Chapter VI: Part I: The Earth (5)

Every green plant we see spreads its leaves to the sun. Every stick of wood we burn, and every lump of coal, is giving back, in the form of light and heat, the energy that came from sunshine and was captured by the green leaves. How long the wood has held this store of heat we may easily compute, for we can read the age of a tree. But the age of coal we cannot accurately state. The years probably should be counted by millions, instead of thousands.

The great inland sea that covered the middle portion of the continent during the Silurian and the Devonian periods, became shallow by the deposit of vast quantities of sediment. Along the lines of the deposits of greatest thickness, a crumpling of the earth's crust lifted the first fold of the Alleghany Mountains as a great sea wall on the east, and on the western shore another formed the beginning of the Ozark Mountain system in Missouri. An island was lifted out of the sea, forming the elevated ground on which the city of Cincinnati now stands. Various other ridges and islands divided the ancient sea into much smaller bodies of water. Hemmed in by land these shallow sea-basins gradually changed into fresh-water lakes, for they no longer had connection with the ocean, and all the water they received came from rain. After centuries of freshets, and of filling in with the rock debris brought by the streams, they became great marshes, in which grew water-loving plants. Generation after generation of these plants died, and their remains, submerged by the water, were converted into peat. In the course of ages this peat became coal. This is the history of the coal measures.

There is no guesswork here. The stems of plants do not lose their microscopic structure in all the ages it has taken to transform them to coal. A thin section of coal shows under a magnifier the structure of the stems of the coal-forming plants. Moreover, the veins of coal preserve above or below them, in shales that were once deposits of mud, the branching trunks of trees, perfectly fossilized. There are no better proofs of the vegetable origin of coal than the lumps themselves. But they are plain to the naked eye, while the coal tells its story to the man with the microscope.

The fossil remains of the plants that flourished when coal was forming are gigantic, compared with plants of the same families now living. We must conclude that the climate was tropical, the air very heavy with moisture, and charged much more heavily than it is now with carbonic acid gas.

These conditions produced, in rapid succession, forests of tree ferns and horsetails and giant club mosses. These are the three types of plants out of which the coal was made. They were all rich in resin, which makes the coal burn readily. The ferns had stems as large as tree trunks. Some have been found that are eighteen inches in diameter. We know they are ferns, because the leaves are found with their fruits attached to them in the manner of present-day ferns. The stems show the well known scar by which fern leaves are joined. And the wood of these fossil fern stems is tubular in structure, just as the wood of living ferns is to-day.

Among the ferns which dominated these old marsh forests grew one kind, the scaly leaves of which covered the stems and bore their fruits on the branching tips. These giants, some of them with trunks four feet in diameter, belong to the same group of plants as our creeping club mosses, but in the ancient days they stood up among the other ferns as trees forty or fifty feet high.

The giant scouring rushes, or horsetails, had the same general characteristics as the little reed-like plants we know by those names to-day.

The highest plants of the coal period were leafy trees with nut-like fruits, that resemble the yew trees of the present. These gigantic trees were the first conifers upon the earth. They foreshadowed the pines and the other cone-bearing evergreens. Their leaves were broad and their fruits nut-like. The Japanese ginkgo, or maidenhair fern tree, is an old-fashioned conifer somewhat like those first examples of this family. Trunks sixty to seventy feet long, crowned with broad leaves and a spike of fruit, have been found lying in the upper layers of the coal-seams, and in sandstone strata that lie between the strata of coal. Peculiar circular discs, which the microscope reveals along the sides of the wood fibres of these fossil trees, prove the wood structure to be like that of modern conifers.

Generation after generation of forests lived and died in the vast spreading swamps of this era. The land sank, and freshets came here and there, drowning out all plant life, and covering the layers of peat with beds of sand or mud. When the water went down, other forests took possession, and a new coal-bed was started. It is plainly seen that flooding often put an end to coal formation. Fifteen seams of coal, one above another, is the greatest number that have been found. The veins vary from one inch to forty feet in thickness. These are separated by layers of sandstone or shale, which accumulated as sediment, covering the stumps of dead tree ferns and other growths, and preserving them as fossils to tell the story of those bygone ages as plainly as any other record could have done.

Fresh-water animals succeeded those of salt water in the swamps that formed the coal measures. Overhead, the first insects flitted among the branches of the tree ferns. Dragon-flies darted above the surface and dipped in water as they do to-day. Spiders, scorpions, and cockroaches, all air-breathing insects, were represented, but none of the higher, nectar-loving insects, like flies and bees and butterflies, were there. Flowering plants had not yet appeared on the earth. Snakelike amphibians, some fishlike, some lizard-like, and huge crocodilian forms appeared for the first time. These air-breathing swamp-dwellers could not have lived in salt water.

Fresh-water molluscs and land shells appear for the first time as fossils in the rocks of the coal measures. On the shores of the ocean, the rocks of this period show that trilobites, horseshoe crabs, and fishes still lived in vast numbers, and corals continued to form limestone. The old types of marine animals changed gradually, but the coal measures show strikingly different fossils. These rocks bear the first record of fresh-water and land animals.

THE MOST USEFUL METAL

It is fortunate for us all that, out of the half-dozen so-called useful metals, iron, which is the most useful of them all to the human race, should be also the most plentiful and the cheapest. Aluminum is abundant in the common clay and soil under our feet. But separating it is still an expensive process; so that this metal is not commercially so plentiful as iron is, nor is it cheap.

All we know of the earth's substance is based on studies of the superficial part of its crust, a mere film compared with the eight thousand miles of its diameter. Nobody knows what the core of the earth--the great globe under this surface film--is made of; but we know that it is of heavier material than the surface layer; and geologists believe that iron is an important element in the central mass of the globe.

One thing that makes this guess seem reasonable is the great abundance of iron in the earth's crust. Another thing is that meteors which fall on the earth out of the sky prove to be chiefly composed of iron. All of their other elements are ones which are found in our own rocks. If we believe that the earth itself is a fragment of the sun, thrown off in a heated condition and cooling as it flew through space, we may consider it a giant meteor, made of the substances we find in the chance meteor that strikes the earth.

Iron is found, not only in the soil, but in all plant and animal bodies that take their food from the soil. The red colour in fruits and flowers, and in the blood of the higher animals, is a form in which iron is familiar to us. It does more, perhaps, to make the world beautiful than any other mineral element known.

But long before these benefits were understood, iron was the backbone of civilization. It is so to-day. Iron, transformed by a simple process into steel, sustains the commercial supremacy of the great civilized nations of the world. The railroad train, the steel-armoured battleship, the great bridge, the towering sky-scraper, the keen-edged tool, the delicate mechanism of watches and a thousand other scientific instruments--all these things are possible to-day because iron was discovered and has been put to use.

It was probably one of the cave men, poking about in his fire among the rocks, who discovered a lump of molten metal which the heat had separated from the rest of the rocks. He examined this "clinker" after it cooled, and it interested him. It was a new discovery. It may have been he, or possibly his descendants, who learned that this metal could be pounded into other shapes, and freed by pounding from the pebbles and other impurities that clung to it when it cooled. The relics of iron-tipped spears and arrows show the skill and ingenuity of our early ancestors in making use of iron as a means of killing their prey. The earliest remains of this kind have probably been lost because the iron rusted away.

Man was pretty well along on the road to civilization before he learned where iron could be found in beds, and how it could be purified for his use. We now know that certain very minute plants, which live in quiet water, cause iron brought into that water to be precipitated, and to accumulate in the bottom of these boggy pools. In ancient days these bog deposits of iron often alternated with coal layers. Millions of years have passed since these two useful substances were laid down. To-day the coal is dug, along with the bog iron. The coal is burned to melt the iron ore and prepare it for use. It is a fortunate region that produces both coal and iron.

Bituminous coal is plentiful, and scattered all over the country, while anthracite is scarce. The cheapest iron is made in Alabama, which has its ore in rich deposits in hillsides, and coal measures close by, furnishing the raw material for coke. The result is that the region of Birmingham has become the centre of great wealth through the development of iron and coal mines.

Where water flows over limestone rock, and percolates through layers of this very common mineral, it causes the iron, gathered in these rock masses, to be deposited in pockets. All along the Appalachian Mountains the iron has been gathered in beds which are being mined. These beds of ore are usually mixed with clay and other earthy substances from which the metal can be separated only by melting. The ore is thrown into a furnace where the metal melts and trickles down, leaving behind the non-metallic impurities. It is drawn off and run into moulds, where it cools in the form of "pig" iron.

The first fuel used in the making of pig iron from the ore was charcoal. In America the early settlers had no difficulty in finding plenty of wood. Indeed, the forests were weeds that had to be cut down and burned to make room for fields of grain. The finding of iron ore always started a small industry in a colony. If there was a blacksmith, or any one else among the small company who understood working in iron, he was put in charge.

To make the charcoal, wood was cut and piled closely in a dome-shaped heap, which was tightly covered with sods, except for a small opening near the ground. In this a fire was built, and smothered, but kept going until all the wood within the oven was charred.

This fuel burned readily, with an intense heat, and without ashes. Sticks of charcoal have the form of the wood, and they are stiff enough to hold up the ore of iron so that it cannot crush out the fire. For a long time American iron was supplied by little smelters, scattered here and there. The workmen beat the melted metal on the forge, freeing it from impurities, and shaping the pure metal into useful articles. Sometimes they made it into steel, by a process learned in the Old World.

The American iron industry, which now is one of the greatest in the world, centres in Pittsburg, near which great deposits of iron and coal lie close together. The making of coke from coal has replaced the burning of charcoal for fuel. When the forests were cut away by lumbermen, the supply of charcoal threatened to give out, and experiments were made in charring coal, which resulted in the successful making of coke, a fuel made from coal by a process similar to the making of charcoal from wood. The story of the making of coke out of hard and soft coal is a long one, for it began as far back as the beginning of the nineteenth century.

In 1812 the first boat-load of anthracite coal was sent to Philadelphia from a little settlement along the Lehigh River. A mine had been opened, the owner of which believed that the black, shiny "rocks" would burn. His neighbours laughed at him, for they had tried building fires with them, and concluded that it could not be done. In Philadelphia, the owners of some coke furnaces gave the new fuel a trial, in spite of the disgust of the stokers, who thought they were putting out their fires with a pile of stones. After a little, however, the new fuel began to burn with the peculiar pale flame and intense heat that we know so well, and the stokers were convinced that here was a new fuel, with possibilities in it.

But it was hard for people to be patient with the slow starting of this hard coal. Not until 1840 did it come into general favour, following the discovery that if hot air was supplied at the draught, instead of cold, anthracite coal became a perfect fuel.

At Connellsville, Pennsylvania, a vein of coal was discovered which made coke of the very finest quality. Around this remarkable centre, coke ovens were built, and iron ore was shipped in, even from the rich beds of the Lake Superior country. But it was plain to see that Connellsville coal would become exhausted; and so experiments in coke-making from other coals were still made. When soft coal burns, a waxy tar oozes out of it, which tends to smother the fire. Early experiments with coal in melting iron ore indicated that soft coal was useless as a substitute for charcoal and coke; but later experiments proved that coke of fine quality can be made out of this bituminous soft coal, by drawing off the tar which makes the trouble. New processes were invented by which valuable gas and coal tar are taken out of bituminous coal, leaving, as a residue, coke that is equal in quality to that made from the Connellsville coal. Fortunes have been made out of the separation of the elements of the once despised soft coal. For the coke and each of its by-products, coal tar and coal gas, are commercial necessities of life.

The impurities absorbed by the melting iron ore include carbon, phosphorus, and silicon. Carbon is the chief cause of the brittleness of cast iron. The puddling furnace was invented to remove this trouble. The melted ore was stirred on a broad, basin-like hearth, with a long-handled puddling rake. The flames swept over the surface, burning the carbon liberated by the stirring. It was a hard, hot job for the man at the rake, but it produced forge iron, that could be shaped, hot or cold, on the anvil.

The next improvement was the process of pressing the hot iron between grooved rollers to rid it of slag and other foreign matters collected in the furnace. The old way was to hammer the metal free from such impurities. This was slow and hard work.

Iron was an expensive and scarce metal until the hot blast-furnace cheapened the process of smelting the ore. The puddling furnace and the grooved rollers did still more to bring it into general use. The railroads developed with the iron industry. Soon they required a metal stronger than iron. Steel was far too expensive, though it was just what was needed. Efforts were made to find a cheap way to change iron into steel. Sir Henry Bessemer solved the problem by inventing the Bessemer converter. It is a great closed retort, which is filled with melted pig iron. A draught admits air, and the carbon is all burned out. Then a definite amount of carbon, just the amount required to change iron into steel, is added, by throwing in bars of an alloy of carbon and manganese. The latter gives steel its toughness, and enables it to resist greater heat without crystallizing and thus losing its temper.

When the carbon has been put in, the retort is closed. The molten metal absorbs the alloy, and the product is Bessemer steel. In fifteen minutes pig iron can be transformed into ingot steel. The invention made possible the use of steel in the construction of bridges, high buildings, and ships. It made this age of the world the Age of Steel.

THE AGE OF REPTILES

Two big and interesting reptiles we see in the Zoo, the crocodile and its cousin, the alligator. In the everglades of Florida both are found. The crocodile of the Nile is protected by popular superstition, so it is in better luck than ours. The alligators have been killed off for their skins, and it is only a matter of time till these lumbering creatures will be found only in places where they are protected as the remnants of a vanished race. Giant reptiles of other kinds are few upon the earth now. The _boa constrictor_ is the giant among snakes. The great tropical turtles represent an allied group. Most of the turtles, lizards, and snakes are small, and in no sense dominant over other creatures.

The rocks that lie among the coal measures contain fossils of huge animals that lived in fresh water and on land, the ancestors of our frogs, toads, and salamanders, a group we call amphibians. Some of these animals had the form of snakes; some were fishlike, with scaly bodies; others were lizard-like or like huge crocodiles. These were the ancestors of the reptiles, which became the rulers of land and sea during the Mesozoic Era. The rocks that overlie the coal measures contain fossils of these gigantic animals.

Strange crocodile-like reptiles, with turtle-like beaks and tusks, but no teeth, left their skeletons in the mud of the shores they frequented. And others had teeth in groups--grinders, tearers, and cutters--like mammals. These had other traits like the old-fashioned, egg-laying mammals, the duck-billed platypus, for example, that is still found in Australia. Along with the remains of these creatures are found small pouched mammals, of the kangaroo kind, in the rocks of Europe and America. These land animals saw squatty cycads, and cone-bearing trees, the ancestors of our evergreens, growing in forests, and marshes covered with luxuriant growths of tree ferns and horsetails, the fallen bodies of which formed the recent coal that is now dug in Virginia and North Carolina. Ammonites, giant sea snails, with chambered shells that reached a yard and more in diameter, and gigantic squids, swam the seas. Sea urchins, starfish, and oysters were abundant. Insects flitted through the air, but no birds appeared among the trees or beasts in the jungles. Over all forms of living creatures reptiles ruled. They were remarkable in size and numbers. There were swimming, running, and flying forms.

Opalized wood from Utah]

Restoration of a carnivorous Dinosaur, Allosaurus, from the Upper Jurassic and Lower Cretaceous of Wyoming. When erect the animal was about 15 feet high]

The fish-reptile, _Ichthyosaurus_, was a hump-backed creature, thirty to forty feet long, with short neck, very large head, and long jaw, set with hundreds of pointed teeth. Its eye sockets were a foot across. The four short limbs were strong paddles, used for swimming. The long, slender tail ended in a flat fin. Perfect skeletons of this creature have been found. Its rival in the sea was the lizard-like _Plesiosaurus_, the small head of which was mounted on a long neck. The tail was short, but the paddles were long and powerful. No doubt this agile creature held its own, though somewhat smaller than the more massively built Ichthyosaurus.

The land reptiles called _Dinosaurs_ were the largest creatures that have ever walked the earth. In the American Museum of Natural History, in New York, the mounted skeleton of the giant Dinosaur fairly takes one's breath away. It is sixty-six feet long, and correspondingly large in every part, except its head. This massive creature was remarkably short of brains.

The strangest thing about the land reptiles is the fact that certain of them walked on their hind legs, like birds, and made three-toed tracks in the mud. Indeed, these fossil tracks, found in slate, were called bird tracks, until the bones of the reptile skeleton with the bird-like foot were discovered. Certain long grooves in the slate, hitherto unexplained, were made by the long tail that dragged in the mud.

When the mud dried, and was later covered with sediment of another kind, these prints were preserved, and when the bed of rock was discovered by quarrymen, the two kinds split apart, showing the record of the stroll of a giant along the river bank in bygone days.

The flying reptiles were still more bird-like in structure, though gigantic in size. Imagine the appearance of a great lizard with bat-like, webbed wings and bat-like, toothed jaws! The first feathered fossil bird was discovered in the limestone rock of Bavaria. It was a wonderfully preserved fossil, showing the feathers perfectly. Three fingers of each "hand" were free and clawed, so that the creature could seize its prey, and yet use its feathered wings in flight. The small head had jaws set with socketed teeth, like a reptile's, and the long, lizard tail of twenty-one bones had a pair of side feathers at each joint. This _Archeopteryx_ is the reptilian ancestor of birds. During this age of the world, one branch of the reptile group established the family line of birds. The bird-like reptiles are the connecting link between the two races. How much both birds and reptiles have changed from that ancient type, their common ancestor!

I have mentioned but a few of the types of animals that make the reptilian age the wonder of all time. One after another skeletons are unearthed and new species are found. The Connecticut River Valley, with its red sandstones and shales of the Mesozoic Era, is famous among geologists, because it preserves the tracks of reptiles, insects, and crustaceans. These signs tell much of the life that existed when these flakes of stone were sandy and muddy stretches Not many bones have been found, however. The thickness of these rocks is between one and two miles. The time required to accumulate so much sediment must have been very great.

Model of a three-horned Dinosaur, _Triceratops_, from Cretaceous of Montana. Animal in life about 25 feet long]

Mounting the forelegs of _Brontosaurus_, the aquatic Dinosaur]

It is not clear just what caused the race of giant reptiles to decline and pass away. The climate did not materially change. Perhaps races grow old, and ripe for death, after living long on the earth. It seems as if their time was up; and the clumsy giants abdicated their reign, leaving dominion over the sea, the air, and the land to those animals adapted to take the places they were obliged to vacate.

THE AGE OF MAMMALS

The warm-blooded birds and mammals followed the reptiles. This does not mean that all reptiles died, after having ruled the earth for thousands of years. It means that changes in climate and other life conditions were unfavourable to the giants of the cold-blooded races, and gradually they passed away. They are represented now on the earth by lesser reptiles, which live comfortably with the wild creatures of other tribes, but which in no sense rule in the brute creation. They live rather a lurking, cautious life, and have to hide from enemies, except a few more able kinds, provided with means of defense.

There were mammals on the earth in the days of reptilian supremacy, but they were small in size and numbers, and had to avoid any open conflict with the giant reptiles, or be worsted in a fight. Now the time came when the ruling power changed hands. The mammals had their turn at ruling the lower animals. It was the beginning of things as they are to-day, for mammals still rule. But many millions of years have probably stood between the age when this group of animals first began to swarm over the earth, and the time when Man came to be ruler over all created things.

Among the reptiles of the period when the sea, the land, and the air were swarming with these great creatures were certain kinds that had traits of mammals. Others were bird-like. From these reptilian ancestors birds and mammals have sprung. No one doubts this. The fossils prove it, step by step.

Yet the rocks surprise the geologist with the suddenness with which many new kinds of mammals appeared on the earth. Possibly the rocks containing the bones of so many kinds were fortunately located. The spots may have been morasses where migrating mammals were overwhelmed while passing. Possibly conditions favored the rapid development of new kinds, and the multiplication of their numbers. Warm, moist climate furnished abundant succulent plant food for the herbivors, and these in turn furnished prey for the carnivors.

The coal formed during the Tertiary Period gives added proof that the plant life was luxuriant. The kinds of trees that grew far north of our present warm zones have left in the rocks evidence in the form of perfect leaves and cones and other fruits. For instance, magnolias grew in Greenland, and palm trees in Dakota. The temperature of Greenland was thirty degrees warmer than it is now. Our Northern States lie in a belt that must have had a climate much like that of Florida now. Europe was correspondingly mild.

A special chapter tells of the gradual development of the horse. One hundred different kinds of mammals have been found in the Eocene rocks, many of which have representative species at the same time in Europe and America. The rocks of Asia probably have similar records.

The Eocene rocks, lowest of the Tertiary strata, contain remains of animals the families of which are now extinct. Next overlying the Eocene, the Miocene rocks have fossils of animals belonging to modern families--rhinoceroses, camels, deer, dogs, cats, horses--but the genera of which are now extinct. The Pliocene strata (above the Miocene) contains fossils of animals so closely related to the wild animals now on the earth as to belong to the same genera. They differ from modern kinds only in the species, as the red squirrel is a different species from the gray.

So the record in the rocks shows a gradual approach of the mammals to the kinds we know, a gradual passing of the mighty forms that ruled by size and strength, and the coming of forms with greater intelligence, adapted to the change to a colder climate.

It sometimes happens that a farmer, digging a well on the prairie, strikes the skeleton of a monster mammal, called the _mastodon_. This very thing happened on a neighbour's farm when I was a girl, in Iowa. Everybody was excited. The owner of the land dug out every bone, careful that the whole skeleton be found. As he expected, the director of a museum was glad to pay a high price for the bones.

Restoration of an aquatic Dinosaur, _Brontosaurus excelsus_, from the Upper Jurassic and Lower Cretaceous of Wyoming. The animal in life was over 60 feet long]

Restoration of the small carnivorous Dinosaur, _Ornitholestes hermanui_, catching a primitive bird _Archaeopteryx_. Upper Jurassic and Lower Cretaceous]

The mastodon was about the size of an elephant, with massive limbs, and large, heavy head that bore two stout, up-curved tusks of ivory. The creature moved in herds like the buffalo from swamp to swamp; and old age coming on, the individual, unable to keep up with the herd, sank to his death in the boggy ground. The peat accumulated over his bones, undisturbed until thousands of years elapse, and the chance digging of a well discovers his skeleton.

Frozen in the ice of northern Siberia, near the mouths of rivers, a number of mammoths have been found. These are creatures of the elephant family, and belonging to the extinct race that lived in the Quaternary Period, just succeeding the Tertiary. The ice overtook the specimens, and they have been in cold storage ever since. For this reason, both flesh and bones are preserved, a rare thing to happen, and rarer still to be seen by a scientist.

The ignorant natives made a business of watching the ice masses at the river mouth for dark spots that showed where a mammoth was encased in the ice. If an iceberg broke off near such a place, the sun might thaw the ice front of the glacier, until the hairy monster could at length be reached. His long hair served for many uses, and the wool that grew under the hair was used as a protection from the Arctic winter. The frozen flesh was eaten; the bones carved into useful tools; but the chief value of the find was in the great tusks of ivory, that curved forward and pointed over the huge shoulders. It was worth a fortune to get a pair and sell them to a buyer from St. Petersburg.

One of the finest museum specimens of the mammoth was secured by buying the tusks of the dealer, and by his aid tracing the location of the carcass, which was found still intact, except that dogs had eaten away part of one foreleg, bone and all. From this carefully preserved specimen, models have been made, exactly copying the shape and the size of the animal, its skin, hair, and other details.

The sabre-toothed tiger, the sharp tusks of which, six to eight inches long, made it a far more ferocious beast than any modern tiger of tropical jungles, was a Quaternary inhabitant of Europe and America. So was a smaller tiger, and a lion. The Irish elk, which stood eleven feet high, with antlers that spread ten feet apart at the tips, was monarch in the deer family, which had several different species on both continents. Wild horses and wild cattle, one or two of great size, roamed the woods, while rhinos and the hippopotamus kept near the water-courses. Hyenas skulked in the shadows, and acted as scavengers where the great beasts of prey had feasted. Sloths and cuirassed animals, like giant armadillos, lived in America. Among bears was one, the cave bear, larger than the grizzly. True monkeys climbed the trees. Flamingo, parrots, and tall secretary birds followed the giant _gastornis_, the ancestor of wading birds and ostriches, which stood ten feet high, but had wings as small and useless as the auk of later times.

With the entrance of the modern types of trees, came other flowering plants, and with them the insects that live on the nectar of flowers. Through a long line of primitive forms, now extinct, flowering plants and their insect friends conform to modern types. The record is written in the great stone book.

The Age of Mammals in America and Europe ended with the gradual rise of the continental areas, and a fall of temperature that ushered in the Ice Age. With the death of tropical vegetation, the giant mammals passed away.

THE HORSE AND HIS ANCESTORS

Every city has a horse market, where you may look over hundreds of animals and select one of any colour, size, or kind. The least in size and weight is the Shetland pony, which one man buys for his children to drive or ride. Another man wants a long-legged, deep-chested hunter. Another wants heavy draught-horses, with legs like great pillars under them, and thick, muscular necks--horses weighing nearly a ton apiece and able to draw the heaviest trucks. What a contrast between these slow but powerful animals and the graceful, prancing racer with legs like pipe-stems--fleet and agile, but not strong enough to draw a heavy load!

All these different breeds of horses have been developed since man succeeded in capturing the wild horse and making it help him. Man himself was still a savage, and he had to fight with wild beasts, as if he were one of them, until he discovered that he could conquer them by some power higher than physical strength. From this point on, human intelligence has been the power that rules the lower animals. Its gradual development is the story of the advance of civilization on the earth. Through unknown thousands of years it has gone on, and it is not yet finished.

Restoration of a Siberian mammoth, _Elephas primogenius_, pursued by men of the old stone age of Europe. Late Pleistocene epoch]

Restoration of a small four-toed ancestor of the horse family, _Eohippus venticolus_. Lower Eocene of Wyoming]

Just when and where and how our savage ancestors succeeded in taming the wild horse of the plains and the forests of Europe or Asia is unknown. Man first made friends with the wild sheep, which were probably more docile than wild oxen and horses. We can imagine cold and hungry men seeking shelter from storms in rocky hollows, where sheep were huddled. How warm the woolly coats of these animals felt to their human fellow-creatures crowded in with them in the dark!

It is believed that the primitive men who used stone axes as implements and weapons, learned to use horses to aid them in their hunting, and in their warfare with beasts and other men. Gradually these useful animals were adapted to different uses; and at length different breeds were evolved. Climate and food supply had much to do with the size and the character of the breeds. In the Shetland Islands the animals are naturally dwarfed by the cold, bleak winters, and the scant vegetation on which they subsist. In middle Europe, where the summers are long and the winters mild, vegetation is luxurious, and the early horses developed large frames and heavy muscles. The Shetland pony and the Percheron draught-horse are the two extremes of size.

What man has done in changing the types of horses is to emphasize natural differences. The offspring of the early heavy horses became heavier than their parents. The present draught-horse was produced, after many generations, all of which gradually approached the type desired. The slender racehorses, bred for speed and endurance rather than strength, are the offspring of generations of parents that had these qualities strongly marked. Hence came the English thoroughbred and the American trotter.

We can read in books the history of breeds of horses. Our knowledge of what horses were like in prehistoric times is scant. It is written in layers of rock that are not very deep, but are uncovered only here and there, and only now and then seen by eyes that can read the story told by fossil skeletons of horses of the ages long past.

Geologists have unearthed from time to time skeletons of horses. It was Professor Marsh who spent so much time in studying the wonderful beds of fossil mammals in the western part of this country, and found among them the skeletons of many species of horses that lived here with camels and elephants and rhinoceroses and tigers, long before the time of man's coming.

How can any one know that these bones belonged to a horse's skeleton? Because some of them are like the bones of a modern horse. It is an easy matter for a student of animal anatomy to distinguish a horse from a cow by its bones. The teeth and the foot are enough. These are important and distinguishing characters. It is by peculiarities in the formation of the bones of the foot that the different species of extinct horses are recognized by geologists.

Wild horses still exist in the wilds of Russia. Remains of the same species have been dug out of the soil and found in caves in rocky regions. Deeper in the earth are found the bones of horses differing from those now living. The bones of the foot indicate a different kind of horse--an unknown species. But in the main features, the skeleton is distinctly horse-like.

In rocks of deeper strata the fossil bones of other horses are found. They differ somewhat from those found in rocks nearer the surface of the earth, and still more from those of the modern horse. The older the rocks, the more the fossil horse differs from the modern. Could you think of a more interesting adventure than to find the oldest rocks that show the skeletons of horses?

The foot of a horse is a long one, though we think of it as merely the part he walks on. A horse walks on the end of his one toe. The nail of the toe we call the "hoof." The true heel is the hock, a sharp joint like an elbow nearly half way up the leg. Along each side of the cannon, the long bone of this foot, lies a splint of bone, which is the remnant of a toe, that is gradually being obliterated from the skeleton. These two splints in the modern horse's foot tell the last chapter of an interesting story. The earliest American horse, the existence of which is proved by fossil bones, tells the first chapter. The story has been read backward by geologists. It is told by a series of skeletons, found in successive strata of rock.

The "Bad Lands" of the arid Western States are rich in fossil remains of horses. Below the surface soil lie the rocks of the Quaternary Period, which included the drift laid down by the receding glaciers and the floods that followed the melting of the ice-sheet. Under the Quaternary lie the Tertiary rocks. These comprise three series, called the Eocene, Miocene, and Pliocene, the Eocene being the oldest. In the middle region of North America, ponds and marshy tracts were filled in during the Tertiary Period, by sediment from rivers; and in these beds of clay and other rock debris the remains of fresh-water and land animals are preserved. Raised out of water, and exposed to erosive action of wind and water, these deposits are easily worn away, for they have not the solidity of older rocks. They are the crumbly Bad Lands of the West, cut through by rivers, and strangely sculptured by wind and rain. Here the fossil horses have been found.

_Eohippus_, the dawn horse, is the name given a skeleton found in 1880 in the lower Eocene strata in Wyoming. This specimen lay buried in a rock formation ages older than that in which the oldest known skeleton of this family had been found. Its discovery made a great sensation among scientists. This little animal, the skeleton of which is no larger than that of a fox, had four perfect toes, and a fifth splint on the forefoot, and three toes on the hind foot. The teeth are herbivorous.

_Orohippus_, with a larger skeleton, was found in the middle Eocene strata of Wyoming. Its feet are like those of its predecessor, except that the splint is gone. The teeth as well as the feet are more like those of the modern horse.

_Mesohippus_, the three-toed horse, found in the Miocene, shows the fourth toe reduced to splints, and the skeleton as big as that of a sheep. In this the horse family becomes fairly established.

_Hypohippus_, the three-toed forest horse, found in the middle Miocene strata of Colorado, is a related species, but not a direct ancestor of the modern horse.

_Neohipparion_, the three-toed desert horse, from the upper Miocene strata, shows the three toes still present. But the Pliocene rocks contain fossils showing gradual reduction of the two side toes, modification of the teeth, and increase in size of the skeleton.

_Protohippus_ and _Pliohippus_, the one-toed species from the Pliocene strata, illustrate these changes. They were about the size of small ponies.

_Equus_, the modern horse, was represented in the Pliocene strata by a species, now extinct, called _Equus Scotti_. This we may regard as the true wild horse of America, for it was as large as the domesticated horse, and much like it, though more like a zebra in some respects. No one can tell why these animals, once abundant in this country, became extinct at the end of the Tertiary Period. But this is undoubtedly true.

The types described form a series showing how the ancestors of the modern horse, grazing on the marshy borders of ancient ponds, lived and died, generation after generation, through a period covering thousands, possibly millions, of years. Along the sides of the crumbling buttes these ancient burying-grounds are being uncovered. Within a dozen years several expeditions, fitted out by the American Museum of Natural History, have searched the out-cropping strata in Dakota and Wyoming for bones of mammals known to have lived at the time the strata were forming in the muddy shallows along the margins of lake and marsh. Duplicate skeletons of the primitive horse types above have been found, and vast numbers of their scattered bones. Each summer geological excursions will add to the wealth of fossils of this family collected in museums.

The Tertiary rocks in Europe yield the same kind of secrets. The region of Paris overlies the estuary of an ancient river. When the strata are laid bare by the digging of foundations for buildings, bones are found in abundance. Cuvier was a famous French geologist who made extensive studies of the remains of the prehistoric animals found in this old burial-place called by scientists the Paris basin. He believed that the dead bodies floated down-stream and accumulated in the mud of the delta, where the tide checked the river's current.

Skeletons of the Hipparion, a graceful, three-toed horse, were found in numbers in the strata of the Miocene time. This animal lived in Europe while the Pliohippus and the Protohippus were flourishing in America.

A great number of species of tapir-like animals left their bones in the Paris basin, among them a three-hoofed animal which may have been the connecting link between the horse and the tapir families. Cuvier found the connecting link between tapirs and cud-chewing mammals.

THE AGE OF MAN

The hairy, woolly mammoth was one of the giant mammals that withstood the cold of the great ice flood, when the less hardy kinds were cut off by the changing climate of the northern half of Europe and America. In caves where the wild animals took refuge from their enemies, skeletons of men have been found with those of the beasts. With these chance skeletons have been found rude, chipped stone spear-heads, hammers, and other tools. With these the savage ancestors of our race defended themselves, and preyed on such animals as they could use for food. They hunted the clumsy mammoth successfully, and shared the caverns in the rocks with animals like the hyena, the sabre-toothed tiger, and the cave bear, which made these places their homes. In California a human skull was found in the bed of an ancient river, which was buried by a lava flow from craters long ago extinct. With this buried skull a few well-shaped but rough stone tools were found. This man must have lived when the great ice flood was at its height.

In southern France, caves have been opened that contained bones and implements of men who evidently lived by fishing and hunting. Bone fish-hooks showed skill in carving with the sharp edges of flint flakes. A spirited drawing of a mammoth, made on a flat, stone surface, is a proof that savage instincts were less prominent in these cave men than in those who fought the great reindeer and the mammoth farther north.

In later times men of higher intelligence formed tribes, tamed the wild horse, the ox, and the sheep, and made friends with the dog. Great heaps of shells along the shores show where the tribes assembled at certain times to feast on oysters and clams. Bones of animals used as food, and tools, are found in these heaps, called "kitchen-middens." These are especially numerous in Northern Europe. The stone implements used by these tribes were smoothly polished. A higher intelligence expressed itself also by the making of utensils out of clay. This pottery has been found in shell heaps. So the rude cave man, who was scarcely less a wild beast than the animals which competed with him for a living and a shelter from storms and cold, was succeeded by a higher man who brought the brutes into subjection by force of will and not by physical strength.

The lake-dwellers, men of the Bronze Age, built houses on piles in the lakes of Central Europe. About sixty years ago the water was low, and these relics of a vanished race were first discovered. The lake bottoms were scraped for further evidences of their life. Tools of polished stone and of bronze were taken up in considerable numbers. Stored grains and dried fruits of several kinds were found. Ornamental trinkets, weapons of hunters and warriors, and agricultural tools tell how the people lived. Their houses were probably built over the water as a means of safety from attack of beasts or hostile men.

In our country the mound-builders have left the story of their manners of life in the spacious, many-roomed tribal houses, built underground, and left with a great variety of relics to the explorers of modern times. These people worked the copper mines, and hammered and polished lumps of pure metal into implements for many uses. With these are tools of polished stone. Stores of corn were found in many mounds scattered in the Mississippi Valley.

The cliff-dwellers of the mesas of Arizona and New Mexico had habits like those of the mound-builders, and the Aztecs, a vanished race in the Southwest, at whose wealth and high civilization the invading Spaniards under Cortez marvelled. The plastered stone houses of the cliff-dwelling Indians had many stories and rooms, each built to house a tribe, not merely a family.

The Pueblo, the Moqui, and the Zuni Indians build similar dwellings to-day, isolated on the tops of almost inaccessible mesas.

Millions of years have passed since life appeared on the earth. Gradually higher forms have followed lower ones in the sea and on the land. But not all of the lower forms have gone. All grades of plants and animals still flourish, but the dominant class in each age is more highly organized than the class that ruled the preceding age.

To discover the earth's treasure, and to turn it to use; to tame wild animals and wild plants, and make them serve him; to create ever more beautiful and more useful forms in domestication; to find out the earth's life story, by reading the pages of the great stone book--these are undertakings that waited for man's coming.

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