52 Astronomy and Geology compared. PT. i. 



their effects ; we have no difficulty in distinguishing 

 their operations from each other, although we 

 cannot trace or explain the nature of this difference 

 from its sources. 



I will not attempt to trace in detail the different 

 stages in Geology through which progress is marked. 

 It is far from my purpose, as it certainly would be 

 beyond my ability, to write a work on the principles 

 of the science, or even to attempt a manual or 

 elementary treatise upon it. I will content myself 

 with referring to the admirable works which have 

 been produced during the present century. Geolo- 

 gical discoveries have required immense labour and 

 research, and vast knowledge in their authors, but 

 they principally rest upon unwearied diligence and 

 mastery of detail in the incessant comparison upon 

 which they are founded. They are not based in the 

 same degree as Astronomy is upon abstruse Mathe- 

 matics, requiring long study of abstract principles. 

 It is not so difficult for us to follow and in a general 

 degree to comprehend the outlines of the Science 

 when they have been traced for us by the sagacity 

 and intellect of these great originators. 



Geology may be divided therefore into these two 

 parts, the first relating to the material structure of 



