two beds, one of which lies upon another, we compare distant parts, it
is quite possible that the upper may be any number of years older than
the under, and the under any number of years younger than the upper.

Now you must not suppose that I put this before you for the purpose of
raising a paradoxical difficulty; the fact is, that the great mass of
deposits have taken place in sea-bottoms which are gradually sinking,
and have been formed under the very conditions I am here supposing.

Do not run away with the notion that this subverts the principle I laid
down at first. The error lies in extending a principle which is
perfectly applicable to deposits in the same vertical line to deposits
which are not in that relation to one another.

It is in consequence of circumstances of this kind, and of others that I
might mention to you, that our conclusions on and interpretations of
the record are really and strictly only valid so long as we confine
ourselves to one vertical section. I do not mean to tell you that there
are no qualifying circumstances, so that, even in very considerable
areas, we may safely speak of conformably superimposed beds being older
or younger than others at many different points. But we can never be
quite sure in coming to that conclusion, and especially we cannot he
sure if there is any break in their continuity, or any very great
distance between the points to be compared.

Well now, so much for the record itself,--so much for its
imperfections,--so much for the conditions to be observed in
interpreting it, and its chronological indications, the moment we pass
beyond the limits of a vertical linear section.