rge
amount of denudation, may be formed.

I am convinced that nearly all our ancient formations, which are
throughout the greater part of their thickness 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 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, will
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 cannot have been accumulated in the shallow parts, which are
the most favourable to life. Still less can this have happened during
the alternate periods of elevation; or, to speak more accurately, the
beds which were then accumulated will generally have been destroyed by
being upraised and brought within the limits of the coast-action.

These remarks apply chiefly to littoral and sublittoral 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 thirty or forty
to sixty 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 in which it was formed; nor would the deposit be much
consolidated, nor be capped by overlying formations, so that it would
run a good chance of being worn away by atmospheric degradation and by
the action of the sea during subsequent oscillations