PART I. 

 DYNAMICAL GEOLOGY. 



As already said, this part treats of agencies now in 

 operation producing structure. These are best treated 

 under four heads viz., atmospheric, aqueous, organic, 

 and igneous agencies. The same agencies have operated 

 from the beginning, though probably with different de- 

 grees of activity. Their accumulated effect, through 

 inconceivable ages, is the present structure of the earth. 

 We observe these operations now, in order to understand 

 the effects of their operation then. 



