( 399 ) 
In the Nile, the La Plata and the Rio Negro and also in Lough 
Neagh this deficit of chlorine, as shown in our table, is extraordinarily 
large. But considering that, according to Murray, the evaporation 
of the rain water in the area of the Nile is more than 14 times as 
high as that observed in the basin of the Meuse (in most of the 
other European rivers a similar proportion is found) the solution of 
salts represented by the water of the Nile at Cairo can be consi- 
dered as a far more concentrated one. If the evaporation were not 
stronger there than in the area of the Meuse, the deficit of chloride 
would only be 2.2 mgrm. For the La Plata the proportion between 
the rainfall and the discharge of the river is only 2.34 times as 
large as that for the Meuse; under similar proportions of evapora- 
tion as in Europe, the deficit of chlorine would therefore be 5.44 
mgrm according to one analysis, 17.71 mgrm according to the other. 
Perhaps the deviation is there too only a seeming one, caused 
by stronger evaporation. Not taking into consideration the rivers 
draining soils rich in salt, as many of the smaller North-American 
rivers, N°.55—75 of our table — and in the case of the Rio Negro 
and Lough Neagh something analogous may be accepted — the 
exceptions, with a great deficit of chlorine are certainly so rare, 
that they cannot alter our conclusion based on what we observe 
in allmost all other cases. 
Most likely only 1/, of the quantity of sodium in the annual 
discharge of the rivers stated by Jory, according to MuRRAY’s esti- 
mate, is really to be attributed to chemical denudation; we then 
have to multiply the (not corrected) period of 99.4 million years, 
calculated, for the geological denudation by the first named author, 
with 4 and arrive at the result of about 400 million years. 
The existing data concerning the quantity of sodium and chlorine 
in river water are therefore not appropriated to use in the problem 
treated by JoLy, if at least the result arrived at by Lord KELVIN, 
or even a period of one hundred million years, is approximatively 
right. 
Thus the opinion, to which other geological facts had led, that the 
greater part of the chloride of sodium in the ocean must have been 
produced, by a process far more rapid than the present process of 
denudation is confirmed. 
