X PEEFACE TO THE FIFTH EDITION. 



geology, and in which, the principal rocks composing the 

 earth's crust and their organic remains were described. In 

 subsequent editions this 4th book was omitted, it having been 

 expanded, 1838, into a separate treatise called the " Elements 

 of Geology," first re-edited in 1842, and again recast and en- 

 larged in 1851, and entitled " A Manual of Elementary Geol- 

 ogy." Of this enlarged work another edition, called the 

 Fourth, was published in 1852. 



Although the subjects of both treatises relate to Geology, as 

 their titles imply, their scope is very different ; the " Princi- 

 ples" containing a view of the modem changes of the earth and 

 its inhabitants, while the " Manual" relates to the monuments 

 of ancient changes. In separating the ©ne from the other, I 

 have endeavored to render each complete in itself, and inde- 

 pendent ; 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. 



It will be seen on comparing " The Contents" of the " Prin- 

 ciples" with the abridged headings of the chapters of the 

 present work (see the following pages), that the two treatises 

 have but little in common ; or, to repeat what I have said in 

 the Preface to 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 con- 

 sidered as different departments of science.* 



CHAKLES LYELL. 



53 Harley-street, London, February 22, 1855. 



* As it is impossible to enable the reader to recognize rocks and minerals at 

 sight by aid of verbal descriptions or figures, he will do well to obtain a well- 

 arranged collection of specimens, such as may be procured from Mr. Tennant (149 

 Strand), teacher of Mineralogy at King's College, London. 



