PROGRESS OF PHYSICAL GEOLOGY. 655 



the orderly succession of organic remains ; the con- 

 sequent fixation of a standard series of formations 

 and strata ; the establishment of the igneous nature 

 of trap rocks ; and the like. These are geological 

 truths which are assumed and implied in the very 

 language which geology uses ; thus showing how in 

 this, as in all other sciences, the succeeding steps 

 involve the preceding But in the history of geo- 

 logical theory, we have to consider the wider at- 

 tempts to combine the facts, and to assign them to 

 their causes. 



The close of the last century produced two an- 

 tagonist theories of this kind, which long maintained 

 a fierce and doubtful struggle ; that of Werner 

 and that of Hutton: the one termed Neptunian, 

 from its ascribing the phenomena of the earth's sur- 

 face mainly to aqueous agency; the other Plutonian 

 or Vulcanian, because it employed the force of 

 subterraneous fire as its principal machinery. The 

 circumstance which is most worthy of notice in these 

 remarkable essays is, the endeavour to give, by 

 means of such materials as the authors possessed, 

 a complete and simple account of all the facts of 

 the earth's history. The Saxon professor, proceed- 

 ing on the examination of a small district in Ger- 

 many, maintained the existence of a chaotic fluid, 

 from which a series of universal formations had been 

 precipitated, the position of the strata being broken 

 up by the falling in of subterraneous cavities, in the 



