VI PKEFACE. 



opposition, are now beginning to find favor in the eyes of the 

 scientific world. That such will he the ultimate fate of others 

 herein contained, and not yet generally received, the author 

 is persuaded. It has been his fortune to enunciate, in very 

 many cases, views for which his fellow-workers were not pre- 

 pared, and after a lapse of years to find these views propounded 

 by others as new discoveries or original conclusions. Natu- 

 rally desirous, however, of vindicating his claims to priority in 

 certain of these matters, he feels that the best way of attain- 

 ing this result is to reprint the original essays. It should be 

 said that two of these, namely, IV. and XII., were given as 

 popular lectures, and are thus unlike the others in method 

 and style. 



The reproduction of the papers on the Geology of the Alps 

 and the History of Cambrian and Silurian requires, it is con- 

 ceived, no explanation, inasmuch as, apart from their general 

 interest, they serve to throw great light upon many questions 

 raised in the essay on the Geognosy of the Appalachians as to 

 the origin and age of their rocky strata. 



As regards the five papers which are placed at the end of the 

 volume, the author reprints them for the reason that, incom- 

 plete and fragmentary as they are, they have a certain value in 

 the history of chemical theory; and, moreover, contain, in 

 his opinion, the germs of a philosophy of chemistry and miner- 

 alogy which he hopes one day to develop himself or to see 

 developed by others. 



In preparing this collection for the press, the author has been 

 compelled by the limits assigned to the volume to omit several 

 papers which would else have found a place here, and to abridge 

 others. In some cases, paragraphs have been rewritten and 

 additions made, which are distinguished by being placed in 

 brackets. Explanatory notes are given, and introductory and 



