and granitic rocks exceed, in the proportion of 19 to
12.5, 12.5, 1872 |
12.5, not only the true coal measures, well known to be here developed in extraordinary force, but likewise the Umbral series, which together compose 1861 |
12.5, 1866 1869 |
the whole
of the newer of the newer 1866 1869 1872 |
newer 1861 |
Palæozoic
formations. formations. 1866 1869 1872 | formation. 1861 |
In many regions the metamorphic and granitic
rocks rocks 1866 1869 1872 | areas 1861 |
would be
found much more widely extended than they appear to be, if found much more widely extended than they appear to be, if 1872 |
greatly increased in size, if we could remove 1861 |
seen to be much more widely extended, if 1866 1869 |
all the sedimentary beds
were removed which were removed which 1866 1869 1872 |
which 1861 |
rest unconformably on them, and which
...OMIT 1866 1869 1872 |
at the line of junction have not been metamorphosed, showing that they 1861 |
could not have formed part of the original mantle under which
they they 1866 1869 1872 | the 1861 |
....... 1866 1869 1872 | granitic rocks 1861 |
were crystallized. Hence it is probable that in some parts of the world whole
formations formations 1869 1872 | formations, 1861 1866 |
...OMIT 1869 1872 |
marking at least sub-stages in the several successive geological epochs, 1861 1866 |
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
....... 1861 1866 1869 1872 | most 1859 1860 |
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
....... 1866 1869 1872 | the productions 1859 1860 1861 |
on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction,
few few 1861 1866 1869 1872 | fewer 1859 1860 |
new varieties or species will be formed; and it is during these very periods of subsidence, that
the deposits which are richest the deposits which are richest 1869 1872 |
our great deposits rich 1859 1860 1861 1866 |
in fossils have been accumulated. ↑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.
|
|
On
the
Absence
of
Numerous
Intermediate
Varieties
in
any
..
Single
Formation
. |
From
these several these several 1861 1866 1869 1872 | the foregoing 1859 1860 |
considerations, considerations, 1866 1869 1872 | considerations 1859 1860 1861 |
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
much more much more 1861 1866 1869 1872 | more 1859 1860 |
difficult to
understand understand 1869 1872 | under- stand, 1859 | understand, 1860 1861 1866 |
why we do not therein find closely graduated varieties between the allied species which lived at its commencement and at its close.
Several Several 1866 1869 1872 | Some 1859 1860 1861 |
cases are on record of the same species presenting
....... 1869 1872 | distinct 1859 1860 1861 1866 |
varieties in the upper and lower parts of the same
formation: formation: 1869 1872 | formation, 1859 1860 1861 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. 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 |
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 |
Although each formation has indisputably required a vast number of years for its deposition,
...OMIT 1869 1872 |
I can see 1859 1860 1861 1866 |
several reasons
can be given why can be given why 1869 1872 |
why 1859 1860 1861 1866 |
each should not
commonly include commonly include 1869 1872 | include 1859 1860 1861 1866 |
a graduated series of links between the species which
....... 1866 1869 1872 | then 1859 1860 1861 |
lived lived 1866 1869 1872 | lived; 1859 1860 1861 |
at its commencement and close; but I cannot at its commencement and close; but I cannot 1866 1869 1872 |
but I can by no means pretend to 1859 1860 1861 |
assign due proportional weight to the following considerations. |
|
Although each formation may mark a very long lapse of years, each
probably probably 1866 1869 1872 | perhaps 1859 1860 1861 |
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
|