existing Physical Causes during stated Periods of Time. 25 
of cubic feet of detritus discharged annually by that river is 
6,368,677,400. (See Lyell’s Principles.) 
6,368,677,400 
11,151,360,000,000 ~ 1751? 
mean level of the Ganges district is 

consequently the reduction of the 

- 7 of a foot annually, or 
v5 
1 foot in 1751 year 
6,368,677 ,440 ie feet of mud discharged < 856 water to 
mud = 5, 444,074,288,640 = the number of cubic feet of water 
annually discharged by the Ganges. 
5,444,074,288,640 
11,151,360,000,000 
discharge of water is equal to about 6 inches of rain on the whole 
area of “400, 000 square miles. 
The Mississippi, on the other hand, would ocenpy 9000 years 
at its present annual rate in reducing to the amount of one foot 
the mean surface-level of the district it drains, which is compu- 
ted at eleven hundred thousand square miles. » ‘The result is ob- 
tained as follows: 
If 3,702,758, 400 @hbic feet of mud are annually carried down 
y the Mississippi (since the mud is to the water as 1 to 3000), 
3,702,758,400 x 3000 = 11,108,275,200,000 = the number of 
cubic feet of water annually carried by the river into the Gulf of 
exico. The area of district drained by this river is stated 
at 1,100,000 square miles — 5280 X 5280 = 27,878,400 = the 
number of superficial feet in a mile—27,878,400 x 1,100,000 = 
30,666,240,000,000 = the namber of superficial feet contained 
in the area ‘ot ) ,100,000 square miles drained solely by the Mis- 
sissippi. 
11,108,275,200,000 
30.666 ,666,240,000,000 foot = $ foot nearly. Consequently the 
water carried down by a river is equal to about 4 inches of rain 
over the surface of land 
if it be assumed that thie ROP of the rivers, lakes, and springs 
are the same in this district at the same period 0 of two consecu- 
tive years, the water sufficient to produce the above-mentioned 
4 inches of the total of rain-fall upon the whole of this district 
must have been annually derived from clouds which have 
thee with vapor in parts of the earth beyond the confines of 
tract of country under consideration ; since, : if the - 4 inches 
‘Tain: leet carried into the Gulf of ) were 1 
rom fi —_ Sources, the levels of the rivers, lakes, and 
Springs must rapidly fall. po CL hee ae 
he estimate i ‘denudation obtained from these countries may 
== about 4 a foot, so , that the mean mee, 



iceipt of rain. Besides, many rivers empty themselves _ 
and inland seas, and other extensive tracts are a. y wi 
Stcoxa Series, Vol, XVII, No, 52.—July, 1854. 
