PREFACE ΤΟ THE FOURTH EDITION. THE present Volume contains above one fourth more letterpress than the Third Edition: being printed closer, and in a fuller page, in order to comprise numerous additional facts, and the important discoveries recently made in Geology. There are five entirely new chapters, beside considerable additions to most of the former chapters. The new chapters in this Edition are:-Chap. XVI. On the Formation of Secondary Limestone and Sandstone, and on the progressive Developement of Organic Life. Chap. XVII. On the Quaternary Strata. Chap. XX. On Subterranean Currents, and on Caverns. Chap. XXII. On the Elevation of Mountain Ranges and Continents. Chap. XXIV. On the Temperature of the Earth; on Central Heat; and on Astronomical Causes illustrative of Geological Theories. Beside two new plates, the present Volume contains also numerous wood-cuts. Since the publication of the Third Edition, the Author has revisited several of the localities which were the scenes of his earliest investigations; he has also examined certain parts of England, of which the geology was dubious; and has inserted in this work such alterations as were deemed necessary. These, however, bear a small proportion to the valuable |