262 Scientific Procecdings, Reyal Dublin Society. 
where gz = number of years, 
A = area of rain basin in sq. geo. miles, 
7 = annual weight of silt discharged, in tons. 
Writing in this formula— 
At 2a) ag 996: 
T = 332,550,000, 
we find, for the upper basin of the Ganges, 
x = 1,146 years. 
Or, that the rainfall of the Upper Ganges scrapes off one foot 
of rock from the whole surface of vts rain-basin im 1,146 years. 
This result is about half that given for the Ganges by Prof. 
Geikie,* who estimates it at 2,358 years. In all probability 
Prof, Geikie compared the discharge of mud at Ghaziptr with 
the whole rain-basin of the Ganges, and so got a doubled result. 
If my result be altered in the proportion of the ram-basin 
above Ghaziptr to the whole rain-basin, we find 
1146 x 319 
143 
which does not differ much from Prof. Geikie’s estimate. 
Whatever may be the explanation of the discrepancy, I feel 
great confidence in the data from which I have obtained my 
result ; which is important in its bearing on the duration of geo- 
logical time, which it obviously tends to diminish. 
= 2556 years, 
“Note IT. 
The Annual Water-discharge of the River Plate. 
Mr. Bateman’s estimate of the December low-water discharge of 
the Rio dela Plata is given in the following extract from a Report 
drawn up by him for the Government of Buenos Ayres, 9th 
January, 1871 :— 
“The Rio de la Plata, formed by ae Junction of the rivers 
Parana and Uruguay, is the widest fresh-water river in the world. 
Assuming it to terminate in a line drawn from Monte Video on the 
north to Piedras point on the south (though it is generally de- 
scribed as extending much further), it .is 60 miles in width at its 
mouth. At 60 miles further up itis still 40 miles wide. At 
Colonia, the narrowest part, and 80 miles from the sea, it is 23 
* Geological Magazine, vol. ¥., p. 250. 
