CHAPTER VIII 
UNDERGROUND WATER 
General Importance. — When rain falls, some sinks 
into the ground, some is returned to the air by evapo- 
ration, and some flows off at the surface to swell the 
rivers. That part which enters the ground commences 
a journey, perhaps of great length and occupying much 
time. During this, work of various kinds may be done, 
and it is this which we will now consider. 
As the water sinks into the soil or rocks, most of 
it chooses the easiest course, and perhaps actually pre- 
pares a path for itself. It may go on deep down into 
the earth and undertake a journey of great length, per- 
haps returning to the surface at some distant point, 
possibly after having remained for ages beneath the 
ground. In such a case, when the water returns, its 
temperature is usually high, possibly even above the 
boiling-point. 
While a certain part of the underground water goes on 
these long journeys, much of it undertakes only a short 
passage, almost at the very surface, and soon reappears, 
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