The Strange Adventures of a Pebble

by Hallam Hawksworth

CHAPTER V

(MAY)

When April steps aside for May,

Like diamonds all the rain-drops glisten;

Fresh violets open every day;

To some new bird each hour we listen.

—Lucy Larcom.

THE FAIRYLAND OF CHANGE

What a wonderful world it is, this world of green fields and perfume and blossoms of pink and gold! Where did it come from? How did it get here out of the white winter? That bleak and barren winter that lay all around us everywhere only a few short weeks ago?

Just suppose we had never seen apple trees in bloom, as we are now seeing them everywhere, and somebody should show us a little brown seed, and a piece of bark, and a piece of root, and a green leaf, and a blossom, and an apple, and tell us they grew out of each other—were all made of the very same stuff.

Well, just as sure as anything, you wouldn't believe it. I wouldn't believe it. We simply couldn't! But we've had this sort of thing all around us ever since we can remember, and we've got so used to it we don't see anything wonderful about it. It is wonderful just the same. The Colossus of Rhodes, and Jupiter of Olympia, and the lighthouse of Alexandria, and all the other Seven Wonders of the World that people used to go so far to see, weren't anything to it.

And to this day, how it all comes about is as much of a mystery as ever. Yet Nature does it right before our eyes, and over and over and over again! Even I, old as I am, and as much as I know, I don't know how she does it, but I do know how it all started; how Nature first began to change one thing into another. It was when she began making marbles, granites, and other kinds of rock out of other kinds. That was ages before she changed little brown seeds into big trees with pink blossoms and red apples on them, or little brown cocoons into big golden butterflies, or anything like that.

I. In the Fairyland of Change

Ahem! Ahem! (Pebble coughing.)

I caught cold some several million years ago and I haven't got over it yet. That's why I'm a granite pebble instead of a slate pebble, or a sandstone pebble, or anything common. It's a part of the story of the fairyland of change, this cold of mine.

Ahem!

Would you mind getting me a lump of sugar? I don't want it for my cold—it never does that any good—but because a lump of sugar goes so well with this part of my story.

You notice the sugar lump is made up of little crystals, little building blocks just as I am, just as all granites are. And the crystals in the sugar and in the stone were made in the same way—by first heating and then cooling the material out of which they are made.

THE CRYSTAL FAIRIES IN THE SUGAR-BOWL]

When the earth's surface first cooled, the melted rock is supposed to have changed to granite. Melted rock, under the same conditions, does that to-day. So, for a while, granite must have been all the kind of rock there was. There was as yet no sandstone, no shells or bones to make limestone, no pebbles to help make conglomerate or "pudding stone," no ground-up rock and soil to make slate.

The rocks of the earth have been made over so many times that it is not probable that any of the granites now "living" (so to speak) are the same rocks that were made when the earth first cooled, but you can see that we have a right to say what I was careful to say when I introduced myself to you in the first chapter, that we belong to one of the very oldest families—we Granites.

Ahem!

There is a variety of rock—a crystallized rock—with bands all through it, called gneiss (say "nice"). Gneiss is made from all kinds of rock including, of course, conglomerate; that is to say "pudding stone"[16] warmed over.

[16] "Pudding stone" is a rock with pebbles all through it, like the plums in a Christmas pudding. Its book name is "conglomerate."

"And what they did not eat that night, the queen next morning fried!"

DOWN IN THE GREAT MELTING-POT

But how is old rock warmed over and made into new? You might easily guess that as the heart of the earth is melted rock the rock layers lying next to it would be melted, too, and so started on their way to becoming crystallized rock. Crystallization in rock takes place from the surface down, in the same way that maple syrup turns to sugar, as it does if allowed to stand undisturbed. So, as the central mass of rock is cooling from above toward the centre, we may suppose granite is still being formed away down there, miles under our feet.

But there are other ways in which rocks make their own heat—rocks far above this central molten heart of the world. One of these ways might remind you of how the mother hen gets her chickens to come out of the eggs, for rocks hatch out new rocks by sitting on one another!

THREE CHAPTERS IN THE STORY OF MARBLE

If you're ever in New York City up around 192d Street, you can read the three chapters in the life of a piece of marble right in the rocks themselves, for there you'll see this mass of rock with that granite dike pushing its way through. The rock on either side of the dike is limestone, and this limestone, owing to the heat of the lava which afterward hardened and became a "dike," is full of crystals; that is, began to turn to marble because of the heat. See how the lava crumpled the limestone as it pushed its way up into the original crack?

The pressure of the upper rocks generates heat in those beneath.

Then when these deeply buried rocks come up into the upper world as parts of mountain chains, and the covering of the softer rocks is, by the rivers and by weathering, worn away, we find the granite. The wrinkling of the rocks which makes mountains also creates immense pressure, and this is another great source of made-over rock. Such rock is found almost entirely in mountain regions. Some rocks, as shown in pebbles stretched out like a piece of gum, are heated by pressure without being crystallized. Often one of these stretched pebbles is the only thing in a crystallized rock that shows what kind of rock it was originally, all the finer material in it has been so changed. The deeper down in the earth the rocks are the more apt they are to be crystallized, because the rocks piled above them help to hold in the heat, just as thick blankets keep you warmest on a cold winter night.

KINDS OF "METAMORPHIC" ROCK

Rock of any kind may be changed to crystallized rock. Where the conditions are not favorable for crystallization the rock is made more solid, and material soaked out of the rocks above filters down into it. The lower layers of sandstone may become almost as solid as glass, and are then called "quartzite." Clay rocks are hardened into slate. Rocks changed in any of these ways are called "metamorphic" rock, from two Greek words meaning "to form over." But by "metamorphic" is usually meant rock that has been crystallized.

NICE HATCHING TEMPERATURE FOR ROCKS

I compared the hatching of new rocks to the hatching of new chickens, because it is done by the rocks sitting on one another. But chicken hatching and rock "hatching" are alike in still another way. The rocks need heat, but not too much heat. Too much heat melts them. It is only when they have cooled down a good deal that they begin to crystallize; and that, you see, wastes time.

A nice hatching temperature for rocks is between 500 and 1000 degrees Fahrenheit.

But we might also compare Mother Nature's way of changing rocks to the cooking that goes on in our kitchens. She uses not only heat, but water and other things, including salt and soda. Both the salt and some of the water in the rocks comes from—you'd hardly guess it—the seas! Not the seas of to-day, but the seas of yesterday, when these rocks were made. Then the pores were filled with water and the water has been kept shut in down there by the rocks above ever since.

From this sea water comes the salt. The salt in the water, when heated, helps to dissolve the rocks so that the different materials in them can separate and come together again in new ways, and so form new rocks. You know when you go to the lavatory to change your hands from dark to light what a lot of difference it makes whether the water is hot or cold and whether you use soap. The soap helps dissolve the dirt on your hands just as the salt helps dissolve the rocks.

The soda which Nature also uses is particularly good for dissolving rock that will hardly dissolve without it; silica, for instance, out of which are made the hardest of the sand grains, the sand in sandstone, the sharp, glassy edges of grass blades, and the blades of wheat, and the stalks of corn. Whenever there is a great deal of silica in rock you find soda mixed right with it. This, having the rocks already salted and mixed with soda before putting them in the oven, Mother Nature has always found so convenient!

ONE PEBBLE MAY PLAY MANY PARTS

I, in my time, may have been many kinds of rock. First, heaved up out of the sea by the earliest wrinkling of the cooling earth as granite; then weathered away into soil and carried by rivers to the sea, where I was remade the first time, maybe, as part of the "dough" in a pudding stone; then up again in an earth wrinkle and again back to sea, this time to be made into some one of the clay stones, and then back to granite again.

Anyhow here I am, a little freckled granite pebble talking myself red in the face because I've got so much to say, such wonderful things to tell, and only a few hundred pages to tell it in!

II. How Do They Know?

But, after all, how do they know that one rock changes into another? No one ever caught a rock doing this, did they?

Not quite, but almost. To explain, I must first tell you about the fossils that are found in stone. Haven't you often noticed in marble curious figures that reminded you of sea-shells? They were sea-shells but have been turned to stone, and things similarly changed while still keeping their original form are called "fossils."

When the plants and the shell creatures of the sea die they fall to the bottom, and mud and sand settles over them and closes them in, much as you shut leaves and flowers between the pages of a book. But while the book presses the leaves of flowers out of shape these bodies of the water-plants and shell creatures are slowly enclosed in a soft mass of mud that doesn't change their shapes at all. Then the particles that go to make up the soft bodies of these buried things are slowly dissolved away, and the minerals in the water and mud above them soak in and take their places. It's like passenger after passenger in a car getting up and other passengers taking the vacant places. Finally this mass of limey shells becomes buried deep under the sea, is turned to limestone, and when in course of time this part of the seashore rises—as we know shores have a way of doing—or is wrinkled up into a mountain, this limestone becomes a part of the face of the land.

From a photograph by the American Museum of Natural History

STORY OF THE LITTLE JEWEL-BOX

A kind of jewel-box? Yes, the kind geologists call a "geode." It began as a piece of limestone in which the underground waters had dissolved a cavity. But these waters had already, in solution, quartz which they had dissolved from quartz rock, and this quartz, deposited little by little in the cavity, formed into crystals. The quartz also made the surrounding walls more solid, so that when the mass of limestone containing this pocket was cut away by erosion this jewel-box remained, and, being rolled about in streams or by the lap and plunge of waves, it was rounded.

WOULDN'T WE SAY THE SAME THING?

Now suppose where some great granite rock stood up through layers of other kinds of rock—looking as if it had pushed itself through like the great granite boss on which Edinburgh Castle stands—you found that wherever this intruder touched the other rock that rock was crystallized. If we had just found all this out for ourselves, as the geology people found it, we would say, just as they said:

FATHER, GRANDFATHER, AND THE CHILDREN IN THE PORPHYRY FAMILY

In this piece of porphyry you see three generations, all living under one roof, as it were. Notice that six-sided crystal near the centre? Compare it with other good-sized crystals that haven't any distinctive shape. The reason for the difference is that the shapeless ones have had some of their substance taken away to form the smaller crystals. The dark mass is lava. In it the big crystals formed. Then, from most of the big crystals the lava reabsorbed material, and this material later turned into little crystals—the "grandchildren" of the three generations.

"I wonder what the granite did to the limestone and the other rocks around it to make them 'sugar,' or, as we say when speaking of rocks, 'crystallize'? Syrup sugars when it is heated and then cooled without stirring. I wonder if this intruding mass that is now granite didn't spout up, in melted form, from down in the earth, and heat the rocks on either side as it burst its way through. Then both this hot rock and its neighbors cooled and crystallized. That's it!"

SPLITTING MARBLE ROCKS IN THE QUARRY

This is a scene in a marble-quarry. The men are splitting up a 120-ton block. A writer in Scribner's Magazine, in which this illustration originally appeared, also describes the process. The wedges, carefully greased, are inserted in the drill-holes which, for a horizontal split, are neither close together nor very deep, as that is the natural plane of cleavage between the strata. Two men with sledges go down the line giving each wedge a blow—not too hard. Then two more men follow, and in go the wedges a little farther. You see it wouldn't do to rush matters, or you'd fracture the marble. The operation is so delicate, indeed, that the foreman himself gives the final blows. Then the marble cracks from hole to hole. For the vertical splits the holes, you notice, are closer together. They are also deeper.

In some places you find these granite masses in great bosses, or domelike rocks; elsewhere in long strips, like an iron bar thrust through other rocks; in still other places in great slabs between other rocks, like a warming pan pushed between the bed-sheets on a cold winter night; but everywhere it touches other rocks these neighbors are crystallized.

Now, coming back to our friends the fossils, we sometimes find limestone bordering one of these intrusive marble rocks with fossils in it, shading off into limestone containing the same kind of fossils. As you get closer to the granite mass the fossils in the marble gradually fade away until you come to marble in which there are no fossils at all.

So there we get the whole story of the life, not only of marble but of granite, and what happened to them in "The Fairyland of Change" and how it happened:

Chapter I.—The limestone was made in the sea and the shell creatures helped to make it.

Chapter II.—Hot melted rock from the inside of the earth broke its way up through these limestone beds.

Chapter III.—Then, as the melted rock cooled, it changed to granite, and the limestone on either side, being first heated and then cooled, crystallized and changed to marble.

Men of science have still other ways of working out this problem as to whether and how and why one kind of rock changes into another.

"But," we might say, "aren't they satisfied? We are. It's all plain enough to us now that one kind of rock does change into another. Then why do these geologist people go on getting more evidence when they've already got enough? It's like a boy learning two lessons when he only has to recite in one; and whoever heard of such a thing!"

THESE BOYS JUST LOVE TO STUDY

The answer is that this "going on" is one of the many delights of study, particularly in Nature's books, when once you get the habit.

From a photograph by Frith & Co., Ltd., Reigate

THE MARBLE ROCKS AT JABALPUR

The gorge of the "Marble Rocks," near Jabalpur, India, is a mile long and of an unearthly beauty of which even this little picture will give you some idea. The walls gleam white and golden in the sun. They are not really marble but limestone, which, as you will learn in this chapter, is the stone that becomes marble in "the fairyland of change." It looks as if nature had begun the making of marble columns in those cliffs, doesn't it? This is because the cliff is cut up by joints. You can also make out in one of the "pillars" the strata, or horizontal divisions of the rock, as it was laid down in the sea.

Among other things, the scientists search the pockets of the rocks, so to speak, for further evidence as to whether one kind changes into another. Chemistry is a great help in doing this, and, of course, the microscope. They find in this way that rocks that are full of crystals, such as granite and marble, and that look so different from the rocks that are not crystallized—such as limestone and sandstone—have in them the very same substances—silica, lime, potash, iron, and so on.

And again they put the oysters on the witness stand. (You remember how, long ago, oysters helped tell that mountains were once a part of the sea bottom.) They put a piece of limestone in a certain acid, and it bubbles and gives off a certain kind of gas. Then they do the same thing to an oyster-shell, and it gives out the same kind of gas. Then they try it on a piece of marble and out comes that very gas again! So all three—the limestone, the oyster-shell, and the marble—must be pretty close relations. Marble is just oyster and other shells warmed up and then allowed to cool.

But they don't stop here—these students of the rocks. It isn't enough that all these facts point to one conclusion. They want to actually try it out. So what do they do but change chalk—which is a kind of very soft limestone—into marble in the laboratory? This they do by heating the chalk and then cooling it under immense pressure.

III. The Fairies of the Fairyland of Change

If there really are fairies in this deep-down fairyland of change—and surely there must be—I should say they were the very same fairies we find in a lump of sugar—the crystals. For it is when these crystals take different shapes—the very thing fairies are always doing, you know—that things change into something else, so different you can hardly believe it. One could easily believe that charcoal and coal are related, they look so much alike in the face; but who would say that a piece of charcoal and a diamond were made of the very same stuff? They are. But diamonds are made of crystals and charcoal is not; and that must be it. The carbon of the charcoal was never touched by the wand of the Crystal Fairy.

SIX MEMBERS OF THE CRYSTAL FAMILY

Introducing six interesting members of the crystal family. The crystals of common salt and of gold, among others, take the form shown at A. Alum and diamonds crystallize as shown at C; while B and F belong to a system of crystals which we find built up into ice and arsenic. D and E are building-blocks for green vitriol, borax, and sulphate of soda.

A strange thing is that big crystals are always made up of little crystals. So what looks like one crystal is really a United States of crystals, all like each other and each like all of them put together, much as our federal government repeats the form of the State governments, and the State governments duplicate the government at Washington on a smaller scale.

THE SAND GRAINS AND THE CRYSTAL FAIRIES

The crystal fairies often give battered sand grains a new lease of life and these pictures show how they do it. Fig. "a" is a single sand grain which has grown into crystal form; "b" shows parallel growths about a grain; "c" is a group of neighboring grains that have crowded each other so in their growth that the crystal facets have been destroyed. Sounds odd to speak of sand grains "growing," doesn't it? But they do!

But why do the little crystals always come together in just such a way as to make big crystals shaped exactly like themselves?

Goodness knows!

But whatever the how and the why of it may be, not only do the crystal people stick as closely to the family pattern in dress as the Scotch Highlanders do to the plaids of their clans, but the crystals are clannish in another way. When a clay rock, for example, is dissolved by the heat, moisture, and chemicals down in the land of change, the particles of the same kind that are scattered through it hunt each other out, and ever after cling together, like Emmy Lou and her "nintimate friends." You've noticed how "spotty" granite is, haven't you? This is because it is made up of different kinds of minerals; but, although the crystals in all follow the granite pattern, the particles of each kind of mineral "flock together." The feldspars and the micas never mix.

JUST TRY IT WITH A PIECE OF PAPER

Now take a piece of writing paper and roll it into a tube and I'll show you something else. Stand the roll up between your two hands and press down on the top. It takes a good deal of pressure to bend or break it, doesn't it? Now lay it on its side and squeeze. It breaks right away.

But how should the crystals in a piece of granite know that a column of anything will stand so much more weight when the pressure comes on the ends than when it comes on the sides? They seem to know; for I'll tell you what they do, away down there in the dark of the earth. The crystals stand at right angles to the pressure on the rock in which they are forming. Sometimes, because of the movements of the earth as it shrinks and cracks, the crystals already formed in granite are crushed over on their sides. Then, in course of time, they form again, but this time they stand upright, with their "heads and shoulders" against the burden—little Atlases supporting the world! And they not only manage to get up and stand up straight when re-formed under pressure, but they stand closer together than they did before; they close up ranks, like soldiers with serious business before them.

A crystal is made up of molecules, that is to say, little parts of itself. You can't see a molecule; you just have to think it. Each different thing in the world—as salt and sugar, boys and bumble-bees, little girls and butterflies—is made up of its own kind of molecules or little parts of itself. In order to grasp the idea of certain scientific facts, the men of science thought of the molecules themselves as being made of little bits of themselves, which the scientists called "atoms." Now they find that it is necessary—in order to work out still further their ideas of how things are made and done and changed, in this wonderful mystery we call the world—to imagine these atoms as made up of what they call "electrons." You mustn't think, however, that this is all mere fancy. We can, of course, think of anything as made up of small particles or parts of itself which we can call "molecules," and that these molecules are made of still smaller parts which we can call "atoms." But there is reason to believe that while each different kind of thing is made of its own kind of molecules and their atoms, all the atoms are made of the same thing—electrons or little bits of electricity. For reasons which need not be gone into here, it is known that electrons actually exist. These electrons are so much smaller than an atom that there is as much room for them to move around in an atom as there is for the planets to move around the sun.

And they do move—travelling round and round. There are, even in so small a thing as a grain of sand, untold numbers of these circling worlds; systems like the sun with its planets and other vast star systems of the sky.

And that, it is thought, may be one of the secrets of the continual change of things; clay rock changing to granite, granite to soil, soil to fruit, fruit to children, and so on—everything on the move and the electrons doing the moving—carrying the changes, so to speak—these wonderful little myriad messenger boys of the universe!

HIDE AND SEEK IN THE LIBRARY

Don't imagine, for all I've talked so long about them, that I've told you everything there is to know about the crystal fairies. For example, did you know that if it wasn't for the crystal people we wouldn't have any ice? (Ice.)

You will also find that if it wasn't for ice—ice and the Greeks—we wouldn't have the word "crystal" at all. (Crystal.)

One of the most striking things in the whole conduct of these clever crystal folks you will find in reading about ice. If it wasn't for a peculiar—a very peculiar—habit the ice crystals have, all the waters of the world that ever freeze at all, would freeze solid to the bottom and never would thaw out!

I'll tell you this much about it:

While everything else in the world—including boys and girls—contracts when it gets cold, ice expands, and so becomes lighter than water, and so floats.

And yet the ice crystals know how to contract as well as expand, and that's why ice sometimes builds stone walls, as we will see when we come to study "The Stones of the Field" in July.

Shaking still water that is cold enough to freeze but hasn't frozen makes the crystal fairies get very busy in their ice factories. And it looks very much as if the fairies themselves warmed up with their work; for, after this shaking, the temperature of the water rises ten degrees at the very same time it is freezing!

You will also find that when the weather is cold enough ice itself freezes, gets harder and harder with the cold; that ice will melt ice; that two blocks of ice will grow into one if you give them a chance; that ice crystals are apt to be born twins; that these twin crystals are fond of gardening—at least, they raise "ice flowers"; that the ice crystals are so punctual in their coming and going in water that they are used to help place the markings on thermometers just right, so that we can tell exactly how cold or hot we are.

All this just about the crystals of the ice, but the work of the crystal people in making snowflakes is even more wonderful. In the bound volumes of St. Nicholas for March, 1882, in your Public Library you will find a most interesting account of a man in Vermont who began studying snowflakes and taking their pictures when he was a boy. He's known all over the world as the great authority on snowflakes. In the Encyclopedia Americana you will find a long article by him in which he tells the many interesting things he has learned about the ways of the fairies of the snow And how many pictures do you suppose he has in his snowflake gallery now? Over a thousand, and no two alike!

Just to think! Some of these wonderful little people of the fairyland of change sit at the table with us at every meal—the sugar crystals. And they are among the most interesting members of the family. Under the word Sugar you will find that the sugar crystals themselves eat and grow. But what do you suppose they eat? Not sugar. (You may easily guess, however, they have a sweet tooth.)

Yes, and at their home table, before they come to your home table, they have their regular meals, and they are not allowed a second helping until they have eaten the first!

Answers to Conundrums in H. & S. No. 4

The east and west rivers in California were there before the mountains rose and so cut their way through; while the north and south rivers between the ranges owe their origin to the mountains themselves.

The big twin river referred to is the Euphrates.

The greatest falls in the world are the Victoria Falls on the Zambesi.