VALLEYS. 
173 
vegetation grows under more or less similar condi- 
tions. 
In the longitudinal valleys, on the contrary, not 
only are the strata often different on the two sides, 
but the northern side, which looks to the south, re- 
ceives more sun, while the southern side is more in 
shadow. The contrast is strongly shown in the 
Valais itself, where the south side is green and well 
wooded, the north, on the contrary, comparatively 
dry and bare. 
In some places, for instance in the valley of the 
Rhone below Visp, the green lines of vegetation which 
follow the “Bisses” or artificial water-courses are very 
conspicuous. 
On the Lake of Zurich, though the vegetation is 
the same on both sides — woods and meadows and 
vineyards — the distribution is quite different. Both 
sides of the Lake are terraced, so that we have flat 
zones and steep slopes. On the northeast side the 
slopes get more sun, and hence the vines are planted 
on them, while the meadows and woods are on the 
terraces. On the west, however, the terraces get 
more sun, and consequently the vines are on the 
terraces and the meadows and woods on the slopes. 
There is another class of valleys, namely, those 
which are due to lines Of fracture or dislocation, and 
