| → independently 1859 |
| subsequently but independently 1860 |
|
| ↑ 3 blocks not present in 1859 1860 1861 1866 1869 1872; present in |
|
|
|
| ↑ 4 blocks not present in 1859 1860; present in 1861 1866 1869 1872 |
| These remarks apply chiefly to littoral and sub-littoral
deposits.
In the case of an extensive and shallow sea, such as that within a large part of the Malay Archipelago, where the depth varies from 30 or 40 to 60 fathoms, a widely extended formation might be formed during a period of elevation
and yet not suffer excessively from denudation during its slow upheaval; but the thickness of the formation could not be great, for owing to the elevatory movement it would be less than the depth,
supposed to be shallow;
the deposit would not generally
be much consolidated, nor would it
be capped by overlying
formations, so that it would run a good chance of being worn away during
subsequent oscillations of level.
It has
been
suggested by Mr. Hopkins, that if one part of the area, after rising and before being denuded, subsided, the deposit formed during the rising movement, though not thick, might become
protected by fresh accumulations, and thus be preserved for an extremely long period,— a consideration which I formerly overlooked.
Mr. Hopkins,
in commenting on this subject, states that he believes the entire destruction of any
sedimentary bed
of considerable horizontal extent to
have been of rare occurrence.
|
|
| ↑ 1 blocks not present in 1859 1860 1861; present in 1866 1869 1872 |
| But all geologists, excepting the few who believe that our present metamorphic schists and plutonic rocks once formed the primordial nucleus of the globe, will probably
admit that rocks of this nature must
have been denuded on
an enormous scale.
|
|
| → our great deposits rich 1859 1860 1861 1866 |
| the deposits which are richest 1869 1872 |
|
| ←Subtitle not present 1859 1860 1861 On
the
Absence
of
Numerous
Intermediate
Varieties
in
any
one
Single
Formation
.
1866 1869 1872 |
|
preserve the remains before they had time to decay. On the other hand, as long as the bed of the sea
stationary,
deposits
have been accumulated in the shallow parts, which are the most favourable to life. Still less
this have happened during the alternate periods of elevation; or, to speak more accurately, the beds which were then accumulated will
been destroyed by being upraised and brought within the limits of the coast-action. |
|
| Thus the geological record will almost necessarily be rendered intermittent. I feel much confidence in the truth of these views, for they are in strict accordance with the general principles inculcated by Sir C. Lyell; and E. Forbes
→independently
arrived at a similar conclusion. ↑ ↑
↑ |
|
| 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
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
on the shores of a continent when first broken up into an archipelago), and consequently during subsidence, though there will be much extinction,
new varieties or species will be formed; and it is during these very periods of subsidence, that
→our great deposits rich
in fossils have been accumulated. Nature may almost be said to have guarded against the frequent discovery of her
or linking forms. →
|
| From
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
difficult to
|
