| → our great deposits rich 1859 1860 1861 1866 |
| the deposits which are richest 1869 1872 |
|
| ←Subtitle not present 1859 1860 1861 On
the
Absence
of
Numerous
Intermediate
Varieties
in
any
one
Single
Formation
.
1866 1869 1872 |
| → 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 |
|
|
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. Nature may almost be said to have guarded against the frequent discovery of her
or linking forms. →
|
| 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 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
|
