The ten years that have passed since the first publication of this book have been years fruitful of results in geological knowledge. Some departments of the subject have been fairly revolutionized and in all there has been great progress, so that any text-book ten years old is necessarily left far behind in the general advance. Revision, indeed rewriting, had become imperative to incorporate the most important and significant parts of the newer results, as well as to remove as many of the defects as I might be able to do. The increase in size is an extremely regrettable feature, but I have not seen my way to avoid it, for it is largely due to the much greater number of illustrations, and these were needed in the interests of clearness.

While many minor changes have been made, the general plan of the book remains the same, for experience has convinced me that the somewhat rigidly conventional arrangement of topics, which has sufficiently evident drawbacks, is of actual assistance to the beginner. It avoids confusing him by any premature attempt to point out the infinitely ramifying relations of every fact of nature. One of the keenest pleasures of intellectual growth is the continual discovery of these unsuspected relations, but for the beginner the simpler and more obvious line of reasoning is the more profitable.

The labour of revision has been greatly lightened by those admirable store-houses of geological learning: the second edition of Kayser's "Lehrbuch," the fourth edition of Geikie's "Text-Book," and the "Geology" of Chamberlin and Salisbury. To all of these my obligations are great, especially for the bibliographies which they contain, and which have rendered the collection of the newer technical literature of monographs and papers a much less onerous task than it could otherwise have been.

In this new edition I have introduced a very considerable number of brief quotations, at the request of some of those who have employed the book as a convenient work of reference and who desire to know the authority upon which the more novel or less familiar statements have been made.

It gives me great pleasure to express my thanks to the many friends who have assisted me in my undertaking. To Mr. C. W. Hayes and Mr. Bailey Willis, of the United States Geological Survey, I am under particular obligations for the kindness which enabled me to profit by the magnificent collection of photographs which the Survey has gathered. It so happened that, but for this kindness, obstacles of a temporary nature would have prevented my enjoyment of this privilege. Mr. Willis was also kind enough to give highly valued assistance and counsel in many other directions.

Professor W. H. Hobbs sent me proofs and manuscript of unpublished books and papers on seismological subjects, a service which it is difficult to describe adequately. Professor Bumpus, director of the American Museum of Natural History, New York, Professor Osborn, Professor R. B. Young of Johannesburg, and Professor R. W. Brock of Kingston, Ontario, have all been most liberal in supplying me with photographs and other means of illustration. My colleagues in the Geological Department of Princeton University have rendered assistance that was literally invaluable; Professor C. H. Smyth, Jr., has read the proofs and has made very many useful and timely suggestions, and Dr. W. J. Sinclair took many photographs especially for the book and has given me the benefit of his experience in using it. Greatest of all are my obligations to Mr. Gilbert van Ingen, to whom the book owes much of whatever good it may possess; he made a large number of the photographs, prepared the maps, selected the invertebrate fossils for the plates, and supervised the admirable drawings upon which Mr. Horsfall has expended such pains and skill, and gave much useful assistance in the stratigraphical part.

As to the figures in the plates, a word of explanation is required. A few only are original; the great majority are taken from monographs by well-known writers, but almost all have been so modified by restoration or otherwise that it did not seem proper to put the responsibility upon the original authority.

During the past ten years I have received many letters containing criticisms of the book and suggestions for its improvement in one or other particular. So far as lay in my power, I have endeavoured to profit by these criticisms and suggestions, and I wish to thank those who have taken the trouble to write them for my benefit.

Finally, I venture to express the hope that the new edition may find a place of usefulness in a crowded field, notwithstanding the defects of which I am very well aware but have not been able to remedy in the time at my disposal.

Princeton, N.J., Oct. 10, 1907.