( 389 ) 
and MgLLARD Reape!) since 1876 indeed “opened out a novel line 
of investigation” by applying many other such analyses in an attempt 
to estimate geological time from chemical denudation. But only 
the estimate of averages by Murray seems to have put the new 
modulus of past time ready to every geologist’s hand. The reputation 
of Sir Jonny Murray contributed to consider that estimate as of 
great value, probably greater than he himself has wished; perhaps 
too it has been the motive of taking those averages without further 
control as starting point even for geological problems of far reaching 
tendency. 
Lately Prof. Jouy, in an important essay, has estimated the age of 
the Earth by comparing the annual supply of sodium by the rivers 
to the ocean, according to MurRAy’s estimate, to the quantity which 
the ocean contains of that element, assuming that the primeval 
ocean only contained a small amount of sodium, assuming moreover 
that but very little is again withdrawn from the ocean when once 
conveyed to it, and accepting uniformity of the removal of the land 
surface by solution since the earliest sediments were laid down 2), 
The quotient of the amount of sodium in the ocean and that annual 
supply, corrected for the sodium obtained by the ocean by means 
of a primeval accelerated denudation and as regards the amount of 
that element which only circulates between the ocean and the land, 
gives the age of the Earth in years. Those corrections are not 
very considerable, but as JoLY does not base them upon determined 
data one can estimate their amount as widely differing from his. 
O. Frsner has explained this in an able review of Jouy’s essay, 
to which it may be permitted to refer here °). 
There has not yet been much doubt expressed concerning the exact- 
ness of the basis of JoLy’s estimate “). As for the one leading factor in 
it, the quantity of sodium in the sea, it seems unnecessary to doubt 
its accuracy. But is it the same with the quantity of sodium 
annually supplied by the rivers, namely with the proportion in 
which sodium is admitted by him to take part in the dissolved 
matter in average river water? This question has such an important 
1) T. MerrarD Reape, Chemical Denudation in relation to Geological Time. 
Londen 1879. 
2) J. Jouy, An Estimate of the Geological Age of the Earth. Scientific Transactions 
of the Royal Dublin Society. Vol 7. (Series 2), p. 23—66. Dublin 1899. 
3) O. Fisner, Geological Magazine. New Series. Decade 4. Vol. 7. (1900), p. 124—132. 
*) Prof Sorras, in his very interesting address to the British Association of 1900, 
discusses the quantity of sodium present in river water. In his opinion the proportion 
in Jouy’s average river water is probably too small, as much sodium is supplied by 
rivers draining voleanous regions. He believes, moreover, that the supply of sodium 
to the ocean has proceeded in a gradually diminishing rate with diminishing temperature 
of the earth’s crust. (Nature, Vol. 62, p. 485). 
26 
Proceedings Royal Acad. Amsterdam. Vol. LV. 
