LVI.
PETRIFIED WOOD.
Under this
denomination are included, without distinction, all woods that have
.undergone such alterations as entitle them to be numbered amongst
minerals.
Here, omitting every other kind, we must give our attention solely to the agate-wood, which most resembles fine stones.
The
petrifaction of wood is a wonderful phenomenon. Trunks, branches and
roots, which once had life, become mixed substances ; remaining for
ages buried in the earth, and preserved by the infiltration they
experience, they at last acquire a great degree of hardness : the
organic fibres of the once vegetating body becoming recipients of
silicious saline materials.
For the petrifaction of wood, it is necessary—·
1st. That it be of a nature to be preserved under ground.
2nd. That it remain there covered from air and running water.
3rd. That it be preserved from the action of corrosives.
4th.
That it be in a place where there is also a concentration of liquids
containing either metallic particles or stony molecules loosened,
which, without destroying the ligneous body, penetrate it and become
assimilated to it, at the same time that its particles dissipate by
slow evaporation.
