vi PREFACE. 



and to elucidate tliem with the history of British and Foreign 

 strata. His book was in advance of the needs of the time, 

 worthy of the University in which he taught, and no doubt the 

 best Manual of Geology which had been written. The law of 

 science, however, is progress. Since 1855, the date of the last 

 edition, geology has grown in every element, has developed new 

 departments of petrology, and become separated from physical 

 geography ; but the plan of the old book still stands, unaffected 

 and excellent. We therefore accepted the responsibility of revis- 

 ing the Manual of Geology, and thus honour the memory of an 

 eloquent teacher, whose geniality reflected the happy influence 

 of nature, who if not a brilliant discoverer had verified much of 

 what was known, and was a sound geologist of balanced philo- 

 sophical habit. 



In this volume I have preserved every page of the original 

 work that was in any way valuable. But the changes necessary 

 to bring the science of the last generation into harmony with 

 current knowledge and thought, have been more serious than 

 were anticipated when the revision began. I have omitted much, 

 have added more, and modified always ; while from exigencies 

 of space I have elected to omit certain subjects, and not to 

 develop others to the length to which they might profitably be 

 followed. Yet with this literary regeneration, the spirit of the 

 old book has been preserved, and it has been revivified with the 

 spirit of the newer geology which is unfolding. 



In endeavouring to sustain that part of the title-page which 

 describes the Manual as theoretical, I have drawn to some extent 

 upon theoretical views enunciated in my lectures during the ten 

 years from 1860 to 1870, for which Professor Sedgwick, F.R.S., 

 deputed to me the practical teaching of Physical Geology and 

 Palaeontology in the University of Cambridge ; not altogether 

 foregoing a hope that days of requisite leisure may yet come, in 

 which the facts dependent upon those views may be elaborated 

 to their legitimate ends. 



The work will be found practical too ; for it aims through- 



