existing Physical Causes during stated Periods of Time. 269 



lines* by breaker-action, and also by the formation of submarine 

 deposits from materials which were brought into the ocean in 

 solution, I now propose to consider that all these causes together 

 might produce an elevation of the sea-level equal to 1 foot in 

 40,000 years, or 3 inches in 10,000 years. 



Mr. Darwin has remarked, that " the knowledge of any result, 

 which, with sufficient time allowed, can be produced by causes, 

 though appearing infinitely improbable, is valuable to the geo- 

 logist, for he by his creed deals with centuries and thousands of 

 years as others do with minutes/^ For these reasons, even if, 

 upon further investigation, it should be found that the true rise 

 in the sea-level is much less than 3 inches in 10,000 years (in 

 periods undisturbed by subsidences and elevation), yet it may 

 still be an important element in accounting for those changes 

 which we are now about to consider. 



Part II. 



Allusions have been already made to the difficulty of proving 

 whether or not the sea-level had been gradually elevated, because 

 the rise of the waters would conceal the evidence of their former 

 height except just at the mouths of rivers, where deposits of flu- 

 viatile alluvium might raise the land from time to time and keep 

 it above the waves. The recent strata formed at a few such loca- 

 lities have been described by the best observers ; and while there 

 are appearances in several cases which might be to some extent 

 explained by the supposition of a gradual rise of the sea-level, 

 yet no proof could be obtained without the concurrent testimony 

 of a much greater number of instances than have yet been 

 brought forward. Sufficient information, it appears, exists to 

 show that the quantity of alluvium in the deltas of such rivers 

 as the Mississippi, Ganges and Po, is so enormous, that the accu- 

 mulation must have occupied a period of time during which it 

 would not be possible to conceive the sea-level stationary. 



Little progress could be made in an inquiry of this kind with- 

 out clear views of the operations of rivers. The recent reports 

 of engineers upon this subject supply an important link in the 

 chain of evidence, and enable us to understand the laws which 



* The rough estimation of the extent of coast-Hne, kindly supplied by 

 Mr. A. K. Johnston (Nov. 1852), is as follows : — 



99,600 116,531 



