| → our great deposits rich 1859 1860 1861 1866 |
| the deposits which are richest 1869 1872 |
|
| ↑ 1 blocks not present in 1866 1869 1872; present in 1859 1860 1861 |
| Nature may almost be said to have guarded against the frequent discovery of her transitional
or linking forms.
|
|
| → but, as they are not common, they may be here passed over. 1866 |
| but, as they are rare, they may be here passed over. 1859 1860 1861 |
| 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 |
|
| → at its commencement and close; but I cannot 1866 1869 1872 |
| but I can by no means pretend to 1859 1860 1861 |
|
|
have been completely denuded, with not a wreck left behind. |
|
| One remark is here worth a passing notice. During periods of elevation the area of the land and of the adjoining shoal parts of the sea will be increased, and new stations will often be formed;— all circumstances
favourable, as previously explained, for the formation of new varieties and species; but during such periods there will generally be a blank in the geological record. On the other hand, during subsidence, the inhabited area and number of inhabitants will decrease (excepting
on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction,
new varieties or species will be formed; and it is during these very periods of subsidence, that
→our great deposits rich
in fossils have been accumulated. ↑
|
| On
the
Absence
of
Numerous
Intermediate
Varieties
in
any
Single
Formation
. |
| From
it cannot be doubted that the geological record, viewed as a whole, is extremely imperfect; but if we confine our attention to any one formation, it becomes
difficult to
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 not common, 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
→at its commencement and close; but I cannot
|
