adjoining shoal parts of the sea will be increased, and new stations will often be formed;— all circumstances
most most 1859 1860 | most 1861 1866 1869 1872 |
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
the productions the productions 1859 1860 1861 | the productions 1866 1869 1872 |
on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction,
fewer fewer 1859 1860 | few 1861 1866 1869 1872 |
new varieties or species will be formed; and it is during these very periods of subsidence, that
our great deposits rich our great deposits rich 1859 1860 1861 1866 |
the deposits which are richest 1869 1872 |
in fossils have been accumulated. Nature may almost be said to have guarded against the frequent discovery of her
transitional transitional 1859 1860 | fine transitional 1861 |
or linking forms. ↑Subtitle not present 1859 1860 1861 |
On
the
Absence
of
Numerous
Intermediate
Varieties
in
any
one
Single
Formation
.
1866 1869 1872 |
|
From
the foregoing the foregoing 1859 1860 | these several 1861 1866 1869 1872 |
considerations considerations 1859 1860 1861 | considerations, 1866 1869 1872 |
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
more more 1859 1860 | much more 1861 1866 1869 1872 |
difficult to
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
|