Thus suppose three strata of grit, A, B, C, are charged unequally
with calcareous matter, and that B is the most calcareous. If consolidation
takes place in B, the concretionary action may spread upward into a part of A,
where the carbonate of lime is more abundant than in the rest; so that a mass, d
e f, forming a portion of the superior stratum, becomes united with B into one
solid mass of stone. The original line of division, d e, being thus effaced, the
line d f would generally be considered as the surface of the bed B, though not
strictly a true plane of stratification. (Figure 50.)
PRESSURE AND HEAT.
When sand and mud sink to the bottom of a deep sea, the particles are not
pressed down by the enormous weight of the incumbent ocean; for the water, which
becomes mingled with the sand and mud, resists pressure with a force equal to
that of the column of fluid above. The same happens in regard to organic remains
which are filled with water under great pressure as they sink, otherwise they
would be immediately crushed to pieces and flattened. Nevertheless, if the
materials of a stratum remain in a yielding state, and do not set or solidify,
they will be gradually squeezed down by the weight of other materials
successively heaped upon them, just as soft clay or loose sand on which a house
is built may give way.
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