been completely melted. Granite
and gneiss, which are of like chemical composition, have been shown, in
various cases, to pass one into the other; as at Valorsine, near Mont
Blanc, where the two, in contact, are observed to "both undergo a
modification of mineral character. The granite still remaining
unstratified, becomes charged with green particles; and the talcose
gneiss assumes a granitiform structure without losing its
stratification." In the Aberdeen-granite, lumps of unmelted gneiss are
abundant; and we can ourselves bear witness that the granite on the
banks of Loch Sunart yields proofs that, when molten, it contained
incompletely-fused clots of sedimentary strata. Nor is this all. Fifty
years ago, it was thought that all granitic rocks were primitive, or
existed before any sedimentary strata; but it is now "no easy task to
point out a single mass of granite demonstrably more ancient than all
the known fossiliferous deposits." In brief, accumulated evidence shows,
that by contact with, or proximity to, the molten matter of the Earth's
nucleus, all beds of sediment are liable to be actually melted, or
partially fused, or so heated as to agglutinate their particles; and
that according to the temperature they have been raised to, and the
circumstances under which they cool, they assume the forms of granite,
porphyry, trap, gneiss, or rock otherwise altered. Further, it is
manifest that though strata of various ages have been thus changed, yet
the most ancient strata have been so changed to the greatest extent;
both because they have been nearer to the centre of igneous agency; and
because they have been for longer periods liable to be affected by it.
Whence it follows, that sedimentary strata passing a certain antiquity,
are unlikely to be found in an unmetamorphosed state; and that strata
much earlier than these are certain to have been melted up. Thus if,
throughout a past of indefinite duration, there had been at work those
aqueous and igneous agencies which we see still at work, the state of
the Earth's crust might be just what we find it. We have no evidence
which puts a limit to the period throughout which this formation and
destruction of strata has been going on. For aught the facts prove, it
may have been going on for ten times the period measured by our whole
series of sedimentary deposits.

Besides having, in the present appearances of the Earth's crust, no data
for fixing a commencement to these proces