236 RETROSPECT. 



the order here indicated. But all these stages are not found 

 anywhere in a regular and unbroken succession. In nature, 

 only some series of rocks have retained their position, as the 

 original stratification has at different times been so modified and 

 revolutionized that the natural sequence of the various forma- 

 tions has only been established by the labour of geologists con- 

 tinued for many years. The whole appearance of the country 

 has been changed by these revolutions and by the phenomena 

 connected with them, and the present form has been given to it. 

 Prof. Heer has already repeatedly referred to these revolutions ; 

 and now all of them must be considered together, so far as is 

 necessary to understand the present configuration of Switzerland. 



