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See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1859
1861
1866
1869
1872

→ numbers of species 1859 1860 1861 1866
many species in several 1869
species belonging to several 1872
→ same group, 1859 1860 1861
same group 1866
main divisions of the animal kingdom 1869 1872
→ Silurian trilobites have 1859 1860 1861 1866
Silurian trilobites are 1869
Cambrian and Silurian trilobites are 1872
→ 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
→ stratum 1859 1860 1861 1866 1872
or Cambrian stratum 1869
→ yet quite unknown, periods of time, 1859 1860 1861 1866
periods 1869 1872
forms
beings
throughout the world, as it would be for a naturalist to land for five minutes on
a
some one
barren point in Australia, and then to discuss the number and range of its productions.
On
On
the
the
sudden
sudden
Appearance
appearance
of
of
Groups
groups
of
of
allied
allied
Allied
Species
Species
in
in
the
the
lowest
lowest
known
known
Fossiliferous
fossiliferous
Strata .
strata .—
There is another and allied difficulty, which is much
more serious.
graver.
I allude to the manner in which →numbers of species of the →same group, 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
are
have
descended from
a single
one
progenitor, apply with
nearly
nearly
equal force to the earliest known species. For instance,
it
I
cannot
be doubted
doubt
that all the →Silurian trilobites have descended from some one crustacean, which must have lived long before the
Cambrian
Silurian
age, and which probably differed greatly from any known animal. Some of the most ancient
Silurian
Silurian
animals, as the Nautilus, Lingula,
&c,
&c.,
do not differ much from living species; and it cannot on
our
my
theory be supposed, that these old species were the progenitors of all the species →of the orders to which they belong, for they
are
do
not
present characters
present characters
in any degree intermediate
in character.
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
the
my
theory be true, it is indisputable
that,
that
before the lowest
Cambrian
Silurian
→stratum was
deposited
deposited,
long periods elapsed, as long as, or probably far longer than, the whole interval from the
Cambrian
Silurian
age to the present day; and that during these
vast
vast,
→yet quite unknown, periods of time, the world swarmed with living creatures.