existing Physical Causes during stated Periods of Time. 277 



informed by Sir Charles Lyell, that the Mississippi in one part 

 of its course cuts through ancient fluviatile beds evidently ante- 

 cedent to those recent deposits we have been considering. This 

 formation is also stated to contain the remains of species of 

 plants and animals now existing ; so that evidence is to be 

 obtained in this district of still greater denudations (by these 

 results) than those of which we have spoken, and which would 

 produce changes on the surface of the earth since the introduc- 

 tion of the present fauna and flora of extent enough almost to 

 realize Hutton's vision of mountains wasted away by the action 

 of rain, the atmosphere, and running- water, and carried along 

 river-courses into the ocean. It is not necessary to take an 

 extreme view of this subject to gain the object we have in view, 

 which is to show that, during the time occupied by the forma- 

 tion of the Mississippi delta, the sea-level might be perceptibly 

 raised* by the agency of physical causes now in operation. 



The reasons for supposing that a rise of 3 inches in each period 

 of 10,000 years might occur, have been already discussed, and 

 it only remains to state that, at the present rate of denudation, 

 it would require five such periods to produce the quantity of 

 detritus said to exist in the valley of the Mississippi ; while it 

 would require fifty such periods to produce the requisite quantity 

 of alluvium on the supposition that only one-tenth of the mud 

 in transitu through the river was appropriated for the accumula- 

 tion of its alluvial plains and delta. Under these circumstances 

 it appears a legitimate conclusion, that the level of the sea can- 

 not be considered permanent for all practical purposes when it 

 may be shown that it might be disturbed by the operation of 

 present causes during the period occupied by the construction of 

 a single geological formation. Elevations and subsidences of 

 the land or sea-bottom would also efi*ect important changes in 

 the height of the sea-level, sometimes counteracting and at others 

 adding to the efi"ects produced by the continuous operation of 

 rivers, &c. The effects produced by these important causes 

 would be an additional reason for not considering the sea-level 

 permanent. 



It is hardly necessary to add, that the continual waste of the 

 earth^s surface by the carrying of materials into the ocean by 

 rivers and breakers particularly attracted the attention of Hutton. 

 He considered t that this was counteracted by elevatory move- 



* This change of level may amount, under certain circumstances, to a 

 great extent, but at the lowest calculation would be 15 feet. 



t These remarks of Hutton are here introduced because he takes an 

 entirely different view of this subject to that promulgated by Sir Charles 

 Lyell, who considers that there has been always an excess of subsidence. 

 (See Principles, 1850, p. 543.) 



