Exact references are given to the original authorities on all questions of importance, and on many points even of minor detail: partly that I might not seem to claim as my own what belongs to others; partly that I might consult for the convenience of those who should wish to investigate more minutely what I have but lightly touched. And here it may be well to observe, with regard to the two classic works of Sir Charles Lyell, his _Elements_ and his _Principles_, which have been reproduced so many times and in so many forms, that I have uniformly referred to the latest edition of each. The Woodcuts which illustrate the Volume will, I venture to hope, help to convey a clear and distinct impression of many natural objects which can be represented but imperfectly in words. Some of the most striking and effective are taken from the admirable Manual of Geology brought out some years ago by the Reverend Doctor Haughton, of Trinity College, Dublin. My best thanks are due to the learned author for the kindness with which he placed his Woodblocks at my disposal. I have also to express my acknowledgments to Sir Charles Lyell, who has allowed me to reproduce some of the drawings that embellish his works; and to the eminent publishers, Messrs. Bell and Daldy of London, and Mr. Nimmo of Edinburgh, who have, with great courtesy, furnished me with electrotypes of several figures from the works of Doctor Mantell and Mr. Hugh Miller. To my colleagues in Maynooth I am much indebted for their judicious suggestions and friendly assistance during the progress of the Work. In particular I desire to testify my obligations to our distinguished Professor of Scripture, the Reverend Doctor M’Carthy, for the unwearied kindness with which he has allowed me to draw at pleasure on his profound and extensive knowledge of the Sacred Text. G. M. SAINT PATRICK’S COLLEGE, MAYNOOTH, _December 1st, 1869_. [Illustration] PREFACE TO THE AMERICAN EDITION. Dr. Molloy has, in the present work, made an important contribution to a department of scientific and theologic literature, which has already been enriched by the labors of several other Catholic Fathers, among whom must be mentioned CARDINAL WISEMAN,[1] FATHER PERRONE,[2] and FATHER PIANCIANI,[3] who, in Italy, maintain substantially, the same ground which, in England, has been sustained by DR. CHALMERS, DR. BUCKLAND, PYE SMITH, and HUGH MILLER, and we may now add with pleasure, by DR. MOLLOY. Names which, in the United States, find their counterparts in DR. HITCHCOCK, PROF. SILLIMAN, PROF. A. GUYOT, DR. THOMPSON, and J. D. DANA.