It is now several years since I first became convinced that a diligent study of the various structures produced by the action of the currents present during the formation of stratified rocks would lead to the knowledge of many very valuable and remarkable facts in connexion with physical geology aud ancient physical geography. Since then I have never willingly lost any opportunity of determining the direction and character of the currents present during the deposition of rocks of every age, and of accumulating information on every kind of subject that could throw light upon the inquiry. I must now have, in my note-books, not less than twenty thousand recorded observations, many of which I have not been able to make use of hitherto, for want of sufficient points of comparison; and, although I am most willing to admit that the subject is quite in its infancy, and that I am a mere student of nature, ready to modify my own opinions or to adopt others which would explain the facts in a more satisfactory manner, yet some of the facts are so definite and distinct, and I have verified them in so many localities, over sufficiently extensive districts, as to warrant the formation of definite conclusions. We all protest against theories without facts; but to accumulate a great number of facts without attempting such explanations as would unite them into a complete and consistent whole would be not less unphilosophical.