594 HISTORY OF GEOLOGY. 



plating such facts, to confine ourselves to descrip- 

 tion and classification. Conjectures and reasonings 

 respecting the causes of the phenomena force them- 

 selves upon us at every step; and even influence our 

 classification and nomenclature. Our Descriptive 

 Geology impels us to endeavour to construct a Phy- 

 sical Geology. This close connexion of the two 

 branches of the subject by no means invalidates 

 the necessity of distinguishing them : as in Botany, 

 although the formation of a Natural System neces- 

 sarily brings us to physiological relations, we still 

 distinguish Systematic from Physiological Botany. 



Supposing, however, our Descriptive Geology to 

 be completed, as far as can be done without consi- 

 dering closely the causes by which the strata have 

 been produced, we have now to enter upon the 

 other province of the science, which treats of those 

 causes, and of which we have already spoken, as 

 Physical Geology. But before we can treat this 

 department of speculation in a manner suitable to 

 the conditions of science, and to the analogy of other 

 parts of our knowledge, a certain intermediate and 

 preparatory science must be formed, of which we 

 shall now consider the origin and progress. 



