The RALPH D. REED LIBRARY 
 
 o 
 
 DEPARTMENT OF GEOLOGY 
 UNIVERSITY OF CALIFORNIA 
 
 LOS ANGELES, CALIF.
 
 
 . >^fc 
 
 LIBHABY
 
 FIRST BOOK IN GEOLOGY 
 
 DESIGNED FOR 
 
 THE USE OF BEGINNERS 
 
 BY 
 
 N. S. SHALER, S.D., 
 
 PROFESSOR OF PALEONTOLOGY IN HARVARD UNIVERSITY 
 
 D. C. HEATH & CO., PUBLISHERS 
 
 BOSTON NEW YORK CHICAGO 
 
 w -> 
 
 O & ' - 525 i,larf6t St \ 
 
 v Garfield 13 'J f 
 
 .
 
 Entered, according to Act of Congress, in the year 1884, by 
 
 N. S. 8HALER, 
 In the Office of the Librarian of Congress at Washington. 
 
 PRINTED IN U. S. A.
 
 INTRODUCTION. 
 
 First Book of Geology is intended to give the 
 beginner in the study of that science some general 
 ideas concerning the action of those forces that have 
 shaped the earth. Only a very small part of the more 
 important facts that constitute the store of the geologist 
 is given within its pages. The effort of the writer has 
 been to select from that ample store such topics as will 
 give the student an idea of the world as a great workshop, 
 
 \ where the geological forces are constantly working towards 
 definite ends. 
 
 The greatest and most easily seen of these agents is 
 water, therefore the book begins with a study of water in 
 
 v its most simple mode of action. Next, the action of heat, 
 in its various ways of working, should command the stu- 
 dent's attention. Finally, the animal and vegetable life 
 of the earth, whose forces come mainly from the action 
 of heat, receive some attention. 
 
 It will be well for the student to have a general idea of 
 the solar system, for all this machinery of the earth's 
 workshop depends in a large measure on the way in which
 
 IV INTRODUCTION. 
 
 the sun acts on the earth. The sun is related to the 
 earth as the boiler to the steam engine, and it is well 
 to know something of its nature, and of the motions of 
 the earth about it, before looking at its effects. Although 
 this preliminary knowledge is desirable, it is not indispen- 
 sable, for the text explains itself. 
 
 However carefully a text-book may be prepared, and 
 however well it may be used, it cannot of itself alone give 
 much insight into nature. This must come from the use 
 of the student's eyes and mind. The most the student 
 can expect from the book is an idea of what is to be seen 
 in the outer world. He will not really know much of this 
 world until he has learned to read the facts himself. The 
 real use of the book to the beginner is to show those 
 things that cannot be readily seen, and to set forth the 
 nature of the forces that act in propelling the earth's 
 machinery. 
 
 It will be noticed that some of the most important 
 points in the mechanism of the earth are repeatedly re 
 ferred to in successive chapters. This has been done with 
 a view to fixing the memory of the most important truths 
 by looking at them from many sides. Every one who has 
 taught geology must have seen the importance of con- 
 sidering each important fact from many points of view. 
 
 In using this book, the student should, under each chap-
 
 INTRODUCTION. V 
 
 ter, seek to find if there are not some facts in his neigh- 
 borhood that have a bearing on the matter given in the 
 text. Some of the chapters give an account of matters 
 which are found only in a few parts of the earth. Rarely 
 will a student find himself in a position to see with his 
 own eyes the structure or action of volcanoes, or the way 
 in which caverns are formed, but there will always be 
 some part of the book where he can help his understand- 
 ing of the matter with his own eyes. 
 
 Let me also urge upon the students who use this little 
 first book that they help themselves to a more pleasant 
 relation with their world by making collections of min- 
 erals, fossils, plants, and other objects that will tell them 
 something of nature. Not only is there to most young 
 people a peculiar charm in owning a collection of this 
 sort, but, if the owner will learn all he can about each 
 object in his collection, he will soon come to have a valu- 
 able fund of precise and well-remembered information that 
 will stay by him all his life ; while the things that have 
 had nothing but words to fix them on the memory will 
 soon fade away. 
 
 But, above all, I beg each reader and student of this 
 book to remember that this earth is full of lessons that 
 can be read by every one who wishes to know them, 
 lessons that will widen the mind and make the soul more
 
 VI INTBODUCTION. 
 
 fit for the duties and pleasures of life. The inattentive 
 eye never gets this teaching; but, to those who learn to 
 look rightly on this world, it gives without stint from its 
 great store of truth. 
 
 The woodcuts in this book were drawn on wood by 
 Mr. Charles E. Robinson. They are mostly original, but 
 I am indebted to the works of Professor J. D. Dana, 
 Joseph Leidy, and H. A. Nicholson, and to the Seaside 
 Studies in Natural History of Mrs. E. C. Agassiz, and 
 
 Alexander Agassiz, for certain figures. 
 
 N. S. SHALER. 
 
 CAMBRIDGE, MASS., Jan. 1. 1884.
 
 QUESTIONS FOR THE USE OF STUDENTS. 
 
 IT should be noticed that sometimes these questions are 
 designed to direct the student to his personal experiences 
 as well as to the statements of the book. A few questions 
 are enclosed in brackets. These may be omitted, as they 
 are a little outside of the text. 
 
 CHAPTER I. 
 
 Lesson I. Page 1. 
 
 1. What variety do we notice in river pebbles? 2. What is the 
 history of these river pebbles? 3. In what way do they journey down 
 stream? 4. Compare the making of boys' marbles with the making 
 of pebbles. 5. How does frost help in the work? 6. How can this 
 be shown by means of a bomb shell ? 
 
 Lesson II. Page 5. 
 
 1. What is a beach? 2. How does the sea-beach wear its pebbles? 
 3. What is formed of the ground-up pebbles ? 4. Is the same grinding 
 up carried on in a river? 5. How do the two processes differ? 
 6. Whereabouts on the beach are the pebbles the largest ? 7. How 
 does the sea begin the process of pebble making ? 
 
 Lesson III. Page 8. 
 
 1. What is a glacier? 2. How do its pebbles differ from those 
 made in rivers and on beaches? 3. What are moraines? 4. How are 
 glacial pebbles made? 5. Finding these pebbles where no glaciers 
 now exist, what do they teach us? 6. Where are glacial pebbles 
 found in North America? 7. If you live in the part of North Amer-
 
 viii QUESTIONS FOB THE USE OF STUDENTS. 
 
 ica where glaciers have been, you will find gravel heaps on the hill- 
 sides and tops, and the newly uncovered bed rocks will be scratched 
 or smoothed. Is this the case in the region where you live ? 
 
 Lesson IV. Page 12. 
 
 1. How do sand grains differ from pebbles? 2. Describe the ap- 
 pearance^df sand. 3. What do we obtain if we melt sand? 4. When 
 and how is sand made ? 5. How does sand help the streams to wear 
 the rocks ? 6. How does the sandblast act in carving glass ? 
 
 Lesson V. Page 15. 
 
 1. Where do we see thaf action of sand the best ? 2. Why do not 
 the waves wear sand beaches very much? 3. Under what circum- 
 stances does the sand get ground up on the beach ? 4. How does the 
 sand escape from the waves into the air? 5. What are dunes? 
 6. Why are they more common in Europe than in America? 7. Where 
 are they very large ? 8. What is the effect of making a hole in the 
 dunes? 9. How does the sand travel out to sea? 10. Where is the 
 most sand made? 11. Why are there dunes on the Sahara? 12. Is 
 sand formed beneath glaciers? 13. What is the effect of blown sand 
 on the rocks it passes over ? 
 
 Lesson VI. Page 2O. 
 
 1. Of what is mud composed ? 2. How is it made ? 3. How does 
 it change in nature as we go down stream ? 4. Is it formed on sea- 
 shores? 5. How is mud made in soils? 6. What is the action of 
 earthworms ? 7. Of plant roots ? 8. Describe the several actions that 
 make mud. 
 
 Lesson VII. Page 24. 
 
 1. On what does all the life of the land depend? 2. Describe a 
 soil. 3. Have you ever noticed how a soil is made? 4. From what 
 things are soils made ? 5. How do soils form on bare rock ? 6. On 
 what does the richness of a soil depend ? 7. Describe the action of 
 tillage on soils. 8. How are soils formed along rivers? 9. How do 
 glacial soils differ from others ? 10. Why do we owe a duty by soils ?
 
 QUESTIONS FOR THE USE OF STUDENTS. ix 
 
 CHAPTER II. 
 
 Lesson I. Page 3O. 
 
 1. When pebbles are connected together, what is the rock called ? 
 2. What is the millstone grit? 3. How are the stones bound together? 
 
 4. How are great quantities of pebbles brought together? 5. What 
 do we learn from the process of making brick? 6. How can the 
 rocks be made very hot ? 7. What changes of shape sometimes occur 
 in the pebbles of pudding-stones? 8. Why do small pebbles last a 
 long time? 
 
 Lesson II. Page 34. 
 
 1. Of what are sandstones made ? 2. Describe the bedding of 
 sandstones. 3. How is cross-bedding made ? 4. Why are sandstones 
 found over so large a part of the world? 
 
 Lesson III. Page 36. 
 
 1. Why are the clay or mud stones found over a wider field than 
 the other rocks ? 2. How do volcanoes help the making of mud on 
 the sea-floor ? 3. What is pumice ? 4. Why can it float very far ? 
 
 5. What is the difference in the rate of making of claystones and sand- 
 stones ? [6. Does this teach us any important fact ?] 
 
 Lesson IV. Page 38. 
 
 1. How do limestones differ from rocks previously described? 
 2. How are they formed? 3. What are coral reefs? 4. Where do 
 coral reefs abound? o. Account for their shapes. 6. Why is a mo- 
 tion of the water necessaiy? 7. Are coral reefs the most powerful 
 makers of limestone? 8. What can you say of f oraminifera ? 9. What 
 changes have been brought about in certain limestones by the action 
 of heat? 10. What effect have these changes on the animal remains 
 buried in the limestone ? 11. How is lime supplied to the sea to re- 
 place that which is constantly being taken from it by animals? 
 12. How do limestones affect soils ? 13. Describe the course of matter 
 from land to sea and from sea back to land. [14. What is the force 
 that brings about this movement?] 
 
 Lesson V. Page 46. 
 
 1. Of what does coal consist? 2. Name the principal varieties of 
 coaly matter. 3. How do plants obtain carbon? 4. What happens
 
 X QUESTIONS FOR THE USE OF STUDENTS. 
 
 when leaves, branches, or trunks of trees fall to the ground ? 5. How, 
 in some cases, is the wood preserved from complete decay? 6. Com- 
 pare the process of decay in a wet and in a dry forest. 7. What is 
 peat? 8. How can peat bogs be converted into coal? 9. How has 
 coal been artificially made ? 10. How can anthracite coal be produced 
 from bituminous coal ? 11. What do we see on the coal field near 
 Kichmond, Va. ? 12. What was the climate during the carboniferous 
 period? 13. Whence comes the heat that we find in coal? 14. How 
 long has coal been in use? 15. Where are the largest coal fields? 
 1G. How is petroleum formed? 17. Where has it long been gathered? 
 18. Where is the greatest amount found? 19. What other form of 
 burnable matter is found in the earth? [20. How does coal affect the 
 prosperity of nations *?] 
 
 CHAPTER III. 
 
 Lesson I. Page 56. 
 
 1. Compare air and ocean. 2. What is the principal gas of the 
 atmosphere ? 3. Of what sort of bits is the air believed to be com- 
 posed ? 4. How do we know that the air can easily move ? 5. How 
 do we know that it can take up particles of water ? 6. How do we 
 know that cold makes it heavier ? 7. What is the effect of the sun on 
 the air at the equator? 8. What is the effect of the lands on the 
 winds? 9. What would be the behavior of winds if the earth were 
 all land or all water? 10. Describe currents of water through air to 
 lands, thence back to seas. 11. What is one important effect? 
 12. How does the air act as a blanket? 13. In what other way does 
 air help life? [14. How do we know that the spaces of the heavens 
 are very cold ?] 
 
 Lesson II. Page 62. 
 
 1. Compare atmosphere and oceans. 2. Describe work of water 
 dependent on its dissolving power. 3. How does water work as a 
 means of carriage of matter? 4. How does it carry heat? 5. What 
 would be the effect if the Gulf Stream ceased to move ? 
 
 Lesson III. Page 66. 
 
 1. What are veins? 2. How are the crevices formed? 3. How are 
 they filled? 4. What valuable substances are found in them? 5. De- 
 scribe some like deposits not in vein crevices. 6. Describe the way in
 
 QUESTIONS FOR THE USE OF STUDENTS. XI 
 
 which metals from veins may pass to the sea. 7. How may the 
 metal then be fixed to the mud ? 8. In what other way may fractures 
 in the rock be filled? 9. How do dykes differ from lava streams? 
 [10. How does the possession of metals affect man ?] 
 
 Lesson IV. Page 74. 
 
 1. Describe the two ways in which rain water goes away from the 
 point where it fell. 2. Describe springs. 3. What may be said of 
 the underground course of strong springs ? 4. What rocks most 
 favor the making of large springs ? 5. What are caverns ? 6. Where 
 are the largest found ? 7. What is the nature of the surface of a 
 country beneath which caverns are found? 8. What are sink-holes, 
 galleries, and domes? 9. How are the domes formed? 10. How do 
 stalactites form ? 11. How do they close the gallery ? 12. What are 
 natural bridges? 13. What is there remarkable about the animals of 
 caves? 14. What are the movements of air into and out of the 
 cavern due to? 15. How are the remains of animals preserved in 
 caves? 16. What other sorts of caves occur, and how are they 
 formed? 17. What is a "spouting horn"? 
 
 CHAPTER IV. 
 
 Lesson I. Page 88. 
 
 1. What part of the earth is known to us by sight? 2. What is a 
 volcano? 3. What gas is most plentiful in volcanic eruptions? 
 
 4. Where are volcanoes found? 5. How do volcanoes originate? 
 (5. What volcanoes are best known to us? 7. Describe the eruption of 
 Vesuvius in 79. 8. What cities were buried? 9. Where is Strom- 
 boli? 10. Describe the flow of a lava stream. 11. What lava streams 
 do we find in California? 12. What part do volcanoes take in the 
 world's machinery? 
 
 Lesson II. Page 98. 
 
 1. What are the two forms of the earth's life? 2. Whence come 
 almost all its motions ? 3. What would be the effect of cutting off 
 the heat of the sun ? 4. In what way does the sun's force come to us ? 
 
 5. What part comes from the fixed stars ? 6. What part of the earth 
 receives the most of the sun's heat? 7. What would happen if the 
 sun's heat stayed where it fell ? 8. What is the effect of the storage
 
 Xll QUESTIONS FOK THE USE OF STUDENTS. 
 
 of heat? 9. How does water carry heat away from the equator? 
 10. What does a paper balloon show us? 11. How can we compare 
 the circulation of the atmosphere with the movement of the air about 
 a heated stove? 12. How would the winds move if the earth stood 
 still on its axis? 13. Why do the winds tend to the west in going- 
 south and to the east in going north ? 14. How can this be illus- 
 trated? 15. How do the trade winds produce the ocean currents? 
 16. In what courses do these currents of the sea move? 17. How do 
 the waters return to the equator? 18. How do the shapes of the 
 lands influence the sea currents? 19. What would be the effect of 
 lowering Alaska and the Aleutian Islands beneath the sea? 20. What 
 are the other causes of changes in the climate ? [21. What do you 
 understand by climate ?] 
 
 CHAPTER V. 
 
 Lesson I. Page 1O7. 
 
 1. What are hills? 2. How do they differ from mountains ? 3. How 
 do the beds of rock lie in mountains? 4. To what are mountains 
 due? 5. What causes the crust to wrinkle? 6. How do we know 
 that most things shrink in losing heat ? 7. How do we know that 
 most mountains rise slowly? 8. What are the Alleghenies like? 
 9. How do. they differ from the Alps ? 10. What happens when 
 mountains cease to grow? 11. What help do mountains give to those 
 who seek the minerals of the earth ? 12. How much do the folds in 
 the rocks differ in size? 13. How do continental folds differ from 
 those of mountains ? [14. What is the striking difference between the 
 movement of heat from the earth's crust and that to the earth's crust 
 from the sun?] 
 
 CHAPTER VI. 
 Lesson I. Page 113. 
 
 1. What should we observe in order to see how valleys are formed ? 
 2. What happens when the lands rise out of the sea? 3. What are 
 the principal parts of a river valley? 4. What do we see in a moun- 
 tain stream? 5. What change is marked when the stream has less 
 fall? 6. How is the alluvial plain made? 7. What is the delta? 
 8. How are falls formed? 9. How is Niagara formed? 10. How the 
 Ohio falls? 11. What are "oxbows"? "moats"? 12. How are ter-
 
 QUESTIONS FOR THE USE OF STUDENTS. Xlll 
 
 races formed? 13. How are canons (pronounced canyons) formed? 
 14. Where is the best example? 15. How was the Yosemite Valley 
 formed? 16. How are tidal valleys formed? 17. Where are good 
 examples ? 18. How do tides affect animal life ? 
 
 Lesson II. Page 125. 
 
 1. What can be said of the way in which lakes are placed? 
 2. What are the important divisions of lakes? 3. Why are certain 
 lakes salt? 4. What of salt deposits? 5. How were most of the lake 
 basins north of 40 latitude formed ? 6. What sort of a surface was 
 given to the land by the glaciers, and why? [7. Why does a lake 
 last but a short geological time?] [8. What will in time happen to 
 the American Great Lakes ?] 
 
 CHAPTER VII. 
 Lesson I. Page ISO. 
 
 1. Describe the events of the Lisbon earthquake. 2. What are the 
 three forms of danger in earthquakes ? 3. Describe the great Missis- 
 sippi earthquake of 1811. 4. What are the worst regions for earth- 
 quakes? 5. What action of the earth may produce the jarring 
 motion of an earthquake ? 6. What effect does it have on the ani- 
 mals of the sea? 7. How does it produce great waves? 8. What is 
 the effect of these waves? 
 
 Lesson II. Page 141. 
 
 1. What is the best proof that the lands have once been sea-floors ? 
 2. What can be said about a lift on the Chilian shore? 3. How does 
 the sea take the lands back to itself ? 4. What would happen if the 
 Isthmus of Darien were to be lowered beneath the sea? 5. What 
 would be the effect of lifting the Malay Archipelago so that a land 
 bridge from Asia to Australia should be formed ? [6. What is the 
 effect of moving animals to new countries?] 
 
 CHAPTER VIII. 
 Lesson I. Page 146. 
 
 1. Whence comes the force that acts in organic life ? 2. What are 
 some of the effects cf life on the earth? 3 What is the best proof of
 
 Xiv QUESTIONS FOE THE USE OF STUDENTS. 
 
 the perfection of the earth's machinery ? [4. Is it reasonable to sup 
 pose that this order is due to chance ?] 
 
 Lesson II. Page 149. 
 
 1. By what marks are organic beings separated from the inanimate 
 world? 2. Give the names of four animals that are closely akin. 
 3. Why are these akin? 4. Give a list of some not closely akin. 
 5. What are the contrivances for measuring time? 6. In what order 
 of relations can you place them ? 7. How many plans of animal 
 structure can you name? [8. Can you classify a bee or a beetle ?] 
 
 CHAPTER IX. 
 
 Lesson I. Page 155. 
 
 1. Contrast living things with things that have not life. 2. Why 
 is there no gradual passage from the mineral to the living world? 
 3. What are the lowliest organized creatures like? 4. What were the 
 first plants? 5. What is the most marked difference between animals 
 and plants? 6. What do plants strive to do in their successive 
 changes? 7. Compare a rose-bush and a sea-weed. 8. What are 
 these changes for? 9. What are the changes in the seed? 10. What 
 purpose do flowers and fruits serve? 11. How do the purposes of 
 animals differ from those of plants ? 12. What is the machinery of 
 intelligence in an animal? 
 
 Lesson II. Page 164. 
 
 1. What are protozoa like? 2. What are radiates like? 3. What 
 are the lowest radiates? 4. What the highest? 5. W T hat about their 
 motion? 6. What about their nervous systems? [7. What about 
 their intelligence?] 
 
 Lesson III. Page 168. 
 
 1. Name some bivalve mollusks. 2. How do they differ from 
 radiates? 3. What forms of bivalves move? 4. Name some single- 
 shelled mollusks. 5. Why are they higher in structure than the 
 bivalves? 6. What are the lowest land animals? 7. How do the 
 squids differ from snails? 8. Why are they higher than snails? 
 9. How do they move? 10. What of their nervous system? 11. Why 
 are mollusks as a whole higher animals than the radiates ?
 
 QUESTIONS FOR THE USE OF STUDENTS. XV 
 
 Lesson IV. Page 175. 
 
 1. Name some articulates. 2. How are they built? 3. How do 
 the worms differ from the crustaceans? 4. How does an insect differ 
 from a crab? 5. Give the names of a dozen different kinds of in- 
 sects? 6. How do the minds of insects differ from those of the lower 
 animals? [7. What is the reason they do not have a more important 
 place in the world ?] 8. Compare the articulates with the mollusks 
 and the radiates. 
 
 Lesson V. Page 179. 
 
 1 . What is the highest of the great groups of animals ? 2. Why is 
 it the highest? 3. What are the peculiar features of the fishes? 
 4. What are the amphibians? 5. What changes do they undergo? 
 6. What are the reptiles? 7. What power of motion do they have? 
 8. How do the birds differ from the reptiles ? 9. What is the advan- 
 tage of warm blood? 10. What is the highest group of animals? 
 11. How is it distinguished? 12. What are the lowest of the mam- 
 mals? 13. Describe the advantages of the vertebrate skeleton. 
 14. How does the nervous system of vertebrates show itself better 
 built than in lower animals ? 15. How do vertebrates give help to 
 their young ? 16. Tell the succession of coming into life of the vari- 
 ous groups of vertebrates. 17. When do the vertebrates first appear 
 on the earth? 18. How do the means of speech in vertebrates com- 
 pare with those of lower animals? 19. How does man differ from 
 the lower animals? 20. How is he related to them? [21. How does 
 his mind differ from the animal mind?] 
 
 CHAPTER X. 
 
 Lesson I. Page 189. 
 
 1. What animals leave no remains on the rocks? 2. What be- 
 comes of hard parts if they are left uncovered on the surface of the 
 earth? 3. What do we find in an old forest? 4. What are the ways 
 in which animals may become buried on the land? 5. Why are 
 fossils more often formed on the sea than on the land? 6. How are 
 fossils preserved? 7. How are they changed after they become deeply 
 buried? 8. Of what use are fossils to the geologist? 9. What do 
 they tell him? [10. What part of all the life that the earth has borne 
 has been fossilized?]
 
 XVi QUESTIONS FOR THE USE OF STUDENTS. 
 
 CHAPTER XL 
 
 Lesson I. Page 195. 
 
 1. How long have we known that life was a very ancient thing in 
 the world? 2. Why must we believe that existing animals have 
 sprung from the more ancient kinds that once existed, but no longer 
 live? 3. What does the Darwinian theory suppose? 4. What do we 
 find among our domestic animals that helps us to understand the 
 changes of animals? 5. How do we know that life may become 
 degraded as well as advanced? [6. Is there any similar truth in 
 morals?] 
 
 Lesson II. Page 2O3. 
 
 1. How do conglomerates or pudding-stones and sandstones show 
 that the earth is old? 2. How do limestones show it? 3. What do 
 we learn from water-falls? 4. From the peninsula of Florida? 
 5. From the elevation of certain countries? 6. How does the history 
 of life show us that the earth is very old? 7. How can we represent 
 the earth's age in years by distance in feet ? 8. How do the beds of 
 rock give us clews to the history of the earth? 9. How many years of 
 life can you remember? 10. What part is this of 1,000,000 years? 
 
 CHAPTER XH. 
 
 Lesson I. Page 209. 
 
 1. What was probably the first condition of the earth? 2. What 
 do we learn from the planet Saturn ? 3. How was the heat of the 
 earth developed? 4. When did the water of the seas come upon the 
 earth? 
 
 Lesson II. Page 213. 
 
 1. What are the oldest rocks called ? 2. Where do we find the first 
 certain evidences of life? 3. What animals were there in the seas? 
 4. What higher animals were wanting? 5. What change in life 
 marks the Devonian period? 6. What marks the carboniferous age? 
 7. What important groups of animals appeared then ? 8. What im- 
 portant groups of animals appear in the Triassic age? 9. What do 
 the Connecticut Valley footprints teach us ? 10. When did the first 
 mammals appear? 11. What were they like? 12. What do the salt 
 deposits of the Triassic time teach us ? 13. What were the reptiles
 
 QUESTIONS FOR THE USE OF STUDENTS. xvii 
 
 of the Reptilian period like? 14. When do the birds first appear? 
 15. How did they differ from our living birds ? 16. What advance 
 took place in the plants of this time? 17. Wliat changes in the land 
 took place in the Cretaceous period? 18. When did the broad-leaved 
 trees begin? 19. In passing from the Cretaceous to the Tertiary 
 period, what was the great change in life? 20. Is it likely that these 
 new forms of animals were suddenly created? 21. What common 
 forms of animals were wanting in the lower Tertiary? 22. What was 
 the nature of the mass of mammals at that time? 23. What were the 
 successive changes by which the five-fingered foot became changed 
 into a horse's foot? 24. What are the splint bones of the horse's foot? 
 25. What can be said about the advance of birds during the Ter- 
 tiary period? 26. What about advance in the insects? 27. What 
 about advance in the cephalopods? 28. What advance is seen in the 
 plants? 
 
 APPENDIX. 
 
 Crystalline Rocks. Page 233. 
 
 1. What are the three physical states of matter? 2. In which state 
 do crystals occur? 3. Give some instances of crystals. 4. What can 
 be said of the shape of crystals of any one substance? 5. What do 
 meteors show us? 6. What do we find in little-changed stratified 
 rocks? 7. How are crystalline rocks made? 
 
 1. What is claystone? 2. How is slaty cleavage made? 3. How 
 is limestone marble made? 4. What is the change that may be 
 made in sandstone? 5. What are dykes? 6. What are veins? 
 7. Give the important points about the following minerals: quartz, 
 felspar, mica, hornblende, pyroxine, calcite, dolomite, gypsum, com- 
 mon salt, pyrite, magnetite, hematite, limonite, siderite, copper, zinc, 
 tin, gold, aluminium, sulphur. 8. Of what minerals are the following 
 rocks composed: granite, syenite, gneiss, mica schist, porphyry, stea- 
 tite, turpentine, quartzite? 9. How are these rocks and crystals de 
 stroyed? 10. How do they return to the crystalline state?
 
 CHAPTER I. 
 
 PEBBLES, SAND, AND CLAT. 
 
 LESSON I. 
 RIVER PEBBLES. 
 
 F ET us take a number of pebbles such as come from the 
 -*-^ bed of a river. We notice that they are of different 
 shapes and of different colors and of many sizes. They are 
 all hard and smooth, but some are smoother than others ; 
 some have faces- that are nearly flat, and some are almost 
 as round as marbles ; some are all of the same sort of stone, 
 and others are made up of several different kinds of stone 
 mingled together. If we could see the way in which these 
 pebbles were formed, we should know much of the history 
 of the world. 
 
 Let us trace the history of these pebbles back into the 
 past. It is a long story ; for, between the time their mak- 
 ing began and the hour in which they were taken from 
 the water, a vast length of years has gone by. If we look 
 at the stream-bed where these pebbles were found, we find 
 that it is so full of them that its bottom and sides are in 
 good part made up of such bits of stone. When they were 
 taken out, they were slowly working down towards the 
 sea. Every flood rolled them a little farther on their way, 
 and were it not for the fact that they are from time to 
 time caught on the sides of the stream, and held by the 
 other stones laid on top of them, or tied by the roots of
 
 2 PEBBLES, SAND, AND CLAY. 
 
 plants, they would travel only a few years before they 
 would be either worn out by the bruising they received 
 on their rough journey, or rolled into the sea. But if we 
 examine the banks of either side of the river, we find that 
 there are great quantities of such pebbles as are now in the 
 stream, that have been stopped in their journey, and built 
 into the strip of level land that makes a plain on either 
 side of the river. The chance was, that if these pebbles 
 had been left where they were found, they too would have 
 often been compelled to wait on the bank; because the 
 stream does not always keep the same bed, but is continually 
 
 Firj. 1. 
 
 Section across River Valley. 
 
 cutting away on one side and filling in on the other. So 
 that each pebble journeys a little way down stream, and 
 then rests awhile on the bank ; while other pebbles, that 
 have been perhaps for thousands of years imprisoned in the 
 bank, are taken out by the changing river and. carried a 
 way down stream, again to be put into their resting-places 
 on the alluvial land. 
 
 Let us look for the place where these pebbles were 
 found. As we go up stream we find the pebbles growing 
 always larger and more angular, until at length we find 
 them so heavy that only the swiftest-running waters can 
 move them ; this is because they wear away by rolling
 
 RIVER PEBBLES. 8 
 
 over each other. This work is copied in the making of 
 boys' marbles ; and it is worth while to notice how in this, 
 as in many' other branches of labor, man succeeds in his 
 tasks by imitating Nature. In making marbles, bits of 
 square stone, all of about the same size and of even hard- 
 ness, are put into a large drum through which a stream of 
 water flows. This drum turns around like a wheel, causing 
 the stones to rub over each other ; the same amount of 
 wear being given to every side, they come out spheres. It 
 might seem at first that we ought to have the same shapes 
 in the river-pebbles, but we notice that these are usually a 
 little larger one way than they are the other ; they are 
 often so flattened that they are called "shingle." This is 
 because stones are generally more easily worn in one direc- 
 tion than in the others. They are not equally soft on all 
 sides. If we should turn them round on a lathe, and then 
 put them in the marble-maker's drum, they would wear 
 into oblong shapes. As soon as a stone is a little flattened, 
 the water finds it easier to push it along on its side than to 
 roll it over and over ; so it wears it into the thin shapes we 
 often find. 
 
 Going up the stream, we come to trie part of its course 
 where it no longer makes its bed in gravel and sand, but 
 tumbles over the hard rocks. Here we can see the place 
 where the making of the pebbles begins. We see large 
 masses of stone that have been broken out of the cliffs 
 that border the streams. These bits are of all sizes : some 
 of them so small that the stream sends them bowling along 
 down its bed ; others great masses as large as a barrel, or 
 larger, that lie still in its bed, and force the water to turn 
 out of its way. When these great masses of stone are very 
 solid, they may last for centuries without being harmed by 
 the stream ; but usually there are some very slight crevices
 
 4 PEBBLES, SAXD, AND CLAY. 
 
 in the stone into which the water finds its way. During 
 the summer season the water can do but little, but when 
 the intense cold of winter comes, and all the stream is 
 frozen to its bottom, this water in the crevice also freezes, 
 and in so doing exerts power enough to split the stone 
 in two. This force the ice has because water in freezing 
 must expand by one-seventh its bulk ; to get this greater 
 space it will push tilings apart slowly, but with all the 
 force of gunpowder. A bomb-shell can be broken by nil- 
 ing it with water, plugging up the hole with an iron screw, 
 and putting it out of doors of a winter's night when the 
 
 Section down a River Bed. 
 
 thermometer goes below zero. We often see how power- 
 ful it is from the bursting of frozen water-pipes. 
 
 This rending by the frost will soon break up most rocks 
 to bits that the river in its flood-times can drive down 
 its bed. But generally the stream grows less swift as it 
 descends toward the sea, so that the stone is urged for- 
 ward with less force than is necessary to move it. When 
 this happens, it lies awhile until the frosts of other winters 
 have divided it again. 
 
 It is this same frost that does the most of the work of 
 breaking the stones out of the cliff sides, so that they may 
 tumble into the brook*
 
 SEA PEBBLES. 
 
 LESSON II. 
 SEA PEBBLES. 
 
 WE have now seen the most common way in which peb- 
 bles are formed ; but there is another pebble-mill on the 
 sea-shore that does much the same sort of work, though it 
 makes pebbles of a somewhat different form. 
 
 If we go to the coast anywhere where the shore follows 
 the wide sea, or around a lake large enough to form great 
 
 Fig. 3. Section of a Cliff Sea-shore. 
 
 waves, on these coasts we find two sorts of shores: when 
 the hard rocks jut out into the sea, there are steep cliffs 
 against which the waves beat (see Fig. 3 ) ; but the larger 
 part of the shore is shelving, being made of pebbles and 
 sand. These shelving shores are called " beaches." They 
 are of the form shown in the figure (see Fig. 4). As we 
 stand on these shores we see that the waves, as they break 
 upon it, run up the beach with great power, and then hurry 
 back only to rush again up the slope and again return. If 
 the waves be strong, this swashing to and fro carries the
 
 6 PEBBLES, SAND, AND CLAY. 
 
 water very swiftly up and down the slope ; and, as it goes, 
 it rolls the pebbles with it. In heavy storms, stones as big 
 as a man's head are easily rolled to and fro for two or three 
 hundred feet of distance. In these storms, the smaller 
 pebbles are often flung out with the foam beyond the 
 sweep of the wave, making the ridge shown in the 
 picture. 
 
 But most of the pebbles of the beach swing to and fro 
 within the waves until they are ground to the finest bits. 
 They are in a mill that never stops working. Although 
 in the course of ages the shore moves about, it is really 
 
 Fir/. 4. 
 Section of a Sea Beach. 
 
 among the most enduring things of the world ; for the waves 
 of the sea have rolled in this fashion against the land ever 
 since the seas were made. A pebble on the beach, unless 
 it gets covered up by other pebbles, wears away very fast. 
 It travels in times of calm a little distance every time the 
 wave strikes ; as this is, say, six times a minute, the stones 
 move a few feet (we may average the distance at ten 
 feet) in all weathers; they would thus travel between 
 twelve and fifteen miles a day. We have only to listen, 
 as the waves rush up and down, to hear the grinding 
 of the pebbles against each other as they are rolled to 
 and fro. It is not only the top pebbles that roll, but the
 
 SEA PEBBLES. 
 
 whole of the beach is moved to the depth of two or three 
 feet. Sometimes the roar of the grinding stones can be 
 heard several hundred feet away from the beach. 
 
 The ground-up pebbles make sand and mud, the history 
 of which we shall follow hereafter. We will now go seek- 
 ing for the origin of the beach pebbles, as we sought it 
 in ascending the stream when we were finding the way in 
 which river pebbles came to be. Nearly all beaches of the 
 sea-shore are crescent-shaped, as in Fig. 4; they have at 
 one or both ends of the horns the place where the peb- 
 bles begin to be made. We find these smallest in the 
 bottom of the hollow, and 
 they grow larger as we pass 
 out toward the place where 
 they begin to form; just as 
 they grew larger as we went 
 up the stream when looking 
 for the place whence the river 
 pebbles came. When we get 
 to the end of the beach we find 
 the beating sea-waves at work &a- 5 - Ma P of a Sea Beach - 
 cutting out the stones of which the pebbles are to be made. 
 If the rock be as soft as a gravel bank is, and many of the 
 beaches of our northern coast are cut in gravelly beds, the 
 sea has little work to do ; the waves soon cut back into the 
 cliff, when the overhanging mass slips down into the sea ; then 
 the pebbles are driven on to the beach, when their rolling to 
 and fro begins. But when the rocks are hard, the sea has a 
 good deal of work to do to force out the blocks of stone ; but 
 by taking those on which it gets a grip, and hurling them 
 against the rock, it slowly but surely manages to cut back 
 a groove so that the rocks overhang and fall of their own 
 weight. When they fall, these masses of rock generally
 
 8 PEBBLES, SAND, AND CLAY. 
 
 break up into pieces that the waves can lift and hurl 
 against the cliff, or against each other, until, by breaking, 
 they become small enough to be kept in constant motion : 
 then they are quickly crushed into pebbles, and rolled to 
 the beach. Thus, the cliff part of the shore feeds the sea- 
 beach, which is a sort of mill for grinding pebbles. 
 
 LESSON III. 
 
 GLACIAL PEBBLES. 
 
 THERE is a third kind of pebble that has a different his- 
 tory from either of the other two. It, too, is the work of 
 water, but of water working in the very different form 
 of ice. In the regions near the poles of the earth, and in 
 the high-up valleys of some great mountains, we have snow 
 that never melts from one year to another. This snow 
 would make an immensely high mass if it had no way to 
 escape ; but a road for it to get into warmer regions where 
 it can melt is provided in this way : 
 
 The eternal snow-fields are always receiving snow both 
 in summer and winter. This snow is pressed down by 
 that which falls upon it, and by this pressure is turned 
 into ice. We easily see how much harder and ice-like 
 snow grows when pressed. A snow-ball, if squeezed hard, 
 becomes a whitish ice, and the snow that gathers on our 
 feet is almost as hard as ice. Now, a great mass of this 
 hardened snow, lying on the sloping ground of the moun- 
 tains, will flow down that slope, becoming more like pure 
 ice as it goes downward. When it gets into the lower 
 valleys, it is a true river of ice, that may be half a mile or 
 more wide, and hundreds of feet deep. In the Alps and 
 Himalayas these streams slowly creep for miles, some- 
 times for as much as thirty miles, down the valleys, until 
 they come to regions warm enough to melt them away.
 
 GLACIAL PEBBLES. 9 
 
 These streams of ice are called "glaciers," from the French 
 word glace, which means ice. They move very slowly, not 
 more than three or four feet a day. They are constantly 
 breaking and soldering together, but still they move on, 
 faster in summer and slower in winter, and so drain away 
 the snow from the regions where it cannot melt. Out 
 from beneath these glaciers there flows a stream. Its 
 water is always very muddy, and it bears away many 
 
 Fig. 6. 
 Section down a Glacier. 
 
 pebbles, which, with the rocks that have been carried on 
 the surface of the ice, make great masses of stones called 
 " moraines." 
 
 If we look closely at these pebbles, we may see that, 
 though they somewhat resemble those from the rivers and 
 the sea-shore, they are yet unlike them. These stones 
 shaped beneath the ice are not so smooth and round as 
 the others ; they often have scratches upon them, as in 
 the figure, which show that they have been held fast 
 in the ice and pushed over some hard substance. (Fig. 7.) 
 We can see the way these scratches are formed if we enter 
 the cave out of which flows the stream that drains the 
 glacier, and find a place where the ice rests on the rock.
 
 10 PEBBLES, SAND, AND CLAY. 
 
 This we can easily do on many a glacier. When the ice 
 rests on the rock, we often find that it has grasped pebbles 
 that are held firmly upon the rock and forced along over 
 it. As the ice slowly melts when it touches the rock, 
 because of the heat of the earth and the heat that comes 
 from the rubbing that takes place there, these stones are 
 pressed on by all the ice above them, so that a stone as 
 big as an apple may have many tons of weight upon it. 
 
 These pebbles scratch the stone over which they are 
 pushed, and in turn are scratched; and so, when they 
 escape at the end of the glacier, they generally bear the 
 
 Fig. 1. Rock surfaces scratched by Glaciers. 
 
 marks of their struggle with the ice and rock. It is not 
 every pebble that has been under the ice that bears these 
 marks, for there are many that never get caught in this 
 way, but are carried on by the stream that flows below 
 the ice, or held up in the ice so that they are not against 
 the rock. 
 
 These pebbles are made out of bits of stone torn out of 
 the rock-bed over which the glacie*r flows, or that fall from 
 the rocky sides of the mountain upon the surface of the 
 ice, and then find their way through the cracks in the ice 
 to the bed of the glacier. 
 
 Figure 6 shows an ice stream, with the heaps of stone
 
 GLACIAL PEBBLES. 11 
 
 upon it that have fallen from the sides of the mountains, 
 and which very often find their way down into the pebble 
 factory at the base of the glacier. 
 
 The muddiness of the water flowing from beneath gla- 
 ciers is noteworthy. This mud is made in the grinding 
 of pebbles and sand in the way that we have seen. There 
 is so much of it that every river in Switzerland which has 
 glaciers on its headwaters is very muddy, while those that 
 flow from lower mountains that have no ice streams are 
 of crystal purity. 
 
 We have now seen how the pebbles are made beneath 
 glaciers, and the reasons why they are more angular than 
 those made by flowing water. We can easily believe that 
 these scratched pebbles tell an important story when we 
 find them in countries where there are at present no 
 glaciers. As there is no other possible way in which peb- 
 bles can be so scratched, we may be sure that wherever we 
 find them thus marked they show that glaciers once ex- 
 isted. Now, such scratched pebbles exist over a large 
 part of North America and Europe, and other countries 
 where there is now no trace of glaciers. If we take a line 
 from New York City through Pennsylvania, and thence 
 across the continent to St. Paul, Minn., then to the Black 
 Hills, then south to the Rocky Mountains of Southern 
 Colorado, then to the sea-shore at the mouth of the Colum- 
 bia River, we may almost always find scratched pebbles 
 along this line, and in nearly all the region to the north 
 of it, as well as some few points to the south of it. If 
 we search below the soil, in these countries, we often find 
 the rocks still scratched by the work of the ice armed with 
 these bits of stone. From these proofs we are certain 
 that a thick sheet of ico once lay over all this country, 
 and moved southwards, scratching pebbles and rocks as
 
 12 PEBBLES, SAND, AND CLAY. 
 
 it went. All through this region these glacial pebbles 
 are very plenty, sometimes forming hills a hundred or 
 more feet in height. So plentiful are these rudely-shaped 
 pebbles in these northern countries, that we find more of 
 them in the streams and on the sea-shore than either 
 streams or sea can make for themselves. There are many 
 times as many pebbles made by this ice-mill now, on the 
 surface of North America, as have been made by the 
 streams or waves and rivers combined. Indeed, a large 
 part of the work now done by the rivers and sea-shore 
 waves consists in shaping out and rearranging the pebbles 
 that the ice has left over the land. We cannot now turn 
 aside to consider the history of this wonderful ice time, for 
 we intend to go only as far as the pebbles serve to show 
 the way ; yet we see that these bits of scratched stone, 
 when we read them aright, open to us a wonderful chapter 
 in the earth's history. So is it with all the things of 
 this world. If we could see all that one of these little bits 
 of stone has lived through, we should be able to look back 
 through a mighty past, that would startle us with its 
 strange scenes. 
 
 LESSON IV. 
 SAND. 
 
 WHILE looking at the history of pebbles, we often find 
 ourselves in company with its numerous humbler kinsmen, 
 the sand-grains. At first sight it might seem that these 
 sand-grains are only little pebbles that are near the 
 end of their long combat with the water, that fight 
 they wage so well, though in the end they are overcome :
 
 SAND. 13 
 
 but, when we look closely at them, we see that although 
 there are pebbles no bigger than large grains of sand, a 
 grain of sand is, after all, a different thing from a little 
 pebble. 
 
 If we take some sand from a river, where, as with 
 pebbles, we will begin our study of sand, we generally 
 find, if we look closely, and especially if we take a common 
 magnifying-glass to aid us, that these grains are sharp- 
 angled, with flattened sides, and that they are generally 
 like bits of glass, letting the light through them, though 
 not exactly transparent. This shows us that sand-grains 
 are in fact crystals, generally of a substance called quartz. 
 We can easily satisfy ourselves that these grains are harder 
 than most stones ; by rubbing sand-grains upon the stones, 
 they will scratch these stones without breaking the sharp- 
 ness of the edges of the grains. The only change that 
 comes over the grains is that many of them break into 
 two or more pieces, which still preserve the sharpness of 
 the larger bits. Even the powdery-looking stuff, if we 
 look closely at it with a microscope, is seen to be made up 
 of small, sharp bits. 
 
 If we compare the sand-grains with a tiny pebble of the 
 same size, using a strong magnifying power to aid our 
 sight, we find that the grains of sand are all composed of 
 one like substance, while the pebble is made up of many 
 grains of different sorts of substances. This substance of 
 most sand is the same as glass ; indeed, glass is made by 
 melting sand, using some potash, soda, or lime only to aid 
 the melting. We know how hard and cutting bits of 
 glass are ; sand-grains are even harder ; for it is necessary 
 to put some other substance into glass to make it melt 
 easily, and this softens it somewhat. 
 
 As we go up-stream, searching for the place where the
 
 14 PEBBLES, SAND, AND CLAY. 
 
 sand is formed, we do not find the grains growing much 
 larger, however far we have to go to find the place vriiere 
 it is made. This is a proof that the sand-grains do not 
 wear so fast as the pebbles ; for the lessening in the size of 
 the pebbles as we go down stream is very marked. Often 
 a good deal of the sftnd comes from the pebbles themselves; 
 for these pebbles are often composed in part of quartz 
 crystals, which break out in the shape of sand-grains when 
 the pebbles are pushed along the bed of the stream and 
 bruised against each other. But when a stream abounds 
 in sharp sand, we shall find that along its course there are 
 some rocks composed in part of quartz, such as granite, 
 or syenite, or sandstone. When these rocks decay, they 
 fall to pieces, and these grains of sand, being lighter than 
 many other things that make rocks, are easily moved by 
 the tiniest rills to the nearest stream, and they can jour- 
 ney down to the sea without any trouble. In all rivers 
 that have anything to make sand of, along their banks, 
 there is a constant stream of sand moving down to the sea, 
 more in times of flood than in low water, but always 
 some. In the Arno, in Italy, on the banks of which 
 these pages are written, we have a good instance of this. 
 Where the stream goes through Florence, it is a rather 
 small river, indeed less than the Merrimac, the Mohawk, 
 or the Great Miami rivers of America. A dam across the 
 stream deadens the current, and helps the sand to settle 
 to the bottom. Boatmen with long scoops are constantly 
 taking out this sand from the pool below the dam, many 
 cartloads a day being thus removed. But there is never 
 any lack of new sand to fill the places ; when one place is 
 cleared, a few days suffice to fill it up again ; yet this is 
 not what would be called a very sandy river. In some 
 parts of the Allegheny mountain country, where all the
 
 SAND OF THE SEA-SHORE. 15 
 
 rocks are sandy and decay quite rapidly, the streams 
 carry so much sand that it is not possible to make a mill- 
 pond that will be of any use, for the basin will be rilled up 
 in a few months' time. 
 
 As these sand-grains have sharp edges, and are harder 
 than any other stones, they cut the stones they slip over. 
 Whenever one stone is driven over another, there are 
 generally some grains of sand below the rock to help to 
 wear them away. The cutting power of a stream of 
 water 1 depends very much on the amount of sand or peb- 
 bles it has in it. If we drive a stream of pure water 
 against a pane of glass, it will not affect it, even if we 
 keep it moving at a high speed for days ; but, if we have 
 a little sand on it, the water will drive the sand against 
 the glass, and in a few minutes it will appear ^ike ground 
 glass, from the cutting action of the sand. In the same 
 way, the river-water gets a power of wearing stones. In a 
 similar fashion, the sand is used in glass-cutting to shape 
 figures on the surface of the glass. If the workman wishes 
 to make a figure like a leaf, he pastes a paper on the glass, 
 leaving the figure of a leaf bare. He then puts the glass 
 in a blast of air, or steam, that drives sand at a high speed 
 against it, and in a short time the bare part is cut so that 
 it appears white, while the paper protects the rest of the 
 surface from the cutting power of the sand. 
 
 LESSON V. 
 
 SAND OF THE SEA-SHORE. 
 
 NOWHERE else in the world can we see sand to so much 
 advantage as on the sea-shore. Indeed, most shores seem 
 at first sight like only sea and sand. On the sea-shore we
 
 16 PEBBLES, SAND, AND CLAY. 
 
 find the sand is the best friend the land has in its eternal 
 combat with the sea. On far more than half the coasts of 
 the world it forms a sort of armor, on which the pebble- 
 armed sea can strike its blows without such destructive 
 effects as it would bring about on bare rocks. 
 
 If we examine a beach when the surf is rolling in upon 
 it, we may see how the sand resists the mighty blows that 
 are struck against it. When the wave lifts itself into a 
 great wall to tumble on to the beach, the hard grains of 
 sand lie close together so compacted that the foot will 
 hardly make a print upon them ; yet between the grains 
 is a little cushion of water which keeps them from wearing 
 against each other. When the blow is struck, the sand 
 hardly feels the effect ; a part of it is stirred, but the 
 grains are so wrapped about with water that they do not 
 harm each other. If they were pebbles, they would pound 
 against each other with a roar that we should hear above 
 the sound of the waves ; but the littleness and lightness 
 of the sand gives it security. It is only when the sand 
 gets between stones, that are pounded together by the 
 waves, that it is much worn ; then some of its grains are 
 ground to fine powder. The most of the sand we find 
 on the sea-shore is made by this pounding of the stones 
 together. In this pounding both stones and mud wear 
 very rapidly, some part of each being ground into the fine 
 powder we call "mud," a form of bruised stone which we 
 have soon to consider. 
 
 Above the point where the waves beat most fiercely, 
 where the broken water of the surf writhes hurriedly about 
 in foaming eddies, the sand moves far more than when it 
 receives the solid blow of the falling waves. Here, too, it 
 moves but little, but it makes a mill where little pebbles 
 and bits of shell, sea-weed, etc., are cut up by its sharp
 
 SAND OF THE SEA-SHORE. 17 
 
 points, and gradually ground into powder. This is an 
 important work for the sand to do, as it makes a great 
 deal of muddy matter, out of which the sea builds rocks, 
 as we shall see hereafter. It also, by grinding up rubbish, 
 keeps the sea-beach the clean, orderly place we always 
 find it to be. 
 
 The heavy storms throw a good deal of sand above the 
 level attained by ordinary waves. This becomes very 
 dry ; few plants can grow upon it, and these are killed by 
 the next heavy storm. When the tides are low, the hot 
 sun soon dries the exposed surface of sand down to near 
 
 Fig. 8. Dunes that destroyed Eccles, Norfolk, England. 
 
 the level of low tide. When the wind blows strongly from 
 the sea, it moves this sand before it. We can at such times 
 see little streams of blown sand moving up the beach until 
 they are beyond the reach of the waves. This sand helps 
 to make the high beach wall that often lies along the 
 shore. On most shores the winds from the land side soon 
 blow most of this back into the water. But if it happens 
 that the winds from the sea are more powerful than those 
 from the land, this sand keeps working inland, and gathers 
 into great heaps called " dunes." These dunes are sometimes 
 more than a hundred feet high, and miles in length. (Fig. 
 8.) The sand from the seaward side keeps blowing over
 
 !# PEBBLES, SAND, AND CLAY. 
 
 to the landward side, and so the dunes slowly wend away 
 from the sea-shore, sometimes marching slowly inland and 
 overwhelming fields and villages as they go. On the 
 Atlantic coast of North America the winds are generally 
 from the west, hence the dunes do not often have a 
 chance to form, for the sand is blown out to sea. But in 
 Europe, the same west winds carry the sand inland. In 
 the head of the Bay of Biscay these sand-heaps are of very 
 great size, and have covered a great deal of land. But 
 for certain plants which flourish even on the sand, and 
 tend to bind it together, it would not be possible to save 
 many fertile regions from these dunes; but the grasses 
 knit them together in a firm way, so that the wind cannot 
 move them. If by any chance a hole is made in this 
 covering of grass, the wind getting into it will sometimes 
 tear the hill away. Even a footstep will sometimes start 
 the break in the bonds the grass puts upon it. 
 
 On the land side the wind tends to take the sand away 
 from the shore ; and on the sea side the currents of the 
 water, especially of the tides, work to pull the sand out to 
 sea. We find, by drawing up specimens of the bottom in 
 dredges, that the sea-floor, for hundreds of miles from the 
 land, is covered by sands that wander to and fro in the 
 sway of the currents that sweep near the shore. These 
 sands have all been formed in the course of ages along 
 the shores or in the rivers. But the most of the work of 
 making sand is probably done on the surface of the land 
 by the decay of the rocks, which fall into sand, and are 
 then carried by the streams into the sea ; where, because 
 of its fineness and lightness, it may easily wander very far 
 even in slight currents. 
 
 If we take up a little of any soil, we are pretty sure to 
 find that it is partly composed of sand. In most regions this
 
 SAND OF THE SEA-SHOKE. 
 
 19 
 
 sand is always part of the soil. So we see how universal 
 this sort of matter is in the world. If by any change of 
 climate a soil becomes too dry for plants to live, as in the 
 Sahara Desert, then the soil becomes the prey of the 
 winds, that sweep it about and make great dunes of mov- 
 ing sand and finer dust. These, as well as the sea-sands, 
 may blow into fertile countries and reduce them to deserts. 
 In this way the African deserts are always trying to gain 
 
 Fig. 9. Nile Delta and neighboring Deserts. 
 
 on the fertile land of Egypt. If it were not for the plants 
 that hold the soil down, so that the wind cannot get hold 
 of it, all our earth's surface would be as uneasy as the 
 sands of the Sahara. 
 
 Sand is also plentifully formed beneath glaciers, even 
 more plentifully than on the shores or in the streams, for 
 there the pressure is far greater, and the stones are easily 
 crushed by it. 
 
 When the sand is sharp, and blown in quantities by the 
 wind, it sometimes cuts the rocks a good deal. In some 
 parts of the Rocky Mountains it polishes and scratches the 
 stones in the process. On some shores, when the wind 
 blows along the coast, the pebbles are slowly worn away 
 by the sharp grains that are constantly swept over them.
 
 20 PEBBLES, SAXD, AND CLAY. 
 
 LESSON VI. 
 
 MUD. 
 
 As the sand comes below the pebbles in size, so these 
 mud grains, which we are about to study, are less than 
 the sand. Mud grains are so small that we cannot see 
 them well without the microscope, and they have none of 
 the charm for the eye- that belongs to clean pebbles or 
 sharp sand ; yet, like all other things that at first sight 
 seem to want beauty, mud is full of interest and of beauty, 
 too, when we come to understand it. 
 
 If we put some mud under the microscope, we find 
 that it is composed of small powdered and battered grains 
 of rock, many kinds commonly being mingled together in 
 the mass. We see that some of the bits are like little peb- 
 bles, being composed of several sorts of stone in the same 
 piece ; others are very small fragments of sand that have 
 become decayed and softened after their long battle with 
 the waters. We also often find little bits of plants, frag- 
 ments of shells, etc. In other words, mud is the result of 
 the constant battering that serves to break the fragments 
 of rock into small pieces, and of the decay that con- 
 stantly divides the bits into yet smaller particles. 
 
 If we put a little of this mud into water, we see that, 
 unlike sand and pebbles, it does not at once fall to the 
 bottom of the vessel, but remains like a cloud, only 
 slowly settling to the bottom. Some of it will go down 
 in a few minutes, some will fall in a day, but even in a bot- 
 tle only six inches high there will be some that will require 
 a day to find its way to the bottom. 
 
 If we go to any stream, we shall find that, if it be a
 
 MUD. 21 
 
 mountain brook, there will be but little mud, and that 
 coarse grained. Stirring the water, we find that the cloud 
 of mud that is raised quickly falls to the bottom, showing 
 that it is coarse grained. This is because the finely divided 
 rock easily runs away in the swiftly flowing water, and is 
 carried off as fast as it is made. Going down stream to 
 where the water flows more slowly, we shall find the mud 
 becoming finer and finer, as is shown by the fact that, if 
 we stir the bottom, the water will remain muddy for a 
 longer time. As we go towards the mouth of a large 
 river, such as the Mississippi, we find the water, though it 
 moves slowly, is always clouded with mud, and the banks 
 are, in the main, made of mud of the finest sort. Such a 
 stream is always rolling out to" sea a great mass of this 
 mud, so finely divided that it may stay afloat for weeks 
 and months, and thus be carried to distant parts of the 
 sea. 
 
 This finely divided rock which we see as mud is abun- 
 dantly formed on the sea-shores, as well as in the streams. 
 The stones grinding together wear into this shape, and the 
 sand that is rubbed between them has the same fate. We 
 see little of the mud on the shore, because the currents 
 formed by the tides and winds easily bear it out to sea ; 
 but, at very low tide, we often see very broad flats made 
 entirely of mud ; and, if we look in the bays along the 
 shore, we often find that thousands of acres of land have 
 been built by the mud that has been drifted in from the 
 sea by the tidal currents, and caught by the salt-water 
 plants. Yet more of this mud from the shore goes far off 
 to sea, and falls on to the deep ocean floors. 
 
 Yet the most of the mud is not ground up by the sea- 
 waves, or the rubbing of stones on the river-bed. It is 
 made in and beneath the soil, by the action of decay,
 
 22 PEBBLES, SAND, AND CLAY. 
 
 brought about by water, and also by the work of plants 
 and animals. If we take some soil from a field, and dis- 
 solve it in water, we find that it is partly composed of sand, 
 in part of decayed plants, but in yet larger part of grains 
 of mud. These mud grains generally make up more than 
 half the whole. In all fertile soils they are much more 
 than half the total mass. If we look closely, we may 
 see what are the means whereby these mud grains are 
 made. 
 
 When water goes through the layer of decaying plants, 
 it takes up certain acids from it. These acids are formed 
 by the decay of the dead plants in the soil. By these 
 acids, as well as by the oxygen, which in part composes 
 it, water has a very great power of rotting the rocks into 
 fine powder. This process is called oxidizing. A famil- 
 iar instance of it is seen when iron rusts in the ground, 
 When the ground freezes and thaws, this dividing of the 
 stones is greatly helped ; for, the water soaking into them, 
 and then swelling when it turns into ice, bursts them into 
 dust. Then a singular work is done by the earth-worms. 
 These creatures get their living by eating their way 
 through the soil. They take the earth into their stom- 
 achs, take from it what there may be that they can digest ; 
 they then cast the earth out again; but, while in their 
 bodies, the earth is exposed to the acids which serve to 
 digest the food, and is more finely divided. Now, as in 
 most soils there are many thousands of these worms to 
 the acre, and as they are always at work, except when the 
 ground is frozen, it is reckoned that they pass all the 
 soil on which they live through their bodies every few 
 years. There is no doubt that these humble creatures do 
 a work that is fit to be compared with that of the rivers or 
 sea-shores, in grinding up the elements of the earth into 
 the finest mud.
 
 MTTD. 23 
 
 In this work of dividing the fine grains of the soil the 
 roots of plants also take an important share. The little 
 fibrils that the roots put out are very slender, sometimes 
 so small that the eye can just perceive them. These, en- 
 tering into the crevices of the mud grains, grow larger, 
 and, as they expand, burst them apart. The roots of the 
 larger plants, as they grow larger, exert an immense force. 
 They may pry rocks apart as if they were wedges of steel. 
 We see a little of their power on the streets, when they 
 sometimes lift the paving stones. The first little thread 
 of the root is so slender that it can insert itself into the 
 crevices that lie between the grains of sand and mud ; and, 
 once there, it can soon gather power to rend them. 
 
 The largest share of the mud we find in a river is not 
 made in its bed, but is carried from the land by the rains, 
 which very easily dissolve it and convey it away. We have 
 only to watch a plowed field to see how large the amount 
 is that goes away with every rain. Were it not that the 
 forces that break up the rocks into this mud are always 
 at work, there would soon be no place for the plants to 
 grow, so fast do the streams carry it away. 
 
 We have now seen in part how the machinery of the 
 waters, aided by other forces, such as frost, roots, and the 
 stomachs of worms, serve to divide up the rocks of the 
 earth into very tiny bits, that can be easily carried by 
 water. When in this divided state, a good part of the 
 matter tarries on the land, and helps make our soils; the 
 rest goes to the sea, and helps make the rocks that are 
 constantly forming there. 
 
 We will now turn aside to consider the history of soils, 
 for on them depends all the usefulness of the world to 
 man. Then, afterwards, we will see what becomes of the 
 mud and sand that goes from the rivers and shores to the 
 Depths of the seas.
 
 24 PEBBLES, SAND, AND CLAY. 
 
 LESSON VII. 
 
 SOILS. 
 
 THE most important result of this battle, that is waged 
 against the rocks by the air, rain, etc., is the chance it 
 gives for life to find a place on earth. All the vegetable 
 life of the land depends upon the existence of soils, and 
 all the animal life would have no chance to exist, if it 
 were not for the plants. Indeed, much, if not the most 
 of the life of the sea, as we shall find further on, is fed by 
 the things the soils produce. 
 
 In any field we have one of the common shapes which 
 this layer of earth takes on the earth's surface. If we look 
 at it closely, we see that there is on the top a layer of a 
 very dark color, which we at once know has its color given 
 to it by the decayed plants it contains. These plants turn 
 black as they rot; and, though they break up into small 
 bits, we can still see on the surface that they are bits of 
 plants. This is plain, for the plants are not altogether 
 decayed, and keep their shape. As we go downward, these 
 bits of dead plants gradually pass into a brownish mould. 
 As we dig yet deeper, this disappears, and we have the 
 earth without any mixture of plant-fragments, but only 
 colored by the stain of decayed plants. As we go yet fur- 
 ther down, the soil becomes harder, until we come to the 
 rock. This rock is generally soft at the top, and broken up 
 by the roots that work into it. Below tliis level it is found 
 to be quite solid. 
 
 This is the common sort of soil over all the world, ex- 
 cept on certain regions, of which we shall speak presently. 
 Such a soil is made by the gradual decay of the rock. If
 
 SOILS. . 25 
 
 we should strip it all away down to the solid rock, it would 
 begin to form again in the following way : After a few 
 years' exposure to the air, the stone would decay a little, 
 and the seeds of lichens falling upon it would find a little 
 softened rock to fix themselves upon. These simple 
 plants need no soil, for they have no roots ; they only 
 need a roughened stone to fix themselves upon. They 
 soon make a close net over the surface, so that it is quite 
 hidden from sight. They keep the surface moist, and the 
 acids made in the water by their decay help to rot the 
 stone. Soon there is a little earth gathered in the small 
 hollows of the rock ; and, in these, grasses and low shrubs 
 find a foothold. These, with their roots, help to break up 
 the decaying stones, so that they may rot the faster. It 
 takes many years, perhaps centuries, to get this beginning. 
 These larger plants, when they die, make a mould that 
 grows thicker and thicker as time goes on, so that it comes 
 to be fit for the roots of trees. The seeds of pines, poplars, 
 willows, and other trees with seeds so small that they need 
 little covering, and so light that they can be carried by 
 the wind, are constantly trying to find places to grow; and, 
 as fast as this soil grows thick enough for their use, they 
 spring up upon it. Soon we have the beginning of a for- 
 est, which is at first very stunted, because the soil is so 
 thin. But this soil now grows rapidly in two ways : first, 
 by the decay of the leaves of the trees, as well as by their 
 trunks and branches when they die ; and, secondly, by the 
 action of the roots, as well as of the frosts, in breaking up 
 the stones at the bottom, so that they may rot the faster. 
 The breaking up of the stones helps the rotting by add- 
 ing to the surface over which decay goes on. If we have 
 a solid mass of rock like a floor, it rots only over its sur- 
 face ; if it breaks up into bits, the surface over which the
 
 26 PEBBLES, SAND, AND CLAY. 
 
 decay goes on may be ten or twenty times as large, and 
 the decaying equally increased in rate. 
 
 All the while the rock is breaking up into bits in this 
 fashion, the rain-water is washing through it, becoming 
 soaked full of acids as it passes through the decaying 
 bed of leaves, and with them dissolving the rock into its 
 waters. In this shape the substances of the soil are ready 
 to be taken into the plant through its tender roots. If the 
 plants are numerous, and the water goes slowly through 
 the soil, a good deal of this stuff the water takes into 
 solution is caught up by the plants into their bodies, and 
 for a while rests above the soil in the light of the sun. 
 By and by it falls by death, decays, and the ceaselessly 
 acting water has another chance to drag it down with it 
 to the sea. All the water that runs from the ground in 
 springs takes some part of this plant-food with it which the 
 soil never recovers ; but, while it robs the soil of a part of 
 its richness, it gives more than it takes, by its effect in 
 helping the decay of the rocks. 
 
 The richness of soil depends upon two things: first 
 and foremost, on the nature of the rock below it, that is 
 to say, on the kind of substances that the rock has in it. 
 If the rock be a limestone with a great many fossils, it is 
 sure to do its part of the soil-making in a perfect way, 
 and give a fertile earth. Next, the soil depends on the 
 action of the plants which yield it the vegetable matter, 
 without which the rocks alone could not make the soil 
 rich, for it is the acids that the water gains from the de- 
 caying plants that enable it to dissolve a sufficient part 
 of the materials, so that the plants can get a hold on 
 them. Of all the mass of a soil, probably not more than 
 the thousandth part is at any one moment ready for plant- 
 food. The greater part stays undissolved, and it only 
 slowly goes into the shape of food for the plants.
 
 SOILS. 27 
 
 Let us see now what is done when man comes to use 
 the soil for the crops on which depend all his arts. The 
 rudest savage ranges through the forest, and takes only 
 its fruits and its wild animals; but such peoples are rare. 
 Almost every tribe in the world gets some profit out of 
 the soil by tillage. This can only be done by stripping 
 away the natural plants, and using their place for those 
 which suit man's needs. On the perfection of his meth- 
 ods in this work depends all his chances of civilization 
 and wealth; for, however much wealth and culture are at 
 times separated from agriculture, they always have their 
 roots in this art, even as the trees, however high, depend 
 on the earth beneath. When he tills the soil, man de- 
 stroys its old natural state, and makes all its processes 
 somewhat unnatural. When the plants are stripped away 
 the rain no longer does the same work of creation alone, 
 but it becomes a destroyer. The sponge-like mass of 
 dead leaves, twigs, and trunks that make up a forest bed, 
 holds the running water away from the soil, until it gets 
 into considerable streams. These generally cut down 
 into the rock, and so harm the soil but little ; they eat 
 only a little away along the river-banks. When the soil 
 is tilled, the rain strikes on the surface of the bare earth, 
 and sweeps great quantities into the streams. If the hills 
 be steep, we often see the whole soil upon them carried 
 away, leaving the bare rock, thus destroying in a few 
 years the slow work of ages. When the soil is upturned 
 by the plow, it is left very open, so that the process of 
 decay goes on rapidly, and it is possible for a great deal 
 of the soil to come into the shape for plant-food ; but the 
 rain is the more able to bear it away, and so the soil loses 
 many things that are necessary for plants. Now the crops 
 take away much of the rarer kinds of substances that are
 
 28 PEBBLES, SAND, AND CLAY. 
 
 necessary for plant-life. While soils are always gaining 
 in depth and fertility, when in their natural crop of grass 
 or forests, they are always becoming Isss deep and less 
 fertile under ordinary tillage. The result is that a great 
 deal of the soil of the earth that once was very fertile has 
 been ruined by the plow. A skilful agriculture, that 
 takes pains that the rains do not wash the soils away, nor 
 the crops take away more than the natural work of decay 
 puts into a state for plant-food, may be maintained with 
 little loss of the earth's fertility for thousands of years. 
 In England, France, and Belgium, where the soils have 
 been carefully husbanded, they yield as much to the acre 
 as they did a thousand years ago or more ; but, in Amer- 
 ica, the tillage is generally very careless, because soils are 
 cheap, and a great deal of the land is ruined, to the perma- 
 nent loss of all the world in this and in ages yet to come. 
 
 It is worth while to look closely to this matter of soils, 
 for on them depends the future of all countries and the 
 life of man. 
 
 While the process of soil-making which we have de- 
 scribed is the method that is followed wherever the soil is 
 constructed on solid rock, there are other and rarer methods 
 followed in particular parts of the earth. Along the river 
 valleys, for instance, there is a strip of what is called 
 alluvial land, which has been made by the earth brought 
 down by the stream. This consists of a very deep mass 
 of finely divided sand, pebbles, and mud, and in it the 
 plants have no hard task of breaking up the rock, nor do 
 they have to wait for the work of the frost, or other 
 decay ; for the amount of finely divided matter is so great, 
 and the layer so deep, that the plants never get to the 
 bottom of it. Indeed, this matter of the alluvial lands is, 
 for the most part, the soil that has been washed away
 
 SOILS. 29 
 
 from regions further up the stream, and left here because 
 the river had more to carry than it could manage to bear 
 along. Such soils are almost inexhaustible. Then, in the 
 regions where the ice of the glacial sheet has acted, there 
 are large tracts that are covered by a great thickness of 
 sand and gravel, so that the plants never get access to th^ 
 bed rock, and have not to wait long for the decay to form 
 the materials out of which to make a soil. These soils are 
 generally less fertile than the other lands; but, because 
 of the great depth of the substances of which they are 
 made, they rarely become less fertile than they were at 
 first. Thus, the New England soils cannot be worn out as 
 those of South America or Virginia, although in the first 
 place they were not so rich. 
 
 We may gather up this account of soils in the follow- 
 ing words : Soils are the wreckage of the rocks, as they 
 wear down under the action of air, rain and frost, the 
 roots of plants, and the stomachs of earth-worms. This 
 wearing has been going on for a very long time in the 
 past, so that the soil now on any country may have grad- 
 ually settled downwards for thousands of feet, as the 
 rocks slowly rotted away and were> carried off by the 
 streams. It is a beautiful fact that the greatest work of 
 ruin that the world knows the decay of the continents 
 themselves should give us the foundations on Avhich to 
 rest all the higher life of the world. All our forests and 
 prairies owe their life to this decay. All the higher ani- 
 mals of the world depend upon this plant-life, and man 
 himself founds his life upon the same mass of ruin. Thus 
 it is through all the life of the world: the death of one 
 thing gives life to others ; the decay of the physical world 
 is the foundation for the higher life of plant and animal.
 
 CHAPTER II. 
 
 THE MAKING OF ROCKS. 
 
 LESSON I. 
 CONGLOMERATE. 
 
 TDEBBLES have been studied in the first lesson, but 
 -*- we stopped our study with the loose pebble, as it 
 lay 011 the river-bottom, the sea-shore, or where the glacier 
 left it. But, as we can see from any specimen, pebbles 
 may take on other shapes. They may be bound together 
 so as to form rocks of a very solid sort, which are termed 
 conglomerates or pudding-stones, so called because of the 
 plum-like look of the pebbles in the mass. There are 
 some beds of rock in the earth's crust, of very great ex- 
 tent, that are full of these pebbles. One of .these sets of 
 rocks is known as the millstone grit, because it is often 
 used for making the stones with which grain is ground. 
 These millstone grits lie under the great coal-beds, whence 
 comes the most of the coal used in the world. There are 
 many other great sets of rocks made of the same sort of 
 pebbly beds. Indeed, it seems that there are pebble-making 
 times in the earth's history, when these bits of rock are 
 made in such quantities that it is hard to account for their 
 production. It is now believed that these pebbly ages are 
 the times when glaciers are peculiarly abundant on the 
 earth, for there is no other machinery that is so well fitted 
 to make them. It is evident that the conglomerates are
 
 CONGLOMEEATE. 81 
 
 mostly made in salt water ; and the only way in which 
 such vast masses of pebbles can get into salt water, is 
 through the action of glaciers. The great rivers do not 
 send pebbles into the sea. None much larger than sand 
 find their way out of the Mississippi River into the Gulf 
 of Mexico. The sea-shores grind up about all that they 
 receive, so that we cannot look to them for the making of 
 the great conglomerate beds. 
 
 We see, from specimens of conglomerate, that the peb- 
 bles are bound together by a sort of cement which gener- 
 ally consists of sand and clay, 
 the whole forming a very 
 hard mass. If we take com- 
 mon pebbles, sand, and clay, 
 and mingle them together, we 
 do not have this solid mass. 
 How, then, could this mix- 
 ture have become thus hard ? 
 This hardness of stones made 
 
 OUt Of bits that were not at ^ 10 " Conglomerate. 
 
 first bound together is explained in part by the pressure 
 that is put upon them when they are buried in the earth. 
 These rocks were once deeply buried beneath a great 
 thickness of other rocks, that have since been worn away 
 by the action of the frost, rivers, and the sea-waves. 
 For a long time thousands of feet of beds lay on top 
 of these compacted rocks, squeezing their mass more 
 powerfully than we can do it by any machinery. We 
 see, in the making of brick or artificial stone, that press- 
 ure will very much harden the mass. Then the rocks 
 have generally been heated. This heating took place 
 in this way: The depths of the earth are very hot. We 
 find in mines and deep wells that the heat grows one
 
 32 
 
 THE MAKING OF ROCKS. 
 
 degree higher for about each sixty feet of depth; so that, 
 if these rocks are buried under twenty thousand feet, 
 or about four miles of rocks, they will lie in a tempera- 
 ture of about 300 Fahrenheit, or 88 above boiling water. 
 Some of these pudding-stones have had a yet higher tem- 
 perature. We see in brick-burning how the heat binds 
 the mass of soft clay together. Then, in the making of 
 artificial stones, it is the custom to use a certain amount 
 of either silicate of potash, called soluble glass, or silicate 
 of magnesia, which hardens like cement, and so binds the 
 stuff together. This is imitated from the processes of the 
 earth, for it is just the way in which the rocks are often 
 hardened. 
 
 Fit/. 11. Pebbles aud shell elongated by pressure (dotted lines show original 
 
 Sometimes we find, in the way the stones behave, proof 
 that the rocks have had great heat and pressure. They 
 often stretch out until, from their original egg-shape, they 
 become like ribbons. At other times, the pebbles of the 
 hardest rocks have been pushed into each other. When 
 these pudding-stones wear away, the pebbles fall out, and 
 are buried in other deposits, so that the same pebbles 
 sometimes find their way out of one bed of rocks and 
 into another of a later age, until at length they are 
 destroyed by the grinding on some sea-beach, or worn
 
 CONGLOMERATE. 33 
 
 out in their long journey down some river, or else they 
 rot to pieces. 
 
 As a pebble grows smaller it gets better able to stand 
 the wear and tear that the world gives to it. A large 
 pebble strikes hard blows when it is swung by the sea or 
 rolled by a river, and so wears rapidly; but the little ones 
 are less heavily beaten. Besides, it is always the very 
 hardest part of a pebble that wears to the end, so the 
 small bits are the best fitted to wear. The smaller a 
 thing is in the battle with the waters of the earth, the 
 safer it is in the fight ; for, as we have seen, sand wears 
 very slowly, on account of the small size of its grains.
 
 34 THE MAKING OF BOCKS. 
 
 LESSON II. 
 
 SANDSTONES. 
 
 WE have seen the sands of the sea and of the rivers in 
 constant motion ; we have now to notice them in the state 
 of repose, in which they are when built into solid rocks. 
 In this shape they make up a large part of the visible 
 crust of the earth. Sandstones are more plentiful than 
 any other rocks on the land, as sand seems more plentiful 
 on the rivers and along the sea-shore than any other sub- 
 stance. Sometimes these sandstones are in the shape of 
 very soft rocks, the grains hardly holding together. Again, 
 they are very firmly bound 
 to each other, and at times 
 the divisions between the 
 grains are hardly visible, the 
 whole then forming a very 
 solid mass. 
 
 When these sandstones are 
 looked upon closely, we see 
 that they always show a cer- 
 
 Fig. 12. Sandstone. , . J . ' ,,. 
 
 tain sort 01 bedding, as is 
 
 indicated in the figure. These are the great .distinct strata, 
 as we may find in the limestones and clay-stones; but, be- 
 sides these, we have also in the sandstones what is called 
 " cross bedding." This is shown in Fig. 13. We see, 
 besides the large separate beds, that there are sloping 
 divisions that run across them. If we would understand 
 how this works, we should watch the sand running in a 
 sandy gutter of a rainy day. We shall see that the bed 
 of sand builds out at the end in sloping banks.
 
 SANDSTONES. 
 
 35 
 
 The arrow shows the direction of the current, and the 
 letters a, i, , e?, e, the successive layers put on one after the 
 other. If we should find a bed below, that had the cross 
 lines sloping the other way, we should be sure that when 
 it was formed the stream ran contrary to the course of 
 the one that is forming. In this way, in sandstones even 
 of the oldest day, we are able to tell which way the cur- 
 rents ran that brought the sands to their place. 
 
 These old sandstones supply a large part of the sand 
 that we find in the rivers and on the sea-shore. The rocks 
 
 Fig. 13. Cross-bedded Sandstone. 
 
 decay under the soil, along the rivers and on the sea-shore ; 
 but the grains that compose them live on and take shape 
 again in rocks, there to rest for ages; but again to be 
 swept out by the water, and brought once more into the 
 active world. 
 
 Sandstones are found over so wide a surface of the 
 world because sands are so easily carried by the waters. 
 Conglomerates are always in rather narrow strips, because 
 they are generally formed along the shore lines, the cur- 
 rents not being able -to carry the pebbles that compose 
 them far to sea.
 
 36 THE MAKING OF BOCKS. 
 
 LESSON III. 
 
 MUD STONES. 
 
 WE have seen that pebbles and sand both exist on the 
 earth in two shapes : in one they are moving in the rivers 
 and on the sea-shore in constant unrest and decay ; in the 
 other they are motionless in the rocks, scarcely changing 
 in millions of years. Water, which, by its motion, forms 
 pebbles and sand, serves also to take them from this state 
 of rest, and return them to the state of activity. The same 
 thing occurs with the finest state of rocks,called mud. Mud 
 is buried in beds firmly bound together, and after a time is 
 lifted into the continents and mountains, to be called from 
 its resting-places by the streams and frosts, or by the 
 decay that takes place beneath the soil. The clay-stones 
 are found over a wider field than either the sandy or 
 pebbly rocks, for the reason that the currents of the sea 
 can carry this fine sediment much further than it can 
 sand, as they can carry sand very much further than they 
 can carry pebbles. When the sand goes out of rivers or 
 drifts off from the sea-shores, it cannot travel far before it 
 must come to rest on the bottom of the sea. But this 
 mud can go much further. Indeed, some of it is constantly 
 dropping over all the sea-floors. The volcanoes which 
 are so plentiful along the shores and on the islands of the 
 oceans throw out a great deal of dust, which is sometimes 
 so light that it will float thousands of miles through the 
 air before it falls to the ground or sea. In the sea-water 
 it will fall even more slowly than in the air. It may be 
 months in getting to the bottom ; and, as the sea-water is 
 always moving, it may be carried thousands of miles away
 
 MUD STONES. 
 
 37 
 
 from the place where it alights on the surface, before it 
 finds a resting-place. These volcanoes also give out a 
 great deal of what is called pumice. This is stone which, 
 when it was melted, became so full of air-bubbles that it 
 would float like cork. This pumice cannot get to the 
 bottom until it rots, which may require tens of years. It 
 does not fall all at once to the bottom, but the surface 
 decays, and falls off in fine grains that slowly sink to the 
 sea-floor. Only when it is much decayed will it sink to the 
 bottom. Thus, those parts of the sea-floor that are far from 
 land have a little mud con- 
 stantly coming down upon 
 them. These mud deposits 
 form very slowly ; an inch 
 may take many years to 
 build; so that, when we see 
 a bed of fine-grained clay- 
 stone, we may generally be 
 
 *"*/ 
 
 Rate of Deposition. 
 
 sure that the time taken in its building must have been 
 much greater than if it had been made of sand, and a bed 
 of sand or lime requires more time than one of pebbles in 
 its making. These beds of clay slate, not thicker than 
 roofing slate, may have required many years, perhaps a 
 century, in their formation. This may give a measure of 
 geological time. When we remember that there are many 
 sheets of clay slate that are thousands of feet thick, we 
 may conceive how long it took them to be built in the old 
 sea-floors where they were formed. 
 
 muss
 
 38 THE MAKING OF ROCKS. 
 
 LESSON IV. 
 
 , LIMESTONE. 
 
 So far we have only noticed the ways by which certain 
 rocks were made by the action of water, frost, waves, and 
 other causes, upon the rocks that form the land. We 
 have seen that through the work of the water a certain 
 part of these rocks is constantly passing into the state of 
 sand, pebbles, or mud, and then, after a journey in the 
 keeping of this water, falls to the sea-floor or to the bottom 
 of lakes, to be built into rocks again. 
 
 There is another sort of rocks we must now study, that 
 differs very widely from those before described. These 
 are the limestones, or rocks containing lime, that abound 
 in every part of the earth. The rivers and the sea-shores, 
 that show us the ways in which the other rocks are made, 
 give us little clew to the origin of limestones. 
 
 Fig. 15. Limestone made of Shells. 
 
 If we look closely at the structure of limestones, we see 
 that they have several different shapes. In the commoner 
 kind the mass of rock consists of little grains as fine as 
 mud, and mingled with them we can almost always find 
 some small bits of shells, or corals; sometimes, .though 
 rarely, the bones of fishes and quadrupeds. This rock is
 
 LIMESTONE. 39 
 
 usually quite solid. If we burn it, a great quantity of 
 carbonic acid gas and some steam escapes, and we have 
 the lime used in making mortar. If we put it in certain 
 acids, the lime is dissolved, and there remains some clay or 
 mud, just like that we find in clay-stones. 
 
 To see the way in which these limestones are formed, 
 we should go to the tropical seas of the world, where 
 the warm water holds a great deal of animal life. Most of 
 the creatures living in those seas have a certain amount 
 of lime built into their bodies. Sometimes this lime 
 serves as a protection to the body of the animal against 
 its foes, as is the case with all the shell-fishes or mollusks, 
 
 Fig. 16. Limestone Building Corals. 
 
 or as a solid support for a community of polyps, as in the 
 branched corals ; sometimes as a skeleton, to support the 
 soft parts of the body, as in the true fishes. When death 
 overtakes these creatures, their heavy skeletons fall upon 
 the sea-floor. On this floor there is a host of animals that 
 get their living by eating these remains of other animals. 
 They bore them through and through, and finally reduce 
 them to a limestone mud. Only now and then do we find 
 specimens that have been well preserved ; but, if we ex- 
 amine it with a microscope, we see that almost any bit 
 of the limestone shows that it has been alive. 
 
 Some of these lime-gathering animals grow very fast. 
 An oyster as big as a man's hand may grow in a year or
 
 40 THE MAKING OF HOCKS. 
 
 two; a great mass of coral branches may be made in a 
 few years, so that the amount of the lime that is brought 
 by them to the sea-floor is in some places very great. 
 
 The coral reefs are among the most active in this work of 
 building limestones. These coral reefs are the most won- 
 derful things that the seas contain, rich as they are in strange 
 creations. They are found in two forms : as strips along 
 the shores of the continents and islands, called " fringing " 
 or "barrier reefs," or as solitary islands far out in the deep 
 seas, called "atols." The figures give an idea of the shape 
 of these reefs. The corals that make them are star-shaped 
 
 Fig. 17. Barrier Keefs and Section of same. 
 
 animals that are akin to our sea-anemones. They live 
 in colonies, their bodies united together resembling a bush 
 with many buds on its several stems. Each colony has a 
 framework of limestone, like those shown in the figures. 
 Some of these frameworks are so strong that they with- 
 stand the beat of the greatest waves that the broad oceans 
 hurl against them. Wherever the ocean sends currents 
 of warm water against the shores, these coral reefs abound. 
 On the eastern shore of Australia there is one over a thou- 
 sand miles long. In the Pacific and Indian Oceans are 
 thousands of islands built by coral animals. These have 
 been formed around volcanic or other islands, that have
 
 LIMESTONE. 41 
 
 slowly sunk down into the sea, while the corals have stead- 
 ily built up towards the surface. They are generally ring- 
 shaped, with a bit of still water fenced around with the 
 ridge of coral. The way in which these coral islands are 
 formed is shown in the figures. 
 
 Each of these great coral towers of the sea is alive only 
 at the top, and for a hundred feet or so below the water; 
 but this crown of living corals supplies a vast amount of 
 limestone to the sea. The waves break away branches 
 from the corals, and throw them up on the beach where 
 they are ground to powder. There is a strong current 
 sweeping by these islands, which carries this powdered 
 lime away, to deposit it far 
 over the sea-floors. These 
 great reefs can grow only 
 where there is a strong mo- 
 tion to the warm water; for 
 they need a great deal of food, 
 which they can get only in 
 the sea- water moving by their 
 
 mouths. As it goes by, they, /% 18 A toiReef. 
 
 with their tentacles, snatch 
 at the tiny creatures that fill the water, and take them 
 into their mouths. This current, which generally runs at 
 the rate of two to four miles an hour, not only serves to 
 feed these vast collections of polyps, but also to bear away 
 the limestone mud formed on the shores of the islands 
 by the beating of the sea-waves. 
 
 These coral communities, or atols, as they are termed, 
 are prodigiously high and steep mountains rising from the 
 floor of the deep ocean. If we could drain away the 
 waters of the Pacific Ocean, and walk over its floor, we 
 should see them rising like great towers, with sides so
 
 42 THE MAKING OF ROCKS. 
 
 steep that we could hardly climb them ; and, on their 
 broad, flat tops, a shallow cup, as is shown in the figures. 
 We do not know just how many of these coral islands 
 there are, but it is likely that there are over five thousand, 
 and they may number ten thousand. If we include with 
 them the reefs that are fixed to the shores, their coast 
 lines, if put together, would probably stretch for a hun- 
 dred thousand miles. On all these shores the waves are 
 ever beating, making clouds of fine mud that stream over 
 the seas, and fall to the bottom to make limestones. 
 
 These coral reefs are no new things on the earth. From 
 very remote ages the seas have been beating on their 
 
 shores, and taking the lime 
 that they separated from the 
 waters, and building rocks of 
 it. Nor are they the most 
 powerful agents- of making 
 limestones, though they are 
 by far the most grand exam- 
 ples of the power of life in its 
 work on the earth's surface. 
 Still, these coral reefs do not 
 
 make the most of the lime deposits. The greater part of 
 the limestone making is done by the smallest and simplest 
 forms of life, that live scattered through the sea-water, or 
 on the floors of the oceans. Of these creatures there is 
 an amazing variety. Thousands of species contribute to 
 the work, each by giving its particular form of body to 
 make up the mass of the sediment that comes direct to 
 the sea-floor and makes limestones. The most effective of 
 these limestone makers are certain very simple animals, 
 called " foraminifera." These creatures are, as far as our 
 limited means of knowing go, mere bits of living jelly,
 
 LIMESTONE. 43 
 
 without mouths, stomachs, or any senses ; but they form 
 about them beautiful shells of lime, showing that they 
 are really far more complicated than they appear. These 
 foraminifera live in myriads in the sea-water, from pole to 
 pole, and when they die, their shells fall like little flakes 
 of snow down on to the sea-floor in a slow shower that has 
 probably never ceased since the earliest ages. 
 
 On the sea-floor there are many other forms that make 
 a great deal of lime. There are small solitary corals, like 
 those shown in the figures, and sometimes fields of crinoids, 
 standing like tall grain with branching heads tangled to- 
 gether. All these and many more shells, corals, etc., 
 kinds that cannot be noticed 
 here, make up the multitu- 
 dinous 'life of the sea-floor. 
 They all give something to 
 the great work of making 
 rocks. All the while this lime 
 is heaping upon the sea-floor, 
 there is a steady rain of mud 
 upon it, some floating out 
 from the rivers, some sent to fiy. 20. Radioiaria. 
 
 the sea from the volcanoes. This mingles with the lime, 
 and makes the clay which we find even in the finest lime- 
 stones. If the lime gathers slowly, the clay will be per- 
 haps the larger part of the rock; if the lime gathers fast, 
 the clay will be a smaller part of the whole, so making 
 anything from pure clay to pure limestone. 
 
 Of all the rocks we see on the surface of the earth, the 
 limestones form not less than one-sixth part ; so the work 
 of animal life, in building the earth's crust, is to be com- 
 pared with the work of rivers or the sea-shores. 
 
 In many limestones we have great changes brought
 
 44 THE MAKING OF ROCKS. 
 
 about in their appearance by the action of heat : they are 
 turned into marble. Marble is crystallized limestone. 
 Heat, which often finds its way into rocks, and water that 
 is always in them, cause this change. When it turns to 
 marble, the limestone no longer shows the fossils we com- 
 monly see in it. They have all been dissolved and made 
 over in the process of crystallizing. 
 
 With so much lime always going into the frames of 
 animals, and at their death on to the sea-floor, the water 
 of the oceans would soon become too poor in this sub- 
 stance to sustain the life it holds, but for the means that 
 are arranged for its supply. This continuous supply is 
 accomplished in the following way : Every drop of water 
 that falls on the lands has a certain power of dissolving 
 lime. When this water goes through the earth, it takes 
 up from the decaying plants a certain amount of a gas they 
 give off, called "carbonic dioxide." This is the gas used 
 in making soda water, and is what gives the suffocating 
 power to burning charcoal. The earth holds a great deal 
 of it, as we can see in the case of wells that often fill with 
 " bad air," which is this gas. Water eagerly sucks in this 
 gas ; and, when charged with it, can easily dissolve the 
 hardest limestone, as it dissolves sugar or alum, and many 
 other substances. We often see this lime gathering around 
 the places where springs come out of the earth. Their water 
 will often encrust anything put into it with a thick coating 
 of lime. In this way the springs bring to the rivers a vast 
 quantity of lime, which constantly restores to the sea the 
 element that the animals fix in the limestone beds. As this 
 lime is completely dissolved in the water, it does not set- 
 tle to the bottom, but remains floating about in the sea, 
 until it is taken out by the living creatures that require it 
 to make their skeletons. In the course of ages, this lime,
 
 LIMESTONE. 45 
 
 now being laid down on the sea-floor, may be lifted up 
 until it is above tne level of the sea, where it in turn will 
 be dissolved by the rain-water, and borne back to the deep. 
 
 We see at once how great the changes of the earth 
 must be, to have lifted to our mountain tops these lime- 
 stones that are now furnishing the lime that goes into the 
 ocean ; and we know that we may look forward to even as 
 great changes in the time to come, when limestones now 
 building on the sea-floor shall be raised to the tops of 
 mountains that have not yet begun to form. 
 
 It is not until we come to study our soils that we know 
 how much we owe to these little creatures that have sepa- 
 rated the lime from the water. Wherever we find lime- 
 stone rocks, there we have soils of rare fertility; for the 
 reason that lime is a very essential thing to most of our 
 crops, especially to grain, and because the same creatures 
 that take out lime from the sea-water separate several 
 other things that serve to enrich soils. The most impor- 
 tant of these is phosphorus. This is the substance we 
 know so well in lucifer matches ; but it .has a very great 
 use when combined with lime, as it enters into the bones 
 and bodies of all the higher animals ; without it man could 
 not live. 
 
 The fact is, the rain-water that passes through the soil 
 takes out of it something of all the substances that the 
 earth contains, and takes them to the sea ; and the river 
 waters are in this way constantly carrying a little of all our 
 metals to the oceans. From the sea, the animals and sea- 
 weeds take these substances, and build them into rocks 
 upon the sea-floor. Some of these rocks we see have been 
 lifted upon the dry land, and these substances are again 
 carried back by the rain-waters to the sea. So the particles 
 move in an eternal circle from the sea-floor to the land, and 
 thence back to the ocean.
 
 46 THE MAKING OF ROCKS, 
 
 LESSON V. 
 COAL. 
 
 THE next chapter that we shall study in the history of 
 the rocks concerns coal. We have just seen that the ocean 
 life, both plant and animal, is constantly doing a great 
 work in the building of the rocks. In coal we have a like 
 work done by plants upon the land. Looking at coal with 
 the microscope, we find that it always consists of a black 
 mass of vegetable matter, generally rather hard and shining. 
 Further study shows us that there are various kinds of 
 coal, which range all the way from soft peat, that we may 
 find in any swamp, through lignite, that is like peat, a 
 harder coal, to bituminous coal, which is soft, and burns 
 with a long flame ; or cannel coal, that is like it, only more 
 flaming; then to anthracite, that is yet harder, has no 
 flame, and is to be burned only with a strong draft ; finally 
 to plumbago, that is so changed that it can no longer be 
 burned by any heat that we can readily apply to it. 
 
 To understand the history of these various kinds of 
 coal, we must, for our first lesson, go to the forests and 
 see what goes on there. Every plant is a contrivance for 
 separating carbon from the air. The leaves of the trees 
 and bushes gather this carbon from the air that sweeps by 
 them, as the corals of the sea gather their food from the 
 ocean. This carbon they find in the air in union with 
 oxygen, forming carbonic acid gas. The oxygen they set 
 free ; the carbon they fix within their bodies. From the 
 soil they take water, and a little of various substances, 
 potash, soda, lime, etc. ; but, of these solid substances, 
 they take only somewhere about the fiftieth part of their
 
 COAL. 
 
 47 
 
 weight. If we cut down a forest, and burn it, the part 
 that goes away in flame and smoke came from the air ; 
 only the ashes came from the ground. When the trees die 
 and fall to the ground, or when their leaves and branches 
 fall, they do slowly what we do quickly by burning, they 
 give their carbon back to its union with oxygen, and in 
 this form it again becomes invisible in the air. In an or- 
 dinary forest this process is always going on. The old 
 trees, as well as their branches and leaves, which are con- 
 stantly tumbling down, fall into the tangle of decaying 
 matter that makes the forest-bed, and then rot, or, in 
 fact, slowly burn, leaving only their ashes. Usually this 
 goes on for ages. The living 
 roots are below, the living 
 trunks, branches, and leaves 
 above, and between them 
 this layer of decayed mat- 
 ter, where the dead parts 
 are taken back into dust, or 
 given to the air by decay. 
 We know that the oldest 
 forest-tree lives, perhaps, a 
 thousand years ; many of 
 them take but four genera- ^- 21 - Rocks, Sub-soil, and Mould, 
 tions in two thousand years, so that some trees now living 
 may be only the grand-children of those that lived when 
 Christ was born. Yet we know enough of our forests, to 
 say that, in many of them, time enough for five or ten 
 thousand such generations to live and die has gone by 
 since they began to be, yet the decayed forest-bed is at 
 most only a foot or two thick. 
 
 If all the trunks, leaves, and branches that have decayed 
 in our ancient forests could have been heaped up unde-
 
 48 THE MAKING OF BOCKS. 
 
 cayed in a solid mass, we should have beds of wood thou- 
 sands of feet thick where we now find only a few inches 
 of black mould. But, in place of staying in the shape they 
 have when they fall, all those parts of trees by decay give 
 their carbon back to the air, whence it returns again and 
 again to the plants. 
 
 It is interesting to consider that the same little particle 
 of carbon now drifting about in the moving air, may at one 
 time be fixed in the branches of a tropical palm, and then 
 rest awhile in a lichen that grows nearer the pole than man 
 has ever been. It may next grow close to the perpetual 
 
 Firj. 22. Growing Peat Swamp. 
 
 snow of the Alps, to pass, when death sets it free, to some 
 seaweed rooted in the caverns beneath an ocean cliff. 
 
 This is the state of the dry forests. If there is a very 
 wet forest-bed, into which the leaves and branches fall, 
 they do not rot, but are preserved in the water. Wood 
 will rot when it is partly wet, or at times wet, and again 
 dry ; but, if it be buried in water, it rots only in part, and 
 not altogether. The most of its substance stays in it, be- 
 coming blackened and softened, as we see the vegetable 
 matter of swamps, called " peat." In any swamp we can 
 generally find a great depth of this black, half-decayed 
 wood ; but in these swamps our ordinary trees will not
 
 COAT,. 49 
 
 grow ; it is only small plants and mosses that flourish there. 
 Yet, even these little plants can make very thick masses 
 of peaty matter. 
 
 All the northern countries have very great and deep 
 bogs of this kind. Sometimes the mass is ten, twenty, 
 or thirty feet in thickness. This is the first stage of 
 the making of a coal-bed: a mass of woody matter kept 
 from complete decay by water, in which, however, it be- 
 comes black, softened, and matted together, until it is like 
 a sponge. The next stage in making coal is brought about 
 in this way. The level of the land sinks, or, what comes to 
 
 Fig. 23. Buried Peat Swamp in condition to become Coal. 
 
 the same thing, the sea rises until it covers this mass of 
 peat. In this water there are currents that bring sand 
 and mud from tha shores, and bury the peat beneath a 
 thick layer of these ground-up rocks. So buried, the peat 
 is pressed together by the weight of the rocks above it, 
 and gradually undergoes changes that bring it nearer and 
 nearer to the state of coal. If the layer of beds laid 
 down upon it is thick enough, it may become somewhat 
 heated, which helps the chemical changes that need to 
 go on. Coal has been artificially made by placing woody 
 matter, like sawdust, under a great pressure, while it 
 was somewhat, but not very much, heated. It has also
 
 50 THE MAKING OF ROCKS. 
 
 happened that a block of wood used for a socket of the 
 shaft of a water-wheel, where it was exposed to a friction 
 that could cause a little heat, was found, after a time, to 
 have changed into a sort of coal. 
 
 To return to our buried peat bog. If it is sufficiently 
 pressed and changed by the slow agents that time brings 
 into action, its first shape is that of brown coal or lignite. 
 This is rather more like a coal than peat ; it burns with a 
 livelier flame and is more solid. It is still of a rather 
 brown than black color, and is never so heavy as coal. 
 A further step of change produces the form known as 
 bituminous coal. In this state the woody matter, still 
 further changed, often breaks into blocks with shining 
 faces. In the fire it partly melts like wax, and it burns 
 with a long, yellowish-white flame. There are many varie- 
 ties of it in this stage of its change, among which cannel 
 or candle coal, so called because it burns with so long 
 and steadfast a flame, is the most conspicuous. This can- 
 nel coal is made from the fine vegetable mud that is laid 
 down on the bottoms of the lakes in the swamps. We 
 can see it forming in such places at the present day. 
 Cannel coal does not have the same appearance as the 
 other bituminous coal. It breaks in a more irregular way, 
 and can be polished like black marble. 
 
 Still further change, brought about by heat and pres- 
 sure, makes what is called anthracite coal. This is much 
 harder than the other sorts of coal, and burns with very 
 little or no flame. This is because all the matter that can 
 form gas has been driven out of the coal, leaving only the 
 carbon, so that it is like coke or charcoal in its nature. 
 We notice that anthracite is very hard to burn ; it will not 
 take fire unless in a good draft of air. Some varieties of 
 it will not burn except in close stoves ; sometimes we find
 
 COAL. 51 
 
 a part of the bed that cannot be burned at all. Still 
 further on in the change, we come to the strange sub- 
 stance called graphite or plumbago. This is the soft 
 material commonly known as black lead. It is used for 
 making pencils, for which its softness and blackness fits 
 it; but larger quantities are used for making what are 
 called crucibles. These are pots for melting substances 
 that require a very great heat, such as steel. Indeed, this 
 graphite is able to stand a greater heat than fire-brick or 
 any stone. Yet it is only carbon, exactly like that of coal, 
 that, in some way unknown to us, but through the action 
 of heat iteelf, has become incapable of being burned by 
 any heat we can ordinarily apply to it. 
 
 In the coal field near Richmond, Va., we can see ex- 
 actly how the heat can change coal. Above one of the 
 coal beds there is a thin sheet of lava, which flowed there 
 after the coal was formed. There is a layer of several 
 feet of sandstone between the coal and the lava, yet the 
 lava, having been as hot as molten iron, has so baked the 
 coal that it is changed into a sort of anthracite. In cer- 
 tain places, where the lava did not reach, the coal is of 
 the ordinary bituminous kind. 
 
 Thus, in this wonderful coal series, we pass from the 
 living plant through a succession of changes, that first 
 give us the various sorts of burnable coals, and finally 
 this most peculiar substance, graphite. 
 
 This making of coal has been going on throughout all 
 the great ages of the earth's history, but there were times 
 when a great deal, and other times when very little, was 
 made. In that age of the earth's history known as the 
 carboniferous or coal period, because of the extensive coal 
 beds that were then deposited, the air of the earth was 
 probably damper than now, and the winter's cold was not
 
 52 THE MAKING OF ROCKS. 
 
 enough to kill delicate plants, even close to the poles. 
 Then the forests had none of our common trees, such as 
 oaks, beeches, maples ; none of the plants We see in our 
 woods to-day existed, but in their place a quantity of others, 
 like our club mosses and our ferns, but growing to the 
 size of small trees. These plants could grow with their 
 roots all the time in the water, which our modern trees, 
 with the exception of the swamp cypress and mangroves, 
 cannot do. Besides this, their tangled roots and close-set 
 stems made a sponge that held water ; and so the swamps of 
 the coal period grew even on hillsides, when they were not 
 steep, as well as on plains. The}' made peaty matter that 
 would turn into coal when buried. As if to make every- 
 thing as it should be for the formation of coal, the lands 
 or the seas in those days were very unsteady. The level 
 of the oceans was often changed, so that a great part of 
 the continents was often lifted above and buried beneath 
 the seas. Thus to these beds we look for the greater 
 part of the coal that is burned in Europe and America. 
 
 If we examine a coal seam, we can always find the bed 
 of earth in which the plants grew ; above that the bed of 
 coal; and, above all, the beds formed upon the swamp 
 sunk beneath the water. These beds are arranged one 
 above the other, so that in some countries there are as 
 many as a hundred coal-beds in a thickness of less than 
 five thousand feet of strata. 
 
 Next to the present soil of the earth, these old buried 
 swamps of the earth are of all the earth's resources the 
 most important for man's welfare. While the present sur- 
 faces give him food, those old buried lands give him heat 
 and power, which he turns into infinitely varied uses. 
 
 Let us consider a moment what this heat and power 
 come from. When plants grow, they do so because they
 
 COAL. 53 
 
 are warmed and lighted by the sun that shines upon them 
 and the air that wraps them round. This force of the 
 sunshine they store up in the substances composing their 
 bodies ; when we burn their wood, or it decays in the 
 mould at their feet, this force is given back at once to the 
 air. When the woody matter is buried in the coal-bed, 
 the force is kept from passing back to the air is stored 
 up in a way to be useful to man. When we burn coal, 
 then we turn the buried sun power of ancient times to our 
 present uses. We warm ourselves with it; we make it 
 turn our mills; and, in this manner, we have our profit out 
 of the light and heat of days so far away that we cannot 
 imagine the years that have elapsed since their light has 
 ceased to shine and their life to exist. 
 
 It is only in the modern times of man's history that he 
 has used coal. Neither the Greeks nor Romans nor He- 
 brews knew anything of it. Its use began in England not 
 more than six hundred years ago, and its great profit was 
 first found in the use of the steam engine. Now, the 
 chance of future wealth of nations depends upon the 
 amount of coal they have beneath the ground in their 
 territories. Although there is a little coal in most coun- 
 tries, the really large and useful supplies seem to be 
 limited to northern Europe, where England has the best, 
 to North America, which is ten times richer than Europe, 
 to China and Australia. The best that is known is in 
 North America, though the largest fields are in China. 
 South America and Africa appear to have but little. The 
 countries about the Mediterranean, once the richest and 
 most powerful in the world, cannot regain their ancient 
 place among nations because they have in their lands 
 scarcely any store of this buried sunshine. 
 
 Thus we see how the most remote events of our earth's
 
 54 THE MAKING OF BOCKS. 
 
 history may come to affect the well-being of man, deter- 
 mining the strength of peoples and the seats of national 
 power. The fact that the English-speaking peoples hold 
 the best supplies of coal, makes it certain that their states 
 are to have the commercial empire of the earth. 
 
 Besides the work of storing up coal, plants and animals, 
 when buried in the rocks, may furnish by their slow 
 decay the substance called petroleum. This substance 
 is formed by a slow chemical change in the bodies of 
 creatures buried in the rocks. These changes then form 
 not only petroleum but a great deal of gas, so that, when 
 we bore a hole into the rocks where it has formed, the gas 
 will drive the oil out with great force. Most all our rocks 
 containing fossil animals or plants make some of this oil, 
 but it is generally pressed out by the gas as fast as it 
 'forms , but when there is a continuous sheet of a very 
 dense, impervious rock, such as clay slate, above them, 
 the oil is retained until it accumulates in a large quantity, 
 so that a well may throw out two or three thousand bar- 
 rels a day whenever the rock in which the oil lies is bored 
 into. 
 
 Many parts of the world have furnished enough of this 
 coal oil to make its gathering profitable. For centuries 
 it has been gathered in India and Japan by means of com- 
 mon wells. But the great source of supply is in western 
 Pennsylvania and West Virginia ; and there, small bored 
 wells, a few inches in diameter, are used to get to the 
 buried store. When the oil is struck, it often blows the 
 boring-rod to the height of several hundred feet into 
 the air; sometimes this fountain catches fire and strews 
 destruction about it. 
 
 Besides these forms of buried force, laid down in the 
 earth by animal and plant life, there are many deposits of
 
 COAL. 55 
 
 clay shale that are full of organic matter, from which 
 coal oil can be distilled ; but, as it is not so cheap as that 
 from the flowing wells, they have not been used since the 
 flowing wells were found. One of these beds of clay 
 shale, in the valley of the Ohio, extends over a region 
 over one hundred thousand square miles in area, and 
 averages over one hundred feet thick. As it contains 
 about one-seventh of its bulk of substances that can be 
 distilled into coal oil, it is equal to a lake of oil three 
 times as large as Lake Superior, having the depth of 
 about fifteen feet. 
 
 In these oil-bearing clay shales there is a store of heat 
 and light-giving materials that will serve the uses of man 
 after he has used up all the coal of the world.
 
 CHAPTER HI. 
 
 THE WOEK OF WATER AND AIR. 
 
 LESSON I. 
 THE AIR. 
 
 WE have already beheld some of those things of the 
 earth that we can grasp with our hands and ex- 
 amine in various other tangible ways, but we now turn to 
 that unseen kingdom of the air, which more or less affects 
 all that occurs upon the surface of the earth. The air, 
 though invisible, is much like the watery ocean; it is 
 made up of one constant fluid or gas called nitrogen, 
 in which are mingled smaller quantities of certain other 
 gases, of which the most important are oxygen, the vapor 
 of water, and carbonic dioxide, or the gas that oxygen 
 and carbon commonly make when they unite. Because 
 the air lets the light freely through its substance, we do 
 not easily see it; but when we look at distant mountains 
 in the clear daylight, they usually look blue, and this 
 sky or mountain blue is the color of air. This great 
 ocean of the air wraps the whole world about. It is 
 densest at the surface, and grows thinner as we rise above 
 the earth, until, at about fifty miles of height, it is so 
 thin that it cannot well be called air at all ; but there is 
 no definite upper limit to the air, it grows thinner and 
 thinner, until it become space or ether. There are good 
 reasons for believing that this air is composed of hummer-
 
 THE AIR. 67 
 
 ably small particles, all dancing to and fro with a great 
 speed. These atoms are so small that if we should take 
 the smallest bit we can see, its bulk would contain mil- 
 lions of these little dancing bodies. They move so swiftly 
 that they would soon work away from the earth, but that 
 they are all held down to the surface by its attraction. 
 Between these atoms there is supposed to lie the yet 
 smaller grains of the matter called ether, which is not 
 attracted by the earth, and so is no thicker at the earth's 
 surface than in the furthest spaces between the stars. 
 This maze of dancing particles constitutes our air. It 
 would be interesting to trace all that is known of their 
 strange ways, for, though they are invisible, we know 
 much about them ; but we are to look now only at the 
 manner in which the air as a whole behaves. 
 
 First, we see that the particles of air are very easily 
 moved. Swing the hand to and fro, and we perceive, 
 that we can just feel them, they slip so easily by. When 
 moved by a strong wind, we feel them press upon us. 
 Next, we notice that when heated this air rises. Look at 
 the column of smoke over a chimney : it goes up because 
 it is heated. Make a little smoke over a stove, and see 
 how it flies to the ceiling. So we perceive that a little 
 difference in heat sets the air moving upwards. Blow tha 
 smoke against a cold window-pane, and see how it falls to 
 the floor. So we know the cold sends the air downwards. 
 This air can take a great deal of water into its tangle of 
 atoms. Moisten the finger, and move it quickly to arid 
 fro, and we feel the water evaporate, and in a few min- 
 utes it is dry ; the water, in the form of vapor, has slipped 
 into the air, where it is unseen. Watch the rain falling, 
 and we see this vapor of water, evaporated from sea and 
 land, turning back into the liquid state again.
 
 58 
 
 THE WORK OF WATER AND AIR. 
 
 On these properties of the air, its fashion of moving up 
 wfrh heat and down with cold, and of taking other gases 
 into its mass, depends, in the main, all the wonderful work 
 it has to do on the earth. 
 
 When the sun rises high in the heavens on a summer 
 noonday, we see it warms the air. We can imagine that 
 under the equator, where the 
 sun is nearly always over- 
 head, the heat is great ; while 
 at the poles, where it never 
 gets half-way up the dome 
 of the sky, and for much of 
 the year never rises, it is very 
 cold. This greater heat at 
 the equater causes the whole 
 Fif/,24. Diagram of Air Currents, air that lies in that region 
 to rise up from the surface. To take its place, the -less- 
 heated air, from regions nearer the poles, flows down 
 towards the equator. This causes a down-draft into the 
 far northern and southern regions ; and, to replace the 
 descending air, there is a current far up in the atmosphere, 
 blowing from equator towards the poles. This is shown 
 in the figure. 
 
 If the earth were all land or all water, this would be 
 the only general movement of the air ; but, as its surface 
 is a great ocean, flecked over with many lands, this great 
 current, from poles to equator and from equator to poles, is 
 broken up, except on the great seas. Under the sun, the 
 land heats more rapidly than the sea, and so there is gen- 
 erally an up-draft made over all the land when the sun is 
 high in the heavens, and the land warmer than the sea ; 
 while a down-draft takes place over the lands if they are 
 colder than the sea. In this manner, and by many other
 
 THE AIR. 59 
 
 differences of a lesser kind, the winds are made variable, 
 so that we cannot reckon on their movements except in 
 certain parts of the earth. But the important fact about 
 the air is that it is always in motion ; for such a thing as 
 a perfectly still air is not known in the world. Ceaseless 
 motion possesses it everywhere and at all times. This fits 
 the air for the important duty of carrying water from the 
 seas to the lands. The heat of the sun slips as easily 
 through the air as its light, and, falling on the seas, so 
 warms them that they give a good deal of vapor to the air ; 
 this, by the motion of the air currents, is borne off over 
 the lands, where it falls in the shape of rain ; so that the 
 first duty of the air is that of a rain carrier, bringing the 
 water back from the ocean to the land as fast as it flows 
 out through the rivers. When we look on a stream like 
 the Mississippi or the Amazon, its mighty tide rushing 
 into the ocean, we may see in the heavens above the 
 channel througL which the winds are constantly carrying 
 the same waters, first up from the sea to the height of sev- 
 eral miles, then in the sailing clouds, along through the air 
 for, it may be, thousands of miles, to the lands where it 
 falls as rain. This eternal circle of the waters has been 
 traversed thousands of times by every atom of water in 
 the world. On this endless journey of the waters de- 
 pends the whole system of feeding the life of the sea and 
 land. The land life could not live without the rain, and 
 the sea life would not be able to live without the rivers 
 bringing back to the ocean the things that are stored in 
 the rocks of the land. So the life of all the world is kept 
 in being by this circuit of the waters. 
 
 The next important work of the air is to furnish a 
 blanket to keep out the outer cold. Life, as we know, 
 cannot exist when water is constantly frozen. Only the
 
 60 THE WORK OF WATER AND AIR. 
 
 birds and mammals (animals that suckle their young) can 
 live at all in a temperature below 32 F. ; but ten miles 
 above the earth there is, and always has been, a cold of 
 below zero. But for the air, this cold would descend 
 upon and stay on the earth. There would be no night 
 even in summer and under the equator, where the tem- 
 perature would not fall to zero or below it. The air pro- 
 tects the earth in this way. The heat that falls from the 
 sun goes through the air with ease, as it does through a 
 pane of glass ; but, when it warms the earth, this heat it 
 gives to the surface cannot go back as easily, especially if 
 the air have some vapor of water in it, as it always has. 
 This heat that has fallen in the day will not be able to go 
 back into space during the night, but is held upon the 
 earth. Thus the air is a trap into which it easily enters, 
 but escapes with difficulty. This work of blanketing the 
 earth against the outer cold is one of the most important 
 effects of the air. 
 
 Yet another, and one more important work of the air, 
 is to supply oxygen to animals and carbon to plants. 
 Both these gases are borne on the air, but in different 
 proportions. About one-fifth the whole weight of the air 
 is oxygen, but only about one two-hundredth is carbonic 
 dioxide, or gaseous carbon. As the air goes by animals 
 and plants, they take what they need of these gases. The 
 animal takes the oxygen by its breathing organs, and gives 
 back to the air carbonic dioxide. The plant takes this 
 carbon and oxygen combined, separates the two, and gives 
 back the oxygen to be carried until it is needed by ani- 
 mals. Even in the sea, every plant gets its carbon from 
 this gas, which is mingled in the water ; and every animal 
 breathes by taking the air that is always similarly mingled 
 in the oceans. If we boil some water, and then put a
 
 AIR. 61 
 
 fish or any other water animal in it, it will die ; for boiling 
 drives out the air that is in water. If we pour the boiled 
 water from one vessel to another for a few times, the air 
 will be again entangled in it, and the creatures will be 
 able to breathe. 
 
 Thus we see that the universal wrap of air that the 
 earth has about it serves as a great medium of exchange 
 in the work of the world. Into it, after death, the ani- 
 mals and plants cast the store of materials which they 
 took from it while alive. If they decay on the surface of 
 the earth, they quickly give it back ; if they are buried as 
 fossils, these substances taken from the air may be con- 
 verted to coal or petroleum ; and only after a long time 
 return to the great storehouse of the air, to be ready for 
 the use of other living things. 
 
 In this way, from the ancient ages, the air has always 
 been ready to lend the things that make up the largest 
 part of animals and plants, taking them back in time for 
 the use of other creatures. As the great agent of trans- 
 portation, the water carrier, the heat carrier that brings 
 the sinews of life to every creature of the land, the air has 
 given to everything that has ever lived the first condition 
 of its existence. 
 
 We have only touched on the principal duties of the 
 air, but we have seen enough to show us that this scarcely 
 visible element, that seems to be the merest thing of 
 chance, has most important duties in the work of the 
 world, and does them with wonderful perfection.
 
 62 THE WORK OF WATER AND AIR. 
 
 LESSON II. 
 
 THE WORK OF WATER. 
 
 THE greater ocean of the air wraps the whole world 
 about. The other great fluid, water, covers only about 
 three-quarters of the surface. Though the oceans are 
 smaller in size and less deep than the air, they weigh 
 more than all the atmosphere. At most, air presses with 
 a weight of only fourteen pounds to the square inch ; but 
 in the deeper seas the water presses with a weight of hah 
 as many tons on an equal surface. These two mobile 
 parts of the earth, the gaseous air and the fluid water, 
 rule the earth's surface. Almost everything that happens 
 here is due in some degree to their work. 
 
 Let us consider how water does its work. We have 
 already seen a good part of this work in tracing the his- 
 tory of pebbles, sand, mud, etc., so what we have now to 
 do is to show the work done by water that does not ap- 
 pear in the history of those things. 
 
 Foremost of all its work, we must place the power of 
 water to dissolve all things. Some it takes up easily, as, 
 for instance, all the different sorts of salt; but all the 
 other things of the world, even the least soluble metals, 
 yield to the water something, which it conveys to the 
 seas. What water cannot do of itself alone in the way 
 of dissolving, it manages to effect when it gets charged 
 with carbonic dioxide gas, as it does in the decaying 
 mould of our forests and elsewhere. In one way and 
 another, it gets even such metals as gold and silver into 
 solution, though in small quantities. To this power that 
 waters have of dissolving all substances we owe the pos-
 
 THE WORK OF WATER. 63 
 
 sibility of animal and vegetable life. Plants and animals 
 grow and live through their circulations. Currents of 
 water in the shape of sap or blood carry numerous sub- 
 stances through their forms, which are built into their 
 frames. The same currents of water bear away the waste 
 or dead parts of the living structure back into the outer 
 world. 
 
 In the life of the whole earth, as in the life of an ani- 
 mal or a plant, water is the great means of carriage. By 
 its motion food is brought to the creatures of the sea, and 
 the matter thrown out by volcanoes, or brought to the sea 
 by the rivers, is carried to the place where it is to be 
 built into new strata on the sea-floor. 
 
 In its large work of carriage, water is charged with the 
 conveying of heat from one region to another. The cur- 
 rents of the oceans take the hot water from the tropics to 
 the poles, and the cold water of the poles to the tropics ; 
 and thus make the earth's climate far more uniform than it 
 would otherwise be. The Gulf Stream, that great current 
 which flows northward in the Atlantic from the Gulf of 
 Mexico, carries more warmth to the Arctic regions than 
 comes to them from the sun. This circulation of water 
 in the seas is not unlike the movement of the blood in 
 our own bodies. As blood carries food and warmth to all 
 the bodily parts, so this system of the waters in the ocean 
 streams, clouds, and rivers, nourishes and warms the whole 
 life of the earth. 
 
 There are many of these great streams of the ocean 
 flowing in circling currents, warm from the tropical re- 
 gions towards the poles, and cold from the polar regions 
 to the tropics. But for the great stream of heat they 
 carry from near the equator, the tropical countries would 
 be too hot for man to live in, and all northern Europe and
 
 04 THE WORK OF WATER AND AIR. 
 
 the most of the United States would be so cold that they 
 would be of little use to man. 
 
 One of the great works of the sea is in building the 
 rocks that afterward, lifted above its surface, form the 
 continents. This work is constantly going on all over its 
 bottom. When the great ocean currents sweep near the 
 land, they take up a large part of the mud brought 
 down by the rivers, and bear it far out to the ocean 
 depths, where it falls to the bottom, and is built into 
 rocks. 
 
 All over the ocean bottom a host of fixed animals are 
 living which are fed by the water and the things the water 
 brings to them ; dying, the bodies of these animals are 
 built into the rocks. Floating wood and seaweed rot and 
 
 Fig. 25. 
 Coast Shelf made by the Tide. 
 
 become water-logged ; then sink to the bottom to mingle 
 with the mud and the remains of animals, the whole being 
 built into rocks. 
 
 Along the shore the waves and the tide are continually 
 taking a part of the mud out into the sea, and making 
 new stratified rocks of them. All along the shores 
 of the continents there is a submarine shelf of this 
 waste that the tide and waves have borne away, which 
 makes a shallow belt of waters near the shore. Along 
 the eastern shore of the United States this shelf has this
 
 THE WORK OF WATER. 65 
 
 Thus, while the sea is continually destroying the land 
 by its waves and tides, or by the water it sends as rain, 
 it is always building them back into rocks again, rocks 
 which may in time, perhaps, be lifted into new lands.
 
 66 THE WORK OF WATER AND AIB. 
 
 LESSON III. 
 
 VEINS. 
 
 IF we look closely at any very old and much changed 
 rocks, we shall find that they have been divided by gashes 
 that cross the bedding, and that these gashes are filled 
 with various stones, sometimes containing metals, as gold, 
 silver, copper, etc. It is from these veins that come our 
 supplies of all the metals used in our arts except iron, so 
 they are of a practical as well as a scientific interest. 
 
 The first question we ask ourselves is how the crevices 
 that hold the veins came to be formed, and then how the 
 minerals that fill them came into their places. 
 
 Fig. 26. Ordinary Fault ; numbers show beds originally continuous. 
 
 Veins are formed in crevices that open in the rocks. 
 They are due to different causes. Sometimes they are the 
 result of a shrinking of the rocks, something like that 
 which takes place in drying clay; at other times the 
 rocks having been pushed from the sides, were forced to 
 break into large fragments, and pieces slipped over each 
 other, as in Fig. 27. 
 
 When these breaks are formed, they leave an opening in
 
 VEINS. 67 
 
 the rocks which is never very wide but may be very deep. 
 This crevice is sometimes ten thousand feet or more 
 from top to bottom, and not- more than a few feet from 
 side to side. Some parts of its walls generally rest against 
 each other, there being at times only a rambling crevice 
 that a mouse could hardly creep through. 
 
 We have now to notice again that some of the sea-water 
 is prisoned in the rocks when they are made, and so is 
 often buried to great depths beneath the surface. When 
 deeply buried, this water is very much heated by the heat 
 that exists in the depths of the earth. When such a rent 
 is made in the rocks, these deep waters find a path to 
 the surface. It also happens 
 
 that some of the rain-water fc^aggg^^ ^^ ' v * 
 that falls on the earth often 
 finds its way to great depths. 
 When in the depths, it be- 
 comes heated, and gets thereby 
 great power of dissolving 
 various substances. We all 
 know that water will dissolve 
 
 more of all the substances Fi <>' 21 - Diagram of a Hot Spring. 
 
 that it takes into solution when hot than when cold. 
 After a time this water is urged towards the surface, and 
 generally creeps up along with some of the water that was 
 buried in the rocks when they were laid down on the sea- 
 floor. 
 
 This mixture of rain and sea-water, by means of its 
 salt, its high heat, and the presence in it of various gases, 
 dissolves a portion of all the substances it touches ; and 
 so, when it starts again for the surface, it has a great load 
 of various minerals in its keeping. The easiest way for 
 it to get to the surface is through just such rifts of the
 
 68 
 
 THE WORK OF WATER AND AIR. 
 
 rock as have been described. When it starts upward, it 
 is at a heat that may be very much above the boiling 
 point of water. In a shallow open vessel, water boils 
 at the heat of 212 F., but if we made the sides of the 
 kettle a mile high, we should have to raise the heat of the 
 water at the bottom to a high point before the water 
 would boil. In many cases, when the water starts up 
 towards the surface, it has more than a mile of water 
 above it, and so it can have a very high temperature, a 
 thousand degrees or more. Water at the temperature of 
 a thousand degrees cuts many stones like an acid, and 
 can hold a wonderful amount of matter in solution. As 
 it creeps up toward the surface, it grows cooler, and has to 
 part with a portion of its bur- 
 den. This is done by laying 
 down certain minerals or met- 
 als on the sides of the crack 
 through which it flows. After 
 a time, the waters becoming 
 cooler, another substance may 
 be laid down, and so on, until 
 the way for the water is quite 
 Fig. 28. Section through a Vein, blocked up. Ill this way the ' 
 
 vein comes to appear in a cross-cutting like the figure. 
 
 The water, when it comes out on the ground level, appears 
 as a hot spring. There are many thousands of these now 
 in the world, and each may be making a lode or vein like 
 that shown in the figure. It is only a part of the veins 
 that are made that have any metallic matter in them. In 
 many cases the water may not have been hot enough to 
 dissolve the metals ; or there may not have been any in 
 the rocks through which it passed. Generally, however, 
 we shall find a small quantity of metals in any vein, but it
 
 VEINS. (39 
 
 is not likely to be great enough to pay the miner for his la- 
 bor in getting it out. We find, when we study hot springs, 
 ample proof that this explanation of the process by 
 which veins are made is true ; gold and other metals have 
 been found in their waters, and they deposit about their 
 mouths just such stones as we 
 often find in veins ; besides 
 these, very hot springs are 
 oftenest found in the regions 
 which are rich in valuable 
 mineral deposits. The great 
 Comstock Lode, which has 
 produced more silver than any 
 other in North America, and " "'~^~ 
 
 more gold than any Other Sandstone becoming Mineralized. 
 
 mine in the world, is still the pathway of hot springs. 
 The miners are constantly fighting water hot enough to 
 scald the skin. 
 
 There are other ways in which deposits somewhat 
 like veins are formed. Sometimes the hot water from 
 below, trying to find its way 
 to the surface, creeps upward 
 through a steep sloping bed of 
 rock which is porous enough 
 to allow the water to crawl 
 through it. 
 
 In Fig. 29 the bed A is 
 supposed to be a sandstone 
 or a pudding stone through 
 which the water can rise Fiy.ao. Hot Spring Caverns, 
 slowly to the surface ; the metals will then be gathered in 
 the little spaces between the stones or sand-grains as it is 
 in a vein. Sometimes, also, the waters of hot springs, as
 
 70 THE WORK OF WATER AND AIR. 
 
 they climb towards the surface, eat out caves in the rocks, 
 especially if they be limestones; in the course of time, 
 when the waters are less hot, they may fill these caverns 
 with mineral deposits, such as gold and silver ores. Some 
 very valuable deposits of this sort have been found in 
 the Rocky Mountains. 
 
 In the countries where there are mineral veins, but no hot 
 springs at present, we find proof that the veins were formed 
 a long time ago, giving time for the movement of hot 
 waters to cease. 
 
 The powers of destruction go always hand in hand with 
 the powers of construction. These veins are not long formed 
 
 Fill. 31. Wearing dowu of Land ; dotted lines show ancient surface. 
 
 before they begin to wear away under the action of rain, 
 frost, or glaciers. If the veins hold gold or platinum, these 
 metals being heavy and hard to dissolve or rust, they are 
 often found gathered in the beds of the streams mixed 
 with the gravel and sand ; but all the other metals are 
 easily rusted, i.e., combined with oxygen, in which state they 
 may be dissolved in the water and washed away to the sea. 
 Even the gold and platinum gradually go into the water, 
 and are borne to the sea ; once in the sea-water they stay 
 there for a long time. When the sea-water evaporates, 
 these metals cannot rise up to the clouds with it ; the only
 
 VEINS. 71 
 
 way out of the water is through the bodies of animals and 
 plants. These creatures each take a little of the many 
 substances in the sea-water, and when they die and decay, 
 leave this little locked up in the mud on the sea-floor into 
 which their remains pass. This mud is slowly changed to 
 rock, and in time may be lifted into the air again. These 
 rocks have veins formed in them again ; the metals may 
 be once more gathered into the crevices, and again worn 
 away by the rivers and carried to the sea. 
 
 This is another of the circles of change through which 
 water leads the things of the earth. And here, as in many 
 others, life has a share in the work. Every particle of 
 gold we see may have been several times through this slow 
 journey from the sea-water to the living being ; thence to 
 the sea mud ; thence, in turn, to compacted stone ; then 
 to the vein ; and, finally, by way of the mountain streams, 
 back to the sea. 
 
 Only a very small part of the gold, silver, tin, lead, or 
 other metals that get into the rocks finds its way into veins ; 
 by far the larger part is never so gathered together in veins, 
 but stays in the scattered form in the rocks, and goes back 
 to the sea when they are worn away. 
 
 There is another way in which these fractures are some- 
 times filled. In place of various mineral substances de- 
 posited by water, the crevice becomes charged with molten 
 rock, lava, as it is commonly called, which is crowded 
 into the space. When filled with this substance, its forms 
 are no longer known as veins ; they are termed trap dykes. 
 It often happens that we find a trap dyke and a vein close 
 together ; but in the lava itself we rarely find any valuable 
 ores in a shape to be mined. It is not quite certain just 
 how these trap dykes are formed, but this is probably their 
 history. When the crevice forms, by the breaking apart
 
 72 THE WORK OF WATER AND AIR. 
 
 of the rocks, it may extend down into the earth to a 
 greater or less depth. If it go very deep, it may find its 
 way to a part where the rock is heated so hot that it can 
 flow like melted lead or iron. This lava is squeezed up 
 into the crack. The pressure that drives it up probably 
 comes from the steam that all the deep rocks seem to hold. 
 This steam is held in by the rocks that lie above it, which 
 close it in like the sheet iron of a steam-boiler. As soon 
 as a crevice is made above this steam, it drives the molten 
 rock up into it. Generally these trap dykes are much 
 wider than most mineral veins. They may also run 
 
 Fig. 32. Some Forms of Dykes. 
 
 deeper into the crust of the earth. In some regions they 
 are exceedingly plentiful, there being one every few feet 
 of distance as we go across the surface. We generally 
 can see that the dyke stone has been very much heated, 
 for it has baked the walls of the crevices. At other times 
 we find pieces of stone torn from the sides of the crevice, 
 with sharp edges in the trap ; showing that it was not hot 
 enough to melt them. 
 
 These dykes come into close relation with the volcanic 
 lavas, the only important difference being that the volcanic 
 lavas are thrown out into the open air, while these traps 
 were formed far beneath the surface, and are therefore geii-
 
 VEINS. 73 
 
 erally much the most solid. We shall see more of these 
 lavas when we come to study their behavior in volcanoes. 
 It is only because they are often connected with mineral 
 veins that they are touched upon here. 
 
 We have now seen that underground water often makes 
 deposits of precious metals in crevices. We will now turn 
 to the action of water in its rarer but even more interest- 
 ing form of working, when it makes caves such as the 
 Mammoth Cave in Kentucky.
 
 74 THE WORK OF WATER AND AIR. 
 
 LESSON IV. 
 
 COURSE OF WATER UNDERGROUND. 
 
 THE greater part of the work done by water is done 
 above the ground ; but there are certain peculiar effects 
 it has, when it works below the surface, that have much 
 interest for us. Some of these we have noticed in the 
 history of mineral veins. There are, however, many other 
 peculiar results that are of a very different character. 
 
 When water falls as rain, a part of it flows at once away 
 to the streams, and a part penetrates into the earth. That 
 which goes below the surface creeps slowly through the earth 
 until it is either sucked up by the plants or escapes into 
 the springs. This underground water that is going towards 
 the springs generally cuts for itself little imperfect chan- 
 nels, by dissolving away the soil so as to make a natural 
 drain, which we imitate when we put pipes under a field 
 for drainage. But these springs that do not have their 
 channels below the level of the soil are always very small, 
 and last only during wet weather. When we find a spring 
 with a strong stream of water, we may be sure that it 
 comes out of the earth from below the level of the soil 
 after a journey through the underlying rock. The ques- 
 tion arises, how does it manage to make a passage through 
 this rock? These rock passages of the underground 
 waters are sometimes among the most wonderful of the 
 works that water makes. If the rock be one that water 
 cannot easily dissolve, such as sandstone, claystone, pud- 
 ding stone, granite, etc., the only chance for water to 
 make springs is to get deep into it through some rift or 
 break in the mass of rock. These are not often found.
 
 COURSE OF WATER UNDERGROUND. 75 
 
 The result is, that such springs are rarely found in regions 
 underlaid by rocks of this sort. The most of the surface 
 of New England, for instance, is almost destitute of good 
 springs because it is generally underlaid by very hard 
 rocks. When, however, the underlying rock is limestone, 
 we generally have very many large rock springs that carve 
 out for themselves great underground channels called cav- 
 erns. These caverns are of very diiferent sizes, sometimes 
 being small tube-like openings that are hardly large 
 enough for the swollen waters in times of rain. These 
 occur when the limestone rocks are bedded with strata, 
 
 /~. i n/^\ 
 
 Fig. 33. Section through Caverns in Limestone Rocks. 
 
 like claystones between, that are not to be dissolved by 
 the water. When, however, the beds of limestone are 
 thick, and without these clay partings, the caverns may 
 become very large indeed. 
 
 Perhaps the largest of these limestone caves are found 
 in Kentucky, where there is a region containing about 
 eight thousand square miles of country that is completely 
 honeycombed with them. Some of these, such as the 
 Mammoth Cave, are so vast that we may walk for days 
 through passages that are often thirty feet or more high
 
 76 THE WORK OF WATER AND AIR. 
 
 and fifty feet wide. Underground rivers and waterfalls, 
 chambers beautifully ornamented with wonderful stalac- 
 tites and stalagmites, and a great number of animals that 
 live in the cavern and nowhere else, make these chambers 
 quite an underground world, where everything differs from 
 the daylight region. 
 
 The way these caverns are formed can easily be seen by 
 studying what is now going on in the country where they 
 occur. This Kentucky cavern district lies in an elevated, 
 level region, where the rocks have never been tilted about, 
 but stay in much the same position as that in which they 
 were made on the sea-floors, before the coal time. When 
 we journey over this country, we see that only the large 
 streams appear at the surface of the ground. These flow 
 in deep gorges, with steep cliffs on either side. The smaller 
 streams do not flow on the surface. They come into the 
 main rivers through cavern mouths, that often lie below 
 the level of the water, along these greater streams. 
 
 The surface of the country between these rivers has no 
 valleys in it, such as have the streams in most parts of 
 the earth, but is arranged in circular shallow pits, called 
 sink holes, such as are shown in figure. Of these 
 there are often several dozen in a square mile of fields. 
 All the water that runs off the surface in a rain goes into 
 these sink holes, and flows down into the earth through a 
 small, ragged tube that descends from the centre of the 
 pit. We can often hear it in times of heavy rain run- 
 ning down into the depths of the earth. Some of these 
 sink holes have large openings, so that a brave explorer 
 can be lowered down into the underground course of the 
 water. In this way, we can see the whole course of the 
 cavern making. The sink hole is shaped as in the figure, 
 which shows a sink hole and the lower chambers cut in 

 
 COURSE OF WATER UNDERGROUND. 
 
 77 
 
 the thick beds of the limestone, which may be as much as 
 three hundred feet in height, from the narrow throat at 
 the top to the base. The entrance from the open air is 
 generally very narrow, but with various irregularities. The 
 opening widens until it is sometimes as much as fifty feet 
 from wall to wall. Whenever there is a strong shelf of 
 rock, there are generally level passages leading off into 
 the distance towards the lower mouth of the cave. We 
 may pass several of these in the descent. When we ar- 
 rive at the bottom, we find a pit generally full of water, 
 and by its side another horizontal passage leading off into 
 the darkness. 
 
 In the bottom of this vertical chamber or dome, if we 
 look closely, we see many bits of flint and other hard 
 stones. They are not a very 
 striking feature of the cav> 
 ern, but they are the key to 
 a part of its work. We must 
 now conceive what happens 
 in wet weather, when down 
 this deep shaft the water 
 rushes with very great force. 
 These hard stones are then 
 driven like miner's drills Fig. 34. Dome of Cave, 
 
 against the rock, and they speedily cut up the soft lime- 
 stone. The lime is easily carried away by the stream 
 through the side passage. The bits of flint themselves 
 are found in the limestone rock. We can often see them 
 sticking out of the walls, and the Indians were in the 
 habit of coming to these caves to get such flints for their 
 arrow-heads. 
 
 Entering into the side galleries that open out of this 
 " dome," we find that they lead off horizontally for great
 
 78 THE WORK OF WATER AND AIR. 
 
 distances; sometimes, as in the great avenues of the 
 Mammoth Cave, we can walk through a passage as large 
 as the aisle of a cathedral for four or five miles. Each oi 
 these side passages or galleries gave a way for the water 
 out to the air, at the time when the dome had not cut 
 deeper than down to the level of the floor of the particu- 
 lar gallery. The "domes" of these caverns are sometimes 
 wonderfully grand. The walls are sculptured by water 
 into fantastic likenesses of columns. When lighted with 
 bright fires, it is hard to believe that we are not looking 
 upon some supernatural work. The galleries, if less grand, 
 
 Jf'iy. 35. .Part of Gallery nearly filled by Stalactites. 
 
 are more beautiful, and in them are found the finest speci- 
 mens of those stalactites that are the chief ornament of 
 these underground chambers. 
 
 These singular structures are of the most varied forms. 
 Sometimes they are like flowers, clustering over the ceil- 
 ings, and shining in the light of the torches ; again, they 
 are like the trunks of trees growing from the floor to the 
 ceiling. Sometimes they appear like fountains ; again, like 
 sculptured monuments ; but always decorated with strange 
 tracery. If we search the cavern, we can find how these 
 singular forms are made. Choosing a place where the roof 
 of the cave is low, we can see that the water slowly trickles
 
 COURSE OF WATER UNDERGROUND. 79 
 
 through the ceiling, and falls, drop by drop, to the floor. 
 This water comes slowly, each drop glistens awhile on the 
 ceiling before it falls ; during this time, when it is still, 
 some of the carbonic dioxide gas escapes from it, and a 
 part of the lime it holds is laid down on the ceiling. We 
 can often see the very beginnings of a little hanging cone 
 formed in this way. Gradually this cone grows until it 
 hangs half way to the floor of the cave. When the drops 
 fall, they splash out and evaporate in the dry air of the 
 cave, leaving the rest of their lime in a little heap on the 
 floor. This heap grows upwards towards the cone that 
 builds down from the ceiling, until at length they are 
 united. Now the drops 110 longer fall, but creep down 
 the sides of the unbroken column, evaporating as they 
 go, leaving their lime on its sides. And so the mass of 
 stalactites constantly grows larger and larger. In time 
 they fill the whole gallery ; and in this way, after centu- 
 ries, this passage of the cavern is destroyed. It is only 
 when the ceiling of the cave is so close that water cannot 
 trickle through it, that this process does not in course of 
 time fill the whole space with stalactite. 
 
 The bottom of these caves can never be lower than the 
 neighboring river, where the underground waters are dis- 
 charged. As the river cuts deeper into the rocks that 
 form its bed, the domes work further down into the rock, 
 and new and lower galleries are formed. 
 
 While this underground work is going on, the decay of 
 the surface is going on also ; so that the uppermost galler- 
 ies are slowly destroyed. Their roofs grow thin and fall 
 in, so that they are opened to the day. Now and then, 
 parts of their ceilings hold on for a long time, and in 
 this shape are called natural bridges. All these natural 
 bridges are the remains of great caverns. Some of the
 
 80 THE WORK OF WATER ANT) AIR. 
 
 finest specimens known are found in Carter County, Ken- 
 tucky, and Rockbridge County, Virginia. At this stage in 
 the decay of a cavern, the ruins look like the figure. 
 
 This wearing down of the caverns goes on for ages, so 
 that over the place where the caves now are we may 
 believe there have been many 
 other caves, perhaps hun- 
 dreds of feet in the air, where 
 the earth once was, in the 
 ages before the level of the 
 ground was worn down to 
 its present position. 
 
 To the students of nature 
 these caverns are full of in- 
 terest. First, they show to 
 them the wonderful dissolving 
 
 Fig. 36. Natural Bridge. power Q f water when it mns 
 
 through limestone rocks. They also contain many strange 
 forms of animal life. Some of the outside animals use 
 these caves as places of shelter. The bears that sleep 
 through the winter often re- 
 sort to caves for shelter ; and, 
 during the winter season, great 
 numbers of bats are found in 
 them. These bats are often 
 to be seen hanging from the 
 ceilings in great bunches, one 
 grasping on the other, the top- 
 most holding to the roof. They 
 Fig. 37. Bats in Cave. are as l eep? an a f or all the win . 
 
 ter time hang motionless, as if dead. When the spring 
 time comes, though the temperature of the air does not 
 change in the least, they know in some way that their
 
 COURSE OF WATER UNDERGROUND. 81 
 
 time for waking has come ; their stagnant blood begins 
 again to flow freely, the heat of their bodies returns, 
 and forth they go to the open air again. 
 
 Besides the many creatures that use the caverns as a 
 place of occasional resort for shelter, there are many 
 animals that live their whole lives in this perpetual dark- 
 ness. There are certain fishes which are found there and 
 nowhere else ; these species have lost not only their sight, 
 but the very machinery of vision. Their eyes have dis- 
 appeared, and a very delicate sense of touch in the parts 
 about the head takes the place of the sight-sense. The 
 same thing occurs in many forms of insects and crayfishes. 
 
 Fiy. 38. Cavern Insects and Blind Fish. 
 
 Their eyes also disappear, and their feelers become length- 
 ened. These facts -are not only curious, but they seem 
 to show the close relation between the conditions in which 
 an animal lives and the form and functions of its body. 
 In this age, when naturalists are trying to find out the laws 
 that have fixed the shapes and organs of living beings, 
 these facts, revealed in the underground world, are of the 
 utmost importance to science. 
 
 There are many other phenomena connected with cav- 
 erns. We can notice only a few of them. If on a sum- 
 mer day we approach the mouth of a cave that opens low
 
 82 THE WORK OF WATER AND AIR. 
 
 down on the cliffs near the stream, we perceive, even at 
 some distance from the cavern's mouth, a strong wind 
 that rushes out of the shadowy opening. This wind is 
 often so strong that it makes the ferns and bushes about 
 the mouth sway to and fro. It is so cold that it sends a 
 chill through us as we step into it from the heated sum- 
 mer air. The hotter the outer air, the stronger this blast 
 from the cavern. In the last part of the night, when the 
 outer air is cooler, the current becomes less strong. In win- 
 ter it turns, and we then find a stream of air entering the 
 cavern, that runs as briskly inward on cold days as it did 
 outward in hot weather. From the sink holes above the 
 cavern, which connect with the domes, we feel the air 
 pouring out in a strong stream. When the day is very 
 cold, we see this warmer air of the cavern, which is some- 
 what moist, condensed in the cold outer air, so that it 
 looks like steam. The reason for this movement is plain. 
 In the summer time, the air in the cavern is much colder 
 than that in the open, and, being colder, is much heavier ; 
 it therefore flows out at the lowest opening of the cave. 
 There is then a current of warm air setting down through 
 the sink holes into the cavern. The cold rocks there soon 
 cool it, so that the blast from the mouth of the cavern is 
 sustained. In the winter time, the cavern air is much 
 warmer, and therefore lighter, than the open air ; and so 
 the cavern gives a current upward through the sink holes, 
 while it draws in through the mouth. This is the same 
 law that rules the great circulation of the air from the 
 equator to the poles. So vast are the interiors of these 
 greater caverns, such as the Mammoth Cave, that, despite 
 these constant currents into it, the temperature constantly 
 remains the same, there hardly ever being a degree of 
 difference between winter and summer. 
 
 I
 
 OOUESZ OF WATZB TTSDEEGBOUXD. 
 
 It may be interesting to the student to know 900 
 concerning the use of these caverns by man. The Indians 
 evidently travelled through most of them, for we find their 
 footprints everywhere. The soft sand that fills many of the 
 passages of these caves will preserve a footprint iimhiujyd 
 for many centuries, and so we can find the tracks of a 
 people that vanished from this land a century ago, the print 
 of the moccasin looking so fresh that it might hare been 
 made but an hour. We also find there torches which 
 they made by filling hollow canes with feiiim, an arrange- 
 ment that makes a very good torch. It is evident that 
 some of these caves were used in times of war as places of 
 retreat, for some of the remote chambers, that a stranger 
 can hardly find his way to, were evidently lived in for a 
 considerable time. In one or two cases the bodies of In- 
 dians have been found who had evidently wandered away, 
 while seeking to find the way out, and were lost in the 
 labyrinth of passages. These bodies have not decayed. 
 but have dried like mummies in the air. The Indians 
 also used these caves as places of buriaL Sometimes the 
 bodies were only thrown in through the sink holes; in 
 this case they were probably those of enemies slain on 
 some battle-field. At other places we find the bodies 
 carefully buried, with all their trinkets and tools about 
 them, with the hope that those things might serve the dead 
 in the long hereafter of plentiful hunting and war that 
 their friends hoped for them. 
 
 The white men, too. have found use for eaves. For 
 many years they were worked for the saltpetre with which 
 our earth abounds. A great deal of the saltpetre and in 
 *nrfrr- gunpowder for the war with Great Britain, in 
 1312-14, came from the Kentucky eaves. Of late yeara 
 other mqujJJBiB have taken its place, and now the caverns
 
 84 THE WORK OF WATER AND AIR. 
 
 are only a little used for growing mushrooms, and storing 
 various fruits and vegetables that keep better in a uniform, 
 rather dry air. This underground world will remain of 
 use to man, by giving him a place in which he can find an 
 utter change from the life of the surface ; a pure air, as 
 well as a weird and wonderfully beautiful scenery. 
 
 European caves have also been of great use to the geol- 
 ogist, from the fact that in them are preserved the remains 
 of many animals that would otherwise be unknown to us. 
 Many of these caverns are very old. Some of them have 
 been in existence for the inconceivable time of a million of 
 years or more. They were 
 open in a day when other 
 animals lived than those now 
 upon the earth. Some of 
 these creatures used the caves 
 for dwellings ; others were 
 swept into them by floods, 
 or dragged in by beasts that 
 preyed upon them. These 
 remains have often become 
 sealed up beneath the stalac- 
 tites that form in the caves, 
 and so have been well preserved from decay. By a care- 
 ful system of excavations it is possible for the geologist to 
 get access to these remains, and from them to infer the 
 character of the land life in times that would otherwise be 
 unknown to him. 
 
 European caves contain more bones than American, 
 because in the old days when they were formed hyenas and 
 jackals abounded there. These creatures have the habit of 
 dragging bones and dead bodies into caverns ; and so they 
 helped to stow away the remains of many animals which
 
 COURSE OF WATER UNDERGROUND. 85 
 
 have ceased to live, and which would be unknown to us 
 but for the bones that are buried in the caverns. 
 
 Many of the most ancient remains of man, which go far 
 back beyond the time of histories, have been found in the 
 European caverns, mingled with the remains of animals 
 that exist no longer. 
 
 There are some rarer sorts of caves that are not formed 
 in the fashion of those in Kentucky. These are of three 
 classes. The first very much resemble those of Kentucky 
 in their general character and history ; they are cut out 
 of limestone by water, but the water is that of hot springs 
 and not of the surface. This hot-spring water, ascending 
 to the surface, may find limestone rocks in its path. In 
 this case it generally dissolves out great chambers. Caves 
 of this character are exceedingly irregular in their form. 
 There are no domes, and, unlike surface caves, they may 
 be formed below the level of the river into which their 
 waters discharge. They are not very numerous, but 
 exceedingly interesting on account of the valuable metallic 
 deposits that they often contain. Some very important 
 deposits of silver and gold ores occur in just such caves as 
 these. The hot spring has first carveu out the limestone, 
 and then filled its space with ore. 
 
 The rarest, yet sometimes the most curious caves of all, 
 are formed in lava streams. The flowing lava hardens on 
 the top, because the air chills it, and makes an arch over 
 the stream; then the supply of melted rock failing, the 
 stream sinks down and leaves this arch, causing a cave 
 that reaches from the base of the volcano to the top. 
 Such a cave may be compared to the arches formed over 
 temporary streams by the sharp cold of a frosty night 
 that follows a winter thaw. The flood sinks away, and 
 leaves the roof of ice hanging in the air above the course
 
 86 THE WORK OF WATER AND AIR. 
 
 that the waters have ceased to flow in. The next eruption 
 of the volcano is apt to destroy this cave ; but sometimes 
 they endure for ages, being deeply buried beneath ashes 
 and other lavas. 
 
 /'/</. 40. Lava Caves on a Volcano. 
 
 We may complete our account of caves by a brief de- 
 scription of those made on the sea-shores by the beating of 
 the waves. 
 
 Wherever the coast is rocky and open to the wide water, 
 the sea, in times of storm, hurls its waves with great power 
 against the shore. If these 
 waves held nothing but water, 
 they, despite the fury of their 
 blows, would not be able to 
 wear the hard rocks to any 
 great extent. But in most 
 cases these waves havein their 
 grip pebbles, or larger pieces 
 of stone, which they hurl 
 Fly. 41. Sea Caves. against the cliffs. Wherever 
 
 there is a soft place in the rocks of the cliffs, the sea soon 
 makes a wedge-shaped opening; into this opening the 
 stones torn from the neighboring shore are collected, so 
 that the waves have a constant supply of rocky fragments
 
 COURSE OF WATER UNDERGROUND. 
 
 87 
 
 with which to batter the rocks. In this way they some- 
 times cut channels extending some hundreds of feet back 
 from the sea front. 
 
 When the rocks of the shore have dykes or veins in 
 them, these deposits are often softer than the rocks on 
 which they lie, and so are excavated by the sea. All 
 along the shores of New England we find many of these 
 furrows, commonly called chasms. When the sea-waves 
 rash freely into these furrows, their spray is sometimes 
 during storms forced high into the air, when the crevice 
 is commonly called a spouting horn. 
 
 These caves worn by the sea are never very large, and 
 have none of the beauty or interest that belongs to those 
 made in limestone rocks by the waters of the land. 
 
 View in Luray Cave.
 
 CHAPTER IV. 
 
 THE DEPTHS OF THE EARTH, 
 
 LESSON I. 
 
 VOLCANOES. 
 
 TTTE should always bear in mind how small a part of 
 * the whole earth is really known, or we can know 
 anything about. Our deepest mines have never gone 
 more than one seven-thousandth part of the way from the 
 surface to the centre. The upturned edges of stratified 
 rocks make it possible for us to see somewhat further into 
 
 Fig. 42. Showing how Rocks are exposed by Tilting. 
 
 conditions of the interior, for they sometimes show us rocks 
 that have been buried twenty thousand feet or more under 
 the earth, and have since been exposed to the light of 
 day by the squeezing and tearing that happens in moun- 
 tain building ; yet, with this help, we can never see in their 
 natural state rocks that have been more than one five-
 
 VOLCANOES. 89 
 
 hundredth of the distance down to the earth's centre. In 
 the diagram, such tilted rocks are shown. 
 
 The only way in which we can form any notion of what 
 goes on at greater depths, is through volcanoes ; they, there- 
 fore, deserve the careful study of every one who wishes to 
 know the little that can be learned of the vast unknown 
 region of the earth's interior. 
 
 Let us first see what volcanoes are, in order that we may 
 learn what they can teach us of this inner mass of the 
 earth. 
 
 Fill. 43. Vesuvius in Eruption. 
 
 A volcano is an opening in the crust of the earth through 
 which molten rock or lava and other stones, along with 
 great quantities of steam, are thrown out with great vio- 
 lence into the air. This steam is heated far above the 
 boiling point of water ; up, indeed, to the melting point 
 of rock, and escapes with such force that it drives the 
 rocks before it, as by an explosion of gunpowder. Some- 
 times these pieces of rock are so pulverized that they are but 
 dust, that floats away in the form of a cloud, and has been 
 known to drift more than a thousand miles before it falls to 
 earth ; but the most of this rock falls near the mouth, and
 
 90 THE DEPTHS OF THE EARTH. 
 
 makes a hill called the volcanic cone. It often but not 
 always happens that the heat of these gases is so intense 
 and long-continued, that the rocks through which the gas 
 forces its way become melted, and flow out of the cone in 
 the form of lava. But the amount of this lava is gener- 
 ally small compared with the cinders and ashes, and very 
 small indeed compared with the escaping steam, which is 
 the principal feature in all volcanic eruptions. 
 
 Volcanoes are never found in the middle of the conti- 
 nents, but only near the sea-shore, and over the bottom 
 of the greater seas and oceans. Whenever we find old 
 volcanoes in the middle of the lands, we find them no 
 longer active, and we can prove that when they were 
 active the sea lay near their bases. 
 
 This shows us that volcanoes are in some way connec- 
 ted with the processes that go on under the sea. There 
 have been a great many theories to account for this rela- 
 tion between volcanoes and the sea ; some have supposed 
 that the sea-water found its way down through crevices 
 to the central hot part of the earth, and was there changed 
 into steam which poured out through the volcanoes ; but 
 we readily see it would be easier for the steam to come 
 out of the passage through which the water went in to 
 the heated region, than for. it to force a new way to the 
 surface, so we must give up this idea. The most reason- 
 able view is, that the volcanoes are outbreaks of the steam 
 that is confined in the rocks beneath the sea or near to it. 
 A certain amount of water is fixed in the rocks when 
 they are formed on the sea-floor. All our rocks made in 
 water have from four to fifteen per cent of their mass 
 made up of imprisoned water. This water becomes heated 
 because the beds laid down on top of it are very thick, 
 and act like a blanket to keep the earth's heat in. In the
 
 VOLCANOES. 
 
 91 
 
 course of ages this water may come to have a heat as great 
 as that of melted iron. Now, if any crack is found in the 
 overlying beds that will let these gases escape, we shall 
 have a volcano. This will account for the fact that vol- 
 canoes are jets of very hot steam, and that they always lie 
 near the sea-shore or on its bottom. 
 
 The reason why volcanoes do not occur far away from 
 sea-floors is probably because it is only on these parts of 
 the surface that the great blankets of rock are laid down 
 on the earth. 
 
 We can help ourselves to figure this effect of beds of 
 rock in raising the heat of rocks below them, if we re- 
 member that over all the 
 earth's surface a constant flow 
 of heat is streaming out 
 through the earth and going 
 away among the stars. Enough 
 of this heat escapes each year, 
 from every square mile of 
 the earth's surface, to boil 
 a great many barrels of water. 
 If the reader could heap any 
 kind of rocks on the ground 
 where he stands, so that the Fig.^. Rise of Heat in Rocks, 
 surface would be covered to the depth of two miles, the 
 water in the soil would, on account of this blanket of rock, 
 rise slowly to a greater heat than that of boiling water. 
 
 Most volcanoes are found in places where civilized men 
 have not had a chance to watch them for a very long 
 while. The history of only three is known for as many 
 as one thousand years. These are Vesuvius and ^tna in 
 Italy, and Skaptar Jokul in Iceland. Of Vesuvius and 
 we have some account for more than two thousand
 
 92 THE DEPTHS OF THE EARTH. 
 
 years. These histories show us that volcanoes are not com- 
 monly in a state of activity. More than half their life is 
 spent in a state of repose, their powers slumbering below 
 the earth. Sometimes these still times continue for sev- 
 eral hundred years. Vesuvius was not even known to be 
 a volcano until the year 79, though the region about it 
 had been dwelt in by the Greeks and Romans for at least 
 four hundred years before that time. It was covered 
 with forests and tilled fields. At that day men had not 
 studied the forms of its surface, else they would have 
 known that its cup-like shape, and the nature of the ashes 
 that made up the mountain, marked it as a volcano. 
 Seventy-nine years after Christ's birth, the silent moun- 
 tain stood amid one of the most fertile and thickly 
 peopled parts of the earth. It was the richest part of the 
 Roman Empire in its most prosperous days. Early in that 
 year there began to be earthquakes in the region about it. 
 Still, though there were volcanoes on the island of Ischia, 
 which lies within sight of Vesuvius, that had proved 
 very destructive to life and property, no one thought of 
 the danger of an explosion from the long silent Vesuvius. 
 Finally, a most frightful explosion took place. The upper 
 part of the mountain was blown to pieces, and the coun- 
 try for many miles about was rained on for days by stones 
 and ashes, falling so thickly that a perfect darkness was 
 made. Men and beasts were killed, even a dozen miles 
 away, by the shower of hot stones, and all this beautiful 
 country was reduced to ruin. The famous Roman natu- 
 ralist, Pliny the elder, who was admiral of a fleet sta- 
 tioned at Misenum in that district, a town about twenty 
 miles from the mountain, lost his life at a point over a 
 dozen miles away from the volcano, having been suffo- 
 cated by the vapors of the eruption in his effort to save
 
 VOLCANOES. 93 
 
 the inhabitants of the shore. So severe was the shower 
 of ashes, that his attendants could not bear his body 
 away from the place where he had met his death. 
 
 At least two large and wealthy cities, Herculaneum 
 and Pompeii, were buried beneath the prodigious masses 
 of ashes or small stones that were thrown out from the 
 volcano, or overwhelmed in the mud made by the heavy 
 rains, which always come with a great eruption. There 
 were doubtless many small villages overwhelmed at the 
 same time, the names of which are unknown to us, for it 
 is only by chance that we learned of the destruction that 
 came upon Herculaneum and Pompeii. The accounts 
 written at the time simply say that many places were de- 
 stroyed. 
 
 After this eruption, others came at long intervals, 
 sometimes over a hundred years going by without the 
 least sign of activity in the mountain, so that a good 
 part became covered with vineyards and gardens. Then, 
 with a period of earthquakes that set all the mountain 
 to trembling, the volcano would again burst forth. It 
 was not until after it had been active for about a thou- 
 sand years that it began to throw out lava. Lava erup- 
 tions have been growing steadily more common than of 
 old, and the eruptions have been growing more frequent 
 and less violent. For, as a general rule with volcanoes, 
 where their eruptions come only at long intervals, they 
 are much more violent than they are when they quickly 
 follow each other. A little volcano, called Stromboli, 
 which lies between Vesuvius and JEtna, has been in con- 
 stant eruption for centuries, scarcely a day passing when 
 it does not throw out some fiery gas and melted stones ; 
 but its eruptions are never very violent. It is to be 
 noticed that the larger the volcano, the more likely it is
 
 94 THE DEPTHS OF THE EARTH. 
 
 to throw out lava. ^Etna has had many worse lava flows 
 than Vesuvius, and is one of the best places to study 
 such streams. 
 
 When lava escapes from a volcano, it is generally very 
 fluid. Sometimes it appears almost as liquid as water, 
 though it really is more like melted lead or quicksilver, 
 which are less fluid than water, though they flow with ease. 
 The lava generally flows very quickly when it escapes 
 from the crater ; but it soon begins to cool, and forms a 
 solid crust upon its surface that makes it hard for it to 
 creep along. Finally, it crawls so slowly, pushing along a 
 mass of broken solid lava in front of it, that it looks like 
 a large heap of rolling stones; yet the lava within the 
 stream stays fluid, and for months it may crawl along in 
 this fashion, making only a, few hundred feet of advance 
 in a day. Still it is strong enough to overwhelm towns 
 and destroy fields in its course. Sometimes the hard coat- 
 ing of frozen lava will break open and let the fluid inte- 
 rior out in a fresh stream, which in time becomes clogged 
 in the same way. It often happens that these lava 
 streams fall into the valleys of rivers. It then drives the 
 water into steam, and effaces the course of the river. 
 After the lava has cooled, the river commonly cuts itself 
 a new bed alongside of the lava ; often there is a stream 
 on either side of the lava, and in time these wear down so 
 deep that the lava is left on a hill-top. This has often 
 occurred in California, where volcanoes, now extinct, 
 once filled to the very brim with lava the valleys that lead 
 from the Sierra Nevada. We know much of these old 
 Californian streams, for their beds contain gold among the 
 gravel, and a good deal of mining is carried on in their 
 ancient beds. In the figure No. 45, the dotted line shows 
 the position of the old valley which has been filled with
 
 VOLCANOES. 
 
 95 
 
 lava, while below we see the present valleys. The old 
 river bed, containing gold, lies under the lava stream, 
 which now caps a hill. 
 
 Although volcanoes rarely give out large amounts of 
 lava, there are some places in the world where there are 
 very large regions that have been covered with these 
 floods of molten rock. One of these in California, Oregon, 
 and Washington Territory, is nearly as large as France. 
 
 Although volcanoes are among the most violent and 
 seemingly disordered of the earth's works, they play a 
 definite and bountiful part in its machinery. If the world 
 
 Old River Beds filled with Lava. 
 
 were without them, it is hard to see how life could long 
 exist. This seems a paradox, but its truth is easily made 
 plain. We have seen that the plants of the earth live by 
 taking the carbonic dioxide from the air. In an atmos- 
 phere without this gaseous carbon plants could not 
 grow ; and, as animals depend on plants for their food, 
 they, too, have the liveliest interest in this element in 
 the air. The amount of this carbon is never large, not 
 exceeding one three-hundredth of its bulk. If there were 
 not means whereby this carbon could come back to the air, 
 it would require only a few centuries to make the supply 
 so small that plants could not grow. A great deal of the
 
 yt> THE DEPTHS OF THE EARTH. 
 
 carbonic dioxide, perhaps nine-tenths, that goes into the 
 plant, comes back to the air in their decay; but every 
 bit of coal that is formed, every grain of limestone that 
 is deposited on the sea-floor, takes so much carbon from 
 the air and lays it away in the rocks ; so that it is certain 
 that the vegetable world could not long endure without 
 some renewal of the carbon supply in the air. The prin- 
 cipal way in which this buried carbon can get back to the 
 air is through the gases that volcanoes throw out in their 
 times of eruption. Although the most of this gas they 
 pour forth is water in the state of steam, there is a con- 
 siderable amount of carbonic acid gas thrown out in every 
 eruption. Sometimes so great is the quantity that it suf- 
 focates the animals for some miles distant about the crater. 
 We do not notice it much in an ordinary eruption, for the 
 reason that the gas is taken into the water and steam, and 
 so locked up there that it does not aifect life ; but in an 
 eruption of Vesuvius or JEtna there is as much of this gas 
 of carbon given forth to the air as would be taken from 
 it by the burial of a large amount of coal or limestone. 
 As volcanoes are continually in eruption in one part of 
 the earth or another, it follows that they play a most nec- 
 essary part in keeping the world fit for life; and the 
 destruction they do is of trifling importance compared 
 with the benefits they confer. This adds another to the 
 many proofs that this earth is wonderfully arranged for 
 the uses of living beings. *We have seen that the orderly 
 work of the air and the waters, in all their manifold actions, 
 seem to foster this life ; but even the most violent and 
 seemingly destructive actions of volcanoes also aid in 
 making the conditions that life requires. When we look 
 at the buried cities of Pompeii and Herculaneum, or 
 behold the ravaged vineyards and olive orchards about
 
 VOLCANOES. 
 
 97 
 
 Vesuvius, we may set against this account of ill the fact 
 that in every eruption of Vesuvius there comes forth the 
 carbon that is to find its place in the life of the whole 
 world ; so that the damage it brings about is trifling com- 
 pared with the benefits it confers. 
 
 Last Stages of a great Eruption of Vesuvius, from a photograph.
 
 98 CURRENTS OF AIR AND SEA. 
 
 LESSON II. 
 ON THE CURRENTS OF AIR AND SEA. 
 
 WE have already spoken of the atmosphere in a preceding 
 chapter. We will now look more closely into the work 
 that comes from the action of its currents, the winds. 
 
 The life of our earth is of two kinds : the life of anima- 
 ted nature, and the life of the inanimate world, shown in 
 the movements of the air and water, and the other motions, 
 such as those of volcanoes. Except the disturbances that 
 come from beneath the earth, all its motions are derived 
 from the sun's heat; all the life of animals and plants, all 
 the currents of the air, the rivers, and the oceans, every 
 stir of its surface, is due to the force that comes from the 
 sun and stars. The motions of our own limbs, even the 
 beating of our hearts, are only forms of force that come 
 to the earth from the great sources of power, the sun and 
 the fixed stars. The sun's heat causes the plants to grow ; 
 and it is this solar force that comes to us in our food, 
 and is the support of all animal bodies. Every wind 
 that blows, every stream that runs, on land or in the 
 sea, moves because impelled by this power from beyond 
 the earth. If our earth could be cut off from these 
 sources of power, all its life would soon become stilled. 
 One night, of a few months' duration, would bring its 
 whole surface to a cold of more than one hundred degrees 
 below zero of Fahrenheit, and all the animate and inani- 
 mate life would be stilled; the seas and rivers would 
 change to motionless ice, and, until the day came again, 
 no motions, save those of the earthquake and the volcano, 
 would occur upon the earth.
 
 CURRENTS OF AIR AND SEA. 
 
 Since this world is moved by the force that comes from 
 the sun, we should get some idea of the way in which this 
 heat comes to us, and the mode in which it works after it 
 has arrived on the earth. 
 
 This solar force comes to the earth in the form of heat 
 and light. Both the heat and light are necessary for the 
 machinery of animal and vegetable bodies, but the move- 
 ments of the winds, the waves, and the currents of the 
 sea require only the heat for their action. The supply of 
 light and heat comes to the earth from two different 
 sources. Somewhere near one-half the heat comes from 
 the fixed stars. This heat from the far-away stars descends 
 equally on all parts of the earth's surface ; but, if it alone 
 came to the earth, there would still be no movement for 
 it ; the oceans would be frozen to their bottoms, and life 
 of all kinds would be impossible. All that this star heat 
 does is to lift the general temperature of the earth's sur- 
 face from a far greater cold to an average temperature of 
 about one hundred degrees below zero of Fahrenheit. 
 Although this seems but a poor gift, it is still of priceless 
 value, as it makes it possible for the sun to do its good 
 work of quickening life on the earth; but for this help 
 from the stars, the sun could not accomplish this task ; 
 it alone would have too much work to do. 
 
 The sun gives us both light and heat ; but, in place of 
 giving it as the stars give their heat, equally over all the 
 surface, it pours a great amount of this light and heat 
 upon the regions between the tropics, and gives much less 
 to the regions about the poles. If this heat stayed where 
 it fell, or if, like the light, it were a momentary thing, 
 disappearing as soon as the earth turned its face away 
 from the sun in the night time, then the world would fare 
 badly ; for, during the mid-day at the tropics, the heat
 
 100 CURRENTS OF AIR AND SEA. 
 
 would be too great for life to endure, and in the night 
 everything would perish in a frost of more than a hundred 
 degrees below zero. 
 
 Fortunately heat can be stored up, as light cannot be. 
 The rocks and the air can take in some of it, and the 
 water can take in a very large quantity. This heat is 
 given out again, after having been stored away for a 
 time. Thus, when the night comes, in place of the ther- 
 mometer falling to one hundred degrees below zero at 
 dawn on a summer's night in the tropics, it rarely goes 
 below sixty above zero ; because these things which have 
 been taking up heat all day proceed to give it out in 
 steady streams. So, too, in the winter, the earth and seas 
 slowly yield up the heat the summer gave them to moder- 
 ate the rigors of the cold seasons. Thus it happens, that 
 islands, even in seas near the poles, have often a some- 
 what uniform climate in winter and summer. The aver- 
 age difference of temperature of the months in Cornwall in 
 southern England is not more than thirty degrees in any 
 one year. But the most important effect of this great heat- 
 storing ability of water is found in the power it has of 
 carrying heat from the equatorial regions to the poles. 
 This it does in the way we shall soon consider. If we 
 watch a heated stove in the middle of a large room, the 
 walls of which are cooled by the outside winter air, we 
 easily see, by the aid of a little smoke in the room, that 
 the air rises over the stove to the ceiling, floats off to the 
 sides of the room, falls down there to the floor, and then 
 runs along it to the stove, making a continuous round. 
 This is because heated air is much expanded, and, there- 
 fore, greatly lighter than the cold. We may illustrate 
 this by means of a paper balloon, with an open mouth 
 below, underneath which a small piece of sponge dipped
 
 CTJEEENTS OF THE AIR AND SEA. 101 
 
 in turpentine or alcohol is hung. This sponge being fired, 
 the heated air will swell the balloon, and lift it far above 
 the earth. The first balloons ever used to lift men into 
 the air were of this nature. 
 
 The circulation of the air about the stove is exactly 
 parallelled by the circulation of the air on the earth. 
 The region between the tropics is so hot that the air is 
 impelled to rise ; to fill the vacant space, the air rushes 
 in from the regions to the north and south in the strong 
 gale we call the trade winds. The upper air streams off 
 towards the poles in a mighty flood as wide as the seas ; 
 
 /'//. 4G. Diagram of Air Curreuts. 
 
 on the high mountains near the tropics we may feel it 
 always blowing a steady gale, never ceasing by day or 
 night for ages. 
 
 If the earth stood still on its axis, these winds would 
 come straight down the surface of the earth towards the 
 equator following the meridians ; but, because the earth 
 spins around on the polar axis from west to east, they come 
 slantingly down upon the equator from the north-east and 
 the south-east. It is a little difficult to give a simple and 
 clear explanation of this slanting course of the winds that 
 blow towards the equator. It may best be understood by 
 spinning a round, flat piece of cardboard on a central
 
 102 CURRENTS OF THE AIR AND SEA. 
 
 point, and trying to roll a marble from the centre to the 
 outer edge. It will be found that the marble will not roll 
 along the short, straight line from the centre to the cir- 
 cumference, but will follow a curved line, coming to the 
 edge as shown in the figure. This is because the marble 
 has in its course always a less rate of spinning than the 
 card over which it is travelling. The friction on the card 
 makes it spin around with it ; but it comes to each part on 
 its course at the rate of the part which it has just left. A 
 particle of air, when it starts in the trade winds on ite 
 journey to the equator, is spinning round with the world 
 on which it lies at the rate of 
 about five hundred miles an 
 hour; when it gets to the 
 equator, it must travel a thou- 
 sand miles an hour. The 
 result is that it lags behind 
 at every stage of the journey, 
 just as the marble does, and 
 so comes obliquely from the 
 Fig. 47. Deflection of Air Currents, north-east and south-east, and 
 not squarely down upon the equator. All this has a great 
 importance, as we shall now see. 
 
 These trade winds blow strongly, so that they send a 
 ship at great speed, and, as may be imagined, they sweep 
 the surface water of the sea along with them at the rate 
 of two or three miles an hour. This water flows in the 
 same direction as the wind ; and so, as there are two streams 
 of water, one from the south-east and one from the north- 
 east, each as wide as the ocean in which they lie, the two 
 pressing against each other at the equator make a current 
 two or three hundred miles wide, flowing towards the 
 west at the rate of several miles an hour, or about as swift
 
 CURRENTS OF THE AIR AND SEA. 103 
 
 as a large river. This water is very warm, from the heat 
 given it by a tropical, overhead sun ; so it is a vast hot 
 stream carrying perhaps more water than all the rivers of 
 the world. 
 
 If there were no lands in the tropics, this river of the 
 sea would flow around the earth as a great girdle of run- 
 ning water ; but when it strikes against the shores, it is 
 split in two, and runs as two streams towards either pole. 
 There are two of these streams in the Atlantic and two in 
 the Pacific Ocean ; in the Indian Ocean, because there is 
 30 much land near by in the northward, the trade winds 
 are not steady enough to make any very distinct current. 
 We know only one of these streams at all well. This is 
 that known as the Gulf Stream, because a part of its 
 water comes out of the Gulf of Mexico, into which it flows 
 from the Caribbean Sea. This stream flows into the north 
 Atlantic. When it starts from the West Indian Islands, 
 it is a stream about one hundred miles wide and several 
 hundred feet deep, flowing at the rate of four miles an 
 hour. As it gets northward it widens and becomes more 
 shallow, and steadily sinks in temperature. As far north 
 as England it has a ver}^ gentle current, but is still much 
 warmer than the air usually is. 
 
 As it goes northward, this stream leaves the American 
 shore which turned it northwards, and moves to the east- 
 ward, crossing the Atlantic. If the reader has seen why 
 the air currents turned to the west in going southward, in 
 the trade winds, it will now be easy to understand why 
 the current of the sea strikes off to the east in going 
 northward. Each particle of water, when it leaves Flor- 
 ida, is moving to the east, in the spinning of the earth 
 on its axis at the rate of several hundred miles an 
 hour. As it goes towards the pole it is constantly coming
 
 104 CURRENTS OF THE AIR AND SEA. 
 
 into regions which have a less movement to the east, so 
 its momentum causes it to outrun the easterly motion of 
 the earth at these points, and to swing off to the east or 
 the direction in which the earth is turning. 
 
 These waters that seek the pole return southwards in 
 the depths of the sea in southward-setting currents that 
 move slowly along the bottom, or creep along the western 
 shores of the oceans. So the waters of the seas are con- 
 stantly sent towards the poles in warm currents, and 
 returned in cold streams to the tropics, to be again charged 
 with the life-giving heat and sent again to high latitudes. 
 
 If the heat of the water stayed where it fell, then the 
 tropics would be too hot for life ; while, all about the poles, 
 even as far south as New England, the ocean would be 
 frozen so there would be only a little strip of the earth in 
 either hemisphere fit for life. But, by this machinery of 
 the moving waters, the temperature of the earth is so bal- 
 anced that but little of it is not suited to some forms of 
 animals and plants. We get an idea of the power of 
 these ocean currents when we know that the Gulf Stream 
 sends as much heat to the region within the Arctic circle 
 as comes upon that part of the earth from the sun. 
 
 Now, heat not only affords the possibility of life, but it 
 is the power that sets all of its machinery in motion ; so 
 it happens that this machinery of the winds serves to dis- 
 tribute the source of life over the .earth, equalizing it so 
 that the whole of the earth's seas and lands give some 
 chance to living beings. 
 
 The winds alone cannot do this work of distributing 
 the earth's heat, for the air cannot hold much heat stored 
 in its particles. If it were not for the currents of the sea, 
 there would be no chance of having enough heat carried 
 to the regions about the poles to keep them from perpet-
 
 CURRENTS OF THE AIR AND SEA. 105 
 
 ual frost, or enough taken away from the tropics to keep 
 their lands and seas from becoming so hot that few living 
 things could endure the climate. But, in a smaller and 
 local way, the winds do a great deal of work. They 
 carry the warmth and moisture from the seas into the 
 lands, giving them their needed quantities of these all- 
 important things. 
 
 It is easy to see that the shape of the lands fixes the 
 course of these ocean streams. The great Gulf Stream, 
 that flows into the north Atlantic, finds an open passage- 
 way far to the north ; on the other hand, the great stream 
 of the Pacific, the Japan Current, is shut out from tbe 
 Arctic Sea by the peninsulas of Alaska and eastern Asia, 
 so that it cannot pour in its warm waters to relieve the 
 cold about the poles. If these lands should sink down 
 beneath the sea, as the lands often do, letting the Pacific 
 stream into the Arctic Ocean, the result would be that the 
 tropics would become cooler, and the northern regions a 
 good deal warmer than they are at present. Many of the 
 wonderful changes of climate that we know to have oc- 
 curred in the past are probably to be explained by such 
 change in the direction in which the ocean currents flow. 
 When they can reach the poles in strong streams, the 
 tropics become cooled by the heat that the waters bear 
 away from them, and the regions around the poles warmed 
 by their waters. When the lands force the ocean cur- 
 rents from the poles, the tropics become hotter, and the 
 lands and seas of high latitudes are given over to intense, 
 life-destroying cold. 
 
 There are probably many other causes of climatic 
 changes in the earth's surface. The sun's heat may vary, 
 or the changes in the earth's path about it may alter so 
 that the winter and summer seasons in any country are
 
 106 
 
 CURRENTS OF THE AIR AND SEA. 
 
 sometimes of nearly the same temperature, and again, 
 more different than they now are. But this change in the 
 course of the ocean streams, depending on alterations in 
 the position of the ocean currents, is probably the princi- 
 pal cause of the great climatic changes in the past history 
 of the earth. We know that the course of these streams 
 depends on the shape of the lands ; we know, also, that 
 the lands are constantly changing their shapes ; so it fol- 
 lows that, as the distribution of the heat on the earth's 
 surface depends mainly on those streams, the temperature, 
 of any place must be made greatly to vary, in different 
 ages of the earth's history. 
 
 Diagram showing the change of Behring's Strait necessary to warm 
 Northern Regions.
 
 CHAPTER V. 
 
 IEREGULAKITIES OF THE EARTH. 
 
 LESSON I. 
 HILLS, MOUNTAINS, VALLEYS, AKD CONTINENTS. 
 
 r "PHE surface of the earth abounds in irregular eleva 
 -*- tions, which have been formed in various ways. 
 When the running water has 
 cut away about a mass of 
 earth or rock, we term it a 
 hill. The figure shows the 
 form of a hill, the dotted lines 
 showing the rock that has 
 been cut away in its forma- 
 tion. As nearly every region 
 has had running water upon 
 it, hills are found every- 
 where. Mountains, at first 
 sight, look like greater hills, 
 but we find that they are 
 built in a different manner. 
 They are made by a folding 
 of the rocks of which they 
 are composed, as shown in 
 the figure. These rocks were 
 originally flat, lying like those Fi f /. 49. 
 
 in the hill, but, by a Way Section of Mountain. 
 
 Fig. 48. 
 Section of Hill.
 
 108 IRREGULARITIES OF THE EARTH. 
 
 which we will now consider, they have been crumpled up 
 so that they lie like a mass of wrinkled paper. If we 
 look closely at any mountain, we see that a great part of 
 it has been cut away by rivers, so that the hill-making 
 forces are as evident there as elsewhere. We may prop- 
 erly say that every mountain is in a certain sense a hill, 
 while hills proper are net mountains. 
 
 The cause of this crumpling of the rocks in a moun- 
 tain is a pressure coming horizontally through the earth. 
 We may represent it by taking a number of sheets of 
 paper, each of which may stand for a layer of rock, and 
 pressing them from the siples, so that they may be forced 
 to wrinkle, as shown in the figure. This is the way in 
 which this wrinkling is brought about: 
 
 The earth is very hot in the inside, as we know from 
 the fact that volcanoes throw out masses of rock melted 
 by heat, and that all our mines grow hotter as they de- 
 scend. Now, the space outside of the earth is extremely 
 cold, as is shown by the fact that all very high mountains, 
 even under the tropics, have snow that does not melt in 
 midsummer. If, in the hottest summer day, we should 
 ascend to the height of five miles above the earth, we 
 should find the air at about zero. This heat of the earth's 
 depths is constantly leaking out into the spaces of the 
 sky ; enough passes off each day to melt somewhere about 
 one hundred cubic miles of ice. Now, as the earth loses 
 heat, it shrinks. All substances, except water, shrink in 
 cooling. A familiar example of this is seen in the rails of 
 a railway. In the heat of summer, they swell until their 
 ends come close together ; in the winter, they shrink until 
 they are some distance apart. A mass of melted stuff, 
 Buch as glass, will generally become one-tenth smaller 
 when it loses enough heat to freeze or become solid
 
 HILLS, MOUNTAINS, VALLEYS, AND CONTINENTS. 109 
 
 From this loss of heat, the earth constantly becomes 
 smaller. Take any point in our solid rocks : it is certain 
 that one thousand years ago this point was a little further 
 from the earth's centre than at present, because the shrink- 
 ing of the earth in one thousand years amounts to a foot 
 or more of its diameter. In this shrinking, it is the deeper 
 part of the earth that grows smaller. The outer part, 
 that is folded into our mountains, has long been so cooled 
 that it had no great amount of heat to lose, and so of late 
 it has not shrunk. All the inner region has been steadily 
 shrinking since the world began. It is easy to see that thi& 
 outer part must wrinkle on the outside. To compare small 
 things to great, we may con- 
 sider an apple as representing 
 the earth, and its skin as 
 answering to the cold outer 
 shell. When the apple dries 
 up, the outer skin wrinkles, 
 because it loses a little of 
 the water that escapes. Con- 
 ceive a loss of heat to bring 
 about the shrinkage in the Fig. so. Wrinkling of : Earth or Apple, 
 apple, and we have a close likeness between the little sphere 
 of the fruit and the world that gave it life. 
 
 If our mountains had not been worn down by the 
 action of water, they would appear vastly higher than 
 they are. The very highest has its top less than six miles 
 above the sea ; but, if we could put on it all that the water 
 has worn away, it would probably be twice as high. 
 
 Yet it must not be supposed that these mountains were 
 ever much higher than at present ; for, in fact, the moun- 
 tains grow slowly upward, while the streams of running 
 water, or the ice streams that often form in their high-up
 
 110 ^REGULARITIES OF THE EARTH. 
 
 valleys, cut them down. So slowly do our mountains 
 generally lift themselves, that a stream flowing across 
 them is sometimes able to keep its bed cut open as the 
 mountain rises, the ridge never moving upwards so sud- 
 denly that the river found an impassable dam in its way. 
 
 The simplest mountains are like the Alleghenies, where 
 a number of long, low ridges, looking something like 
 boats turned upside down, lie side by side, closely crowded 
 together. In more complicated mountains, the smaller 
 folds rest upon larger folds, as shown in the figure below, 
 the whole worn down in a curious way by the streams. It 
 is in such mountains as the Alps, where we have this very 
 
 Fiif. 51. Section through Mt. Blanc. 
 
 complicated structure, that we find the finest mountain 
 scenery. 
 
 If mountains cease to grow, the streams gradually 
 plane them down until the surface becomes nearly level 
 again, and only a geologist can see that the country has 
 its rocks arranged in a mountainous way. There are 
 many countries where such worn-down mountains occur, 
 and they are not infrequent in America, the eastern 
 part of New England, including all of Rhode Island and 
 the most part of Massachusetts and Maine, is upon such 
 worn-down mountains.
 
 HILLS, MOUNTAINS, VALLEYS, AND CONTINENTS. Ill 
 
 One of the advantages of this peculiar structure is, that 
 it enables us to get at many stores of mineral wealth, 
 from which we would otherwise have been debarred by 
 their deep burial. We see 
 by the diagram how a seam 
 of coal or a bed of iron ore 
 may be brought to the light, 
 which otherwise would have 
 been deeply buried in the 
 earth, beyond the reach of 
 man. 
 
 Mountain ridges are rarely 
 found alone. When they ^- 52 - Coal Beds opened by Fold, 
 occur at all, they are generally in long sets of ridges, 
 which have each the same general direction as the main 
 chain. A familiar instance of this is seen in the ridges of 
 the Allegheny mountains or of the larger Appalachian 
 series of mountains, of which the Alleghenies form but a 
 part. Rather more than one-half of the earth's surface 
 has been pushed into the crumpled form of mountain 
 folds. In fact, nearly every part of our rocks that has 
 been made for a long while shows some marks of crump- 
 ling under this pressure that builds mountains, and in 
 time even the most level rocks will probably be twisted 
 by this force pressing against their sides. 
 
 These foldings of the rocks may be of any size, from 
 those that form the greater mountains down through those 
 of less and less dimensions, until the fold is only an inch 
 or so in width. In the larger folds, the thickness of the 
 folded rocks is great ; while, in the smaller folds, the beds 
 may not be thicker than this paper. 
 
 Besides the steep, sharp foldings in the mountains, the 
 earth's crust has folded in broader curves to form the
 
 112 IRREGULARITIES OF THE EARTH. 
 
 continents and great basins. These folds are immensely 
 broad and of very gentle curves. Thus, while a moun- 
 tain may be nearly as high as it is broad, the continental 
 
 Fig. 53. Section across North America. 
 
 fold is from one hundred to one thousand times as wide as 
 it is high. It is not certain just how these continents are 
 formed, but they probably arise from the folding of thicker 
 parts of the earth's crust than are crumpled together in 
 the formation of mountains, a folding that is also due 
 to the gradual escape of heat from the earth's interior. 
 
 It is worth our while to notice that, although the heat 
 that comes to the earth from the sun and stars serves, by 
 setting in motion the machinery of the rains and waves, to 
 wear down the mountains and the continents, the heat that 
 goes from the interior to the stellar spaces causes the 
 mountains and continents continually to rise and replace 
 the wear effected by the ever-falling heat. The heat, fall- 
 ing on to the earth, tends to reduce all its irregularities 
 to a plane ; the heat that flies upward from its depths serves 
 to make it irregular, to build mountain and continent as 
 fast as rain and wave wear them down.
 
 CHAPTER VI. 
 
 ORIGIN OF VALLEYS AND LAKES. 
 
 LESSON I. 
 RIVER VALLEYS. 
 
 A LTHOUGH the continents and mountains form the 
 -^- greatest irregularities of the earth's surface, there 
 are other and commoner features in the land that we can- 
 not pass by. Nearly every part of the earth's surface, 
 above the line of the sea, is formed into valleys, and in 
 many of these valleys there are deposits of fresh or salt 
 water, termed lakes. 
 
 These valleys are of all scales of magnitude, from those 
 that may be bridged with the foot, to those that include 
 half a continent within their bounds. 
 
 To understand how valleys are formed, we should 
 observe the action of rain-water on some area of smoothed 
 land, such as a newly-ploughed field over which a roller has 
 been drawn, bringing its surface to an even slope. We see 
 that the water at once carves out for itself a system of 
 channels which connect with each other, so that a picture 
 of these streamlets will look something like a map of any 
 large river system. 
 
 Whenever the seas give up the lands to the air, they 
 are at once seized upon by the rain-water, and their sur- 
 face brought into such a system of valleys ; the only 
 exceptions being when, as is the case on only a few spots
 
 114 ORIGIN OF VALLEYS AND LAKES. 
 
 upon the earth's surface, there is too little rain to make 
 any rivers at all. 
 
 Each of these river valleys has certain features which 
 are common to all others, though no two are just alike. 
 Every river valley has three principal parts : the place 
 where the river is actually cutting its way, which is 
 termed the channel; the alluvial plain on either side; and 
 the far wider section on either side, which is termed the 
 water-shed of the river. 
 
 The relative proportion and relations of these two ele- 
 ments of the valley vary very much, which gives the most 
 of the variety to our river basins. 
 
 Fig. 54. 
 Section across River Valley. 
 
 The channel of the river is principally due to its 
 mechanical cutting power on the rocks through which it 
 goes. On either side, the alluvial plain marks the place 
 where the stream has recently been at work, but from 
 which it has swung away. On either side, but further 
 away from the channel, is a broad slope towards the stream, 
 which may be miles in width, and is nearly always cut up 
 by tributary streams, each essentially like the main river : 
 only smaller. 
 
 To get a good idea of a river's history, we should go 
 to some of its mountain tributaries, for all very large
 
 RIVER VALLEYS. 115 
 
 rivers head in mountains, see there the first steps of 
 the water ; then trace this stream to the sea. In thiu 
 mountain stream we shall find the water rushing rapidly 
 down a steep slope cut in the solid rocks. These rocks 
 themselves are the waste of old rivers, which was long ago 
 carried to the sea from old lands, built on the sea-floor, 
 and uplifted into the land again, where we find the river 
 now carving them. They may be in the shape of sand- 
 stones, shales, and limestones, or they may have been 
 altered by heat into the .shape of granites or other crys- 
 tallized rocks. We shall find the mountain-stream bed full 
 of great rounded or angular stones, which have been riven 
 from the banks by the roots of trees or the frost, or released 
 by the process of decay, which works into every fissure of 
 the rocks, and leaves them free to fail. In the dry season, 
 the clear water of the stream tumbles about among the 
 stones, making a great deal of noise, but doing little work 
 of wearing ; but in the times of flood we shall find it full 
 of muddy water, and we may see the large stones pounding 
 along, bruising their neighbors, and wearing the bed over 
 which they are forced to move. Now and then, land- 
 slides bring a great amount of rubbish into the bed, so 
 that the stream is dammed for a time ; but its waters 
 soon overcome the barrier, and bear its earth and stones 
 on in the flood. These times of flood are the only occa- 
 sions when the stream becomes a rock-grinding mill ; and 
 its power is due to the swiftness of the waters, and the 
 ease with which they urge the stones down the steep 
 slope of the bed. In this, the torrent part of a river, the 
 stream generally falls fifty feet, or more, to the mile. If 
 its slope is steeper, it often clears away the greater part 
 of the stones, and flows over the lower rock-bed. 
 
 Soon the brook, swollen by tributaries from either side,
 
 116 ORIGIN OF VALLEYS AND LAKES. 
 
 finds its way out of the gorge in which it was born, and 
 enters a wider valley, where it falls less rapidly, and takes 
 on the character of a little river. The first change we 
 notice is that the river no longer flows in a narrow, V-- 
 shaped gorge, with 110 flat land along it, but it now has 
 a little edge of stones, sand, and earth on either side of 
 its waters. Here lie the bits of stone which its dimin- 
 ished current no longer permits it to carry ; for the swift 
 streams above send down larger pebbles than the river 
 can now carry away. They have to remain until they are 
 decayed into pieces small enough for the stream to bear 
 onward. As we descend further towards the mouth, we 
 find that the current, except for occasional falls or rapids, 
 becomes constantly slower, so that these stones lodge on 
 the sides of the stream, making wider and wider terraces 
 on either side of its path. This accumulation of rubbish 
 causes the stream frequently to change its bed. In these 
 ways it cuts away on one side of the alluvial deposit, 
 and fills in 011 the other. Each time it travels over the 
 deposits of pebbles, it takes out the part that is decayed to 
 sufficient fineness to be borne along; the larger pieces 
 soon lodge again in the terrace-beds. 
 
 When the stream is at its flood height, it commonly 
 overflows much of this alluvial plain, and leaves on it 
 a coating of fine mud, which is generally built into a 
 very fertile soil. This soil is often very deep, but below 
 it we find the layer of stones which the stream had not 
 force enough to carry with it. 
 
 Near the mouth of a . great river, these alluvial lands 
 rapidly widen, and form the delta, which is, in reality, 
 not a thing by itself, but is the broadened ends of the 
 alluvial plains that border the stream, from the time it 
 became a river ; that is, when, in its head-waters, the fall
 
 EIVER VALLEYS. 117 
 
 of its bed became too slight to carry all the rubbish the 
 mountain torrents sent into it. 
 
 The only striking variety given to a river is where 
 some harder rocks cross its bed, making a fall. Falls 
 are formed in several ways. One way is when a trap 
 dyke crosses a stream, forming a dam of rock so hard that 
 the stream has difficulty in cutting through it. Such 
 falls are rare ; they hardly occur in any great streams. 
 Another and commoner way is when the bedded rocks that 
 cross the stream slope down towards its head, as shown in 
 the diagram, Fig. 55. In this case, if there be a hard bed 
 also with soft rocks below it, a fall will be formed. The 
 water plunges over the hard 
 bed, and, by dashing the 
 stones about, wears away the 
 soft bed, making a steep and 
 often an over-hanging cliff. 
 
 The falls of Niagara, as rep- 
 resented in the diagram, are 
 formed in this way. On top 
 is a hard limestone, known 
 
 to geologists as the Niagara Fil -'- M - Section of Niagara Falls. 
 
 limestone, which happens to cross the river at this point ; 
 below is a soft slate, which the whirling waters at the 
 foot of the fall easily cut away. From time to time, this 
 undercutting causes the overhanging hard layer to fall to 
 the base, where the surging waters use the fragments as 
 tools to cut away still more of the soft layer. In this 
 work, the beating spray, which lashes against the rock, 
 gives much help. So the fall is slowly working up stream, 
 at the rate of a few feet in a hundred years. All falls 
 of this nature work up stream in the same fashion, be- 
 coming lower as the hard layer sinks downwards towards
 
 118 
 
 ORIGIN OF VALLEYS AND LAKES. 
 
 the stream-bed ; as will be easily seen by inspecting the 
 diagram of Niagara Falls. 
 
 The falls of the Ohio, at Louisville, afford yet another 
 and the rarest sort of fall. There the river flows over an 
 old coral reef, which was built into rocks formed long 
 before the coal measures. This coral reef is much harder 
 than the other rock of the country, so that the river is 
 thrown into cascades where it crosses its surface. 
 
 This is a brief account of the course of the water in 
 the stream itself, and of the causes that give its course 
 and shape its bed. The causes of river-courses, and the 
 many details of its shape, are not easily understood, and 
 
 Fiy. 56. Change of River Channels. 
 
 depend on a thousand local conditions. The constant 
 swings of a river are made to get away from the waste 
 which its current is continually trying to bear along; a 
 work which, from the quantity of this waste, it cannot 
 well do. All our rivers are overburdened by their sedi- 
 ments. In their struggle with the waste, they are thrown 
 into strange turns and windings, called ox-bows, which 
 are found only in sluggish parts of streams. These ox-bows 
 are often cut across by the current, leaving what are some- 
 times called moats, from their likeness to the ditches dug 
 about old castles, and other tower strongholds.
 
 RIVER VALLEYS. 119 
 
 The bed of a river, though it seems to move mainly to and 
 fro through its alluvial plain, is generally cutting downward 
 into the rock that underlies it ; the result is, that it leaves 
 more or less of these alluvial fields high upon the banks 
 on either side of the stream. These shreds of the old 
 alluvial plains show the successive levels of the stream, 
 as it has cut downward in its endless wearing of the rocks 
 over which it flows. Sometimes there are as many as 
 half a dozen of these old levels marked in the terraces 
 of the stream. Very good examples of these occur along 
 the Connecticut River, and most of the other New Eng- 
 land streams. They have been considered as proofs that 
 
 Fiy. 57. Terraces of Kiver Gravel. 
 
 the river was once much larger than it now is, but this 
 is not the case ; for, if the river had ever been able to fill 
 its valley to the level of these high terraces, it would have 
 swept them away altogether on account of the swiftness 
 of its stream. The diagram shows the general position 
 of terraces in a river valley, and the old levels of the 
 river when they were formed. We must imagine that, 
 at each level, the river swung to and fro a great deal, 
 always cutting slowly downwards. 
 
 On each side of the river, as before remarked, there 
 is a gentle slope upward to the "divide," or separation
 
 120 
 
 OBIGIN OF VALLEYS AXD LAKES. 
 
 line between any river valley and the next adjacent 
 stream. This slope is caused in part by the cutting of 
 the small tributary streams, and in part by the dissolving 
 of the rock by the water percolating through the soil. 
 
 Fiy. 58. 
 Divide between two Streams. 
 
 In some few cases where a stream has its head-waters 
 in a country where the rainfall is large, and then flows 
 through a region where there is scarcely any rainfall, the 
 sides of the stream in the desert region have no chance 
 
 Fig. 59. 
 Colorado Canor 
 
 to be cut down, so the river carves out a very deep track, 
 through which it flows. The best example of this in the 
 world is the great Colorado Canon, where the river, plen- 
 tifully fed at its head-waters in the Rocky Mountains, 
 pours for a long distance through a nearly rainless coun-
 
 RIVER VALLEYS. 12j 
 
 try, where it has carved out a very deep bed with walls 
 thousands of feet high on either side. 
 
 In a few cases we have valleys, such as the famous 
 Yosemite, where the trough through which the river flows 
 was probably made by the fracture of the rocks by faults 
 with the down-sinking of the region in which the valley lies. 
 
 Sometimes, as in the case of the Connecticut, the Merri- 
 mac, and other rivers of New England, the river valley is 
 first carved out by a river, and then, becoming the path- 
 way of a glacier, is widened by the ice stream. In this 
 way, many small mountain valleys which are cut into V- 
 shaped trenches by rivers, 
 have been changed into U- 
 shaped valleys by the wider 
 streams of ice that filled them 
 in glacial times. This is be- 
 cause the swift-running brook 
 cuts, at any one time, only 
 the narrow space, perhaps ten 
 feet wide, of its bed. The 
 slow glacier moves, say, three fig.GO. River Gorge widened by ice. 
 
 feet a day, while the living water floy/s, say, sixty miles 
 a day ; so the glacial stream is necessarily a very wide 
 and deep one, and grinds a broad channel. 
 
 We may close our glance at river valleys by stating 
 that they represent the great erosion work of the world. 
 They are the result of a force that comes to the earth 
 through sunshine, and acts through running water, work- 
 ing to bear away the sediment from the land into the 
 sea, where it may be made to nourish life, and to form 
 new strata in the sea-floor, strata which are, it may be, 
 destined to rise again into lands, to be again subject to 
 the wear of the streams in ages to come.
 
 122 ORIGIN OF VALLEYS AND LAKES. 
 
 Besides the valleys carved out by rivers, and the forces 
 that produce lakes, there are some great valleys that 
 have been shaped by the action of the ocean tides, while 
 the lands were under water. Although these sea-carved 
 valleys are rare, it is worth our while to study them, as 
 they give us an idea of the way in which wearing goes on 
 upon the ocean shore and on the bottom of the sea near 
 the land. 
 
 The winds and waves which the sea sends against the 
 shore have no power of cutting valleys. They batter 
 the shore most effectively on the headlands. Their waves 
 weaken as they enter a bay. Thus, in time, they tend to 
 bring the coast to a straight line, by wearing off the head- 
 lands, and filling the waste into the inlets between the 
 promontories. The tides, however, work in the reverse 
 way. On the shores of the ocean, twice each day, there 
 is from the deep a rush of water that passes up every 
 indentation, stirring up the mud, and mixing it with 
 the water. As these tides go out, they drag back ( this 
 dissolved sediment, and draw pebbles along the bottom 
 out into the open sea. Now, these tide-waves, unlike the 
 wind waves, rise much higher in the heads of bays and 
 gulfs than they do on the shore; and, as the force with 
 which they scour away the bottoms of the bays depends 
 on the height to which the water rises with each tide, the 
 effect of tidal action is often much greater in the upper 
 part of bays than at their mouths. Thus, the Bay of Fun- 
 day, between Nova Scotia and New Brunswick, has a 
 tide of about twenty feet at the mouth, while the water 
 rises as much as sixty feet in the interior or innermost 
 part of the bay. The result is that the tides cut away 
 the rocks at the head of the bay with far more force than 
 at the mouth.
 
 RIVER VALLEYS. 123 
 
 In this way it comes about, that wherever there are 
 strong tides, they tend to cut out and deepen the bays 
 along the shore, by the ceaseless rushing of their waters. 
 Shores with strong tides are in this way almost always 
 much cut up into inlets that afford good harbors. 
 
 Some of the finest instances of tide-cutting are found 
 along the British shores, where the tides are generally 
 strong. The channel which separates Great Britain from 
 France and Holland has doubtless been cut through by 
 the tides. The mouth of the Thames and of the Severn 
 have been greatly scoured out by the same action. The 
 Chesapeake and Delaware Bays, on our own coast, are 
 probably due to this cause. Wherever these old tidal 
 bays are elevated above the sea-level, they appear as 
 very broad valleys through which a stream flows. Gradu- 
 ally they are changed in shape until they look much like 
 river valleys. For a long time the steep cliffs on either side 
 show the action of the sea ; but gradually these are worn 
 down, and we can no longer tell that the valley was formed 
 by the tides. 
 
 As the sea is constantly rising and falling along the 
 lands, it is likely that the lower parts of all our large 
 streams have had their shape in part determined by the 
 tidal forces. We can see the marks of this work near the 
 mouths of the Connecticut, Hudson, Delaware, and all 
 the more northern rivers on the eastern shore of this con- 
 tinent, as well as the northern rivers of Europe. 
 
 This tidal force comes upon the earth from the attrac- 
 tion of the sun and moon on all the matter composing the 
 earth. The land is too rigid to give way to the impulses, 
 but the fluid waters swing in the broad waves of the 
 tides. 
 
 These tidal waves produce only a few geological effects
 
 124 
 
 ORIGIN OF VALLEYS AND LAKES. 
 
 of importance. Besides cutting out the bays along the 
 shore, they, by their currents, carry a good deal of sedi- 
 ment from the shore, and lodge it on the bottom some 
 distance out to sea, forming a broad under-water shelf 
 along the coast. 
 
 Fiy. 61 . Channels carved out by Tides. 
 
 The currents that the tides produce in every part of 
 the oceans serve also to feed many forms of life that are 
 fixed to the bottom of the sea, and, therefore, unable to 
 seek their food. As the waters drift by them, on the 
 tide, they can grasp it with their tentacles, and carry it to 
 their mouths.
 
 LAKES. 125 
 
 LESSON II. 
 
 LAKES. 
 
 AMOXG the most beautiful features of the lands are the 
 lakes. It is rather because of their beauty, than because 
 they are very important features in the mechanism of the 
 earth, that we shall give a brief account of them. They 
 are very interesting to the student of nature, for the reason 
 that they show many curious wpys in which the forces of 
 earth and air have worked to produce the form of the lands. 
 
 First, let us notice that lakes are very irregularly scat- 
 tered over the earth's surface : there are certain regions, 
 such as New England, where the land is sown with them; 
 indeed, the whole of North America down to the latitude 
 of about 40 abounds with them, while south of that region 
 they are very rare, indeed ; so that, while Massachusetts has 
 several thousand, counting those above an acre in area, 
 there are many Southern States that have hardly a single 
 water basin that can fairly be called a lake. 
 
 Lakes are so different in their form that they have only 
 one common character : they are basins containing water 
 separated from the main seas, so that if there is any water 
 connection at all with the ocean, it is by means of a river. 
 We may divide these land water-basins into two great 
 classes of salt lakes and fresh-water lakes. Nearly all 
 lakes are fresh, but here and there we find basins contain- 
 ing very salt water. These salt lakes are always without 
 any outlet into the sea ; the reason they do not fill up the 
 basins in which they lie, and overflow into the ocean, is 
 that the streams that feed them cannot make head against 
 the evaporation which the sun brings about, their water
 
 126 ORIGIN OF VALLEYS AND LAKES. 
 
 steams away into the clouds as fast as the rivers bring it in. 
 If the rainfall of the region about our great American lakes 
 should gradually diminish so that it would amount to only 
 one-third of what it now is, the Niagara River would shrink 
 gradually, and in the end no longer flow over the falls. 
 Then the water in the basins of Lakes Erie, Huron, and 
 Michigan would still further shrink until the evaporation 
 from the remaining surface just equalled the amount the 
 streams sent into their basins. In this shape their waters 
 would slowly cease to be fresh, and in the course of ages 
 they would become salter than the sea. This is brought 
 about in the following way: Every stream flowing into 
 the basin carries a little of the various salts that make 
 the sea-water saline ; when this water dries away in the 
 basin, the salt is left behind, for such substances cannot 
 go away with the watery vapor. The result is, the water 
 finally comes to have more salt than it can hold, and this 
 extra charge is laid down in crystals on the lake floor. 
 This is the way in which the great beds of rock-salt have 
 been formed, such as are found in many ancient rocks. 
 Wherever these thick beds of rock-salt have been formed, 
 we may know that the waters in the olden time have 
 been completely evaporated by the sun; and this can only 
 happen where basins of water are cut off from free connec- 
 tion with the sea-water through rivers that discharge their 
 waters into the sea, such as those which drain all our fresh- 
 water lakes. 
 
 Turning now to consider the ways in which the basins 
 that contain lakes are formed, we perceive that they are 
 made by different causes in different parts of the earth. 
 In the regions north of 40 of north latitude, nearly all the 
 lakes have had their basins cut out by the moving ice of the 
 glacial time. The most of the lakes of New England have
 
 LAKES. 
 
 127 
 
 been formed in this way, or are due to the dams of gravel 
 and sand which the glacial streams have left across the val- 
 leys. The same is true of the lakes in Europe, even as far 
 south as those of Italy. It is not easy to conceive just how 
 the ice acted to dig out basins 
 in the rock; but, if we exam- 
 ine the ground beneath a gla- 
 cier, as we may do in many 
 places, we find that the ice 
 eats the soft rock away, leav- 
 ing the harder ; when the 
 glacier disappears, the surface 
 of rock is left with hollows 
 
 upon it, Which form little ^- 62 - Rock and Glacier. 
 
 lakes, until they become filled up or have their boundary 
 ridges cut through by streams. 
 
 When the great glacier of North America passed away, 
 it left the surface with thousands of these rock basins 
 upon it. 
 
 The greater part of them have become filled up, but 
 
 j. G3. 
 Moraine and Lakes. 
 
 many still remain open. Then the rubbish of the glacial 
 period made dams across many hollows, or its surface was 
 irregular, enclosing valleys in which lakes gathered, as is 
 fihown in the figures.
 
 128 ORIGIN OF VALLEYS AND LAKES'. 
 
 The very irregular surface given to the land by the ice* 
 action of a glacial period may be seen by looking; at any 
 of our northern shores from Boston to Greenland or in 
 Scandinavia. We see that these shores are fringed with 
 islands, and cut into innummerable bays. This is be- 
 cause the surface of the land has been made so irregu- 
 lar by the grinding of the ^ce. If the sea had made its 
 shore in any part of the continent of North America north 
 of the great lakes, it would have much the same irregular- 
 ity of coast. On looking at a good atlas of the world, we 
 notice that those northern shores which lie in regions 
 ground over by the ice during the glacial period generally 
 have these irregular shore-lines, while those of regions near 
 the equator generally have straight coasts. Another way 
 in which lakes are formed is this: A great part of our 
 little-changed, stratified rocks are easily dissolved by water. 
 Limestone beds, or beds containing rock-salt, etc., melt 
 down and are dissolved by the long-continued action of 
 water. We see how this comes about if we study the 
 shores of such a basin as Lake Ontario : the waves beating 
 against the shores break down and grind up the soft rocks ; 
 the lime and other easily dissolved substances mingle with 
 the water and pass away to the sea ; the quartz or sand- 
 grains partly dissolve and in part are washed away into 
 the deeper water of the lake. In this way, all our great 
 lakes are increasing their surfaces and diminishing their 
 depths. 
 
 Although this is rather more a means of enlarging than of 
 creating lakes, it is likely that some of the great lakes of 
 the world have originated by this dissolving action of waters 
 acting on beds of rock-salt or other easily dissolved mate- 
 rials. 
 
 There is a third way in which lakes may be formed. When
 
 LAKES. 129 
 
 the lands rise above the sea, they often have deep pockets 
 or basins in them, which, when they are lifted above the sea- 
 level, become lakes. If the rainfall of the country is large, 
 these basins will have more water poured into them than 
 can be evaporated by the sun ; so they will flow over at the 
 lowest part of their edge, and, in time, their salt water will 
 be washed out of them, so that they will be fresh-water 
 lakes. If, on the other hand, the rainfall is too small to 
 fill the basin, then it shrinks to a lake without an outlet, 
 such as the famous Dead Sea of Syria, or the Salt Lake of 
 Utah. 
 
 In some cases the lake is formed by the rising of a moun- 
 tain across the path of the stream ; generally the mountain 
 grows so slowly that the stream keeps its way open, but in 
 some cases the mountain lifts too fast for this down-cutting 
 of the river-bed to keep pace with the uplifting of the dam: 
 then a lake is formed, which, in time, is drained by the 
 deepening of the stream bed. 
 
 These seas of the land, however formed, are but tempo- 
 rary things ; all over the lands we find the floors of drained 
 lakes ; they abound in the desert regions of the Rocky Moun- 
 tains, in Switzerland, and elsewhere. We may look forward 
 to the time when all the lakes that now exist will either be 
 filled up by the rivers that flow into them, or drained by 
 the cutting down of the beds of the streams that drain away 
 their waters to the sea. But new glacial periods will doubt- 
 less create new basins, and others will be made by the dis- 
 solving of the rocks, or by the irregular rising of mountains 
 or the lands ; so that, as long as the world endures, these 
 beautiful features of our landscapes will doubtless exist.
 
 CHAPTER 
 
 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 LESSON I. 
 EARTHQUAKES. 
 
 TpORTUNATELY for the life the earth bears upon it, its 
 surface is generally so steady that it merits the name 
 of terra firma, the firm-set earth, the ancients gave to it ; yet 
 at times this earth's surface is rudely shaken by those jars 
 and tremblings we call earthquakes. It is doubtful if the 
 reader has ever felt such a quake, because in the greater 
 part of North America as well as Northern Europe they 
 are very rare, and usually so slight as to escape notice ; a 
 little rattling of the window panes, or a slight swaying of 
 things hung by cords from the ceiling, being all that com- 
 monly tells us that accidents may happen within the earth 
 that disturb its usual quiet. But in other lands these 
 shocks are much stronger, and produce the most wide- 
 spread destruction of life and property. 
 
 The best way to get an idea of the power of such shocks 
 is to take the history of some great earthquake, and see 
 how it affected the country it ravaged. For this purpose 
 we will take first the earthquake of 1755, which in good 
 part destroyed the city of Lisbon, in Portugal ; not because 
 this is by any means the most violent or the most destruc- 
 tive to life of the many thousand great shocks that are
 
 EARTHQUAKES. 131 
 
 recorded, but because it shows the different sorts of acci- 
 dents that may happen in such convulsions. 
 
 On the first of November, 1755, without any previous 
 warning from the lighter shocks that often foretell the com- 
 ing of a great earthquake, a noise as of loud thunder was 
 heard within the earth, beneath Lisbon, and with it came a 
 convulsion, which in a few minutes laid the larger part of 
 the city in ruins. Out of a population of about two hun- 
 dred thousand persons, over sixty thousand perished. Then, 
 as often in great shocks, a portion of the city built on the 
 hard rocks escaped the worst ravages of the earthquake, 
 while the other portions, built on clay, were reduced to 
 heaps of rubbish. Thousands of the people who had 
 escaped from the falling buildings took refuge on a great 
 marble quay, or landing place, on the banks of the river 
 Tagus, where they were safe from the falling walls. Sud- 
 denly this immense structure went down below the waters, 
 carrying the crowd of people with it. None of the bodies 
 ever rose to the surface ; and, when the place was sounded, 
 very deep water was found to occupy the site where the 
 quay had stood. To complete the work of destruction, 
 there came another of the calamities that often attend 
 earthquakes on the ocean's shore. The sea slowly retired 
 for a long distance, so that, in an hour, parts of its bottom 
 never uncovered before were bared. Then with a roar it 
 came back, in a wave fifty feet in height, that swept over 
 the ruins, giving a speedy death to many of those who had 
 been imprisoned in the falling houses. The ships in the 
 harbor, which had been saved from the evils of the earth- 
 quake itself, were dashed to pieces in this rush of waters. 
 
 Thus, in this earthquake, we have the three forms of dan- 
 ger which these calamities may bring to man : the shud- 
 dering movement of the ground, the engulfing of parts of
 
 132 MOVEMENTS OP THE EATCTH'S SURFACE. 
 
 the surface in fissures or rents in the earth, and the form- 
 ing of vast waves in the sea which roll in great floods into 
 the streams. 
 
 This shock, though it did the most damage at Lisbon, 
 and hence has received its name from that city, shook a 
 portion of the earth's surface larger than four continents 
 such as Europe. In Morocco, a town with over eight thou- 
 sand people, is said to have sunk into the earth as sud- 
 denly as the quay at Lisbon. Even in Scotland the waters 
 of the lakes swayed to and fro as the earth swung beneath 
 them. The hot springs at Toeplitz, in Bohemia, ceased 
 for awhile to flow, and then burst out again in torrents of 
 discolored water, showing that the deeper part of the earth 
 there had been strongly shaken. Far out at sea the ships 
 felt the shock so strongly that their seams were opened, and 
 the men were thrown down upon the decks. The disturb- 
 ance of the ocean reached farther than the shock itself. 
 The sea rolled in great waves on to the shores of Madeira, 
 and even in the West Indies it rose twenty feet above 
 its usual level. There can be no doubt that all the waters 
 of the Atlantic north of the equator were swayed by the 
 shock. 
 
 It is likely that in this earthquake more than one hun- 
 dred thousand people perished outright, and that thousands 
 died from the famines and pestilence that followed from 
 it; so that in this convulsion more human beings perished 
 than in any battle. 
 
 We will now turn to another earthquake which happened 
 in the Island of Jamaica in 1692, which shows us certain 
 other effects of these shocks which are not so evident in 
 the Lisbon earthquake. This beautiful island was the seat 
 of a prosperous colony which had a wealth and promise ex- 
 ceeding that of any English settlement in the New World.
 
 EARTHQUAKES. 133 
 
 To this prosperity the earthquake of 1692 struck a fatal 
 blow. In this series of shocks the ground was swept to 
 and fro in a succession of waves. On the ridges of the 
 earth-waves cracks opened, and, as the wave rolled on, these 
 fissures closed again. People were engulfed in these 
 chasms : many disappeared entirely ; others were thrown 
 out again ; yet others were left partly buried, but squeezed 
 to death in the jaws of the fissures. The buildings over 
 the water sunk down in a standing position into the sea, 
 and were long visible, with their tops many feet below 
 the surface. More than a square mile of land around the 
 harbor of Port Royal was thus carried below the sea. The 
 in-rush of the sea carried a frigate over the tops of build- 
 ings, and left it on the roofs far from the shore. 
 
 This ruin along the shore was equalled in the interior 
 of the island ; though, owing to the fact that there were no 
 large towns, there the loss of life was not so great. The 
 whole surface of the earth was so moved that the soil on 
 the hillsides slid down into the valleys ; the rivers ceased 
 for a while to flow, they were so blocked by the landslides. 
 When they broke through these masses of earth, they ran 
 for days a tide of mud intermingled with timber from the 
 land that had slid down into the streams. The lofty Blue 
 Mountains, which the hour before were covered with ver- 
 dure to their summits, were terribly shaken and rent by 
 the convulsion. After the shock they appeared half bare 
 from the landslides that had carried the soil into the valleys. 
 
 The United States, as before remarked, is mostly free 
 from earthquakes. There are only four regions in it that 
 have ever been visited by shocks of much violence. One of 
 these is in New England ; another, in the Mississippi Valley, 
 just below the mouth of the Ohio ; a third, on the coast of 
 California j the fourth, in the eastern part of South Carolina.
 
 134 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 In New England, there have been three pretty strong 
 earthquakes : the first in 1685 ; the second in 1727 ; the 
 third in 1755. Of these, the last two were very violent. 
 That of 1727 lasted for several years, and principally 
 affected the region near Newburyport, Mass. It was a 
 very curious disturbance ; for, while the shocks of which 
 some hundred were felt, in the course of four years were 
 at first violent, they soon became slight. The strange 
 feature was that, with each, there came from the earth a 
 wonderful thundering, or bellowing noise, loud enough to 
 startle people from sleep, even when they had been long 
 used to it. Many believed that it was the Evil One him- 
 self, raving in his empire beneath the earth, and threaten- 
 ing to burst it asunder in his rage. We shall consider 
 the cause of this noise at a later point in this chapter. 
 
 In November, 1755, occurred the greatest earthquake 
 that ever was felt in New England, since the white men 
 came to the country. This came as a single strong shock, 
 which was most violent at and near Boston, where it threw 
 down a great many chimneys, and for a minute or so was 
 so strong that people could not keep their feet. New 
 England had then mostly wooden buildings, so that the 
 destruction of property was small ; but such a shock at 
 this day would be very dangerous to life, and would cause 
 a vast destruction of property. In that day, chimneys 
 were about the only structures likely to be damaged by a 
 moderately strong shock. 
 
 The Mississippi Valley has had but one great earth- 
 quake, a succession of shocks, which began in November, 
 1811, and lasted until 1813. The first of these quakes 
 was so strong that it probably made more than half the 
 continent tremble for some minutes. The shock was felt 
 jn Florida, New York, Michigan, and the West Indies,
 
 EARTHQUAKES. 135 
 
 Then came, from day to day, successive shocks, which 
 constantly shook a less wide extent of country, until there 
 were only a few square miles of land that trembled at the 
 end of this time of trouble. The worst effects of the move- 
 ment were felt in the region for one hundred miles south 
 of the place where the Ohio River enters the Mississippi. 
 In the first shock, large parts of this region sank down 
 to the depth of several feet below the former level. Into 
 these sunken lands, which occupied many hundreds of 
 thousands of acres, the Mississippi poured its waters in 
 such a flood, that for some hours it ceased to flow towards 
 the gulf, but ran back towards its source. The ground 
 opened in many places, spouting up jets of sand and water 
 above the level of the forest. As the shocks went through 
 the forests, the trees bent over and locked their tops into 
 those of others, or beat their branches to pieces in mutual 
 blows. The low, strong log cabins were shaken to pieces ; 
 and, to protect themselves from the constantly opening 
 and closing fissures, the people cut down trees, so that 
 they fell across the path of the rents, and on these bridges 
 they built shelters, in which they lived for months before 
 the ground became steadfast enough to be trusted again. 
 
 So great was the ruin of the land, that the government 
 was compelled to help the people to find new homes in 
 districts where the earthquake had not done such damage- 
 To this day there remain many marks of this earthquake, 
 though near three-quarters of a century have passed away. 
 Reel Foot Lake and Obion Lake, large sheets of water, 
 were formed at that time. Many of the trees which were 
 standing on the submerged land still lift their blasted 
 trunks above the water, or are visible below its surface. 
 
 The earthquakes of California have been numerous and 
 violent. The only one that led to any destruction of life
 
 136 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 occurred at Santa Barbara, in. 1811, or at about the same 
 time as the Mississippi Valley earthquake. There have 
 been many dreadful shocks in Central America, but, as a 
 whole, the continent of North America has fared better 
 than any other of the great lands except, perhaps, Aus- 
 tralia. The worst regions for earthquakes are found in 
 the west and north border of South America, southern 
 Italy, Asia Minor, and parts of Central Asia, parts of 
 the East Indies, Japan, and in New Zealand ; while in 
 northern Europe, Australia, South Africa, and Brazil, they 
 rarely happen. But every part of the earth is subject to 
 slight shocks. 
 
 It was once supposed that there was some relation 
 between earthquakes and volcanoes. This idea came from 
 the fact that every volcano, while in activity, trembles 
 with repeated shocks ; sometimes it shudders for days and 
 months. But there are many regions, as New England, 
 where there are no volcanoes within a thousand miles, yet 
 strong earthquakes here occurred. 
 
 In trying to understand the cause of earthquakes, we 
 should first notice the theories that throw light on their 
 nature. Experiment shows us that we can make small 
 earthquakes by exploding gunpowder underground, or in 
 any way jarring the earth, which are just like the great 
 shocks in everything but their size. Careful study has 
 shown us that all earthquakes are of the same nature as 
 the jar we can give a table when we strike it a blow with 
 a hammer or with the clenched hand. If we throw a 
 stone into a pool of water, we see that a little wave rolls 
 away in circular, ring-like wrinkles. This is something 
 like an earthquake wave, only it moves very slowly, and 
 an earthquake wave very rapidly. If we strike the head 
 of a drum, a succession of waves flow through it. This is
 
 EARTHQUAKES. 137 
 
 more like an earthquake wave. If we strike the end of a 
 long timber with a hammer, a person holding his hand on 
 the other end feels a jarring motion come to him from 
 the timber. This is exactly like an earthquake shock. 
 In the pool, the drum, and the stick of timber, a wave 
 flies through the body, but the wave differs in its character. 
 In the pool, the wave is only on the surface of the water; 
 but in the timber it is all through it ; every particle of the 
 timber strikes against every other. If we took a sphere of 
 timber or of metal, and struck it in the middle, the waves 
 would run through all parts of it, and give a jar over the 
 whole surface. Now, an earthquake is a jar or wave of 
 just this sort that moves through the earth. It may be 
 made in any one of many ways. We have seen that the 
 rocks under the surface are often pressed strongly to- 
 gether, as in the making of mountain ridges. As these 
 ridges rise, the rocks slip over each other, making a jar, as 
 when we drag a table over the floor ; or they break, form- 
 ing what are called faults, which we know cause jars and 
 tremblings. When melted rock is thrown into fissures, 
 forming dykes, the fractured rocks are struck as with a great 
 hammer by the inrush of molten rock. When the steam 
 and other matters that escape from a volcano force their 
 way along underground, they cause the rocks to expand, and 
 make sharp movements, like steam-pipes when the hot vapor 
 is let into them. As this heat dies away, the rocks contract, 
 as the steam-pipes do when the steam is shut off. In ail 
 these, and many other ways, the earth is subject to sudden 
 blows that give us earthquakes. We will now see more 
 closely how an earthquake behaves. Let us suppose 
 that, in the diagram, the earthquake starts in some sud- 
 den blow at a, and runs in all directions to the surface of 
 the earth, 666; there will be many shocks from one jar ;
 
 138 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 just as, when we strike a drum-head, or twang a guitar- 
 string, there will be many waves follow the one move- 
 ment. These successive waves are indicated by the lines 
 c c' c", etc. Now, where a man is standing just over the 
 shock, at c, it will come straight up beneath his feet, and, 
 if it is strong, he will be thrown vertically up into the air, 
 from a few inches to many feet in height. When he is 
 standing at c' or c", he will find his feet pulled forward, 
 and his body will be thrown to the ground. If there are 
 three buildings, one just over the shock, as at c, and the 
 others at <?' and c", that at c will probably have its walls 
 
 Fig. 64. 
 Diagram showing Earthquake Waves. 
 
 left standing, but the roof and floors will tumble into the 
 cellar. Those at c' and c" will have the walls that are at 
 right angles with the shock thrown down, while the walls 
 parallel to the line in which the shock runs will probably 
 remain standing. 
 
 Just as the waves made by a splash in a pool run out, 
 just as the jar given at one end of a long timber becomes 
 feeble at the further end, so earthquake shocks wear out 
 in running through the rocks of the earth. This causes 
 the shocks to become more and more feeble as we get 
 farther away from the place where they start.
 
 EARTHQUAKES. 139 
 
 On the land, the effects of an earthquake shock are very 
 great; but in the sea they are even greater. The shock 
 kills many animals in the sea. We often find the sea, near 
 where a great earthquake has happened, covered with dead 
 fishes, which have been killed by the blow they received 
 through the water. We can imitate this by exploding a 
 small charge of dynamite below the surface. The blow it 
 gives is just like that which comes through an earthquake. 
 This blow also seems to stir up the mud of the sea-floor, and 
 this mud kills many animals. Then the earthquake lifts the 
 surface of the sea over the place where the shock starts, and 
 a wave rolls away from this place which may be strong 
 enough to cross the widest oceans, and often rolls on the 
 land in a prodigious breaker sixty feet or more in height. 
 It is this wave that so often sends ships far inland, as 
 in the earthquakes of Lisbon and Jamaica. In the earth- 
 quake of 1746, which ravaged the west coast of South 
 America, a Portuguese man-of-mar was carried for a 
 distance of three miles inland, and left stranded, though 
 but little injured. Within twenty-five years, several ves- 
 sels have met with this strange fate. This great wave, 
 though without power to harm the life of the deep seas, 
 is very destructive to all the creatures that live on the 
 shores, grinding them up, and mingling them with the 
 mud. 
 
 When we look over the history of earthquakes, they 
 seem like very cruel agents of destruction. Next to bat- 
 tles and famines, they are the greatest life-destroying 
 accidents that can befall man; and, among the lower 
 animals, they are, perhaps, more destructive than any 
 other sudden convulsion of nature. But, when we con- 
 sider how slight and seldom are the shocks of great 
 destructive power, compared with the great work of lift-
 
 140 
 
 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 ing mountains, forming volcanoes, and otherwise maintain- 
 ing the activities of the earth, we must regard them as very 
 trifling accidents, and rather wonder at the slightness of 
 their effects than regard them as unnecessary convulsions. 
 Everywhere, and at all times in the world, we see such 
 destruction of individual life ; yet the life as a whole goes 
 onward and upwards as steadily as if no death came 
 about from the working of the great machinery of the 
 earth. The Power that rules the world evidently does 
 not regard death as an evil to be avoided ; everything is 
 made quickly to die, that better life may follow it ; and, if 
 we accept death as in the order of nature, the destruction 
 of life by earthquakes, volcanic outbreaks, storms, and all 
 the other violences of the earth need not shake our faith in 
 the merciful plan of all things. 
 
 City ruiued by Earthquake, with Landslides.
 
 CHANGES IX THE SHAPE OF SEA AND LAND. 141 
 LESSON II. 
 
 CHANGES IN THE SHAPE OF SEA AND LAND. 
 
 ALTHOUGH the continents are the very firmest thing we 
 know in nature, although there have been no great changes 
 in the shape of land and sea since the earliest human his- 
 tory, we must not suppose that the lands endure very long 
 in one shape. We know that in the long ages of the past 
 very great changes have come over them. All the rocks 
 that we know in the world have, except possibly some of 
 those thrown out by volcanoes, been formed on the bottom 
 of the sea, which is in itself enough to prove that all our 
 present lands have been sea-floors. We find fossil sea- 
 shells on the tops of our highest mountains, and there is 
 hardly a place in the world where we are more than a few 
 miles from rocks containing the remains of some animals 
 that have lived on the sea-floor. 
 
 The changes in the shape of the land take place so 
 slowly that we cannot recognize many of them within the 
 time of human history; yet, along one coast, which has 
 been known for some hundreds of years, viz., that of 
 Sweden and Norway, the shore is in places rising as fast 
 as three feet in one hundred years. On the west shore of 
 South America, during the great earthquake of 1822, the 
 shore for some hundreds of miles rose suddenly by four 
 feet or more. Many other cases of such changes could be 
 mentioned, but they only show us how slowly accumulated 
 modifications can affect great changes. A few such lifts as 
 that on the Chilian shore would greatly alter the form of 
 a continent, especially if they took place on a shore along 
 which the water was not very deep.
 
 142 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 Besides these alterations that come from the up-lifting 
 or down-sinking of the lands, there are slower-going 
 changes, due to the wear of the sea and of the rivers. 
 The water that falls on the country drained by the Missis- 
 sippi wears away about one foot of its rocks in every seven 
 thousand years, and bears the waste into the sea to form 
 new rocks on the sea-floor. Taking all the river-basins of 
 the world, or, in other words, about all the surface of the 
 land, we have an average down-wear of about one foot 
 in three or four thousand years. This seems slow; yet, 
 when we consider that in the life of the earth a thousand 
 years is but as a day, or, better, an hour in our own lives, 
 it is really a rapid wear. 
 
 Then the sea too does its work of calling back the lands 
 to its depths. Beating against the shore, it undermines 
 cliffs and grinds their fragments to powder, which the cur- 
 rents easily bear away into the depths. When the coast is 
 not faced with very hard rocks, it often cuts back at the 
 rate of several feet a year. In England, for instance, 
 whole townships, that once bore many villages, now lie 
 buried beneath the sea. 
 
 This work of wearing away the rocks is mainly due to 
 the action of the sun's heat. It sets in motion the winds 
 that raise the sea waves, and it fills the winds with water 
 that falls as rain ; but, though it is a work of destruction, 
 it is also a work of preparation for lands that are in time 
 perhaps to be lifted above the sea in their turn to bear life. 
 The most important effects of these changes of the lands 
 are found in their action on the destruction of life over 
 the earth, and in the course of the sea-currents, those great 
 carriers of heat from one part of the earth's surface to 
 another. We can best understand these effects by con- 
 sidering what would happen if the Isthmus of Darien,
 
 CHANGES IN THE SHAPE OP SEA AND LAND. 148 
 
 which is but a slender, low bit of land, were to be deeply 
 submerged beneath the sea. The animals now living in 
 the sea-waters on either side of this isthmus are very 
 different from each other, hardly a species being found 
 both in the Caribbean Sea and in the Pacific Ocean. If 
 the isthmus were buried beneath the sea, these animals of 
 the two seas would be brought into contention with each 
 other. Many animals now limited to the Atlantic waters 
 would extend into the Pacific, and many unknown in the 
 Atlantic would destroy those from the Pacific waters. Many 
 of the weaker kinds would be destroyed by their stronger 
 enemies, and in a few years the life in either ocean near 
 the isthmus would be greatly changed. 
 
 If the down-sinking in the Central American district 
 were carried so far as to lower the northern part of South 
 America beneath the sea, converting it either into open 
 water or into an archipelago, then the great current that 
 becomes the Gulf Stream would no longer flow into the 
 northern Atlantic, but would pass through this gap into 
 the Pacific Ocean. The result of this would be that 
 northern Europe and the most of the United States would 
 become too cold for the life of man, while the tropical 
 regions would have their heat increased. This instance 
 will give an idea of the effects that may come from lower- 
 ing lands beneath the sea. 
 
 Now let us turn to Asia, and imagine what would be 
 the effect if the string of islands, that nearly connect that 
 continent with Australia, were to rise higher above the sea, 
 so that the two continents were connected by a continuous 
 land bridge. In this case the effects would be these, viz. : 
 the currents of warm water that now pass from the Pacific 
 Ocean to the Indian Ocean, through the straits between 
 these islands, would, when barred out from the Indian
 
 144 MOVEMENTS OF THE EARTH'S SURFACE. 
 
 Ocean, turn northward and southward towards either 
 pole, carrying more warmth to the cold regions of the 
 earth and diminishing the heat of the tropics. The con- 
 tinent of Australia has hardly any quadrupeds except 
 creatures akin to our opossums, such as the kangaroos 
 and the like, animals that carry their young about in 
 pouches. Of these animals, there are over one hundred 
 species living on that land. All these creatures are much 
 weaker than the quadrupeds of Asia. As soon as this 
 bridge across to Asia were formed, the tigers, leopards, 
 and other beasts of prey would pass south to Australia, 
 and quickly exterminate the kangaroo tribe, while their 
 place would be taken by the stronger or fleeter-footed 
 elephants, buffaloes, and deer from Asia. 
 
 We know very well that just such changes of level of 
 sea and land as we have imagined to occur in these isth- 
 muses and archipelagoes of America and Asia have very 
 often happened in the history of the earth, so it is fair to 
 presume that they may happen in the future. 
 
 It is hard to conceive this constant up-rising and down- 
 sinking of the shore ; but, if we will consider the matter, 
 we shall see how it must often happen. The shrinking of 
 the earth's interior, from the constant cooling, is constantly 
 causing its surface to wrinkle, deepening the sea-troughs 
 and lifting the lands into the air. The rivers, the sea- 
 waves and the tides are always cutting the land down 
 to the sea level. Broad surfaces of the sea-floor in the 
 great oceans are sometimes sinking, which serves to draw 
 the water away from the other seas, lowering the level 
 of the shores : again they are rising, causing the waters 
 to rise along all the sea-coasts in the world. When a 
 glacial period comes, a great deal of the water which now 
 is in the seas is taken out and heaped as ice on the lam?
 
 CHANGES IN THE SHAPE OF SEA AND LAND. 145 
 
 about ihe poles, and this lowers the level of the sea; 
 when the glaciers melt, this water is returned to the 
 deep, raising its level again. Thus we see that there are 
 abundant reasons for a change in the height of the sea 
 along the lands. 
 
 These changes do not seem ever to destroy any of the 
 continents. From time to time their shapes change, but 
 the greater lands seem to have been constantly growing 
 ever since the earliest times in the earth's history. 
 
 Stages of Growth of North America.
 
 CHAPTER VIII. 
 
 THE PLACE OF ANIMATED THINGS IN THE WORLD. 
 
 LESSON I. 
 THE WORK OF LIFE ON THE EARTH. 
 
 A T first sight, it may not seem to the reader that the 
 -^- animals and plants of the world have any very close 
 relation to its structure, that they have any sufficient 
 claim to our attention when we are considering the geo- 
 logical history of our earth. This, indeed, was the old 
 way of looking at the realm of animated nature ; but, the 
 more we know of the earth's life, the more clearly we 
 perceive that this life, both inorganic and organic, is so 
 bound up together that it is all one in its work. 
 
 The life of the world came out of the earth by laws 
 which we do not understand. Every creature exists by fit- 
 ting itself to the physical forces about it, and when it dies 
 its dust goes back to the soil. As far as its bodily parts are 
 concerned, each creature in the world is but a bit of earth 
 that has become for the moment filled with the forces of 
 life. All the work of its body is determined by laws of the 
 earth's matter from which its body is formed, and of which 
 it always remains a part. 
 
 The force that impels these animated things is derived 
 from their food ; which, in the plants, is either the mineral 
 matter of the soil and the carbon in the air, or, in the 
 case of the animals, it is the vegetable kingdom that sup-
 
 THE WORK OF LIFE ON THE EARTH. 147 
 
 plies the food directly in the herbivora, or at second hand, 
 as in the carnivora. This force is given to the plants by 
 the action of the sun's heat ; by it the plants separate the 
 carbon from the atmosphere, and build into their bodies 
 the mineral substances obtained through their roots. 
 These things the plants consume, and obtain thereby the 
 solar force that the plants built into their structures. 
 In this way we may say that plants, and the animals 
 which they support, owe their life to the same force that 
 sets the winds or the rivers in motion. 
 
 We should notice, also, that the animal and vegetable 
 life of the world plays a very large part in the working 
 of the earth's machinery. The land plants protect the 
 lands from the rain, which would rapidly wear away their 
 surfaces but for the covering the plants afford. The car- 
 bonic acid which these decaying plants furnish to the 
 water give it a great power of dissolving substances of 
 many kinds, and so aids in the formation of mineral de- 
 posits and the excavation of caves, as we have already 
 seen. Plants and animals furnish a vast deal of material 
 for the formation of rocks. More than half the rocks on 
 the earth's surface owe their formation, in whole or in 
 part, to the action of animal or plant life. All our coals, 
 bituminous slates, and limestones are essentially the work 
 of the living things of past times, and the greater part of 
 our sandstones and other rocks are partly their work. 
 
 We should also see that the greatest work of the earth, 
 from ancient ages, has been to afford the place on which, 
 as on a theatre, this life has played its part. We find the 
 most wonderful proof of the earth's perfection in the fact 
 that for a time, so long that our imaginations are too 
 weak to consider it, it has been so well ordered that no 
 convulsions have prevented the animals and plants from
 
 148 THE PLACE OF ANIMATED THINGS IN THE WORLD. 
 
 steadily going forward in their development. Ten miles 
 beneath the surface, there is a heat so great that no life 
 could bear it ; ten miles above, a cold so intense that, if it 
 should come to the earth, nearly all created things would 
 immediately die. Yet for ages the balance has been so 
 preserved, and the temperature of the earth has remained 
 so near what it is at present, that these sensitive living 
 creatures have not been killed, but have prospered from 
 age to age. 
 
 In this way we perceive the intimate relations between 
 life and the world it inhabits ; we see that even the brief 
 and general view of the earth which we are now taking 
 would be too incomplete without at least a glance at tht 
 history of animals and plants.
 
 DIFFERENCE AND RELATIONS AMONG LIVING BEINGS. 149 
 
 LESSON II. 
 
 DIFFERENCE AND RELATIONS AMONG LIVING BEINGS. 
 
 WHEN we look around on the beings that make up the 
 kingdom of animated things, the plants and animals of 
 the world, we easily see that they are in many ways akin 
 to each other. First, we see that they all have some com- 
 mon qualities. They are alive, they grow, they reproduce 
 their kind, and in due time they die, actions which 
 separate them widely from the mineral kingdom. Then 
 we see that the animals are pretty distinctly separated 
 from the plants by the fact that besides their life, growth, 
 etc., features which are common to both, animals have 
 sensations, and show even in the lowest forms signs of 
 something like will in their motions. 
 
 Among animals, we notice a great many different degrees 
 of kinship. We see, for instance, that all our common four- 
 footed animals are akin to each other. Bulls, sheep, deer, and 
 other horned animals are closer related to each other than 
 they are to pigs, elephants, or horses. Crayfishes, lobsters, 
 spiders, and insects are evidently, by their outside jointed 
 structure, more like each other than they are to our back- 
 boned animals. If we compare our own bodies with the 
 lower animals, we see at once that our nearest animal kin- 
 dred are among the ordinary quadrupeds. This matter of 
 relationship may be by study carried much further, for we 
 find that all animals are related to one another in varying 
 degrees. A great part of the study that naturalists have 
 given to living things has had for its object the determin- 
 ing of those relations that exist among them. The result 
 is that we find that these relationships may be expressed
 
 150 THE PLACE OF ANIMATED THINGS IN THE WORLD. 
 
 by what is called a system of classification. At first sight, 
 this scheme of classification looks very complicated; but, 
 if we look at it carefully, we see that it rests on very sim- 
 ple principles. A clear understanding of these principles 
 may be had, if we take some other objects than animals 
 and plants, and apply a system of classification to them. 
 
 For this illustration, let us take the contrivances made 
 by man for measuring time. There have been many differ- 
 ent plans of accomplishing this end, which rest on the fol- 
 lowing plans of working. First, we have the ancient water 
 clocks, where time was measured by allowing water to 
 drop out of a vessel through a small hole. A familiar in- 
 stance of this mechanism is the sand-glass, where sand, 
 slipping through a narrow opening, measures the time. In 
 these there is the common plan of having some particles 
 of water or sand slip through a hole under the influence 
 of the earth's attraction. They differ in the way of car- 
 rying out the plans in the two machines ; or, we may say 
 that there is one plan of structure in these machines, and 
 two divisions, which we may conveniently term classes of 
 structure under the plan. Then we have the sun-dials, 
 where there is a very different plan, and two classes of 
 methods of carrying out the plan. One, when the gnomon, 
 or part that casts the shadow, is fixed ; another, when it is 
 attached to a magnetic compass, so that it may set itself 
 at any time. Examining the structure of fixed dials, we find 
 that sometimes they are horizontal, sometimes vertical, as 
 in those that are placed against a wall. To these divisions 
 we may, as before, give any name we choose, but for con- 
 venience we may term them orders under the class of 
 fixed dials. Looking more closely at these dials, we find 
 yet further differences under each, some of the horizontal 
 dials are set up in columns, and some are placed on the
 
 DIFFERENCE AND RELATIONS AMONG LIVING BEINGS. 151 
 
 pavement. These differences we may, for convenience, 
 term families under the order of horizontal fixed dials. 
 We may go still further in our division. In some cases, 
 we see that the figures denoting the hours are printed on 
 the dial ; in other cases, they are cut into its substance. 
 These differences we may denote by the name genus, and 
 we would make two genera of dials in each of the two 
 families. By careful study, we should find that many 
 such genera could be made. Finally, our examination 
 brings us to groups of sun-dials which are all so alike that 
 we cannot perceive any constant differences among them. 
 They are of about the same size, shape, color, etc. We 
 may even suppose that they came from the same factory. 
 These groups we will term species. 
 
 We can take the same course with the other and more 
 varied plan of time-measurers, clocks and watches. We 
 shall find these classes, orders, families, genera, and species 
 just as we have seen that they exist in sun-dials, only it 
 takes more time and more study of their mechanism to 
 make them out. 
 
 This system of classification can be applied to a great 
 many other structures; indeed, to all forms of human 
 contrivances where men have made many inventions all 
 working towards one result. The reader can see that in 
 instruments for aiding locomotion, such as ships, wagons, 
 balloons, etc., or in contrivances for giving power, such as 
 windmills, steam mills, water mills, etc., or implements of 
 war, such as armor, arms, javelins, spears, swords, guns, 
 etc., the same system of classification can be made. 
 It will be more profitable for the reader to work these 
 out for himself than for them to be described here ; for 
 the only aim of this classification of human products is to 
 show the principle of the classification which is applied to 
 natural objects, which otherwise is hard to understand.
 
 152 THE PLACE OF ANIMATED THINGS IN THE WORLD. 
 
 When we apply this principle of denning relationship or 
 likeness, according to its degrees, to animals and plants, 
 we find that it leads us to essentially the same result as 
 when it is applied to human contrivances. There is al- 
 ways something like a plan which naturalists sometimes 
 call a type ; different ways in which the plan is carried 
 out, called classes; peculiar complications of it, termed 
 orders ; under these orders, variations of the general shape 
 to suit different conditions, called families; still other 
 subordinate divisions, based on details of structure, called 
 genera; and finally, the last division that we can make, 
 which is commonly termed a species. All these divisions 
 rest upon differences in the ways in which animals adapt 
 themselves, by their peculiarities, to the needs of their life. 
 
 Among animals these divisions are clearer and more 
 numerous than among plants, for the reason that animals 
 have more definite and numerous results which they seek 
 to attain than have the plants. 
 
 Among animals, naturalists recognize several different 
 plans of structure. The differences are in the general 
 ways in which the animals are built. These differences 
 may be compared to the various sorts of time-keepers. 
 In time-keepers there is one object, viz., to divide time 
 into intervals ; but, among animals, the creatures must 
 do a number of tasks: they must nourish themselves, 
 protect themselves from enemies, reproduce their kind, 
 all of which the plants do as well, but above all they 
 must have some mechanism of sensation, some fitness for 
 the work of intelligence, however low that intelligence 
 may be. 
 
 These plans of building animal structures for their 
 many uses are five or six in number. The protozoa, the 
 radiates, which group is sometimes divided into two,
 
 DIFFERENCE AND KELATIONS AMONG LIVING BEINGS. 153 
 
 the articulates, the mollusks, and the vertebrates. Some 
 naturalists have made more than these divisions, but 
 those given above are the most clearly to be seen. In each 
 of these groups there are two or more classes ; in each class 
 several orders; in each order many families; and under 
 each family many genera ; under each genus many species 
 are ranged. It is not possible for us to trace these divisions 
 here, that would be a great task, but only to give the 
 reader some idea of the nature of the classification among 
 animals, for that has often to be set before the mind of 
 any one who considers organized beings. To make the 
 matter clearer, we will consider the way in which a natu- 
 ralist looks at an animal when he is classifying it. For 
 this purpose we will take a common honey-bee as an ex- 
 ample of the work. 
 
 First, we notice that the bee is a member of the organic 
 kingdom, because it has, in common with the other ani- 
 mals and plants, the powers of nutrition, growth, repro- 
 duction, etc., qualities that belong to all this group of 
 natural objects. Second, that it belongs to the group of 
 animals, because it has the means of perceiving sensa- 
 tions, and a share of that quality of mind that separates 
 all animals from plants. Third, that it is an articulate 
 animal, because its body is built on the plan of many 
 ring-like segments placed one behind the other, like the 
 worms, lobsters, or cray-fishes. Fourth, that it belongs 
 to the class of insects, because, in common with all the 
 insects, it has three pairs of jointed legs, each pair belong- 
 ing to one of the middle segments of the body, a separate 
 movable head, and an abdomen divided from the parts 
 that bear the legs. Fifth, it belongs to that particular 
 group of the insects called hymerioptera or membranous 
 wings, because it has four wings, not covered with scales,
 
 154 THE PLACE OF ANIMATED THINGS IN THE WOELD. 
 
 as in the group of butterflies, but made of an easily-folded, 
 cloth-like substance, as well as certain peculiarities of the 
 jaws which fit them for very varied work. Sixth, it 
 belongs to the special family of bees, and is separated 
 from the wasps, the saw-flies, and the ants, by its peculiar 
 solid, compact form, which enables us in a moment to see 
 that all the bees belong together. Seventh, it belongs to 
 the genus of bees, because of the special structures about 
 the mouth, etc., which are not present in other members 
 of the family. Eighth and last, it belongs to the honey- 
 bee species, because it has the precise form, the color, and 
 the habits that mark its kindred. Thus, by eight steps of 
 division, we place this creature so as to show the greater 
 differences between itself and the other living things. 
 This process we take in classification with any animal or 
 plant.
 
 CHAPTER IX. 
 
 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 LESSON I. 
 LINES OF ADVANCE IN ORGANIC CREATURES. 
 
 TTTE have already glanced at a part of the machinery 
 ^ * by which the earth carries on its physical life. We 
 have been able to look only at the merest outlines of this 
 work. Yet we have seen that the earth is not a place 
 where mere accidents contend against others, but that its 
 physical work goes on with a stately order ; that even its 
 most violent activities, the volcano, the earthquake, the 
 lifting of the lands from the sea, and the mountains upon 
 the land, are all so accomplished that the alteration 
 does net break the harmony of the whole work, but 
 rather contributes to its perfection. We have now to 
 consider the second and higher form of the earth's life, 
 that which exists in things which we call living, in ani- 
 mals and plants. The lower or physical life of the earth 
 shows us matter in the control of laws that shape it into 
 the lands, the mountains, in sea or air, but leaves it 
 without sensibility, without power to renew itself. Moun- 
 tains or crystals, and other inanimate things are brought 
 to their shape and pass away into the waters without 
 helping themselves in any way. In this regard they are in 
 strong contrast with living beings. All plants and ani- 
 mals grow from within themselves by processes that make
 
 156 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 them living. They can all multiply their kind. In these 
 respects they are strongly contrasted with all the so-called 
 lifeless part of the earth, which, though in a true sense 
 living, exists in other ways. Every animal and every 
 plant feeds in some way or other ; it can take in the mat- 
 ter from the world outside of its body, and by changing 
 the chemical shape of this matter it can accomplish two 
 ends: it can take the matter itself, to build its body or to 
 reproduce its kind, and it can take the force that exists in 
 the matter, and use it for its own purposes, to move its 
 body with, or to carry on the circulation of its blood, or 
 any other of many uses. In this they may be com- 
 pared with a steam engine. For instance, when plants 
 .take in carbonic dioxide, which consists of one part of 
 carbon and two parts of oxygen bound together, they 
 separate the two elements, build the carbon into their 
 bodies, and throw the oxygen into the air. To effect this 
 change, they make use of the light and heat of the sun ; 
 for it takes a certain amount of force to separate these 
 two elements. When an animal eats the plant, it burns 
 part of this carbon in its lungs, by bringing it in contact 
 with the air, and thereby 'gets a good deal of force to use 
 in the various movements of its body. It is this power of 
 taking a force from the outside world, and using it to sus- 
 tain all sorts of activities, that separates the animal and 
 vegetable world from the lower life of the earth, and makes 
 them a kingdom by themselves. Because of this peculi- 
 arity, there can be no passage from the mineral to the 
 living world. 
 
 Animals and plants appear to have begun in a very 
 ancient stage of the earth's history ; we do not know just 
 where, when, or how the beginnings were made ; for the 
 ancient history of life has been lost to us, through the
 
 LINES OF ADVANCE IN ORGANIC CREATURES. 157 
 
 changes that the rocks have undergone, which have de- 
 stroyed all the fossils they ever may have contained. 
 These earliest forms were doubtless of a very simple 
 structure. 
 
 The lowest organized beings we know have many of the 
 features both of animals and plants. They are little bits 
 of a jelly-like substance, having no distinct form, no parts 
 of the body adapted to any special uses, such as eating, 
 digesting, motion, etc., as have our higher animals. From 
 some such simple foundation of life all beings seem to have 
 sprung, through the action of laws that we do not yet 
 fully understand. We can see one kind coming after the 
 
 . 65. Rhizopods. 
 
 other and out of the other, as we go through the records 
 of the rocks from the earliest days to the present time, 
 but we cannot see just how the change from one kind to 
 another is effected. Very early in the history of the 
 world, it is clear that these two kinds of beings, plants 
 and animals, were begun. 
 
 The lower plants were probably seaweeds. The plan on 
 which their structure was built made beings suited for 
 taking carbonic dioxide gas out of the sea-water, which 
 contains a little of this gas, and for building its carbon 
 into the body of the creature. They also took a number
 
 158 A SKETCH OF THE EARTH'S ORGANIC LIFE 
 
 of other substances from the water. There were in them 
 no roots, and they differed from distinct animals in having 
 no arrangement for sensation. This is the really strong 
 difference between animals and plants. Plants work to 
 make structures that get along without any sensations, 
 while animals, from the first, and always, provide for this 
 work of receiving impressions from the outer world. Ani- 
 mals, even the lowest, also have means of making voluntary 
 movements, which either help them in feeding alone, or, 
 when they are not fixed as by a stem to some solid body, 
 enables them to move about at will. Some low plants, and 
 the seed of many plants, have means of moving that at first 
 sight look like those of animals ; but they are plainly 
 involuntary organs, and not connected with any capacity of 
 recurring nervous sensations nor to be compared with the 
 motive parts of true animals. 
 
 When, from the lowest forms of these beings we pass 
 upward to the higher, we find that in plants the following 
 objects are sought to be accomplished. The structure is 
 arranged so as to give a solid stem and branches, and 
 to contain many separate individuals in one community. 
 The work of leaves is separated from the rest of the 
 plant, and the roots are inverted, which enable the plant 
 to draw a certain share of its nourishment from the 
 ground. Especially, it can find water there, which would 
 often be unattainable in the air. While the plants remain 
 water creatures, they do not need their roots : it is only 
 when they come to dwell on the land that their roots be- 
 come developed. In the water they found all they needed 
 for their life without these appliances. 
 
 These steps lead us up from the simplest seaweeds, which 
 have nothing that we can fairly call leaves, stems, or roots, 
 through the higher seaweeds, where the stem becomes dia-
 
 LINES OF ADVANCE IN ORGANIC CREATURES. 159 
 
 tinct from the leaves, through the mosses and lichens, the 
 ferns, the palms, the pines, to our oaks and other familiar 
 trees. 
 
 In this succession of forms, the plant contrives to sepa- 
 rate its parts into the roots, that gather food from the 
 soil, the stem, which supports the upper part of the body 
 
 Fig. 66. Plants with and without 
 Roots and Stems. 
 
 and keeps a connection with the root, and the branches 
 which support the leaves and flowers. At first, the stem 
 and branches have no distinct bark, and they grow by ad- 
 ditions made throughout the mass of the wood ; but in 
 
 Fig. 67. Endogens and Exogens. 
 
 time they devise a way of growing only on the out or 
 bark side, the inner part of stem and branches being very 
 solid, so as to serve for support, while the sap is carried in
 
 160 A SKETCH OF THE EARTH'S ORGANIC LITE. 
 
 the bark alone, and the solid central wood forms a bet- 
 ter support. This contrivance enables the plants to have 
 smaller, stronger branches, and their trunks can carry more 
 top burden of twigs and leaves. 
 
 In its perfected form, the tree consists of many separate 
 individuals, the buds, united together by their common 
 property, the branches and trunk, while the roots below 
 do the work of separating the mineral substances from 
 the water that dissolves them, bearing them in the sap up 
 to the leaves. 
 
 But the changes that take place in the general form of 
 the plant are only a small part of the whole change that 
 occurs in the ascent from the 
 lower to the higher. These 
 are so numerous that we will 
 not try to trace them. There 
 is only one other that needs 
 our attention. In the lower 
 kind, we have only one indi- 
 vidual in one plant. As we 
 go higher, many individuals 
 come to be associated to- 
 gether, as in our common 
 
 Fig. 68. Single and Compound Plants. trees _ An oak? for examp l e> 
 
 is really an association of many different plants, each bud 
 being a distinct plant, all of them uniting in the work of 
 building the stem, branches, and roots, which are the com- 
 mon property of the association. This careful bringing 
 together of many distinct individuals in one community is 
 a peculiarity of the higher plants. 
 
 These changes have for their purpose the better life of 
 the individual plant. There are others, and more impor- 
 tant, which are contrived for the good of the seed. The
 
 LINES OF ADVANCE IN ORGANIC CREATURES. 161 
 
 lowest plants have very small and simple seeds, and noth- 
 ing that can fairly be called a flower. The spores, as these 
 tiniest forms of seeds are called, are very small and very 
 numerous. They are made on the leaves, as in the ferns. 
 In this state, the seed has life alone given it by the parent 
 plant. No food is stored with the germ. In the higher 
 plants, there is a distinct flower, made up of a number of 
 leaves that have changed their shape to make the parts of 
 the blossom. This flower develops seeds of a higher 
 structure than those of the lower plants. Around the 
 life-containing germ is gathered a supply of starch and 
 other food intended to support the young plant in its 
 earliest stages of growth. In this way, the parent gives 
 something of its strength to help the offspring in its 
 period of infancy. 
 
 These changes from the lower to the higher plants are 
 slowly worked out in the course of the long ages of the 
 earth's history. Plants do not move upward in their 
 structure with the same speed as the animals ; still they 
 have advanced age by age, and finally give us our flowers 
 and fruits. The flowers and fruits are offerings the plants 
 make to the insects, birds, and other animals in order to 
 get their help in the work of fertilizing their seed, and con- 
 veying them to places where they may grow. To fertilize 
 a seed in the best way, it is necessary to carry the pollen of 
 one plant to the pistil of the flower that grows on another 
 plant. This is done by the insects. They are attracted 
 by the gay flowers and sweet odors of the plants, and are 
 paid for their labor by the honey and pollen they get by 
 their visits. They go smeared with the pollen from plant 
 to plant, and thus, without intending it, fertilize the seed 
 in the way best suited to their needs. The fruit, by its 
 sweetness, and the seeds, by their nourishment, tempt the
 
 162 A SKETCH OP THE EARTH'S ORGANIC LIFE. 
 
 birds and beasts to eat them, and in this way they are 
 carried about and dropped in places which will give them 
 a chance to grow to advantage. Other seeds, which have 
 hooks upon them, are arranged so as to catch on the fur 
 of animals, and so are carried about until they fall far 
 away from the parent plant. 
 
 There are many other ways in which the plants seek 
 the help of the animal world ; but these few examples will 
 serve to show us how closely knit together are these two 
 kingdoms of life, how they reckon on each other for help 
 in the struggle for existence. In this work, the plants give 
 far more than they receive. They give to animals all their 
 food, for there are no forms of animal life that can take 
 food directly from the mineral world. All must come to 
 them through the plant. In exchange, they receive from 
 the animals only a little help in the fertilizing and the 
 carriage of their seeds. Even this they pay for with their 
 honey, the sweetness of their fruits, or the nutrition of 
 their seed, so that really the plant world gives everything 
 and receives but a trifling recompense. 
 
 The animal kingdom has an altogether different set of 
 purposes from the plants. The animal form appears to be 
 striving to make itself more and more fitted to be the 
 habitation of intelligence. For this purpose, it needs to 
 be very different from the plant. It needs, in the first 
 place, to have a system that shall serve for the reception 
 of sensations, for the seat of the intelligence, and the 
 giving of the commands of the intelligence. This is ac- 
 complished by the making of the nervous system, the 
 machinery of intelligence, which slowly, as we go higher 
 and higher, takes on a more and more perfect character, 
 with eyes, ears, the power of taste, smell, etc., to give 
 communication between the intelligence and the outer 
 world.
 
 LINES OF ADVANCE IN ORGANIC CREATURES. 163 
 
 Then the animal, to be a fit seat for intelligence, needs 
 a variety of parts that shall obey the will, organs for 
 grasping, for motion through the water or air, or over the 
 earth. All this is brought about by the limbs in their 
 many various shapes, under the intellectual control.
 
 164 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 LESSON II. 
 
 PROTOZOA AND RADIATES. 
 
 THE lines of advance among animals are not made in 
 one ascending path, as they are among the plants. There 
 are at least four great groups of animals, each of which 
 takes its own proper line in the effort to work out the 
 problem of how to build a structure fitted for the uses of 
 intelligence. Most naturalists, indeed, consider that there 
 are five of these lines of advance. The lowest of these five 
 is the protozoa, or animals of lowly life ; the simplest of 
 
 Fig. 69. Rhizopods. 
 
 these creatures generally appear to us as mere masses of 
 jelly, that have no distinct mouth or stomach, and no 
 regular organs for moving the body. They do not lay 
 eggs, but increase in numbers by dividing the mass of the 
 body, each part being able to set up life for itself. These 
 forms are all very small, the most of them, indeed, micro- 
 scopic in size ; they are generally transparent ; sometimes 
 they are as easy to see through as a bit of jelly. Yet it 
 will not do to be too certain of their simplicity, for the 
 reason that, though appearing so little complicated, they 
 often build structures of the greatest beauty and symmetry.
 
 PROTOZOA AND EADIATES. 165 
 
 Many species of these protozoa assemble themselves in 
 communities, resembling the communities of individuals 
 that make up an oak or a pine tree ; such, for instance, 
 are the sponges, which are each made by myriads of ani- 
 mals that grow together, and by uniting their work, build 
 a mass many thousand times as large as the individual 
 animals. They all dwell in the water. 
 
 Higher in the scale than the protozoa stand the radiates; 
 these are generally star-like in form ; each ray of the star 
 is made up of a set of parts ; in the middle is a mouth and 
 stomach, which do the work for all the rays. This star- 
 like order of parts is much like what we have in the 
 
 Fig. 70. Sea Anemones, closed and partly opened, akin to Corals. 
 
 plants, which generally show something of a star-like 
 arrangement of parts. They are all water animals. 
 
 The lowest radiates are the corals and jelly-fishes; 
 these creatures generally are grouped together in com- 
 munities, many thousands working to build a common sup- 
 port. This gives them great strength ; while, if separated, 
 they would be very weak animals, quite at the mercy of 
 the waves. 
 
 The next higher radiates, the crinoids, are also usually 
 attached to the bottom of the sea ; but they are much 
 larger creatures, and encased in a solid shell, which stands
 
 166 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 up on a flexible stem. They are no longer such simple 
 
 forms as their lower kinsmen, the corals. 
 
 Next higher, we have the 
 I star-fishes, which are the first 
 animals that can crawl by 
 means of something like feet. 
 They have suckers coming 
 from one side of the arms, 
 that enable them to move 
 along the bottom with some 
 ease. Still the direction of 
 their movement is not deter- 
 mined ; they move quite as 
 Fig. 71. Sea Lily. easily one way as another. 
 
 Having nothing like a head, they have no need of a definite 
 
 direction of movement. 
 
 Then we have the sea-eggs or echini, where the animal is 
 
 condensed into a sphere-like form ; and in the highest of 
 
 Fig. 72. Holothurian. 
 
 these radiate animals we find, for the first, an animal that 
 moves in a definite direction. Although various animals 
 of lower structure move, it is first in the echini that we 
 have this motion fixed in its direction. The creature does 
 all in its power to twist the body into such a shape that 
 the mouth may come at the front end of the body ; but
 
 PROTOZOA AND RADIATES. 167 
 
 the way in which it is built makes this a very difficult 
 thing to do. Finally, in the sea-cucumbers, or the holo- 
 thurians, the creature is turned over so that it walks on its 
 side ; in this way it manages to use two of its bands of 
 suckers as limbs, and the mouth is brought at the advanc- 
 ing end of the animal. These radiates give us the first 
 series of efforts to build a structure fitted for the uses of 
 intelligence ; the only structures out of which they could 
 build limbs were the soft suckers on the arms and the 
 stiff spines ; they do all that can be done with them, but 
 they are not well fitted for this work of motion ; besides, the 
 radiate plan of the body is 
 better suited for a fixed than 
 for a movable form, as we 
 see from the fact that 
 plants are generally radi- 1 
 ate in form. It requires a 
 great deal of time for these | 
 simple experiments of radi- 
 ated animals to be carried 
 through to their half-suc- 
 cessful end. The radiates Fly. 73. star-fish, 
 are among the earliest animals known to us, and it is not 
 until near the present day that all these experiments in loco- 
 motion had been tried. The nervous system on which more 
 than anything else the fitness of the body for the uses of the 
 mind depends, is not even at the end well developed in the 
 radiates ; yet it deserves to be remembered that this system 
 did actually begin in this group, and is carried to a certain 
 state of completeness. We find traces of it in the jelly-fishes, 
 and it is best shown in the sea-eggs (echini) and the sea- 
 cucumbers (holothurians) . It is, however, not to be compared 
 with the perfection of the same system in the higher forms 
 of the other higher groups of animals, as we shall shortly see.
 
 168 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 LESSON III. 
 
 THE MOLLUSKS. 
 
 THE next great group of animals above the radiates is 
 the mollusks, familiarly known to us in our oysters, clams, 
 slugs, snails, squids, cuttle-fishes, etc. This group differs 
 widely from the radiates in the plan on which the body is 
 built. In the radiates, similar parts are arranged about a 
 centre of growth, where the- mouth and stomach are situa- 
 ted ; in the mollusks, the parts are placed on either side of 
 a plane that extends from the front to the rear end of the 
 body. The mouth is at the anterior end of this line. 
 This arrangement of parts is just what is needed in the 
 animal body ; it makes motion possible ; and in this 
 motion the head can go foremost. The nervous sys- 
 tem in the mollusks is better built than in the radiates. 
 It exists even in the lowest forms, and attains a high 
 grade of perfection in the highest creatures of this group, 
 the squids, which are really very perfectly adapted to the 
 uses of intelligence. The simplest mollusks are akin to our 
 clams and oysters. In the lowest, the creature has but 
 slight power of motion, often being fixed to the bottom 
 by the shell or by a sort of rope the animal spins. The 
 higher forms, like our hard shells or the fresh-water clams, 
 are able to move by means of a flesh projection called 
 the foot, that can be pushed outside of the shell, and used 
 in crawling, like the foot of a slug or snail. Our fresh- 
 water clams or unios can travel at the rate of something 
 like fifty feet an hour. This is the most successful walking 
 that has been attained in the animal kingdom up to this 
 level of structure.
 
 THE MOLLUSKS. 
 
 169 
 
 When we come to the single-shelled mollusks, such as 
 snails and their kindred, we have the power of motion 
 more constant than in the bivalve-shelled mollusks. 
 Nearly all of them can crawl. Besides these, we now 
 
 Fig. 74. Common Clam, with siphon protruded. 
 
 have something like a head to the animal. There are 
 structures that do the work of eyes, and feelers that serve 
 for the sense of touch, and perhaps organs that convey 
 the sense of hearing, all gathered about the front end of 
 the body. 
 
 Fig. 75. Sea Snail. 
 
 This group of snail-like, single-shelled gasteropod mol- 
 lusks is also interesting for the fact that it gives us the 
 lowest animals that are able to live upon the land. All 
 the forms of animal life below this level are limited to the
 
 170 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 water. There are several reasons why the lower mollusks 
 cannot come upon the land. Their bodies are all very 
 soft, and have no skin to keep the water from evapor- 
 ating in the air. Then, except some of the bivalve shells, 
 they have no organs for creeping. When they move at 
 all, they only float in the water, helping themselves a little, 
 as the jelly-fish does, by flapping the projections of the 
 body. 
 
 The snails and slugs can live and move on the land be- 
 cause they have a closer skin, that keeps them from drying 
 up so fast, and a foot for crawling ; and they are fitted for 
 breathing air by having air-sacks in place of gills. 
 
 Fig. 76. Land Snails. 
 
 The next important group of mollusks contains our 
 squids or cuttlefishes, the pearly nautilus, and the paper 
 nautilus, as well as the strange form of the ammonites 
 and other chambered shells that no longer exist. In 
 these creatures, we have, among the lowest forms, the 
 nautilus, an animal that lives in the outer room of a 
 chambered shell ; this shell constantly grows longer and 
 wider, and the animal moves forward in it, closing off the 
 chambered part of the tube by a partition. 
 
 Around the head are a number of soft, fleshy arms, that 
 enable the creature to move over the bottom in a slow
 
 THE MOLLTJSKS. 171 
 
 and clumsy way. After a great many changes, the cepha- 
 lopods, as this group is called, succeed in making a better 
 arrangement of their parts. The shell, which serves in 
 the lower forms for moving the body, is straightened 
 out, made more slender, and the body wrapped around 
 it, so that it becomes entirely enclosed in the animal. In 
 this position, it serves as a skeleton, enabling the animal 
 to have strong muscles to move its limbs. These limbs 
 are constructed, with a few changes, out of the soft feelers 
 or suckers which, in the lower forms of cephalopods, the 
 pearly nautilus and its kindred, form two rings around the 
 mouth, having a hundred or more of the feelers in them. 
 
 Fig. 77. Section of Pearly Nautilus. 
 
 These feelers become reduced to eight or ten in number. 
 They grow much stouter than they were on their inner 
 face. Suckers and hooks for grappling are developed. 
 The mouth is provided with a strong beak. The head, the 
 first complete head separated from the body by a neck, is 
 formed ; strong fins are attached to the sides. Unlike the 
 lower mollusks, this group are strong, swift swimmers; 
 though they sometimes move over the bottom by crawling, 
 they are so successful in moving through the water that 
 they seldom need this method of motion. These squids 
 are, of all creatures, the quickest movers in the water,
 
 172 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 unless they are surpassed by some of the most rapid 
 fishes. 
 
 They move in three different ways. By closing the arms 
 like an umbrella, they can dart backwards with great 
 speed. In this motion they are helped by the water, 
 which they can squirt out of the cavity where the gills 
 lie. This water passes through what is called the syphon. 
 Along with this water, they can throw out a quantity of 
 inky fluid, that darkens the water like a cloud, so that the 
 creatures can quickly slip away unseen beyond the ink- 
 clouded water. There is an additional paddling appara- 
 tus in the strong fins that are found on the back end of 
 
 Fig. 78. Cuttle Fish. 
 
 the animal. This gives the squids the most perfect mech- 
 anism for motion in the world. They can move forward 
 or backward with ease, and have the peculiar advantage 
 given by the bag of sepia, that their flight is hidden. Their 
 power of grasping is also greater than that of any other 
 animal. They sometimes grow to a very large size. The 
 grasping arms are as much as thirty feet long, and the 
 body as large as a flour-barrel. They have been known 
 to enfold a fishing-boat in their arms, and only to loose 
 their hold when one of them was cut in two with an axe. 
 The nervous system of these squids is highly organized;
 
 THE MOLLUSKS. 173 
 
 they have such a great amount of nervous tissue in the 
 part we term a head, that they may be said to be the first 
 animals to have a distinct brain. Without this perfect 
 nervous system they could not possibly be as active and 
 powerful as they are. 
 
 The mollusks were on earth in the very earliest time 
 of which we have any certain record of life ; and in this 
 early day we had bivalve shells, shells like our sea-snails, 
 and the lowest cephalopods, the orthoceratites ; but these 
 early forms were inferior to those of to-day, so that we 
 may fairly say that the molluscan life of the earth has 
 grown to its perfection, through the geological ages; though 
 
 Fig. 79. Ancient Mollusks. 
 
 all its most important forms had been developed at a very 
 early time. 
 
 Before leaving this very interesting group, we may 
 notice some important features in which they have gained 
 on the lower animals. They are distinctly better than the 
 radiates, in that they have more perfect powers of motion 
 and of sensation, and do not need the protection that is 
 gained in communities, such as the corals generally form. 
 Only a few low forms of mollusks are combined into com- 
 munities, as are so many of the radiates. In the higher 
 mollusks, the instruments the animal's will controls are far
 
 174 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 more perfect than in the radiates ; these mollusks generally 
 take care of their eggs, choosing distinct places in which to 
 deposit them, and not turning them out into the water with 
 no care, as all the radiates do. This is the lowest form 
 of that care of the mother for the young which is such a 
 wonderful feature in the higher land animals. 
 
 The higher mollusks have very well organized eyes, and 
 large, separate breathing organs ; their digestive system is 
 more effective, and through it they can digest more rapidly 
 and perfectly, and so appropriate a larger store of force 
 than the radiates can. Their circulatory or blood system 
 is now strong, and capable of pushing that life and strength- 
 giving fluid with greater speed through the body.
 
 THE ABTICULATES. 
 
 175 
 
 LESSON IV. 
 
 THE ARTICULATES. 
 
 NEXT higher than the mollusks, in their plan of struc- 
 ture, come the creatures known as articulates or jointed 
 animals. These include all our worms, crabs, lobsters, 
 spiders, and insects. In fact, every creature which has a 
 body made up of rings, placed one after the other, as in 
 the diagram, is an articulate. 
 
 Fig. 80. Worms. 
 
 These successive rings are each very much like the 
 other. This likeness is sometimes so great that in certain 
 worms, if we cut them in two, the front part will heal, 
 and the hind part form a new head, and move on without 
 risk of death. Some worms ordinarily increase in this 
 way. We cannot conceive this in any mollusk, for there 
 are. no such similar parts, or sets of parts, one behind the 
 other. The only repetition of parts in mollusks is on 
 either side of the middle line. In the articulates, at least 
 among their lower forms, the worms, there may be hun- 
 dreds of these rings, each formed on the same pattern, 
 placed one behind the other.
 
 176 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 When we come to the crustaceans, or such creatures as 
 the shrimps, lobsters, cray-fish, and crabs, which are higher 
 than the worms, these rings are fewer in number, and 
 more different one from another. In place of the joint- 
 less, spur-like legs of the worms, we have legs like those of 
 a crab, lobster, or insect, with distinct joints, which allow 
 a great deal of motion. All these parts are covered with 
 a hard, shell-like skin, called ch&tine, which protects them 
 from assailants, and at the same time answers the purpose 
 of a skeleton to support the muscles in their work. This 
 outer skeleton can be moulded into a great variety of 
 
 Fiy. 81. Lobster and Crabs. 
 
 shapes, to suit the needs of the animal it encases. In this 
 way, we have a greater variety of shape among the articu- 
 lates than in all the other great groups of animals. This 
 ringed covering easily fits itself to changes of habits, so 
 that among the articulates the will of the animal finds 
 admirable tools for its use, in a more perfect way than 
 among any of the lower creatures. 
 
 Among the insects, we have a most wonderful variety 
 of structure and habits. They give us such strangely 
 varied forms as the earwigs, th^ spiders, grasshoppers, 
 flies, beetles, bugs, and butterflies. Indeed, the variety is 
 so great that there are more species or distinct kinds
 
 THE ARTICULATES. 177 
 
 among insects than among all the other animals put to- 
 gether. And their habits or instincts are more diversified 
 than among other animals. We now, for the first time in 
 the ascending scale of life, have a most careful nurture of 
 the young by the parents, a care that extends to the most 
 elaborate contrivances for keeping them from danger, and 
 providing them with food. For the first time, we find 
 communities of insects like the ants and bees, which asso- 
 ciate their labor for the common profit of the family or 
 colony. They not only organize societies, but defend 
 themselves with armies, and make warlike expeditions for 
 the supply and profit of their communities. In many cases 
 the young are fed on carefully-chosen food prepared with 
 great labor. They build more carefully-arranged habita- 
 tions than any other animals, their highly-developed feet 
 and jaws serving them well in this work. Indeed, it is 
 first among insects, as we follow up the system of life, that 
 we have any great development of the animal mind. 
 
 The insects and articulates in general are in many ways 
 among the most perfect of animals. This is true of what we 
 call their minds as well as their bodies. In some strange 
 way they do, without teaching, things that no other animal 
 save man can be taught to do. Their only physical defect, 
 that we can notice, is their small size. A very few of the 
 crustaceans are fairly large creatures, but none of the in- 
 sects are over an ounce in weight, and the most of them do 
 not weigh more than a few grains. If they were as large as 
 our quadrupeds, or even our birds, and were proportionatel} 1 " 
 as strong as a wasp is, there would be no place left in the 
 world for any other creatures. As it is, their small size, 
 despite their means of defence, makes them feeble enemies 
 to most large animals. Yet the greatest difficulties man 
 finds, in his efforts to rule the earth, come from the insects.
 
 178 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 He can easily dispose of lions or tigers, but the locusts, the 
 white ants, and some other insects dispute the empire with 
 him in many regions. Besides this, a host of diseases of 
 his own body, and those of his domesticated animals, come 
 from them. 
 
 The articulates are slowly developed in the history of 
 the earth. They begin with the worms and certain low 
 crustaceans called the trilobites ; these two forms are found 
 about as early as we have any distinct animals. At a later 
 date come the crustaceans, like our lobsters and crabs ; but 
 not until just before the time of the coal period do we 
 have the insects; at the present day, these insects are in 
 their prime, while the worms are less important than of 
 old, and the crustaceans have gained little in the later 
 geological ages.
 
 VERTEBRATES. 179 
 
 LESSON V. 
 
 VERTEBRATES. 
 
 THE lower forms of life, the protozoa, radiates, mol- 
 lusks, and articulates, seem to have developed the most 
 of their peculiarities of structure in the earlier stages of the 
 earth's history ; in the later times, the backboned or verte- 
 brate animals, the kindred of man, are the only animals 
 that show us many new plans of structures, or make great 
 advances in the work of building a body for the uses of 
 intelligence. 
 
 The highest of the great groups of animals is the type of 
 vertebrates or backboned ani- 
 mals. In this group we have 
 a plan of structure which is 
 very different from that of 
 the lower plans of radiates, 
 mollusks, or articulates. It 
 includes the fishes, reptiles, 
 birds, and mammals. 
 
 The principal forms of ver- 
 tebrate animals are tolerably Fif >- 82 - Am P hibian - 
 familiar to all, so we may give an even briefer account of 
 them than of the lower animals. 
 
 Lowest in the scale of vertebrate life come the fishes. 
 In them we find the vertebrate body shaped only for 
 swimming : the parts which are feet, or wings, or hands, in 
 their land kindred are, when present, always in the form 
 of fins. There is no distinct neck. Tho animal generally 
 breathes by means of gills placed in the back part of the 
 head, in the mouth cavitv, which take the air from the
 
 180 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 water. They almost always lay eggs, but a few have their 
 young born alive. Their blood is cold. 
 
 Above the fishes in structure, and closely related to 
 them, we find the group of vertebrates known as amphi- 
 bians, a name given to them because they generally live for 
 
 84. Salamanders. 
 
 a part or the whole of their lives in the water, in the form 
 of tadpoles such as those of our common frog. In this 
 group come the water-dogs, the salamanders, and all our 
 frogs and toads, as well as many strange-shaped ancient 
 forms that have disappeared from the earth. These crea- 
 tures are fish-like for some time after they leave the egg, 
 swimming with the long tail-fin, and breathing with gills. 
 Some of them never leave this condition, but others, as 
 our frogs, toads, and salamanders, pass through a wonder- 
 ful change, their tails shrink, their legs sprout out in their
 
 VERTEBRATES. 181 
 
 proper places, and their gills drop away, so that they after- 
 wards breathe the air, and can live on the land. 
 
 Next higher than the amphibians come the reptiles, 
 which include our lizards, crocodiles, alligators, turtles, 
 and snakes, as well as a host of great creatures belonging 
 in the ancient times of the earth, but long since extinct. 
 In these creatures there is no fish-like tadpole state ; they 
 all breathe by means of lungs from the time they leave 
 the egg. 
 
 Fig. 85. Lizard and Flying Reptile. 
 
 These are the first very successful land animals : among 
 them we find flying, swimming, and walking forms; so, 
 for the first time, those forms of progression which gave 
 the vertebrates their great place in the world were brought 
 into use. During the middle ages of the earth's history, 
 and until the suck-giving creatures came, these reptiles 
 were the monarchs of the world. 
 
 While the reptiles were in their prime, the birds, the 
 next higher group of animals, appeared. At first they 
 were a good deal like feathered flying lizards. Their 
 tails were long, like lizards, and theii jaws had sharp, liz- 
 ard-like teeth. The great difference between them and 
 reptiles is in the possession of a covering of feathers, and 
 their very warm blood. It is the warm coating of feathers
 
 182 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 that protects their bodies from the cold, and makes a warra 
 blood possible. This warm-blooded condition is brought 
 about by a stronger and more perfect circulation, so ar- 
 
 Fig. 8(5. Hesperornis and Dinornis. Fossil Birds. 
 
 ranged that each time the blood makes the circuit of the 
 body it is passed through the lungs, where, being exposed 
 to iihe air, a part of its carbon is combined with oxygen, or 
 burned, which gives out a supply of heat to be distributed 
 
 through the body. This supply of heat is greater in 
 birds than in any other animals; and, as the activity of 
 the body depends on the temperature of the blood, they 
 are very strong for their weight. 
 
 Highest of all animals come the mammals. All these
 
 VERTEBRATES. 183 
 
 creatures have their young born alive, and the mother 
 gives them milk. 
 
 There are two principal divisions of this great class of 
 mammals. The lower and earlier to live on earth is that 
 to which the kangaroos, opossums, and their kindred be- 
 long. In these the young are born in a very imperfect 
 state, and are sheltered in a pocket of the skin which 
 covers the teats of the mothers. In this pouch they re- 
 main for some weeks, until they are strong enough to 
 move about, and for some time longer they return to it for 
 the mother's milk and for shelter. 
 
 Fig. 88. Marsupials Kangaroo and Myrmecobius. 
 
 The other great division of the mammals is without this 
 pouch, the young being born in a too perfect condition to 
 need its help. This group includes all our ordinary four- 
 footed beasts and man himself. In the mammals, hair was 
 developed to serve the purpose of keeping in the warmth 
 furnished by the warm blood, which they have in common 
 with the birds. This hair, and the milk-giving by the 
 female, are features that separate the mammals very sharply 
 from all other animals. 
 
 In the vertebrates, we first find an internal jointed 
 skeleton which provides two qhambers for the reception of
 
 184 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 the soft parts of the body ; one enclosed by the ribs for the 
 organs that support the mere animal life of the body, such 
 as the stomach, the heart, and lungs, etc. The other, 
 smaller and more completely enclosed, is formed by the 
 bones of the head and the backbone, and encloses the most 
 important parts of the nervous system, the brain and 
 the spinal cord. These backbone parts of the skeleton are 
 so jointed together as to be at the same time rigid and 
 elastic, and give a better protection to the inner parts 
 while allowing a greater freedom of movement than any 
 other arrangement could do. To this central skeleton 
 there are attached never more than four limbs. These, 
 like the trunk, have an internal skeleton that supports 
 them, and enables their muscles to work them. 
 
 Fig. 89. Irish Elk. 
 
 In the importance of the nervous system, and in the 
 arrangement of the limbs, this group of vertebrates stands 
 apart from all other animals. In no lower group is the 
 nervous system so large or so cared for ; in none are the 
 limbs so determined in their forms, or so fitted for varied 
 work. We see how suited they are for their work, when 
 we consider that by simple yet effective changes they form 
 the fin of a fish, the foot of the horse or the lion, the wing
 
 VERTEBRATES. 185 
 
 of a bat, or the hand of man ; all these varied parts have 
 come by slow changes from one ancient form of limb. 
 
 The nervous system permits the work of a higher intel- 
 ligence than we find in the lower animals. In place of 
 habit or instinct, a blind, unreasoning working of impulse, 
 we have, as we go up on the vertebrates, a constant increase 
 in the likeness of the mind's working to our own. We see 
 among the fishes a certain care for their young. This 
 carefulness of the offspring grows more and more marked, 
 until, in the higher forms, such as the birds and animals 
 that give suck, it takes the form of parental love. 
 
 Not only through the mind, but through the body, these 
 vertebrates give more help to their young than any other 
 group of animals. Among those forms that lay eggs, the 
 fishes, the reptiles, and the birds, we find a contrivance 
 for helping the young that reminds us of what occurs in the 
 plant world. Among the higher plants the young is helped 
 by a store of concentrated food that makes the mass of 
 the seed. While in the lowest forms there is no 'such 
 helpful store. Thus, in the lower animals, the parent gives 
 the young life without placing in the eggs any store of food 
 to sustain it in the earliest work of existence. In the fishes 
 we find that there is some provision in the egg for the sus- 
 tenance of the young while it is making the first stages of 
 its growth, though the amount is but small, for the fishes 
 commonly lay many thousands of eggs at a time, so that 
 not much can be done for any one. In the reptiles we find 
 the eggs greatly diminished in number ; and in each a lar- 
 ger store of food is placed, forming a distinct yolk. In the 
 birds the eggs attain their perfection ; they are still fewer 
 than in the reptile, and are often as much as one tenth the 
 weight of the parent, so large is the store of nutrition that 
 is placed in them for the help of the young in its growth. 
 Besides this, the mother by the nest, the warmth of her
 
 186 A SKETCH OF THE EAETH'S ORGANIC LIFE. 
 
 body, and the food she brings them, does much for her 
 young. In the highest group of vertebrates, the mammals, 
 when the young are born alive, the mother's milk provides a 
 yet better method of helping the young in their growth. In 
 these, the highest groups of vertebrates, the birds and mam- 
 mals, the blood is warm as it is in none of the lower forms. 
 This guards them against changes of temperature, and 
 makes them better fitted to endure the struggle of life in 
 cold regions. Thus, with each step of advance, there is 
 more help given by each generation to that which is com- 
 ing on to take its place. While we can trace the improve- 
 ment of animals, as we rise higher in the scale of being, in 
 a great many ways, there is no other way in which it is so 
 beautifully shown as in these contrivances of mind and 
 body for helping the weakness of the young. 
 
 The vertebrates do riot seem to have lived in the earliest 
 stages of the earth's life-history. They first appear some 
 time after the other groups of animals become known to us. 
 First, come the fishes ; then, at a much later date, in the 
 coal-bearing rocks, we have creatures related to our water- 
 dogs and salamanders ; then, just after coal, we have the 
 kindred of our alligators, which for a long time filled the 
 lands and seas with many strange forms of reptiles ; then, 
 in the Jurassic time, as it is called, that is, some distance 
 above the coal, we have the first mammals. These were lit- 
 tle creatures related to our opossum, and called pouched 
 mammals, because they carry their young in a pouch on 
 the belly for some time after they are born. These first 
 suck-giving animals were insect-eaters, as are many of 
 their kindred at the present day. It is a long time before 
 the mammals begin to have the first place among animals; 
 for many geological ages the reptiles still held the control 
 of the lands, the seas, and the air with their giant forms. 
 Finally, however, these reptiles began to fade away, and
 
 VERTEBRATES. 187 
 
 the mammals to grow larger, more varied, and more power- 
 ful. The higher forms gave up the use of the pouch, 
 which has been kept only on a few species of opossums 
 that live in North and South America, and a hundred or 
 so kinds that are found in Australia. These pouched 
 species are fading away from the earth, and are being re- 
 placed by the non-pouched forms. 
 
 There are, very many other features in which the verte- 
 brates show their advance beyond the conditions of life in 
 the earlier types of animals ; of these we may only men- 
 tion, here and there, a striking case. 
 
 All the radiates and mollusks are entirely voiceless; so, 
 too, are all the crustaceans; only some of the insects 
 having the power of calling to others of their kind ; and 
 in all cases this is done by rubbing hard parts together, and 
 never by anything like the voice, as we understand it. But 
 nearly all the vertebrates above the fishes have some form 
 of call made by driving the air out of the lungs in such a 
 way that it vibrates membranes stretched across its path. 
 This voice is found in its beginning in the fishes, some 
 of which force air out of their air-bladders, which are 
 imperfect lungs, and thereby make a call that their mates 
 can hear. The frogs and toads have distinct voices ; so have 
 many of the higher reptiles. The birds all have some 
 voice, and all the mammals have it. This means of com- 
 munication between one animal and another is a sign of 
 growing sympathy between kindred creatures. Except 
 among the insects, there is hardly a trace of this feeling 
 in the animals below the vertebrates ; it is peculiarly the 
 mark of the mammals ; they feel for and help each other. 
 
 Thus, we see that the advance in the mind of animals 
 seems to go with the bettering of their bodies. The great 
 aim of all animals seems to be to get better and better 
 means for the ever-growing intelligence to use in its work.
 
 188 A SKETCH OF THE EARTH'S ORGANIC LIFE. 
 
 Last of all, among the great results of this world, comes 
 man himself. In his structure we see many relations to the 
 other mammals, and there can be no doubt that his body 
 has been in some way made from the forms of the mam 
 mals below him in structure, so that man, as an animal, 
 stands in close relation to the lower life of the world ; but 
 when we come to consider the mind of man, we find some- 
 thing very widely different from the mind of the lower 
 animals. In the lower animals we find a trace of all the 
 faculties we find in man, but they, unlike man, are not 
 capable of indefinite advance. They are bound down to 
 a certain narrow round of thought and action ; but in man 
 we have a creature able to go forward without limit; so 
 that we may say there is no such relation between his 
 mind and the minds of lower creatures, as there is between 
 his body and those of animals. Mentally, he belongs to 
 another system of creation from the beasts. 
 
 When we study the forms of the lower animals, we do 
 not find one series of steps leading up from the lower to 
 the higher forms, but different groups, each with its own 
 peculiar plan of structure. There have been many experi- 
 ments in the building of habitations for intelligence. The 
 most of these have gained only a partial success, for the 
 reason that the plan of the structure did not allow the 
 necessary perfection of the body. Of all these efforts, that 
 of the vertebrates was the most promising, for it gave by 
 its skeleton, by its careful building of the nervous system, 
 by its plan of limbs, the best chance to go on to a high 
 structure. Out cf the many trials, the great success of 
 man was at length reached. 
 
 The naturalist cannot believe that man was a mere acci- 
 dent; he is rather the being to which the world in all its 
 efforts was constantly tending.
 
 CHAPTER X. 
 
 THE NATURE AND TEACHING OF FOSSILS. 
 
 LESSON I. 
 HOW FOSSILS ARE FORMED. 
 
 TN the later pages of this book we shall often have to 
 -*- speak of fossils, or the remains of animals and plants 
 that are preserved in rocks, so that it is well to get an idea 
 of what they are, and how they are formed. 
 
 A few living things, such as the jelly fishes, the slugs or 
 shelless snails, etc., have soft bodies which at death dis- 
 solve and leave no solid parts behind. But most animals 
 and plants at death leave in the water or upon the earth 
 bodies that have a certain solidity ; woody matter in the 
 case of plants, bones in the case of higher backboned 
 animals, hard skins as in the insects, crabs, lobsters, etc., 
 or shelly matter as in the shells and corals. If these hard 
 parts are left uncovered on the surface of the soil or on the 
 bottom of the sea for a long time, they utterly decay and 
 fall to dust. Examine any old forest ; it has grown for, 
 it may be, hundreds of thousands of years; if it were 
 not for the rapid decay of the leaves and branches that 
 fall on the earth, the waste-heap would be many times 
 deeper than the tallest trees are high ; but there are only a 
 few inches, or, at most, a foot or two of vegetable mould 
 on the ground where it stands. If all the bones of all the 
 birds and beasts that have died in this wood had remained
 
 190 THE NATURE AND TEACHING OP FOSSILS. 
 
 there, the soil would have its surface covered with these 
 remains ; yet we may search for days and not find a single 
 bone in a square mile of forest. All such remains rot 
 away speedily ; the skeleton of an ox left on the surface of 
 the ground is decayed in a score of years and falls to pow- 
 der. So we can say that nearly all the bodies of animals 
 and plants that die on the land fall speedily to dust. Yet 
 there are certain ways in which their remains may in rare 
 cases be preserved. If the trunk of a tree falls into a wet 
 swamp or a pond, and sinks to the bottom, it will only 
 partly decay, turning black, but retaining its shape for 
 many thousand years. Thus, in New Jersey and else- 
 where, they dig out these buried trunks and use them for 
 timber. Sometimes, as in Ireland, they are found even 
 after the forests in which they grew have entirely disap- 
 peared from the region. In such swamps we often find the 
 bones of animals which have been drowned there ; as, for 
 instance, in the swamps of Ireland are found the bones of 
 the great elk, the largest horned creature of the deer 
 tribe that we know. Then, too, we may find the remains 
 of fishes and water shells. If it happens that such a 
 swampy bed is buried under the sea, and covered with 
 other strata, it may preserve to us the remains of a very 
 ancient time; such, in fact, are the coal-beds that are 
 now giving the wealth to the greatest nations of the world. 
 It may sometimes occur that forests and swamps, with 
 the dead and living things they contain, are buried under 
 a shower of volcanic ashes, or the dusty matter thrown out 
 by volcanoes, and so preserved from decay. Or, it may 
 happen that in limestone countries, the remains of animals 
 are swept into caverns, and buried under the floors of 
 stalactite, and so sealed up from the air ; or, in yet other 
 cases, the remains may be buried ia the beds of mud and 
 sand along the banks of rivers.
 
 HOW FOSSILS ARE FORMED. 191 
 
 But all these methods of burial on the land are not able 
 to save much of the forms of land life from utter decay. 
 This we may see by noticing how very seldom it is that 
 we find any remains of the creatures that lived in this 
 country before it was settled by the whites. I doubt if my 
 readers have ever found the bones of a deer, a bear, or a 
 panther anywheie in the fields or in the openings made 
 for roads or cellars, though scores of these animals have 
 died on every acre of the land. There is no provision for 
 their burial, and so they almost always decay. 
 
 So it is on the land, but in the sea it is quite otherwise : 
 there every animal that leaves' at death a solid frame gives 
 its remains to the bottom, unless it goes into the jaws of 
 some enemy, as, in truth, it oftenest does. Once on the 
 sea-floor, it finds a host of animals glad to use anything in 
 the way of food that the body may afford. Yet it happens 
 that very many of the dead that come to the sea-floor are 
 buried in the mud or sand that is constantly gathering 
 there, and in this way are secured from decay. We need 
 only drag a dredge over the sea-floor, at almost any point 
 from near the shore to a depth of twenty thousand feet, to 
 gather a lot of this bottom mud, in which we find shells 
 and, other hard parts of animals that have been already 
 buried in the muddy deposit. We can easily see that in 
 time they would be sealed under a great thickness of this 
 ever-gathering waste that covers the sea-floor in a sheet as 
 wide as the oceans. 
 
 We have now seen most of the ways in which the dead 
 bodies of animals and plants may be buried in the earth's 
 crust; we will next try to show how they are preserved 
 from further decay. It usually happens that when the 
 bodies of animals or plants are buried in the rocks, certain 
 changes occur in them. If the remains -are laid at a little
 
 192 THE NATURE AND TEACHING OF FOSSILS. 
 
 depth beneath the surface, as in human graves, the rain 
 water and air penetrate to them, and they fall into com- 
 plete decay, becoming mere dust that is seized on by the 
 roots of plants, and lifted once again into life. But when 
 these remains are buried where neither the rain-water nor 
 the air can get to them, they may preserve their structure 
 fora very long time; for, when these change-producing 
 agents are kept away, the principal forces that bring decay 
 are not free to act upon the remains. They are then in 
 much the same condition as the preserved vegetables and 
 meats that are enclosed in well-sealed cans, and there is no 
 reason why they should ever decay, for the air, that by its 
 oxygen rots them, is shut out. So it comes about that a 
 mammoth buried in the ice of Siberia can have even its 
 eyeballs preserved for some such time as one hundred 
 thousand years; or that a grass-like plant buried in the 
 far more ancient coal-beds should keep so perfectly that it 
 remains flexible to the present day ; or the shells of the 
 yet remoter Silurian age should keep a little of the color 
 which they had in their time of life. 
 
 But it generally happens that the bodies of these buried 
 creatures undergo certain changes that gradually destroy 
 their original shape. They are often somewhat heated, 
 owing to their deep burial beneath the rocks that are laid 
 down on them, and their consequent holding in of the heat 
 that comes up from the depths of the earth. When this 
 occurs, the hot water that lies around them often takes 
 away the lime of their bodies, and deposits flinty matter, 
 or makes other changes. Thus, it has happened in a mine 
 in Utah, that around the leaves and stems of fossil plants 
 silver has been found deposited. If the heat is greater, it 
 often occurs that the whole of the fossil disappears, leaving 
 only a stain on the rock, or even no trace of its having
 
 HOW FOSSILS ARE FORMED. 193 
 
 been there. When rocks like limestones become crystal- 
 line, all the fossils commonly disappear, though they may 
 have been there in great plenty and excellent preservation. 
 
 Thus, it comes about that while the creatures that live on 
 the land are rarely preserved to us, those of the sea are 
 often buried in the rocks ; and when the rocks in which 
 they are buried are lifted above the sea, and worn by the 
 frost or rain, the fossils appear in great numbers, sometimes 
 so thick as to cover the hillsides with the well-preserved 
 relics of a life that passed away from the earth many mil- 
 lion years ago. 
 
 It is from these remains that the geologist is able to 
 make up the history of life, and to construct a picture that 
 represents the animals and plants that lived from time to 
 time in the past. In this work long practice has given 
 great skill ; so that, from a few bones, or a fragment of a 
 shell, it is possible for a naturalist to form a tolerably clear 
 idea of the creature to which these fragments belonged, 
 and something of its habits of living. Thus, the structure 
 of the teeth will show us whether an animal was flesh or 
 grass eating, as is seen in the case of the dog and sheep, 
 where their teeth are precisely fitted for their different 
 sorts of food. Often, a single tooth of any kind of an 
 animal that has left us no other part, or fragment of an 
 insect's wing that is all which has come down to us, will 
 serve to prove to trained eyes and minds the existence 
 of creatures of a certain mould at a particular time in the 
 past. So, out of the shreds of the life that lived in an- 
 cient days, taking here and there the fragments as they 
 happen to come to us, we can gradually build a tolerable 
 museum that will show us how this life stood at each time 
 in this past. We know in this way, with perfect certainty, 
 that over a vast duration of time the life of the earth's
 
 194 THE NATURE AND TEACHING OF FOSSILS. 
 
 surface has been slowly changing. Now and again par- 
 ticular kinds of animals and plants disappear, and theii 
 places are taken by others. In this way the whole of the 
 animals and plants of our globe has been many times 
 changed, the old kinds giving place to newer and higher 
 forms.
 
 CHAPTER XI. 
 
 THE ORIGIN OF ORGANIC LIFE. 
 
 LESSON I. 
 HOW NEW SPECIES ARE MADE. 
 
 A MONG the questions which the student of the earth 
 --*- finds always before him, in the study of its history, 
 are how animals and plants have come to be ; how this life 
 began ; how, from time to time, these living creatures have 
 disappeared, and been replaced by other kinds. These are 
 all hard questions, and we cannot yet give them full an- 
 swers. Until modern times, students did not know that 
 there had been a very long history to life, in which all the 
 kinds of beings had often been changed, giving place to 
 other kinds ; therefore, until our own day, the general opin- 
 ion was that all the kinds of animals and plants now on 
 the earth had been created from the dust in the shape we 
 find them. But, when in this century it was found that 
 before the coming of each of these living animals and plants 
 there were other forms closely resembling them, yet of dif- 
 ferent species, and that this chain of beings stretched clear 
 back into the past, the animals becoming more simple as we 
 went towards the time when life began, it was gradually 
 learned that these animals had in some way sprung from 
 each other. For we cannot well believe that the Creator 
 would make such relationships between creatures, creating 
 each like that which went before, yet with a difference.
 
 196 THE ORIGIN OF ORGANIC LIFE. 
 
 It is far more reasonable to believe that the living forms 
 have sprung from the kindred forms that have passed away. 
 So strong is this argument, that there is probably not a 
 single person living who has been a careful student of ani- 
 mals or plants who doubts that the life now on earth has 
 sprung from species or kinds that have passed away. The 
 only doubt is as to the means by which the change from 
 one to the other has been brought about. This is the ques- 
 tion to which students of nature are now giving the most 
 of their attention. 
 
 So far but one clear way has been found in which the 
 change can be accounted for, and while it cannot explain 
 more than a part of the puzzle, it is an important help to 
 our knowledge of life. This partial explanation is known 
 as the Darwinian theory, taking its name from the stu- 
 dent who first suggested it. This explanation rests on the 
 fact that each animal and plant in the world has many 
 more offspring than can find a place in the world. Some 
 fish, for example, lay as many as a hundred thousand eggs 
 each year, while, on the average, only one or two of these 
 young live to grow up, the others of the brood falling a 
 prey to enemies of one sort and another. The result is 
 the same with every animal and plant: they have more 
 young than the world can give a place to, for all the seas 
 and lands have about as many animals and plants as they 
 can give a chance to live ; so it comes about that the world 
 of life below man is one great conflict, an unceasing battle 
 for life, where each creature struggles with its neighbor 
 who wants the same food or place. Nearly every living 
 thing has two sorts of enemies in the world: passive 
 enemies, who occupy the place in sea, on land, or in the 
 air which the new-comer needs ; and active enemies in 
 the creatures that prey upon it, and try to make food
 
 HOW NEW SPECIES AKE MADE. 197 
 
 of its body. We see that these creatures are constantly 
 trying new plans to make themselves better fitted to 
 win success out of their difficulties : they become swifter 
 of foot or wing; they get stronger defensive weapons; 
 they invent new habits that will elude their enemies ; in 
 a thousand different ways they change to meet their needs. 
 It is certain that to these chances, which serve to help 
 the creatures in the long battle for life, we owe a great 
 part of the changes that are constantly arising in the 
 forms of living things. The only trouble arises when 
 we try to see just how the change is brought about. We 
 may, in part, explain it in this way: among all the 
 young of any animal or plant, each differs somewhat 
 from any other. These differences are generally slight, 
 but they may be enough to give the particular crea- 
 ture a better chance to live ; it may be stronger limbs 
 for flight or chase, or some difference in habits, or any 
 other profitable quality of its body or mind. In other 
 words, those that vary in the direction of profit will be 
 more likely to survive in the struggle for existence than 
 those that vary in other directions. Next, we must notice 
 the fact that each living creature is likely to give its 
 peculiar traits of body and mind to its descendants, so 
 that they will have a share of the same peculiarities that 
 the parent had, and on these creatures, the same principle 
 of survival of those that are fittest for success will again 
 act, making the profitable feature stronger than it was be- 
 fore. If longer legs or stronger wings saved the parent, 
 it is likely to give those longer legs or stronger limbs to 
 its offspring, which will give them an advantage over the 
 children of those other members of the same species that 
 have not this peculiarity. Some of these descendants of 
 the long-legged or strong-winged animal will probably
 
 198 THE ORIGIN OF ORGANIC LIFE. 
 
 have these parts better developed than the parent, and so 
 its children will get the advantage of its cousins, and thus 
 prevail over them. From generation to generation, the 
 wings become stronger, or the legs larger, until a race is 
 made that differs very far from the creatures from which it 
 originally came: that we call it a different species. In time, 
 all the individuals of the species who have not changed in 
 this way will be destroyed by their enemies, so that the old 
 species will disappear, and the new take its place. 
 
 Although this is a very probable explanation, and may 
 account for many changes that take place among animals, 
 it cannot be said that it is proven, nor can we expect to 
 have a chance to prove it for a long time to come. The 
 life of any one student is but a day compared with the 
 slow-going changes of the world, and we know too little 
 of the struggles of our lower kindred with their enemies 
 to be able to see just how the fight goes with them. The 
 only place where we can see anything like this process of 
 choosing the fit for life, and the unfit for death, is in our 
 household and barnyard animals, and the plants of our 
 tilled grounds, these creatures which man has seized on 
 and forced to help him in his particular battle. These 
 domesticated plants are taken out of the combat of the 
 world; man does not allow the wolves to seize his slow- 
 footed sheep, nor the swift-growing weeds to overcome 
 the plants of his gardens or his fields, but in place of the 
 selection of nature, he uses a selection of his own for 
 his own purposes. When, for instance, he finds among 
 the constant variations of his sheep, an animal with 
 more wool, or with shorter legs, that make it unable to 
 jump fences, he breeds from this animal, and sends the 
 others to the butcher. He seeks among the young of his 
 chosen sheep the lambs that have the best wool, or the
 
 HOW NEW SPECIES ARE MADE. 199 
 
 shortest legs, and sells the others ; and so in certain places 
 he has lengthened the wool and shortened the legs of 
 these animals until they are so unlike their ancestors of 
 fifty years ago, that if we found the two races wild, we 
 should call them different species. 
 
 What, in one case, man does for profit, he does in 
 another to please his fancy. Dogs and pigeons, for in- 
 stance, he breeds for the amusement of having different 
 kinds ; and so our dogs have come to be of many distinct 
 forms, and between the little sky-terrier, the burly mas- 
 tiff, and the long-legged, agile greyhound, there is a 
 greater difference of form than between foxes and wolves, 
 or sparrows and robins, things which we regard as very 
 different species among wild animals. 
 
 The way in which animals change in the hands of man 
 must be regarded as good evidence that they may be mod- 
 ified in the hands of nature where the penalty of death is 
 administered on all who do not conform to the rules of 
 life ; to all who do not strive to go onward in the race. 
 
 Although we cannot regard this theory of changes 
 among animals and plants as perfectly proven, there can 
 be little doubt that it accounts for many of the changes 
 that take place. It is also likely that there is a host of 
 changes, perhaps the greater part of them, with which 
 these selective processes have little to do. It is not likely 
 that anything so wonderfully complicated as the world 
 of life can be due to one cause. We also easily see that 
 this idea, at most, accounts for only a small part of the 
 wonders of animated nature. The real marvel is, not that 
 animals and plants vary, or that their changes lead to the 
 making of new species, but that these changes have not 
 been by haphazard, but in a way that has led from the 
 lowest creatures to man. It is the fact that these changes
 
 200 THE ORIGIN OF ORGANIC LIFE. 
 
 lead to such an end that is the really wonderful thing. 
 We cannot believe that if they occurred at haphazard, 
 any such a world as we have could have been made. 
 
 It must not be thought that all the changes that take 
 place in the world of plants and animals lead to a higher 
 and more perfect life. If the animal adopts modes of life 
 that require a more perfect body or a more active mind, 
 we find that it goes upwards in its changes ; if, on the 
 other hand, it takes up with baser ways than its ancestors, 
 it may become more and more degraded in its body and 
 mind. The snakes, for instance, were once four-limbed 
 
 Fig. 90. Snake, Cheirotes and Bipes. 
 
 animals that moved like the lizards, but through change 
 of habits they came to other and lower needs, so that their 
 limbs were no longer useful, and shrunk away. A few of 
 the serpents have a small pair of forelegs which are so 
 small that they serve scarce any other use, save to show 
 how they have been degraded from higher forms. The 
 sperm whales come from creatures nearly like our bears, 
 that were pretty well up in the world ; but their ancestors 
 took first to living partly in the water and partly on the 
 land : then, finally, to an altogether water-life, so they have 
 lost their hair, their hind limbs have shrunk away, their 
 fore limbs become reduced to paddles, and the whole body
 
 HOW NEW SPECIES ARE MADE. 201 
 
 has taken on the outside form of a fish ; so, since the begin- 
 ning of the tertiary time, the whales have been degraded 
 from a high to a low place among mammals. There are 
 many other cases among animals where the body, in part 
 or in whole, has been lowered from a higher plane of struc- 
 ture to a lower by the change of habits. Some of the most 
 instructive of these examples we find among cavern animals. 
 In them, the eyes sometimes entirely disappear, the creatures 
 having taken on a habit of living where the light can be of 
 no use to them. 
 
 It is a fact that the higher the level of any animal's life, 
 the more the chance, that through some change of habit 
 the creature may lose the gains its ancestors made for him, 
 and fall, far more swiftly than it rose, to a lower level of 
 existence. This is doubtless true of man, as well as of his 
 lower kindred, and especially true of his moral and men- 
 tal nature. Any degradation of habits lowers the indi- 
 vidual, and the degradation will be handed on to his chil- 
 dren. If we realize this truth, it gives us a keener sense 
 of our duty to our whole nature, to our bodies and our 
 souls ; our very life depends upon a wonderful guidance that 
 has led us slowly up the long ladder of life that stretches 
 from things inanimate to man. We stand upon a moun- 
 tain-top nearer to Heaven than all else, with the privileges 
 that are denied to other beings ; yet the very height bids 
 us to tread carefully, lest we fall into the depths below. 
 
 With the coming of man, the progress of life on this 
 earth seems to have been, in the main, completed. Some 
 changes may take place in the lower life ; the insects and 
 other lower groups may become more varied, and rise to 
 a higher level, but man is the highest of all the backboned 
 animals. The earlier days of the earth seem to have been 
 times for the growth of bodies, while our own time is
 
 202 THE ORIGIN OF ORGANIC LIFE. 
 
 peculiarly an age of mind. The future of this wonderful 
 world comes each day more and more into the keeping 
 of man. He subjugates its animals and plants to his uses ; 
 destroys them, or changes their form and habits to his 
 needs ; already he has destroyed several species of birds 
 and other animals, and, though some insects now baffle 
 him, he will doubtless, in the coming ages, have the whole 
 world at his feet. But, when he comes to a sense of the 
 duties which his power lays upon him, he will surely be 
 merciful to this poor dumb life that has fought with his 
 ancestors in the great battle of the world, through all its 
 ages, and has failed to win the crown of life that is his 
 alone.
 
 PROOF THAT THE EARTH IS VERY OLD. 203 
 
 LESSON II. 
 
 PROOF THAT THE EARTH IS VERY OLD. 
 
 IT is only slowly, and with much difficulty, that we have 
 learned how ancient a thing our earth really is. Many 
 figurative accounts of its sudden creation have been 
 found in the sacred books of various Eastern peoples, 
 but these accounts cannot be taken as representing the 
 primal facts of the earth's history. Man is, himself, so 
 short lived, that he cannot imagine the vast duration of 
 the Past since life began upon the earth ; at most he may 
 remember a century of time, yet this term of the longest 
 human life falls like a drop into the great sea of geological 
 time. 
 
 Let us notice some of the simpler proofs of the earth's 
 great antiquity. Take any pebble in hand: consider 
 what time it requires to shape this bit of stone to round- 
 ness ; how it must pound on the seashore, roll in a river- 
 bed, or grind beneath a glacier before it becomes slowly 
 beaten into this shape ; yet there are great masses of rocks, 
 thousands of feet in thickness, and stretching for hundreds 
 of miles, made up of such pebbles. Look at the sands of 
 our shores, or of the tens of thousands of feet of sandstones 
 that cover the earth, and consider how long it must have 
 required to bruise their grains into this small size, and 
 bear them into the sea where they were built into rocks. 
 Then, after they were built on the sea-floors, they have 
 been lifted into the air, and afterwards carved into valleys 
 and hills. 
 
 Take a thick section of limestones, say one thousand 
 feet in depth, such as we may find in many countries;
 
 204 THE ORIGIN OF OEGANIC LIFE. 
 
 consider that all of it has been in the bodies of animals 
 that have grown and died in the sea, slowly giving their 
 dead bodies to make the limey beds, it has thickened, 
 not faster, perhaps, than the hundredth of an inch a year, 
 until at the end of one million two hundred thousand 
 years it would be finished. There are deep valleys carved 
 in this limestone, such as we may find in many regions 
 where streams cut through hills or mountains. Now, in 
 old countries, such as those of Europe, we can often prove 
 how deep the valley has cut in one thousand years, or in 
 the natural term of life of about twenty generations of 
 men ; we find, perhaps, that the valley deepens at the rate 
 of two feet in one hundred years ; but as the valley is, say, 
 three thousand feet deep, we see that it has required, at 
 least, two and a half million years for it to be carved out. 
 In fact, there would be a yet larger time required, for the 
 reason that the hills that form this valley are slowly wear- 
 ing down, as well as the bottom of the valley itself, so that 
 if we go back to the time when water began to run down 
 these slopes and carve them into hills and dales, we might 
 have to go many times as far into the Past. 
 
 Take the Falls of Niagara : these falls have slowly re- 
 treated up stream all the way from Lewistown, near Lake 
 Ontario, to their present place ; they are still mounting up 
 stream, as their edge wears away, at the rate of about foui 
 feet in one hundred years, so that seventy thousand years 
 has certainly elapsed since they began to form. 
 
 In the peninsula of Florida, the southern part of it, at 
 least, has been formed by successive coral reefs, which 
 grow, one after the other, further and further southwards. 
 Agassiz has reckoned that it required hundreds of thous- 
 ands of years for these reefs to grow ; yet both these great 
 works, the building of the Florida reefs and the retreat of
 
 PROOF THAT THE EARTH IS VERY OLD. 205 
 
 Niagara Falls up to its present point, are among the most 
 recent things in the shaping of the world, almost every 
 river-valley and every hill in America is an older monu- 
 ment of the earth's forces. We know that the lands change 
 their level very slowly along most shores ; the change is 
 so slow that we call the land stationary; the greatest 
 change is that which is going on in Sweden, where the land 
 rises as much as three feet in a hundred years; yet we 
 know that many lands have been alternately sunk below 
 the seas, and lifted into the air, perhaps a score of times. 
 To bring about such changes requires an inconceivably 
 long time. 
 
 If we study the life history of the earth, we find other 
 things to show us how long the Past has been. Plants 
 and animals change but slowly ; we know that there 
 has been very little change in the last four thousand 
 years, for in the Egyptian catacombs we find a host of 
 mummied animals and plants, every one the same as the 
 living kinds. The life on the earth changes very slowly, 
 one kind dying and another coming in, so that it requires 
 a vast period altogether to change the life ; yet we know 
 that many times, perhaps fifty times, a nearly complete 
 change of life has come about, so that any creature 
 living through all the ages that living beings have been 
 on earth would have been able to see about all the life 
 renewed by these slow changes, at least fifty successive 
 times in the earth's history. 
 
 There are many other evidences that the duration of 
 the earth's past is far greater than we can imagine, or in 
 any way figure to ourselves. Putting together all the facts 
 that we have, it seems tolerably certain that since the time 
 when the earth was first fit for life, somewhere between 
 one hundred million and four hundred million years have
 
 206 THE ORIGIN OF ORGANIC LIFE. 
 
 gone by. We may build a sort of picture of this great 
 length of time in this way : in one mile there are about 
 five thousand feet ; call the whole time of the longest hu- 
 man life one hundred years ; measure off one long step on 
 this mile of length to represent one such human life, then 
 the whole mile will represent only one-half a million years, 
 and it would require, perhaps, a thousand miles of length 
 to give us a diagram which should represent the time since 
 life came on the earth ; and three feet on this length would 
 represent the years of the longest-lived men. When we 
 have seen what happens in the space of one human life, 
 thousands of earthquakes and volcanic eruptions ; thous- 
 ands of great storms that beat the shores ; vast stretches 
 of land grown dry or sunk beneath the sea ; pestilences 
 and famines, and a myriad other changes, and then mul- 
 tiply these by a thousand times a thousand, we gain some 
 faint idea of what a epoch the world's past has been, and 
 can imperfectly imagine how great the changes have been 
 in such a time. 
 
 A large part of the work of the geologist consists in 
 an effort to trace out the history of this past, to find 
 how the lands and seas were shaped in the different periods 
 of the earth's history, what creatures were living at the 
 several times, and how they were succeeded by other 
 and higher forms. This has been slow and perplexing 
 work, but there have been several thousand persons at 
 work upon it during the past hundred years or more, so 
 that we now have a tolerably clear account of the stages 
 through which the earth has passed in its long history. 
 In the following chapter a brief outline of this wonderful 
 history is given. 
 
 It is not easy to give in a few words an idea of how the 
 geologists have succeeded in patching out this record of
 
 PEOOP THAT THE EAETH IS VERY OLD. 207 
 
 the earth's long history, yet it is important that the reader 
 should get some idea of the ways in which it has been 
 done. 
 
 One of the most useful clews that we have to the his- 
 tory of the earth is had from the beds of rock which we 
 may find on the land. We can show how these beds teach 
 by noticing what is shown in the figure. This represents 
 in a rough way a section from the Blue Ridge of Virginia, 
 westward to beyond Cincinnati, Ohio. On the right, the 
 crumpled rocks are composed of granites and other crystal- 
 line rocks ; to the left, the beds show limestones, sandstones, 
 
 Fig. 91. 
 Section from Blue Ridge to west of Cincinnati, Ohio. 
 
 and slates; those covered with dots, conglomerates-, 
 those shaded black, the beds that bear the coal. Now, as 
 all these beds, except the coal, were formed beneath the 
 sea, we perceive how great must have been the changes 
 since the earliest of them were formed. These changes were 
 as follows : first, the mountains of the Blue Ridge existed 
 as mountains rising above the sea before all the others 
 were formed ; this is shown by the fact that the lowest 
 beds contain pebbles worn from their rocks, and they lie 
 up against the granites, etc., in what is called an unconform- 
 able position ; that is, the newer beds do not slope the 
 same way as the old, showing that the old had been tilted
 
 208 THE ORIGIN OF ORGANIC LIFE. 
 
 and covered before ttie new were formed; we see that 
 these beds including the coal measures are tilted up to 
 form the Alleghenies. 
 
 Going further west, we see a broad ridge in the rocks. 
 At Cincinnati there is a very wide, low mountain. By 
 closely examining the position and character of the rocks 
 here, we can prove that this ridge was in part formed long 
 before the time of the coal. It has on its western side 
 fossil coral reefs, such as are now formed on mountains in 
 the warm seas where a current sets against their shores. 
 Next, we notice that the various rocks that are repre- 
 sented in this diagram are thickest towards the east, 
 and thin out towards the west ; the beds of pebbles 
 abound near the Blue Ridge, and fade out westwardly into 
 sandstones or fine muds. This shows us that the land 
 was to the east of the old sea-floors on which these de- 
 posits were laid down, for pebbles always grow smaller as 
 we go away from the shores. 
 
 There are many other ways in which geologists are able 
 to infer the succession of events, and the conditions that 
 existed on the earth's surface t in past times. There are, 
 indeed, many other well-founded conclusions that can be 
 drawn from this section ; but enough has been noted to in- 
 dicate one of the principal ways in which geologists work. 
 The rocks form a great stone book, the pages are often 
 ragged, and the signs hard to decipher, but the story is 
 still plain if we study it well.
 
 CHAPTER XII. 
 
 BRIEF ACCOUNT OF THE SUCCESSION OF EVENTS 
 ON THE EARTH'S SURFACE. 
 
 LESSON I. 
 THE EARTH BEFORE ORGANIC LIFE BEGAN. 
 
 THE earliest stages of the earth's history are not written 
 in its rocks, so that all we know about the matter 
 comes from the studies of astronomers upon the distant 
 worlds of space, many of which are passing through the 
 changes that our world must have endured in becoming 
 fit for life. These very distant stages of change were 
 probably about as described below. 
 
 92. 
 
 In the beginning our earth, along with the sun and thb 
 other planets of the solar system, existed as a very large 
 mass of finely-divided matter much like a gas. Seen from
 
 210 EVENTS ON THE EABTH's SURFACE. 
 
 the distant stars through a strong telescope, it would have 
 appeared as a faintly shining mass, like what astronomers 
 call nebula. The particles of this gas all attracted each 
 other, which caused them to fall in towards the centre 
 of the mass, and as they fell they all began to swing 
 around in the same direction as the planets now swing 
 around the sun. Then this mass of matter began to divide 
 into circles like those strange rings that girdle the planet 
 Saturn. When these rings became tolerably separated 
 from the mass within them, they broke up, and were 
 gathered into a sphere. As the old outer rings of Saturn 
 
 Fig. 93. Rings of Saturn. 
 
 have been changed into moons, one after another of these 
 rings formed in the great mass of gas, and were gathered 
 into the separate planets. These several planets each 
 then shrank, forming separate small rings, like the great 
 rings from which they were shaped ; these rings breaking 
 to pieces produced the moons or satellites of which all the 
 planets, except possibly Venus and Mercury, have one or 
 more. As if to prove that this was the way in which 
 planets and moons were formed, the planet Saturn pre- 
 serves one of its rings that has not collapsed into a moon, 
 but remains as a ring, as is shown in the diagram. 
 Although not perfectly certain, it is almost so, that this
 
 THE EABTH BEFORE ORGANIC LIFE BEGAN. 211 
 
 is something like the first stage in the development of 
 our earth. 
 
 When it first separated from the great shrinking mass 
 of our solar system and became a sphere-like body, the 
 matter of our world was very likely still a mass of gas, 
 which was more than half a million miles in diameter, 
 extending beyond the orbit of the moon. It then could 
 not have been as solid as the air that now lies on its sur- 
 face. But, as it shrank into more and more solid forms, 
 it too formed an outer ring, which in time was broken up 
 and gathered into our moon. 
 
 As the remaining mass of our earth became more solid 
 from the falling of its particles towards the centre, a great 
 deal of heat was developed. We see when a meteor falls 
 on the earth, or a hammer falls upon iron, that heat is 
 made to appear when the motion is arrested, and as these 
 particles of matter tumbled towards the centre of the 
 earth's mass, the whole gradually became hotter and 
 hotter, until the gas was by the crowding together of its 
 particles converted into a very hot fluid sphere, not much 
 larger than the present earth. As the vacant space out* 
 side of the earth was exceedingly cold, having a temper- 
 ature of one or two hundred degrees below zero, this great 
 boiling mass of earth-matter slowly parted with its heat, 
 until it became solid enough to bear a crust of frozen 
 rocks that enclosed the hotter matter within. Then the 
 water which had been kept in the state of gas above the 
 earth came down upon its surface and wrapped it with 
 the oceans. Now, for the first time, the earth began to 
 be like the world we know ; the machinery of its physi- 
 cal life, the winds, the ocean-currents, and the rivers, 
 came into being, and all was made ready for life to begin. 
 In what way life began we do not know ; we only know
 
 212 EVENTS ON THE EARTH'S SURFACE. 
 
 that all our experiments appear to show that life, even in 
 the lowest forms, seems to be always derived from other 
 life, and not able to start even in the simplest forms from 
 dead matter. But once begun, the whole world of progress 
 became open to it.
 
 HISTORY OF ORGANIC LITE. 213 
 
 LESSON II. 
 
 HISTORY OF ORGANIC LIFE. 
 
 THE geologist cannot find his way back, in the record of 
 the great stone book, to the far-off day when life began. 
 The various changes that come over rocks from the action 
 of heat, of water, and of pressure, have slowly modified 
 these ancient beds, so that they no longer preserve the 
 frames of the animals that were buried in them. 
 
 These old rocks, which are so changed that we cannot 
 any longer make sure that any animals lived hi them, are 
 called the "archsean," which is Greek for ancient. They 
 were probably mud and sand and limestone when first 
 made, but they have been changed to mica schists, gneiss, 
 granite, marble, and other crystalline rocks. When any 
 rock becomes crystalline, the fossils dissolve and disap- 
 pear, as coins lose their stamp and form when they are 
 melted in the jeweller's gold-pot. 
 
 These ancient rocks that lie deepest in the earth are 
 very thick, and must have taken a great time in building ; 
 great continents must have been worn down by rain and 
 waves in order to supply the waste out of which they 
 were made. It is tolerably certain that they took as 
 much time during their making as has been required for 
 all the other times since they were formed. During the 
 vast ages of this archaean the life of our earth began to be. 
 We first find many certain evidences of life in the rocks 
 which lie on top of the archaean rook, and are known 
 as the Cambrian and Silurian periods. There we have 
 creatures akin to our corals and crabs and worms, 
 and others that are the distant kindred of the cuttle-
 
 214 
 
 EVENTS ON THE EARTH'S SURFACE. 
 
 fishes and of our lamp-shells. There were no backboned 
 animals, that is to say, no land mammals, reptiles, or 
 fishes at this stage of the earth's history. It is not likely 
 that there was any land life except of plants and those 
 forms like the lowest ferns, and probably mosses. Nor 
 is it likely that there were any large continents as at the 
 present time, but rather a host of islands lying where the 
 great lands now are, the budding tops of the continents 
 just appearing above the sea. 
 
 Although the life of this time was far simpler than ai 
 the present day, it had about as great variety as we would 
 find on our present sea-floors. There were as many dif- 
 ferent species living at the same time on a given surface. 
 
 Fig. 94. North America in Cambrian time. 
 
 The Cambrian and Silurian time the time before the 
 coming of the fishes must have endured for many mil- 
 lion years without any great change in the world. Hosts 
 of species lived and died ; half a dozen times or more the 
 life of the earth was greatly changed. New species came 
 much like those that had gone before, and only a little gain 
 here and there was perceptible at any time. Still, at the 
 end of the Silurian, the life of the world had climbed some 
 steps higher in structure and in intelligence.
 
 HISTORY OF ORGANIC LIFE. 215 
 
 The next set of periods is known as the Devonian. It 
 is marked by the rapid extension of the fishes; for, al- 
 though the fishes began in the uppermost Silurian, they 
 first became abundant in this time. These, the first strong- 
 jawed tyrants of the sea, came all at once, like a rush of 
 the old Norman pirates into the peaceful seas of Gt. 
 Britain. They made a lively time among the sluggish 
 beings of that olden sea. Creatures that were able to 
 meet feebler enemies were swept away or compelled to 
 undergo great changes, and all the life of the oceans 
 seems to have a spur given to it by these quicker-formed 
 and quicker-willed animals. In this Devonian section of 
 our rocks we have proofs that the lands were extensively 
 covered with forests of low fern trees, and we find the 
 first trace of air-breathing animals in certain insects akin 
 to our dragon-flies. In this stage of the earth's history 
 the fishes grew constantly more plentiful, and the seas 
 had a great abundance of corals and crinoids. Except for 
 the fishes, there were no very great changes in the char- 
 acter of the life from that which existed in the earlier 
 time of the Cambrian and Silurian. The animals are 
 constantly changing, but the general nature of the life 
 remains the same as in the earlier time. 
 
 In the Carboniferous or coal-bearing age, we have the 
 second great change in the character of the life on the 
 earth. Of the earlier times, we have preserved only 
 the rocks formed in the seas. But rarely do we find any 
 trace of the land life or even of the life that lived along the 
 shores. In this Carboniferous time, however, we have very 
 extensive sheets of rocks which were formed in swamps in 
 the way shown in the earlier part of this book. They con- 
 stitute our coal-beds, which, though much worn away by 
 rain and sea, still cover a large part of the land surface.
 
 216 EVENTS ON THE EARTH'S SURFACE. 
 
 These beds of coal grew in the air, and, although the swamps 
 where they were formed had very little animal life in them, 
 we find some fossils which tell us that the life of the land 
 was making great progress ; there are new insects, includ- 
 ing beetles, cockroaches, spiders, and scorpions, and, what 
 is far more important, there are some air-breathing, back- 
 boned animals, akin to the salamanders and water-dogs of 
 the present day. These were nearly as large as alligators, 
 and of much the same shape, but they were probably 
 born from the egg in the shape of tadpoles and lived for 
 a time in the water as our young frogs, toads, and sala- 
 
 Fig, 95. Raniceps Lyelli Coal time salamander. 
 
 manders do. This is the first step upwards from the 
 fishes to land vertebrates ; and we may well be interested 
 in it, for it makes one most important advance in crea- 
 tures through whose lives our own existence became pos- 
 sible. Still, these ancient woods of the coal period must 
 have had little of the* life we now associate with the 
 forests; there were still no birds, no serpents, no true 
 lizards, no suck-giving animals, no flowers, and no fruits. 
 These coal-period forests were sombre wastes of shade, 
 with no sound save those of the wind, the thunder, and 
 the volcano, or of the running streams and the waves on 
 the shores.
 
 HISTORY OF ORGANIC LIFE. 217 
 
 In the seas of the Carboniferous time, we notice 
 that the ancient life of the earth is passing away. Many 
 creatures, such as the trilobites, die out, and many 
 other forms such as the crinoids or sea lilies become 
 fewer in kind and of less importance. These marks of 
 decay in the marine life continue into the beds just after 
 the Carboniferous, known as the Permian, which are really 
 the last stages of the coal-bearing period. 
 
 When with the changing time we pass to the beds 
 known as the Triassic, which were made just after the close 
 of the Carboniferous time, we find the earth undergoing 
 swift changes in its life. The moist climate and low lands 
 that caused the swamps to grow so rapidly have ceased to 
 be, and in their place we appear to have warm, dry air 
 and higher lands. 
 
 Fig. 96. Cycas circinalis, akin to highest plants of coal time. 
 
 On these lands of the Triassic time the air-breathing life 
 made very rapid advances. The plants are seen to un- 
 dergo considerable changes. The ferns no longer make 
 up all the forests, but trees more like the pines began to 
 abound, and insects became more plentiful and more 
 varied. .; 
 
 Hitherto the only land back-boned animal was akin to 
 uur salamanders. Now we have true lizards in abund-
 
 218 
 
 EVENTS ON THE EARTH'S SURFACE. 
 
 ance, many of them of large size. Some of them were 
 probably plant-eaters, but most were flesh-eaters; some 
 seem to have been tenants of the early swamps, and 
 some dwelt in the forests. 
 
 The creatures related to the salamanders have increased 
 in the variety of their forms to a wonderful extent. We 
 know them best by the tracks which they have left on 
 the mud stones formed on the borders of lakes or the edge 
 of the sea. In some places these footprints are found in 
 amazing numbers and perfection. The best place for 
 them is in the Connecticut Valley, near Turner's Falls, 
 
 N^ 
 
 Fig. 97. Foot-prints, Connecticut Sandstones. 
 
 Mass. At this point the red sandstone and shale beds, 
 which are composed of thin layers having a total thickness 
 of several hundred feet, are often stamped over by these 
 footprints like the mud of a barnyard. From the little 
 we can determine from these footprints, the creatures 
 seem to have been somewhat related to our frogs, but 
 they generally had tails, and, though provided with four 
 legs, were in the habit of walking on the hind ones alone 
 like the kangaroo. A few of these tracks are shown in the 
 figure on this page. 
 
 These strange creatures were of many different species. 
 Some of them must have been six or seven feet high,
 
 HISTORY OP ORGANIC LIFE. 219 
 
 for their steps are as much as three feet apart, and seem 
 to imply a creature weighing several hundred pounds. 
 Others were not bigger than robins. Strangely enough, we 
 have never found their bones 
 nor the creatures on which 
 they fed, and but for the for- 
 mation of a little patch of 
 rocks here and there we 
 should not have had even 
 these footprints to prove to 
 us that such creatures had 
 lived in the Connecticut Val- 
 ley in this far-off time. Fig. 98. Foot-print, Turners Falls. 
 
 But these wonderful forms are less interesting than two 
 or three little fossil jaw-bones that prove to us that in this 
 Triassic time the earth now bore another animal more akin 
 
 Fig. 99. 
 Dromotherium Sylvestre and Teeth of Microlestes antiquus. 
 
 to ourselves, in the shape of a little creature that gave 
 suck to its young. Once more life takes a long upward 
 step in this little opossum-like animal, perhaps the first 
 creature whose young was born alive. These little crea- 
 tures, called Microlestes or Dromatherium, of which only 
 one or two different but related species have been found 
 in England and in North Carolina, appear to have been in-
 
 220 
 
 EVENTS ON THE EARTH S SURFACE. 
 
 sect-eaters of about the size and shape of the Australian 
 creature shown in Fig. 100. So far we know it in but few 
 specimens, altogether only an ounce or two of bones, 
 but they are very precious monuments of the past. 
 
 In this Triassic time the 
 climate appears to have been 
 rather dry, for in it we have 
 many extensive deposits of 
 salt formed by the evapora- 
 tion of closed lakes, of seas, 
 such as are now forming on 
 the bottom of the Dead Sea, 
 and the Great Salt Lake of 
 Utah, and a hundred or more 
 other similar basins of the 
 present day. 
 
 In the sea animals of this time we find many changes. 
 Already some of the giant lizard-like animals, which first 
 took shape on the land, are becoming swimming animals. 
 
 Fig. 101. Icthyosaurus and Plesiosaurus. 
 
 They change their feet to paddles, which, with the help 
 of a flattened tail, force them swiftly through the water. 
 
 The fishes on which these great swimming lizards 
 preyed are more like the fishes of our present day than
 
 HISTORY OP ORGANIC LIFE. 221 
 
 they were before. The trilobites are gone, and of the cri- 
 noids only a remnant is left. Most of the corals of the 
 earlier days have disappeared, but the mollusks have not 
 changed more than they did at several different times in 
 the earlier stages of the earth's history. 
 
 After the Trias comes a long succession of ages in 
 which the life of the world is steadily advancing to 
 higher and higher planes; but for a long time there is no 
 such startling change as that which came in the passage 
 from the coal series of rocks to the Trias. This long set 
 of periods is known to geologists as the age of reptiles. 
 
 Fig. 102. Reptiles of Jurassic Period. 
 
 It is well named, for the kindred of the lizards then had 
 the control of the land. There were then none of our 
 large fish to dispute their control, so they shaped them- 
 selves to suit all the occupations that could give them a 
 chance for a living. Some remained beasts of prey like 
 our alligators, but grew to larger size ; some took to eat- 
 ing the plants, and came to walk on their four legs as our 
 ordinary beasts do, no longer dragging themselves on 
 their bellies as do the lizard and alligator, their lower 
 kindred. Others became flying creatures like our bats, 
 only vastly larger, often with a spread of wing of fifteen 
 or twenty feet. Yet others, even as strangely shaped, 
 dwelt with the sharks in the sea.
 
 222 EVENTS ON THE EARTH'S SURFACE. 
 
 In this time of the earth's history we have the first bird- 
 like forms. They were feathered creatures, with bills car- 
 rying true teeth, and with strong wings ; but they were 
 reptiles in many features, having long, pointed tails such 
 as none of our existing birds have. They show us that 
 the birds are the descendants of reptiles, coming off from 
 them as a branch does from the parent tree. The tor- 
 toises began in this series of rocks. At first they are 
 marine or swimming forms, the box-turtles coming later. 
 Here too begin many of the higher insects. Creatures 
 like moths and bees appear, and the forests are enlivened 
 with all the important kinds of insects, though the species 
 were very different from those now living. 
 
 In the age of reptiles the plants have made a consid- 
 erable advance. Palms are plenty ; forms akin to our 
 pines and firs abound, and the old flowerless group of 
 ferns begins to shrink in size, and no longer spreads its 
 feathery foliage over all the land as before. Still there 
 were none of our common broad-leaved trees ; the world 
 had not yet known the oaks, birches, maples, or any of our 
 hard-wood trees that lose their leaves in autumn ; nor 
 were the flowering plants, those with gay blossoms, yet 
 on the earth. The woods and fields were doubtless fresh 
 and green, but they wanted the grace of blossoms, plants, 
 and singing-birds. None of the animals could have had 
 the social qualities or the finer instincts that are so com- 
 mon among animals of the present day. There were prob- 
 ably no social animals like our ants and bees, no merry 
 singing creatures; probably no forms that went in herds. 
 Life was a dull round of uncared-for birth, cruel self- 
 seeking, and of death. The animals at best were clumsy, 
 poorly-endowed creatures, with hardly more intelligence 
 than our alligators.
 
 HISTORY OF ORGANIC LIFE. 223 
 
 The little thread of higher life begun in the Micro- 
 lestes and Dromatherium, the little insect-eating mammals 
 of the forest, is visible all through this time. It held in 
 its warm blood the powers of the time to come, but it 
 was an insignificant thing among the mighty cold-blooded 
 reptiles of these ancient lands. There are several species 
 of them, but they are all small, and have no chance to 
 make headway against the older masters of the earth. 
 
 The Jurassic or first part of the reptilian time shades 
 insensibly into the second part, called the Cretaceous, 
 which immediately follows it. During this period the 
 lands were undergoing perpetual changes; rather deep 
 seas came to cover much of the land surfaces, and there 
 is some reason to believe that the climate of the earth 
 became much colder than it had been, at least in those 
 regions where the great reptiles had flourished. It may be 
 that it is due to a colder climate that we owe the rapid 
 passing away of this gigantic reptilian life of the previous 
 age. The reptiles, being cold-blooded, cannot stand even 
 a moderate winter cold, save when they are so small that 
 they can crawl deep into crevices in the rocks to sleep the 
 winter away, guarded from the cold by the warmth of the 
 earth. At any rate these gigantic animals rapidly ceased 
 to be, so that by the middle of the cretaceous period they 
 were almost all gone, except those that inhabited the sea ; 
 and at the end of this time they had shrunk to lizards in 
 size. The birds continue to increase and to become more 
 like those of our day ; their tails shrink away, their long 
 bills lose their teeth ; they are mostly water-birds of large 
 size, and there are none of our songsters yet; still they 
 are for the first time perfect birds, and no longer half- 
 lizard in their nature. 
 
 The greatest change in the plants is found in the conv
 
 224 EVENTS ON THE EARTH'S SURFACE. 
 
 ing of the broad-leaved trees belonging to the families of 
 our oaks, maples, etc. Now for the first time our woods 
 take on their aspect of to-day; pines and other cone- 
 bearers mingle with the more varied foliage of nut-bearing 
 or large-seeded trees. Curiously enough, we lose sight of 
 the little mammals of the earlier time. This is probably 
 because there is very little in the way of land animals of 
 this period preserved to us. There are hardly any mines 
 or quarries in the beds of this age to bring these fossils 
 to light. In the most of the other rocks there is more to 
 tempt man to explore them for coal ores or building 
 stones. 
 
 In passing from the Cretaceous to the Tertiary, we enter 
 upon the threshold of our modern world. We leave be- 
 hind all the great wonders of the old world, the gigantic 
 reptiles, the forests of tree ferns, the seas full of ammo- 
 nites and belemnites, and come among the no less wonder- 
 ful but more familiar modern forms. We come at once 
 into lands and seas where the back-boned animals are the 
 ruling beings. The reptiles have shrunk to a few low 
 forms, the small lizards, the crocodiles and alligators, 
 the tortoises and turtles, and, as if to mark more clearly 
 the banishment of this group from their old empire, the 
 serpents, which are peculiarly degraded forms of reptiles 
 which have lost the legs they once had, came to be the 
 commonest reptiles of the earth. 
 
 The first mammals that have no pouches now appear. 
 In earlier times, the suck-giving animals all belonged to 
 the group that contains our opossums, kangaroos, etc. 
 These creatures are much lower and feebler than the 
 mammals that have no pouches. Although they have 
 probably been on the earth two or three times as long as 
 the higher mammals, they have never attained any emi-
 
 HISTORY OF ORGANIC LIFE. 225 
 
 nent success whatever ; they cannot endure cold climates ; 
 none of them are fitted for swimming as are the seals and 
 whales, or for flying as the bats, or for burrowing as the 
 moles ; they are dull, weak things, which are not able to 
 contend with their stronger, better-organized, higher kin- 
 dred. They seem not only weak, but unable to fit them- 
 selves to many different kinds of existence. 
 
 In the lower part of the Tertiary rocks, we find at once 
 a great variety of large beasts that gave suck to tkeir 
 young. It is likely that these creatures had come into 
 existence in a somewhat earlier time in other lands, 
 where we have not been able to study the fossils ; for to 
 make their wonderful forms slowly, as we believe them to 
 have been made, would require a very long time. It is 
 probable that during the Cretaceous time, in some land 
 where we have not yet had a chance to study the rocks, 
 these creatures grew to their varied forms, and that in the 
 beginning of the tertiary time, they spread into the re- 
 gions where we find their bones. 
 
 Beginning with the Tertiary time, we find these lower 
 kinsmen of man, through whom man came to be. The 
 mammals were marked by much greater simplicity and 
 likeness to each other than they now have. There were 
 probably no monkeys, no horses, no bulls, no sheep, no 
 goats, no seals, no whales, and no bats. All these animals 
 had many-fingered feet. There were no cloven feet like 
 those of our bulls, and no solid feet as our horses have. 
 Their brains, which by their size give us a general idea of 
 the intelligence of the creature, are small ; hence we con- 
 clude that these early mammals were less intelligent than 
 those of our day. 
 
 It would require volumes to trace the history of the 
 growth of these early mammals, and show how they, step
 
 226 EVENTS ON THE EARTH'S SURFACE. 
 
 by step, came to their present higher state. We will take 
 only one of the simplest of these changes, which happens 
 to be also the one which we know best. This is the 
 change that led to the making of our common horses, 
 which seem to have been brought into life on the conti- 
 nent of North America. The most singular thing about 
 our horses is that the feet have but one large toe or 
 finger, the hoof, the hard covering of which is the nail of 
 that extremity. Now it seems hard to turn the weak, 
 five-fingered feet of the animals of the lower tertiary feet 
 which seem to be better fitted for tree-climbing than any- 
 thing else into feet such as we find in the horse. Yet 
 
 Fig. 103. Feet of Tertiary Mammals. 
 
 the change is brought about by easy stages that lead the 
 successive creatures from the weak and loose-jointed foot 
 of the 'ancient forms to the solid, single-fingered horse's 
 hoof, which is wonderfully well-fitted for carrying a large 
 beast at a swift speed, and is s6 strong a weapon of de- 
 fence that an active donkey can kill a lion with a well- 
 delivered kick. 
 
 The oldest of these creatures that lead to the horses is 
 called Eohippus or beginning horse. This fellow had on 
 the forefeet four large toes, each with a small hoof and 
 a fifth imperfect one, which answered to the thumb. The
 
 HISTORY OF ORGANIC LIFE. 
 
 227 
 
 hind feet had gone further in the change, for they each 
 had but three toes, each with hoofs, the middle-toed hoof 
 larger and longer than the others. A little later toward 
 our day we find another advance in the Orohippus, when 
 the little imperfect thumb has disappeared, and there are 
 only four toes on the forefeet and three on the hind. 
 
 Yet later we have the Mesohippus or half-way horse. 
 There are still three toes on the hind foot, but one more 
 of the fingers of the forefeet has disappeared. This time 
 it is the little finger that goes, leaving only a small bone 
 to show that its going was by a slow shrinking. The 
 creature now has three little hoofs on each of its feet. 
 
 Fiy. 104. Development of Horse's Foot. 
 
 Still nearer our own time comes the Miohippus, which 
 shows the two side hoofs on each foot shrinking up so 
 that they do not touch the ground, but they still bear 
 little hoofs. Lastly, about the time of man's coming on 
 the earth, appears his faithful servant, the horse, in which 
 those little side hoofs have disappeared, leaving only two 
 little " splint " bones to mark the place where these side 
 hoofs belong. Thus, step by step, our horses' feet were 
 built up ; while these parts were changing, the other parts 
 of the animals were also slowly altering. They were at 
 first smaller than our horses, some of them not as large
 
 228 EVENTS ON THE EARTH'S SURFACE. 
 
 as an ordinary Newfoundland dog ; others as small as 
 foxes. 
 
 As if to remind us of his old shape, our horses now 
 and then, but rarely, have, in place of the little splint 
 bones above the hoof, two smaller hoofs, just like the foot 
 of MioJiippus. Sometimes these are about the size of a 
 silver dollar, on the part that receives the shoe when 
 horses are shod. 
 
 In this way, by slow-made changes, the early mammals 
 pass into the higher. Out of one original part are made 
 limbs as different as the feet of the horse, the wing of a 
 bat, the paddle of a whale, and the hand of man. So 
 with all the parts of the body the forms change to meet 
 the different uses to which they are put. 
 
 At the end of this long promise, which was written in 
 the very first animals, comes man himself, in form closely 
 akin to the lower animals, but in mind immeasurably apart 
 from them. We can find every part of man's body in a 
 little different shape in the monkeys, but his mind is of 
 a very different quality. While his lower kindred cannot 
 be made to advance in intelligence any more than man 
 himself can grow a horse's foot or a bat's wing, he is con- 
 stantly going higher and higher in his mental and moral 
 growth. 
 
 So far we have found but few traces of man that lead 
 us to suppose that he has been for a long geological time 
 on the earth, yet there is good evidence that he has been 
 here for a hundred thousand years or more. It seems 
 pretty clear that he has changed little in his body in 
 all these thousands of generations. The earliest remains 
 show us a large-brained creature, who used tools and 
 probably had already made a servant of fire, which so 
 admirably aids him in his work.
 
 HISTORY OF ORGANIC LIFE. 229 
 
 Besides the development of this wonderful series of 
 animals, that we may call in a certain way our kindred, 
 there have been several other remarkable advances in this 
 Tertiary time, this age of crowning wonders in the earth's 
 history. The birds have gone forward very rapidly ; it is 
 likely that there were no songsters at the first part 
 of this period, but these singing birds have developed 
 very rapidly in later times. Among the insects the most 
 remarkable growth is among the ants, the bees, and their 
 kindred. These creatures have very wonderful habits ; 
 they combine together for the making of what we may 
 call states, they care for their young, they wage great 
 battles, they keep slaves, they domesticate other insects, 
 and in many ways their acts resemble the doings of man. 
 Coming at about the same time as man, these intellectual 
 insects help to mark this later stage of the earth as the 
 intellectual period in its history. Now for the first time 
 creatures are on the earth which can form societies and 
 help each other in the difficult work of living. 
 
 Among the mollusks, the most important change is in 
 the creation of the great, strong swimming squids, the 
 most remarkable creatures of the sea. Some of these have 
 arms that can stretch for fifty feet from tip to tip. 
 
 Among the plants, the most important change has been 
 in the growth of flowering plants, which have been con- 
 stantly becoming more plenty, and the plants which bear 
 fruits have also become more numerous. The broad- 
 leaved trees seem to be constantly gaining on the forests 
 of narrow-leaved cone-bearers, which had in an earlier 
 day replaced the forests of ferns. 
 
 In these Tertiary ages, as in the preceding times of the 
 earth, the lands and seas were much changed in their
 
 230 EVENTS ON THE EARTH'S SURFACE. 
 
 shape. It seems that in the earlier ages the land had 
 been mostly in the shape of large islands grouped close 
 together where the continents now are. In this time, 
 these islands grew together to form the united lands of 
 Europe, Asia, Africa, Australia, and the twin American 
 continents ; so that, as life rose higher, the earth was 
 better fitted for it. Still there were great troubles that 
 it had to undergo. There were at least two different 
 times during the Tertiary age termed glacial periods, 
 times when the ice covered a large part of the northern 
 continents, compelling life of all sorts to abandon great 
 regions, and to find new places in more southern lands. 
 Many kinds of animals and plants seem to have been de- 
 stroyed in these journeys; but these times of trial, by 
 removing the weaker and less competent creatures, made 
 room for new forms to rise in their places. All advance in 
 nature makes death necessary, and this must come to 
 races as well as to individuals if the life of the world is 
 to go onward and upward. 
 
 Looking back into the darkened past, of which we yet 
 know but little compared with what we would like to 
 know, we can see the great armies of living beings 
 led onward from victory to victory toward the higher 
 life of our own time. Each age sees some advance, 
 though death overtakes all its creatures. Those that es- 
 cape their actual enemies or accident fall a prey to old 
 age: volcanoes, earthquakes, glacial periods, and a host of 
 other violent accidents sweep away the life of wide re- 
 gions, yet the host moves on under a control that lies 
 beyond the knowledge of science. Man finds himself 
 here as the crowning victory of this long war. For him 
 all this life appears to have striven. In his hands lies the
 
 HISTORY OF ORGANIC LIFE. 231 
 
 profit of all its toil and pain. Surely this should make 
 us feel that our duty to all these living things, that have 
 shared in the struggle that has given man his elevation, is 
 great, but above all great is our duty to the powers that 
 have been placed in our bodies and our minds.
 
 APPENDIX. 
 
 CRYSTALLINE ROCKS. 
 
 /^vUR rapid glance at the machinery of the world has 
 ^-^ shown us some little of most of the great engines 
 that are at work within, upon, or without it, engines 
 that make it the wonderful workshop that it is. Let us 
 now turn back to see some of the lower, but still more 
 important, portions of its mechanism which are given to 
 us in that part of inorganic nature known as the kingdom 
 of crystalline forms. 
 
 First, let us notice that nearly all substances in nature 
 have three states of existence : the gaseous, the fluid, and 
 the solid. We are familiar with these three shapes of 
 water because there is only a little difference of tempera- 
 ture needed to carry it through all the stages. Over a 
 fire, a lump of ice will quickly become fluid, and in a 
 short time it will pass into steam, as we are accustomed 
 co term its gaseous state. We do not commonly see this 
 behavior in other substances, because, in iron, for instance, 
 the temperature necessary to carry it from the solid, 
 through the fluid, to the gaseous state, is perhaps thirty 
 or forty times as great as is required to pass water through 
 these stages. It is now believed that all simple sub- 
 stances, such as our metals, and a great many of the more 
 complicated substances, made up by the union of several 
 simple substances, can exist in these three conditions; so 
 that we may accept it as a general truth in nature that
 
 234 APPENDIX. 
 
 substances have usually the three possible states of solid, 
 fluid, and gas. 
 
 While in the state of gas or fluid, all matter seems to 
 remain in a uniform shapeless condition ; but when the sub- 
 stance becomes solid, it generally enters into the crystalline 
 form. The best way to get an idea of this peculiar condi- 
 tion is to examine a number of crystalline substances, as, 
 for instance, salt, sugar, alum, quartz, etc. Every day we 
 come in contact with a dozen or more out of the thou- 
 sands of substances that take this shape. 
 
 If we look closely at crystals of one substance, we see 
 that they have the same form, or have shapes that arise 
 from slight changes of a particular form. For instance, 
 crystals of common salt have one shape, while crystals 
 of quartz have a very different shape. The number of 
 sides and the slope of these sides to each other give the 
 peculiar forms. 
 
 We do not know what causes different substances to 
 take these different forms, but we do know that from the 
 beginning of the earth each substance has its form, and 
 that they are the same for all time. Further than this, 
 the meteoric stones that fall from the heavens show us 
 that the same rules of form affect the substances in the 
 other planets of our solar system or other solar systems, 
 whence it is supposed that these stones come. 
 
 The rules that control the forms of these crystals and 
 make them the subject of the science of crystalography 
 are very interesting, but the matter is too difficult for dis- 
 cussion here. These rules are so precise that this subject 
 is really a branch of geometry as well as a part of chem- 
 istry and geology. * 
 
 We must next notice that if we examine the rocks of 
 the earth's surface, we find that a part of them belong to
 
 CRYSTALLINE ROCKS. 235 
 
 the class of stratified deposits, and generally show no signs 
 of crystalline minerals except in cracks which have evi- 
 dently been filled in by the action of water. Such rocks 
 are generally distinctly bedded, and show us that they 
 have been little changed since they were formed on the 
 bottoms of old seas or lakes. 
 
 Then there is another class of rocks, called "crystal- 
 line," from the fact that crystals abound all through their 
 masses. These rocks we suppose to have been stratified 
 rocks that have been so much heated that the particles 
 were free to move together as they pleased, and so have 
 gathered into the crystalline form. This heat may have 
 actually melted the rocks, as was the case with some of 
 our granites ; or, the rocks having been made very hot, the 
 water they held in their interstices was able to dissolve the 
 various minerals, and so make them free to take on the 
 shape of crystals. When a mass of limestone is deeply 
 buried in the earth, it becomes heated because it is 
 brought near the hot interior of the earth, and the water 
 that is contained in it dissolves the lime, and so enables 
 the crystals of lime carbonate to form. In this way, our 
 rocks made of limestone mud may be changed to crys- 
 talline marble, its different ingredients being gathered 
 together into their several peculiar crystals. 
 
 When these stratified rocks, which were once lime- 
 stones, mud, sand, and gravel, have their various sub- 
 stances changed into crystals, the rocks then become very 
 different from what they were before. The alteration is 
 often so great that we cannot say what the rock was 
 before the change came upon it. 
 
 It is from the action of the crystallizing forces on rocks 
 that the most puzzling changes are brought about, and the 
 science of mineralogy comes to exist. The principal un-
 
 236 APPENDIX. 
 
 crystallized rocks are named from their evident characters, 
 independent of any crystals they may contain. They are 
 made up of various substances, which will be described 
 under their names and with their crystalline forms. 
 
 We have already considered these familiar uncrystal- 
 line rocks ; we will now recall them, and give a statement 
 of the changes that heat and other metamorphic agents may 
 bring to them. 
 
 Claystone or Clay Slate. Made of fine mud particles. 
 It may be principally of clay, or partly of lime or quartz. 
 It may contain some carbon, as in the shales near the 
 coals. Useful for building-stones or flagging, etc. ; or, when 
 in the shape of true slate, for roofing houses, for which its 
 thin, leaf-like sheets are well fitted. The peculiar struc- 
 ture of roofing-slate is called slaty cleavage, because it is 
 found only in rocks of this description, never in limestones 
 or the coarse-grained rocks. This cleavage is produced in 
 the following way. The slate rock is made up of small 
 bits of many different stones, little fragments of quartz, 
 of feldspar, etc. Among these substances there are gener- 
 ally very numerous, though very small, flakes of mica. 
 These bits of mica are always very thin, generally a dozen 
 or more times as wide as they are thick. When the rock 
 was built in its first form as a soft mud, these flakes fell 
 upon the bottom in many different positions, so that their 
 long faces lie in all sorts of ways. When the rock hardens, 
 they seem to bind it together, somewhat as the hair holds 
 the plasterer's mortar together. Now, if it happens that 
 the rock filled with these mica flakes is very much 
 squeezed, as rocks are when they are forced together by 
 the mountain building forces, it may hg forced to stretch 
 itself out in any direction, like dough under the cook's 
 rolling-pin. We can easily see that these several mica
 
 CBYSTALLHTE BOCKS. 237 
 
 flakes will then all lie in about the same direction. Per- 
 haps this will be more easily seen if we imagine the flakes 
 of mica mingled in dough and then rolled out. The 
 result will be that their longer faces will generally lie 
 parallel with the surface of the flattened cake. It is 
 easy to imagine that when all these flakes are turned by 
 the stretching of the rock, so that their planes are par- 
 allel to each other, the rock will split much more easily 
 along the line of their faces than it will across them. It 
 is this adjustment of mica planes that causes our common 
 roofing slate to split so easily into thin sheets. 
 
 This slaty cleavage is the simplest of the changes that 
 come over clay stone when it enters into the great labora- 
 tory beneath the earth's surface by its burial beneath 
 other rocks. If it is deeply buried, if ten or twenty thou- 
 sand feet of rocks are laid down upon it, it may undergo 
 very great changes. Thus deeply buried, it becomes very 
 much heated by the inner heat of the earth. This affords 
 the particles of the rock a chance to become dissolved in 
 water and rearranged in the crystalline form. This gives 
 us a mica schist, or other similar rock, in place of the 
 original slate. If still further heated, so that the rock 
 melts, the mass may become a trap-like rock, and lose all 
 trace of its original structure and character. 
 
 Limestones and Limestone Marbles. When limestones are 
 subjected to the action of heated water, the rock becomes 
 more solid, the fossils are dissolved away, and the whole 
 mass takes on a more or less crystalline form. These crys- 
 tals are generally of lime carbonate, but sometimes of 
 lime sulphate or gypsum, or other salts of lime. In this 
 changed form, limestone affords the greater part of the 
 polished stone used in building and for table-tops, etc. 
 
 Sandstones. Heat and heated water work to change
 
 238 APPENDIX. 
 
 sandstones into more compact rocks, termed " quartzites." 
 In these rocks we can no longer see the distinct grains of 
 sand, but the whole is converted into a rather solid mass 
 of flinty matter. The grains of sand are taken to pieces 
 in the heated water and re-made so that the crystals are 
 all close set and locked together. 
 
 In these changes of claystones, limestones, and sand- 
 stones, the alteration is so slight that the mass is still dis- 
 tinctly a bedded rock. But the changes may go still 
 further. The rocks may be so kneaded together by the 
 strong movements that take place in the depths of the 
 earth that the bedding which so distinctly marked the wa- 
 ter origin of the material can no longer be traced. It also 
 happens that other chemical substances, besides those origi- 
 nally in the rock, are gradually brought in by the perco- 
 lating waters, so that the chemical nature, as well as the 
 shape, of the mass is changed. It is probably in this way 
 that a host of rocks, which are termed "gneisses," "gran- 
 ites," and "syenites," are formed. In some cases we can 
 still trace a remnant of the bedding of these greatly 
 changed rocks, enough to show that they were originally 
 made on sea-floors as stratified deposits. 
 
 If the heat or the action of heated water still further 
 affect the rocks, they may take on either of two other 
 shapes. They may be converted into dykes or into veins. 
 
 Dykes are formed when the rock is so heated that it 
 more or less completely melts. In this melting, it is aided 
 by the water that all rocks contain. In this melted state, 
 it is squeezed into crevices of other rocks, as before de- 
 scribed. This trap matter is generally highly crystallized, 
 and, of course, has lost all trace of its stratification. 
 
 Veins are deposits of matter nearly always in the crys- 
 tallized form, where the carriage of the matter into a
 
 CRYSTALLINE ROCKS. 239 
 
 crevice has been brought about by the action of water, 
 which first dissolves the substances, and then allows them 
 to deposit as crystals. In the several ways above de- 
 scribed, a great variety of crystals is formed, and from the 
 association together of different crystals a great many rocks 
 are made. 
 
 Of these crystals, which altogether amount to several 
 hundred species or kinds, the following are the most im- 
 portant and the most common in rocks. 
 
 1. Quartz, by far the commonest crystals found on the 
 earth. Almost all sand consists of broken crystals of this 
 substance. Its usual form is that of a six-sided prism, 
 with a six-sided pyramid at 
 
 the end. Sometimes there is 
 a pyramid at each end. It 
 also, but very rarely, crystal- 
 lizes six-sided tables. Ordina- 
 rily, these crystals are trans- 
 parent and glass-like, but they 
 may be colored of many tints, 
 as of a violet or amethyst 
 color. They are always too **ff- 105 - Q uartz > common forms, 
 hard to be scratched by steel. Quartz is very often 
 found in the uncrystallized form, as in flint, agate, chal- 
 cedony, etc. 
 
 2. Feldspar. This is, next after quartz, the commonest 
 crystal in the rocks. It is about as heavy and as hard 
 as quartz, about two and one-half times the weight of 
 water. Its crystals split in two directions, breaking easily 
 into parallelograms, with smooth, waxy-looking, lustrous 
 sides, while quartz crystals do not split in this fashion. 
 The crystals vary so much in form that they cannot be 
 represented here.
 
 240 
 
 APPENDIX. 
 
 3. Mica. This is a very common crystal, which easily 
 splits in thin, elastic flakes. Sometimes the crystals are 
 as transparent as glass, but more commonly they are 
 yellow, wine-colored, green, or smoky in hue. Commonly, 
 the crystals are small, as in granites, but when occurring 
 in veins they are sometimes a 
 foot or more across. Flakes 
 from these large crystals are 
 used for stove windows, for 
 covering photographs, or for 
 the battle lanterns and win- 
 dows of our ships, where glass 
 would be broken by the jar of 
 guns or of the enemies' shot. 
 Fit/, loe. Mica. This substance may easily be 
 
 distinguished from all others by the fact that undecayed 
 crystals will always yield elastic flakes when divided with 
 the knife. The thin flakes broken from mica crystals are 
 very buoyant and float far in the water. They may be 
 seen glistening in most sandstones. 
 
 Hornblende. Next after the three above named, one of 
 the commonest minerals is 
 hornblende. It is very vari- 
 able in all its qualities. It 
 may take the shape of oblong 
 prisms, of tufts, of crystals, 
 or of hair-like fibres laid close 
 together. Sometimes these 
 fibres are so long and elastic 
 that they may be spun and 
 woven like cotton. In this 
 shape, the mineral is termed " asbestos," which means 
 unburnable. This name has been applied to it because it 
 
 Fiy. 107. 
 Hornblende, common forms.
 
 CRYSTALLINE ROCKS. 
 
 241 
 
 has been used in making a cloth which is quite fireproof. 
 Among the ancients, such cloth was sometimes used to 
 wrap the dead on the funeral pyre, so that the ashes 
 of the consumed body might not be scattered. 
 
 This mineral is composed of the elements silica, lime, 
 magnesia, and iron. 
 
 Pyroxene is closely akin to hornblende in composition, 
 but the crystals have the form shown in the figure. It is 
 never fibrous, nor does it show the brush-like crystals 
 common in the latter mineral. 
 
 Fig. 108. Pyroxene. Fig. 109. Calcite. 
 
 Calcite. This is one of the commonest minerals. It is 
 the shape taken by ordinary limestone or lime carbonate 
 when crystallized. The crys- 
 tals have the form shown in 
 the diagrams. They are soft, 
 and easily scratched with a 
 knife. It may be of several 
 different colors, and is often 
 transparent. It is composed 
 of 44 parts of carbonic acid 
 and 56 of lime. 
 
 Dolomite is akin to calcite, Fi u- no - Dolomite, 
 
 from which it differs in having carbonate of magnesia
 
 242 
 
 APPENDIX. 
 
 along with carbonate of lime. It is much less abundant 
 than calcite. The forms of the crystals are shown in the 
 figures. 
 
 An easy test for these minerals is made by dipping them 
 in a powdered shape into muriatic acid diluted with 
 one-half its bulk of cold water. Calcite will cause the 
 mixture to foam or effervesce freely at once, while it will 
 be necessary to heat the acid and water before the dolo- 
 mite will give off its gas, except in a very sparing way. 
 
 Gypsum is a very common mineral. It is a combination 
 of sulphuric acid and lime with water. When burnt, it is 
 the plaster of paris of the arts, much used in making casts 
 of statues and various fine mouldings. It occurs in two 
 forms. In one, it is combined with some water, when it 
 crystallizes in the shape shown by Fig. 111. In the other, 
 it is without any water in its combination, when it takes a 
 rectangular shape. 
 
 Fig. 111. Gypsum. Fig. 112. Common Salt. 
 
 Common Salt. This is a compound of sodium and chlo- 
 rine. Its crystals have the form shown in the figures. It 
 often makes beds hundreds of feet in thickness. In this 
 form, it is generally of a brownish color, and only partly 
 transparent; but sometimes this rock salt is as transparent 
 as ice. It is formed wherever salt water is enclosed in a
 
 CRYSTALLINE ROCKS. 
 
 243 
 
 basin, where it receives so little rain water that it evapo- 
 rates. It is then thrown down in crystals on the bottom. 
 Salt is now depositing in many shallow, land-locked pools 
 along those portions of the seashore that have little rain, 
 and also in many inland seas that have no outlet, as, for 
 instance, in the Salt Lake of Utah, the Dead Sea of Asia, 
 etc. There were certain periods in the past history of the 
 earth when salt was very extensively deposited. They 
 were probably the times of least rainfall. 
 
 The foregoing are the commonest crystalline minerals 
 of the rocks. There are others, which, though less fre- 
 quently found, are still common, and should be recognized 
 by the student. First among these, we may notice certain 
 ores of the important metals. It will be noticed that all 
 of them are not found in the form of crystals. 
 
 Pyrite, or Pyrites, is composed of sulphur and iron. It 
 commonly has a light yellow hue, which causes it to be 
 often mistaken for gold, whence it receives the popular 
 name of "fools' gold." Its 
 crystals are shaped as in Fig. 
 113. These crystals, when ex- 
 posed to the air, quickly take 
 up oxygen, and rust or burn 
 sometimes with such rapidity 
 that they give an intense heat. 
 As they often occur in large 
 quantity in coal, their burning 
 frequently fires coal-mines or 
 ships laden with the coal. Hundreds of ships have been 
 lost in this way. By allowing these crystals to burn, 
 sulphuric acid may be produced. 
 
 Magnetite. This is a crystalline ore of iron, occurring 
 in the shapes shown in the figure. It is of a grayish or
 
 244 APPENDIX. 
 
 blackish color. The peculiarit}' which distinguishes it from 
 other minerals, is that the crystals strongly attract the 
 magnetic needle. This min- 
 eral occurs both in beds and 
 in veins. It is as yet not 
 known what causes the mag- 
 netic character. It may be 
 due to the action of heat. A 
 large part of the iron now 
 in use is derived from mag- 
 netite. 
 
 Fig. 114. Magnetite. Hematite, so named from 
 
 its blood-red color, is sometimes found in crystals, but 
 more often in the massive form. It generally occurs in 
 beds. It stains the hand red, and is hence frequently 
 called " dye-stone ore." This ore is often fossiliferous, the 
 fossil shells, etc., having been converted into the iron oxide. 
 It is composed of two parts of iron to three of oxygen. 
 
 Limonite is much like the preceding, except that it does 
 not occur in crystals, and is of a brownish or yellowish 
 color. It may be formed by the combination of water 
 with the hematite ore. 
 
 Hematite and limonite are often found together as dis- 
 tinctly bedded iron ores. The}' represent the little- 
 changed iron ores that are often found interbedded in 
 our limestones, sandstones, and slates. 
 
 Siderite, or Iron Carbonate, is a combination of carbonic 
 acid and iron, and is made by the infiltration of iron ox- 
 ide into limestone beds, which takes away a part of the 
 lime, replacing it with iron. It readily decays, so that 
 while it at first is of a bluish or whitish color, and looks 
 like limestone, on exposure to the air it soon becomes a 
 iimonite, or, in some cases, a hematite. It is generally in
 
 CRYSTALLINE ROCKS. 
 
 245 
 
 massive, stratified form ; but, when crystallized, it takes 
 the shapes shown in the figures. 
 
 Fig. 115. Siderite. Fig. 116. Metallic Copper. 
 
 Ores of Copper. Copper is often found as a pure 
 metal, scattered through various rocks in the form of 
 grains or sheets. Especially is it abundant in this form 
 on the southern shore of Lake Superior. In its metallic 
 state, it is sometimes crystalline, as in the forms shown in 
 the figures. More commonly, it occurs as ore, of which 
 the following is the most important, viz. : 
 
 Copper Pyrites, or Chalcopyrite, composed of sulphur 
 and iron, with a variable proportion of copper. It is 
 closely related to iron pyrites, 
 and differs from it by the 
 presence of copper. 
 
 There are many other ores 
 of copper formed by its mix- 
 ture with other metals, but 
 the principal production of 
 copper is from the two forms 
 above given. 
 
 Lead. This substance is Fig. in. Galena, 
 
 never found in the metallic state. Its principal ore is 
 galena, or lead sulphate. It has the color of lead when
 
 246 
 
 APPENDIX. 
 
 the crystals are fresh. It contains 13 per cent of sulphur. 
 It always occurs in crystals that have the form given in 
 the figure. It is commonly found in veins, but sometimes 
 in beds, where the galena has been gathered in the shape of 
 obscure veins. The crystals have the shape shown in the 
 figure. They are easily split along the sides of the crystals. 
 Lead generally contains more or less silver, and a large 
 part of the silver of the world is extracted from galena. 
 
 Silver occurs in the form 
 of various oxides, but some- 
 times it is found in the metal- 
 lic form as threads or sheets 
 running through the rock. 
 When crystallized, its crystals 
 have the form shown in the 
 figure. The principal ores of 
 silver are formed by combina- 
 Fiy. n. Silver. tions with sulphur, bromine, 
 
 chlorine, but its commonest form of occurrence is in 
 mixture with galena or with copper ores. 
 
 Zinc. This metal is, like lead, not naturally found in 
 the metallic state. Its com- 
 mon form of occurrence is in 
 the shape of sphalerite or 
 zinc blende, a combination of 
 33 parts of sulphur and 67 
 of zinc. The crystals are ot 
 various colors, from yellow 
 to black. When powdered, 
 they give a white dust. The 
 *%.H9. Sphalerite. crystalline forms are shown 
 
 in the figures. This metal is frequently associated with 
 lead in ordinary veins or veinlets in bedded rocks.
 
 CRYSTALLINE KOCKS. 
 
 247 
 
 Tin. This is one of the rarest metals in America, being 
 the only one of the important metals that has never been 
 profitably mined in this country. It is generally found in 
 the shape of thin veins in granite rocks. Its only impor- 
 tant form is that of cassiterite or tin oxide, in which shape 
 
 Fir/. 120. Cassiterite. Fig. 121. Streamer Nugget Gold. 
 
 it is a dark-brownish, very heavy, ore. The crystals are 
 found in the shapes shown in the figure. These crystals 
 do not easily dissolve ; so, when the rock wears away, they 
 often are gathered in the river-beds like gold and plati- 
 num, and are called " stream tin." The most of the tin of 
 commerce has been collected in this way. 
 
 G-old. This metal is, with the possible exception of 
 platinum, the metal that is 
 least disposed to combine with 
 other substances. It is there- 
 fore generally found in the 
 metallic state, usually in the 
 form of grains, sheets, or 
 fibres in the rocks or in the 
 sands of rivers. Though the 
 most sparingly accumulated 
 in masses of all metals, it is ^' 122 ' Crystals of Gold, 
 perhaps the most generally disseminated of all. The most
 
 248 
 
 APPENDIX. 
 
 of our clays and sands contain traces of it. In its crys- 
 talline shapes, which it rarely assumes, it has the forms 
 shown in the figure. 
 
 Aluminum. This metal is never found in the metallic 
 state, though it is perhaps the most plentiful of all the 
 metals that could be used by 
 man in his arts. In its ordi- 
 nary form, it exists as a com- 
 pound of alumina and silic 
 oxide, and is a most important 
 element in all our common 
 clays. This metal is of a sil- 
 very-white color ; it is won- 
 derfully light, being scarcely 
 
 Fig. 123. Corundum. heavier than heavy wood, and 
 
 remarkably strong. But for the fact that it is exceedingly 
 costly to reduce it to the form of a metal, it would be perr 
 haps, after iron, the most important of all to man. 
 
 Sulphur. This substance plays a large part in the geo- 
 logical world. It is rarely found in the crystalline form, 
 
 Fig. 124. Sulphur. 
 
 Fig. 125. Baryta. 
 
 except in the neighborhood of volcanoes. The crystals 
 have the well-known resinous-looking yellow color. They 
 have the shapes shown in the figures.
 
 CRYSTALLINE BOCKS. 
 
 249 
 
 There are several other less important crystals that may 
 be mentioned. Among these barytes, or heavy spar, a 
 compound of sulphuric acid and baryta, is the heaviest of 
 the crystals after those of metallic substances. It has the 
 form shown in Fig. 125. Fluorite, or fluor-spar, a com- 
 pound of fluorine and calcium, is one of the handsomest of 
 our crystals. Its colors range from white to blue or yel- 
 low. See Fig. 126. Arrogonite, a form of lime carbonate, 
 gives crystals shown in Fig. 127. 
 
 . 126. Fluorite. 
 
 Fig. 127. Arrogonite. 
 
 When certain of the foregoing crystals are associated 
 together in a mass of rock, the rock receives particular 
 names, according to the crystalline substances that enter 
 into its composition. Of these rocks, named from the 
 crystals they contain, the following are the most im- 
 portant. 
 
 G-ranite, composed of intermingled crystals of quartz, 
 feldspar, and mica, irregularly crowded together. The 
 proportion of the several sorts of crystals may vary, as 
 well as the forms of the crystals themselves. 
 
 Syenite is a name given to rock composed, like granite, 
 in part of quartz and feldspar crystals, but having some 
 form of hornblende crystals in place of mica. 
 
 Gneiss. When the rock has the crystals crowded to
 
 250 APPENDIX. 
 
 gether in a banded form, the rock is called "a gneiss." 
 In some cases, this banded arrangement is the remains of 
 stratification planes that once marked the rock in a dis- 
 tinct way as a water-made deposit. If the mica crystals 
 are present, it is called a " granitic gneiss " ; if the horn- 
 blende crystals are present, it is called a " syenitic 
 gneiss." 
 
 Mica Schist. When the mica plates are very abundant, 
 and the feldspar less considerable, the rock becomes very 
 easily splitable, and shines all over from the reflection of 
 the mica plates. It is then called a " mica schist." When 
 the hornblende is abundant, it is called a "hornblende 
 schist." 
 
 Porphyry. This is a name given to any rock when 
 there is a cementing mass of feldspar or quartz in which 
 distinct crystals of feldspar, or feldspar and quartz, are 
 lodged. There are very many kinds, and, as most of 
 them are handsome when polished, they have been much 
 used for decorative stones. 
 
 The following-named rocks are not crystalline. They 
 are found in association with the crystalline rocks, and 
 deserve the attention of the beginner in geology. 
 
 Steatite, or fioapstone, a rock largely composed of mag- 
 nesia, generally of a mottled, greenish-white color, thick 
 bedded or entirely massive. It has a curious soapy feel. 
 Much used in making stoves, fire-backs, and in other 
 places where heat must be endured. 
 
 Serpentine. Also largely composed of magnesia, and 
 much resembling soaps tone, except it feels less soapy. 
 Like soapstone, it is easily cut with the saw. It is more 
 mottled than soapstone, takes a good polish, is generally 
 of a beautiful greenish co^, and hence is much used for 
 decorative purposes.
 
 CRYSTALLINE ROCKS. 251 
 
 Quartzite. This is a sandstone that has had its grains 
 more closely cemented together than in ordinary sand- 
 stones. Sometimes the grains are so blended that they 
 are no longer visible. In this shape, it is often called 
 "chert," or "flint." Sometimes, by changes which we do 
 not understand, the quartzite becomes flexible, so that a 
 slender piece can be bent in the hand. It is then called 
 Itacolumite, from a mountain in Brazil, where it was 
 first found. It occurs plentifully in North and South 
 Carolina. 
 
 There are many hundred forms of crystals, and some 
 score of rocks, composed in larger or smaller part of these 
 crystals, which are not mentioned here, for the reason 
 that they are not of common occurrence on the earth's 
 surface. 1 The most important of these omissions is the 
 series of volcanic rocks. These are, it is generally be- 
 lieved, the ordinary stratified rocks, that have been com- 
 pletely melted and driven up to the surface. Their varia- 
 tions are due in part to the original chemical nature of 
 the rocks, and in part to the way in which they have 
 cooled from their melted state. 
 
 In general, we may say that the crystalline rocks repre- 
 sent those portions of the earth's crust which have been 
 the most changed by heat, acting directly or through hot 
 water, that penetrates the rocks. When the crystalline 
 rocks wear down, their crystals are generally broken to 
 pieces, and go to make mudstones, sandstones, or lime- 
 stones, to be again gathered into crystals when they are 
 deeply buried in the earth's crust, and so exposed to the 
 action of heat. 
 
 1 For further information concerning crystals, see Professor J. D. Dana's 
 System of Mineralogy, 5th edition, New York, 1873 ; also his Manual of 
 Geology, New York, 1880, from which, in part, this brief account is taken.
 
 252 APPENDIX. 
 
 Thus we see that the rocks, and the minerals found in 
 them, revolve in an eternal circle by the action of water. 
 They are constantly changing into the condition of mud. 
 When they have long been buried in the crust of the 
 earth, they become changed to the crystalline structure. 
 Their change to this condition is largely the effect of 
 water action. As the lands wear down, the rocks once 
 again pass into the control of water, and are returned to 
 the sea-floor.
 
 INDEX. 
 
 A. 
 
 Advance in organic creations, 155. 
 ^Etna, 94. 
 
 African deserts, 19. 
 Age of earth, 203. 
 Air, the, 56. 
 
 heat-retaining action, 59. 
 
 currents, 99. 
 Aluminium, 248. 
 Ammonites, 170. 
 Amphibians, 180. 
 
 Animal kingdom, objects sought, 162. 
 Animals, degradation of, 200. 
 Arno River, sand of, 14. 
 Articulates, 175. 
 Artificial stones, 32. 
 Australia, great reef of, 40. 
 
 Barytes, 249. 
 Birds, 181. 
 
 with tails, 222. 
 Blue Ridge, section from 
 Bogs, 49. 
 
 coal from, 49, 50. 
 Bomb, bursting of, by ice, 4. 
 
 C. 
 
 Calcite, 241. 
 Cambrian, 213. 
 Carbonic acid (CO 2 ), 44. 
 Carboniferous period, 215. 
 Cassiterite, 247. 
 Caverns, fossils in, 84. 
 
 life of, 80. 
 
 of Kentucky, 85. 
 
 sea-shore, 86. 
 
 limestone, 75. 
 
 volcanic, 85. 
 Cephalopods, 170. 
 Chalcopyrite, 245. 
 
 Chili shore, changes of, 14L 
 Cincinnati axis, 208. 
 Classification, 150. 
 Coal, 46. 
 
 anthracite, 50. 
 
 bituminous, 50. 
 
 cannel, 50. 
 
 of different regions, 53. 
 
 period, 51. 
 
 Richmond, Va., 51. 
 
 seam, 52. 
 
 use of, 53. 
 
 Colorado cafion, 120. 
 Conglomerate, 30. 
 Connecticut, 119. 
 Continents, 111. 
 Copper, ores of, 245. 
 Coral reefs, 40. 
 Cretaceous, 223. 
 Crinoids, 43. 
 Cross-bedding, 34. 
 Crystalline rocks, 233. 
 Crustaceans, 176. 
 
 D. 
 
 Darwinian Theory, 196. 
 
 Degradation among animals, 200. 
 
 Devonian, 215. 
 
 Difference and relations among animals 
 
 149. 
 
 Dolomite, 241. 
 Domesticated animals, 199. 
 Dromatherium, 219. 
 
 Earth, before organic life, 209. 
 Earthquakes, 120. 
 
 Lisbon, 131. 
 
 of Mississippi Valley, 134. 
 
 New England, 134. 
 
 Calif ornian, 135. 
 
 waves, 166.
 
 254 
 
 INDEX. 
 
 Earthworms, action of, 22. 
 Echini, 166. 
 Egypt, sand of, 19. 
 
 mummies of, 205. 
 Kohippus, 226. 
 
 Events on earth's surface, 209. 
 Expansion in freezing of water, 4. 
 
 F. 
 
 Falls (water), 117. 
 
 Niagara, 204. 
 
 of Ohio, 118. 
 Felspar, 239. 
 Fishes, 180. 
 Fluorite, 249. 
 Foraminifera, 42. 
 Forests, age of, 47. 
 Fossils, formation of, 189. 
 
 conclusions from, 193. 
 
 G. 
 
 Gasteropoda, 199. 
 Glacial pebbles, 10. 
 
 scratches, 10. 
 Glaciers, 8. 
 
 extent of, 11. 
 Gneiss, 249. 
 Gold, 247. 
 Gulf Stream, 103. 
 Gypsum, 242. 
 
 H. 
 
 Heat of iron, 99. 
 
 Hills, 107. 
 
 History of earth, 209. 
 
 organic life, 240. 
 Holothurians, 167. 
 Hot springs, 68. 
 
 I. 
 
 Insects, 176. 
 Instincts, 177. 
 Iron carbonate, 244. 
 Iron pyrite, etc., 243. 
 
 J. 
 
 Jamaica, earthquake of, 132. 
 Japan current, 105. 
 Jurassic period, 223. 
 
 Kentucky, caverns in, 76. 
 
 Lakes, 125. 
 
 salt, 125. 
 
 glacial, 127. 
 Lava, 94. 
 
 Californian, 94. 
 Lead, 245. 
 Life, work of, 146. 
 Limestone, 23, 38. 
 
 fertility from, 45. 
 Limonite, 244. 
 Lisbon earthquake, 131. 
 Lode, Comstock, 69. 
 
 Magnesite, 249. 
 
 Magnetite, 243. 
 
 Mammals, 182. 
 
 Mammoth Cave, 78. 
 
 Marbles, 238. 
 
 Mesohippus, 227. 
 
 Metals, method of deposition, 71. 
 
 Mica, 240. 
 
 schist, 250. 
 Microlestes, 219. 
 Millstone grit, 30. 
 Miohippus, 227. 
 Mollusks, 168. 
 Mountains, 108. 
 Mud, 20. 
 
 stones, 36. 
 
 N. 
 Nebular hypotheses, 209. 
 
 O. 
 
 Ocean currents, 102. 
 Ohio Falls, 118. 
 Opossums, 183. 
 Origin of life, 195. 
 Oyster, rate of growth, 39. 
 
 P. 
 
 Pebbles, river, 1, 2, 3, 4. 
 
 glacial, 8. 
 
 sea, 5, 7. 
 
 scratched, 32. 
 Petroleum, 54. 
 Plants, advances in, 158. 
 Pliny, death of, 92. 
 Porphyry, 250.
 
 INDEX. 
 
 '255 
 
 Pressure (effects) ,31, 
 Proof of earth's age, 203. 
 Protozoa, 164. 
 Pumice, 37. 
 Pyrite, 243. 
 Pyroxine, 241. 
 
 Quartz, 239. 
 Quartzite, 251. 
 
 Q. 
 
 it. 
 
 Radiates, 164. 
 
 Reptiles, 181. 
 
 Richmond, Va., coal, 51. 
 
 Rivers, 114. 
 
 Rocky Mountains, sand in, 19. 
 
 Roots of plants, action of, 23. 
 
 effects of, 31. 
 
 rule of formatic 
 
 Sahara, 19. 
 Salt, 242. 
 Salt lakes, 125. 
 Saltpetre in caverns, 85. 
 Sand, river, 12. 
 
 sea-shore, 15. 
 of Arno River, 14. 
 of Sahara, 19. 
 polishing by, 19. 
 Sandstones, 34. 
 Saturn's rings, 210. 
 Scyenite, 249. 
 Sea eggs, 166. 
 
 cucumbers, 167. 
 
 weeds, 157. 
 
 pebbles, 6. 
 
 beach, 7, 67. 
 
 wearing action of, 142. 
 Shrinkage of earth, 108. 
 Siderite, 244. 
 Silurian, 214. 
 Silver, 246. 
 Soapstone, 250. 
 
 Soils, 24. 
 
 structure of, 24, 25. 
 
 working of, 26. 
 
 action of man on, 27. 
 
 glacial, 28. 
 
 of Virginia, 29. 
 Species, how made, 195. 
 Stalactites, 78. 
 Steatite, 250. 
 Stratified rocks, 
 Stromboli, 93. 
 Sulphur, 248. 
 
 T. 
 
 Tertiary, 224. 
 
 Tides, cutting acHon, 122. 
 
 life-feeding action, 124. 
 Tin, 247. 
 Trap dykes, 72. 
 Triassic, 217. 
 Turner's Falls, 218. 
 
 U. 
 
 Underground water, 74. 
 
 V. 
 
 Valleys, 13. 
 Veins, mineral, 66. 
 Vertebrates, 179. 
 Vesuvius, 92. 
 Voice of animals, 187. 
 Volcanoes, 88. 
 
 dust of, 36. 
 
 cause of, 90. 
 
 W. 
 
 Water, expansion in freezing, 4. 
 
 dissolving action of, 44, 62. 
 heat-carrying power of, 64 
 work of, 62. 
 underground, 74. 
 
 Y. 
 
 Yosemite Valley, 121. 
 
 Z 
 
 Zinc, 246. 
 
 blende, 246.
 
 This book is DUE on the last date stamped below 
 
 flOV i 7 193J 
 
 
 
 OEC K^ 1 
 
 
 
 jQV 5 1935 
 
 
 
 APR 1 5 1946 
 
 
 
 
 
 
 JUN 1 fc Ty4jj 
 
 
 
 NOV9 1951 1 
 
 
 
 
 
 ) 
 
 Form L-9-10m-5,'28 
 
 
 
 The FV.^n r ' "" n ; ""ARY 
 
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