INFLUENCE OF STRATA UPON SCENERY. 
273 
and elsewhere, large districts with very few streams, 
and here and there copious springs, where the water 
is brought to the surface by some more impervious 
stratum. A glance at any geological map will show, 
for instance, that the districts occupied by the 
Upper Jurassic rocks are especially waterless, there 
being many square miles without even the smallest 
rivulet. 
The distribution of springs naturally affects that 
of villages. Thus in several of the valleys of the 
Jura we find a row of hamlets along the outcrop of 
the impervious Purbeck strata. 
The influence of different rocks upon vegetation 
is another way in which they affect the character 
of the scenery. The principal contrast is between 
Crystalline and calcareous strata. 
Cargneule gives fertile pasturage, as do the Lower 
and Middle Jura owing to the quantity of Marl they 
contain. 
The Cretaceous rocks furnish sweet but not 
abundant herbage, and the Lias is but moderately 
favourable to vegetation. The Urgonian districts are 
arid and barren, and can be distinguished even at a 
distance from the Neocomian, which bears a luxuriant 
vegetation. 
Flysch supports a vegetation, vigorous indeed, 
Scenery of Switzerland . /. 1 ^ 
