Comparison with 1859 |
|
On
On
1859 1860 1861 |
On
1866 1869 1872 |
the
the
1859 1860 1861 |
the
1866 1869 1872 |
sudden
sudden
1859 1860 1861 |
sudden
1866 1869 1872 |
appearance
appearance
1859 1860 1861 |
Appearance
1866 1869 1872 |
of
of
1859 1860 1861 |
of
1866 1869 1872 |
groups
groups
1859 1860 1861 |
Groups
1866 1869 1872 |
of
of
1859 1860 1861 |
of
1866 1869 1872 |
Allied
Allied
1859 1860 |
allied
1861 |
allied
1866 1869 1872 |
Species
Species
1859 1860 1861 |
Species
1866 1869 1872 |
in
in
1859 1860 1861 |
in
1866 1869 1872 |
the
the
1859 1860 1861 |
the
1866 1869 1872 |
lowest
lowest
1859 1860 1861 |
lowest
1866 1869 1872 |
known
known
1859 1860 1861 |
known
1866 1869 1872 |
fossiliferous
fossiliferous
1859 1860 1861 |
Fossiliferous
1866 1869 1872 |
strata
.—
strata
.—
1859 1860 1861 |
Strata
. 1866 1869 1872 |
|
There is another and allied difficulty, which is much
graver. graver. 1859 1860 1861 | more serious. 1866 1869 1872 |
I allude to the manner in which numbers of species
of the
same group, same group, 1859 1860 1861 |
same group 1866 |
main divisions of the animal kingdom 1869 1872 |
suddenly appear in the lowest known fossiliferous rocks. Most of the arguments which have convinced me that all the existing species of the same group have
descended from one
progenitor, apply with nearly
equal force to the earliest known species. For instance, I
cannot doubt
that all the Silurian trilobites have
descended from some one crustacean, which must have lived long before the Silurian
age, and which probably differed greatly from any known animal. Some of the most ancient Silurian
animals, as the Nautilus, Lingula, &c.,
do not differ much from living species; and it cannot on my
theory be supposed, that these old species were the progenitors of all the species
of the orders to which they belong, of the orders to which they belong, 1859 1860 1861 |
belonging to the same group which have subsequently appeared, 1866 |
belonging to the same groups which have subsequently appeared, 1869 1872 |
for they do
not present characters
in any degree intermediate between them. If, moreover, they had been the progenitors of these orders, they would almost certainly have been long ago supplanted and exterminated by their numerous and improved descendants. |
|
Consequently, if my
theory be true, it is indisputable
that that 1859 1860 1861 1872 | that, 1866 1869 |
before the lowest Silurian
stratum
was deposited,
long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian
age to the present day; and that during these vast,
yet quite unknown, periods of time,
the world swarmed with living creatures. ↑4 blocks not present in 1859 1860 1861 1866; present in 1869 1872 | Here we encounter a formidable objection; for it seems doubtful whether the earth
in a fit state for the habitation of living creatures
has lasted long enough.
Sir W. Thompson concludes that the consolidation of the crust can hardly have occurred less than 20 or more than 400 million years ago, but probably not less than 98 or more than 200 million years.
These very wide limits show how doubtful the data are; and other elements may have to
be introduced into the problem.
Mr. Croll estimates that about 60 million years have elapsed since the Cambrian period, but this, judging from the small amount of organic change since the commencement of the Glacial epoch, seems
a very short time for the many and great mutations of life, which have certainly occurred since the Cambrian formation; and the previous 140 million years can hardly be considered as sufficient for the development of the varied forms of life which certainly
existed towards
the close of the
Cambrian period.
|
↑1 blocks not present in 1859 1860 1861 1866 1869; present in 1872 | It is, however, probable, as Sir William Thompson insists, that the world at a very early period was subjected to more rapid and violent changes in its physical conditions than those now occurring; and such changes would have tended to induce changes at a corresponding rate in the organisms which then existed.
|
|
|
To the question why we do not find
records of these vast primordial periods, records of these vast primordial periods, 1859 1860 1861 |
richly fossiliferous records of these vast primordial periods, 1866 |
rich fossiliferous deposits belonging to these assumed earliest periods, 1869 |
rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, 1872 |
I can give no satisfactory answer. Several
of the most of the most 1859 1860 1861 |
OMIT 1866 1869 1872 |
eminent geologists, with Sir R. Murchison at their head,
are are 1859 1860 1861 |
were until recently 1866 1869 1872 |
convinced that we
see see 1859 1860 1861 | beheld 1866 1869 1872 |
in the organic remains of the lowest Silurian stratum the
dawn dawn 1859 1860 1861 | first dawn 1866 1869 1872 |
of life
on this planet.
Other highly competent judges, as Lyell and
|