The Story of Our Continent. A Reader in the Geography and Geology of North America. For the use of schools

Preface

. Those who read this book will at once perceive that both in the subject-matter and arrangement it departs widely from the ordinary text-books which give an account of North America. It should be understood that the end which the writer sought to attain is not that which may be secured by the ordinary school geographies. Such works undertake to afford the student a large body of detailed information concerning the existing state of the country, and with little or no reference to the steps by which the land came to its present estate. The aim of this work has been to pre sent only those features which can be shown in their relation to the geological development of the continent. The expectation of the author has been that this work will be used as a reader along with some geography which treats in a thorough way the facts of a political and economic nature, such as these text-books ordi narily present.

Used in this way, it will naturally lead the student to perceive how the present state of the country is due to the processes which have gone on in the remote past, and in this way to attain to some of the most enlarging conceptions which the geological history of the earth unfolds. CONTEN T S. CHAFsER I. PACE Geography of North America i

Chapter I. Geographv Of North America

Method of study. Cause and effect of climate. Influence of geographic conditions on animals and plants; on the life of man. Character of the soil. Origin of its fertility. General influence of geologic and geographic conditions on mankind. In beginning the study of the geography of North America, it is well for us to form a clear idea as to the object which we should have in view in this task. With a distinct aim before us, it is easily seen that labor may be spared in the effort. It is a large task to form even the most general idea of the history and condi tions of a great area of the earth's surface. The amount of knowledge concerning any one of the continents is so vast that to secure a general view of its conditions we have to neglect the greater part of the details con cerning its growth and structure.

If our plan be clearly marked, we can more easily put the unnecessary learn ing aside. The most of our school geographies seek to present to the student a picture of the existing conditions on the earth's surface, to show him the shape of the lands, the boundaries of states, the character of the imi portant natural features, the conditions ot commerce ; in other words, to give him a picture of the earth, or a par ticular part ot it, as it now is. In this little volume we are to consider something more than is commonly presented in such work, the intention being to show the student in a general way how the continent of North America has come by its shape, through what steps it has become a land, how the stages of its growth have affected its climate, and thus have influenced the charac ter of living things which have found a place upon its lands, and finally in what manner the past history of the continent, by determining the store of mineral materials under the earth, the shape of its surface, the nature of its soil and climate, measures its fitness for the uses of man ; in a word, how the history of its people has been influenced by geographic conditions, and thus depends on the laws which have controlled the development of a continental mass.

In the effort to see how the geography of any country has influenced the life of the animals and plants which have found a place upon it, it is well for the student to begin his task by noticing a number of familiar facts, so familiar, indeed, that they readily escape attention, which may serve to illustrate the effect of surrounding conditions on the sensitive living creatures. It is easy to see that all the living tenants of the lands and waters are readily and largely influenced by the conditions of the nature about them. Any one who has made himself moderately familiar with the round of the seasons has observed the profound effect arising from changes of climate. In the regions north and south of the tropics each year brings periods of winter and of summer ; with the change in the amount of heat the living beings pass from the sleep of the winter season to the activity of summer time.

In the springtime, when the sun rises higher above the horizon and sends more heat to the earth, we perceive the effect of the alteration on the development of life. The seeds are stimulated to growth, and most of the animals which have reposed in hidden places come forth and enter on their busy lives. Every year thus affords a beautiful lesson on the effects of simple changes in the events of the outer world. As the sun ascends higher, it brings with it a tropical climate, which marches over the surface nearly to the poles; then as the sun returns south in its annual course, the conditions of polar cold sweep down towards the equator. The difference be tween the tropical belt of the world and the regions beyond it lies in the fact that within the tropics it is al ways warm with something like the warmth of summer in higher latitudes, while near the poles the temperature is tropical for only a short time.

If the summer heat continued throughout the year in any high latitude, palms and other plants which cannot withstand the cold would develop over nearly all the earth's lands. After we have in mind the effect produced by the alternate rising and sinking of the sun in high latitudes, it is well next to note the effects on the district about us caused by differences in the geographic character of the land. In any country where there is a range of heights of even a few feet, where there are streams and hills however small, we may with a little study see how the nature of the surface, by determining the character of the soil, and the amount of water it con tains, affects the lives of the plants and animals. In a lake or arm of the sea we note that in the deeper water there are no plants such as we have upon the land ; the vegetable life is limited to certain soft forms which are without leaves, or roots, or seeds of a distinct kind.

These aquatic plants live altogether be neath the surface of the waters, or at times tolerate the air for a few hours at low tide. Close to the shore, where the water is shallow, we may, if the water be fresh, find certain higher plants, such as our lilies, and rushes, which have distinct leaves, roots, and seed, and can maintain themselves with their roots below the surface of the water, but with their upper parts within the air. Next the shore, if the ground happens to be marshy, — that is, neither wet nor dry, — bushes and a few kinds of trees may grow, forms which cannot inhabit the water, and are equally incapable of living on the high land. Passing yet further above the water to the lands of a medium degree of wetness, yet other forms of lowly plants or trees possess the land. On the arid hilltops we find another assemblage of plants unlike any of those which dwell on lower ground.

Although it is not easy to see that the animal life is limited in the same narrow way by geographic condi tions as is the vegetable world, closer inquiry shows us that in fact most animals, because they depend for their subsistence on particular kinds of plants, are also pro foundly affected by peculiarities of the soil. This is particularly the case with insects, a group which con tains more kinds of creatures than all the rest of the animal kingdom put together. Most insects require particular parts of plants for their food. Even those forms which live on other insects have to maintain themselves where their prey is plentiful. The insects of the swamp differ in a clear way from those of the upland. Thus in the state of nature, in every country, the living beings are distributed with reference to the character of the soil, whence all land life springs.

The character of this soil depends upon the geography of the country. The underlying rocks, the rivers, lakes, hills, and mountains, mainly determine the nature of that soil, whether it be wet or dry, of clay, sandy or stony. All these features are fixed by the geological history of the country : they can be accounted for only where we know its past history, — how it came to have its present form. Not only is the higher life of a land shaped by its geographic conditions, but the life of man is influenced even more than that of any other animal by the circum stances which surround him. If he be a farmer, the character of the crops he cultivates will be determined partly by the nature of the soil, and yet more by the character of the climate, — the amount of heat which the sun sends to him, or the share of rainfall which comes to his fields.

He rears those crops which are made possible by the heat, the rain, and the nature of the earth on which they fall. In the Southern states of this country cotton is the leading product of the fields. It is profitable to grow it there, for the reason that the plant requires a very long summer to mature its bolls, and during this summer there must be a considerable fall of rain, and all the while a rather high temperature. Moreover, cotton requires a sandy rather than a clayey soil, and the ancient history of that part of the continent, as we shall see hereafter, favored the construction of soils of this nature. The farmers of the Northwestern states find their profit in raising grain. That region is the granary of the continent, — indeed, we may say of Europe as well, — for the reason that the short, rather dry summer affords a suitable climate for the development of such crops, and the soil is generally of a clayey nature, having this quality given it by the geological conditions of the rocks made in the time when the con tinent was forming.

Geographic conditions, those now existing or those which have ceased to be, but have left their marks on the character of the soil, make it im possible for cotton to be profitably reared in the North west, or wheat in the Carolinas. Or, to take another instance, the state of Florida is unfit for the tillage either of grain or of cotton ; the latter crop will grow there, but the soil is not of a nature to make it profitable. Florida is the field of fruit culture. Its semi-tropical climate favors the development of oranges, lemons, pineapples, and many forms of fruit and vegetables. The soil is generally so poor that these plants have to be grown with the aid of artificial manures, and so that portion of the country is by nature set aside for garden ing. The character of the soil, combined with the character of the climate of a country, serves to fix the occupations of the people who win food from the earth.

Now the soil, simple as it seems to be at first sight, has always a very wonderful history. So much depends upon this history that we must ask the reader to turn his attention for a moment to the nature and origin of this film of loose material on the surface of the earth in which the plants find root. All soils consist in the main of fine bits of rock, the particles of clay and sand which have been worn from the compact, firm-set under-rocks of the earth, by the action of rain, frost, rivers, waves, and the roots of plants, as well as by the decay which the atmosphere brings to all rock material. If we take a pinch of soil and spread it out thinly upon a sheet of white paper and inspect it with a magnifying-glass, we find that the greater part of the material is commonly made up of tolerably coarse grains, large enough to be seen by the naked eye or by a simple microscope.

Mixed with these hard bits there are very many fragments of de cayed roots, leaves, and stems, which are in part so finely divided that they give the mass a dark color. Sinking through the soil, the rain-water constantly takes a little of the decayed rock into solution as salt dissolves in water. This dissolved rock material is taken up by the roots of plants, and affords the ashy matter of their bodies, — material without which they could not grow. On the proportion of lime, potash, phosphatic matter, soda, and various other materials which the decaying rock affords to the soil-water, depends the fertility of the soil ; that is, its fitness to nourish crops, whether those of wild nature or of the tilled fields. If the bits which make the soil are largely composed of limestone, which generally contains not only lime, but some phos phatic matter, soda, potash, and the other materials required to make the bodies of plants, the soil will be fertile.

If, however, it be in the main made up of quartzy bits of sand, the plants can obtain from the soil water but little nutriment, and therefore the fields will be sterile, and the forests or the cultivated crops scanty. The proportion of fertilizing materials contained in the soil depends upon the conditions which existed when the rocks from which the soil is derived were forming. Nearly all our rocks were formed on old sea floors. If the geography of those old sea-floors, that is to say, the conditions of temperature and other circumstances, were such as to make a plentiful life of shell-fish or corals on the bottom, then the rocks formed from the remains of these creatures will abound in materials fit for plant growth. When this rock matter is subjected to decay and accumulates in the soil, the plants will flourish upon it.

Each wheat plant will appropriate the waste of these old creatures of the sea-floor, and convert the chemical materials which they contributed to the rock into good grain. Thus we readily see that the character of our soils depends upon geographic conditions in very remote time. A striking instance of this effect may be found in the case of the very fertile limestone lands which are found in the so-called blue-grass district of Kentucky and Tennessee. These soils are of extraordinary fertility and of such endurance to cultivation that they have been tilled in corn without manuring for one hundred years or more. They owe their fertility to the fact that the rock contains a large number of the remains of animals somewhat akin to the shrimps. These creatures had the habit of storing in their hard parts a great deal of lime phosphate, which is the most important ingredient in soils which are to feed grain.

The rocks beneath the blue-grass district are thin sheets of limestone laid one above the other to the thickness of a thousand feet or more ; here and there there are beds, generally only a few inches thick, mainly composed of the remains of these little creatures, which are ex posed to the atmosphere. These beds decay to a fine powder which works down through the hillsides, min gles with the soil, and so gives it its great fertility for crops of grain and grass. The growth of ancient animals which built their re mains into rock was determined, as is the growth of creatures of to-day, by geographic conditions. Other circumstances of the earth's crust determined that in the course of time these old sea-bottoms should be elevated into dry land and exposed to the actions which make soil. Thus we see that each stage in the earth's history prepares the way for the later stages of its development.

Our life of to-day depends upon the conditions of remote times. Although it is through the soil and climate that geological conditions most intimately affect the life of man, there are very many ways in which the geography of the past and present influence his career. Let us, for example, note the influence of the sea on the occupations of men. Wherever men's dwelling-places are along the shore, they find a considerable share of their food in the animals of the sea. They are thus tempted to seafar ing, to the construction of boats, and come to have the peculiar needs which such life imposes on man. Yet later in their development they find a profit in the trade which the fields of the sea lay wide open to those who dwell upon its borders. Thus, while inland people are limited to the district just about them for their field of action, the folk next to the shore have a vastly wider range of employment.

The peculiarities of their life depend upon the way in which the lands have grown to their present shape. The fitness of the shore for the uses of the mariner varies greatly. Where the coast is very sandy and there are no large rivers passing across the shore to the sea, there is apt to be a dearth of harbors. Only small boats which can be dragged through the surf to the dry land can be used, and so it comes about that the people along such coasts usually make but limited use of the ways of the ocean. On the other hand, in regions where harbors abound, as along the northern coast of the United States, both on its eastern and western faces, or in the region of Northern Europe, Scandinavia, Holland, and England, the people may become deep-sea sailors and range over the oceans to the furthest lands of the earth.

These peculiarities of coast lines, whether they afford good harbors or no, depend upon the ancient his tory of the shores. As we shall see further on, the sin gular abundance of harbors about the North Atlantic, which have made the people of those lands the sailors of the world, is immediately due to the fact that in for mer stages of the earth's development this part of the coast was deeply carved by glaciers or streams of ice. If now we turn our attention from the industries of men, which are related to the mere surface of the earth, to the work which depends on the underground features, we find a yet more striking instance of the effect brought about by the ancient history of our sphere. Next after the wealth which comes for man's use from the soil, we must place that which comes from the mines.

In looking over a map of North America which shows the mineral fields of the country, we observe that, although more than half of its area has nothing of particular use to man to be won from below the soil, there are large districts where the under-earth is richly stored with a great variety of materials to be gained by mining. There are at present over fifty different substances of great use to man which are obtained in one way or another from the realm of the earth which lies below the soil covering. Iron, copper, lead, zinc, gold, and sil ver, and several other valuable metals ; coal, petroleum, natural gas, materials which serve for light, warmth, and the sources of power ; our building-stones ; various sub stances which serve to fertilize the fields worn by crops ; and a host of other less important supplies for our arts are derived from this nether realm.

Wherever these mineral substances abound, the profit from winning them is so considerable that often, to the neglect of agriculture, the population seeks subsistence from the deeper earth below the soil. Where these substances are won, as in most cases they are, by delv ing deep beneath the surface, the men who follow these pursuits become peculiar in their methods of life, their ways of thought and action. These peculiarities of the miner's life manifestly depend on the existence of par ticular substances in limited parts of the world. The presence of these substances in the crust of the earth depends upon the former history of the area in which they lie ; in a word, upon its old geographic conditions. If the substance sought in the mine be coal, we know that it is present, because in a very ancient day that particular field was occupied by great swamps, in which peaty matter was deposited in the manner in which we may now see it accumulating in our ordinary bogs.

After a thick layer of peat was formed, the land it occu pied sank beneath the sea, and sand and clay were accumulated upon it, which, while concealing it and pre serving it from complete decay, converted the mass to coal. By further change it has been re-elevated, so that it is accessible to man. Ancient climate and ancient geography, in other words, led to the production of the coal bed. So with all the other substances won by the miner ; each owes its abundance in the particular field to conditions of the climate or of the other geological features which occurred in the past. It is hard to give the reader a clear idea as to the intimate way in which the geography of the present day determines the life now existing on the earth's surface ; yet it is important he should see something of these facts, even if the instances he can consider are but few in number.

Perhaps the best illustrations of how closely the life of the earth depends upon surrounding circumstances are afforded by field and garden plants. A good example is found in the principal American grain, — the maize or Indian corn, which furnishes by far the most valuable grain crop of the continent. It is of the utmost importance to the farmer to have a crop of this corn ; but in the northern parts of the tilled portion of North America, generally in the region north of the Great Lakes, the summer is too short for the plant to mature its seeds. They are killed by frost before they are fully developed. By carefully choosing each year the plants which mature earlier than their neighbors in the field, and using seed from these, varieties have been formed which hasten their growth, and so in a measure adapt themselves to the needs of the short northern summer.

The maize of Alabama requires five months in its round from seed to seed ; by selection particular varieties have been formed which will come to maturity in regions where it is but three months between the frost of spring and autumn. Further than this it seems impossible to go, and so there is a limit determined by the temperature beyond which the maize cannot be grown with profit. The distribution of animals in the sea is even more closely determined by the temperature than that of the plants on the land. Thus in the warm waters south of Cape Cod there are many kinds of animals which cannot pass around this small cape into the colder waters of Massachusetts Bay. The most vigorous and active fish south of the Cape, the blue-fish, a creature there greatly developed, cannot maintain itself north of the Cape.

Occasionally, in the last two centuries, it has in the warmer seasons worked around the promontory, and for a year or two gained a place in Massachusetts Bay. It has seemed likely that it would permanently win this new field, but each time it has been driven back by the cold of the water. The difference is also marked in the mollusca, or shell-fish ; a number of species flourish just south of the Cape, which do not appear in the some what colder waters a few miles to the northward. The difference between the temperature of the waters north and south of Cape Cod is brought about by the influ ence of this small promontory, projecting only forty miles from the main shore, on the movement of the cold current which creeps down the coast of New Eng land and Nova Scotia from the Arctic regions, and which is finally arrested in its movement by the hook of Cape Cod.

We need to comprehend these effects of differences of a geographic sort, and conceive them as applying, in a greater or less measure, to all living or extinct species of animals and plants, in order to understand how far the history of the earth in the past has served to affect the beings of to-day, particularly the highest of them, — man. Most animals and all plants are, as regards heat, delicate thermometers. They are affected, too, by the winds, by the moisture of the air and soil, and by the qualities of the soil itself, the plants directly, and animals through plants ; and so the world of life is swayed about by every accident which affects these circumstances. Every geographic change alters the height of the land or the shape of the sea, and thus affects the currents of the air bringing heat and moisture, the rivers which flow from the continents, or the marine currents which convey the waters of the sea hither and thither over its surface.

The most important lessons which naturalists have learned by the study of fossils contained in rocks con cern the succession of life in various stages of the earth's history. At the present time there are somewhere about half a million different kinds of animals and plants on the surface of the earth. Each species resembles more or less closely other related species, so that we have to look carefully to see the difference between them, as, for instance, between the different kinds of sparrows or the several sorts of oaks. The greater number of groups are separated in character by wider differences, such as those which distinguish the beech from the oak ; but the white oak does not produce any thing but white oaks from its seed, and the sparrows each rear broods of their own kind. If we search the rocks which were formed on the earth's surface say half a million years ago, — a very recent time in the earth's history, — we find by the fossils they contain that there were also oaks and beeches and sparrows, and these were of species related to those now living, undoubtedly the forefathers of living forms, but they differed from them in most cases in a clear way : they differ as much from living oaks or beeches as the species of these plants now do from each other.

Thus, stage by stage, we can go back into the remote past of the earth, each step separated, it may be, from the preceding by a million years, until we have found somewhere near a hundred different stages in the earth's history, each showing by its fossils that the life, though akin to that which went before and that which came after, had a particular character. Studying these facts, geologists have one and all come to the conclusion that all the life of to-day has come down to our time from ancestors of earlier days, and has indeed descended from the first beings which came into existence on the surface of this sphere. A yet more important conclusion derived from the study of these plants and animals of the past and their relation to the living creatures of to-day is that, though many kinds of animals have perished at various periods in the past, leaving no descendants in our time, life as a whole, both that of animals and plants, has always steadily been going upward in its organization towards higher states of being.

If we consider the earlier stages, — as, for instance, that known as the Cambrian, which is near the time when life came upon the earth, — we find in the fossils of the beds then laid down on the sea-floor no fishes, no insects ; only animals as lowly in structure as our shell-fish, or worms, or certain kindred of our crustaceans. There were apparently no land plants, only imperfect sea-weeds, or perhaps mosses and lichens, on part of the continents which had arisen from the sea. There were no lizards, frogs, birds, or four footed beasts of any kind. The lands were probably destitute of life, except for the lower kinds of plants and perhaps for a few worm-like animals, or, it may have been, the lowest grades of insects. In the latter chapters of the great stone book, the leaves of which are the strata or rock beds of the earth, we find stage by stage the higher animals and plants appearing.

First among the plants come the ferns, and then palm-like creatures, and only in a relatively late day our flowering plants and those which bear fruit and large seeds make their appearance. The back-boned animals also show the same steadfast advance : first come the fishes ; then, after a long time, the reptiles ; then the birds, at first with long, lizard-like tails and teeth, then the higher song birds. Sucking animals are wanting until a late day ; then they came with lowly forms related to the kangaroo. Later, higher kinds appear ; and finally the history is rounded with the appearance of man. All the while these wonderful changes which have led life upward in the scale of being have been going on, the continents have been growing, slowly rising from the sea-floor, gradually dividing the oceans into separate seas, shaping the paths of rivers, and generally determining the geographic influences which, as we have seen, have so much to do with the conditions of life.