understand, understand, 1860 1861 1866 | under- stand, 1859 | understand 1869 1872 |
why we do not therein find closely graduated varieties between the allied species which lived at its commencement and at its close.
Some Some 1859 1860 1861 | Several 1866 1869 1872 |
cases are on record of the same species presenting
distinct distinct 1859 1860 1861 1866 | distinct 1869 1872 |
varieties in the upper and lower parts of the same
formation, formation, 1859 1860 1861 1866 | formation: 1869 1872 |
but, as they are rare, they may be here passed over. but, as they are rare, they may be here passed over. 1859 1860 1861 |
but, as they are not common, they may be here passed over. 1866 |
thus, Trautschold gives a number of instances with Ammonites; and Hilgendorf has described a most curious case of ten graduated forms of Planorbis multiformis in the successive beds of a fresh-water formation in Switzerland. 1869 1872 |
Although each formation has indisputably required a vast number of years for its deposition,
I can see I can see 1859 1860 1861 1866 |
OMIT 1869 1872 |
several reasons
why why 1859 1860 1861 1866 |
can be given why 1869 1872 |
each should not
include include 1859 1860 1861 1866 | commonly include 1869 1872 |
a graduated series of links between the species which
then then 1859 1860 1861 | then 1866 1869 1872 |
lived; lived; 1859 1860 1861 | lived 1866 1869 1872 |
but I can by no means pretend to but I can by no means pretend to 1859 1860 1861 |
at its commencement and close; but I cannot 1866 1869 1872 |
assign due proportional weight to the following considerations. |
|
Although each formation may mark a very long lapse of years, each
perhaps perhaps 1859 1860 1861 | probably 1866 1869 1872 |
is short compared with the period requisite to change one species into another. I am aware that two palæontologists, whose opinions are worthy of much deference, namely Bronn and
Woodward, Woodward, 1859 1860 1861 1872 | Wood-ward, 1866 | Wood- ward, 1869 |
have concluded that the average duration of each formation is twice or thrice as long as the average duration of specific forms. But insuperable difficulties, as it seems to me, prevent us
coming coming 1859 1860 1861 | from coming 1866 1869 1872 |
to any just conclusion on this head. When we see a species first appearing in the middle of any formation, it would be rash in the extreme to infer that it had not elsewhere previously existed. So again when we find a species disappearing before the
uppermost uppermost 1859 1860 1861 | last 1866 1869 1872 |
layers have been deposited, it would be equally rash to suppose that it then became
wholly wholly 1859 1860 1861 | wholly 1866 1869 1872 |
extinct. We forget how small the area of Europe is compared with the rest of the world; nor have the several stages of the same formation throughout Europe been correlated with perfect accuracy. |
|
With With 1859 1860 1861 1866 1869 |
We may safely infer that with 1872 |
marine animals of all
kinds, kinds, 1859 1860 1861 1866 1869 | kinds 1872 |
we may safely infer we may safely infer 1859 1860 1861 1866 1869 |
there has been 1872 |
a large amount of migration
during during 1859 1860 1861 1866 1869 | due to 1872 |
climatal and other changes; and when we see a species first appearing in any formation, the probability is that it
|