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have been omitted in order to bring under discussion as many as possible of the essential problems.

The book is not intended to be a complete treatise upon paleontology, nor a detailed report of the relation of fossils to geological formations or to time. It is rather a reconnaissance of a fascinating region, from which the few explorers who have already penetrated it have brought back accounts of the most remarkable and unexpected discoveries. A reconnaissance aims to discover the characteristic features and the relative importance of the various elements making up the territory traversed, and is merely introductory to a more minute and careful survey; its purpose is to aid the judgment, to direct the course of further research, and when difficulties of travel and distances are great, it is particularly useful in preventing distraction from the most expeditious way to the facts of chief importance.

The tendency of modern science is now, and for more than a quarter of a century has been, so much to specialization, and our minds have become so fascinated by the minute and the particular, that our common judgments of the true proportion of things have become more or less distorted. Theories and ideas which have been drummed into our ears have come to appear the most important truths in the world, and all our thoughts have become colored by them. We cannot read the newspapers or listen to the talk on the street without being convinced that the thought of the people, however little they may know of the sciences involved, is thus biased by current theories about life and organisms. The bearing of biological theories upon our judgments of the rightness or wrongness of conduct, both of ourselves and of society, is too direct to admit of any uncertainty regarding the validity of their foundations or their precise import. While the facts and phenomena upon which some of the theories rest are purely biological, others of them, which concern most intimately, have their chief evidence in the historical records of geology.

Among the latter none is more important than those gathered about the phenomena of evolution; but it is evident upon reflection that the biologist proper, who deals alone with the organisms now living upon the earth, must rest with a theoretical interpretation of the laws of evolution. To the geologist the records of evolution are open for direct examination, and geological biology is a scientific treatment of the observed facts of evolution.

While there are no end of books on evolution, and modern biologists seem content to assume that some theory of evolution is true, without being able to decide which it shall be ; and although the students of sociology, the moralist, and the theologian are basing their theories about man on the “working hypotheses” of the naturalist as if “ law and gospel,"—it seems to have escaped serious attention that we have open for study a genuine record of the actual evolution of organisms, extending from near the beginning of life up to the present time.

Men have been speculating in all conceivable directions to form some theory as to how evolution ought to work, and as to what the history of organisms ought to be: it is the province of geological biology to tell us what the history of organisms has actually been. The geologist does not ask what is the theory of evolution, but what are the facts of evolution. “ The primary and direct evidence in favor of evolution can be furnished only by paleontology. The geological record, so soon as it approaches completeness, must, when properly questioned, yield either an affirmative or a negative answer: if evolution has taken place, there will its mark be left; if it has not taken place, there will lie its refutation.” The late Professor Huxley, who framed this most true and pertinent sentence, knew very well the evidence which those records furnish, although he often treated evolution as if it were a doctrine requiring argumentative defense, rather than a science which only needs elucidation.

The treatment which evolution receives in these pages is designed for those who wish to know what the chief facts and factors of evolution are, not those who are looking for further debate of the arguments either for or against a theory of evolution. To the student who approaches the subject from the historical side evolution becomes the very key to the mystery of organic life. The phenomena of growth are fairly well understood, the development of the individual has been systematized into a science of embryology; and as we also discover the grand features of the evolution of species and races and kinds of organisms, life begins to assume the proportions of one of the fundamental forces in the world.

When considered from this point of view the question what causes the evolution of organisms seems as impertinent as what causes the motion of the celestial spheres. The answer to both is the same.

That the form and functions of successive organisms should be accurately adjusted to their organic and physical environments is no more surprising than that the size and weight of the revolving planets should be accurately adjusted to the orbits in which they swing; but once grant that the systems are in motion, and it is not reasonable to suppose in either case that at any point in the succession of phenomena misadjustment should occur which would require any hypothetical selective force to put them right again. Evolution thus becomes one of the fundamental expressions of life force, requiring no theory to support it, but calling only for investigation to reveal its laws; and it is in geological biology that we find the direct evidences of the course of its operation. But evolution is not all of biology, and therefore sufficient illustration of their respective phenomena has been borrowed from physiology and embryology to present a comprehensive view of all the three great factors of organic life, viz., growth, development, and evolution.

A few of the chapters are somewhat technical in their language, and deal with particulars of slight interest to those unfamiliar with the nomenclature of natural history. These chapters may be omitted by readers willing to take the author's statements without verification. Such persons may omit the purely geological part of the book by passing directly from Chapter I to Chapter V, where the discussion of the biological problem begins. The more technical passages are Chapter II; Chapter IV, except the summary at the close; pages 98 to 110 of Chapter V; all but the summary of Chapter VII; the latter parts of Chapters XII and XIII; and the fine print of Chapters XVIII and XIX. The remainder of the book, although occasionally expressed in scientific terms, will be found, it is hoped, fully intelligible to the ordinary reader.

Special students of paleontology and geology will miss the expected descriptions of fossils and the means for identifying them and for recognizing the horizons they indicate. To such readers the author has to say that this book is offered only as an introduction to the grand field of study open before them, with the hope that it may be useful in guiding and suggesting methods of investigation, and in encouraging that deep research which will be found necessary to interpret the full story of the history of organisms, of which only a glimpse is here attempted.

H. S. W. NEW HAVEN, October 5, 1895.

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