36 



THE PAST CONDITION 



Let C y (Fig. 4) be the sea-bottom^ y D the sbore> 

 X y the sea-level, then the coarser deposit will subside 



Fig. 4. 



over the region B, the finer over A, while beyond 

 A there will be no deposit at all ; and, consequently, 

 no record will be kept, simply because no deposit 

 is 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 W'ill be at ?/*, .r' y'^, being the 

 new sea-level. The consequence will be that the 

 layer of mud (A), being now, for the most part, fur- 

 ther than the force of the current is strong enough 

 to convey even the finest debr'is, 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 re- 

 garding 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, — • 



