| → 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 |
|
| → I can see 1859 1860 1861 1866 |
| OMIT 1869 1872 |
|
| → why 1859 1860 1861 1866 |
| can be given why 1869 1872 |
|
| → but I can by no means pretend to 1859 1860 1861 |
| at its commencement and close; but I cannot 1866 1869 1872 |
|
| → With 1859 1860 1861 1866 1869 |
| We may safely infer that with 1872 |
|
| → we may safely infer 1859 1860 1861 1866 1869 |
| there has been 1872 |
|
|
why we do not therein find closely graduated varieties between the allied species which lived at its commencement and at its close.
cases are on record of the same species presenting
varieties in the upper and lower parts of the same
→but, as they are rare, they may be here passed over. Although each formation has indisputably required a vast number of years for its deposition,
→I can see
several reasons
→why
each should not
a graduated series of links between the species which
→but I can by no means pretend to
assign due proportional weight to the following considerations. |
|
| Although each formation may mark a very long lapse of years, each
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
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
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
layers have been deposited, it would be equally rash to suppose that it then became
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
marine animals of all
→we may safely infer
a large amount of migration
climatal and other changes; and when we see a species first appearing in any formation, the probability is that it
|
