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The text of the original has been somewhat curtailed in the translation, both in order to meet the wish of the author, and to secure uniformity with the other volumes of the Con temporary Science Series. I have omitted entirely a chapter of seventy-seven pages on Topographical Geology, which was more special in character than any of the other chapters. I have also omitted the lists of books of reference, taking care to embody in the text all the more important publications; and have condensed the subject-matter wherever it seemed possible to do so without detracting from the scientific value of the Hz'slory. These changes have been made with the author's approval. It only remains to add that, as a former pupil of Geheimrath Professor von Zittel's, and one who bears very grateful feelings towards him, it has afforded me great pleasure to translate this work.
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