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In the Preface to the former edition of the Principles of Geology, I gave a brief account of the progress of the work up to the publication of the Third Volume in 1833. This account I shall now repeat with some omissions, and with the addition of such information as I think will be useful to the reader respecting the latest alterations made in the work.The original MS. of the Principles of Geology was delivered to the publisher at the close of the year 1827, when it was proposed that it should appear in the course of the year following, in two volumes octavo. Many causes concurred to delay the completion of the work, and considerably to modify the original plan. In May, 1828, when the preliminary chapters on the History of Geology, and some others which follow them in the first volume, were nearly finished, I became anxious to visit several parts of the continent, in order to acquire more information concerning the tertiary formations.
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