s going on. Now, suppose
that the whole land, C, D, which we have regarded as stationary, goes
down, as it does so, both A and B go further out from the shore, which
will be at y1; x1, y1, being the new sea-level. The consequence will be
that the layer of mud (A), being now, for the most part, further than
the force of the current is strong enough to convey even the finest
'debris', will, of course, receive no more deposits, and having attained
a certain thickness will now grow no thicker.

We should be misled in taking the thickness of that layer, whenever it
may be exposed to our view, as a record of time in the manner in which
we are now regarding this subject, as it would give us only an imperfect
and partial record: it would seem to represent too short a period of
time.

[Illustration: Fig.4.]

Suppose, on the other hand, that the land (C D) had gone on rising
slowly and gradually--say an inch or two inches in the course of a
century,--what would be the practical effect of that movement? Why, that
the sediment A and B which has been already deposited, would eventually
be brought nearer to the shore-level, and again subjected to the wear
and tear of the sea; and directly the sea begins to act upon it, it
would of course soon cut up and carry it away, to a greater or less
extent, to be re-deposited further out.

Well, as there is, in all probability, not one single spot on the whole
surface of the earth, which has not been up and down in this way a great
many times, it follows that the thickness of the deposits formed at any
particular spot cannot be taken (even supposing we had at first obtained
correct data as to the rate at which they took place) as affording
reliable information as to the period of time occupied in its deposit.
So that you see it is absolutely necessary from these facts, seeing that
our record entirely consists of accumulations of mud, superimposed one
on the other; seeing in the next place that any particular spots on
which accumulations have occurred, have been constantly moving up and
down, and sometimes out of the reach of a deposit, and at other times
its own deposit broken up and carried away, it follows that our record
must be in the highest degree imperfect, and we have hardly a trace
left of thick deposits, or any definite knowledge of the area that they
occupied, in a great many cases. And mark this! That supposing even
that the whole surface of the earth had been accessible to the