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and discussion followed before it was seen that both these theories were necessary to a complete explanation.

Sometimes it was necessary that one science should reach a certain degree of perfection before it could shed the necessary light on important questions of another; and in others the whole world had to be pretty well known before the true theory could be framed. There was a great attraction in making fresh discoveries, the interest the questions raised constantly increased, and, as every part of the earth became more fully known to the civilized world, the dark points were gradually cleared up. A theory that is nearest the truth will explain the largest number of facts, and, led on by increasing breadth and clearness of explanation, men of science slowly and painfully conquered the difficulties in their way.

But, if the conquest was slow and painful, it was also sure, for it had the solid basis of nature to rest on. If they made mistakes, examined too hastily, and formed conclusions without the most mature consideration, the ever accumulating facts would convict them of error. In this way they learned extreme caution, sought the most accurate instruments and methods to aid their investigations, and, in our own day, have become renowned for the precise and patient care bestowed on their labors. "Scientific Accuracy" implies the most thorough study and the most absolute certainty which the nature of the subject admits.

The glory of all past ages pales before the achievements of the scientific world of our generation and of that which immediately preceded it. The warriors, the statesmen, the artists and the thinkers of past ages appear childish bunglers when compared with these broad-minded, clear-sighted, intellectual and practical giants of our time. The almost miraculous development of the industries and comprehensive activities of recent years, the means by which distance and other obstacles have been deprived of their power to separate men and keep them in ignorance of each other, all come, directly or indi

rectly, from scientific discoveries. So useful has science become to practical life that it has been made, to a great extent, the general superintendent of the business undertakings, of the social and political affairs, and of the thought of the world. If it has too lately received that high position to have banished false principles and injurious violation of the laws of nature, of business and of association, it is yet steadily and vigorously working toward that end, and can not well fail of ultimate success.

Science has acquired this great influence by doing its work within its own special field with great and conscientious thoroughness. It will take nothing for granted, it requires proof; it shuns no labor to arrive at certainty, it will not deceive others nor itself, and declines to pronounce upon a theory until all the facts have been sufficiently examined and reasonable doubts removed. These are its fundamental principles. Some of its teachers, indeed, fail to be always governed by these principles, for they are often more or less imperfectly imbued with its spirit, but their influence is lost in proportion as they are unable to sustain their positions by convincing proof. Science belongs to the material world, the world of facts which are capable of being proved, and it has taught the world the carefulness in receiving such proof that it uses in seeking for it.

Geology has been perfected with this painstaking care. Several miles of the original depth of the rocks of the earth have been turned up to the light of day by the immense forces that assisted in its structure, and they have laid bare, somewhere, nearly every leaf of its journal of its own life and history. By long and patient study its alphabet has been learned and the strange journal read. Chemistry, Zoology, Botany, Physiology, Astronomy, and many other sciences have aided in its work, for they are all branches of one great Science of Nature. As the special energies of each department of nature had their part in making the earth, so the facts of each science

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now assist in explaining how it was made. Not everything is known. On the contrary, study seems only now to have fairly commenced. It has surveyed the general field, it has disciplined its workers, organized its forces, and found out the right way to use them. It has exercised its eye, its hand and its judgment so thoroughly that they can work together with great rapidity and certainty.

It has learned that nature is not a confused collection of contradictions, but that the different parts form a consistent, wellproportioned and harmonious whole; that the laws now controlling its operations are universal, that they always and everywhere produce the same effect under the same circumstances. This unity of nature enables science to transport its students to distant times and far away regions of the universe. The laws of proportion in the animal frame are so well known that, with a few bones, it can reconstruct the whole animal, discover its habits and the circumstances that surrounded it while liv. ing. The chemical constitution of the rocks and the animal or vegetable remains found in them, or absent from them, reveal the condition of the seas and the land during the period from which they date. Thus science walks back and forth through the long ages of the past, and studies each period, each class of vegetable or animal life and the operation of the forces that produced it, with even more ease and certainty than a traveler can study a country and its productions, as they stand in all their completeness before his eyes, at the present day. In some respects the observer can get nearer to the secrets of the past than those of the present. Here he can not always go behind the curtain, but there the curtain is drawn, and he has a closer view of causes.

Science sometimes meets with agents and methods of study that make the most important and wonderful revelations. For instance, light, as reflected by different objects, was found to make various revelations as to the nature of those objects, and by this means a multitude of facts in regard to the constitu

tion and condition of the sun, and other distant bodies, were very positively made out. So much clear and precise knowledge has been gained in the last fifty years, that it would be presumptuous to undertake to mark the future boundaries between the known and the unknown, or perhaps to say that any subject awakening the interest and curiosity of men will. not be sufficiently investigated and cleared up to fully satisfy that curiosity.

The outlines of what science has revealed of the past of one of the most important regions of the earth, are given in the First Part of this work. So far as we can discover all the labors of nature are directed toward an ultimate end in connection with man. The Mississippi Valley seems to have been formed with peculiar care on a broad and simple plan and to have been supplied with a variety, abundance and excellence of useful materials seen nowhere else in the world.

It can not but be of interest to note how and when the original plan of the great Valley was drawn, and how the operations that stored it with so many treasures were conducted. Science is able to give a very clear and connected history of this long process, and also to furnish a most interesting tale of an ancient and mysterious people of whom written history knows almost nothing, or at least nothing definite. The facts and the manner in which they have been studied and their meaning learned are contained in a multitude of books. The details must be sought in those. It is only the general conclusions that are here given.

CHAPTER I.

HOW NATURE FORMED THE GREAT VALLEY.

The Book accepted as a Divine Record and Revelation by the Jews, and afterwards by Christians, opens with a brief and partial outline of the origin of the earth and its progressive fitting up for the use and residence of man. Nature itself must be a revelation, if its narrative can be read, and the two records should be in harmony. The Bible account contains a very brief summary, and leaves wide gaps in the outlinetouching but few points. Naturally it would not be fully comprehended until the outline was completed and explained by a multitude of details. This was the task of science, and the more definite and unmistakable its conclusions become, the more decisive appears the agreement between the two records.

The Bible commences with "the beginning," when the elements, which came ultimately to their present state, were formless, confused, and utterly "dark;" confines its statements concerning the early periods chiefly to the origin and development of light, to the gradual introduction of plants and animals, and, finally, of man. Science commences with an examination of the finished work-with the earth as it is now-and follows the process back, step by step, to the time when no life existed, and when it first became possible for the earth to be illuminated as it is now. It confirms, explains and fills up the Bible outline so far as it can reach positive conclusions. It discovers evidences of a heated state in which rocks. and metals were melted, or existed only in the form of gas or vapor, through which the light of the sun could not penetrate. The earth gradually cooled, a crust formed over the