thus a fossiliferous formation thick enough, when upraised, to resist
any amount of degradation, may be formed.
I am convinced that all our ancient formations, which are rich in
fossils, have thus been formed during subsidence. Since publishing my
views on this subject in 1845, I have watched the progress of 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 certainly
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. Consequently formations rich in fossils and
sufficiently thick and extensive to resist subsequent degradation, may
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 remained stationary, _thick_ deposits
could not have been accumulated in the shallow parts, which are the
most favourable to life. Still less could this have happened during the
alternate periods of elevation; or, to speak more accurately, the beds
which were then accumulated will have 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
most favourable, as previously explained, for the formation of new
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