evisting Physical Causes during stated Periods of Time. 223 
of what has passed into the Gulf of Mexico; and this can readily 
be believed when we reflect upon the depth and breadth of the 
_ channel, and upon the short period of the year that the stream 
would throw any large quantity of mud into the plains even if 
there were no artificial banks. We must also bear ip mind that 
in the more level parts of any district. It is therefore possible 
that, during the reduction of the mean surface-level of the land 
drained by the Mississippi to the amount of 100 feet, some por- 
tions of the area might be lowered many times that amount, 
‘IS not necessary to take an extreme view of this subject to 
84in the object we have in view, which is to show that, dnring 
Sea-level might be perceptibly raised} by the agency of physical 
Satises uow in operation. 2 
. Ube reasons for supposing that a rise of 3 inches in each perioc 
of 10,000 years might occur, have been already discussed, and it 
only remains to state that, at the present rate of denudation, it 
* The data for cal ino the annual quantity of detritus carried over the river's 
banks, in aa ae tad "en to the sea, are very imperfect. Further 
“pretton on this subject i b needed. : 
+ This change ae saan sch paccd, under certain circumstances, toa great ex- 
teat, but at the Jowest calculation would be 15 fect. 
