PHYSICAL GEOLOGY. 



CHAPTER VII. 



PROGRESS OF PHYSICAL GEOLOGY. 



Sect. 1. Object and Distinctions of Physical Geology. 



BEING, in consequence of the steps which we have attempted to 

 describe, in possession of two sciences, one of which traces the 

 laws of action of known causes, and the other describes the pheno- 

 mena which the earth's surface presents, we are now prepared to ex- 

 amine how far the attempts to refer the facts to their causes have 

 been successful : we are ready to enter upon the consideration of 

 Theoretical or Physical Geology, as, by analogy with Physical Astro- 

 nomy, we may term this branch of speculation. 



The distinction of this from other portions of our knowledge is 

 sufficiently evident. In former times, Geology was always associated 

 with Mineralogy, and sometimes confounded with it ; but the mistake 

 of such an arrangement must be clear, from what has been said. Ge- 

 oloo-v is connected with Mineralogy, only so far as the latter science 



J3,/ O* * v 



classifies a large portion of the objects which Geology employs as 

 evidence of its statements. To confound the two is the same error as it 

 would be to treat philosophical history as identical with the knowledge 

 of medals. Geology procures evidence of her conclusions wherever 

 she can ; from minerals or from seas ; from inorganic or from organic 

 bodies ; from the ground or from the skies. The geologist's business 

 is to learn the past history of the earth ; and he is no more limited to 

 one or a few kinds of documents, as his sources of information, than 

 is the historian of man, in the execution of a similar task. 



Physical Geology, of which I now speak, may not be always easily 

 separable from Descriptive Geology : in fact, they have generally been 

 combined, for few have been content to describe, without attempting 

 In some measure to explain. Indeed, if they had done so, it is proba- 



