Hence, when water has sunk into the earth,
it does not by any means soak through it in an equable degree. It is an
easier matter for it to ooze many miles, along a layer of gravel, than to
penetrate six inches into a layer of clay that may bound the gravel.
Therefore, whenever a porous earth or a fissured rock crops out to the
light of day, there is, in ignorance of all other facts, some chance of a
spring being discovered in the lowest part of the outcrop. A favourable
condition for the existence of a large and permanent fountain, is where a
porous stratum spreads over a broad area at a high level, and is
prolonged, by a gradually narrowing course, to an outlet at a lower one.
The broad upper part of the stratum catches plenty of water during the
wet season, which sinks into the depths as into a reservoir, and oozes
out in a regular stream at its lower outlet. A fissured rock makes a
still easier channel for the water.
[Fig 1 and Fig. 2].
As examples of ordinary cases of fountains, we will take those
represented in the following figures. Fig. I is a mountain. Fig. 2 is a
model, made to explain more clearly the conditions represented in fig. I.
It will be observed that there is a ravine, R, in front; a line of fault,
L, M. N, on its left side, Supposed to be filled with water-tight rock;
and a valley, V (fig. 1), on the extreme right.
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