VALLEYS. 
1 8 1 
run S.W. and N.E. the subsidiary ones would be 
N.W. and S.E. 
If these considerations are correct it follows that, 
though the main valleys of Switzerland have been 
c' ) 
Fig. 43. — Diagram in illustration of Mountain Structure. 
immensely deepened and widened by rivers, their 
original course was determined by tectonic causes. 
Again, they indicate why the long valleys are not 
more continuous. If we look for instance at a map 
of the Jura, we see that though the ridges follow the 
same general curve from one end to the other, they 
are not continuous, but form a succession of similar, 
