The Project Gutenberg EBook of Earth and Sky Every Child Should Know, by Julia Ellen Rogers This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org Title: Earth and Sky Every Child Should Know Easy studies of the earth and the stars for any time and place Author: Julia Ellen Rogers Release Date: May 30, 2010 [EBook #32598] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK EARTH AND SKY *** Produced by Juliet Sutherland, Christine D. and the Online Distributed Proofreading Team at http://www.pgdp.net Pike's Peak, Colorado Pike's Peak, Colorado EARTH AND SKY EVERY CHILD SHOULD KNOW EASY STUDIES OF THE EARTH AND THE STARS FOR ANY TIME AND PLACE BY JULIA ELLEN ROGERS AUTHOR OF "THE TREE BOOK," "THE SHELL BOOK," "KEY TO THE NATURE LIBRARY," "TREES EVERY CHILD SHOULD KNOW." ILLUSTRATED BY THIRTY-ONE PAGES OF PHOTOGRAPHS AND DRAWINGS NEW YORK GROSSET & DUNLAP PUBLISHERS COPYRIGHT, 1910, BY DOUBLEDAY, PAGE & COMPANY PUBLISHED, OCTOBER, 1910 ALL RIGHTS RESERVED, INCLUDING THAT OF TRANSLATION INTO FOREIGN LANGUAGES, INCLUDING THE SCANDINAVIAN ACKNOWLEDGMENTS A number of the photographs in this volume are used by permission of the American Museum of Natural History. The star maps and drawings of the constellations are by Mrs. Jerome B. Thomas. The poem by Longfellow, quoted in part, is with the permission of the publishers, Houghton, Mifflin & Co. CONTENTS PART I. THE EARTH PAGE The Great Stone Book 3 The Fossil Fish 6 The Crust of the Earth 9 What Is the Earth Made of? 14 The First Dry Land 22 A Study of Granite 27 Metamorphic Rocks 31 The Air in Motion 35 The Work of the Wind 44 Rain in Summer, by Henry W. Longfellow 50 What Becomes of the Rain? 51 The Soil in Fields and Gardens 58 The Work of Earthworms 63 Quiet Forces That Destroy Rocks 68 How Rocks Are Made 72 Getting Acquainted With a River 78 The Ways of Rivers 84 The Story of a Pond 90 The Riddle of the Lost Rocks 93 The Question Answered 96 Glaciers Among the Alps 98 The Great Ice Sheet 104 Following Some Lost Rivers 110 The Mammoth Cave of Kentucky 114 [Pg vii] [Pg viii] Land Building by Rivers 121 The Making of Mountains 126 The Lava Flood of the Northwest 130 The First Living Things 134 An Ancient Beach at Ebb Tide 138 The Lime Rocks 147 The Age of Fishes 152 King Coal 155 How Coal Was Made 160 The Most Useful Metal 167 The Age of Reptiles 175 The Age of Mammals 180 The Horse and His Ancestors 186 The Age of Man 194 PART II. THE SKY Every Family a "Star Club" 201 The Dippers and the Pole Star 207 Constellations You Can Always See 213 Winter Constellations 219 Orion, His Dogs, and the Bull 223 Seven Famous Constellations 231 The Twenty Brightest Stars 239 How to Learn More 241 ILLUSTRATIONS Pike's Peak Frontispiece FACING PAGE Sand Dunes in Arizona 44 Grand Cañon of the Colorado 45 Castles Carved by Rain and Wind 52 Where All the Water Comes From 53 The Richest Gold and Silver Mines 72 Rocks Being Ground to Flour 73 A Pond Made by a Glacier 88 The Struggle Between a Stream and Its Banks 89 Ripple Marks and Glacial Striæ 102 Glacial Grooves and Markings 103 Crinoid and Ammonite 140 Fossil Corals, Coquina, Hippurite Limestone 141 Fossil Fish 152 Meteorite 153 Eocene Fish and Trilobite 156 How Coal Was Made 157 Banded Sandstone. Opalized Wood 176 [Pg ix] [Pg x] Allosaurus 177 A Three-horned Dinosaur 178 Remains of Brontosaurus 179 Restoration of Brontosaurus 182 Ornitholestes, a Small Dinosaur 183 A Mammoth 186 An Ancestor of the Horse 187 Orion, His Dogs, and the Bull 214 Other Fanciful Sketches of Constellations 215 The Sky in Winter 244 The Sky in Spring 244 The Sky in Summer 244 The Sky in Autumn 244 PART I THE EARTH THE GREAT STONE BOOK "The crust of our earth is a great cemetery where the rocks are tombstones on which the buried dead have written their own epitaphs. They tell us who they were, and when and where they lived."—Louis Agassiz. Deep in the ground, and high and dry on the sides of mountains, belts of limestone and sandstone and slate lie on the ancient granite ribs of the earth. They are the deposits of sand and mud that formed the shores of ancient seas. The limestone is formed of the decayed shells of animal forms that flourished in shallow bays along those shores. And all we know about the life of these early days is read in the epitaphs written on these stone tables. Under the stratified rocks, the granite foundations tell nothing of life on the earth. But the sea rolled over them, and in it lived a great variety of shellfish. Evidently the earliest fossil-bearing rocks were worn away, for the rocks that now lie on the granite show not the beginnings, but the high tide of life. The "lost interval" of which geologists speak was a time when living forms were few in the sea. In the muddy bottoms of shallow, quiet bays lie the shells and skeletons of the creatures that live their lives in those waters and die when they grow old and feeble. We have seen the fiddler crabs by thousands on such shores, young and old, lusty and feeble. We have seen the rocks along another coast almost covered by the coiled shells of little gray periwinkles, and big clumps of black mussels hanging on the piers and wharfs. All these creatures die, at length, and their shells accumulate on the shallow sea bottom. Who has not spent hours gathering dead shells which the tide has thrown up on the beach? Who has not cut his foot on the broken shells that lie in the sandy bottom we walk on whenever we go into the surf to swim or bathe? Read downward from the surface toward the earth's centre— Table of Contents Part Rock Systems Dominant Animals Dominant Plants VII. Recent Man Flowering kinds { Quaternary VI. Pliocene Mammals Early flowering [Pg 1] [Pg 2] [Pg 3] [Pg 4] Tertiary { Miocene Eocene V. Mesozoic Reptiles Cycads IV. Carboniferous Amphibians Ferns and Conifers III. Devonian Fishes Ferns II. Silurian Molluscs Seaweeds I. Fire-formed No life No life It is by dying that the creatures of the sea write their epitaphs. The mud or sand swallows them up. In time these submerged banks may be left dry, and become beds of stone. Then some of the skeletons and shells may be revealed in blocks of quarried stone, still perfect in form after lying buried for thousands of years. The leaves of this great stone book are the layers of rock, laid down under water. Between the leaves are pressed specimens—fossils of animals and plants that have lived on the earth. THE FOSSIL FISH I remember seeing a flat piece of stone on a library table, with the skeleton of a fish distinctly raised on one surface. The friend who owned this strange-looking specimen told me that she found it in a stone quarry. She brought home a large piece of the slate, and a stone-mason cut out the block with the fish in it, and her souvenir made a useful and interesting paper-weight. The story of that fish I heard with wonder, and have never forgotten. I had never heard of fossil animals or plants until my good neighbour talked about them. She showed me bits of stone with fern leaves pressed into them. One piece of hard limestone was as full of little sea-shells as it could possibly be. One ball of marble was a honeycombed pattern, and called "fossil coral." The fossil fish was once alive, swimming in the sea, and feeding on the things it liked to eat, as all happy fishes do. Near shore a river poured its muddy water into the sea, and the sandy bottom was covered with the mud that settled on it. At last the fish grew old, and perhaps a trifle stupid about catching minnows. It died, and sank to the muddy floor of the sea. Its horny bones were not dissolved by the water. They remained, and the mud filtered in and filled all the spaces. Soon the fish was buried completely by the sediment the river brought. Years, thousands of them, went by, and the layer of mud was so thick and heavy above the skeleton of the fish that it bore a weight of tons there, under the water. The close-packed mud became a stiff clay. After more thousands of years, the sea no longer came so far ashore, for the river had built up a great delta of land out of mud. The clay in which the fish was hidden hardened into slate. Water crept down in the loose upper layers, dissolving out salt and other minerals, and having harder work to soak through, the lower it went. The water left some of the minerals it had accumulated, calcium and silica and iron, in the lower rock beds, making them harder than they were before, and heavier and less porous. When the river gorge was cut through these layers of rock, the colour and thickness of each kind were laid bare. Centuries after, perhaps thousands of years, indeed, the quarrymen cut out the layers fit for building stones, flags for walks and slates for roofing. In the splitting of a flagstone, the long-buried skeleton of the fish came to light. Under our feet the earth lies in layers. Under the soil lie loose beds of clay and sand and gravel, and under these loose kinds of earth are close-packed clays, sandstones, limestones, shales, often strangely tilted away from the horizontal line, but variously fitted, one layer to another. Under these rocks lie the foundations of the earth—the fire-formed rocks, like granite. The depth of this original rock is unknown. It is the substance out of which the earth is made, we think. All the layered rocks are made of particles of the older ones, stolen by wind and water, and finally deposited on the borders of lakes and seas. So our rivers are doing to-day what they have always done—they are tearing down rocks, grinding and sifting the fragments, and letting them fall where the current of fresh water meets a great body of water that is still, or has currents contrary to that of the river. Do you see a little dead fish in the water? It is on the way to become a fossil, and the mud that sifts over it, to become a layer of slate. Every seashore buries its dead in layers of sand and mud. THE CRUST OF THE EARTH [Pg 5] [Pg 6] [Pg 7] [Pg 8] [Pg 9] It is hard to believe that our solid earth was once a ball of seething liquid, like the red-hot iron that is poured out of the big clay cups into the sand moulds at an iron foundry. But when a mountain like Vesuvius sets up a mighty rumbling, and finally a mass of white-hot lava bursts from the centre and streams down the sides, covering the vineyards and olive orchards, and driving the people out of their homes in terror, it seems as if the earth's crust must be but a thin and frail affair, covering a fiery interior, which might at any time break out. The people who live near volcanoes might easily get this idea. But they do not. They go back as soon as the lava streams are cooled, and rebuild their homes, and plant more orchards and vineyards. "It is so many years," say they to one another, "since the last bad eruption. Vesuvius will probably sleep now till we are dead and gone." This is good reasoning. There are few active volcanoes left on the earth, compared with the number that were once active, and long ago became extinct. And the time between eruptions of the active ones grows longer; the eruptions less violent. Terrible as were the recent earthquakes of San Francisco and Messina, this form of disturbance of the earth's crust is growing constantly less frequent. The earth is growing cooler as it grows older; the crust thickens and grows stronger as centuries pass. We have been studying the earth only a few hundred years. The crust has been cooling for millions of years, and mountain-making was the result of the shrinking of the crust. That formed folds and clefts, and let masses of the heated substance pour out on the surface. My first geography lesson I shall never forget. The new teacher had very bright eyes and such pretty hands! She held up a red apple, and told us that the earth's substance was melted and burning, inside its crust, which was about as thick, in proportion to the size of the globe, as the skin of the apple. I was filled with wonder and fear. What if we children jumped the rope so hard as to break through the fragile shell, and drop out of sight in a sea of fiery metal, like melted iron? Some of the boys didn't believe it, but they were impressed, nevertheless. The theory of the heated interior of the earth is still believed, but the idea that flames and bubbling metals are enclosed in the outer layer of solid matter has generally been abandoned. The power that draws all of its particles toward the earth's centre is stated by the laws of gravitation. The amount of "pull" is the measure of the weight of any substance. Lift a stone, and then a feather pillow, much larger than the stone. One is strongly drawn to the earth; the other not. One is heavy, we say, the other light. If a stone you can pick up is heavy, how much heavier is a great boulder that it takes a four-horse team to haul. What tremendous weight there is in all the boulders scattered on a hillside! The hill itself could not be made level without digging away thousands of tons of earth. The earth's outer crust, with its miles in depth of mountains and level ground, is a crushing weight lying on the heated under-substance. Every foot of depth adds greatly to the pressure exerted upon the mass, for the attraction of gravitation increases amazingly as the centre of the earth is approached. It is now believed that the earth is solid to its centre, though heated to a high degree. Terrific pressure, which causes this heat, is exerted by the weight of the crust. A crack in the crust may relieve this pressure at some point, and a mass of substance may be forced out and burst into a flaming stream of lava. Such an eruption is familiar in volcanic regions. The fact that red-hot lava streams from the crater of Vesuvius is no proof that it was seething and bubbling while far below the surface. Volcanoes, geysers, and hot springs prove that the earth's interior is hot. The crust is frozen the year around in the polar regions, and never between the Tropics of Cancer and Capricorn. The sun's rays produce our different climates, but they affect only the surface. Underground, there is a rise of a degree of temperature for every fifty feet one goes down. The lowest mine shaft is about a mile deep. That is only one four-thousandth of the distance to the earth's centre. By an easy computation we could locate the known melting-point for metals and other rock materials. But one degree for each fifty feet of depth below the surface may not be correct for the second mile, as it is for the first. Again, the melting-point is probably a great deal higher for substances under great pressure. The weight of the crust is a burden the under-rocks bear. Probably the pressure on every square inch reaches thousands of tons. Could any substance become liquid with such a weight upon it, whatever heat it attained? Nobody can answer this question. The theory that volcanoes are chimneys connecting lakes of burning lava with the surface of the earth is discredited by geologists. The weight of the overlying crust would, they think, close such chambers, and reduce liquids to a solid condition. Since the first land rose above the sea, the crust of the earth has gradually become more stable, but even now there is scarcely a day when the instruments called seismographs do not record earthquake shocks in some part of the earth; and the outbreaks of Vesuvius and Ætna, the constant boiling of lava in the craters of the Hawaiian Islands and other volcanic centres, prove that even now the earth's crust is very thin and unstable. The further back in time we go, the thinner was the crust, the more frequent the outbursts of volcanic activity, the more readily did wrinkles form. The shores of New Jersey and of Greenland are gradually sinking, and the sea coming up over the land. Certain parts of the world are gradually rising out of the sea. In earlier times the rising or the sinking of land over large areas happened much more frequently than now. [Pg 10] [Pg 11] [Pg 12] [Pg 13] [Pg 14] WHAT IS THE EARTH MADE OF? "Baking day" is a great institution in the comfortable farm life of the American people. The big range oven is not allowed to grow cold until rows of pies adorn the pantry shelves, and cakes, tarts, and generous loaves of bread are added to the store. Cookies, perhaps, and a big pan full of crisp, brown doughnuts often crown the day's work. No gallery of art treasures will ever charm the grown-up boys and girls as those pantry shelves charmed the bright-eyed, hungry children, who were allowed to survey the treasure-house, and sample its good things while they were still warm. You could count a dozen different kinds of cakes and pies, rolls and cookies on those pantry shelves, yet several of them were made out of the same dough. Instead of a loaf of bread, mother could make two or three kinds of coffee cake, or cinnamon rolls, or currant buns, or Parker-House rolls. Even the pastry, which made the pies and tarts, was not so different from the bread dough, for each was made of flour, and contained, besides the salt, "shortening," which was butter or lard. Sugar was used in everything, from the bread, which had a table-spoonful, to the cookies, which were finished with a sifting of sugar on top. How much of the food we eat is made of a very few staple foodstuffs,—starch, sugar, fats! So in the wonderful earth and all that grows out of it and lives upon it. Only seventy different elements have been discovered, counting, besides the earth, the water and the air, and even the strange wandering bodies, called meteorites, that fall upon the earth out of the sky. Like the flour in the different cakes and pies, the element carbon is found in abundance and in strangely different combinations. As a gas, in combination with oxygen, it is breathed out of our lungs, and out of chimneys where coal and wood are burned. It forms a large part of the framework of trees and other plants, and remains as charcoal when the wood is slowly burned under a close covering. There is a good proportion of carbon in animal bodies, in the bones as well as the soft parts, and carbon is plentiful in the mineral substances of the earth. The chemist is the man who has determined for us the existence and the distribution of the seventy elements. He finds them in the solid substances of the globe and in the water that covers four-fifths of its surface; in the atmosphere that covers sea and land, and in all the living forms of plants and animals that live in the seas and on the land. By means of an instrument called the spectroscope, the heavenly bodies are proved to be made of the same substances that are found in the rocks. The sun tells what it is made of, and one proof that the earth is a child of the sun is in the fact that the same elements are found in the substance of both. Of the seventy elements, the most important are these: Oxygen, silicon, aluminum, iron, manganese, calcium, magnesium, potassium, sodium, carbon, hydrogen, phosphorus, sulphur, chlorine, nitrogen. Oxygen is the most plentiful and the most important element. One-fifth of the air we breathe is oxygen; one-third of the water we drink. The rock foundations of the earth are nearly one-half oxygen. No fire can burn, no plant or animal can grow, or even decay after it dies, unless oxygen is present and takes an active part in each process. Strangely enough, this wonderful element is invisible. We open a window, and pure air, rich in oxygen, comes in and takes the place of the bad air but we cannot see the change. Water we see, but if the oxygen and the hydrogen which compose the colourless liquid were separated, each would become at once an invisible gas. The oxygen of solid rocks exists only in combination with other elements. Silicon is the element which, united with oxygen, makes the rock called quartz. On the seashore the children are busy with their pails and shovels digging in the white, clean sand. These grains are of quartz,—fine crystals of a rock which forms nearly three-quarters of the solid earth's substance. Not only in rocks, but out here in the garden, the soil is full of particles of sand. You cannot get away from it. Aluminum is a light, bluish-white metal which we know best in expensive cooking utensils. It is more abundant even than iron, but processes of extracting it from the clay are still expensive. It is oftenest found in combination with oxygen and silicon. While nearly one-tenth of the earth's crust is composed of the metal aluminum, four-fifths and more is composed of the minerals called silicates of aluminum—oxygen, silicon, and aluminum in various combinations. It is more plentiful than any other substance in rocks and in the clays and ordinary soils, which are the finely ground particles of rock material. Iron is one of the commonest of elements. We know it by its red colour. A rusty nail is covered with oxide of iron, a combination which is readily formed wherever iron is exposed to the action of water or air. You have seen yellowish or red streaks in clefts of the rocks. This shows where water has dissolved out the iron and formed the oxide. The red colour of New Jersey soil is due to the iron it contains. Indeed, the whole earth's crust is rich in iron which the water easily dissolves. The roots of plants take up quantities of iron in solution and this mounts to the blossoms, leaves, and fruit. The red or yellow colour of autumn leaves, of apples, of strawberries, of tulips, and of roses, is produced by iron. The rosy cheeks of children are due to iron in the food they eat and in the water they drink. The doctor but follows the suggestion of nature when he gives a pale and listless person a tonic of iron to make his blood red. Iron is rarely found free, but it forms about five per cent. of the crust of the earth, and it is believed to form at least one- fifth of the unknown centre of the earth, the bulk of the globe, the weight of which we know, but concerning the substance of which we can say little that is positive. Manganese is not a conspicuous element, but is found united with oxygen in purplish or black streaks on the sides of rocks. It is somewhat like iron, but much less common. [Pg 15] [Pg 16] [Pg 17] [Pg 18] Calcium is the element that is the foundation of limestones. The skeletons and shells of animals are made of calcite, a common mineral formed by the uniting of carbon, oxygen, and calcium. Marbles are, perhaps, the most permanent form of the limestone rocks. "Hard" water has filtered through rocks containing calcite, and absorbed particles of this mineral. From water thus impregnated, all animal life on the earth obtains its bone-building and shell-building materials. Carbon forms a large part of the tissues of plants and animals, and in the remains of these it is chiefly found in the earth's crust. When these burn or decay, the carbon remains as charcoal or escapes to the air in union with oxygen as the well known carbonic acid gas. This is one of the most important foods of plants. Joined with calcium it forms the mineral calcite, or carbonate of lime. Hydrogen is one of the two gases that unite to form water. Oxygen is the other. Many kinds of rock contain a considerable amount of water. Surface water sinks into porous soils and rocks, and accumulates in pockets and veins which feed springs, and are the reserve water supply that keeps our rivers flowing, even through dry weather. More water is held by absorption in the earth's solid crust than in all the oceans and seas and great lakes. Hydrogen, combined with carbon, occurs in solid rocks where the remains of plants and animals have slowly decayed. From such processes the so-called hydrocarbons, rock oil and natural gas, have accumulated. When such decay goes on above ground, these valuable products escape into the air. Marsh gas, whose feeble flame above decaying vegetation is the will-o'-the-wisp of swamps, is an example. Magnesium, potassium, and sodium are found in equal quantities in the earth's crust, but never free. In union with chlorine, each forms a soluble salt, and is thus found in water. Common salt, chloride of sodium, is the most abundant of these. Water dissolves salt out of the rocks, and carries it into the sea. Clouds that rise by the evaporation of ocean water leave the salt behind, hence the seas are becoming more and more salty, for the rivers carry salt to the oceans, which hold fast all they get. Phosphorus is an element found united with oxygen in the tissues of both plants and animals. It is most abundant in bones. Rocks containing fossil bones are rich in lime phosphates, which are important commercial fertilizers for enriching the soil. Beds of these rocks are found and mined in South Carolina and elsewhere. Sulphur is well known as a yellow powder found most plentifully in rocks that are near volcanoes. It is a needed element in plant and animal bodies. It occurs in rocks, united with many different elements. In union with oxygen and a metal it forms the group of minerals called sulphates. In union with iron it forms sulphide of iron. The "fool's gold" which Captain John Smith's colonists found in the sand at Jamestown, was this worthless iron pyrites. Chlorine is a greenish, yellow gas, very heavy, and dangerous to inhale. If it gets into the lungs, it settles into the lowest levels, and one must stand on one's head to get it out. As an element of the earth's crust it is not very plentiful, but it is a part of all the chlorides of sodium, magnesium, and potassium. In salt, it forms two per cent. of the sea water. It is much less abundant in the rocks. To these elements we might add nitrogen, that invisible gas which forms nearly four-fifths of our atmosphere, and is a most important element of plant food in the soil. Most of the seventy elements are very rare. Many are metals, like gold and iron and silver. Some are not metals. Some are solid. A few are liquid, like the metal mercury, and several are gaseous. Some are free and pure, and show no disposition to unite with others. Nuggets of gold are examples of this. Some exist only in union with other elements. This is the common rule among the elements. Changes are constantly going on. The elements are constantly abandoning old partnerships and forming new ones. Growth and decay of plant and animal life are but parts of the great programme of constant change which is going on and has been in progress since the world began. THE FIRST DRY LAND When the earth's crust first formed it was still hot, though not so hot as when it was a mass of melted, glowing substance. As it moved through the cold spaces of the sky, it lost more heat and its crust became thicker. At length the cloud masses became condensed enough to fall in torrents of water, and a great sea covered all the land. This was before any living thing, plant or animal, existed on our planet. Can you imagine the continents and islands that form the land part of a map or globe suddenly overwhelmed by the oceans, the names and boundaries of which you have taken such pains to learn in the study of geography? The globe would be one blank of blue water, and geography would be abolished—and there would be nobody to study it. Possibly the fishes in the sea might not notice any change in the course of their lives, except when they swam among the ruins of buried cities and peered into the windows of high buildings, or wondered what new kind of seaweed it was when they came upon a submerged forest. In that old time of the great sea that covered the globe, we are told that there was a dense atmosphere over the face of the deep. So things were shaping themselves for the far-off time when life should exist, not only in the sea, where the first life did appear, but on land. But it took millions of years to fit the earth for living things. The cooling of the earth made it shrink, and the crust began to be folded into gentle curves, as the skin of a shrunken [Pg 19] [Pg 20] [Pg 21] [Pg 22] [Pg 23] apple becomes wrinkled on the flesh. Some of these creases merely changed the depth of water on the sea bottom; but one ridge was lifted above the water. The water parted and streamed down its sloping sides, and a granite reef, which shone in the sunshine, became the first dry land. It lay east and west, and stretched for many miles. It is still dry land and is a part of our own continent. Now it is but a small part of the country, but it is known by geologists, who can tell its boundaries, though newer land joins it on every side. It is named the Laurentian Hills, on geological maps. Its southern border reaches along the northern boundary of the Great Lakes to the head-waters of the Mississippi River. From this base, two ridges are lifted, forming a colossal V. One extends northeast to Nova Scotia; the other northwest to the Arctic seas. The V encloses Hudson Bay. Besides this first elongated island of bare rocks, land appeared in a strip where now the Blue Ridge Mountains stretch from New England to Georgia. The other side of the continent lifted up two folds of the crust above sea level. They are the main ridges of the Colorado and the Wasatch Mountains. Possibly the main ridge of the Sierra Nevada rose also at this time. The Ozark group of mountains, too, showed as a few island peaks above the sea. These first rocks were rapidly eaten away, for the atmosphere was not like ours, but heavily charged with destructive gases, which did more, we believe, to disintegrate the exposed rock surfaces than did the two other forces, wind and water, combined. The sediment washed down to the sea by rains, accumulated along the shores, filling the shallows and thus adding to the width of the land areas. The ancient granite ridge of the Laurentian Hills is now low, and slopes gently. This is true of all very old mountains. The newer ones are high and steep. It takes time to grind down the peaks and carry off the waste material loosened by erosion. Far more material than could have been washed down the slopes of the first land ridges came directly from the interior of the earth, and spread out in vast, submarine layers upon the early crust. Volcanic craters opened under water, and poured out liquid mineral matter, that flowed over the sea bottom before it cooled. Imagine the commotion that agitated the water as these submerged chimneys blew off their lids, and discharged their fiery contents! It was long before the sea was cool enough to be the home of living things. The layers of rock that formed under the sea during this period of the earth's history are of enormous thickness. They were four or five miles deep along the Laurentian Hills. They broadened the original granite ridge by filling the sea bottom along the shores. The backbones of the Appalachian system and the Cordilleras were built up in the same way —the oldest rocks were worn away, and their débris built up newer ones in strata. When these layers of rock became dry land, the earth's crust was much more stable and cool than it had ever been before. The vast rock-building of that era equals all that has been done since. The layers of rocks formed since then do not equal the total thickness of these first strata. So we believe that the time required to build those Archæan rock foundations equals or surpasses the vast period that has elapsed since the Archæan strata were formed. The northern part of North America has grown around those old granite ridges by the gradual rising of the shores. The geologist may walk along the Laurentian Hills, that parted the waters into a northern and a southern ocean. He crosses the rocky beds deposited upon the granite; then the successive beds formed as the land rose and the ocean receded. Age after age is recorded in the rocks. Gradually the sea is crowded back, and the land masses, east, west, and north, meet to form the continent. Nowhere on the earth are the steps of continental growth shown in unbroken sequence as they are in North America. How long ago did those first islands appear above the sea? Nobody ventures a definite answer to this question. No one has the means of knowing. But those who know most about it estimate that at the least one hundred million years have passed since then—one hundred thousand thousand years! A STUDY OF GRANITE In Every village cemetery it is easy to find shafts of gray or speckled granite, the polished surfaces of which show that the granite is made of small bits of different coloured minerals, cemented together into solid rock. Outside the gate you will usually find a place where monuments and gravestones may be bought. Here there is usually a stonecutter chipping away on a block with his graving tools. He is a man worth knowing, and because his work is rather monotonous he will probably be glad to talk to a chance visitor and answer questions about the different kinds of stone on which he works. There are bits of granite lying about on the ground. If you have a hand-glass of low power, such as the botany class uses to examine the parts of flowers, it will be interesting to look through it and see the magnified surface of a flake of broken granite. Here are bits of glassy quartz, clear and sparkling in the sun. Black and white may be all the colours you make out in this specimen, or it may be that you see specks of pink, dark green, gray, and smoky brown, all cemented together with no spaces that are not filled. The particles of quartz are of various colours, and are very hard. They scratch glass, and you cannot scratch them with the steel point of your knife, as you can scratch the other minerals associated with the grains of quartz. Granite is made of quartz, feldspar, and mica, sometimes with added particles of hornblende. Feldspar particles have as [Pg 24] [Pg 25] [Pg 26] [Pg 27] [Pg 28] wide a range of colour as quartz, but it is easy to tell the two apart. A knife will scratch feldspar, as it is not so hard as quartz. The crystals of feldspar have smooth faces, while quartz breaks with a rough surface as glass does. Feldspar loses its glassy lustre when exposed to the weather, and becomes dull, with the soft lustre of pearl. Mica may be clear and glassy, and it ranges in colour from transparency through various shades of brown to black. It has the peculiarity of splitting into thin, leaf-like, flexible sheets, so it is easy to find out which particles in a piece of granite are mica. One has only to use one's pocket knife with a little care. Hornblende is a dark mineral which contains considerable iron. It is found in lavas and granites, where it easily decays by the rusting of the iron. It is not unusual to see a rough granite boulder streaked with dark red rust from this cause. The crumbling of granite is constantly going on as a result of the exposure of its four mineral elements to the air. Quartz is the most stable and resistant to weathering. Soil water trickling over a granite cliff has little effect on the quartz particles; but it dissolves out some of the silicon. The bits of feldspar are even more resistant to water than quartz is, but the air causes them to decay rapidly, and finally to fall away in a sort of mealy clay. Mica, like feldspar, decays easily. Its substance is dissolved by water and carried away to become a kind of clay. The hornblende rusts away chiefly under the influence of moist air and trickling water. We think of granite as a firm, imperishable kind of rock, and use it in great buildings like churches and cathedrals that are to stand for centuries. But the faces that are exposed to the air suffer, especially in regions having a moist climate. The signs of decay are plainly visible on the outer surfaces of these stones. Fortunate it is that the weathering process cannot go very deep. The glassy polish on a smooth granite shaft is the silicon which acts as a cement to bind all the particles together. It is resistant to the weather. A polished shaft will last longer than an unpolished one. Granites differ in colouring because the minerals that compose them, the feldspars, quartzes, micas, and hornblendes, have each so wide a range of colour. Again, the proportions of the different mineral elements vary greatly in different granites. A banded granite the colours of which give it a stratified appearance is called a gneiss. We have spoken before of the seventy elements found in the earth's crust. A mineral is a union of two or more of these different elements; and we have found four minerals composing our granite rock. It may be interesting to go back and inquire what elements compose these four minerals. Quartz is made of silicon and oxygen. Feldspar is made of silicon, oxygen, and aluminum. Mica is made of silicon, oxygen, and carbon, with some mingling of potassium and iron and other elements in differing proportions. Hornblende is made of silicon, oxygen, carbon, and iron. The crumbling of a granite rock separates the minerals that compose it, reducing some to the condition of clay, others to grains of sand. Some of the elements let go their union and become free to form new unions. Water and wind gather up the fragments of crumbling granite and carry them away. The feldspar and mica fragments form clay; the quartz fragments, sand. All of the sandstones and slates, the sand-banks and sand beaches, are made out of crumbled granite, the rocky foundations of the earth. METAMORPHIC ROCKS In the dawn of life on the earth, soft-bodied creatures, lowest in the scale of being, inhabited the sea. The ancient volcanoes the subterranean eruptions of which had spread layers of mineral substance on the ocean floor, and heated the water to a high degree, had subsided. The ocean was sufficiently cool to maintain life. The land was being worn down, and its débris washed into the ocean. The first sand-banks were accumulating along sandy shores. The finer sediment was carried farther out and deposited as mud-banks. These were buried under later deposits, and finally, by the rising of the earth's crust, they became dry land. Time and pressure converted the sand-banks into sandstones; the mud-banks into clay. The remains of living creatures utterly disappeared, for they had no hard parts to be preserved as fossils. The shrinking of the earth's crust had crumpled into folds of the utmost complexity those horizontal layers of lava rock poured out on the ocean floor. Next, the same forces attacked the thick rock layers formed out of sediment—the aqueous or water-formed sandstones and clays. The core of the globe contracts, and the force that crumples the crust to fit the core generates heat. The alkaline water in the rocks joins with the heat produced by the crumpling and crushing forces, acting downward, and from the sides, to transform pure sandstone into glassy quartzite, and clay into slate. In other words, water-formed rocks are baked until they become fire-formed rocks. They are what the geologist calls metamorphic, which means changed. In many mountainous regions there are breaks through the strata of sandstone and slates and limestones, through which streams of lava have poured forth from the heated interior. Along the sides of these fissures the hot lava has changed all the rocks it touched. The heat of the volcanic rock matter has melted the silica in the sand, which has hardened again into a crystalline substance like glass. Have you ever visited a brick-yard? Here men are sifting clay dug out of a pit or the side of a hill, adding sand from a [Pg 29] [Pg 30] [Pg 31] [Pg 32] sand-bank, and in a big mixing box, stirring these two "dry ingredients" with water into a thick paste. This dough is moulded into bricks, sun-dried, and then baked in kilns themselves built of bricks. At the end of the baking, the soft, doughy clay block is transformed into a hard, glassy, or dull brick. From aqueous rock materials, fire has produced a metamorphic rock. Volcanic action is imitated in this common, simple process of brickmaking. Milwaukee brick is made of clay that has no iron in it. For this reason the bricks are yellow after baking. Most bricks are red, on account of the iron in the clay, which is converted into a red oxide, or rust, by water and heat. Common flower pots and the tiles used in draining wet land are not glazed, as hard-burned bricks are. The baking of these clay things is done with much less heat. They are left somewhat porous. But the tiles of roofs are baked harder, and get a surface glaze by the melting of the glassy particles of the sand. As bricks vary in colour and quality according to the materials that compose them, so the metamorphic rocks differ. The white sand one sees on many beaches is largely quartz. This is the substance of pure, white sandstone. Metamorphism melts the silica into a glassy liquid cement; the particles are bound close together on cooling. The rock becomes a white, granular quartzite, that looks like loaf sugar. If banded, it is called gneiss. Such rocks take a fine polish. Pure limestone is also white and granular. When metamorphosed by heat, it becomes white marble. The glassy cement that holds the particles of lime carbonate shows as the glaze of the polished surface. It is silica. One sees the same mineral on the face of polished granite. Clays are rarely pure. Kaolin is a white clay which, when baked, becomes porcelain. China-ware is artificially metamorphosed kaolin. In the early rocks the clay beds were transformed by heat into jasper and slates. In beds where clay mingled with sand, in layers, gneiss was formed. If mica is a prominent element, the metamorphic rock is easily parted into overlapping, scaly layers. It is a mica schist. If hornblende is the most abundant mineral, the same scaly structure shows in a dark rock called hornblende schist, rich in iron. A schist containing much magnesia is called serpentine. The bricks of the wall, the tiles on the roof, the flower pots on the window sill, and the dishes on the breakfast table, are examples of metamorphic rocks made by man's skill, by the use of fire and water acting on sand and clay. Pottery has preserved the record of civilization, from the making of the first crude utensils by cave men to the finest expression of decorative art in glass and porcelain. The choicest material of the builder and the sculptor is limestone baked by the fires under the earth's crust into marble. The most enduring of all the rocks are the foundation granite, and the metamorphic rocks that lie next to them. Over these lie thick layers of sedimentary rocks laid down by water. In them the record of life on the earth is written in fossils. THE AIR IN MOTION Most of the beautiful things that surround us and make our lives full of happiness appeal to one or more of our five senses. The green trees we can see, the bird songs we hear, the perfume of honey-laden flowers we smell, the velvety smoothness of a peach we feel, and its rich pulp we taste. But over all and through all the things we see and feel and hear and taste and smell, is the life-giving air, that lies like a blanket, miles in depth, upon the earth. The substance which makes the life of plants and animals possible is, when motionless, an invisible, tasteless, odourless substance, which makes no sound and is not perceptible to the touch. Air fills the porous substance of the earth's crust for a considerable distance, and even the water has so much air in it that fishes are able to breathe without coming to the surface. It is not a simple element, like gold, or carbon, or calcium, but is made up of several elements, chief among which are nitrogen and oxygen. Four-fifths of its bulk is nitrogen and one-fifth oxygen. There is present in air more or less of watery vapour and of carbon dioxide, the gas which results from the burning or decay of any substance. Although no more than one per cent. of the air that surrounds us is water, yet this is a most important element. It forms the clouds that bear water back from the ocean and scatter it in rain upon the thirsty land. Solid matter in the form of dust, and soot from chimneys, accumulates in the clouds and does a good work in condensing the moisture and causing it to fall. It is believed that the air reaches to a height of one hundred to two hundred miles above the earth's surface. If a globe six feet in diameter were furnished with an atmosphere proportionately as deep as ours, it would be about an inch in depth. At the level of the sea the air reaches its greatest density. Two miles above sea-level it is only two-thirds as dense. On the tops of high mountains, four or five miles above sea level, the air is so rarefied as to cause the blood to start from the nostrils and eyelids of explorers. The walls of the little blood-vessels are broken by the expansion of the air that is inside. At the sea-level air presses at the rate of fifteen pounds per square foot in all directions. As one ascends to higher levels, the air pressure becomes less and less. The barometer is the instrument by which the pressure of air is measured. A glass tube, closed at one end, and filled with mercury, the liquid metal often called quicksilver, is inverted in a cup of the same metal, and so supported that the [Pg 33] [Pg 34] [Pg 35] [Pg 36] [Pg 37] metal is free to flow between the two vessels. The pressure of air on the surface of the mercury in the cup is sufficient at the sea-level to sustain a column of mercury thirty inches high in the tube. As the instrument is carried up the side of a mountain the mercury falls in the tube. This is because the air pressure decreases the higher up we go. If we should descend into the shaft of the deepest mine that reaches below the sea level, the column of air supported by the mercury in the cup would be a mile higher, and for this reason its weight would be correspondingly greater. The mercury would thus be forced higher in the tube than the thirty-inch mark, which indicates sea-level. Another form of barometer often seen is a tube, the lower and open end of which forms a U-shaped curve. In this open end the downward pressure of the air rests upon the mercury and holds it up in the closed end, forcing it higher as the instrument is carried to loftier altitudes. At sea level a change of 900 feet in altitude makes a change of an inch in the height of the mercury in the column. The glass tube is marked with the fractions of inches, or of the metre if the metric system of measurements is used. It is a peculiarity of air to become heated when it is compressed, and cooled when it is allowed to expand again. It is also true that when the sun rises, the atmosphere is warmed by its rays. This is why the hottest part of the day is near noon when the sun's rays fall vertically. The earth absorbs a great deal of the sun's heat in the daytime and through the summer season. When it cools this heat is given off, thus warming the surrounding atmosphere. In the polar regions, north and south, the air is far below freezing point the year round. In the region of the Equator it rarely falls below 90 degrees, a temperature which we find very uncomfortable, especially when there is a good deal of moisture in the air. If we climb a mountain in Mexico, we leave the sultry valley, where the heat is almost unbearable, and very soon notice a change. For every three hundred feet of altitude we gain there is a fall of one degree in the temperature. Before we are half way up the slope we have left behind the tropical vegetation, and come into a temperate zone, where the plants are entirely different from those in the lower valley. As we climb, the vegetation becomes stunted, and the thermometer drops still lower. At last we come to the region of perpetual snow, where the climate is like that of the frozen north. So we see that the air becomes gradually colder as we go north or south from the Equator, and the same change is met as we rise higher and higher from the level of the sea. It is only when air is in motion that we can feel and hear it, and there are very few moments of the day, and days of the year, when there is not a breeze. On a still day fanning sets the air in motion, and creates a miniature breeze, the sound of which we hear in the swishing of the fan. The great blanket of air that covers the earth is in a state of almost constant disturbance, because of the lightness of warm air and the heaviness of cold air. These two different bodies are constantly changing places. For instance, the heated air at the Equator is constantly being crowded upward by cold air which settles to the level of the earth. Cold streams of air flow to the Tropics from north and south of the Equator, and push upward the air heated by the sun. This constant inrush of air from north and south forms a double belt of constant winds. If the earth stood still, no doubt the direction would be due north and due south for these winds; but the earth rotates rapidly from west to east upon its axis, carrying with it everything that is securely fastened to the surface: the trees, the houses, etc. But the air is not a part of the earth, not even so much as the seas, the waters of which must stay in their proper basins, and be whirled around with other fixed objects. The earth whirls so rapidly that the winds from north and south of the Equator lag behind, and thus take a constantly diagonal direction. Instead of due south the northern belt of cold air drifts south-west an...