XI 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 



z '2 



