158 A TREATISE ON METAMORPHISM. 



environment complete. In so far as the adjustment is not complete, changes 

 are going on, and the conditions are everywhere those of chemical dynamics, 

 although the chemical action may be so slow that if the operations were 

 conducted in a laboratory it might be concluded that the conditions were 

 those of chemical statics. This, however, but illustrates the importance of 

 time in geological operations. 



Thus far the treatment of the circulation and work of ground water 

 has been general. There are many other factors concerned in the circula- 

 tion which have not yet been considered, but these are factors special to 

 the different belts and zones. They will therefore be treated in Chapters 

 VI, VII, and VIII, on the belt of weathering, the belt of cementation, and 

 the zone of anamorphism, respectively. 



