Part III.] OR POISONED BY VEGETABLE GROWTH ? 
197 
vegetationand by fencing these thousands of 
square miles, man acts as a very universal con¬ 
servative. 
The existence of upper valleys, or dry rivers 
of soil, proves that, were there no such things as 
rivers on the globe, the scooping power of rain 
would still give the same alternation of hills 
with valleys sloping to the sea which now ob¬ 
tains, and the same waste and denudation from 
lateral wash would still take place. The river 
only makes its own channel (which is much en¬ 
larged by rain floods), and in that channel as¬ 
sists in conveying away the denudation brought 
to it by rain, which would otherwise travel more 
slowly along the valley, and out of the valley, by 
the same force which brought it into the valley, 
—rain. 
I believe that in many cases where the country 
is composed of soft and porous materials, as 
chalk, the depth of the valleys and channels 
scooped out by rain lays open the springs, and 
forms the rivers, instead of the rivers forming 
the valleys. How many dry valleys are there 
sloping to the sea without having laid open a 
spring, and therefore without any stream ? And 
what formed these valleys ? How many lateral 
o 3 
