220 ECONOMIC GEOLOGY
smoke, acids, and bacteria. Snow collected off the roof of
the Lancet Office in London contained ~—
Soot, coal dust, and tar .
Mineral matter in solution
Organic matter in solution
Free ammonia .
Organic ammonia
Sodium chloride
Sulphuric acid
Nitric acid
30°32 grs. per gall,
420 ,,
784 ”
07
01
3;
3:30 1”
Traces.
The rain near the sea contains sea-salt derived from
evaporated spray, and some is carried far inland. This salt
is harmless in moderate quantities, but introduces uncertainty
in the use of chlorine as a test of organic pollution.
ConnaTE—Some water is enclosed in sedimentary rocks
during their deposition and is stored in them as “ connate
water.”
Prutonic or JuveniLE WaTer—There was for long wide-
spread reluctance to admit the existence of any water on
land other than that derived from the rain. Deep wells,
hot springs, and volcanoes were regarded as all discharging
meteoric water which had percolated underground and been
forced to the surface, either by the internal heat of the earth,
or by the pressure of water at higher levels in the water-
bearing bed. Thus at the Conferences on * Water Supply
and Distribution ” in 1884, G. J. Symons, the meteorologist,
declared that “all water supply comes from the clouds,”
and James Mansergh, representing the engineers, said ** all
supplies of water, whether found upon the surface or below
it, in underground depths, are derived from the rain which
falls upon the earth.” C. S. Slichter (U.S.G.S.. Wat. Sup.
Pap., 67, 1902) adopts the same view.
Geologists have long held that the rainfall is supplemented
by water from the interior of the earth, which is described
as plutonic, or magmatic, or * juvenile ’ (cf. p. 22).
Nearly all primary rocks contain water, which is seen under
the microscope in the fluid cavities of quartz in granite. This
water usually amounts to between I to 5 per cent. in igneous
rocks ; and owing to their bulk a small percentage amounts
to a prodigious quantity. This water tends to escape and
