408 
ACKROYD : ON THE CIRCULATION OF SALT. 
instituting a comparison I have, therefore, confined myself to the 
ratio of the related ions, chlorine and bromine. Usiglio's figures 
for the Mediterranean at Cette give 
CI. Br. 
100 : 2-1 
which are practically the same as Von Yibra's for the Atlantic at 
the Equator — 
CI. Br. 
100 : 2-09 
The analyses of Dead Sea surface-water made by Terrell give 
the following ratios : — 
CI. 
Br. 
Near Rasdale 
100 
0-95 
Lagune, North of Sodom 
100 
2-7 
Near Island 
100 
3-6 
Average 
100 
2-4 
The closeness of this average to the Mediterranean and Atlantic 
Ocean figures is somewhat remarkable, and although it will not be 
taken as absolute proof that the Dead Sea has obtained its salt from 
the Mediterranean, it at least destroys the contention that the dis- 
solved constituents of the two seas are so dissimilar that one cannot 
have been derived from the other. 
The Geological Age of the Earth as Measured by the Rate 
OF Soi-VENT Denudation. 
I now pass to the bearing of the foregoing facts and others I 
shall adduce on Professor Joly's way of calculating the age of the 
earth since the first ocean was formed.^ The method may be thus 
briefly put — 
NaCl + NaNoo + Na-^SOj in the seas. 
= Age of the Earth. 
Annual addition of NaCl + NaNOo + NaoSOj 
by rivers, 
or more particularly, the sodium contents of the seas, divided by the 
sum of the annual sodium increments furnished by the affluent rivers^ 
* Trans. Roy. Dublin 8oc., VII. (Series IT.), 23-66; and B.A. Report, 
1900, pp. 369-379. 
