Page 24 - 1915, Springs of CA.

24 SPRINGS OF CALIFORNIA.
Some spring waters are rendered opalescent or slightly milky by finely
divided silica or calcium carbonate. A few spring waters are ren-
dered black by iron sulphide in suspension.
Radioactivity is a property that is possessed by some waters, and
it has been offered as an explanation of the curative virtues of some
mineral springs. No acceptable proof of its healing value has been
made, however, and rfc has been shown to be a property that is rapidly
lost.1 In connection with it may be mentioned the electrical or
magnetic property that is claimed for some waters, chiefly well waters.
Careful examination, however, has always shown that such prop-
erty, if present, belongs to the well casing, not to the water, and is a
magnetized condition that probably has been produced by the
action of the drill used in sinking the well.

TEMPERATURE OF NATURAL WATERS.
The temperature of the water of many springs remains nearly
constant throughout the year and practically coincides with the
mean annual temperature of the locality. Springs that are fed by
melting snow are of course noticeably below the normal tempera-
ture ; others are considerably above it. Observations of the tempera-
ture in deep mines and deep borings indicate that in regions of
comparatively uniform and undisturbed rock, below the first 50
feet (in which the underground temperature is affected by seasonal
variation in temperature of the air), the temperature increases at
the rate of 1° F. for about each 50 or 60 feet of increase in depth.
In favorable localities this increment may be safely assumed in
estimating the depth from which the heated water rises. In the
greater number of places where thermal springs issue, however, this
increment is valueless as a basis for estimating the depth from which
the water rises. The high temperature of the water of most hot
springs can usually be assigned to faults or displacements in the
rock formations, to volcanic activity, or to chemical action, rather
than to normal increase of temperature with depth. The rocks
along fault zones are probably heated considerably above a normal
temperature by the great pressure and friction that have been
produced. Water from deep sources passes upward along these
zones and is additionally heated by contact with the heated rocks.
In some areas of volcanic rocks there are probably masses below
the surface that have not yet cooled to a normal temperature, and
they heat water which comes near them. Chemical reactions
notably the oxidation of pyrite liberate heat and may increase the
temperature of underground water.
1 Schlundt, Herman, and Moore, R. B., Radioactivity of the thermal waters of Yellowstone National
Park: U. 8. Geol. Survey Bull. 395, 1909.