PREFACE TO THE FIFTH EDITION. ix 



and rewrite a portion of these chapters. New proofs are cited in favor of 

 attributing cleavage to mechanical force, p. 603, and for inferring in many 

 cases a connection between foliation and cleavage, p. 608. At the same 

 time, the question — how far the planes of foliation usually agree with 

 those of sedimentary deposition, is entered into, p. 607. 



Chap. XXXVUI. — To the account formerly published of mineral 

 veins, some facts and opinions are added respecting the age of the rocks 

 and alluvial deposits containing gold in South America, the United 

 States, California, and Australia. 



I have already alluded to the assistance afforded me by the 

 late Professor Edward Forbes towards the improvement of 

 some parts of this work. His letters suggesting corrections 

 and additions were continued to within a few weeks of his 

 sudden and unexpected death, and I felt most grateful to him 

 for the warm interest, which, in the midst of so many and 

 pressing avocations, he took in the success of my labors. His 

 friendship, and the power of referring to his sound judgment in 

 cases of difficulty on paleontological and other questions, were 

 among the highest privileges I have ever enjoyed in the course 

 of my scientific pursuits. Never perhaps has it been the lot of 

 any Englishman, who had not attained to political or literary 

 eminence, more especially one who had not reached his fortieth 

 year, to engage the sympathies of so wide a circle of admirers, 

 and to be so generally mourned. The untimely death of such 

 a teacher was justly felt to be a national loss ; for there was a 

 deep conviction in the minds of all who knew him, that genius 

 of so high an order, combined with vast acquirements, true 

 independence of character, and so many social and moral ex- 

 cellences, would have inspired a large portion of the rising 

 generation with kindred enthusiasm for branches of knowledge 

 nitherto neglected in the education of British youth. 



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 pub- 

 lications. The first five editions of the " Principles" comprised 

 a 4th book, in which some account was given of systematic 



