DRAINAGE. 61

 

  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
   
   
  
 
  
   

The mean annual temperature of the strata over

which the waters flow can, therefore, be ascertained
by plunging a thermometer into the water as tt
comes out of the spring.
\ Hot or Thermal Springs range in temperature
from 60° Fahr. to the boiling-point. In geysers
the temperature of the water far down in the tube
is considerably above the boiling-point at the sur-
face.

Hot springs which occur in the neighborhood
of active -volcanoes owe their high temperature to
the vicinity of their reservoirs to beds of recently-
ejected lava.

Hot springs, however, are common in regions
distant from volcanic disturbance. In such cases
their high temperature must be attributed to the dis-
tance of their reservoirs from the earth’s surface, the
heat being derived directly from the interior.

In some cases the source of the heat is to be attributed
to chemical action in neighboring strata.

Thermal springs, whose reservoirs are at comparatively
moderate depths, may discharge their waters by ordinary
hydrostatic pressure; but where, from the great depth of
the reservoirs, this force would be insufficient, the waters
are probably raised to the surface by the pressure of super-
heated steam or compressed gas.

Since the temperature rises 1° for about every 55 feet of
descent, in cases where the increased temperature is due
solely to depth, if the issuing waters have a tempera-
ture of 149° Fabr., the reservoirs must be about one mile
below the surface, or fifty-five times the difference between
149° and 60°, the temperature of ordinary springs. In
many cases the waters probably rise from profound depths
as columns of steam, condensing in reservoirs that are less
profound.

Source of Deep-seated Waters.—Deep-seated waters
are probably derived by infiltration from the bed of the
’ ocean. The natural porosity of large areas is greatly in-
creased by the immense pressure of the water, which in
the deep ocean is equal to thousands of pounds per square
inch.

Mees

a

        

   

 

    

    
 
  
   
  
  

 

 

 

Fig, 69, Artesian Well.

 

pressure on their reservoirs, so that pumping is
not necessary to raise the water. Such wells are
therefore true springs.

The reservoirs are basin-shaped, and generally
consist of several water-logged, porous strata, con-
tained between two, curved, impervious strata. If
the upper porous layer be pierced, the waters will
flow out by reason of the pressure of the liquid
inthe higher parts. The reservoirs of many
natural springs are of this kind, the upper im-
pervious strata being broken in one or more
places by some natural force.

Artesian wells have been sunk to great depths, and it is
a significant fact that the temperature of the issuing
waters is always proportional to the depth, showing a
nearly constant increase of 1° above the temperature of
ordinary springs—viz. about 60° Fahr.—for every 55 feet
of descent. In the case of the artesian well of Grenelle,
Paris, the successful boring of which was accomplished
only after many years of the most discouraging labor,
and which reached a depth of nearly 1800 feet, the tem-
perature of the water was 92° Fahr. A well at Neusalz-
werk, Prussia, has penetrated 2200 feet; its temperature
is 91° Fahr.

163. Geysers are boiling springs which, at in-
tervals more or less regular, shoot out huge col-
umns of water with great violence. They are

 

 

Fig. 60. Geyser in Eruption.

confined to the neighborhood of volcanic dis-
tricts, and, by some, are classed with subordinate
voleanic phenomena. The jets of water some-

  
 

162. Artesian Wells differ from ordinary wells
in that their waters are discharged by natural