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1859
1860
1861
1866
1869
1872

Compare with:
1859
1861
1866
1869
1872

I am inclined to believe, has 1859 1860 1861
has probably 1866 1869 1872

separated 1859 1860
in most cases separated 1861 1866 1869 1872

for 1859 1860 1861 1866
of great length; for 1869 1872

be 1859 1860
generally be 1861 1866
as a general rule be 1869 1872

of fossiliferous formations 1859 1860 1861
of strata rich in fossils 1869 1872
OMIT 1866

lowest Silurian strata, 1859 1860 1861
lowest Silurian strata 1866
Cambrian formation, 1869 1872

I can only recur 1859 1860 1861
of formations rich in fossils of many kinds, I can recur only 1866
I can recur only 1869 1872

chapter. 1859 1860 1861 1866 1869
chapter; namely, that though our continents and oceans have endured for an enormous period in nearly their present relative positions, we have no reason to assume that this has always been the case; consequently formations much older than any now known may lie buried beneath the great oceans. 1872

1 blocks not present in 1859 1860 1861 1866 1869; present in 1872
With respect to the lapse of time not having been sufficient since our planet was consolidated for the assumed amount of organic change, and this objection, as urged by Sir William Thompson , is probably one of the gravest as yet advanced, I can only say, firstly, that we do not know at what rate species change as measured by years, and secondly, that many philosophers are not as yet willing to admit that we know enough of the constitution of the universe and of the interior of our globe to speculate with safety on its past duration.

which I require, 1859 1860 1861 1866
required by our theory, 1869 1872

all species have 1859 1860 1861 1866
species have all 1869 1872

which my theory requires, 1859 1860 1861 1866
required, 1869
required by the theory, 1872

formations distant from each other in time. 1859 1860 1861 1866
widely separated formations. 1869 1872

can 1859 1860 1861 1866 1869
as far as I can see, may 1872

improved;
proved;
and when they
have
do
spread,
and are
if
discovered in a geological formation, they
will
will
appear as if suddenly created there, and will be simply classed as new species. Most formations have
been,
been
intermittent in their accumulation; and their
duration
duration,
I am inclined to believe, has been shorter than the average duration of specific forms. Successive formations are separated from each other by
enormous
enormous
blank intervals of
time
time;
for fossiliferous
formations
formations,
thick enough to resist future
degradation
degradation,
can be accumulated only where much sediment is deposited on the subsiding bed of the sea. During the alternate periods of elevation and of stationary level the record will
generally be
be
generally blank.
blank.
During these latter periods there will probably be more variability in the forms of life; during periods of subsidence, more extinction.
With respect to the absence of fossiliferous formations beneath the lowest Silurian strata, I can only recur to the hypothesis given in the
tenth
ninth
chapter. That the geological record is imperfect all will admit; but that it is imperfect to the degree which I require, few will be inclined to admit. If we look to long enough
in- tervals
intervals
of time, geology plainly declares that all species have changed; and they have changed in the manner which my theory requires, for they have changed slowly and in a graduated manner. We clearly see this in the fossil remains from consecutive formations invariably being much more closely related to each other, than are the fossils from formations distant from each other in time.
Such is the sum of the several chief objections and difficulties which may
be justly
justly be
urged against
the
my
theory; and I have now briefly recapitulated the answers and explanations
which,
which
can be
given.
given
to
to
them.
them.
I have felt these difficulties far too heavily during many years to