412 
ACKROYD : ON THE CIRCULATION OF SALT. 
itself where large volumes of water are concerned ; thus in the hun- 
dreds of samples analysed from the source of the Aire during our 
investigations of the underground waters, there has been no notice- 
able variation from normal ; these, however, have only been summer 
experiments. There must be variations due to periods of excessive 
evaporation and of storm. The Nile furnishes a striking example. 
Wanklyn."^ in 1874 and 1875, obtained the following chlorine figures 
for this river : — 
Parts i)er l()0,Of»0. 
1874.— June 8th 2-5 
July 9th 
August 12 th 
September 20th 
October 12th 
November 12 th 
December 1 2 th 
1875. -April 
May Uth 
The annual fluctuation is better giasped fr 
(Plate LXYIIL, fig. 3.) 
Similar observations are wanted for all the rivers of the world. 
i'o 
0-4 
0-5 
0-5 
0-7 
0- e 
1- 4 
1-7 
om the plotted curve. 
Conclusion. 
To sum up, then, salt circulation in Nature forms an important 
and, up to now, inadequately realised phenomenon, and to it we un- 
doubtedy owe much of the saltness of present day salt-lakes. In 
the solvent denudation method of arriving at the age of the Earth, 
too little allowance has been made for the mass of sodium chloride 
carried by the rivers, which has been brought from the ocean by 
atmospheric transportation, and consequently too high a figure 
has been adopted for the variable proportion of sodium derived from 
the Earth. But although little satisfaction may be received from 
the numerical results obtained by this in common with other ways 
of trying to solve the mystery of the Earth's age, they are at least 
* Water Analysis, 6th Edition, p. 151. 
