point to which you have come. If I were 
 to ask you to make a short abstract of the foregoing 
 lessons you would probably jot down such a summary 
 as the following : 
 
 (i.) The surface of the land is worn away by rain 
 and by streams, and a vast deal of mud, sand, and 
 gravel is consequently formed. 
 
 (2.) This material worn from the land accumu- 
 lates at the mouths of rivers, in lakes, and over the 
 floor of the sea, so as to form great deposits, which 
 will in the end harden into Sedimentary Rocks. 
 
 (3.) Leaves, twigs, trunks, and other parts of plants, 
 together with the remains of animals, become im- 
 bedded and preserved as Fossils in these sedimentary 
 accumulations. 
 
 (4.) Plants and animals of themselves sometimes 
 form thick and extensive deposits upon the surface 
 of the earth. 
 
 (5.) The rocks of which the dry land is made have 
 been formed, for the most part, under the sea. 
 
 (6.) Old land-surfaces which, like the coal-seams, 
 once spread out into luxuriant forests, are now buried 
 deep beneath the present surface under masses of 
 solid rock. 
 
 162. You have advanced step by step to these con- 
 clusions, and are quite sure of them, for you have 
 tested everything on the way. Again and again you 
 have met face to face with proofs that in some way
 
 74 SCIENCE PRIMERS. [IGNEOUS 
 
 or other land and sea have often changed places. 
 You have found old sea-bottoms even up among the 
 crests of the mountains. You have found old forests 
 buried in the form of coal-seams deep in the bowels of 
 the earth. How can these wonderful changes have 
 taken place ? To be able to answer this question you 
 must find out something about the history of the third 
 of the three great groups into which we divided the 
 stones of the earth the Igneous Rocks. 
 
 IGNEOUS ROCKS. 
 I. What Igneous Rocks are. 
 
 163. Turning back to one of the early Lessons of 
 this book (Art. 44), you find that we divided stones 
 into three great classes, of which the third was named 
 the Igneous class. This word igneous, means literally 
 fiery. It does not very accurately describe the rocks 
 to which it is applied, but it has long been in use 
 to include all rocks which have been actually melted 
 within the earth, or which have been thrown out at the 
 surface by the action of volcanos. So that the Igneous 
 Rocks owe their origin to some of the effects of the 
 internal heat of the earth, about which you have 
 already learnt something (Physical Geography Primer, 
 Arts. 252 265), and must now learn more. 
 
 164. The first thing to occur to you when you begin 
 to search for examples of igneous rocks, will probably 
 be the fact that they are by no means so abundant 
 as the other two great classes of rocks. Take Great 
 Britain as an illustration. If you traversed the 
 country from end to end, you would meet everywhere 
 with rocks belonging to the Sedimentary, and the
 
 ROCKS.] GEOLOGY. 75 
 
 Organic series. But you would travel over con- 
 siderable spaces without meeting with any of the 
 Igneous class. The whole of that part of England, 
 for example, which lies to the south-east of a line 
 drawn from Lyme Regis, by Leicester, to Flamborough 
 Head, contains not a single mass of igneous rock. 
 And yet were you to cross over into North Wales, or 
 Cumberland, or the midland valley of Scotland, you 
 would find rocks of that kind in abundance, protruding 
 through the surface, and forming many of the highest 
 and most picturesque hills and crags in these parts of 
 the island. So that though igneous rocks are not 
 universally diffused, they occur abundantly enough 
 in many places. Even in so small a space as Britain 
 they are plentiful ; they are likewise to be met with in 
 most parts of the world. They have a very curious and 
 important history, and hence it is desirable that you 
 should know what they really are, and how you 
 could recognize them. 
 
 165. In the account given of volcanos in the Physical 
 Geography Primer (Art. 258) you will find that the 
 solid materials cast up by volcanos were stated to be 
 of two kinds ist, streams of molten rock called lava 
 poured down the sides of a volcanic mountain 
 during an eruption ; and 2nd, immense quantities of 
 dust, sand, and stones, cast up into the air from 
 the mouth of the volcano, and falling down upon the 
 mountain, sometimes even all over the surrounding 
 country for a distance of many miles. 
 
 1 66. Here then are two very dissimilar kinds of rock- 
 material discharged from the interior of the globe. 
 The lava cools and hardens into a solid rock. The 
 loose ashes and stones, likewise, are in time pressed
 
 76 SCIEXCE PRIMERS. [IGNEOUS 
 
 and hardened into more or less firm beds of stone. So 
 that two totally distinct kinds of rock are laid down 
 upon the surface of the earth by the volcano. In the 
 case of the lava, the rock, if you look at it with a 
 magnifying glass, is seen to be made up of distinct 
 crystals all matted together. The beds of ashes, on 
 the other hand, no matter how compact they may 
 have become, are found to be made up of irregu- 
 lar fragments of various kinds of stone, and of all 
 sizes, from the finest dust up to big blocks. By 
 attending to this very simple and intelligible differ- 
 ence you could arrange igneous rocks into two great 
 
 FIG. 25. Piece of Lava, showing the crystals and the steam-holes. 
 
 groups ist, the Crystalline, that is, those which 
 are made up of crystals, and which have once been 
 in a melted state ; and 2nd, the Fragmental, that 
 is, those which consist of the loose materials thrown 
 out during volcanic explosions. 
 
 167. i. Crystalline Igneous Rocks. The 
 piece of Granite which we have examined (Art. 26) 
 is an example of one form of the rocks of this class. 
 We have seen how greatly it differs from such rocks 
 as sandstone or chalk. But there are many other 
 varieties of crystalline igneous rock. In Fig. 25, for 
 example, one of these varieties is drawn. It is a
 
 ROCKS.] GEOLOGY. 
 
 fragment broken from a current of lava which in a 
 molten state ran down the side of a volcano. You 
 observe the little angular crystals, some of them 
 black and large, others mere white specks in the 
 general mass of the stone. But besides the crystals 
 
 FIG. 26. View of the north side of the volcanic cone of the Island of Vol- 
 cano, showing a stream of black lava which has not flowed down to the 
 bottom of the slope. 
 
 you notice a number of rounded holes or cavities, as 
 if little water-worn pebbles had fallen out of the 
 rock. When the rock was still melted it was full of 
 imprisoned steam and gas which were constantly 
 striving to escape to the surface. It was this steam
 
 SCIENCE PRIMERS. 
 
 [IGNEOUS 
 
 which collected into little bubbles and formed the 
 curious set of holes in the mass of the still molten 
 rock. In the same way the holes which you often 
 see in the heart of a loaf of bread were formed by 
 the struggles of the steam to escape from the dough 
 as it was heated in the oven. 
 
 1 68. All lava belongs to this class of rocks. One 
 or two pictures may serve to show you some of the 
 more simple and striking features of these lava 
 
 FIG. 27. View of Lava-stream issuing from one of the extinct volcanic cones 
 of Auvergne, in Central France. (Scrope.j 
 
 masses. In Fig. 26, a drawing is given of part of 
 the Island of Volcano, in the Mediterranean, in which 
 you will see how the lava has risen up the inside or 
 throat of the volcanic hill to the edge of the crater 
 (see Physical Geogeraphy Primer, Art. 256), and run 
 down the outside of the slope. When that took 
 place the lava was of course thoroughly molten 
 like liquid iron, and hardened as it cooled in 
 moving. You observe that it has not been able to
 
 ROCKS.] GEOLOGY. 79 
 
 reach the bottom of the hill. It was in truth a 
 very small stream, cooling and hardening before it 
 got even down to the foot of the slope. But look 
 now at Fig. 27. You there perceive that a much 
 more copious stream of lava has issued, that one 
 side of the volcanic cone has been broken down so 
 as actually to let you see into the crater, and that 
 the lava has burst out, and poured down the sloping 
 ground. Thus, each outburst of lava is the escape 
 of a river of molten rock from the top or the side 
 of "a volcano. Like an ordinary river of water, it 
 of course sweeps into the readiest hollow or valley 
 it can reach, so that round an active volcano the 
 valleys often get quite filled up and buried under 
 the vast sheets of lava which are poured out. Like 
 rivers, too, the streams of lava vary greatly in size. In 
 Fig. 26, you see one which was too feeble to reach the 
 base of the hill, but in the famous eruption of Skaptar 
 Jokul, Iceland, in the -year 1783, two enormous 
 streams were poured out, one of them flowing to a 
 distance of forty-five, and the other of forty miles. 
 They ranged from less than seven to twelve or fifteen 
 miles in breadth, with a thickness of a hundred, and 
 sometimes in confined valleys even six hundred feet. 
 
 169. If you paid a visit to any ordinary stream of 
 lava after it had come to rest and cooled, you would find 
 its surface to be an irregular accumulation of rough 
 black or dark brown fragments very like the <; slags " 
 or "clinkers" from a furnace. Down below this 
 rough surface the rock is more compact, usually dark 
 in colour, containing various crystals scattered through 
 its mass, and often full of holes, as shown in Fig. 
 25. In some cases the lava as it grew solid has
 
 8o SCIENCE PRIMERS. [IGNEOUS 
 
 assumed a curious and beautiful internal arrange- 
 ment into columns. The pillars of Fingal's Cave 
 in Staffa, and of the Giant's Causeway in Antrim, 
 have been produced in this way. At both of these 
 places the rock was once a molten lava. As it grew 
 cold and solid it contracted, and in so doing became 
 divided into these regular columns. You might imitate 
 
 
 of the Island of Staffa, with Fingal s Cave. 
 
 this arrangement by putting starch in warm water, 
 stirring it well round, and then letting it stand. By 
 degrees you would observe that as the starch grows 
 solid it assumes an internal columnar arrangement, 
 not unlike the basalt. 
 
 170. Next let us see where rocks of this kind are to 
 be met with. Of course you would expect to find them
 
 ROCKS.] GEOLOGY. Si 
 
 round the flanks of an active volcano. And indeed, 
 at most volcanos, as Vesuvius or Etna, or those of 
 Iceland, they abound. But you would trace them too 
 round volcanos no longer in activity, as for example 
 in that part of Central France where the extinct 
 volcanos occur of which one is drawn in Fig. 27. 
 And as you travelled over the world, you would 
 recognize them in hundreds of places where no volcanic 
 eruption has ever been known since human history 
 began. In fact they would be the witnesses to you 
 of where old volcanos had once been at work. In 
 this way by learning how to detect these forms of 
 ancient lava, you would be able to prove that there 
 had been volcanos in very far distant times in dis- 
 tricts where there are now busy cities or fertile fields. 
 
 171. For example, though no active volcanos exist 
 in Great Britain at the present day, they can be shown 
 to have often broken out here in olden times, long 
 before man appeared upon the earth. Some of the 
 oldest traces of volcanic action are to be met with 
 in North Wales, where not a few of the lava-beds 
 form prominent features in the scenery of that rugged 
 district. Much younger are the sheets of various 
 ancient lavas which stretch across the middle of 
 Scotland, and there compose most of the hills. But 
 the latest of the British volcanos were those which 
 ranged in a long line from Antrim in Ireland, through 
 the Western Islands, and away north by the Faroe 
 Islands into Iceland. The vast terraced mountains 
 of Antrim, Mull, Skye, and Faroe have been built up 
 of piles of lava-sheets. 
 
 172. But there are other crystalline igneous rocks 
 besides those which come to the surface and flow out
 
 82 SCIENCE PRIMERS. [IGNEOUS 
 
 there as molten lava. Granite, for example, which we 
 have already examined (Art. 26), is an admirable illus- 
 tration of the crystalline character. But instead of 
 coming to the surface to cool there, granite appears to 
 have crystallized and cooled deep down beneath great 
 masses of other rocks. Yet it now forms bare, naked, 
 lofty mountains. Many of the Scottish Highland hills 
 for example, as Ben Nevis, Ben Macdui, and Cairn 
 Gorm, consist of granite. It rises high, too, in the 
 centre of the chain of the Alps. Granite often sends 
 out veins into the rocks which lie above and around 
 it. It could not have done this unless it had been in 
 a fluid or pasty state. 
 
 173. But you may ask, if granite has not crystallized 
 at the surface, but under masses of other rocks, how 
 does it come to be at the surface now, and not there 
 only, but even forming the crests of bare lofty moun- 
 tains ? This question is not quite so easy to dispose 
 of, but you will probably be able to see how it is to 
 be answered after you have come to that portion of 
 these Lessons which treats of what is called the Crust 
 of the Earth. (See Art. 239.) 
 
 174. 2. Fragmental Igneous Rocks. The 
 piece of stone represented in Fig. 29 is a fragment 
 from a bed of consolidated volcanic ashes. You 
 notice that it is made up of irregular and angular frag- 
 ments. These are little bits of lava and other rocks 
 which have been blown into the air by the discharges 
 of the volcano. You observe too that when they fell 
 to the ground and accumulated above each other there 
 they took a stratified form. That layer of coarse frag- 
 ments at the bottom points to a shower of coarservol- 
 canic ashes, while the layers of smaller fragments above
 
 ROCKS.] 
 
 GEOLOGY. 
 
 show how showers of finer dust afterwards fell through 
 the air. Now this is the kind of material under which 
 the old Roman city of Pompeii was buried (Physical 
 Geography Primer, Art. 259). It fell upon the streets 
 and houses and gradually covered them up as the 
 eruption of the neighbouring volcano continued. 
 And at this day when they excavate the ruins, the 
 workmen find the streets and chambers all choked up 
 with layers of coarser and finer volcanic ash and 
 dust arranged just as you see in Fig. 29. 
 
 FIG. 29. Piece of Volcanic Tuff a rock formed of consolidated Volcanic 
 ashes. 
 
 175. Of course if the volcanic ashes fell over the 
 sea or a lake they would settle down beneath the 
 water and form deposits there. They might cover 
 up and preserve, too, the remains of any plants or 
 animals which might be lying on the bottom at the 
 time of the eruption. This has often happened in 
 past times. In the mountain of Snowdon in Wales, 
 for example, many hundreds of feet of such consoli- 
 dated volcanic dust still exist, and on examining this 
 material you may still pick out shells and other marine 
 organisms which show that the volcanic materials 
 fell into the sea. Again in Scotland many beds of
 
 8a SCIENCE PRIMERS. [IGNEOUS 
 
 similar nature are found lying among seams of coal. 
 These masses of consolidated volcanic dust and 
 stones are known by the name of TufI 
 
 II. Where Igneous Rocks come from. 
 
 176. If I ask you from what source the Igneous 
 Rocks have been derived, you will reply that they 
 have come up from the intensely hot regions within 
 the earth. In the Physical Geography Primer (Arts. 
 252 265) some account is given of the inside of the 
 earth, and of the proofs that it has a high temperature. 
 I need not remind you what a very little part of the 
 outer portion of our planet we can actually see, even 
 from the top of the highest mountain to the bottom of 
 the deepest mine. Let us go over in this Lesson a little 
 more in detail the evidence for the great heat of the 
 earth's interior, and the connection between that heat 
 and certain movements and changes at the surface. 
 
 177. Deep Borings and Mines. If you were 
 taken down to the bottom of a deep mine in England 
 you would find the temperature much warmer there 
 than near the surface, and a similar increase of heat 
 would meet you in the deep mines of every country 
 in the world. You would soon discover, too, that on 
 the whole the deeper the mine the greater the warmth 
 would be. In the same way were you to bore a deep 
 narrow hole into the earth for several hundreds of 
 feet and let a thermometer down to the bottom, you 
 would find that the mercury would rise in the tube. 
 
 178. Experiments of this kind have been made all 
 over the globe, with the result of showing that after we 
 get down for a short and variable distance below the 
 surface, we reach a temperature which remains the
 
 ROCKS.] 
 
 GEOLOGY. 
 
 same all the year, and that underneath that limit the 
 temperature rises about i Fahrenheit for every fifty 
 or sixty feet of descent. If this rate of increase con- 
 tinues we should get uncomfortably hot before having 
 descended very far. For instance, at a depth of 
 about two miles water would be at its boiling-point, 
 
 of Hot Springs or Geysers, Iceland. 
 
 and at depths of twenty-five or thirty miles, the metals 
 would have the same temperatures as those at which 
 they respectively melt on the surface of the earth. 
 It is clear from this kind of evidence that the inside of 
 our planet must be in an intensely heated condition.
 
 86 SCIENCE PRIMERS. [IGNEOUS 
 
 177. Proofs of another kind lead to the same con- 
 clusion. The city of Bath has long been famous for 
 its wells. Now these come out of the earth at a tem- 
 perature of 120 Fahr., that is, rather hotter than the 
 water is usually made in a hot bath. And this warm 
 water has been rising to the surface and flowing to the 
 sea ever since the Romans were in this country, and 
 probably long before that. In many other parts of 
 
 FIG. 31. Vesuvius, as it appeared at the beginning of the Christian Era, 
 when it was a dormant volcano. 
 
 the world similar Hot Springs occur. Iceland, for 
 example, furnishes some remarkable examples called 
 Geysers, where at intervals the boiling water and steam 
 rush out with a great noise, and rise high into the 
 air (Fig. 30). To keep up such hot springs in every 
 quarter of the globe there must assuredly be great 
 stores of heat within the earth. 
 
 1 80. Neither the heat of deep mines nor of hot 
 springs affords such an impressive lesson as to the
 
 ROCKS.] 
 
 GEOLOGY. 
 
 earth's internal high temperature as is furnished by 
 Volcanos. The hot vapours and steam which rise 
 from the craters of volcanos, the torrents of hot water 
 which sometimes issue from their sides, the streams 
 of molten lava which break out and roll far down the 
 slopes of a volcanic mountain, burning up and burying 
 trees, fields, gardens, and villages are all tokens of 
 
 
 FIG. 32. Vesuvius as it appears at the present time an active volcano. 
 
 the intense heat of the inside of the earth from which 
 they come. 
 
 1 8 1. At the present time there are, it is said, about 
 270 volcanos either constantly or at intervals throwing 
 out steam, hot ashes, and lava, in different parts of the 
 globe. You will comprehend how widely they are 
 distributed if you again take a map of the world and 
 note upon it the lines of active volcanos (see Phy- 
 sical Geography Primer, Art. 260). First of all, down 
 the whole line of the mountains which range along 
 the western margin of the American continent, vol-
 
 88 SCIENCE PRIMERS. [IGNEOUS 
 
 canos are numerous, some of them of vast height 
 like Cotopaxi (18,877 feet). From the northern ex- 
 tremity of America they extend, by way of the Aleutian 
 Islands and Japan, to the Malay Archipelago, where 
 in Java they greatly abound. From that point they 
 may be traced at wide intervals into New Zealand on 
 the one hand, and on the other through the centre of 
 Asia by way of the Red Sea and the Mediterranean, 
 up to Iceland and down to the Azores, and thence 
 across to the West Indies and the centre of America. 
 Even among the perpetual snows of the South 
 Polar regions they have been met with, and also 
 far within the Arctic Circle at the Island of Jan 
 Mayen. 
 
 182. But besides these volcanos which are still active, 
 many others occur from which no eruptions have ever 
 been seen to take place, and which are therefore called 
 dormant or extinct (see Figs. 27 and 31). If you 
 were to put down upon a map the position of every 
 volcano which either now or at some past time has 
 given out hot gases, steam, ashes, or lava, you would 
 probably find very few large areas of the earth's surface 
 in which no trace of volcanic action can be found. 
 Britain, for instance, is now wholly free from any vol- 
 canic disturbance, and yet, as already pointed out 
 (Art. 171), you would need to mark many places on 
 the map of this country as having once been the scene 
 of long-continued volcanic eruptions. You would 
 have to put some dots upon the map round Exeter 
 to mark the position of some ancient volcanos ; a 
 good many in Wales, some in Derbyshire, and others 
 in Cumberland. You would have to cover almost all 
 the centre of Scotland with such dots, for that region
 
 ROCKS.] GEOLOGY. 
 
 is full of volcanic rocks, and in Ireland too there 
 would be a good many scattered marks. 
 
 183. In this way you would come to see how uni- 
 versal volcanic action has* been, on the whole, over 
 the globe, and therefore how powerfully and general. y 
 the heat of the interior has manifested itself at the 
 surface. 
 
 184. But in igneous rocks you do not see the only 
 evidence of how the internal heat affects the surface 
 of the earth. There can be little doubt that Earth- 
 quakes (Physical Geography Primer, Art. 262) must 
 be mainly due to commotions which take their origin 
 from the effects of this heat. 
 
 185. Perhaps you will ask, why, since the inside of the 
 planet is so hot, does it not melt the outside, or at least 
 why is the outside not warmer ? There can be no 
 doubt that, at one time many millions of years ago, the 
 globe was immensely hotter than it is now. In fact it 
 then resembled our burning sun, of which it once pro- 
 bably formed a part, and from which it and the other 
 planets were one by one detached. During the vast 
 interval which has passed away since then it has been 
 gradually cooling, and thus the heat in the inside is 
 only the remains of that fierce heat which once marked 
 the whole planet. The outer parts have cooled and 
 become solid, but they are bad conductors of heat, 
 and allow the heat from the inside to pass away into 
 space only with extreme slowness (Physics Primer, 
 Arts. 64, 65). Hence, in spite of the high tempera- 
 ture of the interior, we are not sensible that it warms 
 the outer surface of the earth. 
 
 1 86. To illustrate this point suppose that you could 
 see a volcano in the very act of pouring a great
 
 90 SC1EXCE PRIMERS. [THE CRUST 
 
 stream of molten lava down its slopes. At first the 
 torrent would be at a white heat, glowing so fiercely 
 that you could hardly keep your eyes upon it. But 
 a few yards below the point from which it emerged 
 it would begin to assume a reddish hue, which would 
 get duller and darker, just as a live coal does when 
 'it falls from the grate upon the hearth, and the 
 surface of the lava would at the same time get cool 
 and solid so quickly that in a few days you might 
 stand upon it, even though it was still red hot only a 
 foot or two below. You might come back to it a 
 dozen of years afterwards. Its surface would be per- 
 fectly cold a mere rough sea of black bristling lumps 
 of rock and yet down in the depths of the mass the 
 rock would be still hot, and you might even meet with 
 cracks from which the heat escapes along with wreaths 
 of steam, and where therefore you could not hold your 
 hand without having it burnt. Now if a mere river of 
 lava takes so long to cool down to its centre, you can 
 realize perhaps why it is that the huge mass of our 
 globe should still be intensely hot inside even though 
 its outer portions have been solid and cool for long 
 ages. 
 
 187. You are already familiar with the fact that 
 bodies expand when they are heated, and contract as 
 they cool (Physics Primer, Art. 49). When the earth 
 was vastly hotter than now it must also have filled 
 more space. While cooling it has been contracting. 
 As it is still cooling it must be still contracting, but so 
 slowly that on the whole we are not sensible of the 
 process. But some of the effects are visible enough 
 among the rocks. The contraction could not fail to 
 cause an enormous pressure or strain on the outer
 
 OF THE EARTH.] GEOLOGY. 91 
 
 parts, which, since they are made of such very various 
 materials Sedimentary, Organic, and Igneous Rocks 
 would yield to the stress more in some places than 
 in others. And thus, somewhat like the skin of a 
 dried and shrivelled apple, the surface of the globe 
 would be ridged up in one region, or would sink down 
 in another, besides being squeezed and broken. What 
 evidence we have for all this will be told in the next 
 Lessons. 
 
 THE CRUST OF THE EARTH. 
 
 I. Proofs that parts of the Crust have been 
 pushed up. 
 
 1 88. We have now completed the first part of the task 
 which was proposed in an earlier Lesson (Art. 7) 
 to find out what the materials are of which the great 
 stone floor of the earth is made. We have learnt 
 something about three great classes of rocks which 
 form. that floor how they were made, and where they 
 are -to be seen. But while learning these facts about 
 the earth, we have seen that the rocks are not a 
 mere thin covering like a wooden floor below which 
 we should come to something quite different. We 
 cannot get down beneath the rocks. Deep as the 
 deepest mine the same kind of rocks may be found 
 which elsewhere exist at the surface. It is always 
 through rock of some kind that we must descend as 
 far as we can penetrate into the bowels of the earth. 
 
 189. This solid rocky outer part of the earth on which 
 we live, into which men sink mines and out of which 
 springs arise, is called the Earth's Crust. This
 
 92 SCIENCE PRIMERS. [THE CRUST 
 
 name came into use when people supposed that all 
 the inside of the planet was an intensely hot liquid 
 mass with a cool and comparatively thin crust outside. 
 A great deal of dispute has arisen as to whether the 
 main mass of the inside of the earth is liquid or 
 solid, but those who dispute, whatever their view may 
 be, agree to use this phrase the Earth's Crust as 
 meaning that part of the earth which men can observe 
 from the top of the highest mountain to as far below 
 the deepest mine as they can reasonably infer what the 
 rocks must be. 
 
 190. The rocks of which this crust consists belong 
 mostly to the Sedimentary series, a large number to the 
 Organic series, and a smaller, but still considerable 
 proportion, to the Igneous series. In Britain, for 
 example, if we could put all the different series of 
 sedimentary and organic rocks together, one above 
 another, in the order in which they were deposited, 
 they would form a mass at least ten or twelve miles 
 thick. Out of such materials the solid earth is built 
 up as far down into its depths as man has been, able 
 to descend. 
 
 191. But from what has been stated in previous 
 Lessons it is clear that many of these rocks are not 
 now in their original positions. Our quarry, for ex- 
 ample (Art. 119), told us how the rocks in which it 
 lay had once formed a part of the sea-bottom. Then 
 again the coal-seams, buried so deep in the earth, were 
 once verdant forests or jungles at the surface (Art. 
 139). How could a sea-floor become dry land, and how 
 could a forest on the surface of the land come to be 
 covered by hundreds of feet of solid stone ? 
 
 192. Let us begin by considering how it is that a
 
 OF THE EARTH.] 
 
 GEOLOGY. 
 
 93 
 
 portion of the floor of the sea can be changed into good 
 dry land. And in order to follow the change as clearly 
 as possible we shall choose one of the simplest ex- 
 amples, and one moreover which many of us may 
 have the opportunity of verifying for ourselves. 
 
 193. Round the coast-line of some parts of the British 
 Islands there runs a low flat terrace bounded by the 
 sea on the one hand and by a cliff or inland slope 
 
 FIG. 33. View of a R; 
 
 on the other. Seaport towns have been built upon 
 this terrace, such for instance as parts of Glasgow, 
 Greenock, and Leith. It is so level that roads run 
 along its surface for miles among cornfields, meadows, 
 and villages. You may gather some notion of its 
 general appearance from Fig. 33, which shows how flat 
 it is and how little elevated above the sea at its
 
 94 SCIENCE PRIMERS. [THE CRUST 
 
 outer edge. Along its inner margin there often rises 
 a line of cliff pierced with caves, as represented in the 
 drawing. If you were standing on some part of this 
 terrace and looking along its level surface as it winds 
 in and out against the cliffs and slopes of the land, 
 would not the idea of an old coast-line at once 
 suggest itself to your mind ? You can without diffi- 
 culty picture the sea covering that terrace and beating 
 against the base of those cliffs and slopes. 
 
 194. Could you prove this fancy of yours to be any- 
 thing more than a fancy ? Let us see. Cross to the 
 inner margin of the terrace and consider attentively the 
 line of caves you find there. How did these excava- 
 tions come to be drilled into the solid rock all along the 
 same line and exactly at the same level, so that the 
 floor of each of them should just open upon the flat 
 terrace? Suppose that you visit one of these caves. 
 Festoons of ivy and honeysuckle hang perhaps in 
 tangled luxuriance about its mouth, and you may have 
 to force your way through a brushwood of strong 
 briars. But you gain at last the floor of the cave, 
 which you find to be roughened with rounded, water- 
 worn stones. The roof is partly hung with ferns, 
 mosses, and liverworts, and the sides too have their 
 drapery of green. But the bare rock appears abun- 
 dantly, and you notice that it has been rubbed smooth, 
 and has the same water-worn character as the stones 
 under your feet. Now go outside and look at the 
 bare rocks of the cliff above ; you see how rough and 
 sharp-edged they are, as from time to time they split 
 up under the influence of the weather. The walls of 
 the cave have been ground smooth from one cause, 
 the face of the cliff has been made rough from another.
 
 OF THE EARTH.] GEOLOGY. 95 
 
 195. The explanation of this difference will be appa- 
 rent if you remember what takes place where a sea- 
 cliff of hard rock has its base washed by the waves 
 (Arts. 7375). You have seen how the rocks, wherever 
 the waves can reach them, are worn smooth by the 
 ceaseless grinding of the gravel and stones to and fro. 
 And every cave into and out of which the waves drive 
 the gravel is ground down in the same way. A single 
 forenoon spent on such a coast-line gives you a lesson 
 you can never forget as to the way in which rocks have 
 their surfaces smoothed by the waves. But all which 
 lies above the reach of the breakers comes under the 
 influence of other forces. Rain, frost, and springs com- 
 
 P resent ocach / . . . ?-^~^-^-~ r ~T~^~- 
 
 FIG. 34. - Section of a Raised Beach. 
 
 bine to make the cliff crumble down, and fragments to 
 split off from its face so as to give that rough angular 
 appearance which contrasts so well with the water- 
 worn rocks below. 
 
 1 96. After having observed in this way what is taking 
 place now along a sea-cliff, you can hardly doubt that 
 the line of cliff which rises from the inner margin of our 
 terrace was once a sea-cliff too, with the waves beating 
 against its base and boring that line of caves there, 
 as they are still doing elsewhere. The line of that 
 cliff thus becomes in your mind the line of a former 
 sea- shore.
 
 96 SCIENCE PRIMERS. [THE CRUST 
 
 197. But further proofs of the former presence of the 
 sea present themselves if you put questions to the terrace 
 itself. Dig beneath the surface of that terrace any- 
 where, and what do you find it to consist of? Sand 
 and gravel, sometimes with abundance of shells. Look 
 at the outer margin of the terrace where the sea \-> 
 gradually cutting it away, and you find there that the 
 sand and gravel are laid down in layers, just as they 
 are on the beach below, and that the shells belong to 
 the common kinds which are washed up by every tide 
 upon the sands. You discover that in truth the terrace 
 is simply an old beach, and that the sea must have 
 laid down the materials of the terrace when it was 
 scooping out the caves at the foot of the cliff. Thus 
 the terrace and the caves combine to prove a change 
 in the coast-line. 
 
 198. By measuring the height of the floor of the 
 caves and the height of the terrace above the present 
 high-water mark, you would ascertain the difference 
 of level between the present beach and the old one. 
 Let us suppose that this difference is in the present 
 case twenty feet ; it is plain that the land must have 
 risen, or the sea must have sunk, to the extent of 
 twenty feet. 
 
 199. When you watch the restlessness of the sea, with 
 its ebbing and flowing tides, its waves and currents, 
 and then when you contrast with this ceaseless motion 
 the calm steadfastness of the land, you may naturally 
 suppose that, in any changes of the relative position 
 of land and sea, it is much more likely that the sea 
 should have shifted its place than that any alteration 
 should have happened to the land. But reflect for a 
 moment on what would be involved in a change in
 
 OF THE EARTH.] GEOLOGY, 97 
 
 the sea-level at any place. If I deepen the bottom 
 of one end of a pond, does the level of the water fall 
 just over that part where I have been at work? 
 Assuredly not : the level of the whole pond is lowered. 
 Tn the same way, if I empty a quantity of stones and 
 earth so as to make one part of the pond very much 
 shallower, do I raise the level of the water only over 
 that part ? By no means : the influence of what I 
 have been doing extends through every part of the 
 pond, and the level of the water is uniformly raised 
 over the whole. 
 
 200. Now instead of the pond, think of the great 
 ocean, which is only an enormously large continuous 
 sheet of water. You see that an alteration of its level 
 in one region must necessarily extend over the whole 
 globe, until the same general uniformity of level is re- 
 stored. If the sea has sunk from our terrace (Figs. 33, 
 34) to the extent of twenty feet, there must have been 
 at the same time a general lowering of the sea-level 
 all over the world. But is it so? How would you 
 set about to ascertain this point ? 
 
 201. Plainly if the terrace has been left by a 
 sinking down of the bed of the sea, you should meet 
 with a corresponding terrace all over the globe. 
 But you would not require to travel far before you 
 ascertained that no such universal terrace is to be 
 seen. Even around the coast of Britain you would 
 find enough to show you that there has not been any 
 general subsidence of the ocean. Throughout a great 
 part of the margin of our island no terrace occurs at 
 all. Only in certain districts is such a terrace to be 
 met with, and its height is not always the same. 
 
 202. Sometimes a series of terraces maybe seen rising
 
 98 SCIENCE PRIMERS. [THE CRUST 
 
 one over another, each marking a former coast-line. 
 In the north of Norway they occur in great perfec 
 tion (Fig. 35), up to heights of several hundred feet. 
 They look perfectly horizontal to the eye, yet when 
 they are measured accurately they are found some- 
 times to rise towards the upper end of the long inlets 
 on the sides of which they run, so that a terrace 
 which at the sea-ward end may stand at a height 
 of 80 feet above the sea, is as much as 90 or 100 
 
 
 FIG. 35. Terraces [Raised Beaches) of the Alien Fjord, Norway. 
 
 feet at the land-ward end. Now such a difference 
 of level in a short distance proves that something 
 else must have taken place than a mere subsidence of 
 the sea, for had that been the cause of the terraces 
 being left, they should all have been as horizontal as 
 the surface of the sea itself, and at least traces of 
 them should have been found at corresponding heights 
 in our own country and all over the world.
 
 OF THE EARTH.] GEOLOGY. 99 
 
 203. Strange as it may seem to you, it is nevertheless 
 true, that it is the land which rises, not the sea 
 which sinks. If that be the case, it is easy to see how 
 there should be terraces in some countries and not in 
 others, and how the same terrace should vary in 
 height at different parts of its course. For the land 
 may have been pushed up at one place and not in 
 others, and more at one place than in another. The 
 old sea-terrace (Fig. 33) is called a Raised Beach, 
 because it consists of gravel, sand, and other beach 
 deposits, which have been raised above the level of 
 the sea. Every such raised beach points to a former 
 sea-margin, and to an elevation of that sea-margin 
 into dry land. Where a great many terraces occur 
 one above another, as in Norway (Fig. 35), they show 
 us how the land has been raised up at intervals for a 
 long period, the time when the land was stationary 
 between two upheavals being marked by a terrace or 
 raised beach. Of course the highest terrace must 
 needs be the oldest, and for that reason is often less 
 perfect than the newer ones, having suffered more 
 from the various forces such as rains, frosts, and 
 streams, which are so busy in making the surface of 
 the land crumble away. (Physical Geography Primer. 
 Art. 126.) 
 
 204. In some parts of the world we can detect 
 the ground in the very act of rising. In the south- " 
 east of Sweden, for example, rocks have been marked 
 at the place where high-water reached them, and in 
 the course of years have been found to be consider- 
 ably above their former level. From observations of 
 this kind it has been inferred that the land there is 
 rising at the rate of about two or three feet in a century.
 
 ioo SCIENCE PRIMERS. [THE CRUST 
 
 This appears to be but a very slow movement, too 
 slow to be appreciated, except by careful measure- 
 ment ; and yet if it were to go on for another thou- 
 sand years, what is now the beach would have risen 
 to a height of twenty or thirty feet above the sea- 
 level. 
 
 205. You see, then, that the upraising of the bottom 
 of the sea, strange as it may seem to us, is not entirely 
 a thing of the past. It is going on slowly at the pre- 
 sent time in several parts of the globe. And just as 
 the coast of Sweden is rising with no violence or 
 shock, so in old times the upraising of the sea-bed 
 into dry land may have been a gentle and quiet 
 process. 
 
 206. The rocks of every country furnish abundant 
 evidence that the sea-bottom has again and again 
 been elevated into land. This evidence is furnished 
 as you now know, chiefly by the remains of corals, 
 star-fishes, shells, and other sea-creatures, which may 
 be traced imbedded in the rocks. The height at 
 which these remains are found affords us some idea 
 of the extent of the elevation. The shells of our 
 raised beach (Art. 197) indicated a rise of only some 
 twenty feet. But if you found such sea-shells at a height 
 of twenty thousand feet they would prove that the bed 
 of the sea had been elevated at least to that extent 
 (Art. 128). By this kind of evidence it can be shown 
 that by much the greater part of the dry land has been 
 raised, piece by piece, out of the sea, and that the 
 movements have been far from regular or uniform, 
 seeing that some parts have been upheaved to a 
 much greater height than others.
 
 OF THE EARTH.] GEOLOGY. 
 
 II. Proofs that parts of the Crust have 
 sunk down. 
 
 207. We have now traced out some facts which show 
 that the surface of the globe has from time to time 
 been pushed up, so that parts of the sea-bottom have 
 become dry land. But other movements of exactly 
 an opposite kind have turned parts of the land into 
 the bed of the sea. Let us follow some ' of the evi- 
 dence for these depressions, and take, as before, our 
 illustrations from places which are easily visited, and 
 in our own country. 
 
 208. Along some parts of the coast-line of Britain, 
 as for example on the coasts of Devon and Cornwall, 
 and on that of the Firth of Tay, a very curious and 
 interesting feature occurs between high and low-water 
 mark. From the flat sandy surface of the beach a 
 number of dark stumps may be seen sticking up, which 
 on closer examination prove to be the lower ends of 
 
 LOW WATER MARK 
 
 FIG. 36. Section of a Submerged Forest. 
 
 trees. Scraping away the sand of the beach you meet 
 with dark loam or earth, out of which the tree- 
 stumps protrude, and from which you may pick up 
 hazel nuts, leaves, twigs, and, now and then perhaps, 
 the wing-case of a beetle, or the bone of some land 
 animil. As you trace stump after stump along the
 
 102 SCIENCE PRIMERS. [THE CRUST 
 
 beach, you see that they are all in the usual upright 
 posture in which trees grow. The dark earth in which 
 the tree-roots spread is clearly an ancient soil, in 
 which to this day may be gathered the very leaves, 
 twigs, and nuts which fell from the trees, and fragments 
 of the insects which lived amid their decaying timber. 
 These stumps on the beach are evidently parts of 
 an old forest or wood. 
 
 209. But could the trees ever have grown where their 
 remains are now to be seen ? By no means. The 
 hazel, birch, alder, and oak, of which the stumps 
 mostly consist, would be killed if their roots and 
 trunks were to be permanently submerged in the sea. 
 You never see any of these trees growing below tide- 
 mark now, and you cannot suppose ihat they ever did 
 so. If the trees on the beach must have grown where 
 their remains still exist, and if they could not have 
 grown up in the sea, then, either the sea must have 
 risen up so as to cover them, or the land must have sunk 
 down so as to submerge them. But we have already 
 learnt (Art. 203) that in all such cases of change of 
 level we cannot believe that the sea alters its level 
 to any appreciable extent, so that we must conclude 
 that the submergence of the old trees has been due to 
 a sinking down of the land. These Submerged 
 Forests, therefore, are to be regarded as evidence of 
 subsidence of the earth's surface, just as the raised 
 beaches are taken as proofs of upheaval. 
 
 210. You can understand that it must be more 
 difficult to trace evidence of ground having sunk than 
 of its having risen in level. Because when any district 
 has gone down below the sea, the waves gradually 
 obliterate all trace of the former land surface, as they
 
 OF THE EARTH.] 
 
 GEOLOGY. 
 
 103 
 
 are now washing away the submerged forests ; while, 
 on the other hand, when the bed of the sea is turned 
 into dry land such traces as raised beaches, and old 
 sea-worn caves, remain to mark the space which the 
 salt water once covered. 
 
 211. In different parts of the globe it has been ob- 
 served that the sea appears to be gradually rising upon 
 
 FIG. 37. Sectioi 
 
 of the Strata in a Coal-pit, c, Coal-s 
 fracture of the rocks. 
 
 ams. f, a fault ot 
 
 Jie land. In reality it is the land which is there 
 sinking below the sea. For example, the southern 
 part of Greenland for several hundred miles has during 
 the last few centuries been slowly subsiding, so that 
 rocks which once lay above the limits of the tides are 
 now submerged, and the dwelling-houses of the inhabi- 
 tants have had to be shifted further and further inland. 
 10
 
 104 SCIENCE PRIMERS. [THE CRUST 
 
 212. Other proofs of the same fact have already 
 been referred to in the foregoing Lessons. The beds 
 of coal, for example, which once flourished as green 
 forests at the surface are now found buried deep within 
 the earth. By what process did they get there ? Let 
 us return for a while to the Coal-pit referred to in 
 Art. 137. 
 
 213. In many parts of Britain the coal-pits are more 
 than a thousand feet deep. And yet down at the 
 bottom of each of these pits lies the coal-seam. 'which 
 we have found to be a buried swamp or jungle. If 
 you could look at all the rocks which have been cut 
 through in making the long shaft of the pit, you would 
 usually find among them other coal-seams than the 
 one at the bottom. In fact, several seams are some- 
 times worked for coal at different levels in the same 
 pit. You will understand their position from the 
 section in Fig. 37, which shows how the rocks lie one 
 above another in one of these pits. You notice 
 that the seam down to which the shaft has been 
 sunk is the fifth of the series, but it is chosen in the 
 meantime, probably because it is a better kind of 
 coal than the other four seams above it, and therefore 
 brings more money in the market 
 
 214. In such a section as that in Fig. 37, which 
 shows only what may be met with in any coal-field. 
 we see that the strange revolution whereby a green 
 waving forest has been buried underground must 
 have happened not once only, but many times ; for 
 every separate coal-seam was evidently at one time 
 a verdant plain, open to the sun, and bright with 
 many a graceful tree and fern. And still more, 
 besides the evidence of the coal-seams, upright stems
 
 OF THE EARTH.] 
 
 GEOLOGY. 
 
 105 
 
 of trees, now turned into stone, are sometimes found 
 standing in the sandstones and shales, in the very 
 position in which they grew with their roots even 
 yet imbedded in the ancient soil. (Fig. 38)'. 
 
 FIG. 38 Section of a. part of the Cape Breton Coal-field, showing seven 
 ancient soils, with remains of as many forests. (R. Brown.) a, Sand- 
 stones, b znde, Shales; c. Coal-seams ; d, Underclays, or Soils. 
 
 215. The lowest strata are of course the oldest (see 
 Art 122). Hence the undermost coal-seam must
 
 io6 SCIENCE PRIMERS. [THE CRUST 
 
 have been buried before the later forests could spring 
 up on its site. It grew probably in a wide, marshy 
 plain, which when the ground sank down became a 
 wide sheet of water. Sand and mud were carried 
 into this water, and laid down upon the submerged 
 forest. These sedimentary deposits may now be traced 
 in the beds of sandstone and shale which overlie the 
 coal-seam. The sand and mud brought into the wide 
 and shallow sheet of water might in the end fill it 
 up so that at length, as the muddy bottom rose 
 to the surface, a new mass of vegetation would take 
 root and form as luxuriant a growth as the buried 
 forest had done. But after this had taken place 
 the downward movement of the ground again showed 
 itself, for this second forest was carried beneath the 
 water and covered with renewed accumulations of 
 sand and mud. 
 
 216. Hence we learn that our coal-fields were formed 
 in regions which were sinking, and that the downward 
 movement was not continuous, but went on at in- 
 tervals. That it must have been prolonged through 
 vast periods of time is apparent from the fact that 
 the strata of the coal-fields are many thousands of 
 feet thick, and must hence have needed long ages 
 for their formation. 
 
 217. Two facts are now very clear to you about the 
 crust of the earth ist, it has often been pushed out- 
 wards, so as to rise above the level of the sea ; and 
 2nd, it has also often sunk inwards so as to carry 
 parts of the land deep beneath the sea-level. But it 
 could not undergo these movements without suffer- 
 ing other changes, which will be considered in the 
 next Lesson.
 
 OF THE EARTH.] GEOLOGY. JO? 
 
 III. Proofs that the Rocks of the Earth's 
 Crust have been tilted, crumpled, and 
 broken. 
 
 218. If you think about the movements described in 
 the two previous Lessons, and consider how often the 
 crust of the earth must have been pushed up or let 
 down, you will not be surprised to find that the rocks 
 have not only been shifted up or down, but have been 
 crumpled up and broken across. Hence the crust of 
 the earth, instead of being made of regular layers 
 one above another, like the coats of an onion, has 
 been so squeezed and fractured, that in many cases 
 the bottom or oldest rocks have been pushed up 
 far above the newest. Let us clearly understand 
 how this statement can be made out; and for that 
 purpose we shall begin as before with the simplest 
 case. 
 
 219. Look back again for a moment at the view and 
 section of the Raised Beach in Figs 33 and 34. The 
 old sand and gravel beds have there unquestionably 
 been raised up above their former level, but they have 
 not otherwise been disturbed. They still lie out hori- 
 zontally as they used to do. But would this be the 
 case everywhere along that terrace ? You remember 
 that we ascertained that the terrace cannot be traced 
 all round the country, that it dies out in certain 
 directions, and consequently that the elevation which 
 produced it was not universal but local. Now it is 
 clear that though the upheaved tract rose so uniformly 
 that the raised beach may retain the same level for 
 many miles, still, between the horizontal strata which 
 were upraised, and those which, lying outside of the
 
 loS SCIENCE PRIMERS. [THE CRUST 
 
 elevated district, remained unchanged in level, there 
 must be an intervening space, longer or shorter, where 
 the strata slope down from the raised to the stationary 
 ground. 
 
 220. To make this clearer, suppose byway of illus- 
 tration that we place upon a table a number of sheets 
 of cloth to represent the different strata with which we 
 are dealing. The cloths, like the strata, lie there hori- 
 zontally. But if we push them up anywhere they 
 will be found to slope away from the elevated to the 
 unmoved part. Put a flat plate, for instance, under- 
 neath them, so as to raise a considerable surface. 
 Over the flat surface of the plate the cloths are flat, 
 as they are in our raised beach, but from that upraised 
 area they slope down to the undisturbed parts around. 
 So that you see how a local elevation, even though 
 it may raise up strata over a wide district without 
 disturbing their flatness, must yet give rise to an 
 inclination of the strata round the outskirts of the 
 movement. 
 
 221. Wherever, therefore, strata are pushed up or 
 let down more at one place than at another, without 
 being actually broken across, they must be thrown 
 into an inclined position. Now this unequal and 
 irregular kind of movement has taken place many 
 times in every quarter of the globe. If you look at 
 the stratified rocks, in most parts of this and other 
 countries, you will seldom find them quite flat 
 usually they are inclined, sometimes gently, some- 
 times steeply, so that they have not only been up- 
 heaved out of the sea (Art. 206), but have been 
 moved irregularly and unequally. 
 
 222. In the quarry which we formerly visited
 
 OF THE EARTH.] 
 
 GEOLOGY. 
 
 109 
 
 (Art. 119) the strata were horizontal. But in many 
 quarries you would find them turned up as in Fig. 
 38, where the right-hand portion has gone up (or 
 
 FIG. ^8. Inclined Strata. 
 
 the left-hand parts have gone down) more than the 
 others. In some places, indeed, you will meet with 
 
 FIG. 39. Vertical Strata. 
 
 the rocks so tilted up as to stand fairly on end 
 (Fig. 39), like a row of books on a shelf. As they 
 are made of sediment which gathered on a flat or
 
 SCIENCE PRIMERS. 
 
 [THE CRUST 
 
 gently sloping bottom, you see at once that they 
 never could have been placed on end originally, but 
 have been tilted into this position by underground 
 changes. 
 
 223. But this is not all. If when the cloths were lying 
 flat on the table (Art. 220) you had squeezed them 
 from either end, they would have been thrown into 
 crumplings (Fig. 40). In the same way during the 
 
 FIG. 40. Cloths crumpled by pressure. 
 
 movements by which the strata have been raised up a 
 great deal of similar crumpling has taken place. In 
 Fig. 41, for instance, the hard rocks are shown to have 
 been twisted and folded over as if they had been 
 mere layers of cloth. How enormous must have 
 been the pressure to which they were exposed before 
 they were squeezed into these shapes ! 
 
 224. One difference between the cloths and the strata 
 will occur to you. The one are soft and pliable, 
 the others hard and rigid. But we may make even 
 the most unyielding rocks to bend a little, and if this
 
 OF THE EARTH. ] 
 
 GEOLOGY. 
 
 can be done even with the comparatively feeble force 
 which man can employ, we may perceive how, under 
 the enormous pressure which they underwent in the 
 depths of the earth before they were upheaved, the 
 rocks should have been crumpled up like mere pliable 
 layers of cloth. 
 
 225. Still there must sometimes have been a point 
 beyond which they would rather break than bend any 
 
 FIG. 41. View of contorted strata. 
 
 further. Cracks would then be formed, and the strata 
 would be thrust up or made to sink down. You see one 
 of these cracks, or faults, as they are called, at /, in 
 Fig. 37, where the coal-seams and the strata between 
 them have been broken across those on one side of the 
 fracture being now found at a lower level than those
 
 SCIENCE PRIMERS. 
 
 [THE CRUST 
 
 on the other. Dislocations of this kind are of such 
 frequent occurrence that the whole surface of the earth 
 may be looked upon as a network of cracks. They 
 greatly interfere with the working of coal-mines, as 
 shown in Fig. 37, where the galleries which are driven 
 along the coal-seams from the pit towards the left-hand 
 will need to be altered where the coal is cut off by the 
 dislocation / 
 
 226. It has often happened that into the cracks thus 
 formed masses of melted or igneous rocks from the 
 
 FlG. 42. Section of Igneous Rock forced UD into Cracks 
 of the Larth's Crust. 
 
 C 
 
 id Fissures 
 
 interior have been pressed, so as to rise up and inter- 
 sect the other rocks. In the section in Fig. 42, for ex- 
 ample, two such dislocations have occurred in a series 
 of stratified rocks, so that three different groups, A, B, 
 and C, have been displaced. Into one of these cracks 
 a mass of igneous rock (I) has forced its way for some 
 distance. But in the other, that to the right hand, 
 a much larger body of melted rock has risen so as 
 completely to separate the stratified rocks B and C, 
 and not only so, but to break through the group B,
 
 OF THE EARTH.] GEOLOGY. 113 
 
 ascending even to what is now the surface of the 
 earth. 
 
 IV. The Origin of Mountains. 
 
 227. It is common to speak of the "eternal hills" 
 as if they had existed from the very beginning of the 
 world's history. And certainly few objects upon the 
 surface of the globe convey to the mind such an impres- 
 sion of vast antiquity. As far back as history or tradi- 
 tion can go the mountains have remained without 
 sensible change ; and thus, because they have always 
 appeared to man to be what they still are, he is apt to 
 think of them as parts of the original architecture 
 of the planet. 
 
 228. And yet from what has been learned in some 
 of the foregoing Lessons, you will be prepared to find 
 that old as the mountains undoubtedly are, they do not 
 belong to the beginning of things. It is still possible 
 to trace out their origin, and to get back to the records 
 of earlier times before they existed at all. If I ask 
 how this knowledge can he gained you will doubtless 
 answer that it can only be by examining the rocks of 
 which the mountains consist. You have already learnt 
 how rocks tell their story. It is only a further stage of 
 the same kind of reasoning to inquire what the rocks 
 tell regarding the birth of the mountains. 
 
 229. First of all, then, when any chain of mountains 
 is examined it is found to be made of rocks belong- 
 ing to one or more of the three great classes with 
 which you are already acquainted. In particular, 
 the great mass of most mountain chains consists of 
 various kinds of stratified rocks such as sandstones,
 
 ii4 SCIENCE PRIMERS. [THE CRUST 
 
 conglomerates, limestones, and others. Now you have 
 found that these rocks have been laid down under 
 water, most of them under the sea. They often 
 contain the remains of shells, corals, sea-urchins, or 
 other marine creatures, and these remains may be 
 taken out of the rocks even at the summits of the 
 mountains (Art. 160). No clearer proof than this 
 could be required to show that mountains are not so 
 old as "the beginning of things," for these fossils 
 prove that where the mountains now stand wide seas 
 once rolled. 
 
 230. Again, mountains which consist of rocks formed 
 originally under the sea must owe their existence to 
 some force which could raise up the bed of the sea 
 into high land. That force has been already (Art. 
 187) alluded to. As a consequence of the slow cool- 
 ing of our planet, its outer crust, under the enormous 
 strain of contraction, has been forced up into ridges 
 in different places, with wide, sunk spaces between. 
 The ridges form mountain chains, while the sunk 
 spaces are filled with the waters of the ocean. If you 
 look at a map of the world you may trace out the 
 principal lines of elevation, as they are called, 
 over the globe. Perhaps the most remarkable of all 
 the folds or puckerings into which the surface of the 
 earth has been ridged up is the long line of moun- 
 tains which runs down the whole of the continent of 
 America. You observe that the various ridges of the 
 Rocky Mountains, of Central America, and of the 
 Cordilleras and Andes, are prolonged in one vast line 
 of elevation. Other minor foldings are seen on the 
 same continent, as, for instance, the chain of the 
 Alleghanies, in the eastern part of the United States.
 
 OF THE EARTH.] GEOLOGY. 115 
 
 ]n Europe we have a line of elevation stretching 
 across the continent, and throwing off spurs in its 
 course. It is seen in the Pyrenees, then in the Alps, 
 whence, after sending southwards the ridges of the 
 Apennines, it is carried eastward by the chain of the 
 Carpathians, and then by the Caucasus to the Caspian 
 Sea. The same line, however, reappears on the other 
 side of that inland sea, and crosses the vast continent 
 of Asia in two divergent lines ; one of which turns 
 south-eastward, to form the grand Himalayas, while 
 the other trends eastward across the great Asiatic 
 table-land to the shores of the Pacific Ocean. When 
 you reflect upon these enormous mountain-chains as 
 the results of the cooling and contraction of the 
 mass of the globe, you begin to feel how enormous 
 
 FIG. 43. Section of a series of Sedimentary Rocks originally deposited 
 horizontally on the sea-bottom. 
 
 must be the force which could crumple up solid rock 
 into ridges many thousands of miles long and thou- 
 sands of feet high. 
 
 231. But as the globe has been cooling and con- 
 tracting since the very first, we may reasonably expect 
 to find that mountains have been uplifted at various 
 limes, and, therefore, that they differ from each other 
 in age. A little attention to the rocks is enough to 
 show not only that mountains are not all of the same 
 age, but that even the same mountain has not been 
 formed entirely at one time, but that one part has been 
 raised up long before another. 
 
 232. Suppose, for example, that a series of ordinary
 
 u6 
 
 SCIENCE PRIMERS. 
 
 [THE CRUST 
 
 sedimentary rocks, such as the sandstones, conglome- 
 rates, and shales, described in earlier Lessons, has been 
 laid down upon the sea-bottom. These rocks would 
 be formed one above another in flat beds (Fig. 43), 
 until they had accumulated into a mass perhaps many 
 thousands of feet in thickness. They might remain 
 undisturbed for a long time. Let us further suppose, 
 
 
 FIG. 44. Section of a mountain formed of crumpled rocks, A, which have 
 been contorted before the deposition of the flat rocks, B. 
 
 however, that they happen to lie in one of those 
 weaker parts of the crust which, when the accumulated 
 effects of the long-continued contraction of the earth's 
 mass begin to make themselves felt, are pushed out- 
 ward by the subsiding spaces on either side. Squeezed 
 together by the pressure of these sinking areas the 
 
 
 FIG. 45. Section of a mountain in which the rocks A were upheaved before 
 the series B, and the latter before series c. 
 
 formerly horizontal rocks will be crumpled up into 
 folds (like our cloths in Fig. 40, when similarly 
 squeezed), and be made to rise above the level of the 
 surrounding tracts (Fig. 44). A ridge or mountain- 
 chain would thus arise upon the surface of the earth.
 
 OF THE EARTH.] GEOLOGY. 
 
 233. Such a ridge or chain formed out of sedimen- 
 tary rocks (A), once horizontal but now contorted, 
 could not rise up into the atmosphere without becom- 
 ing a prey to those various forces, which, as you have 
 learnt (Physical Geography Primer, Arts. 126 142), 
 are ceaselessly at work in wearing down the surface of 
 the globe. The air, rain, springs, rivers, frosts, or the 
 waves of the sea, would attack the newly formed 
 mountain, and begin to waste its surface as soon as 
 it raised its head above the level of the ocean. Deep 
 furrows would in time be carved out of its sides, and 
 all its decayed fragments would be washed down to 
 the lower grounds. There these fragments would 
 form new deposits, which would be laid down upon 
 the edges of the older rocks, as in Fig. 44 the newer 
 series B is seen to lie upon the older A. 
 
 234. Now such a section as this (Fig. 44) would 
 enable you to fix, relatively at least, the date of the 
 mountain. You could assert positively that, ist, there 
 was a time when the mountain did not exist, but when 
 its place was occupied by a sea in which the sedi- 
 mentary rocks A were deposited ; 2nd, that the moun- 
 tain was formed by the crumpling up of these rocks, 
 and that this took place before any of the rocks of 
 series B began to be formed ; and 3rd, that after the 
 formation of the strata marked B the whole mass was 
 further uplifted so as to raise these strata out of water 
 into dry land. 
 
 235. But suppose that in some other part of the 
 chain we discover such an arrangement of rocks as 
 that shown in Fig. 45. Here, as before, we see that 
 the series A was upturned before the series B could 
 be laid down on it. But in the present case series B
 
 ii8 SCIENCE PRIMERS. [THE CRUST 
 
 has also been tilted up out of its original horizontal 
 position. Such a mountain would indicate three suc- 
 cessive periods of upheaval, the first older than the 
 time of B, the second older than the time of c, while 
 the third came after the formation of c, for it raised 
 that series of strata into land. 
 
 236. It is in this kind of way that the relative 
 ages of mountain-chains are determined. Wherever 
 you meet with sedimentary rocks turned up on end or 
 crumpled, you know that they have been disturbed, 
 and whenever these disturbed rocks have their broken 
 edges covered by others, you see that the uplifting 
 must be older than the second set of rocks. 
 
 237. If now you could find out any means of recog- 
 nizing the same series of rocks in different countries : 
 if, for example, you could be sure that the groups A 
 and B of Figs. 44 and 45 occurred both in England and 
 Germany, you would be able to compare the relative 
 ages of the mountains of the two countries. If in the 
 one country a mountain shows the structure repre- 
 sented in Fig. 45, and if in the other country a moun- 
 tain formed of the same series of rocks is built up in 
 the way shown in Fig. 44, you would infer that the 
 former mountain was newer than, or, rather, had 
 received a push upward after, the latter. 
 
 238. In the next Lesson it will be shown how geo- 
 logists identify the same series of rocks in different 
 countries viz. by Fossils. With this kind of evidence 
 it becomes possible to decide which are the oldest and 
 which the newest mountain-chains. In this way we 
 learn that the giant Alps, towering so far above the 
 plains of Europe, are less ancient than many a green 
 hill in Wales and Scotland.
 
 OF THE EARTH.] 
 
 GEOLOGY. 
 
 119 
 
 239. But another singular and important fact about 
 mountains is made plain by such sections as those in 
 Figs. 44 and 45. The series of rocks marked A is the 
 oldest part of the mountain in each case. You might 
 naturally suppose that the oldest parts ought to be 
 those which are buried deep under other portions. 
 "And yet on examination it is found that the most 
 ancient parts are not always those which lie at the 
 
 lowest level, but that, as in the two cases we have 
 supposed, they may have been pushed up so as now 
 actually to form the loftiest peaks and ridges. But if 
 you get away to the flanks of the mountain you find 
 that the oldest rocks do really pass under the newer 
 ones, as series A in the drawings passes under B. 
 240. The crumbling down of the surface of the
 
 120 SCIENCE PRIMERS. [THE CRUST 
 
 earth is so constant and so wide-spread, that in pro- 
 cess of time every mountain-chain undergoes great 
 and manifold changes. Its summits and sides are 
 wasted and lowered. Its crests get splintered into 
 peak and pinnacle, as the rains and frosts of ages 
 do their work upon them. Crag and cliff are carved 
 out of its sides ; ravine and gorge, wider glen and still 
 wider valley, are excavated in its rocks by the never- 
 ending flow of rill and river. Hence, though the 
 original line of elevation remains, the upheaved tract 
 is cut into innumerable ridges and valleys as the pro- 
 cess of waste goes on. (See Physical Geography 
 Primer, Art. 126.) 
 
 241. So enormous have been the effects of that 
 process over the surface of the earth, that great table- 
 lands or broad masses of high land have been cut down 
 into mere ridges and detached hills. In Fig. 46 you 
 may as it were watch how the excavation proceeds. 
 That is a drawing of part of a table-land in Spain. 
 You observe how the streams as they descend and 
 become larger in size, dig wider and deeper trenches out 
 of the rocks, how their ravines widen out into valleys, 
 how the high ground between them is being cut into 
 irregular ridges, and how these ridges, still further cut 
 into separate hills or mounds, lose height as the rains 
 and frosts attack their summits and sides. In every 
 quarter of the globe illustrations of these changes 
 may be found. In Britain, for example, our mountains 
 are only fragments, like those in the drawing, which 
 have been left after the excavation of the valleys that 
 surround them. The great Ghauts of India, and the 
 Table Mountain of the Cape, are likewise conspicuous 
 instances of the same kind of origin.
 
 OF THE EARTH.] GEOLOGY. 
 
 242. The same forces which have carved out 
 valleys and left mountain-ridges standing out between 
 them are still busy at their work. Every year adds to 
 the waste. And thus, although when we gaze at a 
 mountain-chain we know that first of all it was heaved 
 up by movements from below, we nevertheless learn to 
 recognize that all the familiar forms which it now 
 assumes have since that early time of upheaval been 
 carved upon it by the very same forces rains, frosts, 
 springs, glaciers, and the rest which are busy sculp- 
 turing its surface still. 
 
 V. How the Rocks of the Crust tell the 
 History of the Earth. 
 
 243. When a historian betakes himself to write the 
 history of a country, his first care is to make him- 
 self acquainted with all the scattered documents 
 likely to throw light upon the transactions which 
 he will have to describe. He ransacks the papers 
 in the public archives and libraries, gleans what he 
 can from printed books, and even it may be travels 
 into foreign countries in search of contemporary 
 writings which may explain what is dark or un- 
 certain at home. Only after prolonged labour of 
 this kind, is he able to gather up the sum of all he 
 has learnt, and to weave it into a continuous narrative. 
 In the course of his researches he will no doubt find 
 some periods much better illustrated by contempo- 
 rary documents than others, while of some he may 
 possibly be hardly able to collect any satisfactory 
 information, for in the course of time the papers 
 which would have supplied him with the facts are
 
 122 SCIENCE PRIMERS. [THE CRU^T 
 
 lost or destroyed. Hence his history is not all 
 equally full and reliable. There may even be gaps 
 in it which no amount of industry in his search for 
 information has enabled him to fill up. 
 
 244. Now what is thus true of the historian of any 
 country, is true also of the geologist. As already 
 pointed out (Art. 38), and as must now be very clear 
 to you, the earth has a history as well as the people 
 who dwell upon its surface. A geologist may be 
 called a historian of the earth. His great aim is to 
 collect all the evidence which remains of the changes 
 that have happened upon the earth's surface, and to 
 arrange them in the order in which they have occurred, 
 so as to show the grand march of events down to the 
 present time. 
 
 245. What papers and inscriptions, coins and books 
 are to the historian, the rocks of the earth's crust are 
 to the geologist. They contain all the real evidence at 
 his disposal. What he can gather from them at one 
 place must be compared with what he collects from 
 them at another. He must journey far and wide in 
 search of facts which are not to be found at his own 
 door. Gaps will certainly occur, which even the skill 
 and industry of many years may never completely 
 bridge over ; for the rocks, as we have already seen, 
 are subject to revolutions quite as destructive in their 
 way, as those which have swept away the archives of 
 cities and nations. The geologist, therefore, can only 
 at the best produce an imperfect chronicle. But it 
 is one which has a profound interest for all of us, for 
 it is the story of our own globe of its continents 
 and oceans, its mountains and valleys, its rivers and 
 lakes, of the tribes of plants and animals which people
 
 OF THE EARTH.] GEOLOGY. 123 
 
 its surface, and of the advent and progress of man 
 himself. 
 
 246. Regarding the earliest stages of the earth's his- 
 tory no direct evidence is now to be obtained from the 
 rocks. When the earth was detached from its parent 
 sun, it must have been a fiercely hot mass as the sun is 
 still. Not until long after that period could any such 
 rocks as we now see have been formed. So that 
 although the rocks carry us a vast way back into the 
 past, they cannot bring us to the beginning of the 
 earth's history as a separate planet. That early time 
 can only be inferred from other and chiefly astro- 
 nomical evidence. 
 
 247. In the foregoing pages you have learnt how 
 the rocks m'ay each be made to give up its little bit 
 of earth-history. You succeeded in discovering, for 
 example, from the rocks of a single quarry the site of 
 an old sea-floor with some of the remains of the sea- 
 creatures which lived upon it (Arts. 118 131). Again, 
 you found how a peat-moss might enable you to trace 
 out the limits of a long-vanished lake on which our 
 rude forefathers launched their oak canoes (Arts. 144 
 152) ; and how the rocks of a coal-pit could furnish 
 forth a record of forest after forest which had each 
 flourished green and fair at the surface, but which 
 had sunk down one after the other, and were now 
 buried deep within the -earth. (Arts. 137 and 212.) 
 
 248. In these and all such illustrations, while each 
 series of rocks tells its own story, that story is only a 
 part of the general history of the earth. The more 
 carefully we can gather each separate narrative, the 
 fuller will be that general chronicle of the earth's his- 
 tory which it is the object of geology to compile.
 
 124 SCIENCE PRIMERS. [THE CRUST 
 
 249. According to the law of superposition (Art. 
 122) the undermost stratified rocks are the oldest. We 
 can reach but a little way down into the earth. The 
 deepest mines descend but a very few thousand feet 
 into the rocks. If, therefore, these rocks still lay 
 flat as they were deposited, we should be able to 
 make ourselves acquainted only with those near the 
 surface. But in consequence of the way in which the 
 rocks have been bent and broken, and pushed up and 
 down (Arts. 188, 218 226), we not only see the 
 topmost parts of the series, but even some of the 
 oldest masses. Instead of lying flat, the rocks are 
 very commonly found to slope into the earth more or 
 less steeply, and we can walk over their- upturned 
 edges, like the backs of so many rows of books. 
 (See Figs. 38 and 39.) So far therefore from the 
 bottom rocks being still buried under the thousands 
 of feet of solid rock beneath which they once lay, 
 they are often found rising into the summits of lofty 
 mountain ranges (Art. 239). And thus the geologist 
 is saved the trouble of sinking deep bores and pits to 
 find out the order of the rocks under his feet. By 
 making careful sections from what can be observed at 
 the surface (as in Figs. 44 and 45), he determines that 
 order with certainty, and when he has done so he 
 knows which are the oldest parts of his chronicle, and 
 which are the newest. 
 
 250. The crust of the earth, so far at least as we can 
 examine it, is chiefly made up of Sedimentary and 
 Organic Rocks. In these rocks, therefore, must the 
 chief sources of evidence for the history of the earth 
 be sought. If we could pile them up, one above 
 another, in the order of their formation, they would
 
 OF THE EARTH.] GEOLOGY. 125 
 
 form a mass probably more than a dozen miles thick. 
 This, then, is the library out of which geological 
 history must be compiled. 
 
 251. Besides the order of superposition, however, the 
 geologist has another clue to the relative age of rocks. 
 By comparing the different series of rocks with each 
 other he has discovered that the fossils, or remains of 
 plants or animals (Art. 117), of one series differ from 
 those of another. For example, to turn again to Fig. 
 45, it is ascertained that if fossils occur in the set of 
 rocks marked A, they will be found to differ from 
 those in the series B, and these again from those in c. 
 If, starting from the plants and animals of to-day, we 
 go back into older and yet older rocks, we learn that 
 the fossil plants and animals become, on the whole, 
 more and more unlike those which are still living. 
 Each great division of rocks is found to have its own 
 characteristic fossils. So that, over and above the test 
 by Order of Superposition, we can discriminate 
 between these divisions by means of Fossils. 
 
 252. By these methods of classification the vast com- 
 plex mass of Stratified Rocks may be divided into a 
 few great divisions, these into subdivisions, these again 
 into minor compartments, and these into still' smaller 
 zones or bands, so that when a bed of rock is found 
 it can be referred to its own particular part of the 
 whole vast series. This method of arrangement is 
 necessary for the sake of clearness, very much in the 
 same way that a work on history requires to be divided 
 into volumes, these into separate books, these again 
 into chapters, and these into pages and lines. 
 
 253. Making use, therefore, of every kind of evi- 
 dence which the rocks afford, the geologist endeavours
 
 126 SCIENCE PRIMERS. [CONCLUSION. 
 
 to weave together his narration of the history of the 
 earth. He shows h'ow land and sea have often 
 changed places, how time after time volcanos have 
 broken out in all quarters of the globe, how continents 
 have, one by one, arisen, how mountain-chains have 
 been successively formed, how valleys, and ravines, 
 and lakes, have been excavated, how climates have 
 slowly changed from tropic heat to arctic cold. Amid 
 all these revolutions of the solid earth itself, he finds 
 that there have been at the same time vast changes in 
 the plants and animals which have peopled its surface. 
 He can trace how Life, beginning in the remotest 
 past with the simplest organisms, has advanced through 
 long ages, in more and more highly organized forms 
 (Art. 132), up to the present time. He can mark how 
 group after group of shells, or fishes, or reptiles, has 
 come into existence, and, after living for protracted 
 periods, has slowly died out to make way for newer 
 tribes, until towards the close of the history Man has 
 appeared upon the scene. 
 
 254. Geological history brings before us, in this way, 
 many facts well calculated to impress our minds with 
 the great antiquity of our planet, and with the mar- 
 vellous chain of changes by which the present order 
 of things has been brought about. We learn from it 
 that mountains and valleys have not come suddenly 
 into existence, such as we now see them, but have 
 been formed gradually, by a long series of processes 
 similar to those which are even now slowly doing the 
 same work. We discover that every part of the land 
 under our feet can yield us up its story, if we only know 
 how to question it. And, strangest of all, we find 
 that the races of plants and animals which now tenant
 
 CONCLUSION.] GEOLOGY. 127 
 
 land and sea, are not the first or original races, but 
 that they were preceded by others, these again by 
 others still more remote. We see that there has been 
 upon the earth a history of living things, as well as of 
 dead matter. At the beginning of that wonderful 
 history we detect traces merely of lowly forms, like 
 the foraminifera of the Atlantic ooze. At the end we 
 are brought face to face with Man thinking, working, 
 restless Man, battling steadily with the powers of 
 Nature, and overcoming them one by one, by learning 
 how to obey the laws which direct them. 
 
 CONCLUSION. 
 
 255. It is not the design of this little book to enter 
 further into the history of the Earth. It has led you 
 to the threshold whence you can see the kind of 
 interest in store for you if you advance beyond. You 
 have now learnt something of the general principles 
 upon which the history is based. Looked at in the 
 light of geological teaching, the very stones of the 
 street and the pebbles of the shore have each a mean- 
 ing for you now. You will no longer be content to 
 gather minerals and rocks merely because they are 
 pretty objects to look at. Apart from their beauty 
 you will seek to discover what they are, and how they 
 came to be where they are found. 
 
 256. A landscape will lose none of its beauty in your 
 eyes though you seek to discover how the rocks of its 
 hills were formed, how ridge and valley came into 
 existence, why a crag should rise in one part and a 
 wide plain stretch away for miles in another. When 
 you stand by the brink of a foaming river there will 
 
 12
 
 128 SCIENCE PRIMERS. [CONCLUSION. 
 
 be no lessening of your pleasure in its rush and roar, 
 if you think of the river as one of nature's most 
 powerful engines, busy day and night in digging out 
 its channel in the rocks, and carrying the waste of the 
 mountains down to the plains and to the depths of the 
 ocean. The shores of the sea will wear a new charm 
 when you trace along their cliffs and caves the progress 
 of decay, and on their beaches of sand and shingle the 
 counterpart of those sedimentary deposits out of which 
 whole mountains are built up. 
 
 257. Every quarry and ravine where the naked rock 
 comes to view, offers an attraction, if you seek to 
 find there the remains of some of those lost forms of 
 plants which covered the land, or of those long extinct 
 tribes of animals which once tenanted the sea. These 
 fossils will become, in your hands, not mere things to 
 wonder at. ^ou will try to learn, from friend or book, 
 what they resemble most in the present living world. 
 And you will not rest contented until you have seen 
 all that you can discover of the light which they throw 
 upon the former condition of the district in which you 
 find them. 
 
 258. Geology will thus be no longer a task to be 
 conned from books, but a delightful companion in every 
 walk and ramble. You may never become geologists, 
 but you will never regret the time you have spent in 
 trying to master the principles on which geological 
 science is based, and to trace out under their guidance 
 the marvellous History of the Earth.
 
 QUESTIONS, 
 
 INTRODUCTION. 
 
 1. Mention some of the most familiar kinds of stone and the 
 uses to which they are applied. 
 
 2. What are brick and moitar made of? 
 
 3. How is iron obtained ? 
 
 4. Whence are limestone, slate, marble, and coal obtained? 
 
 5. Under what kind of covering do the rocks of a country for 
 the most part lie ? 
 
 6. What is the general character of the surface of Britain 
 along a line drawn from Liverpool to Harwich ? 
 
 7. What is the general character of the surface of Britain 
 along a line drawn from Skye to Montrose? 
 
 8. Explain why this difference of character should exist in two 
 parts of the same country. 
 
 DIFFERENT KINDS OF STONES, p. 6. 
 
 1. What is meant by a principle of classification ? 
 
 2. Show how mere colour or hardness and softness would not 
 be sufficient as a principle of classification of stones. 
 
 3. Describe the characters of a piece of sandstone. 
 
 4. From these characters how would you define a sandstone ? 
 
 5. Describe in the same way the characters of a piece of 
 granite. 
 
 6. Give a definition of granite from these characters. 
 
 7. Describe the characters of a piece of chalk, and explain 
 how the examination of the specimen should be carried on. 
 
 8. Give a short definition of chalk from these characters. 
 
 WHAT STONES HAVE TO TELL US, p. 14. 
 
 I. Are the different kinds of stone scattered at random over 
 the surface of a country? Illustrate this answer by reference to 
 the stones which underlie the soil of Britain.
 
 130 SCIENCE PRIMERS. 
 
 2. What kind of history is made known to us by stones? 
 Give illustrations from the stones of Britain. 
 
 3. What is the subject of the science of Geology? 
 
 SEDIMENTARY ROCKS. 
 I. What Sediment is, p. 19. 
 
 1. Into what groups may the different kinds of stone be 
 divided ? 
 
 2. Define the sense in which the word "rock" is used in 
 Geology. 
 
 3. What is sediment? 
 
 4. What are sedimentary rocks? 
 
 5. Describe a piece of conglomerate, and show out of what 
 materials it has been formed. 
 
 6. Of what materials do sandstone and shale consist? 
 
 7. What two questions about their origin do sedimentary 
 rocks suggest to us ? 
 
 II. How Gravel, Sand, and Mud are made, p. 23. 
 
 1. What question is it well to put to ourselves when we try to 
 find out the history of any kind of rock? [Art. 57.] 
 
 2. What is the difference between gravel and cand, and how 
 may this be shown ? 
 
 3. Describe the origin of the rubbish which covers the slopes 
 of mountains and high hills. 
 
 4. This rubbish has usually sharp-edged fragments which get 
 more and more rounded as they descend the neighbouring 
 streams. Explain this change. 
 
 5. Why does fine mud travel further down a stream than 
 coarse gravel ? 
 
 6. In what form is the debris of the mountains strewn over 
 the plains? 
 
 7. On a rocky sea-coast what is the difference between the 
 surface of the rocks of the cliffs and those of the beach ? Explain 
 the cause of this difference. 
 
 8. What becomes of the fragments which fall from the face of 
 a sea-cliff? 
 
 III. How Gravel, Sand, and Mud become Sedimentary 
 Rocks, p. 32. 
 
 i. What is the relation between the rate of motion of a stream 
 and the deposit of sediment at the bottom oi the water?
 
 GEOLOGY. 131 
 
 2. What would you infer from beds of gravel, of sand, and of 
 mud as to the rate of movement of the water in which ^these 
 deposits are laid down ? 
 
 3. How would you apply your knowledge of the origin of 
 gravel and mud to the history of rocks like conglomerate and 
 shale? 
 
 4. Where and in what way are sedimentary materials arranged 
 by rain upon a roadway ? 
 
 5. How is the sediment disposed of by the Rhone at the Lake 
 cf Geneva? 
 
 6. What becomes of the sand and mud brought down by a 
 river to the sea ? 
 
 7. Define the terms Stratification and Stratified Rocks. 
 
 8. Why have sedimentary rocks usually become harder than 
 they originally were ? Explain the terms Pressure and Infiltra- 
 tion with reference to the history of those rocks. 
 
 9. Define a Sedimentary Rock. 
 
 IV. How the Remains of Plants and Animals come to 
 be found in Sedimentary Rocks, p. ^4. 
 
 1. How are the remains of land -plants buriedin modern 
 sedimentary deposits? 
 
 2. Explain how plants have been often imbedded in sandstone 
 and shale. 
 
 3. Explain the origin of the remains of marine animals in 
 many shales and limestones. 
 
 4. Why may we expect any marine sedimentary deposits to be 
 full of traces of once-living creatures ? 
 
 5. What is a fossil ? 
 
 V. A Quarry and its Lessons, p. 50. 
 
 1. What is usually the most obvious feature in a quarry among 
 stratified rocks? 
 
 2. W'hich are the oldest of the different beds in the quarry, and 
 why? 
 
 3. Define the term Order of Superposition. 
 
 4. What are ripple-marks in rocks, and what light do they 
 cast on the history of the rocks among which they occur ? 
 
 5. What are rain-prints in rocks, and what evidence do they 
 furnish as to the conditions under which the rocks were formed ? 
 
 6. How could you determine from the evidence of fossils 
 whether a rock had been formed in fresh water or in the sea ? 
 
 7. Mention any facts which show the extent of sea-formed 
 recks over the earth.
 
 132 SCIENCE PRIMERS. 
 
 ORGANIC ROCKS, OR ROCKS FORMED OF 
 THE REMAINS OF PLANTS AND ANIMALS. 
 
 I. Rocks formed of the Remains of Plants, p. 56. 
 
 1. Explain the term Organic Remains, 
 
 2. Briefly describe the characters of a p'ece of coal. 
 
 3. Describe the way in which coal occurs among other rocks. 
 
 4. What is the nature of the under-clay of a coal-seam? 
 
 5. Whit has been the origin of the coal ? 
 
 6. Describe a peat -moss or bog. 
 
 7. What is peat ? What have been the stages in the history of 
 a peat-moss ? 
 
 II. Rocks formed out of the Remains of Animals, p. 66. 
 
 1. W T hat is the origin of the white marl commonly found on 
 the bottom of fresh-water lakes ? 
 
 2. What is the ooze of the At'antic bed ? 
 
 3. In what respects does chalk resemble the Atlantic ooze ? 
 
 4. What is the origin of limestone containing the remains of 
 corals and slfells ? 
 
 5. Give from various parts of the world examples of large 
 districts and whole mountains m-de up of such limestone. 
 
 6. Give a summary of the geological changes represented by 
 the sedimentary rocks. [Art. 161.] 
 
 IGNEOUS ROCKS. 
 I. What Igneous Rocks are, p. 74. 
 
 1. In what sense has the word " igneous " been used in geology, 
 and what is meant by igneous rocks? 
 
 2. Into what groups may the materials ejected by volcanos be 
 divided ? 
 
 3. How are the rocks of these two groups broadly to be dis- 
 tinguished from each other, and what names may consequently 
 be given to them ? 
 
 4. What are the characters of lava? [Arts. 165, 166, 167.] 
 
 5. In what forms does lava issue from a volcano? [Arts. 168, 
 169.] 
 
 6. Give examples of the occurrence of lava-rocks in different 
 parts of the world. 
 
 7. How does granite occur? 
 
 8. W T hat are the characters of a piece of volcanic tuff? 
 
 9. How has volcanic tuff been formed ? Give some examples 
 of its occurrence.
 
 GEOLOGY. 133 
 
 II. Where Igneous Rocks come from, p. 84. 
 
 1. What evidence is furnished by deep bores and mines as to 
 the temperature of the interior of the earth ? 
 
 2. What is the testimony of hot springs on this subject ? 
 
 3. What lesson do volcanos teach us as to the condition of 
 the earth's interior? 
 
 4. Briefly describe the distribution of active volcanos over the 
 surface of the globe. 
 
 5. What evidence is afforded by dormant and extinct volcanos ? 
 d. How are earthquakes related to this subject? 
 
 7. How would you explain the present high temperature of 
 the earth's interior ? Show how the cooling of a lava-stream 
 helps to make this clearer. [Arts. 185, 186.] 
 
 THE CRUST OF THE EARTH. 
 
 I. Proofs that parts of the Crust have been pushed 
 
 up, p. 91. 
 
 1. What is meant by the earth's crust ? 
 
 2. Of what materials does the earth's crust consist ? 
 
 3. By what kind of evidence could you show that the rocks 
 of the earth's crust are not now in their original position ? 
 
 4. Describe a raised beach. [Art. 193.] 
 
 5. What evidence is furnished by raised beaches as to move- 
 ments of the earth's crust ? 
 
 6. Why do we say that, in ordinary changes of level of sea 
 and land, it is the land which rises or falls rather than the sea ? 
 
 7. What inference may be drawn from such ten-aces as those 
 of the north of Norway ? [Art. 201.] 
 
 8. In a series of successive raited beaches, which are the 
 oldest, and why? 
 
 9. What facts have been observed in Sweden regarding re- 
 cent movements of the earth's crust ? 
 
 10. How could you show that the greater part of the dry land 
 ' has been raised out of the sea, and that the upheaval has been 
 
 very unequal ? 
 
 II. Proofs that parts of the Crust have sunk down, p. 101. 
 
 1 . Describe a submerged forest. 
 
 2. What conclusion is to be drawn from submerged forests 
 as to movements of the earth's crust ?
 
 134 SCIENCE PRIMERS. 
 
 3. Why is it more difficult to find proofs of submergence than 
 of upheaval ? 
 
 4. What facts about submergence have been observed in 
 Greenland ? 
 
 5. How does a series of coal-seams prove former submergence 
 of the land? [213-216.] 
 
 6. Mention the two conclusions as to the movements of the 
 earth's crust which must be drawn from the evidence brought 
 before us in these lessons. 
 
 III. Proofs that the Rocks of the Earth's Crust have 
 been tilted, crumpled, and broken, p. 107. 
 
 1. Besides upheaval and depression, mention some further 
 changes which have been undergone by the rocks of the earth's 
 crust. 
 
 2. Why are rocks often found in highly-inclined positions, and 
 how could you prove that these were not their original positions? 
 
 3. Are solid beds of rock ever folded and crumpled ? 
 
 4. What are faults ? 
 
 5. What use of faults has often been made by igneous rocks? 
 
 IV. The Origin of Mountains, p. 113. 
 
 1. Of what materials are mountain-chains built up ? 
 
 2. By what proofs can it be shown that many mountains are 
 not original parts of the earth's su? face ? 
 
 3. What are lines of elevation, and how have they been 
 formed on the face of the globe? 
 
 4. Describe some examples of such lines. 
 
 5. Briefly state the nature of the evidence by which it can be 
 shown that mountain-chains differ from each other in age, and 
 that the same mountain may have been upheaved at successive 
 wide intervals. [Arts. 231-236.] 
 
 6. Why are the lowest and oldest rocks often found to form 
 the higher ridges of a mountain-chain ? 
 
 7. What effects are produced upon the external forms of 
 mountains during the general waste of the surface of the land? 
 
 V. How the Rocks of the Crust tell the History of 
 the Earth, p. 121. 
 
 1. What is geological history, and from what kind of evidence 
 is it compiled ? 
 
 2. Why is geological history necessarily imperfect ?
 
 GEOLOGY. 135 
 
 3. What does astronomical evidence point out as probably the 
 early condition of the earth ? 
 
 4. How does the geologist learn which are the oldest and 
 which the newest parts of his chronicle ? 
 
 5. How thick is the mass of sedimentary and organically- 
 formed rocks out of which geological history is compiled? 
 
 6. How do fossils aid the geologist in the study of the history 
 of the earth ? 
 
 7. Give some account of what is meant by geological history. 
 [Arts. 253, 254.]
 
 LIST OF SPECIMENS to illustrate the 
 GEOLOGY PRIMER. 
 
 Sedimentary Rocks See Primer, page 19 
 
 1. Conglomerate 21 
 
 2. Sandstone - ... 9 
 
 3. Shale 22 
 
 4. Shale containing Plant-remains (portion of a Fossil- 
 
 Fern) 44 
 
 5. Shale containing Animal-remains (Trilobites, &c. ) . 47 
 
 Organic Rocks 56 
 
 I. FORMED OF PLANT-REMAINS 56 . 
 
 6. Peat 62 
 
 7. Coal, showing stratified structure 57 
 
 II. FORMED OF ANIMAL-REMAINS .... 66 
 
 8. Fresh-water Shell-marl 66 
 
 9. Ooze from bottom of Atlantic prepared for the 
 
 microscope 68 
 
 10. Chalk with Shell in it 69 
 
 11. Grains of Chalk prepared for microscope ... 12 
 
 12. Limestone containing Encrinites, &c 71
 
 SCIENCE PRIMERS. 
 
 137 
 
 Fossils 
 
 I. PLANTS. 
 
 Plants out of which ' 
 
 coal has been partly } 
 formed. 
 See also Nos. 4, 6, and 7. 
 
 II. ANIMALS. 
 
 13. Stigmaria, or Sigillaria 
 
 14. Lepidodendron . . 
 
 PAGE 
 
 49 
 
 61 
 
 15. Cup Coral . 
 
 1 6. Piece of Encrinite 
 
 17. Spirifer, a marine 
 
 Animals of which the re- ' 
 mains sometimes form thick ' 
 masses of limestone. 
 
 shell . 
 
 See also Nos. 5, 8, 9, 10, 11, and 12. 
 Igneous Rocks 
 
 18. Granite 
 
 19. Mica . . 
 
 20. Quartz Crystal j 
 
 21. Lava showing crystals and steam-holes . 
 
 22. Volcanic Tuff . 
 
 54 
 
 74 
 ii 
 
 Substances found in granite . . 1 1 
 
 7 6 
 
 THE END.
 
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 PRIMERS. 
 
 Science Primers, 
 
 CHEMISTRY : Prof, ROSCOE, 
 PHYSICS; BALFOU& STEWART, 
 PHYSICAL, GEOGRAPHYi A. GE1SI& 
 GEOLOGY? A, GEIKIL. 
 PHYSIOLOGY: M. FOSTER, 
 ASTRONOMY: J. N. LQCKYER, 
 BOTANY r J. D, HOOKEK, 
 LOGIC; W, S. JEVOXS. 
 
 INVENTIONAL GEOMETRY? SPENCER, 
 PIANOFORTE: FRANKLIN TAYLOR, 
 
 Literature Primers, 
 
 ENGLISH GRAMMAR; R, MORRIS. 
 
 HILOLOGY; j. 
 
 CLASSICAL GEOGRAPHY: H. F 
 SHAKESPEARE; ED. DCAVDEN* 
 STUDIES IN BRYANT- JOSEPH ALPEK, 
 
 History Primers, 
 
 GREECE-, C A. FvFFfc 
 
 ROME; M. CREIGHTON, 
 
 EUROPE; E- A, FREEMA\% 
 
 OLD GREEK LIFE: j. p, MAHAFFV, 
 
 ROMAN ANTIQUITIES: A, 
 
 OEOGRAPH'V'r GEORGE GROVE.