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of ancient and modern causes are next considered (Chap. W. to p. 89, Vol. I.), and it is contended that neither the imaged universality of certain sedimentary formations (Chap. V.), nor the different climates which appear to have formerly pervaded the northern hemisphere (Chaps. VI. VII. VIII.), nor the alleged progressive development of organic life as inferred from the study of fossil remains (Chap. IX.), lend any solid support to the assumption. The numerous topics of general interest brought under review in discussing this fundamental question are freely enlarged upon, in the hope of stimulating curiosity; and the author is aware that in endeavouring to attain this object, he has occasionally carried the beginner beyond his depth. It is presumed, however, that the reader will understand enough to be convinced that the forces formerly employed to remodel the crust of the earth were the same in kind and energy as those now acting: or, at least, he will perceive that the opposite hypothesis is very questionable; and if so, he will enter upon the study of the two treatises which follow on the Changes now in progress in the Organic and Inorganic World (Books II. and III.) with a just sense of the importance of their subject matter, and their direct bearing on Geology. The first of these treatises, or that relating to the changes known to have taken place in the inorganic creation within the historical era, is divided into two parts. In the first, an account is given of the observed effects of aqueous causes, such as rivers, springs, tides and currents (Book II. Chaps. I. to VIII.); in the second, the igneous causes, such as the volcano and earthquake, and all subterranean movements, are considered (Book II. Chaps. IX. to XIX.). The other treatise, or that on the changes of the organic world, is also divided into two parts; the first of which comprehends all questions relating to the real existence and variability of species, and the limits assigned to their duration (Chaps. I. to XI. Book III.). The second explains the processes by which the remains of animals and

cussed in the first part of the Third Book; after reading which, the student comes in a great degree prepared to follow the views and speculations of the author on the laws by which the extinction and successive disappearance of species may be governed. From these remarks it will be seen that a study of systematic treatises on the recent changes of the organic and inorganic world afford a good preliminary exercise for those who desire to interpret geological monuments. They are thus enabled to proceed from the known to the unknown, or from the observed effects of causes now in action to the analogous effects of the same or similar causes which have acted at remote periods. It was necessary to dwell thus fully on the connexion of the Second and Third Books with the Fourth, because the relation of these parts of the work to each other is the least obvious. In order to comprehend the plan of other parts, it will be sufficient to peruse the abridged Table of Contents.

London, October 1836.

PRINCIPIEES OF GEOLOGY.

BOOK I.

CHAP TER I.

Geology defined—Compared to History—Its relation to other Physical Sciences— Not to be confounded with Cosmogony.

Geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature: it inquires into the causes of these changes, and the influence which they have exerted in modifying the surface and external structure of our planet.

By these researches into the state of the earth and its inhabitants at former periods, we acquire a more perfect knowledge of its present condition, and more comprehensive views concerning the laws now governing its animate and inanimate productions. When we study history, we obtain a more profound insight into human nature, by instituting a comparison between the present and former states of society. We trace the long series of events which have gradually led to the actual posture of affairs; and by connecting effects with their causes, we are enabled to classify and retain in the memory a multitude of complicated relations— the various peculiarities of national character—the different degrees of moral and intellectual refinement, and numerous other circumstances, which, without historical associations, would be uninteresting or imperfectly understood. As the present condition of nations is the result of many antecedent changes, some extremely remote and others recent, some gradual, others sudden and violent, so the state of the natural world is the result of a long succession of events; and if we would enlarge our experience of the present economy of nature, we must investigate the effects of her operations in former epochs.

Vol. I.-C

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