| → subsequently but independently 1860 |
| independently 1859 |
|
| ↑ 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.
|
|
|
Geology, and have been surprised to note how author after author, in treating of this or that great formation, has come to the conclusion that it was accumulated during subsidence. I may add, that the only ancient tertiary formation on the west coast of South America, which has been bulky enough to resist such degradation as it has as yet suffered, but which will hardly last to a distant geological age, was
deposited during a downward oscillation of level, and thus gained considerable thickness. |
|
| All geological facts tell us plainly that each area has undergone numerous slow oscillations of level, and apparently these oscillations have affected wide spaces.
formations rich in fossils and sufficiently thick and extensive to resist subsequent degradation,
have been formed over wide spaces during periods of subsidence, but only where the supply of sediment was sufficient to keep the sea shallow and to embed and 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
→subsequently but 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
|
