| → first bed of the Silurian 1859 1860 1861 1866 |
| Cambrian 1869 1872 |
|
| → I 1859 1860 1861 |
| We now know that animals, and probably plants, lived at an epoch immensely remote, long anterior to the primordial zone of the Silurian system, but I 1866 |
| We now know that at least one animal did then exist; but I 1869 1872 |
|
| → as far as we can see, 1859 1860 1861 |
| OMIT 1866 1869 1872 |
|
| → for an enormous period extended, 1859 1860 1861 |
| extended for an enormous period, 1866 1869 1872 |
|
| → Silurian epoch; 1859 1860 1861 |
| commencement of the Silurian epoch; 1866 |
| commencement of the Cambrian system; 1869 1872 |
|
| → all be 1859 1860 1861 |
| only as remnants 1866 1869 1872 |
|
| → seem to me simply to follow on 1859 1860 1861 1866 1869 |
| agree admirably with 1872 |
|
| → natural 1859 1860 1861 1866 1869 |
| variation and natural 1872 |
|
| → of the larger 1859 1860 1861 1866 |
| belonging to large and 1869 1872 |
|
|
may overlook how important a part migration
played, when the formations of any one great
as
of Europe, are considered; he may urge the apparent, but often falsely apparent, sudden coming in of whole groups of species. He may ask where are the remains of those infinitely numerous organisms which must have existed long before the
→first bed of the Silurian
system was
→I
can answer
question only
by
that
→as far as we can see,
where our oceans now extend they have
→for an enormous period extended,
and where our oscillating continents now stand they have stood
since the
→Silurian epoch;
but
long before that
the world
presented a
different aspect; and that the older continents, formed of formations older than any known to us,
now
→all be
in a metamorphosed condition, or
lie
under the ocean. |
|
| Passing from these difficulties,
the other great leading facts in palæontology
→seem to me simply to follow on
the theory of descent with modification through
→natural
selection. We can thus understand how it is that new species come in slowly and successively; how species of different classes do not
change together, or at the same rate, or in the same degree; yet in the long run that all undergo modification to some extent. The extinction of old forms is the almost inevitable consequence of the production of new forms. We can understand why when a species has once disappeared it never reappears. Groups of species increase in numbers slowly, and endure for unequal periods of time; for the process of modification is necessarily slow, and depends on many complex contingencies. The dominant species
→of the larger
dominant groups tend to leave many modified
|
