THE PAL^ETIOLOGICAL SCIENCES. 535 



for our example, we must have, first Descriptive 

 or Phenomenal Geology ; next, the exposition -6f 

 the general principles by which such phenomena 

 can be produced, which we may term Geological 

 Dynamics ; and, lastly, doctrines hence derived, as 

 to what have been the causes of the existing state 

 of things, which we may call Physical Geology. 



These three branches of geology may be found 

 frequently or constantly combined in the works 

 of writers on the subject, and it may not always 

 be easy to discriminate exactly what belongs to 

 each subject 4 . But the analogy of this science with 

 others, its present condition and future fortunes, 

 will derive great illustration from such a distribu- 

 tion of its history ; and in this point of view, there- 

 fore, we shall briefly treat of it; dividing the history 

 of Geological Dynamics, for the sake of convenience, 

 into two Chapters, one referring to inorganic, and 

 one to organic, phenomena. 



4 The Wernerians, in distinguishing their study from Geology , 

 and designating it as Geognosy, the knowledge of the earth, 

 appear to have intended to select Descriptive Geology for their 

 peculiar field. In like manner, the original aim of the Geological 

 Society of London, which was formed (1807) " with a view to 

 record and multiply observations," recognized the possibility of a 

 Descriptive Geology separate from the other portions of the 

 science. 



