See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1859
1860
1866
1869
1872

underlying 1859 1860 1861 1866
older and underlying 1869 1872

and older bed; 1861 1866
bed; 1859 1860 1869 1872

with 1859 1860 1861 1866 1869
by intermediate varieties with 1872

points of structure. 1859 1860 1861
respects. 1866 1869 1872

be compelled to 1859 1860 1861 1866 1869
OMIT 1872

no golden rule by which to distinguish species and varieties; they grant some little variability to each species, but when they meet with a somewhat greater amount of difference between any two forms, they rank both as species, unless they are enabled to connect them together by
the closest
close
intermediate
gradations;
gradations.
and
And
this,
this
from the reasons just
assigned,
assigned
we can seldom hope to effect in any one geological section. Supposing B and C to be two species, and a third, A, to be found in an underlying and older bed; even if A were strictly intermediate between B and C, it would simply be ranked as a third and distinct species, unless at the same time it could be
most
most
closely connected with either one or both
forms.
forms
by
by
intermediate
intermediate
varieties.
varieties.
Nor should it be forgotten, as before explained, that A might be the actual progenitor of B and C, and yet
would
might
not
at all
at all
necessarily be strictly intermediate between them in all points of structure. So that we might obtain the parent-species and its several modified descendants from the lower and upper beds of
the same
a
formation, and unless we obtained numerous transitional gradations, we should not recognise their
relationship,
blood-relationship,
and should consequently be compelled to rank them
all
all
as distinct species.
It is notorious on what excessively slight differences many palæontologists have founded their species; and they do this the more readily if the specimens come from different sub-stages of the same formation. Some experienced conchologists are now sinking many of the very fine species of
D''Orbigny
D'Orbigny
and others into the rank of varieties; and on this view we do find the kind of evidence of change which on
the
my
theory we ought to find. Look again at the later tertiary deposits, which include many shells believed by the majority of naturalists to be identical with existing species; but some