240 



STRUCTURAL GEOLOGY. 



or ivrinklcs are mountain-ranges. So much it was neces- 

 sary to say to render what follows intelligible ; but the 

 origin of mountains is best taken up in connection with 

 their structure. 



Structure and Origin of Mountains. 



Mountain-ranges are always made up of series of strata 

 of immense thickness thrown into folds, as if they had 

 been crushed together horizontally, and swelled up verti- 



I: 



FIG. 143. 



cally. To illustrate : Suppose we had a number of layers 

 of wax, or clay, or other plastic substance of different 

 colors laid one atop another, as in Fig. 143, A ; suppose, 

 further, that the middle portions were softened a very 

 little by gentle heat below, and the whole was then 

 crushed together horizontally,' as represented by the 

 arrows. The middle softer portions would yield and be 



FIG. 144. Section across the Uintah. 



mashed together, thrown into folds and swelled up, as 

 shown in Fig. 143, B. Now, this is exactly the way in 



