ADVERTISEMENT. 



Although but a few years have elapsed since the 

 last edition of these volumes issued from the press, 

 the great advancement of Geology and the collateral 

 Sciences rendered it necessary to compose the entire 

 work anew, that the most important recent disco- 

 veries in Palaeontology, and the new or modified views 

 of geological phenomena resulting from the progress 

 of knowledge, might be incorporated in the respec- 

 tive Lectures. 



The time and labour required for the preparation of 

 the present edition have, therefore, been considerable; 

 and since, like all my former works, these volumes 

 have been composed in the intervals of arduous pro- 

 fessional avocations, I venture to claim indulgence 

 for any inaccuracies, repetitions, or omissions. 



I would especially entreat the favourable consi- 

 deration of any author whose statements or opinions 



