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SECOND AMERICAN FROM THE FOURTH LONDON EDITION,

EDITED BY
PROF. B. SILLIMAN.

NEW HAVEN:

HEZEKIAH HOWE & Co.

1833.

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Entered according to Act of Congress, in the year 1833, by HEZEKIAU IMOWE & Co., in the Clerk's

office of the District Court of Connecticut.

Printed by Hezekiah Howe & Co.

PREFACE TO 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. XV. On the Formation of Secondary Limestone and Sandstone, and on the progressive Development of Organic Life. Chap. XVII. On the Quaternary Strata. "Chap. XX. On Subterranean Currents, and on Carerns. 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 labours of foreign and English geologists, during the last five years, of which an account is given in different parts of the voluine. In a preliminary dissertation on certain living species of animals that elucidate fossil conchology, and also in the work itself, the author has endeavoured to direct the attention of geological students to a subject hitherto much neglected. Great importance is attached to the study of fossil shells; but the character of the animals that inhabited them, or the power they might possess of modifying the form of the shell under various circumstances, has scarcely been thought of. Some French conchologists are endeavouring to establish the doctrine that fossil conchology, independent of the succession and stratification of rocks, is the only true basis of geology; and a trifling difference in the form of a shell, is deemed sufficient to constitute a new species, and to warrant the most important conclusions respecting the age of rock formations. Cato, when the Roman Haruspices were gravely examining the entrails of the sacred victims, to ascertain the future revolutions of empires by the convolutions of the intestines, said, that he much wondered how they could refrain from laughing, whenever they looked each other in the face. Surely we might say the same to fossil conchologists, when they gravely attempt to ascertain the past revolutions of the globe by the convolutions of a shell.

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If the same conchologists were interrogated respecting the power which the ancient inhabitant of the shell might possess of changing its structure when placed in different circumstances, they would be compelled to confess their ignorance. A knowledge of fossil shells is highly useful to the geologist in cases where the superposition of strata cannot be ascertained; but fossil shells alone, give us less positive information respecting the ancient condition of the globe, than the organic remains of other classes of animals, or of vegetables ; because, for any thing we know to the contrary, all the species of molluscous animals that inhabited these shells, may have been capable of living in the same medium, and under the same conditions. But different species of vertebrated animals, and plants, must have existed under very different conditions, on land or in water. Boué, an enlightened and indefatigable continental geologist, to whose labours the science is greatly indebted, is meritoriously endeavouring to resist the absurd attempt, to force Fossil Conchology into the chair of Geology. I trust his example will be followed by English geologists. Indeed, I am convinced that many of the frivolous distinctions introduced by conchologists will soon pass away, as those of mineralogy have already passed ;* and that these two branches of natural history, will take their proper stations as auxiliaries subservient to geology.

It will be seen, by the titles to the new chapters in the present volume, that they comprise various subjects connected with important enquires relating to the Theory of the Earth. The opinions of the author have not been rashly advanced, to oppose or maintain the systems of other geologists: they are the result of long-continued reflection, on what appeared to him the most probable explanations of geological phenomena. The author says probable, because he considers that the words truth and certainty cannot yet be introduced with advantage into geological theories.

The author requests the experienced geologist, who may honour this volume with the perusal, to refer to Chap. XXII., in which he will find that the doctrine of the elevation of mountain ranges, at different epochs, was distinctly announced, and was published by him in the year 1823, supported by the same principles, as those recently advanced by M. Elie de Beaumont. He has farther proved, that the elevation of large islands, and continents, was long posterior to the elevation of mountain ranges.

. See the end of the Preface to the first edition. Some of the distinctions in Mineralogy, on which most important conclusions have been founded respecting the formations of rocks, are now known to be erroneous : magnesian minerals were all stated to be of aqueous origin. Pyroxene (Augite) was considered as an unerring criterion of igneous products, and to be an entirely distinct species from Amphibole (Hornblende): they are now proved to be identical minerals, convertible into each other, according to the degree of temperature under which they are crystallized. Observations on the true value of Fossil Conchology will be found in Chapter XVII.

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