28 Joty—An Estimate of the Geological Age of the Earth. 
the sea, and the order of magnitude to be ascribed to an allowance for the 
latter, are briefly considered in the paper, as well as other questions which 
arise. 
When all corrections are made and the requisite latitude of error taken into 
account, it would appear that the consideration of solvent-denudation, points to 
an Age for the Earth, dating from the settlement of water upon its surface, of 
between 80 and 90 millions of years. 
I.—The Estimate of Geological Time. 
On the basis that the ocean possesses an average depth of 2000 fathoms, and 
occupies ;8; of the area of the globe, its total mass is calculated to be 1:322 x 10% 
tons.* Its ingredients in solution are :— 
Chloride of sodium, . : : . 77.758 
» of magnesium, : ; . 10°878 
Sulphate of 3 : : - 4:737 
“ of lime, ‘ : Eo 6.00 
», of potassium, : : . 2°465 
Bromide of magnesium, : . o (pile 
Carbonate of calcium, : Te OsO-o 
100-000 
and the total salts are approximately 3°5 per cent. of the mass of the whole. 
On these data, the absolute masses of the ingredients of the ocean are 
calculable :— 
NaCl, ; é : . 985990 x 10” tons. 
Mela eiahiel.) [Ste S03. ene 
MeS0O,, ‘ 0 : S202 ear ar 
CaSO, ‘ : c 5 IG . », 
KASOi pe eee hee eel 
Mebr, : ¢ : : HOO enee As 
Ga@Oyy) Te nf VIET ALI Te BiG one aimee 
4623 30am iss 
Of the sodium chloride, 39°32 per cent. is sodium. In the sea, there is, 
therefore, a mass of sodium in solution amounting to 14,151 x 10” tons. 
Sir John Murray,t as the result of the analyses of 19 rivers—many of which 
* Encyclopedia Britannica—Article, ‘‘ Sea.’ The analyses are Dittmar’s from the Reports of the 
‘* Challenger’ Expedition. 
+ Scottish Geographical Magazine, 1887, p. 76. 
