[Illustration: FIG. 32.--From the mingling of two liquids a solid is
sometimes formed.]
Suppose water from different sources enters a crack in a rock,
bringing different substances in solution; then the mingling of the
waters may cause precipitation, and the solid thus formed will be
deposited in the crack and fill it up. Hence, while ground water tends
to make rock porous and weak by dissolving out of it large quantities
of mineral matter, it also tends under other conditions to make it
more compact because it deposits in cracks, crevices, and pores the
mineral matter precipitated from solution.
|