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.
[Illustration: Banded sandstone from Calico Canon, South Dakota]
[Illustration: _By permission of the American Museum of Natural History_
Opalized wood from Utah]
[Illustration: _By permission of the American Museum of Natural History_
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.
[Illustration: _By permission of the American Museum of Natural History_
Model of a three-horned Dinosaur, _Triceratops_, from Cretaceous of
Montana. Animal in life about 25 feet long]
[Illustration: _By permission of the American Museum of Natural History_
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.
[Illustration: _By permission of the American Museum of Natural History_
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]
[Illustration: _By permission of the American Museum of Natural History_
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.
[Illustration: _By permission of the American Museum of Natural History_
Restoration of a Siberian mammoth, _Elephas primogenius_, pursued by men
of the old stone age of Europe. Late Pleistocene epoch]
[Illustration: _By permission of the American Museum of Natural History_
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?