If it be by means of heat and fusion that strata have been consolidated,
then, in proportion to the degree of consolidation they have undergone
from their original state, they should, _caeteris paribus_, abound more
with separations in their mass. But this conclusion is found consistent
with appearances. A stratum of porous sand-stone does not abound so much
with veins and cutters as a similar stratum of marble, or even a
similar stratum of sand-stone that is more consolidated. In proportion,
therefore, as strata have been consolidated, they are in general
intersected with veins and cutters; and in proportion as strata are
deep in their perpendicular section, the veins are wide, and placed at
greater distances. In like manner, when strata are thin, the veins are
many, but proportionally narrow.
It is thus, upon chemical principles, to be demonstrated, That all the
solid strata of the globe have been condensed by means of heat, and
hardened from a state of fusion. But this proposition is equally to
be maintained from principles which are mechanical. The strata of the
globe, besides being formed of earths, are composed of sand, of gravel,
and fragments of hard bodies, all which may be considered as, in their
nature, simple; but these strata are also found composed of bodies which
are not simple, but are fragments of former strata, which had been
consolidated, and afterwards were broken and worn by attrition, so as
to be made gravel.
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