roperties some particular substance goes
out of the fluid, which may in the end emerge in the form of a warm or
hot spring, the water of which contains but little mineral matter.
Where, however, the temperature is high, some part of the deposit,
even a little gold, may be laid down just about the spring in the
deposits known as sinter, which are often formed at such places.

In many cases the ore deposits are formed not only in the main channel
of the fissure, but in all the crevices on either side of that way. In
this manner, much as in the case of the growth of stalactitic matter
between the blocks of stone in the roofs of a cavern, large fragments
of rock, known as "horses," are often pushed out into the body of the
vein. In some instances the growth of the vein appears to enlarge the
fissure or place of the deposit as the accumulation goes on, the
process being analogous to that by which a growing root widens the
crevice into which it has penetrated. In other instances the fissure
formed by the force has remained wide open, or at most has been but
partly filled by the action of the water.

It not infrequently happens that the ascending waters of hot springs
entering limestones have excavated extensive caves far below the
surface of the earth, these caverns being afterward in part filled by
the ores of various metals. We can readily imagine that the water at
one temperature would excavate the cavern, and long afterward, when at
a lower heat, they might proceed to fill it in. At a yet later stage,
when the surface of the country had worn down many thousands of feet
below the original level, the mineral stores of the caverns may be
brought near the surface of the earth. Some of the most important
metalliferous deposits of the Cordilleras are found in this group of
hot-water caverns. These caverns are essentially like those produced
by cold water, with the exception of the temperature of the fluid
which does the work and the opposite direction of the flow.

In following crevice water which is free to obey the impulses of
gravitation far down into the earth, we enter on a realm where the
rock or construction water, that which was built into the stone at
the time of its formation, is plentiful. Where these two groups of
waters come in contact an admixture occurs, a certain portion of the
rock water joining that in the crevices. Near the surface of the
ground we commonly find that all the construction water has been
was