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xr PHENOMENA OF ORGANIC NATURE 339 
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. 
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 move- 
“ment? Why, that the sediment A and B which 
has been already deposited, would eventually be 
brought nearer to the shore-level and again sub- 
“jected 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 way, 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 
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