38 Joty—An Estimate of the Geological Age of the Earth. 
atomic ratios of the constituents of these rocks, sodium appears as 2°68 per cent. 
The entire mass of rock reduced to detrital sediment and brought into solution to 
supply this amount can, of course, be estimated from this. It amounts to 
73 x 10" tons. On Professor Wagner’s determination already referred to, the 
area of the globe is about 1965 x 10° square miles; and taking the specific gravity 
of the original rock to be that of Diorite (2°95), we find the amount denuded would 
cover the Earth to a depth of 157 feet. 
The most careful estimate of the present mean rate of subaerial denudation 
of eruptive and crystalline rocks amounts to about 1 foot in 3000 years, removed 
from the surface, partly in solution, partly by transportation, to the rivers and 
sea. The primeval ocean was, according to our view, a dilute solution of 
HCl. 
Bearing in mind the fact that the solution of hydrochloric acid would become 
impoverished as time progressed, and insoluble residues cover up a fraction of the 
Earth’s surface, it would seem to be sufficient to assume that its mean rate of activity 
was five times that of present subaerial agents. This affords 1 foot in 600 years; 
or to denude 157 feet of rock, 94,200 years. In fact, even at the present rate of 
denudation, the large surface we have assumed as exposed to denudation reduces 
the period of time required to remove such a rock-layer to a negligible duration. 
The only correction that is admissible would be a unit in the decimal place of our 
correction of 12°5 x 10° years, reducing the correction to 12:4 x 10° years, and 
leaving geological time, dated from the condensation of water upon the globe, 
to be 87 x 10° years. 
The foregoing corrections involve not only the assumption that the hydro- 
chloric acid was free, but also that we may assume from the mean analyses of 
igneous, eruptive, and crystalline rocks, a knowledge of the primeval crust exposed 
to denudation. The latter assumption appears justified, not only for the reason that 
any other is gratuitous and prima facie unwarranted, but also from the fact that 
the sodium contents of the sedimentaries, as now existing, if increased by what is 
now the ocean, reverts very nearly to that of Clarke’s primary crust. 
The assumption of this acidic denudation of the primeval rocks leaves the 
ocean charged principally with chlorides at the dawn of geological history. 
Carbonates must also have entered into the composition of the primeval ocean, 
probably as minor constituents. Sulphates possibly also existed in relatively 
small quantities. 
Sterry Hunt believed that the waters imprisoned in the pores of the older 
stratified rocks, and which are ‘vastly richer in salts of lime and magnesia 
than those of the present sea,” might be regarded as the fossil sea-waters of the 
ancient ocean. He gives a theory of the subsequent changes in ocean chemistry : 
suggesting that the carbonates of the alkalies and the alkaline earths in 
