'^^ 



lis 





'^" 





55 <U t^ 55 



-ill 



existing Physical Causes during stated Periods of Time. 263 



of the land must take place by de- 

 nudation before a volume of de- 

 tritus would be conveyed into the 

 sea sufficient to displace enough 

 water to occasion an elevation of 

 one foot on the ocean-level. (See 

 fig. 3.) 



There is great need of further 

 information respecting the amount 

 I of sediment carried down by other 

 u rivers besides those mentioned; 

 ^ yet if the rate of denudation ob- 

 § tained from the statistics of the 

 S Ganges and Mississippi be any 

 o guide to what is occurring on the 

 B remainder of the globe, we cannot 

 I suppose that an indefinite time 

 °" would be required for the per- 

 ^ formance of a denudation, which 

 § should reduce the mean surface- 

 '^ level of the land 3 feet, and raise 

 > that of the ocean 1 foot. It was 

 J during the contemplation of the 

 w changes of level that might have 



been produced by the operations 



1 of ordinary physical agents upon 

 ^ the surface of the earth, that Hut- 

 g ton was led to remark that it was 

 I not necessary to suppose the area 

 % of the land always maintained the 

 I same extent, but that from time 

 g to time new land would be formed 

 ^ by the elevatory movements of the 

 « sea-bottom to compensate for what 

 § had been carried into the ocean by 

 3 the continued operations of rivers 

 g and breakers*. In speaking of 

 s the elevation of the sea-level, I 

 « only refer to the intervals between 

 c those movements of the land which 



might neutralize in an instant all 

 that had been effected by the ope- 

 ration of rivers for immense periods 

 of time. 



It would add very much to 

 the interest of this inquiry if any 



* " It is not necessary that the present land should be worn away and 



