THE PHYSICS OF THE EARTH. 



217 



peated several times. When several successive ranges of mountains 

 are thus developed in the process of expulsion under the margin of 

 the sea, it is easy to see that the central range may finally be driven 

 upward and flared out at the top exactly as in the Alps. Thus all 

 this movement occurs in the sea, and eventually the range becomes 

 like that now seen in Switzerland, as depicted by Heim, of Zurich. 



J5ed level 



\. Mountain fiiange r/'sing //it^e Sea 



5. Movement from both s>i<ieb continued- 



b 



Q. Whole /fountain Range rising from the sea. 



Ley si _. 



l.Rhm^from f/ie^ea continuea,giy/r7g fan-shapeu structures and O'erturned dl/>s. 



Fig. II. Illustration of Formation of Complex Range, such as the Swiss 

 Alps. The bending of the crust has caused it to pull apart at the top and 

 bottom of the folds, where it is largely covered by sedimentary deposits and 

 filled by molten rock from beneath, so that the breaks do not show at the 

 surface, unless erosion has laid bare parts of the underlying structure. In 

 these figures the thickness of the crust is less than half the width of the 

 folds; and for clearness the depth of the sea is exaggerated. 



