In consequence of the rapid sale of the third edition of the "Manual," of which 2000 copies were printed in January last, a new edition has been called for in less than a twelvemonth. Even in this short interval some new facts of unusual importance in palÆontology have come to light, or have been verified for the first time. Instead of introducing these new discoveries into the body of the work, which would render them inaccessible to the purchasers of the former edition, I have given them in a postscript to this Preface (printed and sold separately), and have pointed out at the same time their bearing on certain questions of the highest theoretical interest.[v-A]

As on former occasions, I shall take this opportunity of stating that the "Manual" is not an epitome of the "Principles of Geology," nor intended as introductory to that work. So much confusion has arisen on this subject, that it is desirable to explain fully the different ground occupied by the two publications. The first five editions of the "Principles" comprised a 4th book, in which some account was given of systematic geology, and in which the principal rocks composing the earth's crust and their organic remains were described. In subsequent editions this book was omitted, it having been expanded, in 1838, into a separate treatise called the "Elements of Geology," first re-edited in 1842, and again recast and enlarged in 1851, and entitled "A Manual of Elementary Geology."

Although the subjects of both treatises relate to geology, as their titles imply, their scope is very different; the "Principles" containing a view of the modern changes of the earth and its inhabitants, while the "Manual" relates to the monuments of ancient changes. In separating the one from the other, I have endeavoured to render each complete in itself, and independent; but if asked by a student which he should read first, I would recommend him to begin with the "Principles," as he may then proceed from the known to the unknown, and be provided beforehand with a key for interpreting the ancient phenomena, whether of the organic or inorganic world, by reference to changes now in progress. Owing to the former incorporation of the two subjects in one work, and the supposed identity of their subject matter, it may be useful to give here a brief abstract of the contents of the "Principles," for the sake of comparison.

Abstract of the "Principles of Geology," Eighth Edition.

Book I.

• 1. Historical sketch of the early progress of geology, chaps. i. to iv.
• 2. Circumstances which combined to make the first cultivators of the science regard the former course of nature as different from the present, and the former changes of the earth's surface as the effects of agents different in kind and degree from those now acting, chap. v.
• 3. Whether the former variations in climate established by geology are explicable by reference to existing causes, chaps. vi. to viii.
• 4. Theory of the progressive development of organic life in former ages, and the introduction of man into the earth, chap. ix.
• 5. Supposed former intensity of aqueous and igneous causes considered, chaps. x. and xi.
• 6. How far the older rocks differ in texture from those now forming, chap. xii.
• 7. Supposed alternate periods of repose and disorder, chap. xiii.

Book II.

CHANGES NOW IN PROGRESS IN THE INORGANIC WORLD.

• 8. Aqueous causes now in action: Floods—Rivers—Carrying power of ice—Springs and their deposits—Deltas—Waste of cliffs and strata produced by marine currents: chaps. xiv. to xxii.
• 9. Permanent effects of igneous causes now in operation: Active volcanos and earthquakes—their effects and causes: chaps. xxiii. to xxxiii.

Book III.

CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS.

• 10. Doctrine of the transmutation of species controverted, chaps. xxxiv. and xxxv.
• 11. Whether species have a real existence in nature, chaps. xxxvi. and xxxvii.
• 12. Laws which regulate the geographical distribution of species, chaps. xxxviii. to xl.
• 13. Creation and extinction of species, chaps. xli. to xliv.
• 14. Imbedding of organic bodies, including the remains of man and his works, in strata now forming, chaps. xlv. to l.
• 15. Formation of coral reefs, chap. li.

It will be seen on comparing this analysis of the contents of the "Principles" with the headings of the chapters of the present work (see p. xxiii.), that the two treatises have but little in common; or, to repeat what I have said in the Preface to the 8th edition of the "Principles," they have the same kind of connection which Chemistry bears to Natural Philosophy, each being subsidiary to the other, and yet admitting of being considered as different departments of science.[vi-A]

Charles Lyell.

11 Harley Street, London, December 10. 1851.